US1736161A - Segmental grinding wheel and method of assembling the same - Google Patents

Description

, O 1929- T. LARSSONET AL 1,736,161

SEGMENTAL GRINDING WHEEL AND METHOD OF ASSEMBLING THE SAME Filed March 18, 1926 Times sea .33 I Uhurefiagstfilin 34% S u flugow. e

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BETH, OF WORCESTER, MASSACHUSETTS, ASSIGNORS Fri" TO NORTON COMPANY, OF WORCESTER, MASSACHUSETTS, A CORPORATION OF MAS- SACH'USETTS SEGMENTAL GRINDING WHEEL Ann mmfnon or ASSEMBLING THE SAME Application filed March 18, 1926. Serial No. 95,772.

This invention relates to abrasive wheels and a method of assembling the same and more particularly to wheels of the type shown patent to Greenwood No. 1,469,723 dated October 2, 1923, which are particularly grinding logs into wood pulp. Y

A pulp-stone wheel of this class comprises an iron drum on which abrasive segments are mounted. In order to hold the segments rigidly in place and prevent movement during the grinding operation, each segment is provided with a dovetailed portion having bevelled clamping surfaces, and wedge blocks are clamped against these surfaces and adjustably bolted to the drum. I

The segments are made ordinarily of abrasive grains bonded by means of vitrified and under such a heat treatment as will serve to vitrify the bond. This vitrification process causes the clay ingredients of. the bond to become vitrified or glassy and thus adhere by a physical union to the abrasive grains and unite them into an integral mass. It will be understood, therefore, that the segments are somewhat fragile inasmuch as the bond is of the nature of glass or porcelain, hence the enormous forces to which the pulpstone is ordinarily subjected may be sufficient to disruptthe abrasive segments unless the wheel is properly built and the segments are rigidly supported on the drum and properly pro- 1 tected.

For grinding wood pulp it is desirable to have a-very large wheel, because of the size and weight of the logs to be ground, and in order to sustain the enormous forces to which the wheel must be subjected. One kind of pulp grinding stone in practical use is more than five feet in diameter and weighs over eight tons. The logs of wood are forced against the surface of the wheel under hydraulic pressure which may amount to 30 to pounds per square inch. The wheel is rotated at about 250 revolutions per minute, and

under normal grinding conditions this may require as much as 1400 horsepower. The friction of the grinding operation generates a large amount of heat, and it is the practice in this country to permit the water which is flowed over the wheel to attain a temperature of about 160 F., so that the heat may aid in loosening the bonds which hold the wood fibres together. This temperature results in considerable expansion of various parts of the wheel and is an important factor which must be considered in designing the wheel. It moreover is necessary to take into consideration the various major forces involved in grinding logs with such a large wheel, whichinclude the centrifugal force set up by rotat- 3 ing the wheel rapidly, the logs against the segments, the tangential drag of the logs on the segments and the clamping pressure applied through the wedge blocks, all of which tend to disrupt the wheel. This disruptive action is particularly due to the fact that the coeflicients of expansion of the radial pressure of the abrasive segments and of the iron drum are different. Moreover, the heat applied to 'or generated 'in the peripheral portion of the abrasive annulus, due to the friction of the grinding action or other causes, tends to expand this portion and so create a greater stress on the clamping or securing members.

As a result there is a tendency for the segthem.

'In accordance with the prior practice, and as shown, in the Greenwood patent the shoulders of the dovetailed portions of the segments have been located quite near to the drum inorder' .to provide as much abrasive material as possible which might be utilized in. the grinding operation. As a result the clamping pressure re'-' quired to hold the wedgeblock against the segment has often beenso-highas'to cause the corner of'the segment to be sheared off or to be crushed during use of the wheel. This shearing action seems to be caused by the effort of the logs dragging on the wheel tending to twist or rotate the segment about one of the wedge blocks and thereby to shear i off the opposite corner portion.

construct and arrange the parts of a segmental grinding wheel of this type that the segments may be mounted on a drum and held securely thereto under a high clamping pressure so that the wheel may be used for a long life of service without breakage.

Another object is to provide a grinding wheel, having an abrasive body rigidly mounted on a rotatable support, in which provision is made to compensate for any slight change in size of the support or the abrasive body, or a segmental portion thereof, which may be' caused by temperature variations, whereby the abrasive body will not be broken but will remain rigidly in position during normal conditions of use.

A further object is to provide a method of assembling such a wheel correctly and particularl to make it feasible to locate the segments rst loosely in their proper positions and then to clamp them rigidly in place, whereby the clamping pressures will be uniformly distributed and breakage of the segments, due to their being improperly located, will be minimized.

