CA2057325C - Method and assembly for compensating the bending of a doctor blade beam - Google Patents
Method and assembly for compensating the bending of a doctor blade beam Download PDFInfo
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- CA2057325C CA2057325C CA 2057325 CA2057325A CA2057325C CA 2057325 C CA2057325 C CA 2057325C CA 2057325 CA2057325 CA 2057325 CA 2057325 A CA2057325 A CA 2057325A CA 2057325 C CA2057325 C CA 2057325C
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- frame
- doctor blade
- temperature
- deflection
- heat transfer
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
- D21G3/00—Doctors
- D21G3/005—Doctor knifes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05C11/00—Component parts, details or accessories not specifically provided for in groups B05C1/00 - B05C9/00
- B05C11/02—Apparatus for spreading or distributing liquids or other fluent materials already applied to a surface ; Controlling means therefor; Control of the thickness of a coating by spreading or distributing liquids or other fluent materials already applied to the coated surface
- B05C11/04—Apparatus for spreading or distributing liquids or other fluent materials already applied to a surface ; Controlling means therefor; Control of the thickness of a coating by spreading or distributing liquids or other fluent materials already applied to the coated surface with blades
- B05C11/041—Apparatus for spreading or distributing liquids or other fluent materials already applied to a surface ; Controlling means therefor; Control of the thickness of a coating by spreading or distributing liquids or other fluent materials already applied to the coated surface with blades characterised by means for positioning, loading, or deforming the blades
- B05C11/042—Apparatus for spreading or distributing liquids or other fluent materials already applied to a surface ; Controlling means therefor; Control of the thickness of a coating by spreading or distributing liquids or other fluent materials already applied to the coated surface with blades characterised by means for positioning, loading, or deforming the blades allowing local positioning, loading or deforming along the blades
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- Coating Apparatus (AREA)
- Paper (AREA)
Abstract
The present invention discloses a method and assembly for compensating the deflection of a doctor blade beam in a coater. The doctor blade beam comprises a box-section frame (11), together with a doctor blade (1) in a blade holder (2), and a compensation channel (5, 6) adapted to said frame (11) in the vicinity of said blade holder (2), whereby said channel is capable of stabilizing the temperature in the vicinity of the blade holder (2) at a constant level. Deflections caused by doctor blade beam weight and blade loading are compensated for by altering temperature at desired points of the frame (11) by means of the heat transferring channels (7...11) adapted to the frame (11).
Description
~~~'~~2~
Method and assembly for compensating the bending of a doctor blade beam The present invention relates to a method for compensating the deflection of a doctor blade beam in accordance with the preamble of claim 1.
The invention also concerns an assembly suitable for adapting the method to a doctor blade beam.
Paper and similar web-like material are coated by applying onto the moving web a coating mix which is then spread into an even layer onto the web surface with the help of a doctor blade. In the coater the web to be coated passes through a gap formed between the doctor blade and a suitable backing member, conventionally a rotating roll. The blade doctors excess coating away from the . web surface and levels the coating mix into an even layer on the web surface. In order to achieve a layer as even as possible, the gap formed between the web and the blade should have a constant spacing in the cross direction of the web over its entire width. The linear force applied to press the doctor blade against the web should be high and constant over the entire width of the blade in order to attain an even spreading of the coating mix onto the web also at high web speeds.
For several reasons, the spacing in the gap between the material web and the doctor blade cannot be maintained exactly constant. During machining, the doctor blade and its frame are fixed to the machining unit base with strong fixtures into a positian simulating their operating position. Despite the exact placement of the fixtures, defects will develop during fabrication of the doctor blade and its frame causing a error to appear in the parallel alignment between the web surface and the doctor blade tip. As the doctor blade of the coater is pressed against the moving web, the blade is loaded with a linear force. Due to the pivotal support of the doctor blade frame provided by bearings mounted at both ends of the frame, the deflection induced by the linear load force at the center of the blade will be greater than at the supported ends, whereby the blade spacing between the blade tip and the web will be smaller at the edges of the web than at the center. Since the linear force exerted by the blade onto the surface of the web or the backing roll is smaller in the middle as compared to the supported ends, any possible bumps on the web as well as variations in the density and viscosity of the coating mix can lift the blade tip away from the web.
In order to alleviate the aforementioned disadvantages, several different designs for the attachment of the doctor blade have been presented. In the prior-art l0 constructions, a homogeneous loading of the blade over the entire web width has been attempted by means of a t7exible blade combined with an adjustable blade holder assembly. In these embodiments the blade is attached to the blade holder so that the blade can be pressed against the web by means of a resilient element, e.g., a pneumatically or hydraulically loaded rubber hose, which extends across the entire length of the blade. Because of the equal pressure prevailing in the hose along its entire length, the hose presses the blade against the web with a constant linear force over the entire width of the web. The blade pressure against the web can then be adjusted by altering the pressure in the hose.
