US1815108A - Grinding wheel - Google Patents

Description

y 21, 1931- T. LARSSON ETAL 1,815,108

GRINDING WHEEL Filed Dec.

anomalous THWE LHR'SSON Hum IMHBETH atfoz m2 q Patented July 21,1931

NTED STATES PATENT OFFICE THURE LARSSON AND HUGO W. H. BETH, 0F WORCESTER, MASSACHUSETTS, ASSIGNORS TO NORTON COMPANY, OF WORCESTER, MASSACHUSETTS; A CORPORATION OF MAS SAGHUSETTS enmnme wnnnr.

Applicatlion filed December 17, 1928. Serial No. 326,546.

This invention relates to grinding wheels and more particularly to very large wheels.

made of abrasive segments mounted on a rotatable support, such as are used for. grinding wood pulp.

A pulp grinding stone of the type shown in the patent to Greenwood No. 1,469,723 is exceedingly heavy and strongly built in order to withstand the enormous forces'involved in grinding wood pulp. Such a wheel may be five or six feet in diameter as well as length and the segments of abrasive material may be about one foot in thickness. When this huge wheel is used for grinding wood pulp in accordance with the method prevailing on this continent it is rotated in a pit containing water, and there is so much friction involved in the grinding operation that the water is heated to about 160 F., and is kept at approximately this temperature during normal use of the wheel. water supply should fail and the wheel were run dry fora while, the outer portion of the wheel would be greatly heated by the friction of the grinding operation and even -to such an extent as to melt out the metal which is normally placed in the crevices between the segments. This enormous heat expands the outer abrasive portion of the wheel, and it is likely to cause some of the segments to break out of their settings. It will therefore be seen that there are two temperature conditions which must be faced in using such a large wheel. One is the normal change of temperature from the below zero conditions of storage in a cold winter to the temperature of the water in the grinding pit. The other is the abnormal heating of the wheel due to running the wheel dry for any length of time or to other conditions which tend'to expand the wheel beyond the usual extent. Both of them tend to break the wheel.

It is accordingly the main purpose of this invention to provide a grinding wheel made up of abrasive segments mounted on a rotatable support which is so constructed that it will automatically compensate for the normal temperature changes met in the usual grinding operation and which is so constructed that a part will yield under any If however the abn'o'rnial forces set up by undue expansion of the wheel and so prevent the abrasive segments themselves from being broken.'

With this and other objects in view as will be apparent to one skilled in the art, this invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

In accordance with the invention, compensation may be made for expansion of the wheel due to temperature changes by utilizing an elastic medium which is so located that expansion of the segments or differential expansion between the abrasive annulus and the su port therefor may be permitted without a ecting the rigidity of the wheel or seriously loosening the segments on their mountings. In order that the expansion of the wheel may take place circumferentially, it is preferred to place a compressible medium in the crevices between the segments; and these crevices are preferably filled with material which will prevent all movement of the segments during a normal grinding operation and serve to support the corners of each segment and prevent their being struck and broken by the object being ground. In

pands and this may be accomplished by so constructing the parts that this yieldable material engages the abrasive segment in a comparatively small area of contact, thereby permitting one to use a strong and normally rigid material for this purpose.

In the preferred form of the invention, this may involve placing in a crevice between two adjacent segments a member capable of serving as a mold form and then casting a filler in the crevice, the mold form being so shaped and arranged as to provide a filler portion capable of yielding when subjected to a compressional force due to a temperature change. This mold form may be a strip of a compressihle medium, such as cork, which is sufliciently thin so that it will not compress unduly but will yield a calculated extent as required and a segment with a medium such as lea or a Babbitt metal, or for certain uses with such materials as Lavasul, which is a sulfur and coke mixture." This filler flows'through the small holes in the cork and thus forms posts or strutswhich'engage or substantially engage the side""of*the abrasive segment. These spaced posts during normal use of the wheel servetotake the lateral-thrust and to hold the segments rigidly in position, but if the wheelis permitted to expand abnormally, then these posts will yield and become slightly shorterandfsopermit the segments to approach each other. 1

Referring to the drawings which illustrate one embodiment of the invention as applied to a wheel of the Greenwood type:

Fig. 1 is a fragmentary perspective view of a portion of a drum-havmg abrasive segments mounted thereon andprovided with both an elastic and a yielding medium in the crevice between adjacent segments; and

Fig. 2 is a fragmentary sectional view of the same. In a grinding wheel'of this type, a plurality of separately fashioned abrasive segments 10 are removably mounted on a drum 1101 other suitable support and they are clamped "in position by meansv of wedge blocks 12 which engage beveled shoulders 13 within grooves 14 between the segments. In this type of wheel as used for grinding wood pulp, a shoe 16 of suitable material, such as lead or Babbitt metal, is placed or cast on each shoulder of the abrasive segment in order that the wedge block 12 may make a proper contact therewith and not crush the abrasive material. Similarly, a shoe 18 of suitable material, such as metal, cement, and the i like, is molded or cast onto the bottom of-the abrasive segment or otherwise located between the segment and the drum, and it is preferably so shaped, as by casting it in place or by initially molding it in a form, that it will fit quite accurately against the surface 19 of the drum 11. have beveled faces 20 engaging the upper surfaces of the shoes 16 on the beveled shoulders 13 of the wheel segments, whereby the wedge blocks may adjust themselves to the shoulders of the two adjacent segments and so serve tohold them both rigidly and securely in place. Each wedge block is secured to the drum 11 by means of bolts 22 and nuts 23, the bolts being screw-threaded at their up- The clamping blocks 12 per ends into the wedge block and passing through holes in the drum and being there secured by the nuts engaging the under side thereof. In order to compensate for expansion and contraction in the wheel due to a temperature change, the bolts may each be made of an elastic material which is capable of being elongated under elastic tension so that the segments may be yieldingly held in place. Such a bolt is placed under an initial tension which is sufficient to elongate it slightly but to such an extent that the bolt will always resiliently hold the clamping blocks against the shoulders of the se ments and even when the wheel contracts in size and the segments may move inwardly. "If the wheel expands then the bolts may become 7 elongated to a further extent and so permit the segments to move outwardly radially.

A particular feature of this invention, as

applied to a segmental grinding wheel in which the segments are held in position by {the above described clamping devices or by any other suitable securing means, involves the'provlsion of a medium located between a segment and another wheel part which will compress slightly when subjected'to a high compressional force due to a temperature change. This medium preferably comprises a filler in the crevice between adjacent segably shaped in position by a casting o eration, and the mold therefor may be a de ormable body located in the crevice adjacent to one segment face. this purpose is a thin strip of pure cork taken from the bark of the cork tree, and for a large pulpstone this cork strip may be about one sixteenth of an inch thickto give the desired degree of deformability. This cork strip 26 is preferably cemented or otherwise secured to one face of a segment in order to hold it properly in position.

Supplementing this cork strip in the crevice betweentwo adjacent segments is a suitable filling material capable of transmitting the lateral forces and keeping the crevice filled during the grinding operation. This filling material 27 is preferably poured intothe crevice between the segments after the latter have been assembled on the drum, and a suitable material for this purpose is a low melting metal, such as lead, zinc or a Babbitt metal which is capable of A suitable material for 4 wearing away at substantially the same rate as the abrasive material wears away on its peripheral surface-during a normal grinding operation. This filler may also be made of other suitable materials, such as a mixture of sulfur and ground coke, known under the trade name of Lavasul, or other materials which have been found suitable in this. grinding wheel art for like purposes. A suitable Babbitt metal composition useful for both the shoes and the filler may be made of 91%by weight of tin and l each of antimony and copper.

In order to form the compressible portion or-posts of the filler, the cork strip may be provided with'a large number of small perforations so that the filling material 27 may enter these perforations and form small posts or struts 28 which project through the cork and come substantially into contact with the adjacent face of the abrasive se ment. These posts may be pre-fashioned efore assembly of the wheel, but they are more easily formed from the filling material itself when it is cast or poured into the crevice. If a molten metal is utilized, then when it cools after the casting operation it will shrink very slightly and these small posts or struts 28 will draw away from the face of the segment to a very slight extent; and

it is preferred that the conditions of manufacturebe so predetermined, which includes regulating the temperature of the wheel during the casting operation, that, when the wheel has been thus assembled and afterward heated up in the normal grinding operation to the temperature of the water in the grind- "ing pit, these small posts or struts will come substantially into contact with the abrasive segment and so make a rigid connection between the two adjacent segments and thus hold the wheel parts rigid and firmly in position.

During normal use of the wheel, which may be throughout its entire life, the very slight movement of thesegments required for the normal breathing, as it were, of the wheel, due to expansion and contraction, will be compensated for by the elastic bolts 22 if they are used. If at any time an accident occurs whereby the water in the pit is shut,

off and the friction of grinding while the wheel is dry, which may' be enough to melt the metal filler, heats the wheel abnormally and the segments attempt to expand, this will be permitted by the yielding of the little posts or struts 28 which are utilized for this purpose. Any excessive pressure on these posts will cause them tobuckle,bend,compress or otherwise yield and in that way it will be possible for the segments to move very slightly laterally. After this particular abnormal condition has departed, then the wheel will resume its normal condition due to the elasticity of the bolts 22 but of course the little posts or struts 28 will remain in their compressed condition. However, such an abnormal usage of the wheel is unlikely to occur more than once during its life and in that case the posts or struts will have taken care of the emergency. It will also be noticeable that the metal filler in the outer portions of the vary, according to the nature of the materialused and the type of the grinding operation, yet we have found it feasible to use in a wood pulp grinding wheel of from 54 to 67 inches in diameter a cork strip which-is about one sixteenth of an inch thick and has holes about three sixteenths of an inch in diameter and spaced about one to one and one half inches apart.

To keep out dirt and moisture from between the adjoining abrasive segments and the wedge blocks, it is desirable to fill the intervening space with a cement or other suitable material. To prevent the cement from hindering movement of the wheel segments and thus r'elieve strains and stresses occasioned by temperature changes, we propose to cement or otherwise secure a plain, thin cork strip 29 'to one of the adjacent faces of the segments as shown in the illustration. small rubber strip 30 is placed on the bottom of the wedge block whereupon the intervening space may be filled with a cement 31 or other suitable material. 1

The grinding wheel has been illustrated in the drawings as comprising a' single row of segments, for the sake of clarity of illustration, but it will be apparent that one may utilize either a single row of segments, as may be employed for metal grinding operations, or several rows of segments mounted on the drum in accordance with the showing of the Greenwood patent. This grinding wheel has utility in various fields. In view of the above disclosure various modifications of this invention will be apparent to one skilled in the art and the claims are to be construed accordthe segment rigidly in position but will yield under excessive pressure due to temperature expansion of the wheel.

2. A grinding wheel comprising a rotatable cylindrical support, a plurality of abrasive segments peripherally arranged thereon,

. means to" secure the segments on the support and a deformable non-elastic medium located between adj acent segments which normally aids in holding the segments rigidly in position but yields under an excessive pressure support, an annulus of abrasive segments mounted on said support to form a cylindrical grinding surface, means to fasten the segments securely thereon, a deformable medium located in but not filling the crevices between two adjacent segments which normally contacts with bothsegments and aids in holding them rigidly in position but is adapted to yield and permit lateral movement of the crevice faces of the segments under a temperature change in the wheel.

5. A grinding wheel comprising a rotatable support, an annulus of abrasive segments thereon, means to secure the segments on the support, and an expansion compensating medium located between the faces of adjacent segments comprising spaced deformable members normally arranged to receive lateral thrusts from the segments and to aid in holding themrigidly in position but which yield under excessive pressure.

6. A grinding wheel comprising a rotatable support, a plurality of abrasive segments mounted thereon, means to secure the segments to the support, and means including a filler between the segments and yieldable mal force and so permit a-slight expansive movement of the annulus.

' 8. A grinding wheel comprising a rotatable support, a plurality of abrasive segments mounted thereon, means to secure the seg-. ments upon the drum, a perforated compressible strip in a crevice between adjacent segments, and a filler between said strip and one of the segments which enters the perforations of the strip and forms spaced posts therein.

9. A grinding wheel comprising a rotatable *support, a plurality of abrasive segments secured in position on the support, a perforated strip of compressible material in a crevice between adjacent segments, and a filler cast into the crevice between said strip and a segment and forming posts in the perforations of the strip, said posts being capable of yielding under an abnormal force applied thereto and so permitting expansion of the wheel.

10. A segmental grinding wheel comprising a plurality of abrasive segments arranged to form a grinding surface, a member in the crevice between two adjacent segments serving as a mold form and a filler cast in the crevice and shaped by said form'which provides a portion capable of yielding when sub jected to a compressional force due to a temperatu-re change.

11. A segmental grinding wheel comprising a plurality of abrasive segments arranged to form a grinding surface, a member in the crevice between two adjacent segments which provides a plurality of spaced mold forms and a filler cast in said crevice having a plurality of posts shaped by said forms which are capable of yielding when subjected to a compressional force due to a temperature change.

Signed at Worcester, Massachusetts, this 15th day of December, 1928.

THUR-E LARSSON. HUGO \V. H. BETH.

posts which will normally hold the segments separated but will yield slightly when subjected to an abnormal compressive force.

7. A grinding wheel comprisinga rotatable support, an annulus of abrasive segments thereon,-means to secure-the'segments on the support, an elastic medium permitting normal expansion of the wheel, and means including a plurality of yieldable posts between a' segment and another part of the wheel which will yield when subjected to an abnor-

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