US2092978A - Grinding disk - Google Patents

Description

p 1937- T. L. F. LARSSON 9 GRINDING DISK Filed Dec. 5, 1934 W/ TNE 5 3 5 77/1/05 1. FZFRJ'J'O/V (TJWWR H. ca

Patented Sept. 14, 1937 UNITED STATES PATENT OFFICE cnmnmc. msx

Application December 5, 1934, Serial No. 756,137 I 3 Claims.

This invention relates to a bonded abrasive disk and especially to a sector type of grinding disk such as a, grinding wheel which presents an extensive fiat grinding face.

Grinding disks as used heretofore for performing abrading operations with their flat annular faces have usually comprised homogeneous, unitary, bonded abrasive bodies, such as a flat faced grinding wheel which is cemented or otherwise suitably fastened to arigid rotatable-support, whereby the entire fiat face of the abrasive body may be employed for a grinding operation. Grinding disks of this type are adapted for various heavy duty grinding operations such as, for example, dry grinding the ends of large coil springs. However, much difiiculty has been encountered in suitably securing such an abrasive disk to its backing plate with sufiicient tenacity to withstand the various heavy duty grinding operations to which this particular shape and type of grinding disk is especially adapted.

Heretofore in the manufacture of grinding disks of this general type, the abrasive bodies.

' often become loosened from their metal supporting plates or various serious structural cracks and ruptures frequently developed within the bonded abrasive body itself. Furthermore, due to the excessive changes occasionedin such a grinding disk during a grinding operation, it has been found that a large grinding disk is incapable of withstanding a heavy duty grinding operation. It has also been found that many of these disks are unsuited for dry grinding operations since their operative surfaces are rapidly brought to a high temperature due to the friction of grinding and this high temperature on the operative wheel, face is attained long before other wheel portions experience any appreciable temperature change. As a result, the operative wheel face tends to expand at an extremely rapid rate, while other portions of the grinding wheel and its rigid backing support tend to resist this expansion, thereby resulting in uneven internal stresses which usually cause wheel breakage. Furthermore, the coefiicients of expansion of the bonded abrasive disk and the metal backing support are so unrelated that they expand to greatly different extent due to heat of grinding and frequently cause the bonded abrasive body and its metal backing member to break apart during a grinding operation, thereby subjecting the machine operator to considerable danger and often resulting in spoilage of the work and damage to the grinding machine.

and sudden temperature.

' In attempts to surmount these difliculties and compensate for the expansions and contractions of an operative wheel face due tofrictionalheat of grinding, various types of abrasive disks have been composed of a large number of spaced seg- 5 ments or sectors fastened together in annular form. However, these various attempts have proved unsatisfactory. For example, various devices, such as chucks,'have been utilizedto clamp a plurality of spaced abrasive blocks to a rotat- 10 able rigid support so-that each of the blocks may be continuously moved through the same circular path and thus cooperate to provide a grinding operation. These chucks have been unsatisfactory in many respects, since they are cumber- 15 some, expensive devices and the abrasive blocks themselves are relatively narrow, so that the total operativegrinding surface only includes a very small portion of the area within the circular path through which the blocks are rotated. Abrasive blocks of this type must be carefully shaped and in many instances they must be ccmented to precisely shaped clamping members so that they -may be accurately seated within their respective chuck jaws, thereby providing a 2 construction which is not only expensive but also difiicult and slow to assemble.

It has also been proposed to secure a plurality of abrasive sectors on a rotatable metal backing plate by means of suitable clamping devices, such as nuts which are embedded within the rear face of each wheel sector and engaged by bolts passing through the backing plate, whereby the sectors may be rigidly secured in desired grinding position. However, constructions of this type 35 have usually proved unsatisfactory for heavy duty grinding operations since the clamping nuts tend to tear loose from their embedded positions. Furthermore, these embedded nuts also cause a considerable portion of the abrasive disks to be 40 wasted since they preventutilizing a large portion of the lower part of each grinding sector for an abrading operation, thereby making it impossible to employ all of theavai-lable abrasive material for a grinding operation. 45

The principal object of this invention is to overcome the inherent disadvantages of prior grinding disk constructions and to provide a sector type of grinding disk capable of heavy duty grinding operations and which may be easily and 50 {inexpensively manufactured and permanently .s. timed to a rigid backing support as an integral unit therewith in such a manner that all of the abrasive material may beemployed for :a grinding operation and wherein uneven expan- I 5 sions occasioned within the disk due to sudden temperature changes may be compensated for.