These kinds of embodiments occasionally use a doctor blade which is divided into narrow sections along its length. The advantage of this approach is a more flexible blade that offers an improved conformance with the shape of the web and the backing roll.
The above-described approaches have several drawbacks. Because of the limited deformation capability of the resilient loading element, this design is incapable of compensating for large variations in the spacing between the blade and the web or loading of the blade. The adjustment range of blade loading remains restricted and, if a higher coating speed is desired, the blade must be pressed against the web with an actuator element attached to the doctor blade. A higher blade laading results in an increased stiffness of the blade holder element, whereby the blade becomes incapable of conforming to the web surface in a desired manner.
Method and assembly for compensating the bending of a doctor blade beam The present invention relates to a method for compensating the deflection of a doctor blade beam in accordance with the preamble of claim 1.
The invention also concerns an assembly suitable for adapting the method to a doctor blade beam.
Paper and similar web-like material are coated by applying onto the moving web a coating mix which is then spread into an even layer onto the web surface with the help of a doctor blade. In the coater the web to be coated passes through a gap formed between the doctor blade and a suitable backing member, conventionally a rotating roll. The blade doctors excess coating away from the . web surface and levels the coating mix into an even layer on the web surface. In order to achieve a layer as even as possible, the gap formed between the web and the blade should have a constant spacing in the cross direction of the web over its entire width. The linear force applied to press the doctor blade against the web should be high and constant over the entire width of the blade in order to attain an even spreading of the coating mix onto the web also at high web speeds.
For several reasons, the spacing in the gap between the material web and the doctor blade cannot be maintained exactly constant. During machining, the doctor blade and its frame are fixed to the machining unit base with strong fixtures into a positian simulating their operating position. Despite the exact placement of the fixtures, defects will develop during fabrication of the doctor blade and its frame causing a error to appear in the parallel alignment between the web surface and the doctor blade tip. As the doctor blade of the coater is pressed against the moving web, the blade is loaded with a linear force. Due to the pivotal support of the doctor blade frame provided by bearings mounted at both ends of the frame, the deflection induced by the linear load force at the center of the blade will be greater than at the supported ends, whereby the blade spacing between the blade tip and the web will be smaller at the edges of the web than at the center. Since the linear force exerted by the blade onto the surface of the web or the backing roll is smaller in the middle as compared to the supported ends, any possible bumps on the web as well as variations in the density and viscosity of the coating mix can lift the blade tip away from the web.
In order to alleviate the aforementioned disadvantages, several different designs for the attachment of the doctor blade have been presented. In the prior-art l0 constructions, a homogeneous loading of the blade over the entire web width has been attempted by means of a t7exible blade combined with an adjustable blade holder assembly. In these embodiments the blade is attached to the blade holder so that the blade can be pressed against the web by means of a resilient element, e.g., a pneumatically or hydraulically loaded rubber hose, which extends across the entire length of the blade. Because of the equal pressure prevailing in the hose along its entire length, the hose presses the blade against the web with a constant linear force over the entire width of the web. The blade pressure against the web can then be adjusted by altering the pressure in the hose.
These kinds of embodiments occasionally use a doctor blade which is divided into narrow sections along its length. The advantage of this approach is a more flexible blade that offers an improved conformance with the shape of the web and the backing roll.
The above-described approaches have several drawbacks. Because of the limited deformation capability of the resilient loading element, this design is incapable of compensating for large variations in the spacing between the blade and the web or loading of the blade. The adjustment range of blade loading remains restricted and, if a higher coating speed is desired, the blade must be pressed against the web with an actuator element attached to the doctor blade. A higher blade laading results in an increased stiffness of the blade holder element, whereby the blade becomes incapable of conforming to the web surface in a desired manner.
The frame of the doctor blade must be constructed extremely stiff in order to make it possible to compress the flexible blade against the web. Flexible and adjustable doctor blade holder constructions are complicated; blade changes are awkward and damage to the pressure-exerting elements may result during blade changes. The blade holder construction becomes large and heavy.
Calenders use deflection-compensation rolls having a load-bearing basic roll in the center of the roll. Pressure-exerting elements are placed between the basic roll and the shell of the roll, whereby changing the shape of the elements permits the straightening of the roll shell. A deflection compensated doctor blade beam based on similar construction is described in the US patent 4,907,528. Therein, the doctor blade beam has four pressure-exerting elements symmetrically located about a round frame beam and enclosed by a tubular shell which itself is supported to the square frame of the doctor blade assembly. By way of adjusting the operating pressure of the pressure-exerting elements, the frame of the doctor blade assembly can be deformed appropriately to compensate for the deflection of the doctor blade beam of the coater.
