US2078120A - Grinding disk - Google Patents

Description

April 93 H. w. H. BETH 2,078,120

GRINDING DI SK Filed March 27, 1933 Husa 14 H. 851 71 WITNESSES I (7M 6; Q? I H: 3% N1 Mm,

Patented Apr. 20, 1937 PATENT OFFICE GRINDING DISK Hugo W. H. Beth, Worcester, Mass, assignor to Norton Company, Worcester, Mass" at corporation oi Massachusetts Application March 27,

4 Claims.

This invention relates to a bonded abrasive grinding disk, and especially to a grinding disk which presents an extensive flat surface, for a grinding operation.

Heretofore, grinding disks adapted for grinding with their flat faces have comprised solid abrasive bodies cemented or otherwise suitably secured to a rotatable support, such as a rotatably mounted metal plate,whereby the entire flat wheel face may be employed for a grinding operation. It has been found that grinding wheels of this type are unsatisfactory for many of the strenuous grinding operations to which grinding disks are commonly subjected. One of the many common uses for a disk type of grinding wheel is a dry grinding operation, wherein the leaf of a spring, such as commonly used in vehicles of today, is passed between two rapidly rotating disks so arranged that both of the opposed, substantially flat faces of the spring leaf are simultaneously ground. A dry grinding operation of this type rapidly brings the abrading surface of the grinding disk to an extremely high temperature. This high tempera ture on the operative wheel face is usually reached long before other portions of the wheel or its supporting plate experience any appreciable change in temperature due to the heat of grinding. As a consequence, the operative face of the grinding wheel tends to expand at a very rapid rate, while the rest of the wheel and its supporting plate resist said expansion, thereby resulting in uneven internal wheel stresses which usually result in wheel breakage, often spoiling the work and endangering the machine operator.

To overcome these difficulties, various devices, such as chucks, have been employed to clamp separate small abrasive blocks to a rigid support so that their end faces could be moved in a fixed circular path and cooperate to produce a grinding operation. These chucks have proved to be cumbersome, expensive devices, and the abrasive blocks are narrow so that the total grinding surface presented thereby covers but a very small portion of the area bounded by the circular path 5 within which the blocks are rotated. Abrasive blocks commonly used in these chucks must be carefully shaped, and in some cases they must be cemented to precisely shaped clamping members so that they may be accurately seated within 50 their respective chuck jaws, thereby resulting in an expensive construction.

It is, therefore, the primary object of this invention to provide an inexpensive grinding disk construction comprising an abrasive body of any de- 55 sired thickness having an extensive fiat operative 1933, Serial No. 662,857

face occupying the major portion of the area included within the wheel periphery and wherein uneven expansions within the disk due to sudden temperature changes may be properly compensated for.

A still further object is to provide a simple arrangement whereby a plurality of individually fashioned abrasive sectors, or a unitary grinding wheel having sectorportions, may be removably but rigidly secured to a rotatable disk-shaped support.

A further object of this invention is to hold an expansible grinding disk of sector formation, whether made as an integral body or as spaced units, on a rigid disk-shaped supporting plate in such a manner that even if fracture of the disk occurs between adjacent sectors, the abrasive body will be firmly secured in position, whereby every sector will be individually mounted and positively secured to the supporting plate.

With these 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 following description and appended claims.

In the drawing illustrating a grinding disk and support therefor embodying this invention:

Fig. 1 shows a plan view of thepreferred type of grinding disk as covered by this invention;

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

Fig. 3 shows a modified construction of a grinding disk embodied in this invention;

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 shows a further modification of this invention; and

Fig. 6 is a detailed view of a preferred type of disk anchoring device.

In accordance with this invention, there has been provided a bonded abrasive grinding disk having a substantially flat grinding face arranged to expand without breakage or surface distortion when subjected to localized surface heat caused by the friction of grinding. The disk is composed of bonded abrasive sectors, which may be formed as an integral body or as spaced, individually manufactured segments, These sectors are of such size and shape, without reference to the definition of the geometrical term sector, that they cooperate to provide an extensive flat grinding surface which covers the major portion of the area bounded by the disk periphery. To provide for expansion of the grinding surfaces, the operative face of the disk is cut by a series of narrow grooves which are preferably radial of the disk and are of sufiicient depth and widthto permit the grinding face to expand under heat of grinding, without causing breakage'of the disk face. If the disk is composed of separate bonded abrasive sectors, they are secured to a suitable rigid support in sufficient spaced relation to compensate for surface expansion of the disk grinding face. The spaces between the adjacent grinding sectors may be left open, or they may be partially filled with a suitable cementitious medium which may allow for a slight expansion of the surface portion of each abrasive sector and yet be of suflicient strength to hold the sectors together as an easily transportable unit. The sectors are arranged as an annulus having a substantially continuous grinding face, in which the spaces therebetween are preferably only wide enough to permit of expansion and permit ready assembly. In some cases, the spaces may be wholly filled with cementitious material which permits lateral expansion of the individual sectors.