With these and other objects in .view as .will be apparent to one skilled in the art from the following disclosure, our'invention resides in the combination of parts set forth in the specification as covered by the claims.

appended hereto. 1

Referring to the drawings in which like reference numerals indicate like parts:

Figure 1 is a fragmentary sectional view of one embodiment of my invention;

Fig. 2 is a perspective view of an abrasive segment; and v t Fig. 3 is a similar view of a wedge block, clamping bolt, and a fragment of the spacer block and shims.

As shown, a grinding wheel which is particularly adapted for grinding wood pulp comprises a drum 1 having abrasive'csegments'2 mountedthereon. The drum, which is suitably mounted for rotation, has a sub; stantially cylindrical outer surface 3 and several rows of abrasivesegmentsgare fastened thereon with their'inner peripheral surfaces fitting the drum and with their outer surfaces forming a substantially cylindrical peripheral grinding surface 5. The rows of abras1ve segments are so shaped as to fit together along radlal or other planes as shown for example in the Greenwood patent, and they are clamped in position on the drum by means of wedge blocks 6, each of which is adjustably The wedge blocks are located between the segments in grooves in the sides of adjacent segments, the wedge blocks having beveled faces and the grooves being correspondingly shaped so that tightening the bolts to draw the blocks inwardly forces the segments into a tightfiton the drum.

As heretofore provided, the clamping bolts have been made of the ordinary material so that, after the segments have been fastened in place with all the pressure on the clamping blocks that was feasible, the segments havenevertheless become loose when the wheel was used for the grinding operation. This has permitted a slight twisting of the segment in its setting .so that it often broke or sheared.

off a proximately along the line cv-a2 indicate in the drawing.

-As the result of our experimentation, we have found that in order to overcome the danger of such shearing action, the segment should be so made and the clamping blocks so requires locating the wedge so that the distance along the line a-a is substantially onehalf of the distance ab between the clamping grooves. This arrangement is such that the disruptive forces are no more likely to shear the segment along the line H than they are to break the segment along the line ab which is atithe narrowest and conse- .quently the weakest portion of the abrasive mass. As a result one may safely subject the segment to a' clamping pressure which is very high and which is limited mainly by the strength of the material employed throughout the mass of the segment.

As a further important feature, we provide a grinding wheel, having an abrasive body rigidly secured on a'rotatable support, which is so constructed that the support or the abrasivebody or a segmental portion thereof may be permitted to change in size and move to any. required extent when there is a temperature variation which; would normally tend to disrupt the wheel or cause the abrasive .body to become loose on its support.

.\ This is accomplished by means of an elastic medium so arranged that while the abrasive body, or an individual segment thereof, is

ature variation, this elastic medium compensates for, absorbs or neutralizes such-expan- S1011 or contractlon and so permits a change 1n size in the wheel or a relative movement.

between two parts ofthe wheel which have 65 fastened to the drum by means of the bolts 7. different coefiicients of expansion, and so insecured firmly on'its support and movement 32 may be connected by strips 34 which lie in grooves in the face of the segment which aid in holding the shoes in place. After the segments have been assembled on the drum, a

' babbitt which is poured while molten into the crevice and which has such durability, toughness and other physical characteristics that it will wear away at substantially the same rate as the abrasive segments and so protect their edges from breakage. The surface of this metal filler will ordinarily be such that it will wear into a slightly hollow form and will not project above the cylindrical surface of the wheel. harder than the segments and formed a projecting ridge, it would bump against the logs, which might result in breaking the segment. One side of each segment may be provided with grooves 36 arranged to assist in holding the filler in position against the action of centrifugal force.

Having thus described our invention, what we claim as new and desire to secure .by Letters Patent is:

1. An abrasive wheel comprising in combination, a support, an abrasive annulus secured to the support, said annulus and said support being of materials of different co- I efficients of expansion wherefore temperature changes in said wheelcause movement of the annulus and the support relative to each other, and an elastic medium which serves to compensate for said movement.

2. .A grinding wheel comprising a rotatable support, an abrasive annulus surrounding and mount-ed on the support and elastic means to compensate for differences in exp'ansionbeable support, an annulus of abrasive segtween the-annulus and the support.

3. 'A grinding wheel comprising a substantially cylindrical support, an abrasive annulus supported thereon and providing a cylindrical grinding surface',-clamping means engaging the annulus, and elastic means to compensate for differences of expansion between the annulus and the cylindrical support.

4. An abrasive wheel comprising a rotatable support and an abrasive annulus mount ed on the support which are adapted to be subjected to a temperature variation tending to cause a slight change in the size of one of said portions of the wheel, and elastic means to compensate for' said change so that the abrasive-annulus will remain rigidly in position under all normal conditions of use.