However, the construction of the above-described beam becomes complicated, resulting in a considerably high weight. Thence, the inherent weight of the beam contributes to 2 o its deflection, thus requiring more powerful means of compensation.
Furthermore, the shape of the beam is not freely selectable by the designer, because the frame of the coater must necessarily have a square shape and the number of pressure-exerting .
elements is fixed to four in all cases.
2 5 It is an object of the present invention to achieve a novel method and assembly for compensating the deflection of doctor blade beam in a coater. The invention makes it possible to design a deflection-compensated doctor blade beam.
A method for compensating the deflection of doctor blade beam in a coater, in which method the compensation of the beam's deflection is achieved by inducing at least one 3a temperature stress component on the beam, said stress causing in the beam an essentially opposing displacement to the beam's deflection, characterised in that s - the temperature of the frame of the doctor blade beam is maintained constant in that part of the beam to which the blade holder is attached, and - the temperature of the frame of the doctor blade beam is altered at least in one point of the frame with respect to said stabilized constant temperature so that the stress caused by the temperature difference induces in the beam a displacement which is opposing to the beam's deflection.
A deflection-compensated doctor blade beam comprising:
- a frame and 2 0 - a blade holder with a doctor blade, attached to said frame, characterized by - at least one heat transferring element arranged to the 2 5 vicinity of said blade holder, said element being capable of maintaining a constant temperature of the frame in the vicinity of said blade holder, and at least one other heat transferring element by means of which the temperature of the frame can be altered at the location of said transferring element.
The invention is based on maintaining the temperature of the beam constant at the doctor blade holder and compensating the deflection of the beam by altering the temperature of the beam at appropriate points with the help of heating or cooling elements. Consequently, the deformations of the beam are compensated by causing deflections of opposite by the induced temperature changes.
to The present invention achieves a coater construction in which the doctor blade conforms to the web and the backing roll even at high linear loads of the blade. The coating speed can be increased yet attaining a high-quality coat with several different kinds of coating mixes. The linear load of the blade is kept constant over the entire length of the blade. Due to the constant loading of the blade, its wear is even over the entire blade length, which contributes to an increased blade life. The compensation system disclosed herein does not cause an unbearable increase in the weight of the blade beam. Deflection compensation in a blade beam of lightweight construction is easier than for a heavy beam, because the contribution by beam's weight itself in the 2 o deflection remains smaller. The compensation system is easy to design and implement in the beam, since the deformations caused by temperature changes need not be known exactly. During the coating process, the compensation system is controlled by measuring the straightness of the beam or the coat thickness profile across the coated web. As the direction of the deflection changes caused by each heating/cooling element 2 5 are known, the measured deflections can be compensated for automatically by controlling the compensation system via a feedback loop, or alternatively, the operator of the coater can steer the compensation system manually.
The invention is next examined with the help of exemplifying embodiments illustrated in the attached drawings, in which Figure 1 shows a cross section of a doctor blade beam accoxding to the invention.
Figure 2 shows diagrammatically a compensation system according to the invention.
'The dactor blade beam according to the invention can be built staxting from a conventional doctor blade beam. The doctor blade beam shown in Fig. 1 is comprised of a triangular box-section frame 11, a blade holder 2 attached to the frame 11, fixture elements 3 and 4, and bearings 12 at the ends of the frame 11, whereby the doctor blade beam is pivotally rotatable in the bearings. The blade holder 2 with its doctor blade 1 is attached outside the frame 11 close the one corner of the triangular box-section frame 11. The box-section frame 11 forms a tubular cavity. Inside the frame 11 are adapted stabilization channels S and 6, and compensation channels 7...10. The channels 5...10 are fabricated by welding a shaped steel trough at its edges to the inside surface of ttze frame 11.
Consequently, the walls of the channels 5...10 are formed by the inner surface of the frame 11 and the trough attached to it. Each channel is comprised of two parts, namely an inlet duct and a return duct. The inlet duct S of the stabilization channel is adapted to the frame 11 under the blade holder 2, while the return duct 6 is adapted to the upper inside surface of the frame 11 adjacent to the inlet duct 5. The compensation channels are adapted to the other corners of the triangle formed by the triangular box-section frame 11 so that the inlet duct 7, 9 is adapted to one side wall of the acute angle, while the return duct 8, 10 is adapted to the opposite side wall for each angle, respectively. The inlet ducts are connected to their respective return ducts at the end of the doctor blade beam.
Liquid is recirculated in the ducts 5...10, entering the frame 11 via the inlet duct 5, 7, 9 and exiting through the return duct 6, 8, 10. The ducts 5...10 extend over the entire length of the doctor blade beam.
