US2148400A - Grinding wheel - Google Patents

Description

. cRoMPTvoN, JR 2,148,400

GRINDING WHEEL Feb. 2l, 1939.

Filed Janv. 1s, 1938 Eli dii

Patented Feb. 2l,A 1939 `UNITED STATES PATENT OFFICE GRINDING WHEEL George Crompton, Jr., Worcester, Mass., assignor to Norton Company, Worcester, Mass., a. corporation. ot Massachusetts `Application January 13, 1938, Serial N0. 184,749

`Claims. (Gl. Eil- 273) The invention relates to grinding wheels, and

with regard to its more specific features to cutting-ofi Wheels.

One object of the invention is to provide a sharper cutting-01T wheel. .Another object of the hitherto 4been provided. Another'object or the invention is to form a grinding wheel with cutting edges which simulate the action of a lathe. Another object ci the invention is to provide a grinding wheel having oriented abrasive oi any desired thickness.

Other objects will be in part obvious or in part pointed out hereinafter'.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and'in the several steps and relation and order of yeach of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope oi the application oi which will be indicated in the following claims.

In the accompanying drawing, in which is illustrated one of many possible embodiments oi the mechanical features oi this invention,

Figure l is a longitudinal cross sectional view of a mold for producing the abrasive aggregates used in making :the grindingv wheel of the invention.

Figure 2 is a transverse sectional view of the mold of Figure 1, taken on the line 2--2 of Figure l.

Figure 3 is a perspective view of the abrasive stick produced by the mold of Figures l. and 2.

Figure 4 is an elevation of apparatus for breaking oi short pieces of the stick of Figure 3, thereby producing abrasive aggregates consisting of triangular prisms.

Figure 5 is a verticalv sectional view of a rotating mold apparatus which is preferably used in carrying out the invention.

Figure 6 is an enlarged view ot the mold of Figure 5 after it has been filled and just preparatory to pressing.

Figure 7 is a fragmentary transverse sectional View of the completed article.

Figure 8 is a fragmentary axial sectional view of a multilayer grinding Wheel accordance with the invention.

constructed in Referring first to Figures l and 2, I provide a mold comprising a rectangular parallelepiped outer mold ring it having a rectangular parallelepipedal hole in which are inserted side mold sections i i and 'i2 and a top mold member I3 5 which is 'i' shaped in cross section, as shown in Figure 2. The cavity It oi the mold terminates in a V shapcdbottom iii, the apex of the dihedral angle of which forms the dividing line between the sidemold sections ii and i2. The bottom 1o of the top mold plate il! constitutes an elongated narrow plane surface.

I provide a mixture of abrasivegrain and suitu able bond. A grinding wheel mixture ofy any desired type is contemplated bythe: present inld vention. PreferablyI use vitriable bond, that is to say a mixture of appropriate clays and a temporary binder, if desired.' A suitable amount of moisture may be incorporated in the mix. Preparation-of mixes of clays, temporary binders and 2oplace this in a mixing pan and wet the grain with water. I then add a powdered mixture oi clays, for example including ball clay, slip clay and feldspar. I then edect a mixing, adding a small quantity of temporary binder, such as dextrlne, during the mixing.

After this mixing of the abrasive grains and the bond is achieved, I place a definite quantity oi' the mixture in the space ill of the mold of Figures l and 2. I then transfer the mold to a hydraulic press and press the plate id downwardly. I then strip the mold in any suitable su Way, this mold being readily separable as is apparent from its construction. In pressing the` mixture in the mold space M, I may precalculate the volume percentage of abrasive grain and bond and pores to achieve a desired structure. When the mold parts Il, i2 and I3 are removed from the mold ring i0, the pressed mixture which is in the form of a green abrasive stick I5 shown in Figure 3 is readily removed.' I take this stick with others of like character to a. ceramic kiln and vitrify at an appropriate tem'- perature, for example of the order of cone l2. After the required period of firing, the stick i5 `is a vitrified abrasive stick constituting a tribearings 54 and 55.

an equilateral triangle according to the preferred form of the invention.

Referring now to Figure fi, I provide an apparatus comprising an anvil 28 having a hole 2| therethrough which is triangular in cross section and just large enough to receive an abrasive stick I with suiiicient clearance to provide for ready movement of the abrasive stick. The anvil 28 may be made in two or more parts welded, pinned' or bolted together for ease of manufacture. At the left-hand side of the anvil 28 is attached a long support 22 which forms a slideway for a ratchet bar 23. The ratchet bar is of a size such that it can move into the hole 2|. A paWl .24 pivoted at 25 on a bell crank lever 26 pivoted at 21 in a fork 28 attached to the support 22 constitutes means for moving the ratchet bar 23 by the distance of one tooth for each actuation of the bell crank 26 which may readily be operated by hand. A spring 29 normally moves the handle 38 of the bell crank lever 26 upwardly. This spring 29 is supported by a U shaped standard 3| which straddles the bell crank lever 26 and forms an upper stop for the bell crank lever 26. A lower stop for the bell crank lever 26. is preferably provided, for example in the form of an angle bar 32 adjustably fastened at 33 to the support 22.