The back of each sector is provided with anchoring devices imbedded therein by suitable cement, such as Babbitt metal, sulphur or other material. The sectors are removably secured to a rotatable support, such as a rigid metal disk, by'clamping members passing therethrough and engaging the imbedded anchoring devices which take all of the rotative and frictional thrust of grinding. Each sector is preferably held in place by more than one clam-ping member, whereby the sector is definitely located and positively secured in position.

When the grinding disk comprises an integral unitary bonded abrasive body, its fiat operative grinding face is cut by a plurality of narrow grooves forming surface cutting sectors thereon. In this type of grinding disk, any breakage caused during the abradingoperation will necessarily occur along the line of the grooves in the disk and cannot interfere with the grinding operation, since the clamping members will still serve to hold the sectors firmly secured as individual members to their rotatable support. The grooves are preferably very narrow and of sufflcient depth to permit lateral expansion of the sectors due to heat of grinding and yet provide a rigid grinding disk structure which may be easily transported as a unit without any backing support.

The preferredembodiment of this invention, as illustrated in Figs. 1 and 2 of the drawing, comprises a support Ill for a grinding disk which is made of metal or other suitably rigid material of any required shape and size. As illustrated, the support In is preferably a disk-shaped member or plate having a central aperture ll adapted to slidably fit over a hub I2 on the end of a supporting shaft l4 which may be mounted for positive rotation in any convenient manner. A plurality of holes |5 are provided in spaced relation close to the aperture II and arranged to receive mounting screws l6 which pass through the plate l0 to positively secm-e it to the end of shaft l4 for rotation therewith.

. Thegrinding disk preferably comprises a plurality of abrasive sectors 20 of suitably bonded abrasive material, and preferably grains of alumina, or silicon carbide bonded by vitrified ceramic material, rubber, resinoids, sodium silicate, shellac or other suitable bonds, as are well known in the art. These sectors are of any desired size and are individually and removably secured adjacent to the supporting face 2| of theplate III in such a manner as to form an extensive, fiat, substantially continuous grinding surface 22. As illustrated, the sectors are preferably so shaped as to cooperate and provide an annular grinding member having a relatively small central hole23, through which access may be had to the screws l6 which serve to fasten the plate III to the rotatable shaft M. In order to provide a maximum size for the grinding disk face, the central hole 23 is small in diameter. The screws 6 and holes l5 passing through the plate ID are located as close to the hub l2 as practicable so that they may be accessible at all times for mounting the grinding disk assembly. Each abrasive sector 20 may be constructed as a separate article of manufacture independent of its support, and it is so made that it may be individually and removably fastened to the plate It) by means of suitable clamping devices. The preferred type of clamping device, as illustrated, may comprise an anchoring member fastened to each sector and adjustably secured to the backing disk Ill. The anchor members may comprise the nuts 24, each of which is imbedded in a recess 26 in the rear face of a sector and is positively and permanently secured thereto by any suitable material 21, such as a Babbitt metal, sulphur or other cementitious medium which may serve to secure the nut integrally with the abrasive sector. I

As illustrated in Figs. 2'and 6, each nut 24 is provided with a reduced portion 29 terminating in a flat engaging surface 30 which lies slightly above the rear surface'3l of each sector when properly located and secured within its recess so that the engaging faces 30 may locate against the face 2| of plate III to provide a positive sector mounting surface and hold the sector faces parallel with the disk. The nuts 24 are each secured within their respective recesses 26 with the reduced portions 29 near the rear faces of the sectors so that the cementitious medium 21 may engage each of said reduced surfaces with ,a wedging action to firmly hold the nuts 24 in their respectively correct positions integral with the sectors. Hence, any force tending to pull the nuts from the sectors will result in wedging them more securely in their respective recesses. The plate I0 is further provided with a series of holes 33 passing therethrough at predetermined locations and arranged to receive screws 34 therein, each of which has a threaded portion arranged to engage one of the nuts 24 and thereby tightly clamp each sector in correct operative position relative to the plate Ill and the other sectors. It will be appreciated that the screws 34 will pull the nuts 24 towards the plate l0 until the nut faces 30 engage the face 2| of plate l0 and thereby serve to positively locate the sectors 20. Since the nuts project slightly from the rear faces of the sectors, there will be no tendency for the clamping screws to pull the nutsaway from the sectors, and a positive sector support will be assured.