Fig. 2 illustrates diagrammatically a system suitable for recirculating the liduid in the ducts 5...:10 of the frame. The liduid is pumped into the inlet ducts 5, 7, ) by means of pumps 15, which are connected to inlet pipes 13 of the system. The liquid exits the return ducts 6, 8, 1() via return pipes 14 to heat exchangers 16, which are provided with means for cooling and heating the liquid. Each channel has a separate heat exchanger 16 and a recirculation system 13...15. Thus, the temperatures of liquid flows recirculating in the channels can be adjusted l0 independently from each other.
Liquid temperature in the stabilization channel 5 located under the blade holder 2 is set to a constant level which can be, e.g., ambient temperature.
Alterations in liquid temperatures of the recirculating flows in the compensation channels 6...10 induce changes in the temperature distribution in the cross-sectional plane of the beam. In this manner, one compensation channel can control deflection in a single direction, and if the number of compensation channels is two as in the described embodiment, temperature control of the liquid recirculating in the compensation channels makes it possible to compensate deviations in two separate directions, whose combined effect results in complete straightening of the doctor blade beam.
On the basis of the location of the compensation channels 7...10, the geometry of the doctor blade beam and the material thicknesses, it is possible to determine the matrix equations defining the relationships between displacements and temperature changes using conventional theories of strength analysis:
x1 K11 K12 T11 3 0 y1 X21 K22~ T21 In the above matrix equation the coefficients K are constants which can be ~(~'~'~~~
Calenders use deflection-compensation rolls having a load-bearing basic roll in the center of the roll. Pressure-exerting elements are placed between the basic roll and the shell of the roll, whereby changing the shape of the elements permits the straightening of the roll shell. A deflection compensated doctor blade beam based on similar construction is described in the US patent 4,907,528. Therein, the doctor blade beam has four pressure-exerting elements symmetrically located about a round frame beam and enclosed by a tubular shell which itself is supported to the square frame of the doctor blade assembly. By way of adjusting the operating pressure of the pressure-exerting elements, the frame of the doctor blade assembly can be deformed appropriately to compensate for the deflection of the doctor blade beam of the coater.
However, the construction of the above-described beam becomes complicated, resulting in a considerably high weight. Thence, the inherent weight of the beam contributes to 2 o its deflection, thus requiring more powerful means of compensation.
Furthermore, the shape of the beam is not freely selectable by the designer, because the frame of the coater must necessarily have a square shape and the number of pressure-exerting .
elements is fixed to four in all cases.
2 5 It is an object of the present invention to achieve a novel method and assembly for compensating the deflection of doctor blade beam in a coater. The invention makes it possible to design a deflection-compensated doctor blade beam.
A method for compensating the deflection of doctor blade beam in a coater, in which method the compensation of the beam's deflection is achieved by inducing at least one 3a temperature stress component on the beam, said stress causing in the beam an essentially opposing displacement to the beam's deflection, characterised in that s - the temperature of the frame of the doctor blade beam is maintained constant in that part of the beam to which the blade holder is attached, and - the temperature of the frame of the doctor blade beam is altered at least in one point of the frame with respect to said stabilized constant temperature so that the stress caused by the temperature difference induces in the beam a displacement which is opposing to the beam's deflection.
A deflection-compensated doctor blade beam comprising:
- a frame and 2 0 - a blade holder with a doctor blade, attached to said frame, characterized by - at least one heat transferring element arranged to the 2 5 vicinity of said blade holder, said element being capable of maintaining a constant temperature of the frame in the vicinity of said blade holder, and at least one other heat transferring element by means of which the temperature of the frame can be altered at the location of said transferring element.
The invention is based on maintaining the temperature of the beam constant at the doctor blade holder and compensating the deflection of the beam by altering the temperature of the beam at appropriate points with the help of heating or cooling elements. Consequently, the deformations of the beam are compensated by causing deflections of opposite by the induced temperature changes.
to The present invention achieves a coater construction in which the doctor blade conforms to the web and the backing roll even at high linear loads of the blade. The coating speed can be increased yet attaining a high-quality coat with several different kinds of coating mixes. The linear load of the blade is kept constant over the entire length of the blade. Due to the constant loading of the blade, its wear is even over the entire blade length, which contributes to an increased blade life. The compensation system disclosed herein does not cause an unbearable increase in the weight of the blade beam. Deflection compensation in a blade beam of lightweight construction is easier than for a heavy beam, because the contribution by beam's weight itself in the 2 o deflection remains smaller. The compensation system is easy to design and implement in the beam, since the deformations caused by temperature changes need not be known exactly. During the coating process, the compensation system is controlled by measuring the straightness of the beam or the coat thickness profile across the coated web. As the direction of the deflection changes caused by each heating/cooling element 2 5 are known, the measured deflections can be compensated for automatically by controlling the compensation system via a feedback loop, or alternatively, the operator of the coater can steer the compensation system manually.