The operator may depress the handle portion 39 of the bell crank lever 26 and thus move the ratchet bar 23 tothe right by a controlled amount. 'I'he apparatus further includes a shear rod 35 supportedfor vertical movement in a guide block 36 and normally held in the upper position shown by a spring31. 'I'he shear rod 35 has a head 38 which is of fairly massive construction. With a heavy-hammer the operator can strike the head 38 which will move the rod 35 downwardly, striking a shearing blow against the projecting portion of the vitriiied stick l5. By alternately moving the bell crank lever 26 with one hand and striking the head 38, the operator can readily produce sheared particles of vitried abrasive material which are of equilateral triangular shape in cross section and of relatively short length as compared to one of the sides thereof. For example, a triangular prism of a length approximately one half of any of its sides may be made in this manner. It may be noted that the shape of the hole 2| in the anvil 28 is such that the top part is a horizontal plane surface. The action is a shearing action and produces nearly a plane surface on the fractured pieces of bonded abrasive. These, because of their resemblance to irregularly shaped fragments of bonded abrasive material, I term aggregates 48. They differ from previously existing aggregates in that they are all of regular shape and specifically equilateral triangular prisms.

I further provide a mold rotating apparatus, as shown in Figure 5. This may comprise a base 45 in which is supported a journal 46 having a vertical axis in which is located a spindle 41 having keyed to its upper portion a table 48. I may provide a lower journal 49 for thc spindle 41 and a thrust bearing 58. Keyed to the spindle 41 is'a gear 5| meshing with a pinion 52 fastened to a shaft 53 which is journalled in upper and lower The pinion 52 may be formed on a sleeve 56 with which is also integrally formed a bevel gear 51 meshing with a bevel gear 58 secured to the armature shaft of an electric motor 59. 'Ihis is preferably a direct current motor which is connected by a conductor 68 to a suitable source of direct current, such as a battery 6|, the other end of which is connected by a conductor 62 to a rheostat 63, the movable part of which constitutes a treadle 64 pivoted at 66. The contact 86 attached to the treadle 64 and constituting part of the rheostat 83 is connected by a suitable conductor to a conductor 61 which is connected to the other terminal of the motor 59. A suitable spring 18 may be provided normally to hold the treadle 64 in the upper or full resistance position shown. A suitable switch 1| is interposed in any of the conductors forming the motor circuit.

The operator may cause the table 48 to revolve by closing the switch 1| and thereafter may control its speed within limits by use of the treadle 64. As shown in Figures 5 and 6, I provide further a more or less conventional mold which may comprise an outer supporting plate 12, an annular mold ring 13, a mold bottom plate 14, a mold top plate 15, an outer top plate 16. and a mold plug 11. 'I'he outer supporting plate 12 has a hole 18 in which ts a plug 19 fastened to the top of the spindle 41 in order to center lthe mold on the table 48.

Placing the plug 11 in the bottom plate 14, as shown in Figure 5, with the mold ring 13 around the bottom plate 14, I insert in the mold and against the bottom plate 14 an annular disk of unvulcanized rubber compound 88. I then place these mold parts on the table 48, as shown in Figure 5. With the aidof a suitable hopper, shovel, trowel or other manual implement, I scoop up a quantity of triangular aggregates 48 from a container or box in which they may have been collected and dump them into the mold ring 13 on top of the rubber on the bottom plate 14. I place in the mold a quantity approximately sumcient to form a ring 8| of aggregates 4l, all in contact with the mold ring 13. Centrifugal force will force the aggregates 48 against the ring 13 and by adding or subtracting aggregates 48 and with the use of a stick or guide held in the hand, a ring or circle 8| of aggregates located close together may quickly be formed. The only way that the aggregates 48 can be assembled in a rotating mold in close spaced relation is with one side of each alternate aggregate nearly tangent to' the circle of the mold ring 13, as shown. As quickly as one row 8| is formed, I introduce more aggregates 48 and form another row 82. The procedure may be repeated for rows 83, 84, 85 and so on until the entire mold is filled with aggregates 48 to a depth of one layer, all of them being in oriented position, as shown in Figure 7. I then place another annular disk |08 of unvulcanized rubber compound on top of the aggregates 48 and place the top plate 15 and outer mold plate 16 in position, as shown in Figure 6. I then close the mold in a suitable hydraulic press, strip the mold, and remove the pressed article and vulcanize it. The result is a grinding wheel which is shown in cross section in Figure 7, constituting triangular abrasive aggregates 48 oriented as shown in Figure 7 and bonded together with rubber bond. 'I'he rubber mixture for the annular disks 88 and |88 preferably has enough sulphur to form a hard rubber and may have a filler comprising a certain quantity of abrasive grain in order to increase its hardness. In certain cases, however, a rubber mixture having no abrasive grain will preferably be used. The rubber compound for the disks 88 and |88 may vary widely and any of the known formulae for manufacturing rubber bond for rubber bonded grinding wheels may be used, many such formulae now being known to those skilled in this art.