5. An abrasive wheel comprising a rotatable support, a plurality of abrasive segments mounted thereon to forman abrasive surface, said segments being adapted to be subjected to a'temperature variation tending to cause a change in size thereof, and elastic means to compensate for said change so t at the seg- If the metal were lus supported thereon and providing a cylindrical grinding surface, securing members engaging the abrasive annulus and adapted to be connected to the support-to hold the annulus in position, and elastic means cooperating therewith to compensate for any movement or change in size of the annulus due to a normal temperature change.

8. A grinding wheel comprising a rotatable support, an integral abrasive annulus surrounding and mounted on the support and being normally immovable relative thereto, said parts being adapted to be subjected to a temperature variation tending to cause a,, slight change in size of the annulus, and an elastic medium interposed between the annulus and the drum which compensates for such change in size so that the annulus may remain rigidly and securely in position during all normal conditions of use.

9. A grinding wheel comprising a rotatable support, an annulus of separately fashioned abrasive segments mounted on the support, means forming a seat for each segment which fits the support and positions the segment accurately, and elastic means to compensate for a slight change in'size of the abrasive annulus caused by a temperature variation.

10. A grinding wheel comprising a rotatments mounted thereon, a filler in the crevsame laterally, and elastic means to compensate for any change in size of the segments 1 due to a temperature variation.

11. A grinding wheel comprising a rotatable support, a plurality of abrasive segments mounted thereon, means beneath the segments to seat them on the support, means including an elastic medium to compensate for a change in size of a part of the wheel due to a temperature change, and a filler in the crevices between the segments. I

12. A grinding wheel comprising a rotate able support, an annulus of separately fash- -ioned abrasive segments surrounding the, support, and means to mount the segments thereon including a clamping wedge block andan' elasticf medium which compensates for expansion of the annulus under a temperature change.

13..A grinding wheel comprising a rotatable support, a plurality. of abrasive segi-g' sures that the abrasive body will be held rigidly and securely in position under all-normal conditions of use. In the form illustrated we employ a clamping member having a high degree of elasticity or resiliency which is of such size and is so arranged that it will compensate for any tendency of the segments to move and become loose on the drum. While we may silient members for this purpose, we prefer a suitable such as a nickel steel, which is heat v treated by methods well known in metalmay also lurgical practice to give it the desired elastic limit and tensile strength. The bolt is arrangedin the assembled wheel so as to pro vide a relatively long distance between its 0pposite ends or points at which stress is applied, and it is placed therein under such a tension as to elongate it an amount which will exceed, with a large factor of safety, any decrease in the distancebetween the points of stress thereon that may be caused by external forces or heat expansion during assembly of the wheel and normal usage so that the bolt will always be under a resilient tension tending to shorten it and draw the segments into position. v

s an aid in assembling the wheel, we prefer to mount every other clamping block rigidly in place before placing the segments on the drum. These serve as locating members which insure getting the segments into approximately correct positions, after which the remaining wedge blocks may be inserted endwise between the segments and the latter drawn ti htly into place. The'fixed blocks be made adjustable by the use ofremovable shims-25 (Fig. 3) which permit the blocks to be initially fixed for locating the segments and which may then be removed to permit tightening theblocks. I r

In the drawings, we have illustrated a grinding wheel embodying'a combination of the various features of our invention as discussed above. In the form shown, each wedge block 6 is provided with radially disposed holes 11 which are screw threaded to receive the upper ends of the clamping bolts 7. 'Each bolt 7 is reduced in cross sectional size throughout its entire medial portion 12 between'the threads 13 at the upper end and a similar series of threads 14 at the lower end and this reduced portion fits loosely in; the hole 15 within the drum. At the inner end of the clamping bolt, we provide suitable cans for fastening it to the drum, such as l nuts 17 threaded thereon which engage a 'collar 18 resting against the inner surface of B01 the drum. In our preferred form of mounting, the

I bolts and wedge blocks 6 are freely movab e inwardly so as to clamp thesegments with the right amount of pressure against the drum. As will be observed, however, the

employ various types of elastic or reranged to present smooth .be clamped. Similarly,

initially in a fixed position by a spacer block 20 arranged to limit the inward movement of the wedge block during assembly of the Wheel. The spacer 20 is slightly separated from the depending portion 21 of the wedge block, and the spacer is provided with a tongue 22 interfitting with a groove 23 in the wedge block. to hold them in proper alignment. The spacer 20 rests in a slight depression 24 formed in the outer surface of the drum so as to locate it properly. During assembly of the abrasive segments on the drum, thin shims 25 are placed between the spacer 20 and the depending portion 21 of the wedge block after which the blocks are drawn down securely in place by tightening the bolts. This serves to fix every other one of the wedge blocks so that the segments may be accurately located. After the movable wedge blocks on each side of the fixed one have been set tightly in place, the shims are then withdrawn, thus making it possible to tighten the bolts which 'hold these formerly stationary wedge blocks and give the same clamping pressure on each side of the segment.

