CA1051243A - Doctor blade for a papermaking machine - Google Patents
Doctor blade for a papermaking machineInfo
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- CA1051243A CA1051243A CA302,325A CA302325A CA1051243A CA 1051243 A CA1051243 A CA 1051243A CA 302325 A CA302325 A CA 302325A CA 1051243 A CA1051243 A CA 1051243A
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Abstract
ABSTRACT OF THE DISCLOSURE
A doctor blade system for use in papermaking including a rotating cylindrical member and a doctor blade member for removing a paper web from the cylindrical member, where the doctor blade member comprises an elongated flexible composite including a plurality of ceramic segments, each segment having at least two opposite surfaces that are flat and parallel. The segments are aligned in stacked relationship with their flat faces in abutting face-to-face relation and forced toward each other in the direction of their composite length with a force which is sufficient to maintain the segments in compression when subjected to conditions of thermal change and/or flexing of the member during use. The ceramic member is provided with a smooth elongated working surface which defines an area of contact with the cylindrical member. A method for making the ceramic member is disclosed.
A doctor blade system for use in papermaking including a rotating cylindrical member and a doctor blade member for removing a paper web from the cylindrical member, where the doctor blade member comprises an elongated flexible composite including a plurality of ceramic segments, each segment having at least two opposite surfaces that are flat and parallel. The segments are aligned in stacked relationship with their flat faces in abutting face-to-face relation and forced toward each other in the direction of their composite length with a force which is sufficient to maintain the segments in compression when subjected to conditions of thermal change and/or flexing of the member during use. The ceramic member is provided with a smooth elongated working surface which defines an area of contact with the cylindrical member. A method for making the ceramic member is disclosed.
Description
lOS~Z43 This invention relates to papermaking systems including two members that are movable relative to one another, and more particularly to a wear-resistant, flexible member which is a doctor blade member for removing a paper web fr~m a cylinder where the member is to be subjected to conditions of thermal change and/or forces tending to bend the member along its length. This application is a divisional of our Canadian Patent ~pplication No.
222,181 filed March 17, 1975.
The physical properties and/or the chemical inertness of ceramic materials frequently suggest such materials for use in applications wherein the material is to be subjected to potential physical and/or chemical degradation as by frictional forces, corrosion, or other erosive forces. Not infrequently, ceramic elements or members are of considerable length and subjected to thermal change or forces, such as vibration or frictional drag, which tend to bend or deflect the member along its longitudinal axis.
Because of the relatively high cost and difficulty of manufacturing ceramic members in continuous lengths, for example lengths greater than about two feet, ceramic materials have heretofore been generally limited to use in those situations where their relatively high cost is justified in order to obtain the advantages from the physical and/or chemical properties of the ceramic materials. Even in such special situations where ceramic lengths have been employed, it has been important to assure that the elongated ceramic members neither bend nor are subjected to localized stresses, so as to avoid cracking and/or breaking of the elongated member. Conse~uently, the circumstances under which elongated ceramic members could be used heretofore have been severly limited.
Commonly in papermaking systems, there are two members, one of which is movable relative to the other ~nd in frictional .
lOSlZ43 engagement therewith. In these s~stems, at least one of the members will possess a working or wear surface defining an area of contact between the members. The invention is concerned with a particular system of this kind, notably a doctor blade for use in contact with rotating drums or other mo~ing cylindrical members. In these systems, the member having the wear surface frequently is of elongated geometry and has a leng~h as great as 20 to 30 feet, or greater.
In papermaking machines, e.g. a Fourdrinier machine, a twin wire machine, or t~- like, a dilute slurry of wood fibers in a water medium is deposited on a moving screen known in the art as a wire. Water drains and/or is withdrawn from the slurry and through the openings in the wire to produce a self-sustaining paper web. These wires may be made of a metal or plastic as known in the art.
Various drainage devices have been employed hereto-fore for aiding withdrawal of water from the slurry by developing suction on that side of the wire opposite the slurry carried thereon,and a ceramic foil which performs this function i8 the subject of the aforesaid parent Canadian Patent Application No.
222,181.
In certain papermaking systems the paper web from the press section is fed over a cylindrical dryer such as the well-known Yankee Dryer for further drying of the web. In these systems the web is trained about a portion of the peripheral surface of the dryer and dried by heat transferred through the cylindrical shell thereof. Steam introduced into the interior of the dryer shell is commonly used to heat the shell. The dry paper web is doctored from the shell by means of a doctor blade comprising an elongated blade member extending transversely of the direction of the rotation of the dryer and frequently in contact with the exterior cylindrical ~051243 surface of the dryer along a line extending across the dryer surface substantially parallel to the rotational axis of the dryer. In operation of these dryers, the surface of the dryer shel;l becomes irregular due to it being heated by the steam. In order to keep the doctor blade in contact with the shell for doctoring the web from the shell, it is necessary to bend the doctor blade so that it conforms to the irregularites from the shell surface. In this and other systems of this type, it is desired that the elongated blade member be flexible and have -~
a good wear surface.
It is therefore an object of the present invention to provide an elongated flexible ceramic member useful in a papermaking system as a doctor blade.
In accordance with the present invention, in a paper-making system including a rotating cylindrical member carrying a paper web on the outer cylindrical surace thereof and an elongated doctor blaae disposed adjacent said surface for removing said web from said surface, the doctor blade comprises:-an elongated flexible assemblage including a plurality of ceramic segments, each having at least two opposite surfacesthat are substantially flat and parallel, said segments being aligned with their flat faces in abutting face-to-face relation and in respective planes that are oriented substantially perpen-dicularly to the composite length of said plurality of segments, and tension means extending between opposite ends of said assemblage and adapted to force said segments toward each other in a direction along their composite length and substantially perpendicular to their respective parallel faces with a preload force on said tension means calculated as set out hereinafter.
Other features of the invention will be recognized from the following description and claims, including the drawings in which: lOSlZ43 FIGURE 1 is a representation, in perspective and partly ~ ~-cut-away, of a foil for a paper making machine and which embodies various features of the doctor blade of this invention;
FIGURE 2 is an enlarged fragmentary view, partly in section, showing a portion of the foil of FIGURE l;
FIGURE 3 is an end view, partly cut-away, of the foil shown in FIGURE l;
FIGURE 4 is a representation of a segment of the ~ .
foil s~own in FIGURE l;
FIGURE 5 is a front view of the segment shown in FIGURE 4;
FIGURE 6 is a representation of an elongated segmented ceramic doctor blade member embodying various features of the invention;
FIGURE 7 is a representation of a segment of the member shown in FIGURE 7;
FIGURE 8 is a representation of one embodiment of a system including at least two relatively movable members and showing various features of the invention;
FIGURE 9 is a grossly exaggerated representation of a plurality of segments deflected in a manner to aid in explaining certain calculations attending the disclosed invention; and FIGURE 10 is a grossly exaggerated representation of a portion of a deflected composite of ceramic segments.
In accordance with the present disclosure, there is provided a ceramic doctor blade member formed from a plurality of segments, each having opposite flat faces that are aligned with their flat faces in abutting face-to-face relation, the segments being held in their abutting relation by tension means which maintains the segments in compression such that the abutting . .
lOS~243 segment faces do not separate and form a gap or gaps there^
between when the member is subjected to flexing forces or to thermal change.
FIGURES 1-5 depict a system including a foil as specifically claimed in co-pending parent Canadian Application No. ~22,181. The foil 10 is positioned transversely of and in contact with the wire 15 of a papermaking machine which moves thereacross with the front edge 13 of the foil in contact with the wire. The foil includes a trailing edge 17 which diverges from the wire to form an acute angle therebetween. It has been found that the foil can be provided with the desirable wear characteristics of a ceramic material and also be made sufficiently flexible to enable the foil to withstand the maximum deflection of the foil anticipated in a papermaking machine.
The illustrated foil 10 comprises a support structure 11 on which there is mounted an assemblage 14 of ceramic segments or wafers 12, each being of generally rectangular geometry and having two opposite parallel faces 16 and 18.
The sel~ments are disposed in face-to-face relation with their parallel faces abutting the parallel faces of adjacent segments to define an elongated assemblage 14 of a length sufficient to extend fully across the width of the wire 15 moving across the foil. As will appear hereinafter, the abutting faces of adjacent segments are subjected to a compressive force applied at substantially right angles to the faces. To prevent cracking or breaking of the seg-ments due to unevenly applied stresses, the faces 16 and 18 are each substantially flat and are oriented substantially parallel to each other and substantially perpendicular to the longitudinal axis of the assemblage 14. Each of the parallel faces is flat and smooth to within less than about 20 microinches (AA) so that when the individual segments are placed in face-to-face relation, the abutting flat faces of 105~Z43 adjacent segments lie in contact with each other over sub-stantially the entire areas of the abutting faces without significant open space therebetween. An opening 20 extending between the opposite flat faces 16 and 18 of each segment is aligned with similar openings of the abutting segments to provide a channel 22 through the assemblage.
Each illustrated segment further includes a flat top surface 26, a flat bottom surface 28, and forward and rear surfaces 30 and 32, respectively. The forward surface 30 extends upwardly from the bottom surface 28 to join the forward edge of the top surface 26 and define an acutely angled leading edge 34. As indicated, the top surface 26 of each segment is flat. The rear edge of such flat surface 26 transists into a diverging trailing surface 36. In the illustrated segments, the trailing surface 36 is generally arcuate to provide an increasingly greater acute angle between the trailing surface 36 and the Fourdrinier wire 15 passing over the foil (see FIGURE 3). It may be desired in certain applications to not use the foil in withdrawing water, in which case the entire top surface of each segment may be flat. Alternatively, the trailing surface 36, itself, may be substantially flat so as to form a constant angle with the wire.