Considering the action of the abrasive wheel of Figure 7, which is a cutting-on wheel, it will be seen that the triangular abrasive aggregates are located so that sharp cutting edges face in both circumferential directions and as the wheel wears down, new sharp cutting edges are automatically provided. That is'to say, as each triangular aggregate 40a whose flat side is substantially tangent to the periphery is reduced on that side by reason of wearing away of the wheel, it still presents a cutting edgerwhich is inclined thirty degrees to the radius of the wheel at that point, this being quite an effective cutting edge. Intermediate aggregates Mib whose apexes abut .the periphery fill the gaps between the other a`g gregates. They do some cutting on account of their abrasive action but the major portion of the cutting is done by theaggregates' 40a.- The rubber is forced between the several aggregates as the filling method described can be carried out very readily without packing the aggregates iii too tightly. The rubber .being softer, wears away readily and provides' a Vclearness for the chips cut from the metal b'eing cut off.

By simply providing a higher mold ring 'I3 or thicker plates ld and 15, or' both, I can fill the mold of Figures and 6` with a plurality of layers oi triangular aggregates 6B.' The top disk lill) of rubber compound will form the bottom disk for the next layer. A wheel so constructed is l shown in the fragmentary cross sectional view dit or Figure 8. This may be used for purposes other than cutting-ori and preferably is, being particularly adapted for cylindrical or other grinding where a relative reciprocatory traverse of wheel and work piece is provided.

One feature oi the invention involves the formation and orientation of abrasive particles which have cutting edges which will operate substantially as a lathe tool does, and preferably in both directions so that it is immaterial in which direction the wheel is revolved. With this feature ci advantage is coupled a method of manufacture which can be carried out without expensive equipment and at areasonable labor cost so that the wheels shall not cost excessively more than those made by previously known methods.

While the oriented feature described herein in detail is a feature of advantage of `this invention, it will be understood that a triangular-prism on its side as distinguished from its edge constitutes an abrasive particle which presents a sharpedge in one direction of rotation however it is oriented and accordingly, so far as certain features of the invention are concerned, the shaped aggregates may be placed in a mold haphazard without orientation and the wheel formed therefrom will have excellent cutting properties.

lt will thus be seen that there has been provided by this invention an article, method and apparatus in which the' various objects hereinabove set forth together with many thoroughly -practical advantages are successfully achieved.

As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

l'. clainn- 1. A grinding wheel comprising triangular abrasive aggregates oriented with sides tangent to concentric circles of the wheel bonded together into an integral whole.

2. A. grinding wheel comprising abrasive aggregates equilateral triangular prisms in shape and a bond holding the aggregates together in an integral structure with a great number of the triangular prism aggregates oriented so that one fiat side of each is substantially tangent to a concentric circle of the wheel.

3. An abrasive body comprising a plurality of triangular aggregate prisms in like position and a plurality ofabrasive aggregate triangular prisms in similar opposed position interspersed between the first named triangular prisms in substantially regular order and bonded together with bond. A

4. An abrasive wheel comprising a great number of 'aggregates each comprising abrasive grains bonded with vitriiied bond and in the shape of -4 equilateral triangular prisms oriented so that substantially one half of the prisms have sides tangent to concentric circles of the wheel and the other half of said aggregates are likewise oriented,V the first half having their apexes pointing inwardly and the second half having their apexes 'pointing outwardly, and organic bond holding all of said aggregates together in an integral wheel.

5. The method of making a grinding wheel which comprises pressing a quantity of abrasive grain and bond to form a stick which is a triangular prism, maturing the bond thereof, shearing.

off small sections of the triangular prism to form abrasive aggregates of small thickness as respects any side thereof, and constituting triangular prisms in shape, providing a rotating mold, filling the mold slowly with aggregates to form a ring thereof against the periphery of the mold, continuing the filling to form additional rings until the mold is lled, incorporating suitable bond to bond the aggregates together, pressing and maturing.

GEORGE CROWTON, JR.

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