- In practice, the nuts 17 are initially drawn up until the bolts are elongated within'their elastic limits to such an extent that after the segments have been used in grinding, the bolts will still remain under tension suificient to take care of any normal changes in position of thesegments. The bolts are made large enough in cross sectional area and long enough between the threaded port-ions so that they may be elongated to a considerable extent and yet possess the necessary strength to hold the massive segments in place. It will be understood that heat expansion of the drum tends to separate the segments, thus letting the Wedge blocks slide down the clamping faces and causing the bolts tos horten. Assembling the parts of the wheel after they have been heated to the temperature of grinding aids materially in making a wheel which will be rigid when cold .and when used in grinding. It is to be noted that in addition to compensating for heat expansion, it is necessary'to provide an elastic elongation of the bolt sufficient to "take up the settling together of the segments when the large forces of grinding are applied. i The grooves in the sides of the abrasive segments have metal shoes 30 which maybe made of zinc or babbitt cast in place and are arand accurate surfaces against which the wedge block s'are to a shoe of suitable metal such as babbitt of zinc is located on the inner periphery of each segment adjacent its outer corner, as illustrated; This shoe is formed with a partial cylindrical surface 33 which fits accurately against the outer drum surface and thereby serves as a means to seat the segment on the drum. The shoes 30 and clamping surfaces,

, and contract during normal usage and the ments mounted thereon surface, and means to secure the segments on the support, including which has an initial stress sufficient to hold each segment under pressure against its support irres ective of any expansion and contraction o the wheel incident to normal usage.

14. A grinding wheel comprisin'ga metal support, a plurality of abrasive segments mounted on its periphery to form a grinding surface, lugs on the segments providing clamping blocks engaging said surfaces, and adjustable means including resilient members which are under an initial stress when assembled suflicient to secure the blocks to the support and hold the segments firmly in position during the expansion and contraction incident to the normal usage of the vwheel.

15. A grinding wheel comprising a metal drum, abrasive segments mounted thereon to form a cylindrical grinding surface, clamping blocks engaging the segments, and means including bolts made of a material of high tensile strength and a high elastic limit to s ecure the blocks to the drum, said bolts being elongated within their elastic limits suflicient to hold the segments under pressure against the drum under all conditions of normal temperature changeand usage. I

16. A grinding wheel comprising a drum, a row of abrasive segments thereon forming a cylindrical grinding surface, adjacent segments having opposed grooves eled clamping. lugs, a wedge block movably located in the grooves betweenvthe segments, and means including an elastic bolt for adj ustably fastening the block to the drum and thereby clamping the segments in position, said bolt being made of a material of high tensile strength and a high elastic limit and being stretched under high tension within its elastic .limit so that the wheel may expand segments will yet 'be secured firmly to the drum.

17. A grinding wheel comprising a drum, a plurality of bonded abrasive segments mounted thereon to form a cylindrical grinding surface, each segment having oppositely disposed grooves forming clamping lugs,

clamping blocks engagmg said lugs, and

means for adjustably securing the blocks to the drum and thereby hold ing the segments rigidly in position, ranged at such a distance fromthe inner surface of each segment and the parts being so proportioned that the force required to shear off the segment beneath the is substantially equal to the tensile strength of the block between the grooves.

18. A grinding wheel comprising a metal drum, a plurality of abrasive segments mounted on said drum which have beveled clamping surfaces-,wedge blocks adjustably to form a grinding a resilient member forming bevclamping blocks engaging said surfaces, and resilient tension members adjustably fastened to the drum and the inner surface of the segmentthat the force required to shear off the portion beneath a clamping surface is substantially equal to the tensile strength of the segment between the grooves.

19. A grihding wheel comprising a rotatable drum, a row of abrasive segments mounted on the drum which'have grooves providing clamping faces, removable clamping blocks in the grooves between the segments an engaging said clamping faces, means for adjustably securing all of the blocks to the drum and for drawing both sides of each segment into position, and means cooperating therewith which permits only a slight movement of alternate clamping blocks whereby they may be located substantially in their final positions and so serve to locate the segments initially .in their correct positions and thereafter permit clamping adjustment thereof. 20. The method of wheel having with clamping shoulders which are mountedon a support having spaced adjustable clamping blocks engaging said shoulders, comprising the steps of fixing alternate clamping assembling a grinding blocks temporarily in position to locate the mounting the segments on the support, drawing the other segments loosely in place,

position the seg- Massachusetts, this the grooves being arabrasive segments providedthen tightening all of

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