The invention is next examined with the help of exemplifying embodiments illustrated in the attached drawings, in which Figure 1 shows a cross section of a doctor blade beam accoxding to the invention.
Figure 2 shows diagrammatically a compensation system according to the invention.
'The dactor blade beam according to the invention can be built staxting from a conventional doctor blade beam. The doctor blade beam shown in Fig. 1 is comprised of a triangular box-section frame 11, a blade holder 2 attached to the frame 11, fixture elements 3 and 4, and bearings 12 at the ends of the frame 11, whereby the doctor blade beam is pivotally rotatable in the bearings. The blade holder 2 with its doctor blade 1 is attached outside the frame 11 close the one corner of the triangular box-section frame 11. The box-section frame 11 forms a tubular cavity. Inside the frame 11 are adapted stabilization channels S and 6, and compensation channels 7...10. The channels 5...10 are fabricated by welding a shaped steel trough at its edges to the inside surface of ttze frame 11.
Consequently, the walls of the channels 5...10 are formed by the inner surface of the frame 11 and the trough attached to it. Each channel is comprised of two parts, namely an inlet duct and a return duct. The inlet duct S of the stabilization channel is adapted to the frame 11 under the blade holder 2, while the return duct 6 is adapted to the upper inside surface of the frame 11 adjacent to the inlet duct 5. The compensation channels are adapted to the other corners of the triangle formed by the triangular box-section frame 11 so that the inlet duct 7, 9 is adapted to one side wall of the acute angle, while the return duct 8, 10 is adapted to the opposite side wall for each angle, respectively. The inlet ducts are connected to their respective return ducts at the end of the doctor blade beam.
Liquid is recirculated in the ducts 5...10, entering the frame 11 via the inlet duct 5, 7, 9 and exiting through the return duct 6, 8, 10. The ducts 5...10 extend over the entire length of the doctor blade beam.
Fig. 2 illustrates diagrammatically a system suitable for recirculating the liduid in the ducts 5...:10 of the frame. The liduid is pumped into the inlet ducts 5, 7, ) by means of pumps 15, which are connected to inlet pipes 13 of the system. The liquid exits the return ducts 6, 8, 1() via return pipes 14 to heat exchangers 16, which are provided with means for cooling and heating the liquid. Each channel has a separate heat exchanger 16 and a recirculation system 13...15. Thus, the temperatures of liquid flows recirculating in the channels can be adjusted l0 independently from each other.
Liquid temperature in the stabilization channel 5 located under the blade holder 2 is set to a constant level which can be, e.g., ambient temperature.
Alterations in liquid temperatures of the recirculating flows in the compensation channels 6...10 induce changes in the temperature distribution in the cross-sectional plane of the beam. In this manner, one compensation channel can control deflection in a single direction, and if the number of compensation channels is two as in the described embodiment, temperature control of the liquid recirculating in the compensation channels makes it possible to compensate deviations in two separate directions, whose combined effect results in complete straightening of the doctor blade beam.
On the basis of the location of the compensation channels 7...10, the geometry of the doctor blade beam and the material thicknesses, it is possible to determine the matrix equations defining the relationships between displacements and temperature changes using conventional theories of strength analysis:
x1 K11 K12 T11 3 0 y1 X21 K22~ T21 In the above matrix equation the coefficients K are constants which can be ~(~'~'~~~
adjusted to desired values in the beam design by altering the beam shape, mater-ial thicknesses and placement of the compensation channels. The coefficients K
are advantageously adjusted so that K12 and K22 are as close to zero as possible, whereby the displacements x and y are essentially orthogonal to each S other. Then, the control algorithm needed for governing the beam deflection by temperature changes becomes as simple as possible. Furthermore, because the relationship of the induced displacements to temperature changes is linear, the formulation of the control algorithm is uncomplicated. The coefficients K also define the direction of displacements with respect to the bending center of the blade 1 and the doctor blade beam, so for the control algorithm it is sufficient to know the direction of displacement caused by a temperature change in each of the channels, whereby the deflection of the beam can be determined by either a direct measurement of beam displacement or indirectly from the coat weight profile in order to induce a desired displacement with the help of a feedback loop controlling the temperatures of liquid recirculations in the compensation channels. Because the beam deflection is primarily caused by the inherent weight of the beam and the applied blade loading, the compensating displacements can be arranged by proper design of the beam dimensions and placement of the compensation channels to act in an opposingly compensating manner to the displacements caused by the deflection.