In producing a foil of given length, a sufficient number of segments 12 are assembled in face-to-face relation with their respective openings 20 aligned to obtain the desired foil length. The assembled segments are secured together with a force applied substantially in the direction of the length of the assemblage 14 and substantially perpendicular to the flat parallel faces of the segments. This force is sufficient to place the segments in elastic compression and is suitably applied as by a tension means applying a compressive force to opposite ends 37 and 39 of the assemblage 14. One suitable lOS~'~43 tension means is a cable 24 inserted through the aligned openings 20 of the assembled segments, pulled to the required length, anchored at the opposite ends of the assemblage as by swage fittings 41, and released to exert a compressive force to the assemblage at its opposite ends. Alternatively, other tension means may be used to establish the desired compression of the segments in the assemblage. One such other means includes a rod disposed in the aligned openings 20 of the segments and fitted with a nut at one or both of its ends so that tightening of the nuts tensions the rods and places the segments in compression. One suitable cable for applying the desired compression force to the segments is made of carbon steel and of the general type employed in prestressed concrete structures.
The cable 24 may be chosen with a diametral dimension less than the diametral dimension of the opening 20 in each segment and after the segment is in place on the cable the space between the cable and the inside surface of the opening 20 in the segment may be filled with agrout 44, such-as r~id polyurethane, to position the cable within the openings 20 and to provide added assurance that the segments do not rotate about the cable and that the faces of adjacent segments remain flush with each other. One suitable grout is a liquid casting urethane polymer designated as LD-2699, sold by E. I. Du Pont de Nemours Company, Trenton, New Jersey. This grout also accommodates the axial movement of the segments with respect to the compression cable during compression of the stacked array.
In one embodiment, the assemblage of segments is provided with a plate or other means such as a metallic segment 40 at each end of the assemblage to provide for distribution of the compressive force over the face of each encl segment to protect it from destruction by localized forces. A plurality of tension means may be employed to force the segments into lOS~;~43 the desired compression and in those instances where the desired compression is relatively great, such provide greater compxession capability. Multiple, spaced apart, tension means also aid in more evenly distributing the compressive forces over the abutting faces of the segments.
In the assemblage 14 of segments, the individual segments 12 are oriented with respect to each other in a manner such that their common surfaces lie in common planes to combine with each other to define an elongated substantially flat top surface 46 extending along the length of the foil and adapted to contact and support a Fourdrinier wire 15 moving thereacross. The combined aligned faces also define an elongated trailing surface 48 which is a continuation of the flat surface 46 but diverges downwardly away from the wire 15 to define a generally triangular (cross-section) zone 50 between the trailing surface 48 and the Fourdrinier wire 15.
It i5 in this zone 50 that the usual relatively low pressure is developed which assists withdrawal of water from a slurry of paper fibers carried on the wire. The elongated assemblage 14 of ceramic segments further includes an inclined forward ~urface 52, defined by the combined forward faces of the segments, that joins the forward edge of the flat top surface 46 to define an acutely angled leading edge 13 extending the length of the foil and which functions to scrape water from the wire as it moves past the stationary foil. Alignment of the segments so that their common surfaces combine to provide the described foil surfaces is accomplished during assembly.
In the illustrated foil 10, the stack 14 of ceramic seg-ments 12 is mounted in a support saddle 56 which in turn is mounted on existing superstructure of a usual Fourdrinier paper-making machine (not shown). Such papermaking machines, their structure and operation, are well known in the art and need not be discussed herein. Preferably, the support saddle ~6 is removably 105~243 secured in position on the papermaking machine as by means of bolts 60 that join the support saddle at spaced apart locations to an elongated bar 58 that extends between opposite sides of the papermaking machine and which is itself secured at its opposite ends to the papermaking machine. The support saddle 56 and the bar 58, being securely joined to each other at relatively closely spaced points, exhibit thermal expansion characteristics that are some combination of the individual thermal characteristics of the saddle 56 and bar 58. It will be recognized that if the saddle and bar are of the same material, they will exhibit the thermal expansion characteristic of such material.
The support saddle 56, in the illustrated foil, includes an elongated bottom portion 82 in FIGURE 1 which re~ides on and is bolted to the bar 58 to join the saddle to the bar referred to above. A rear wall portion 64, formed integrally with the bottom p~rtion, extends upwardly from the bottom portion 62 of the saddle. The upper surface 66 of the bottom section 62 and the forward surface 68 of the rear wall 64 receives the bottom surfaces 28 and at least a portion of the rear surfaces 32 of the stacked segments to provide support for the segments and position them for engage-ment with the wire 15. At the juncture of its surface 66 and its surface 68, the support saddle is cut away along its length to accommodate the bottom rear corners 70 of the segments.
In the illustrated support saddle, these surfaces 66 and 68 define an acute angle therebetween into which the corners 70 of the segments fit thereby restraining the segments against upward movement out of the support saddle. ~urther support and retention of the segments in the saddle 56 is provided by a plurality of clamps 72 that are removably attached as by bolts 74 to the bottom portion 62 of the saddle at locations spaced along the length of the foil. A generally semi-circular (cross-section) groove 76 extending parallel to the longitudinal axis of the foil is provided on that face 78 of the clamp next to the segments. A similar groove 80 is provided on the forward face of each segment so that the two grooves define a generally circular channel between each clamp and the segments faced by the clamp. A relatively non-yielding cylindrical rod 82 is fitted into the channel defined by the grooves 76 and 80 to prevent movement of the segments with respect to the clamps 72 and thereby hold the segments in position in the saddle 56.
One e~.~odiment of a system which includes an elongated flexible ceramic member and which includes at least two members, one of which is movable relative to the other and in frictional engagement therewith is the doctor system depicted in FIGURES 6-8~ This depicted system includes Yankee Dryer 200 on which a paper web 202 is dried and creped.
The web is trained about a portion of the peripheral surface of the dryer 20 and dried by heat transferred through the cylindrical shell 204 therof. Steam introduced into the interior of the dryer shell is commonly used to heat the shell. The ', paper web 202 is dGctored from the shell 204 by means of a doctor blade 206 as is well known in the art to provide a creped paper web 208. In this embodiment, the dryer shell 204 compri~es a first member of the system and is movable relative to and in frictional engagement with the doctor blade 206 which comprises a second member of the system.
In the system depicted in FIGURE 8 , the doctor blade 206 is positioned with respect to the dryer surface 204 and to the paper web 202 by support means shown generally at 210 including a pair of jaws 212 and 213 having shoulders 214 and 215, respectively, that engage mating slots 216 and 217 in opposite surfaces of the doctor blade 206. Other suitable -mountlng means will be readily recognized by one skilled in the art.
In operation of the depicted system, the surface of the shell 204 becomes irregular due to its being heated by the steam. In order to keep the doctor blade in contact with the shell for doctoring the web from the shell, it is necessary to bend the doctor blade so that it conforms to the lrregularities in the shell surface.
In such a system it is desired that the doctor blade be flexible and have a good wear surface that is engaged by the shell. It has long been desired that such a doctor blade be made of a ceramic material to take advantage of the wear resistance of this material. Continuous lengths of ceramic are pro-hibitively costly. Members having small ceramic inserts dlsposed along the length of the member to define a wear surface have been tried but such members develop gaps between the inserts where the member bends during use so that the edges and/or corners of the separated segments become points of excessive wear.
The illustrated doctor blade system comprises an elongated flexible member including a plurality of ceramic segments 220 each having at least two opposite substantially parallel flat faces 224 and 226 (FIGURE 7 ). Each of the depicted segments 220 further includes an upper flat surface 230 which joins a forward upright surface 232 to define a leading edge 234, and an opening 236 extending through each segment between its opposite flat surfaces 224 and 226. A
plurality of these segments are assembled in face-to-face abut~ing relationship with their leading edges aligned to define the doctor blade 206. As illustrated, the flat faces 224 and 226 of each segment are disposed substantially perpendicular to the longitudinal axis, i.e. the composite length, of the com~osite memb~ . The aligned segments 220 ~05~243 are forced toward each other by a tension means 238, anchored to opposite ends of the composite, with a force which elastically compresses the segments.
Each of the segments of each of the elongated members of the present disclosure is fabricated from a hard dense ceramic material that is available at a reasonable cost.
The ceramic preferably is an impervious crystalline material that combines high mechanical strength with extreme hardness, inertness, refractoriness, and high chemical - lla -.: :
: .
resistance properties. Because these properties are retained over a wide range of application and environmental conditions that many other materials cannot withstand, such ceramics suitably serve under conditions adverse to other materials.
Alumina, silicon carbide, boron carbide and silicon nitride materials possess those properties required in many industrial applications, and economically feasible for such end uses.
Alumina is particularly suitable and is preferred for use in the present ceramic member because of its properties and its availability at relatively low cost when formed in relatively short segments.
The alumina segment is formed by compacting finely ground oxide powers with fluxing agents and inhibitors at relatively high pressures as is known in the art. Forming methods include dry pressing, isostatic pressing, casting, extrusion, and injection molding. After forming, the resulting "green" ceramic segment i5 fired at a high temperature for a specific length of time. Firing temperatures vary but usually range between 2,500F. and 3,250F. During firing the ceramic shrinks; therefore, segments are formed while in the green state to allow for the physical reduction caused by firing.
After firing, the ceramic segment is strong, hard and dense, composed substantially of pure alumina of controlled crystal size. Machining of the ceramic segments is possible either before or after firing. Fired segments are ground or lapped to obtain the desired surfaces thereof. Grinding usually must be done with diamond-impregnated wheels, although silicon-carbide or alumina wheels are sometimes used.