In the drawing which illustrates this invention and in which like numerals indicate like parts:

Fig. 1 shows a plan view of a grinding disk embodying my invention;

Fig. 2 is a sectional view taken approximately along line 2--2 of Fig. 1; and

Fig. 3 shows a modified form of my invention.

In accordance with this invention, I have pro vided a sector type of bonded abrasive grinding disk having a plurality of spaced bonded abrasive segments or sectors which are suitably shaped and assembled to provide an extensive flat annular grinding face including the major portion of the area within the disk periphery. To facilitate expansions and contractions of the operative grinding face, the sectors are assembled in spaced relation to each other and they are cemented together as well as to a rigid backing support by means of suitable vulcanizabie compounds, such as rubber, which may be resilient or slightly deformable between the adjacent opposed sectors to compensate for the individual expansions and contractions of each sector. This construction is provided to relieve the operative grinding portion of each sector of its stresses without permitting them to be transmitted to adjacent sectors and thereby accumulate and tend to cause rupture of the grinding body. It will be 'appreciated, however, that the cementing medium also serves to so locate the sectors relative to each other that they form an integral, substantially unitarygrinding disk having a substantially continuous flat grinding face. In the preferred type of my invention, the abrasive sectors are integrally secured to a rigid backing member, such as a metal supporting plate, by means of a layer of vulcanized hard rubber. Furthermore, this invention provides a highly efficient type of grinding disk wherein all of the abrasive material may be employed for grinding operations. In fact, it has been found that a grinding disk of this type may be appreciably stronger than a unitary grinding disk of the same grade and shape when used for certain heavy duty grinding operations, since the internal stresses and strains within the grinding member are relieved within each wheel sector and hence have no opportunity to accumulate sufficiently to produce disruptive forces.

It has been found that rubber containing 20% or more of combined sulphur by weight which is vulcanized to a hard, tough condition of the general nature of ebonite or vulcanite, and commonly referred to as "hard rubber, provides a highly eflicient and tenacious means for securing a plurality of spaced bonded abrasive sectors in fixed relation to each other on a rigid backing member. A hard rubber of this general type has been found to readily adhere directly to an iron supporting plate without necessitating any special preparation of the plate or the rubber compound itself aside from that of adequately cleaning and slightly roughening the surface of the backing plate by any suitable method, such as a sand-blasting operation.

Similarly, it has been found that rubber, commonly'known as soft rubber", containing 5% or less of combined sulphur by weight and which is vulcanized to a soft, resilient, deformable condition, may also be employed to cement a plurality of abrasive sectors to a suitable rigid backing member.

The interstices between the spaced abrasive sectors may be filled with any suitable cementitious material, such as a hard or soft rubber or other suitable vulcanizable compounds which will permanently adhere to the adjacent opposed sectors and alsoto the layer of rubber compound which secures the sectors to the backing member; or, if desired, the interstices between the adjacent sectors may be partially filled leaving the operative wheel face interrupted by a series of narrow grooves, whereby the individual sector faces may be free to expand during the grinding operation. In any event, thematerial be tween the adjacent sectors is so composed or so positioned that expansions and contractions of each operative sector face may be compensated for without transmitting stresses and strains to Other portions of the grinding disk.

Since the material between the adjacent opposed abrasive sector faces is composed of a vul canizable compound, it will integrally unite with the layer of rubber compound securing the abrasive disk to the backing member, and thereby further aid in securing the abrasive sectors integrally with the backing member and in correct grinding position. A. grinding disk of this type may be manufactured in any convenient size and its operative grinding face which is often subjected to excessively high temperatures of grinding will be free to expand and contract without setting up internal wheel stresses which tend to cause wheel breakage in prior types of grinding disks.

As illustrated, the preferred type of my invention comprises a disk shaped grinding wheel III, of any desired diameter and thickness, composed of a plurality of spaced bonded abrasive sectors I2, which are separately manufactured and assembled in the form of an annulus having a substantially continuous fiat grinding face I4, outer and inner peripheral faces I5 and I6, respectively, and a supporting face II. In the present instance, for convenience of illustration, my grinding disk is shown composed of six separately manufactured bonded abrasive sectors, but it will be appreciated that any number of sectors may be employed within the scope of this invention. Each of these sectors is composed of abrasive grains, such as crystalline alumina or silicon carbide, suitably bonded together into the desired shape by vitrified ceramic materials, rubber, resinoids, sodium silicate, or other suitable bonding materials that are well known in the art. Each sector is further provided with two converging side faces I8 which, in my preferred construction, are substantially perpendicular to the operative grinding face and substantially radial of the assembled grinding disk.

The sectors are permanently secured and evenly supported in grinding position by means of a backing member 20 composed of any suitable rigid material. As illustrated in my preferred construction, this backing member may comprise a substantially fiat, thin, circular iron plate of the same diameter as the disk periphery I5, and of such thickness that it will rigidly and evenly support the abrasive sectors during a grinding operation.

The backing member is provided with a supporting face 22,.which is shown as substantially flat and arranged to be integrally secured to the bonded abrasive disk supporting face I1 by means of an intermediate layer of a suitable vulcanizable rubber compound 23, which is relatively thin in comparison to the thickness of the backing plate. This layer of rubber compound is vulcanized in position under the influence of suitable heat and pressure. The term "rubber as used in the claims also relates to any vulcanizable material, such as various synthetic materials of the general behavior of rubber or rubber containing various fillers, etc. The term hard rubber as specified in various claims relates specifically to any vulcanizable rubber compound containing at least 20% of combined sulphur by weight and which will vulcanize into a hard, substantially non-resilient body of the type of ebonite or vulcanite. The term soft rubber relates to any rubber compound containing 5% or less of combined sulphur by weight and which will vulcanize into a soft, resilient, deformable, tough material. The interstices between the adjacent opposed sector faces l8 may be. filled with any suitable vulcanizable material, such. as a rubber compound 25, which may be vulcanized in position and will adhere to the opposed faces l8, and unite with the rubber compound 23, permanently securing said members together and thereby aiding in forming the abrasive sectors into an integrally united annulus.- In my preferred construction, this rubber compound 25 is preferably of such a composition that it may deform slightly during the grinding operation and thereby compensate for any expansions or contractions of the operative grinding face I occasioned by the frictional heat of grinding, so that the stresses and strains within any of the individual sectors may be compensated for and not transmitted throughout the entire-grinding disk. It will be appreciated that the rubber compound 25 may or may not be of the same composition as that of the rubber compound 23. In any event, the layer of rubber between the adjacent sectors should be so positioned or of such a composition that the individual sector grinding faces may be free to breathe or expand and contract towards and from one another under the influence of the frictional heat of grinding.

If desired, a modified form of my invention, as

' shown in Fig. 3, may embody a similar disk construction wherein the interstices between the ad-. jacent opposed sector faces I8 are partially filled with a layer of vulcanizable rubber compound 21 in such a manner that the operative grinding face I4 is interrupted by a series of spaced narrow grooves which permit expansions and contractions of the individual sector grinding faces. The intervening layers of rubber compound 21 are vulcanized in position and serve to integrally unite with the rubber compound 23, as well as to aid in securing the sectors l2 together as an integral grinding annulus 31 the same manner as in my preferred construction.

Any suitable devices may be employed to removably fasten the disk assembly to any convenient rotatable support in grinding position. One method of accomplishing this comprises a series of countersunk holes 26 passing through the backing plate, as shown, whereby screws 28 may be employed to removably mount the backing plate on any suitable rotatable supporting member 30. The backing member 20 may be further provided with a central aperture 32 adapted to slidably fit over a protruding hub 33 projecting from the end of the rotatable supporting member 30 which aids in axially locating the disk relative to its support. It will be appreciated, of course, that any one of many various well-known devices may be utilized to removably clamp the backing plate 20 to any suitable rotatable support in any convenient manner to perform a grinding operation.

In the construction of my invention, the backing plate has its supporting face 22 suitably .cleaned and roughened by any convenient method such, for example, as a well-known type of sandblasting operation. If desired, the supporting face may be further provided with suitable channels, reentrant grooves or holes which will aid the rubber cementing compound in firmly gripping the back plate. A suitable layer of raw plastic rubber compound 23 containing the desired amount of sulphur and, if desired, a suitable vulcanization accelerator is cut in the shape of an annulus having the same outer and.inner diameter as the grinding annulus l0 and then placed upon surface 22. The bonded abrasive sectors l2 are then placed in spaced relation upon the layer of rubber compound 23 in the form of an annulus whose periphery coincides with that of the backing plate 20. A layer of suitable rubber compound 25 or 21 is then placed within the interstices between each of the opposed segment faces ill in such a manner that it either entirely or partially fills each of said crevices, as the case may be in accordance with the 7 type of grinding'disk desired. The abrasive sectors and backing member are thereafter clamped together in any suitable mannerand sufiicient heat, such as 200 or 250 C., is applied for a desired period to vulcanize all of the rubber compounds in position and secure the abrasive sectors and backing member into an integral unitary tegrally secured to the rubber 23 and the sectors l2 ,by a subsequent vulcanizing operation. It will be appreciated that the rubber compound 23 will vulcanize in position and serve to intimately unite the surface I! of the abrasive disk and surface 22 of the backing member, since it securely adheres to both of said surfaces. By applying various clamping pressures between the abrasive sectors and the backing plate, the intervening layers of rubber compounds may be caused to impregnate the surfaces l1 and I8 of the grinding disk to any desired extent and thereby secure it to the backing plate with the required tenacity.

While I have specifically described my invention as particularly adapted to a sector type of abrasive wheel arranged to grind with its flat face, it will be appreciated by'those skilled in the art that various other abrasive articles may be easily produced and secured to backing plates or supporting members in the same manner. Such modifications or substitutions of this invention 'as lie within the. scope of the appended claims are,

ing faces and flat grinding faces which are ar-v ranged to provide an extensive, substantially flat grinding surface, a rigid backing member therefor, a layer of (rubber compound vulcanized in position between the backing and the supporting faces and serving alone to secure the segments to the backing, and deformable rubber compound vulcanized in position within. the spaces be tween each of the adjacent sectors, said vulcanized rubber compounds securing the sectors and backing together as an integral grinding unit and compensating for expansions and contractions of the grinding iaces under the influence oi frictional heat of grinding.

2. A grinding disk comprising a plurality of separately manufactured bonded abrasive sectors having flat grinding faces arranged in closely spaced relationship to each other to provide an extensive, substantially continuous, flat annular grinding face, a rigid, disk shaped metal backing plate therefor adapted to support the abrasive sectors, a layer of rubber compound vulcanized in position between the sectors and the backing plate and serving alone to secure the segments on the plate, a deformable rubber compound partially filling the interstices between opposed side faces of adjacent abrasive sectors and vulcanized in position to aid in securing the sectors together as an integral grinding unit and yet leave the outer portions of the sectors separated by free spaces and permit expansion and contraction of the grinding face, and means to removably secure the backing plate to a rotatable support.

3. A grinding wheel comprising a rigid backing plate having a plane mounting surface, a plurality of separately manufactured, vitrified bonded abrasive sectors having plane supporting faces and opposed plane grinding faces which are secured to the backing plate in a widely spaced relationship but provide an extensive annular grinding face extending from near the axial center of the backing plate to its periphery, a layer of rubber compound vulcanized inposition between the backing and the adjacent sector faces and serving alone to secure the sectors to the backing plate, a deformable rubber compound completely filllng the spaces between the opposed side faces of adjacent abrasive sectors which is vulcanized in position and unites the sectors as an integral grinding unit and yet per-' mits expansion and contraction thereof, and means accessible within the hole of thewheel for removably securing the backing plate to a rotatable support.

THURE L. F. LARSSON.

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