The deflection of the doctor blade beam typically is in the range 0.1 ...
0.2 mm/m. Consequently, the displacement of a 10 m beam at its middle is generally less than 2 mm. To compensate such a deflection requires temperature changes of the order of approx. 10° K. The temperature changes are easy to implement with the help of the recirculating liquid flow. The mass flow rate of the liquid circulation need not be high, and the heating/cooling of the liquid is readily arranged by means of commercially available equipment.
In addition the above described, the present invention can have other embodiments. The number of the compensation channels can be varied as ~(~~7:~2~
s necessary. Each compensation channel serves for the control of a single displacement component in the direction of the cross-sectional plane of the beam, and correspondingly, a greater number of channels offers compensation of an additional displacement component per channel. An advantageous number of compensation channels is two, because it is sufficient for compensation of all de-flections in the cross-sectional plane of the beam by means of the combined control effect of two displacements. The shape and construction of the doctor blade beam and the location and structure of the heat transferring channels are freely variable; only the stabilization channel 5, 6 must be placed close to the blade holder 2 in order to maintain its temperature constant. The channels 5...10 can naturally have a unidirectional duct structure, whereby liquid enters the beam from one end and exits at the opposite end of the beam. The channels 5...10 need not extend over the entire length of the beam, but instead, they can be placed at desired points along the length of the beam, or alternatively, a greater number of channels can be used lengthwise in paxallel.
Different kinds of liquids and gases are possible as heat transferring media.
The heat transferring channels 5...10 can also be replaced by, e.g., electrical heater elements, infrared radiators or other heating means, whereby the temperature compensation of the beam at the blade holder is accomplished by placing a desired type of heating element close to the blade holder and then heating the doctor blade beam at the blade holder to a stabilized temperature above ambient. In this case the input power control of the heating elements used for compensation allows the adjustment of temperatures at the points to be deflection-compensated to a higher or lower value with respect to the area of stabilized temperature, thus achieving a similar control method as applied in the described exemplifying embodiment. Obviously, the doctor blade beam and its compensation elements can be designed and placed so that a sufficient degree of compensation is attained solely by heating the beam at the compensating areas.
Of course, the heat transferring channels and heat transfer elements can also be placed outside the frame 11, or alternatively, they can be attached to the frame to any other suitable point. Tf radiating heater elements are used as the heating means, they can be placed close to the beam at a suitable distance.
The control of the compensation system can be implemented with the help of an automatic control loop which adjusts the straightness of the beam on the ba.~sis of direct displacement measurement or coat weight profile, or alternatively, the operator of the coater can perform a manual control of the beam's straightness.
When desired, the deflection of the doctor blade can be adjusted with the help of the described assembly to a value different from zero.
are advantageously adjusted so that K12 and K22 are as close to zero as possible, whereby the displacements x and y are essentially orthogonal to each S other. Then, the control algorithm needed for governing the beam deflection by temperature changes becomes as simple as possible. Furthermore, because the relationship of the induced displacements to temperature changes is linear, the formulation of the control algorithm is uncomplicated. The coefficients K also define the direction of displacements with respect to the bending center of the blade 1 and the doctor blade beam, so for the control algorithm it is sufficient to know the direction of displacement caused by a temperature change in each of the channels, whereby the deflection of the beam can be determined by either a direct measurement of beam displacement or indirectly from the coat weight profile in order to induce a desired displacement with the help of a feedback loop controlling the temperatures of liquid recirculations in the compensation channels. Because the beam deflection is primarily caused by the inherent weight of the beam and the applied blade loading, the compensating displacements can be arranged by proper design of the beam dimensions and placement of the compensation channels to act in an opposingly compensating manner to the displacements caused by the deflection.
The deflection of the doctor blade beam typically is in the range 0.1 ...
0.2 mm/m. Consequently, the displacement of a 10 m beam at its middle is generally less than 2 mm. To compensate such a deflection requires temperature changes of the order of approx. 10° K. The temperature changes are easy to implement with the help of the recirculating liquid flow. The mass flow rate of the liquid circulation need not be high, and the heating/cooling of the liquid is readily arranged by means of commercially available equipment.
In addition the above described, the present invention can have other embodiments. The number of the compensation channels can be varied as ~(~~7:~2~
s necessary. Each compensation channel serves for the control of a single displacement component in the direction of the cross-sectional plane of the beam, and correspondingly, a greater number of channels offers compensation of an additional displacement component per channel. An advantageous number of compensation channels is two, because it is sufficient for compensation of all de-flections in the cross-sectional plane of the beam by means of the combined control effect of two displacements. The shape and construction of the doctor blade beam and the location and structure of the heat transferring channels are freely variable; only the stabilization channel 5, 6 must be placed close to the blade holder 2 in order to maintain its temperature constant. The channels 5...10 can naturally have a unidirectional duct structure, whereby liquid enters the beam from one end and exits at the opposite end of the beam. The channels 5...10 need not extend over the entire length of the beam, but instead, they can be placed at desired points along the length of the beam, or alternatively, a greater number of channels can be used lengthwise in paxallel.
