US2137986A - Method of making a composite abrasive wheel - Google Patents

Description

Nov. 22, 1938. E B. SANFORD E 2,137,986

METHOD OE MAKING A COMPOSITE ABRAsIvE WHEEL. Y Y

' Filed Jan. l2, 1937 EN n* FEg. 1.

` Baalis Sanford l @Mom/WM Patented Nov. 22, 1938 UNITED STATE PAT METHOD OFMAKING A COMPOSITE ABRASIVE WHEEL num suma, worcester, Mass., mmm io'Norton Company, Worcester, Mass., a corporation of Massachusetts Application January-12, 1931, sex-m No. 120.276

3 Claims.

This invention relates to the manufacture of composite grinding wheels and particularly wheels of the type which have a solid supporting center carrying a rim of bonded diamonds or other l abrasive material.

It has been proposed to make a grinding wheel by first premolding a supporting center of a suitable material, suchgas a resinoid body pressed to its final form, and then. compressing a rim of l abrasive material onto the periphery of the support. Various problems are involved in the manufacture of that type of wheel and particularly in controlling the structure and density of the abra- 'sive rim and of insuring a substantially integral union between the rim and the support. In that method, the central resinoid supporting body formed a part of the mold and it was necessary to compress the abrasive mixture within the mold space lying between the central support and the mold band to a thickness which was materially less than that of the central support. This required cutting away the face of the central support in order that it would not project beyond the abrasive rim. The objects of the present invention are to provide a method of making such a composite wheel which will serve for shaping an vabrasive rim and uniting it integrally with a central support prior to the step of maturing the bond, and to provide a mold device which will insure making duplicate structures without requiring that either the abrasive material or the support be cut away to shape the article further after the molding operation. Further objects will be apparent in the following disclosure.

One embodiment of a mold structure suitable for carrying out the method of this invention is illustrated in the drawing in which:

Fig. l is a diametrical section through the mold 4D showing the central wheel support and the abra'- sive mixture in the mold cavity prior to the pressing operation;

Fig. 2 is a similar view showing the mold closed and the parts in their nal pressed condition;

and

Fig. 3 shows the mold parts in' a disassembled relation, which indicates how the grinding wheel is removed therefrom. s

In accordance with this invention, I have provided a special mold construction by which an abrasive and bond mixture may be compacted onto a supporting center. This may comprise a mold band I0 of substantially L-shaped cross section which has two internal annular surfaces of diierent diameters. 'I'he larger annular surfaceV II is arranged to carry a ring I2 slidably fitted therein. The outer plane surface of the ring I2 is ush with the bottom of the mold band when its upper surface contacts with the shoulder .i3 of the ring I0. Slidably mounted within '5' the ring I2 is a central disk shaped mold plate Il which is adapted to support the wheel center I5 made of a resinoid or rubber which has been previouslygmolded by another operation. In the -present embodiment, the premolded wheel center I5 and the mold plate I4 are disk shaped bodies having the same diameter. Mounted above the center support I5 in their assembled relationship is a further mold plate I6 which is slidable against the inner surface Il of the upper 15 smaller diametered portion of the mold band I0. .This arrangement is such that when the parts are assembled as shown in Fig. 1, the'mold band III, the two plates I4 and I6, themold ring I2 and the wheel center I5 leave an annular mold "20 cavity I8 which is considerably thicker than the plate I5, as indicated in Fig. 1, whereby this cavity I8 may be filled with a mixture of abrasive grains and a suitable bond therefor whichmay be thereafter compacted onto and integrally united with the supporting body I5. The band I0 and ring I2 could be made integral as an L- shaped mold (in cross section) but it is preferable to have them separable for the purpose of removing the molded body. 30

'I'he central wheel support I5 is made in a separate operation of a suitable material, which .is preferably of the same type as 'that used for the vabrasive bond. That i's, a resinoid support may be used for a resinoid'and abrasive rim and a rubber support for a rimof rubber and abrasive, but other materials may be usedfor the central support, if desired. The resinoid may beV a V "Bakelite phenolic aldehyde condensation product or other synthetic material capable of being y heat set to a hard non-plastic condition, and various fillers, such as wood iiour, silica, etc., may be incorporated therein in suitable amounts to insure that its volume will not change materiallyA during the iinal pressing operation involved in mounting the abrasive rim thereon. The support I5 may be pressed in a suitable mold to the disk shape shown in the drawing, or other requiredl shape, and it may be left in its unconverted state, if desired, untilafter the rim has been` pressed thereon. In that case, the uncured body I5 is in a plastic condition and it may be made slightly over size in thickness, as predetermined to give a required plastic ow, outwardly into a firm union with the abrasive rim during the iinal 5 5' during the nal molding step.

Likewise, the support I5 may be made of vulcanized hard rubb'er compound or of a yvulcanizable compound of raw rubber, sulfur and an accelerator proportioned to form hard rubber. In

either case, the rubber compound should beinitially pressed to substantially its final volume before it is assembled with the rim material. 'Ihe rubber compound may include various well known fillers and which may be proportioned to insure a uniform volume for ythe rubber body.