Most of those physical properties desired in the ceramic segments improve as the purity of the ceramic increases especially hardness, compressive strength, wear resistance and lOSlZ43 chemical resistance. For example, alumina ceramic compositions having aluminum oxide contents less than about 85~ lose certain of their properties to an unacceptable degree. Preferably, the alumina ceramics contain about 90.0% or more aluminum oxide.
The compressive strength of the ceramics exceed that for most materials. For example, compressive strengths as high as 550 ! pSi have been obtained in certain relatively pure alumina ceramics. Suitable compressive strengths for the ceramic segments range upwardly from about 200,000 psi.
Each of the segments is provided with two opposite sub-stantially flat and parallel faces. The segments are disposed in face-to-face relation with their parallel faces abutting the parallel faces of adjacent segments to define the elongated composite of a desired length and subjected to a compressive force applied at substantially right angles to the faces. The flatness and parallelism of the abutting segment faces help to prevent cracking or breaking o the segments due to unevenly applied stresses or localized stresses ky distributing the compressive forces evenly over the abutting faces. Abutting segment faces, each of which is flat to within about 0.0002 inches and has a surface finish of less than about 20 microinches arithmetic average (AA) have been found to be suitable for these purposes. When such individual segments are placed in face-to-face relation without grout or adhesive, the abutting flat faces of adjacent segments lie in intimate contact with each other over substantially the entire areas of the abutting faces without significant open space therebetween so that the abutting faces supply support to each other especially when the surface of the member is being ground as will be described hereinaftern In one embodi-ment, each segment is provided with an opening ~xtending betweenthe opposite flat faces thereof. This opening in a segment is aligned with similar openings of abutting segments to provide 1051Z43 ~ ~
a channel through the composite for receiving a tension means for compressing the segments in the direction of their composite length.
As noted above, in producing an elongated member of given length, a sufficient number of segments are assembled in face-to-face relatlon with their respective openings aligned to obtain the desired length. The assembled segments are secured together with a force applied substantially in the direction of the length of the composite and substantially perpendicular to the flat parallel faces of the segments.
This force is sufficient to place the segments in elastic compression, and produce a significant compressive strain, and is suitably applied as by a tension means applying a compressive force to opposite ends of the composite. One suitable tension lS means is a cable inserted through the aligned openings extending between the opposite faces of each of the assembled segments, pulled to the required length, anchored at the opposite ends of the composite as by swage fittings to exert a compressive force upon the composite at its opposite ends. Alternatively, other tensioning means may be used to establish the desired compression of the segments in the composite. One such other means includes a rod disposed in the aligned openings of the segments and fitted with a nut at one or both of its ends so that tightening of the nuts tensions the rod and places the segments in compression. One suitable cable for applying the desired compression force to the segments is made of carbon -~- steel and of the--general type employed in prestressed concrete structures.
The cable may be chosen with a cross sectional area 30 less than the cross sectional area of the opening in each segment and after the segment is in place on the cable the space between the cable and the inside surface of the opening , ......... . .
lOSlZ43 in the segment may be filled with a grout 44 (FIGURE 2) such as rigid polyurethane, to position the cable within the openings.
One s~itable grout is a liquid casting urethane polymer designated as L~-2699, sold by E. I. Du Pont de Nemours ~ompany, Trenton, New Jersey. This grout aIso accommodates the axial movement of the segments with respect to the compression cable during compression of the composite and/or relative movement between the segments and the cable in the event the member is subjected to thermal change during use.
As illustrated, the composite of segments may be provided with a plate or other means such as a metallic segment at each end of the composite to provide for distribution of the compressive force over the face of each end segment to protect it from damage by localized forces. In those instances where the desired compression is relatively great a plurality of tension means, e.g~ cables, provides greater compressive capability. In that event, the plurality of cables are desirably threaded through spaced apart, aligned openings through the segments. Such construction aids in more evenly di~tributing the compressive forces over the abutting faces of the segments.
The flexibility of the ceramic member is made possible by employing relatively short segments (e.g. on the order of one inch long) held together with a compressive force such that when the elongated composite deflects by a distance d, along its length (see FIGURES 9-10 ), at least a part of the compression, e.g. compressive strain, in those portions 240 and 242 of the abutting faces 244 and 246 of adjacent segments disposed on the outside of the line of curvature A of the deflected composite is relieved, permitting those portions of the segments to expand to accommodate the deflection without physically separating. Importantly, the lOSlZ43 compressive force holding the segments together is less than the maximum compressive strength of the ceramic material by an amount which permits those portions 248 and 250 of the abutting faces 244 and 246 of adjacent segments on the inside of the line of curvature A of the deflected composite to be compressed by an additional amount, causing these portions of the segments to compress by an amount sufficient to accommodate the deflection without destruction of the segments.
In addition, the length of the individual segments is chosen to be sufficiently small as permits their manufacture at minimized costs taking into consideration the anticipated compressive forces to which the segments are to be subjected in order to obtain the desired response to the composite incident to deflective forces.
In addition to the deflective forces, consideration must be given to thermal changes affecting the element in that ~uch will usually produce different responses in the ceramic segments and the tension member. Such thermal changes can arise by differences in the start-up and operating temperatures s of the machine or system in which the element is installed, and/or changes in ambient temperature of the element during assembly, shipping or installation.
In calculating the compression required to accommodate the maximum anticipated deflection of a member of given length without separation of the segments, it is assumed that the deflection of the member will take the shape of a uniformly loaded simple beam and that the maximum deflection will be sufficiently small (less than about 1% of the member length) to permit the use of calculations based on circular arcs, rather than re exact curves. The latter could be used in those circumstances where more exact calculations are required;
iOSlZ43 however, it has been found that such is not necessary in constr~lcting flexible members for most end uses. More specifically, and with reference to FIGURES 14 and 15, for a ceramic member of given length, Q tin inches), having a longitudinal axis subjected to a maximum anticipated deflection, d (in inches), along a line of curvature A, and made up of a plurality of segments each being of a known length, and a dimension, h (in inches, across the segments, in the direction of the applied deflective force and a cross-sectional area, A , in square inches, the preloading on the tension member, e.g. cable 24 (FIGURE 1), which will impart to the ceramic segments the necessary compressive force that precludes separation of the segments is calculated using the equation / 8dh p ECAc \ 12 + 4d ) Eq. (1) where:
Ec = the modulus of elasticity of the ceramic;
Ac = the cross-sectional area of a ceramic segment in a plane perpendicular to the composite length of the member, in square inches;
d = the maximum anticipated deflection of the member, in inches;
h = the dimension of a ceramic segment in the plane perpendicular to the composite length of the member and in alignment with the direction of the deflective force, in inches; and ~ = the overall length of the member_ With reference to Equation (1), it is noted that the initially determined preloading is divided by 2 to give the preloading to be used in tensioning the cable. This fact arises beca~se of the manner in which the ceramic segments are stressed when the member is deflected while under compression. More specifically, assuming the cable is dispose!d midway between the ends of the segment dimension h, when the member is in an undeflected state, the stress on each compressed ceramic segment is the same at any point along the dimension h. When the member is deflected, the stress in that portion of a segment on the outside of the line of curvature (on the outside end of the dimension h) is reduced toward zero and the stress in that portion of the same segment on the inside of the line of curvature is doubled. Thus when preloading the aligned segments, the stres~ imparted to the segments is taken as the aYerage of the stresses along the dimension h when the member is deflected by a maximum amount.
The effect of thermal change upon the ceramic member must also be taken into account. Thermal changes occur most frequently by reason of the ceramic member being manufactured at a first temperature, room temperature for example, and i- ~ thereafter encountering a substantially higher operating temperature. In such circumstances, the strain in the cable decreases when its temperature increases by reason of the cable expanding when heated. Expansion of the cable cross-section as well as along its length is of importance. Theceramic also expands when heated, but usually to a lesser extent than the cable,~so that there is added to the preload calculated for deflection in accordance with Equation (1), an additional preloading which will compensate for the effect of thermal change upon the cable and the ceramic and provide the desired preloading for accommodating deflection up to a maximum temperature. Such additional preloading of the 10$1243 tension means is calculated using the equation (~B ~C) ~ T
PT 1 1 Eq. (2) A E + A E
S s c c Where:
C~ s = the coefficient of thermal expansion of the tension member;
c = the coefficient of thermal expansion of the ceramic;
~ T = degrees of temperature change anticipated, in degrees F;
As = cross-sectional area of the tension member, in square inches;
Es = the modulus of elasticity of the tension member;
Ac ~ the cross-sectional area of a ceramic segment in a plane perpendicular to the length of the member, in square Lnches;
Ec = the modulus of elasticity of the ceramic.
Combining Equations (1) and (2) gives ( ~ + 4d ) + ~ s c)~ T
AsEs AcEc where P is the total preloading of the tension member which wi11 prevent separation of the segments of the member 30 when the member is deflected up to a maximum amount d while at a temperature less than an anticipated maximum temperature it will be noted that in those situations where the ceramic member will not experience a thermal change, ~ T will be zero and PT [including its equivalent expression in Equation ~3)] will be zero and no additional preloading will be required lOS~243 to account for thermal changes.
Thus, in any given situation where the elongated ceramic member is to be subjected to aeflection forces, it is possible to select a composite which exhibits the desired non-separation of abutting segment faces when the composite is def:Lected along its composite length. As shown in Equation (1), the preloading force (compressive force) applied to the aligned segments, for any given maximum anticipated deflection and total length of the segmented member, depends upon the length of each individual segment and the dimension h of each segment. Thus, if the deflection capability of a given composite of ceramic segments is less than that which precludes physical separation of the abutting faces of the segments under the anticipated deflection, an adjustment can be made, in many lS instances, in either the length or width of the individual segments, or in both the length and width. Of course, con~ideration must be given to the added compression experienced by those portions of the abutting segment faces disposed on the inside of the line of curvature of the deflected composite.
~he preloading force exerted upon the ceramic segments is kept below that amount of force which will compress the ceramic material to within about one-half, and preferably to within about 20 percent, of its maximum compressive strength to insure that localized stresses which may occur within the composite do not exceed such maximum compressive strength with resultant damage to one or more segments. This preferred preloading also provides a substantial margin of safety against damage to the segments by inadvertent over-loading of the segments to produce undue deflection. In any event, the preloading of the segments is sufficient to shsrten the length of each segment, hence shorten the overall length of the composite.
Further, in the preferred preloading, the segments are sufficiently deformed at the interface between lOS1~43 abutting segment faces as results in substantial loss of joint identity at such interface. Such deforn~ation is known to occur when the segments are preloaded to between about 15% and 20% of the maximum compressive strength of the ceramic. This substantial loss of joint identity has been found to be important in establishing the working surface on the member in that such allows the composite to be ground to a suitable smoothness. Less preloading is acceptable but at a loss of certainty of achieving the desired properties in the composite. Thus, the preloading of the ceramic segments must be sufficient to maintain the segments abutting when the member is deflected by a maximum amount d but less than that preloading which will compress the ceramic to more than one-half its total compressive strength.
It is understood that in the present discussion each of the segments is substantially identical to each other segment in a given composite~ Such is assumed for purposes of simpli-fying the disclosure. It is not required, however, that all of the segments be identical. For example, it may be desirable to provide a segmented member which is deflected by different degrees along it9 length. In such an embodiment, the deflective characteristics of the member will differ in different portions of its length and the segments in each such portion may differ in length from the segments in other portions of the length of
222,181 filed March 17, 1975.
The physical properties and/or the chemical inertness of ceramic materials frequently suggest such materials for use in applications wherein the material is to be subjected to potential physical and/or chemical degradation as by frictional forces, corrosion, or other erosive forces. Not infrequently, ceramic elements or members are of considerable length and subjected to thermal change or forces, such as vibration or frictional drag, which tend to bend or deflect the member along its longitudinal axis.
Because of the relatively high cost and difficulty of manufacturing ceramic members in continuous lengths, for example lengths greater than about two feet, ceramic materials have heretofore been generally limited to use in those situations where their relatively high cost is justified in order to obtain the advantages from the physical and/or chemical properties of the ceramic materials. Even in such special situations where ceramic lengths have been employed, it has been important to assure that the elongated ceramic members neither bend nor are subjected to localized stresses, so as to avoid cracking and/or breaking of the elongated member. Conse~uently, the circumstances under which elongated ceramic members could be used heretofore have been severly limited.
Commonly in papermaking systems, there are two members, one of which is movable relative to the other ~nd in frictional .
lOSlZ43 engagement therewith. In these s~stems, at least one of the members will possess a working or wear surface defining an area of contact between the members. The invention is concerned with a particular system of this kind, notably a doctor blade for use in contact with rotating drums or other mo~ing cylindrical members. In these systems, the member having the wear surface frequently is of elongated geometry and has a leng~h as great as 20 to 30 feet, or greater.
In papermaking machines, e.g. a Fourdrinier machine, a twin wire machine, or t~- like, a dilute slurry of wood fibers in a water medium is deposited on a moving screen known in the art as a wire. Water drains and/or is withdrawn from the slurry and through the openings in the wire to produce a self-sustaining paper web. These wires may be made of a metal or plastic as known in the art.
Various drainage devices have been employed hereto-fore for aiding withdrawal of water from the slurry by developing suction on that side of the wire opposite the slurry carried thereon,and a ceramic foil which performs this function i8 the subject of the aforesaid parent Canadian Patent Application No.
222,181.
In certain papermaking systems the paper web from the press section is fed over a cylindrical dryer such as the well-known Yankee Dryer for further drying of the web. In these systems the web is trained about a portion of the peripheral surface of the dryer and dried by heat transferred through the cylindrical shell thereof. Steam introduced into the interior of the dryer shell is commonly used to heat the shell. The dry paper web is doctored from the shell by means of a doctor blade comprising an elongated blade member extending transversely of the direction of the rotation of the dryer and frequently in contact with the exterior cylindrical ~051243 surface of the dryer along a line extending across the dryer surface substantially parallel to the rotational axis of the dryer. In operation of these dryers, the surface of the dryer shel;l becomes irregular due to it being heated by the steam. In order to keep the doctor blade in contact with the shell for doctoring the web from the shell, it is necessary to bend the doctor blade so that it conforms to the irregularites from the shell surface. In this and other systems of this type, it is desired that the elongated blade member be flexible and have -~
a good wear surface.
It is therefore an object of the present invention to provide an elongated flexible ceramic member useful in a papermaking system as a doctor blade.
In accordance with the present invention, in a paper-making system including a rotating cylindrical member carrying a paper web on the outer cylindrical surace thereof and an elongated doctor blaae disposed adjacent said surface for removing said web from said surface, the doctor blade comprises:-an elongated flexible assemblage including a plurality of ceramic segments, each having at least two opposite surfacesthat are substantially flat and parallel, said segments being aligned with their flat faces in abutting face-to-face relation and in respective planes that are oriented substantially perpen-dicularly to the composite length of said plurality of segments, and tension means extending between opposite ends of said assemblage and adapted to force said segments toward each other in a direction along their composite length and substantially perpendicular to their respective parallel faces with a preload force on said tension means calculated as set out hereinafter.
Other features of the invention will be recognized from the following description and claims, including the drawings in which: lOSlZ43 FIGURE 1 is a representation, in perspective and partly ~ ~-cut-away, of a foil for a paper making machine and which embodies various features of the doctor blade of this invention;
FIGURE 2 is an enlarged fragmentary view, partly in section, showing a portion of the foil of FIGURE l;
FIGURE 3 is an end view, partly cut-away, of the foil shown in FIGURE l;
FIGURE 4 is a representation of a segment of the ~ .
foil s~own in FIGURE l;
FIGURE 5 is a front view of the segment shown in FIGURE 4;
FIGURE 6 is a representation of an elongated segmented ceramic doctor blade member embodying various features of the invention;
FIGURE 7 is a representation of a segment of the member shown in FIGURE 7;
FIGURE 8 is a representation of one embodiment of a system including at least two relatively movable members and showing various features of the invention;
FIGURE 9 is a grossly exaggerated representation of a plurality of segments deflected in a manner to aid in explaining certain calculations attending the disclosed invention; and FIGURE 10 is a grossly exaggerated representation of a portion of a deflected composite of ceramic segments.
In accordance with the present disclosure, there is provided a ceramic doctor blade member formed from a plurality of segments, each having opposite flat faces that are aligned with their flat faces in abutting face-to-face relation, the segments being held in their abutting relation by tension means which maintains the segments in compression such that the abutting . .
lOS~243 segment faces do not separate and form a gap or gaps there^
between when the member is subjected to flexing forces or to thermal change.
FIGURES 1-5 depict a system including a foil as specifically claimed in co-pending parent Canadian Application No. ~22,181. The foil 10 is positioned transversely of and in contact with the wire 15 of a papermaking machine which moves thereacross with the front edge 13 of the foil in contact with the wire. The foil includes a trailing edge 17 which diverges from the wire to form an acute angle therebetween. It has been found that the foil can be provided with the desirable wear characteristics of a ceramic material and also be made sufficiently flexible to enable the foil to withstand the maximum deflection of the foil anticipated in a papermaking machine.
The illustrated foil 10 comprises a support structure 11 on which there is mounted an assemblage 14 of ceramic segments or wafers 12, each being of generally rectangular geometry and having two opposite parallel faces 16 and 18.
The sel~ments are disposed in face-to-face relation with their parallel faces abutting the parallel faces of adjacent segments to define an elongated assemblage 14 of a length sufficient to extend fully across the width of the wire 15 moving across the foil. As will appear hereinafter, the abutting faces of adjacent segments are subjected to a compressive force applied at substantially right angles to the faces. To prevent cracking or breaking of the seg-ments due to unevenly applied stresses, the faces 16 and 18 are each substantially flat and are oriented substantially parallel to each other and substantially perpendicular to the longitudinal axis of the assemblage 14. Each of the parallel faces is flat and smooth to within less than about 20 microinches (AA) so that when the individual segments are placed in face-to-face relation, the abutting flat faces of 105~Z43 adjacent segments lie in contact with each other over sub-stantially the entire areas of the abutting faces without significant open space therebetween. An opening 20 extending between the opposite flat faces 16 and 18 of each segment is aligned with similar openings of the abutting segments to provide a channel 22 through the assemblage.
Each illustrated segment further includes a flat top surface 26, a flat bottom surface 28, and forward and rear surfaces 30 and 32, respectively. The forward surface 30 extends upwardly from the bottom surface 28 to join the forward edge of the top surface 26 and define an acutely angled leading edge 34. As indicated, the top surface 26 of each segment is flat. The rear edge of such flat surface 26 transists into a diverging trailing surface 36. In the illustrated segments, the trailing surface 36 is generally arcuate to provide an increasingly greater acute angle between the trailing surface 36 and the Fourdrinier wire 15 passing over the foil (see FIGURE 3). It may be desired in certain applications to not use the foil in withdrawing water, in which case the entire top surface of each segment may be flat. Alternatively, the trailing surface 36, itself, may be substantially flat so as to form a constant angle with the wire.
In producing a foil of given length, a sufficient number of segments 12 are assembled in face-to-face relation with their respective openings 20 aligned to obtain the desired foil length. The assembled segments are secured together with a force applied substantially in the direction of the length of the assemblage 14 and substantially perpendicular to the flat parallel faces of the segments. This force is sufficient to place the segments in elastic compression and is suitably applied as by a tension means applying a compressive force to opposite ends 37 and 39 of the assemblage 14. One suitable lOS~'~43 tension means is a cable 24 inserted through the aligned openings 20 of the assembled segments, pulled to the required length, anchored at the opposite ends of the assemblage as by swage fittings 41, and released to exert a compressive force to the assemblage at its opposite ends. Alternatively, other tension means may be used to establish the desired compression of the segments in the assemblage. One such other means includes a rod disposed in the aligned openings 20 of the segments and fitted with a nut at one or both of its ends so that tightening of the nuts tensions the rods and places the segments in compression. One suitable cable for applying the desired compression force to the segments is made of carbon steel and of the general type employed in prestressed concrete structures.
The cable 24 may be chosen with a diametral dimension less than the diametral dimension of the opening 20 in each segment and after the segment is in place on the cable the space between the cable and the inside surface of the opening 20 in the segment may be filled with agrout 44, such-as r~id polyurethane, to position the cable within the openings 20 and to provide added assurance that the segments do not rotate about the cable and that the faces of adjacent segments remain flush with each other. One suitable grout is a liquid casting urethane polymer designated as LD-2699, sold by E. I. Du Pont de Nemours Company, Trenton, New Jersey. This grout also accommodates the axial movement of the segments with respect to the compression cable during compression of the stacked array.
In one embodiment, the assemblage of segments is provided with a plate or other means such as a metallic segment 40 at each end of the assemblage to provide for distribution of the compressive force over the face of each encl segment to protect it from destruction by localized forces. A plurality of tension means may be employed to force the segments into lOS~;~43 the desired compression and in those instances where the desired compression is relatively great, such provide greater compxession capability. Multiple, spaced apart, tension means also aid in more evenly distributing the compressive forces over the abutting faces of the segments.
In the assemblage 14 of segments, the individual segments 12 are oriented with respect to each other in a manner such that their common surfaces lie in common planes to combine with each other to define an elongated substantially flat top surface 46 extending along the length of the foil and adapted to contact and support a Fourdrinier wire 15 moving thereacross. The combined aligned faces also define an elongated trailing surface 48 which is a continuation of the flat surface 46 but diverges downwardly away from the wire 15 to define a generally triangular (cross-section) zone 50 between the trailing surface 48 and the Fourdrinier wire 15.
It i5 in this zone 50 that the usual relatively low pressure is developed which assists withdrawal of water from a slurry of paper fibers carried on the wire. The elongated assemblage 14 of ceramic segments further includes an inclined forward ~urface 52, defined by the combined forward faces of the segments, that joins the forward edge of the flat top surface 46 to define an acutely angled leading edge 13 extending the length of the foil and which functions to scrape water from the wire as it moves past the stationary foil. Alignment of the segments so that their common surfaces combine to provide the described foil surfaces is accomplished during assembly.
In the illustrated foil 10, the stack 14 of ceramic seg-ments 12 is mounted in a support saddle 56 which in turn is mounted on existing superstructure of a usual Fourdrinier paper-making machine (not shown). Such papermaking machines, their structure and operation, are well known in the art and need not be discussed herein. Preferably, the support saddle ~6 is removably 105~243 secured in position on the papermaking machine as by means of bolts 60 that join the support saddle at spaced apart locations to an elongated bar 58 that extends between opposite sides of the papermaking machine and which is itself secured at its opposite ends to the papermaking machine. The support saddle 56 and the bar 58, being securely joined to each other at relatively closely spaced points, exhibit thermal expansion characteristics that are some combination of the individual thermal characteristics of the saddle 56 and bar 58. It will be recognized that if the saddle and bar are of the same material, they will exhibit the thermal expansion characteristic of such material.
The support saddle 56, in the illustrated foil, includes an elongated bottom portion 82 in FIGURE 1 which re~ides on and is bolted to the bar 58 to join the saddle to the bar referred to above. A rear wall portion 64, formed integrally with the bottom p~rtion, extends upwardly from the bottom portion 62 of the saddle. The upper surface 66 of the bottom section 62 and the forward surface 68 of the rear wall 64 receives the bottom surfaces 28 and at least a portion of the rear surfaces 32 of the stacked segments to provide support for the segments and position them for engage-ment with the wire 15. At the juncture of its surface 66 and its surface 68, the support saddle is cut away along its length to accommodate the bottom rear corners 70 of the segments.
In the illustrated support saddle, these surfaces 66 and 68 define an acute angle therebetween into which the corners 70 of the segments fit thereby restraining the segments against upward movement out of the support saddle. ~urther support and retention of the segments in the saddle 56 is provided by a plurality of clamps 72 that are removably attached as by bolts 74 to the bottom portion 62 of the saddle at locations spaced along the length of the foil. A generally semi-circular (cross-section) groove 76 extending parallel to the longitudinal axis of the foil is provided on that face 78 of the clamp next to the segments. A similar groove 80 is provided on the forward face of each segment so that the two grooves define a generally circular channel between each clamp and the segments faced by the clamp. A relatively non-yielding cylindrical rod 82 is fitted into the channel defined by the grooves 76 and 80 to prevent movement of the segments with respect to the clamps 72 and thereby hold the segments in position in the saddle 56.
One e~.~odiment of a system which includes an elongated flexible ceramic member and which includes at least two members, one of which is movable relative to the other and in frictional engagement therewith is the doctor system depicted in FIGURES 6-8~ This depicted system includes Yankee Dryer 200 on which a paper web 202 is dried and creped.
The web is trained about a portion of the peripheral surface of the dryer 20 and dried by heat transferred through the cylindrical shell 204 therof. Steam introduced into the interior of the dryer shell is commonly used to heat the shell. The ', paper web 202 is dGctored from the shell 204 by means of a doctor blade 206 as is well known in the art to provide a creped paper web 208. In this embodiment, the dryer shell 204 compri~es a first member of the system and is movable relative to and in frictional engagement with the doctor blade 206 which comprises a second member of the system.
In the system depicted in FIGURE 8 , the doctor blade 206 is positioned with respect to the dryer surface 204 and to the paper web 202 by support means shown generally at 210 including a pair of jaws 212 and 213 having shoulders 214 and 215, respectively, that engage mating slots 216 and 217 in opposite surfaces of the doctor blade 206. Other suitable -mountlng means will be readily recognized by one skilled in the art.
In operation of the depicted system, the surface of the shell 204 becomes irregular due to its being heated by the steam. In order to keep the doctor blade in contact with the shell for doctoring the web from the shell, it is necessary to bend the doctor blade so that it conforms to the lrregularities in the shell surface.
In such a system it is desired that the doctor blade be flexible and have a good wear surface that is engaged by the shell. It has long been desired that such a doctor blade be made of a ceramic material to take advantage of the wear resistance of this material. Continuous lengths of ceramic are pro-hibitively costly. Members having small ceramic inserts dlsposed along the length of the member to define a wear surface have been tried but such members develop gaps between the inserts where the member bends during use so that the edges and/or corners of the separated segments become points of excessive wear.
The illustrated doctor blade system comprises an elongated flexible member including a plurality of ceramic segments 220 each having at least two opposite substantially parallel flat faces 224 and 226 (FIGURE 7 ). Each of the depicted segments 220 further includes an upper flat surface 230 which joins a forward upright surface 232 to define a leading edge 234, and an opening 236 extending through each segment between its opposite flat surfaces 224 and 226. A
plurality of these segments are assembled in face-to-face abut~ing relationship with their leading edges aligned to define the doctor blade 206. As illustrated, the flat faces 224 and 226 of each segment are disposed substantially perpendicular to the longitudinal axis, i.e. the composite length, of the com~osite memb~ . The aligned segments 220 ~05~243 are forced toward each other by a tension means 238, anchored to opposite ends of the composite, with a force which elastically compresses the segments.
Each of the segments of each of the elongated members of the present disclosure is fabricated from a hard dense ceramic material that is available at a reasonable cost.
The ceramic preferably is an impervious crystalline material that combines high mechanical strength with extreme hardness, inertness, refractoriness, and high chemical - lla -.: :
: .
resistance properties. Because these properties are retained over a wide range of application and environmental conditions that many other materials cannot withstand, such ceramics suitably serve under conditions adverse to other materials.
Alumina, silicon carbide, boron carbide and silicon nitride materials possess those properties required in many industrial applications, and economically feasible for such end uses.
Alumina is particularly suitable and is preferred for use in the present ceramic member because of its properties and its availability at relatively low cost when formed in relatively short segments.
The alumina segment is formed by compacting finely ground oxide powers with fluxing agents and inhibitors at relatively high pressures as is known in the art. Forming methods include dry pressing, isostatic pressing, casting, extrusion, and injection molding. After forming, the resulting "green" ceramic segment i5 fired at a high temperature for a specific length of time. Firing temperatures vary but usually range between 2,500F. and 3,250F. During firing the ceramic shrinks; therefore, segments are formed while in the green state to allow for the physical reduction caused by firing.
After firing, the ceramic segment is strong, hard and dense, composed substantially of pure alumina of controlled crystal size. Machining of the ceramic segments is possible either before or after firing. Fired segments are ground or lapped to obtain the desired surfaces thereof. Grinding usually must be done with diamond-impregnated wheels, although silicon-carbide or alumina wheels are sometimes used.
Most of those physical properties desired in the ceramic segments improve as the purity of the ceramic increases especially hardness, compressive strength, wear resistance and lOSlZ43 chemical resistance. For example, alumina ceramic compositions having aluminum oxide contents less than about 85~ lose certain of their properties to an unacceptable degree. Preferably, the alumina ceramics contain about 90.0% or more aluminum oxide.
The compressive strength of the ceramics exceed that for most materials. For example, compressive strengths as high as 550 ! pSi have been obtained in certain relatively pure alumina ceramics. Suitable compressive strengths for the ceramic segments range upwardly from about 200,000 psi.
Each of the segments is provided with two opposite sub-stantially flat and parallel faces. The segments are disposed in face-to-face relation with their parallel faces abutting the parallel faces of adjacent segments to define the elongated composite of a desired length and subjected to a compressive force applied at substantially right angles to the faces. The flatness and parallelism of the abutting segment faces help to prevent cracking or breaking o the segments due to unevenly applied stresses or localized stresses ky distributing the compressive forces evenly over the abutting faces. Abutting segment faces, each of which is flat to within about 0.0002 inches and has a surface finish of less than about 20 microinches arithmetic average (AA) have been found to be suitable for these purposes. When such individual segments are placed in face-to-face relation without grout or adhesive, the abutting flat faces of adjacent segments lie in intimate contact with each other over substantially the entire areas of the abutting faces without significant open space therebetween so that the abutting faces supply support to each other especially when the surface of the member is being ground as will be described hereinaftern In one embodi-ment, each segment is provided with an opening ~xtending betweenthe opposite flat faces thereof. This opening in a segment is aligned with similar openings of abutting segments to provide 1051Z43 ~ ~
a channel through the composite for receiving a tension means for compressing the segments in the direction of their composite length.
As noted above, in producing an elongated member of given length, a sufficient number of segments are assembled in face-to-face relatlon with their respective openings aligned to obtain the desired length. The assembled segments are secured together with a force applied substantially in the direction of the length of the composite and substantially perpendicular to the flat parallel faces of the segments.
This force is sufficient to place the segments in elastic compression, and produce a significant compressive strain, and is suitably applied as by a tension means applying a compressive force to opposite ends of the composite. One suitable tension lS means is a cable inserted through the aligned openings extending between the opposite faces of each of the assembled segments, pulled to the required length, anchored at the opposite ends of the composite as by swage fittings to exert a compressive force upon the composite at its opposite ends. Alternatively, other tensioning means may be used to establish the desired compression of the segments in the composite. One such other means includes a rod disposed in the aligned openings of the segments and fitted with a nut at one or both of its ends so that tightening of the nuts tensions the rod and places the segments in compression. One suitable cable for applying the desired compression force to the segments is made of carbon -~- steel and of the--general type employed in prestressed concrete structures.
The cable may be chosen with a cross sectional area 30 less than the cross sectional area of the opening in each segment and after the segment is in place on the cable the space between the cable and the inside surface of the opening , ......... . .
lOSlZ43 in the segment may be filled with a grout 44 (FIGURE 2) such as rigid polyurethane, to position the cable within the openings.
One s~itable grout is a liquid casting urethane polymer designated as L~-2699, sold by E. I. Du Pont de Nemours ~ompany, Trenton, New Jersey. This grout aIso accommodates the axial movement of the segments with respect to the compression cable during compression of the composite and/or relative movement between the segments and the cable in the event the member is subjected to thermal change during use.
As illustrated, the composite of segments may be provided with a plate or other means such as a metallic segment at each end of the composite to provide for distribution of the compressive force over the face of each end segment to protect it from damage by localized forces. In those instances where the desired compression is relatively great a plurality of tension means, e.g~ cables, provides greater compressive capability. In that event, the plurality of cables are desirably threaded through spaced apart, aligned openings through the segments. Such construction aids in more evenly di~tributing the compressive forces over the abutting faces of the segments.
The flexibility of the ceramic member is made possible by employing relatively short segments (e.g. on the order of one inch long) held together with a compressive force such that when the elongated composite deflects by a distance d, along its length (see FIGURES 9-10 ), at least a part of the compression, e.g. compressive strain, in those portions 240 and 242 of the abutting faces 244 and 246 of adjacent segments disposed on the outside of the line of curvature A of the deflected composite is relieved, permitting those portions of the segments to expand to accommodate the deflection without physically separating. Importantly, the lOSlZ43 compressive force holding the segments together is less than the maximum compressive strength of the ceramic material by an amount which permits those portions 248 and 250 of the abutting faces 244 and 246 of adjacent segments on the inside of the line of curvature A of the deflected composite to be compressed by an additional amount, causing these portions of the segments to compress by an amount sufficient to accommodate the deflection without destruction of the segments.
In addition, the length of the individual segments is chosen to be sufficiently small as permits their manufacture at minimized costs taking into consideration the anticipated compressive forces to which the segments are to be subjected in order to obtain the desired response to the composite incident to deflective forces.
In addition to the deflective forces, consideration must be given to thermal changes affecting the element in that ~uch will usually produce different responses in the ceramic segments and the tension member. Such thermal changes can arise by differences in the start-up and operating temperatures s of the machine or system in which the element is installed, and/or changes in ambient temperature of the element during assembly, shipping or installation.
In calculating the compression required to accommodate the maximum anticipated deflection of a member of given length without separation of the segments, it is assumed that the deflection of the member will take the shape of a uniformly loaded simple beam and that the maximum deflection will be sufficiently small (less than about 1% of the member length) to permit the use of calculations based on circular arcs, rather than re exact curves. The latter could be used in those circumstances where more exact calculations are required;
iOSlZ43 however, it has been found that such is not necessary in constr~lcting flexible members for most end uses. More specifically, and with reference to FIGURES 14 and 15, for a ceramic member of given length, Q tin inches), having a longitudinal axis subjected to a maximum anticipated deflection, d (in inches), along a line of curvature A, and made up of a plurality of segments each being of a known length, and a dimension, h (in inches, across the segments, in the direction of the applied deflective force and a cross-sectional area, A , in square inches, the preloading on the tension member, e.g. cable 24 (FIGURE 1), which will impart to the ceramic segments the necessary compressive force that precludes separation of the segments is calculated using the equation / 8dh p ECAc \ 12 + 4d ) Eq. (1) where:
Ec = the modulus of elasticity of the ceramic;
Ac = the cross-sectional area of a ceramic segment in a plane perpendicular to the composite length of the member, in square inches;
d = the maximum anticipated deflection of the member, in inches;
h = the dimension of a ceramic segment in the plane perpendicular to the composite length of the member and in alignment with the direction of the deflective force, in inches; and ~ = the overall length of the member_ With reference to Equation (1), it is noted that the initially determined preloading is divided by 2 to give the preloading to be used in tensioning the cable. This fact arises beca~se of the manner in which the ceramic segments are stressed when the member is deflected while under compression. More specifically, assuming the cable is dispose!d midway between the ends of the segment dimension h, when the member is in an undeflected state, the stress on each compressed ceramic segment is the same at any point along the dimension h. When the member is deflected, the stress in that portion of a segment on the outside of the line of curvature (on the outside end of the dimension h) is reduced toward zero and the stress in that portion of the same segment on the inside of the line of curvature is doubled. Thus when preloading the aligned segments, the stres~ imparted to the segments is taken as the aYerage of the stresses along the dimension h when the member is deflected by a maximum amount.
The effect of thermal change upon the ceramic member must also be taken into account. Thermal changes occur most frequently by reason of the ceramic member being manufactured at a first temperature, room temperature for example, and i- ~ thereafter encountering a substantially higher operating temperature. In such circumstances, the strain in the cable decreases when its temperature increases by reason of the cable expanding when heated. Expansion of the cable cross-section as well as along its length is of importance. Theceramic also expands when heated, but usually to a lesser extent than the cable,~so that there is added to the preload calculated for deflection in accordance with Equation (1), an additional preloading which will compensate for the effect of thermal change upon the cable and the ceramic and provide the desired preloading for accommodating deflection up to a maximum temperature. Such additional preloading of the 10$1243 tension means is calculated using the equation (~B ~C) ~ T
PT 1 1 Eq. (2) A E + A E
S s c c Where:
C~ s = the coefficient of thermal expansion of the tension member;
c = the coefficient of thermal expansion of the ceramic;
~ T = degrees of temperature change anticipated, in degrees F;
As = cross-sectional area of the tension member, in square inches;
Es = the modulus of elasticity of the tension member;
Ac ~ the cross-sectional area of a ceramic segment in a plane perpendicular to the length of the member, in square Lnches;
Ec = the modulus of elasticity of the ceramic.
Combining Equations (1) and (2) gives ( ~ + 4d ) + ~ s c)~ T
AsEs AcEc where P is the total preloading of the tension member which wi11 prevent separation of the segments of the member 30 when the member is deflected up to a maximum amount d while at a temperature less than an anticipated maximum temperature it will be noted that in those situations where the ceramic member will not experience a thermal change, ~ T will be zero and PT [including its equivalent expression in Equation ~3)] will be zero and no additional preloading will be required lOS~243 to account for thermal changes.
Thus, in any given situation where the elongated ceramic member is to be subjected to aeflection forces, it is possible to select a composite which exhibits the desired non-separation of abutting segment faces when the composite is def:Lected along its composite length. As shown in Equation (1), the preloading force (compressive force) applied to the aligned segments, for any given maximum anticipated deflection and total length of the segmented member, depends upon the length of each individual segment and the dimension h of each segment. Thus, if the deflection capability of a given composite of ceramic segments is less than that which precludes physical separation of the abutting faces of the segments under the anticipated deflection, an adjustment can be made, in many lS instances, in either the length or width of the individual segments, or in both the length and width. Of course, con~ideration must be given to the added compression experienced by those portions of the abutting segment faces disposed on the inside of the line of curvature of the deflected composite.
~he preloading force exerted upon the ceramic segments is kept below that amount of force which will compress the ceramic material to within about one-half, and preferably to within about 20 percent, of its maximum compressive strength to insure that localized stresses which may occur within the composite do not exceed such maximum compressive strength with resultant damage to one or more segments. This preferred preloading also provides a substantial margin of safety against damage to the segments by inadvertent over-loading of the segments to produce undue deflection. In any event, the preloading of the segments is sufficient to shsrten the length of each segment, hence shorten the overall length of the composite.
Further, in the preferred preloading, the segments are sufficiently deformed at the interface between lOS1~43 abutting segment faces as results in substantial loss of joint identity at such interface. Such deforn~ation is known to occur when the segments are preloaded to between about 15% and 20% of the maximum compressive strength of the ceramic. This substantial loss of joint identity has been found to be important in establishing the working surface on the member in that such allows the composite to be ground to a suitable smoothness. Less preloading is acceptable but at a loss of certainty of achieving the desired properties in the composite. Thus, the preloading of the ceramic segments must be sufficient to maintain the segments abutting when the member is deflected by a maximum amount d but less than that preloading which will compress the ceramic to more than one-half its total compressive strength.
It is understood that in the present discussion each of the segments is substantially identical to each other segment in a given composite~ Such is assumed for purposes of simpli-fying the disclosure. It is not required, however, that all of the segments be identical. For example, it may be desirable to provide a segmented member which is deflected by different degrees along it9 length. In such an embodiment, the deflective characteristics of the member will differ in different portions of its length and the segments in each such portion may differ in length from the segments in other portions of the length of
2~ the member.
As disclosed, one of the members of the system is movable with respect to the other member. In many embodiments, one member is held stationary while the other member moves thereover in frictional engagement therewith. Similarly, in ; 3~ many embodiments the stationary member will be the flexible ceramic member and will include a leading edge which is initially contacted by the moving member as it moves over the ceramic member. In such instances it is important that such leading edge be straight and free of irregularities such as gaps resulting from chipping of the leading edge inasmuch as such irregularities, among other things, hinder or prevent align-ment between the two members and create wear points ~etweenthe moving members.
The segmented ceramic member, being intended for use in a system where it is in frictional engagement with a further member and there is relative movement between the members, is provided with an elongated smooth working surface (surfaces 46, FIGURE 3; surface 230, FIGURE 6). This surface extends along the length of the ceramic member and defines an extended area of contact between the relatively moving members. Mini~um wear of this surface and of the other of the moving members is obtained by maximizing the smooth-ness of this working surface. This is accomplished by grinding the working surface after the segments have been formed into the composite and preloaded as desc~ibed hereinabove.
2~ In a typical grinding operation the segmented ceramic member is anchored on the bed of a grinding machine. A diamond impregnated grinding wheel, preferably of the type having an annular planar grinding surface is used in the grinding process.
This grinding wheel is moved into contact with the segmented member with the plane of the grinding surface of the grinding wheel disposed at a slight angle with respect to the plane of the surface to be ground so that only a portion of the rotating grinding surface is in contact with the segments at a given time. Preferably the grinding surface plane is also disposed with respect to ~he working surface so that grinding of the surface takes place as the annular grinding surface moves onto the surface and little or no grinding takes place as the grinding surface is moving away from the surface being ground.
The rotation of the grinding wheel, when grinding a leading edge of the type shown in FIGURE 1, is such that the grinding surface initially contacts the leading edge, e.g.
edge 13 of FIGURE 1, as the grinding surface moves toward the edge. In this manner, the grinding forces exerted upon the segments are directed inwardly of the segments to aid in preventing chipping of the segment edges during grinding.
Preferably, the grinding action at the leading edge is in a direction substantially perpendicular to the leading edge.
Variations of greater than about 10 degrees from such perpendi-cular relationship may provide relatively poor edges.
In the grinding operation the compression of the segments in the direction of their composite length maintains the edges of abutting segments in supporting relationship to each other. In addition to this p~ysical support of one segment by its neighbor, the compression in the segments is sufficient to prevent the force of the grinding operation from placing the segment edges in tension as the grinding wheel drags across the segment, thereby enhancing the resistance of the segments to edge chipping during grinding.
EXAMPLE
The manufacture of a doctor blade is described here-inafter as illustrative of the manufacture of the disclosedcomposite ceramic members of the system described herein.
Doctor blades for doctoring a paper web from the surface of a cylindrical dryer shell normally are deflected by different amounts along different portions of their length due to undulations in the dryer shell across its width. In making a ceramic composite doctor blade the most severe anticipated deflection is chosen and the total deflection capability of the blade is made sufficient to accommodate such. In this Example the length, ,e,, of the chosen deflected portion is 50 inches.
The doctor blade in the configuration illustrated in FIGI;JRE 1 is made from one inch long alumina segments 5 (AD-99S from Coors Porcelain Co.) each having a cross-sectional area (Ac) of 0.78 square inches. The dimension (h), the dimension in the direction of the application of the deflective forces, is 0.875 inch. These segments are aligned with ~ -their flat parallel faces abutting and compressed in the , 10 direction of their composite length by a stainless steel cable of 0.14 square inches cross-sectional area threaded through aligned openings in the segments.
The maximum anticipated deflection of the doctor -~
blade over the chosen 50 inch length, ,e , is determined to, 15 be 0.027 inch and the anticipated thermal change is from 70F to 300F. (~ T = 230F). The preloading for the cable which passes through the segments is calculated using Equation
As disclosed, one of the members of the system is movable with respect to the other member. In many embodiments, one member is held stationary while the other member moves thereover in frictional engagement therewith. Similarly, in ; 3~ many embodiments the stationary member will be the flexible ceramic member and will include a leading edge which is initially contacted by the moving member as it moves over the ceramic member. In such instances it is important that such leading edge be straight and free of irregularities such as gaps resulting from chipping of the leading edge inasmuch as such irregularities, among other things, hinder or prevent align-ment between the two members and create wear points ~etweenthe moving members.
The segmented ceramic member, being intended for use in a system where it is in frictional engagement with a further member and there is relative movement between the members, is provided with an elongated smooth working surface (surfaces 46, FIGURE 3; surface 230, FIGURE 6). This surface extends along the length of the ceramic member and defines an extended area of contact between the relatively moving members. Mini~um wear of this surface and of the other of the moving members is obtained by maximizing the smooth-ness of this working surface. This is accomplished by grinding the working surface after the segments have been formed into the composite and preloaded as desc~ibed hereinabove.
2~ In a typical grinding operation the segmented ceramic member is anchored on the bed of a grinding machine. A diamond impregnated grinding wheel, preferably of the type having an annular planar grinding surface is used in the grinding process.
This grinding wheel is moved into contact with the segmented member with the plane of the grinding surface of the grinding wheel disposed at a slight angle with respect to the plane of the surface to be ground so that only a portion of the rotating grinding surface is in contact with the segments at a given time. Preferably the grinding surface plane is also disposed with respect to ~he working surface so that grinding of the surface takes place as the annular grinding surface moves onto the surface and little or no grinding takes place as the grinding surface is moving away from the surface being ground.
The rotation of the grinding wheel, when grinding a leading edge of the type shown in FIGURE 1, is such that the grinding surface initially contacts the leading edge, e.g.
edge 13 of FIGURE 1, as the grinding surface moves toward the edge. In this manner, the grinding forces exerted upon the segments are directed inwardly of the segments to aid in preventing chipping of the segment edges during grinding.
Preferably, the grinding action at the leading edge is in a direction substantially perpendicular to the leading edge.
Variations of greater than about 10 degrees from such perpendi-cular relationship may provide relatively poor edges.
In the grinding operation the compression of the segments in the direction of their composite length maintains the edges of abutting segments in supporting relationship to each other. In addition to this p~ysical support of one segment by its neighbor, the compression in the segments is sufficient to prevent the force of the grinding operation from placing the segment edges in tension as the grinding wheel drags across the segment, thereby enhancing the resistance of the segments to edge chipping during grinding.
EXAMPLE
The manufacture of a doctor blade is described here-inafter as illustrative of the manufacture of the disclosedcomposite ceramic members of the system described herein.
Doctor blades for doctoring a paper web from the surface of a cylindrical dryer shell normally are deflected by different amounts along different portions of their length due to undulations in the dryer shell across its width. In making a ceramic composite doctor blade the most severe anticipated deflection is chosen and the total deflection capability of the blade is made sufficient to accommodate such. In this Example the length, ,e,, of the chosen deflected portion is 50 inches.
The doctor blade in the configuration illustrated in FIGI;JRE 1 is made from one inch long alumina segments 5 (AD-99S from Coors Porcelain Co.) each having a cross-sectional area (Ac) of 0.78 square inches. The dimension (h), the dimension in the direction of the application of the deflective forces, is 0.875 inch. These segments are aligned with ~ -their flat parallel faces abutting and compressed in the , 10 direction of their composite length by a stainless steel cable of 0.14 square inches cross-sectional area threaded through aligned openings in the segments.
The maximum anticipated deflection of the doctor -~
blade over the chosen 50 inch length, ,e , is determined to, 15 be 0.027 inch and the anticipated thermal change is from 70F to 300F. (~ T = 230F). The preloading for the cable which passes through the segments is calculated using Equation
(3) as follows:
E A ( ~ ( ) a T
AsEs + ACEC
(54 x 106) (0.78) 8(50);~27)+ ((8070)27)~ +
[(6.3 x 10-6) -(3;5 x 10 6)] 230 25(0.16) (29 x 106) (0.78) (54 x lOV) P= 1~79.5 + 2385.19 P = 3964.69 pounds This preloading imparted a compressive force to the ceramic which is about 1.54% of the 330,000 psi approxi-30- mate maximum compressive strength for AD-995 alumina. This degree of compression provides for the anticipated deflection, occurring at a temperature of 300F, without complete relief .
lOSlZ43 of the compression in those portions of the ahutting segment faces furtherest from the longitudinal axis of the member along which the deflection occurs and, importantly, provides for additional compression of those portions of the abutting segment faces nearest the longitudinal axis of the member as necessary to accommodate the deflection.
The working surface 230 of the segmented member 222 is ground while the member is supported along its entire length on the bed of a grinding machine. A 220-grit diamond impregnated wheel, having an annular grinding surface, as sold by the Norton Company is employed in the grinding operation.
The grinding wheel has a diameter of 10 inches, and is rotated at approximately 3600 revolutions per minute. The wheel is moved along the length of the working surface at a speed between about 10 and 20 feet per minute. The position of the grinding wheel relative to the working surface and its rotational movement i5 a~ described above. The grinding operation provides a surface finish of about 20 microinches (AA) with no significant chipping of the leading edge 234.
In addition to the advantages of flexibility and resistance to gaping between segments, the present ceramic member offers the advantage of providing a wear-resistant surface that can be ground smooth to the extent desired.
Because the abutting faces of the ceramic segments are held in exceptionally close contact with each other, when the combined top surfaces of the segments are ground smooth, their edges support each other to prevent chipping of their adjacent edges so that in the finished surface, even though the dividing line be~ween segments may be visible as a "hair line" crack, there is no substantial opening or gap therebetween. The wear surface of the disclosed ceramic member is ground and/or lapped smooth to less than about 20 microinches AA and preferably to within a few wavelengths of light to provide exceptionally low-friction contact between the relatively moving members of the system. In this manner, the useful lives of both members are prolonged. ~
While preferred embodiments have been shown and ~ -desc:ribed, it will be understood that there is no intent -to limit the invention by such disclosure, but rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.
,.. . . . . .
E A ( ~ ( ) a T
AsEs + ACEC
(54 x 106) (0.78) 8(50);~27)+ ((8070)27)~ +
[(6.3 x 10-6) -(3;5 x 10 6)] 230 25(0.16) (29 x 106) (0.78) (54 x lOV) P= 1~79.5 + 2385.19 P = 3964.69 pounds This preloading imparted a compressive force to the ceramic which is about 1.54% of the 330,000 psi approxi-30- mate maximum compressive strength for AD-995 alumina. This degree of compression provides for the anticipated deflection, occurring at a temperature of 300F, without complete relief .
lOSlZ43 of the compression in those portions of the ahutting segment faces furtherest from the longitudinal axis of the member along which the deflection occurs and, importantly, provides for additional compression of those portions of the abutting segment faces nearest the longitudinal axis of the member as necessary to accommodate the deflection.
The working surface 230 of the segmented member 222 is ground while the member is supported along its entire length on the bed of a grinding machine. A 220-grit diamond impregnated wheel, having an annular grinding surface, as sold by the Norton Company is employed in the grinding operation.
The grinding wheel has a diameter of 10 inches, and is rotated at approximately 3600 revolutions per minute. The wheel is moved along the length of the working surface at a speed between about 10 and 20 feet per minute. The position of the grinding wheel relative to the working surface and its rotational movement i5 a~ described above. The grinding operation provides a surface finish of about 20 microinches (AA) with no significant chipping of the leading edge 234.
In addition to the advantages of flexibility and resistance to gaping between segments, the present ceramic member offers the advantage of providing a wear-resistant surface that can be ground smooth to the extent desired.
Because the abutting faces of the ceramic segments are held in exceptionally close contact with each other, when the combined top surfaces of the segments are ground smooth, their edges support each other to prevent chipping of their adjacent edges so that in the finished surface, even though the dividing line be~ween segments may be visible as a "hair line" crack, there is no substantial opening or gap therebetween. The wear surface of the disclosed ceramic member is ground and/or lapped smooth to less than about 20 microinches AA and preferably to within a few wavelengths of light to provide exceptionally low-friction contact between the relatively moving members of the system. In this manner, the useful lives of both members are prolonged. ~
While preferred embodiments have been shown and ~ -desc:ribed, it will be understood that there is no intent -to limit the invention by such disclosure, but rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.
,.. . . . . .
Claims
1. In a papermaking system including a rotating cylindrical member carrying a paper web on the outer cylindrical surface thereof and an elongated doctor blade disposed adjacent said surface for removing said web from said surface, the doctor blade comprising an elongated flexible assemblage including a plurality of ceramic segments, each having at least two opposite surfaces that are substantially flat and parallel, said segments being aligned with their flat faces in abutting face-to-face relation and in respective planes that are oriented substantially perpen-dicularly to the composite length of said plurality of segments, tension means extending between opposite ends of said assemblage and adapted to force said segments toward each other in a direction along their composite length and substantially perpendicular to their respective parallel faces with a preload force on said tension means, when said assemblage is in an undeflected condition, that is at least the force calculated by the equation:
Where:
P is the preload of said tension means, in pounds;
Ec is the modulus of elasticity of the ceramic material;
Ac is the cross-sectional area of ceramic segment in a plane perpendicular to the composite length of said assemblage, in square inches;
d is the maximum anticipated deflection of said assemblage, in inches;
h is the dimension of a ceramic segment in the plane perpendicular to the composite length of said assemblage and in alignment with the direction of said deflective force, in inches;
? is the overall length of said assemblage;
?s is the coefficient of thermal expansion of said tension means;
?c is the coefficient of thermal expansion of said ceramic;
.DELTA.T is the degree of temperature change anticipated, in degrees F.;
As is the cross-sectional area of said tension means;and Es is the modulus of elasticity of said tension means, but said force being less than the amount of force which will compress said ceramic to over about one-half of its maximum compressive strength, an elongated smooth working surface extending along the length of said doctor blade and defining an elongated area of contact with said cylindrical surface, and means supporting said doctor blade relative to said cylindrical surface with the longitudinal dimension of said doctor blade oriented generally transversely of the direction of rotational movement of said cylindrical member whereby loading forces exerted upon said doctor blade are directed thereagainst in a direction substantially perpendicular to the longitudinal dimension thereof and deflection of said doctor blade pursuant to such loading forces is compensated for in said compressed segments by further compression of said segments in those portions of the abutting faces thereof disposed along the inside of the line of curvature of said assemblage and by relief of less than all of the compression in those portions of said abutting faces that are disposed along the outside of said line of curvature of said assemblage without physical separation of said segments at their abutting faces.
Where:
P is the preload of said tension means, in pounds;
Ec is the modulus of elasticity of the ceramic material;
Ac is the cross-sectional area of ceramic segment in a plane perpendicular to the composite length of said assemblage, in square inches;
d is the maximum anticipated deflection of said assemblage, in inches;
h is the dimension of a ceramic segment in the plane perpendicular to the composite length of said assemblage and in alignment with the direction of said deflective force, in inches;
? is the overall length of said assemblage;
?s is the coefficient of thermal expansion of said tension means;
?c is the coefficient of thermal expansion of said ceramic;
.DELTA.T is the degree of temperature change anticipated, in degrees F.;
As is the cross-sectional area of said tension means;and Es is the modulus of elasticity of said tension means, but said force being less than the amount of force which will compress said ceramic to over about one-half of its maximum compressive strength, an elongated smooth working surface extending along the length of said doctor blade and defining an elongated area of contact with said cylindrical surface, and means supporting said doctor blade relative to said cylindrical surface with the longitudinal dimension of said doctor blade oriented generally transversely of the direction of rotational movement of said cylindrical member whereby loading forces exerted upon said doctor blade are directed thereagainst in a direction substantially perpendicular to the longitudinal dimension thereof and deflection of said doctor blade pursuant to such loading forces is compensated for in said compressed segments by further compression of said segments in those portions of the abutting faces thereof disposed along the inside of the line of curvature of said assemblage and by relief of less than all of the compression in those portions of said abutting faces that are disposed along the outside of said line of curvature of said assemblage without physical separation of said segments at their abutting faces.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US455678A US3871953A (en) | 1972-07-19 | 1974-03-28 | Papermaking system including a flexible ceramic member having a pre-loaded tensile force applying means |
| CA222,181A CA1035985A (en) | 1974-03-28 | 1975-03-17 | System including a flexible ceramic member and method for making such member |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1051243A true CA1051243A (en) | 1979-03-27 |
Family
ID=25667866
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,325A Expired CA1051243A (en) | 1974-03-28 | 1978-05-01 | Doctor blade for a papermaking machine |
| CA302,324A Expired CA1047815A (en) | 1974-03-28 | 1978-05-01 | Suction box for a papermaking machine |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,324A Expired CA1047815A (en) | 1974-03-28 | 1978-05-01 | Suction box for a papermaking machine |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1051243A (en) |
-
1978
- 1978-05-01 CA CA302,325A patent/CA1051243A/en not_active Expired
- 1978-05-01 CA CA302,324A patent/CA1047815A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1047815A (en) | 1979-02-06 |
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