Different kinds of liquids and gases are possible as heat transferring media.
The heat transferring channels 5...10 can also be replaced by, e.g., electrical heater elements, infrared radiators or other heating means, whereby the temperature compensation of the beam at the blade holder is accomplished by placing a desired type of heating element close to the blade holder and then heating the doctor blade beam at the blade holder to a stabilized temperature above ambient. In this case the input power control of the heating elements used for compensation allows the adjustment of temperatures at the points to be deflection-compensated to a higher or lower value with respect to the area of stabilized temperature, thus achieving a similar control method as applied in the described exemplifying embodiment. Obviously, the doctor blade beam and its compensation elements can be designed and placed so that a sufficient degree of compensation is attained solely by heating the beam at the compensating areas.
Of course, the heat transferring channels and heat transfer elements can also be placed outside the frame 11, or alternatively, they can be attached to the frame to any other suitable point. Tf radiating heater elements are used as the heating means, they can be placed close to the beam at a suitable distance.
The control of the compensation system can be implemented with the help of an automatic control loop which adjusts the straightness of the beam on the ba.~sis of direct displacement measurement or coat weight profile, or alternatively, the operator of the coater can perform a manual control of the beam's straightness.
When desired, the deflection of the doctor blade can be adjusted with the help of the described assembly to a value different from zero.
Claims (8)
1. A doctor blade beam for use in a web coating apparatus, provided with means for compensation for deflection of the beam, comprising:~
- a box shaped frame (11) having a triangular cross-section;
- a blade holder (2) secured to the frame (11) holding a doctor blade (1) in proximity to a first angle of the triangular cross-section;
- a first heat transfer means disposed at said first angle of the triangular cross-section underneath the blade holder and provided to maintain, at said first angle, a constant temperature of the frame (11) at a portion thereof adjacent to a counter-roll;
- a second heat transfer means disposed at a second angle of the triangular cross-section and adapted to transfer, at said second angle, a selectively variable temperature different from said constant temperature of the frame, in reference to the constant temperature of the frame at said first angle;
- a third heat transfer means disposed at a third angle of the triangular cross-section and adapted to transfer, at said third angle, a selectively variable temperature different from said constant temperature of the frame, in reference to the constant temperature of the frame at said first angle.
- a box shaped frame (11) having a triangular cross-section;
- a blade holder (2) secured to the frame (11) holding a doctor blade (1) in proximity to a first angle of the triangular cross-section;
- a first heat transfer means disposed at said first angle of the triangular cross-section underneath the blade holder and provided to maintain, at said first angle, a constant temperature of the frame (11) at a portion thereof adjacent to a counter-roll;
- a second heat transfer means disposed at a second angle of the triangular cross-section and adapted to transfer, at said second angle, a selectively variable temperature different from said constant temperature of the frame, in reference to the constant temperature of the frame at said first angle;
- a third heat transfer means disposed at a third angle of the triangular cross-section and adapted to transfer, at said third angle, a selectively variable temperature different from said constant temperature of the frame, in reference to the constant temperature of the frame at said first angle.
2. The doctor blade beam of claim 1 wherein all the heat transfer means are channels provided on said frame, said channels being adapted to conduct a heat transfer medium.
3. The doctor blade beam of claim 1 wherein all said heat transfer means are electrical heater elements.
4. The doctor blade beam of claim 1 wherein all said heat transfer means are radiant heaters.
5. The doctor blade beam of claim 4 wherein the radiant heaters are infrared radiators.
6. A method for compensating for deflection of a doctor blade in a coating apparatus, comprising the steps of:
- providing a box-shaped frame of a triangular cross-section and extending the full width of the coating apparatus and a doctor blade holder at a first corner of said frame;
- providing a heat transfer means at each corner of the triangular frame, whereby said heat transfer means at said first corner is disposed underneath the doctor blade holder;
maintaining the temperature of the frame at said first corner at a constant, stabilized value by controlling the temperature of the heat transfer means at said first corner;
- controlling the temperature of said box-shaped frame separately at each of the remaining second and third corners in relation to the value of said stabilized constant temperature, whereby deflection of the frame can be effected in two directions.