Y If the mold parts I Il, I2 and I4 are assembled as indicated in Fig. 1, with the part I4 temporarily mounted on shims to hold it in the indicated position, then the previously molded sup-` port IB may be laid on this plate Ilin a central position as indicated. If the wheel is to have a central hole, a pin 20 of suitable shape may be inserted in holes through the plates I4 and I6 in order to prevent distortion of the support I5. The helghth of the shim which positions the plate Il will have been previously determined to provide a space I8 in the mold which is suillcient for holding the correct amount of abrasive and bond mixture to be compacted in place. This initial cavity may be twice as large as the .nal

, pressed rim material. A

This abrasive and bond mixture may be made of suitable abrasive material, such as diamond grains of desired grit size, e. g. 100 grit, rincorporated with a heat settable, organic bond having the capacity of being plastic and owing when compressed in the mold so as to make an integral union with the body I5. Of the various organic materials'which may be employed for this purppose I may utilize an unconverted resinoid powder of the type of Bakelite phenolic formaldehyde condensation product together with inert fillers, if desired, such as asbestos, wood powder, silica or other pulverized mineral substances. A precalculated amount of the mixture of abrasive grainsand the bond, such as 25 to 50% by volume of diamonds and 75 to 50% of resinoid bond, is then placed in the mold cavity I8, as shown in Fig. 1, and carefully leveled olf and such other precautions as may be needed are taken to insure a uniform distribution of the material within the annular space. Then the mold plate I6 is slidably fitted within the mold band I and the assembly is placed in a power press with the shims originally placed under the mold plate I 4 now removed.

' Upon applying pressure to the top of the mold plate I6 and the bottoms of the band I0 and ring l2, the material in the cavity I8 will be compacted .while lateral pressure is applied to the side of the resinoid support I5. This pressure will close the mold or bring all of its outer faces into alignment with two parallel planes as indicated in Fig. 2; and the material I8 will have been compacted to the exact thickness of the premolded central support I5, since the mold parts will have been sized for this result. If the premolded support I has not been converted by heat to the solid, non-plastic condition then the pressure of the plates I4 and I6 thereon will arenoso v lpositions, the outer faces of the plates and ring will be in the planes of the two Vfaces of the mold band and the annular abrasive material I8 will have been compacted to the same thickness Aas that of the center support I5. Hence, it is not necessary to shave ofi' or to grind away either the surface of thesupport I5 or the side of the abrasive rim I8 to insure that the sides of the two parts of the grinding wheel are in two par- 'allel planes.

I'he mold with its compacted mass, as shown in Fig. 2, may be subjected to heat and the article thus cured while under pressure. In this case, a set screw 22 is threaded through the mold band I0 so as to engage a groove 2l in the mold ring I2 and lock the parts in assembled relationship. This screw is to be removed later for disassembling the mold parts. It is equally feasible to remove the molded article from the mold and to cure it in a separate apparatus as desired, so as -to convert the resinoid or rubber material to its solid iniusible condition. Standard practice may be followed for the curing operation.

The mold'assembly has been so constructed thatthe molded article may be readily removed therefrom either before or after the heating or curing operation. As indicated in Fig. 3, it is merely sufficient to loosen the set screw 22 and force the mold plate I6 downwardly through the mold band Ill and thus drive the plate I4 and ring I2 out of the band and-leave the molded grinding wheel exposed. When the band I0 and the upper plate I6 have been removed, the molded article may be taken from its lower support and treated as desired.

It will now be appreciated that I have thus provided a special type of mold and a method whereby a precalculated amount of abrasive and bond may be pressure molded onto the periphery of a central support of suitable material. The molding of the abrasive rim is done independently of anyv pressure applied. to the support, hence it may be compacted to any desired density, depending on the proportions and weights of abrasive and bond selected. 'I'his method insures a strong union with the periphery of the support, and particularly where the latter is not heat set prior to` the pressing operation and is caused to flow radially outwardly by pressure applied to the plates I4 and I6 while the bond and abrasive mixture is being pressed by the ring I 2 and associated parts.

I claim: t

1. The method ,of making a composite abrasive wheel comprising the steps of premolding a heat settable compound to form a central support having substantially its nal volume, providing a mixture of abrasive grains and a heat settable plastic bond proportioned in amount to form an abrasive rim of required width and the same lthickness as the central support when compacted to its nal density, confining the support within a mold which provides walls defining a mold cavity around the support which is higher than thel thickness of the support and will hold the precalculated amount of abrasive and bond, and

then compressing the abrasive and bond laterally until it attains the 'same thickness as the support and is united therewith, but without applying pressure directly to the support, after which the its nal, hard, non-plastic condition prior to the step of molding the abrasive rim thereon.

3. 'I'he method of making a composite Wheel according to claim 1, wherein the central support is made slightly oversize in thickness and the rim is initially compressed to the thickness of the= support, after which the rim and support are compressed simultaneously to cause lateral ow thereof into a firm union.

BAALIS SANFORD.

Images