If desired, a soft, compressible paper pad 35, commonly known in the art by the term wheel blotter, may be inserted between the sectors and the face 2| of the plate I to further aid in supporting the sector wheel upon its back plate I0. If a wheel blotter is used, holes are cut therethrough so that the nuts 24 will have their respective surfaces 30 positively engage the face 2|--of supporting plate Ill andcooperate withthe screws 34 tdprovi'de positive locating devices for the abrasive sectors.

These sectors are preferably so' shaped and the locating devices 24 are 'so positioned that the assembled sectors are mounted in spaced relation relative to each other. This spacing between the adjacent sectors is preferably small, but it must be sufiicient to provide for expansion of the individual sectors due to the heat of grinding and it must be sufiicient to permit replacement of the individual sectors when desired. For example, one type .of sector grinding disk especially adapted for dry grinding the flat faces of large springs wherein an excessive heat of grinding is quickly developed is 20 inches in diameter, 2 inches thick and has six sectors which are spaced only 3 of an inch apart. It will be clear to one skilled in the grinding art that these dimensions may be varied, depending upon the type of work to beground.

A modification of this invention embodies a grinding disk construction, as illustrated in Figs. 3 and 4, wherein a plurality of bonded abrasive sectors Ml similar in form to the sectors 20 may be secured together in predetermined spaced relation around a central hole 44 to form an annular shaped grinding disk which may be easily transported as a unitary member independently of any supporting plate and yet is so constructed that it may allow for expansion of the individual sectors clue to heat of grinding without breakage of the sectors. To accomplish this, the opposed faces M of each of the adjacent sectors are secured together by any suitable cementitious medium 42 which may allow for slight expansion of the adjacent abrasive sectors'due to heat of grinding and yet be of sufiicient strength to hold the sectors together as an easily transportable annular unit. Such a cement may be composed of glycerin and litharge. or sulphur, or sulphur and finely divided coke of a composition known as lavasul, or a resinoid such as a reaction product of phenol and formaldehyde or their homologues. This cement 32 may completely fill the interstices between the opposed faces of adjacent sectors, or it may only partially fill the spaces between the adjacent sectors, as shown in Fig. 4, so that the upper or face portions of the adjacent sectors will be free to expand as required by the temperature gradient between the cold backing and the heated grinding face.

One type of integral sector grinding diskwhich may be employed in a dry grinding operation, wherein the operative grinding face of the disk is subjected to sudden changes in temperature due to the friction of grinding, comprises a grinding disk having six sectors forming an. annulus 20 inches in diameter and 2 inches thick. These sectors are spaced approximately 1; of an inch apart and the cemen titious me dium therebetween fills the lower half of the space, leaving a groove or air space between the adjacent opposed sector faces 4! which is about 1% inches deep.

To prevent collapse of the grinding disk during shipment, thecementitious medium completely fills the space between the adjacent sector faces M close to the periphery of the grinding annulus. This cementitious portion 33 need not extend radially inwardly very far, and in the instance of the wheel cited, extends from the wheel periphery toward the wheel center for approximately one inch.

To further strengthen the annular unit, both during shipment and in use, the periphery may be wound with several turns at a tough resilient wire under sufficient tension to resist the centrifugal force of disk rotation, and the adjacent turns of wire may be. suitably secured together at various positions, as by a solder or other means.

.engages the periphery of the assembled disk unit.

The wire'is wound around the disk under resilient tension, the amount of which depends upon the size of the disk and the centrifugal force to which the unit will be subjected. The cement 42 located between the sector unit 40 fills a suiiicient portion of each crevice between the sector spaces 4| so as to hold the sectors in fixed spaced relation against the inward pressure of the resilient tensioned wire. In this manner, the major portion of the centrifugal force set up by rotating the grinding disk is received by the resilient wire and not by the anchoring devices or nuts 24 embedded within the sectors and the cooperating screw bolts 35. Without the wire engaging the periphery of the disk, centrifugal force might tend to tear the embedded nuts 24 loose from the sectors, it being observed that these embedded nuts are near the inner faces of the sectors and that the center of gravity of the individual sector lies in a plane outside of the anchoring devices.

The assembled annulus is removably secured to I a rotatable metal plate 41 in the same manner as disclosed in my preferred construction illustrated in Figs. 1 and 2 and described heretofore.

It will be appreciated that a construction of this type permits the sectors of the grinding disk to expand individually towards each other, and the upperportion of each sector close to and within the grinding zone may be free to expand at a different rate from that of the backing plate without causing internal stresses within the sectors which, in the case of a solid grinding disk, have usually caused breakage.

. A further modification of this invention embodies the use of a unitary or integral abrasive disk 5% (Fig. 5) having an extensive, substantially fiat grinding face 55 divided by a plurality of grooves 52. This disk is made in one piece by the standard methods of bonding abrasive grains, in which the bond may be vitrified ceramic material, rubber, resinoid, etc. The grooves 52 are preferably arranged to run radially oi the disk, and they are of sufficient width and depth I to permit the various sector-shaped portions of the cutting face to expand under heat changes in the surface of the disk caused by the friction of grinding without resulting in fractures of the grinding disk through its operative face. For an ordinary dry grinding operation, the disk may be approximately 20 inches in diameter, 2 inches thick and separated by grooves 1 inch deep and it; of'an inch wide in to six or more sectors. The grooves in a unitary grinding disk of this type serve to separate the disk body into spaced sectors which may individually expand and contract. As shown in Fig. 5, these sectors have their clamping'devices so located that they are individually secured to the supporting plate 55. If, through abuse, excessive stresses cause breakage of the grinding disk, it will occur along the weakened sections below the rooves. However, such breakage of the disk will be immaterial, since the sectors are individually and rigidly secured in place. When the sectors are individually fashioned before mounting, as shown in the preferred type of this invention, this construction simply amounts to a pre-breakage of the disk sectors along sections where the grooves exist in the integral wheel structure. It will be appreciated that it is preferable to make the 5 grooves 52 as deep as practicable and still have the grinding disk strong enough for shipment as a unit without other support. A grinding disk of this type may be removably secured to a rigid,

rotatable supporting plate 55 in the same manner as disclosed in the preferred construction illustrated in Figs. 1 and 2.

It is to be understood that the term disk shaped support as used in the claims is intended to cover any construction such as spiders or equivalent supports, wherein clamping members may be rigidly supported in correct positions to engage anchoring devices within the grinding disk.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent is:

1. A grinding disk comprising a plurality of bonded abrasive sectors spaced apart by open grooves and arranged to provide an extensive fiat grinding surface which is free to expand under heat of grinding, an anchoring device embedded within the lower portion of each sector and having a portion projecting therefrom, a rotatable disk shaped support engageable only with the anchoring devices, and separate clamping members removably and rigidly fastening the anchoring devices to the support at various predetermined positions and serving as the sole means to position the segments relative to each other and in predetermined spaced relation to the support. 2. A grinding device comprising a rotatable disk shaped support, a plurality of separate spaced sectors of bonded abrasive material thereon which are arranged to provide an extensive flat grinding surface, a cementitious medium -partialiy filling the lower portions of the spaces between and uniting the adjacent sectors to form an-integral annular grinding structure which is transportable as a unit independently of its rotatable support, the upper portions of the spaces between the adjacent sectors being left open to provide for the individual expansion ofthe face portions of each sector when subjected to temperature changes due to the friction of grinding, anchoring devices imbedded within the sectors, clamping members engageable with the rotatable support which removably and rigidly engage the anchoring devices and serve as the sole means to locate and transmit rotation to the sectors and position them with respect to the rotatable support.

3. A grinding device comprising a rotatable I disk shaped support, a bonded unitary abrasive grinding disk having an extensive flat grinding face including the major portion of the area within its periphery, said face being provided with a plurality of relatively narrow grooves extending substantially radially of the disk, which serve to separate the disk into closely adjacent integrally united grinding sectors, and which provide for expansion of the grinding portions of the sectors. anchoring devices imbedded within and proiecu ing laterally from the rear face of the abrasive disk, and clamping members engageable with the rotatable support secured to the anchoring devices, said clamping members and anchoring devices serving as the sole means to secure the abrasive disk to its rotatable support in spaced relation therefrom.

4. A grinding device comprising a disk shaped rotatable support, a plurality of bonded abrasive sectors arranged in spaced relation thereon to provide an abrasive. annulus having a cylindrical periphery and a fiat grinding surface, anchoring devices embedded within and cemented to each sector, clamping members engaging the anchoring devices and removably and individually securing the sectors to the rotatable support, a resilient wire wound around and secured in position against the peripheral surface of the disk under a tension sufficient to resist the centrifugal forces set up during normal rotation of the grinding device but to permit expansion of the sectors due to heat of grinding, and a cementitious medium partially filling each crevice between adjacent sectors to resist the pressure of the tensioned-wire but maintain the operative grinding faces of the sectors separated by grooves sufficient to provide for expansions thereof caused by the heat of grinding.

HUGO W. H. BETH.

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