- providing a box-shaped frame of a triangular cross-section and extending the full width of the coating apparatus and a doctor blade holder at a first corner of said frame;
- providing a heat transfer means at each corner of the triangular frame, whereby said heat transfer means at said first corner is disposed underneath the doctor blade holder;
maintaining the temperature of the frame at said first corner at a constant, stabilized value by controlling the temperature of the heat transfer means at said first corner;
- controlling the temperature of said box-shaped frame separately at each of the remaining second and third corners in relation to the value of said stabilized constant temperature, whereby deflection of the frame can be effected in two directions.
7. The method of claim 6 including the step of measuring the frame deflection and then, while maintaining the temperature of the frame at said first corner at the constant, stabilized value, adjusting the temperature of at least one of said second and third corners to a value, the magnitude of which is determined relative to said constant, stabilized temperature value, until a state is achieved where the degree of the frame deflection is at a zero.
8. The method of claim 7 wherein the measurement of the frame deflection is effected by measuring a coat weight profile obtained from a web exiting from the coating apparatus, and continuing the adjustment of the temperature of at least one of said remaining corners until the weight profile is uniform, whereupon the ratio of the temperatures at said remaining angles to said stabilized value is used as a correct ratio for a given deflection of the frame.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI906132A FI88755C (en) | 1990-12-13 | 1990-12-13 | Foerfarande och anordning Foer compensating av boejningnen hos en bladbalk |
| FI906132 | 1990-12-13 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2057325A1 CA2057325A1 (en) | 1992-06-14 |
| CA2057325C true CA2057325C (en) | 2006-07-11 |
Family
ID=8531568
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2057325 Expired - Fee Related CA2057325C (en) | 1990-12-13 | 1991-12-10 | Method and assembly for compensating the bending of a doctor blade beam |
Country Status (6)
| Country | Link |
|---|---|
| CA (1) | CA2057325C (en) |
| DE (1) | DE4141214C3 (en) |
| FI (1) | FI88755C (en) |
| FR (1) | FR2670514B1 (en) |
| GB (1) | GB2251562B (en) |
| SE (1) | SE510368C2 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19751098C2 (en) * | 1997-11-18 | 2003-02-20 | Voith Paper Patent Gmbh | Method and device for adjusting an elongate component, which extends in the width direction of a running material web |
| ES2185565T3 (en) | 1999-02-11 | 2003-05-01 | Alcan Int Ltd | PROCEDURE AND APPLIANCE FOR PROFILE CONTROL IN A DIRECT COATING MACHINE. |
| FI108653B (en) * | 2000-09-18 | 2002-02-28 | Metso Paper Inc | Method for adjusting deflection and / or position of deflection compensated blade beam |
| AT506514B1 (en) | 2008-03-05 | 2013-03-15 | Metso Paper Inc | BAR CONSTRUCTION FOR PAPER AND CARTON MANUFACTURING MACHINES AS WELL AS A METHOD FOR THE PRODUCTION THEREOF |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI94032C (en) * | 1987-06-10 | 1995-07-10 | Voith Gmbh J M | Smoothing device for a coating machine |
| FI100311B (en) * | 1988-09-23 | 1997-11-14 | Voith Gmbh J M | Smoothing device for a coating machine |
| DE3908386A1 (en) * | 1989-03-15 | 1990-09-27 | Jagenberg Ag | METHOD AND DEVICE FOR COATING MATERIAL SHEETS, ESPECIALLY PAPER OR CARDBOARD SHEETS |
-
1990
- 1990-12-13 FI FI906132A patent/FI88755C/en active IP Right Grant
-
1991
- 1991-12-06 GB GB9126008A patent/GB2251562B/en not_active Expired - Lifetime
- 1991-12-10 CA CA 2057325 patent/CA2057325C/en not_active Expired - Fee Related
- 1991-12-11 FR FR9115350A patent/FR2670514B1/en not_active Expired - Fee Related
- 1991-12-13 DE DE19914141214 patent/DE4141214C3/en not_active Expired - Fee Related
- 1991-12-13 SE SE9103693A patent/SE510368C2/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| CA2057325A1 (en) | 1992-06-14 |
| DE4141214C3 (en) | 2003-11-13 |
| GB2251562B (en) | 1994-08-03 |
| SE9103693D0 (en) | 1991-12-13 |
| GB2251562A (en) | 1992-07-15 |
| FI88755B (en) | 1993-03-15 |
| FI88755C (en) | 1993-06-28 |
| FR2670514A1 (en) | 1992-06-19 |
| DE4141214A1 (en) | 1992-06-17 |
| SE9103693L (en) | 1992-06-14 |
| SE510368C2 (en) | 1999-05-17 |
| DE4141214C2 (en) | 2001-03-08 |
| FR2670514B1 (en) | 1997-01-10 |
| FI906132A (en) | 1992-06-14 |
| GB9126008D0 (en) | 1992-02-05 |
| FI906132A0 (en) | 1990-12-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |