US2121746A - Composite abrasive wheel - Google Patents

Description

B. SANFORD COMPOSITE ABRASIVE WHEEL Filed Jan. 12, I 1937 lllllljJW/ ii aali sanford Skim/mug I I Al I z 1 I 2 z z 1 5 h a m Patented June 21, 1938 UNITED STATES COMPOSITE ABRASIVE WHEEL Baalis Sanford, Worcester, Mass., assignor Norton Company, Worcester, Mass., a corpora-- tion of Massachusetts Application January 12, 1937, Serial No. 120,275 2 Claims. (Cl. 51-278) This invention relates to the manufacture of composite grinding wheels and particularly wheels of the type which have a non-abrasive central support carrying a rim 'of bonded diamonds or other abrasive material.

It has been proposed to make a diamond wheel by pressing a rim of diamond grains and a suitable bond onto a resinoid backing plate which has been previously molded, and thereafter to convert the resinoid to its solid infusible condition by heating the entire wheel structure. 0w-' ing to the expense involved as well as' the long life of the diamonds, it has been preferred to make the abrasive rim quite narrow. However, in making certain types of wheels, difiicuities have been encountered in securing a thin diamond and resinoid rim to a backing plate, due in part to the fact that a thin layer of the plastic resinoid may not flow uniformly and the thickness of thetabrasive rim thus varies to an undesired exten The primary object of this invention is to overcome such problems and to provide a method of making a composite abrasive wheel of this type 25 and particularly to shape an abrasive rim correctly and secure it firmly to a premolded central support. Other objects will be apparent in the following. disclosure.

Referring-to the drawing which illustrates two types of wheel molds and. a method of shaping wheels therein: d

Fig. 1 is a diametrical sectional view showing in a disassembled relationship and distorted sizes a premolded abrasive rimand a premolded backing support with a paper cementing strip therebetween which are adapted to be secured together to form a cup shaped wheelf Fig. 2 is a. similar'sectional view showing the parts assembled in a mold and ready to be pressed into an integral relationship; and

Fig. 3 is a similar view showing an arrangement of. mold and wheel parts for forming 9. cylindrical wheel support with the abrasive rim secured on the periphery thereof.

In accordance with this invention, an abrasive rim and particularly one made of diamond grains and a resinoid bond or other suitable bonding material, such as vulcanizable rubber, is first premolded to the required shape and di-' mansions and this ring shaped member is fully cured by means of heat so that the bond is set to-a non-plastic and infusible condition. Thereafter, this abrasive ring is secured to a backing support either by a separate cementitious material or by means of plastic flow of the backing support into an integral union therewith, or by a combination of both features.

Assuming first that a thin flat ring or disk,is to be secured onto the side of a grinding wheel, such as the cup shaped rim indicated in Fig. 1. then the following procedure may be adopted. The thin rim ill of premolded abrasive and a suitable bond, which may be far thinner than indicated in the drawing, is preferably made from a suitable mixtureof diamond. boron carbide, silicon carbide, crystalline alumina or other suitable abrasive grains of required grit size and an unconverted resinoid powder, such as a Bakelite phenolic formaldehyde condensation product in required proportions. such as toparts by weight of diamond grains with the remainder made up of the resinoid bond and suitable fillers, such as silica, wood flour, asbestos. clay or other granular material. This mixture may be placed in a suitable mold and pressed to a, required density, and the pressing operation may be either done simultaneously with or followed by a heating operation which sets the resinoid to a solid, non plastic condition in intimate association with the abrasive grains. The

heat setting conditions of temperature and extent of pressure will be in accordance with stand ard practice. If rubber is employed as the bond then various procedures may be adopted, such as milling a desired quantity of the abrasive grains into a strip of raw rubber compounded with sulfur anda vulcanization accelerator in proportions for making hard rubber. This-may be accomplished in accordance with standard methods by repeatedly passing the rubber compound between power driven rollers after folding a quantity of loose abrasive grains into the raw rubber compound. After the rubber and abrasive mixture has been satisfactorily compounded, then 'the material may be subjected to heat sufllcient to vulcanize the rubber to a hard, non-plastic condition.

For the central support II, which in Fig. 1 is shown as a cup shaped member provided with a central hole, it is preferred that this member be made of a material similar to that of the bond of the abrasive ring Ill. That is, a resinoid center isvused with a resinoid bonded rim,-and a rubber center with a rubber bonded rim. In making a resinoid center, a. suitable filler if used and the unconverted resinoid in powdered'form, or if desired in a liquid condition, are intermixed and placed in a mold and then shaped under adequate pressure to cause the mass to assume substantially its final density. It ispreferred that this resinoid compound be one of low" molding shrinkage, that is, having a high percentage of a filler such asflint, wood flour, asbestos and other suitable compounds, so that during the subsequent molding operations the central backing support will retain substantially its original volume. The resinoid of this backing support should preferably remain unconverted to the non-plastic condition so as to make use of that property of plastic flow which the material possesses when subjected to the high pressure of the next step of the-molding operation; butit may be converted, if desired, to its final non-plastic condition prior to the step of fastening the premolded abrasive rim thereon.

For a cementing medium to secure the two premolded parts together, I may employ a Bakelite resinoid varnish or lacquer, or other suitable cementing resinoid material in the uncured stage, such as a resinoid powder capable of plastic flow when subjected to heat and pressure. This cement is employed as a thin film between the parts, and this may take the form of a thin paper impregnated with liquid Bakelite resinoid in the uncured stage. One or more layers of this impregnated paper l4, which has been cut to the desired annular shape as indicated in Fig. 1, is interposed between the premolded and precured abrasive rim l0 and the annular plane face of the cup l2. Then this assembly of the three parts is compressed in a suitable mold and heat is applied to set the cement.

The mold shown in Fig. 2 may comprise a metal mold band l6 having two metal plates i1 and I8 slidably mounted therein, with a further metal plate i9 fitting the inner portion of the cup. A metal core 20 may be inserted in holes in the metallic parts l1, l8 and I9 as well as the central hole 2| of the cup, so as to prevent deformation of the cup during the pressing operation. The parts will be so sized that the mold plates H or i8 will initially project slightly outside of the mold band i6. Then, when the mold with its assembled wheel parts is placed between the two platens of a power press, and pressure is applied to the plates I1 and i8,.these plates will be forcedtowards each other until the mold is closed, or until the press platens rest on the top and bottom plane surfaces of the ring l6.

Prior to this final molding assembly opera- .tion, it is feasible to roughen the 'opposed flat surfaces of the abrasive rim IO'and the top face of the cup l2, such as by means of a grinding wheel or abrasive cloth, so that the cementitious material will make a more intimate contact with each of the opposed bodies. i Moreover, it is desirable that the cup l2 be not in a heat set condition so that the roughened surface opposed to the abrasive rim will be capable of flowing slightly into every intimate union with the resinoid cement and the rim.

Thereafter, the resinoid of the cement and of the backing support l2 are cured by means of heat, in accordance with the standard practice. This may be accomplished by heating the assembled parts of the pressure mold with the wheel enclosed therein and maintaining such temperature conditions as will cause theresinoid to be converted to its flnalhard infusible condition. Upon disassembling the mold parts, it will now be found that the abrasive rim II has been made integral with its backing plate l2.

The same procedure will be in general adopted -ifv a rubber backing plate is to be employed, and

in this case a previously compressed and shaped surface 21.

mass of rubber and sulfur compound which has not been fully vulcanized will be employed for the backing plate. The rubber compound comprises raw rubber, sulfur and a vulcanization accelerator proportioned for making hard rubber, according to standard practice. A rubber cement, with or without a plastic layer of raw .rubber compound, or other suitable rubber cementing material, is preferably interposed between thisbacking cup and the rubber bonded abrasive rim Ill. The rubber cementing layer l4 will be provided with sufficient vulcanizing compound, such above described of abrasive grains together with a resinoid' or rubber bonding compound and these two ingredients may be suitably shaped in a mold having movable parts arranged to provide a cavity of the required dimensions. After the ring 25 is shaped, it may be cured in its original mold or apart therefrom as is'desired, so as to form a fully cured body which is to be integrally united with the central support24. This "support will be preferably formed as above described of either a resinoid compound or vulcanizable rubber. These two separately fashioned bodies 24 and 25 may be placed in a mold and there united under heat and pressure.

The pressure mold may comprise a metal band 26 which is L-shaped in cross section so as to provide two inner faces 21 and 28 and an inner shoulder 29. This shoulder 29 is of the'exact width of the ring 25, as illustrated in the drawing, so that the premoldedand precured ring 25 will be supported wholly on the band 26. A mold plate 30 is slidably mounted within the inner peripheral face 28 of the band, and another press plate 3| slidably fits within the larger peripheral If desired, the mold band 26 and the upper plate 3| may be removably secured together by a series of set screws-32 which fit into a groove' in the edge of the peripheral face of the plate so and thus serve to lock the plate 3| tothe iold band 26 during either the pressing or the 'heating operation. The central supporting body 24 is preferab slightly .oversize in thickness so as to provide material for plastic flow, and if desired an appropriate resinoid or rubber cement 33 as above described may be interposed between this central support and the abrasive rim 2 5. 'A metal core 34 is suitably mounted in the central holes in the plates and wheel support 24, so as to support the body 24 against distortion during the pressing 24 which is in a slightly plastic condition. This causes a flow of the resinoid material of-the support 24 in an outward or a radial direction and thus forces'this'central mass into a very intimate and complete contact with the matured rim 2|. This rim can stand the lateral pressure of the plastic flowing material but it is preferred to although it is preferred piication of pressure on the abrasive rim. The

central supporting body is comparatively large and so is capable of withstanding the pressure usually employed in a power press, which may be as much as 1 ton per square inch. Also, if the rim lies flat against its support, as shown in Figs. 1 and 2,. it may be subjected to the full pressure; whereas pressure should not be applied against the narrow face of the rim when the parts are arranged as shown in Fig. 3.

'The methods above described may be varied widely within the knowledge of one skilled in the art; but in any case it is desirable that the rim be not only premolded but also heat set prior to its assembly with the central support. Furthermore, the cementing medium employed between the rim and the support may be suitably varied, to have it of the same general class of materials as is used for the abrasive bond. Both forms of rim are to be cemented in place, but the pressure applied to the wheel parts during the assembly molding operation insures a very close union therebetween. This is particularly true it the central body 24 of Fig. 3 is not heat set until after the parts have been united. It will be understood that the sizes of the wheel parts and mold parts will sive grains, a premolded menting layer securing be suitably chosen where the body 24 is to be made slightly oversize in thickness so that it may flow laterally to the desired extent before the mold is closed.

I claim:

1. The method of making a composite abrasive wheel having a central support and an abrasive rim comprising the steps of premolding a heat settable material selected from ing of an unconverted resinoid and a vulcanizable rubber compound, and thereby forming a plastic for the desired results and particularly the class consistsupporting body having substantially its final v volume, separately molding a mixture of abrasive grains and the support to form an abrasive rim, heat setting the rim to its final non-plastic condition, thereafter assembling the central support and rim in heat settable cement a pressure mold with a therebetween, pressing the wheel parts without distorting the rim and causing a plastic flow of the support into a firm union with the rim and heating the wheel to set the unconverted material of the support and cement into a final hard condition.

2. A grinding wheel comprising a thin annular rim of premolded, heat set resinoid and abrasupport of heat set resinoid and a filler, and an intermediate cethe rim to the support impregnated with heat BAALIS SANFORD.

which is made of paper set resinoid.

a bond of the type selected for

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