US2488276A

US2488276A - Grinding wheel

Info

Publication number: US2488276A
Application number: US515907A
Authority: US
Inventors: John R Erickson
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1943-12-28
Filing date: 1943-12-28
Publication date: 1949-11-15
Anticipated expiration: 1966-11-15

Description

Nov. 15, 1949 J, R. ERlCKsoN 2,488,276

@BINDING WHEEL Filed Deo. 28, 1943 ze/ /H-y- 2 Sheets-Sheet l JOHN R. ERICKSON Nov' 157 J. R. ERICKSON GRINDING WHEEL Filed Dec. 2e, 1 943 2 Sheets sheet 2 Q/ 'OA )(53 -1 u w Ryn JOHN R. EmcKSON m @MNM rPatented Nov. l5, 1949 GRINDING WHEEL John R. Erickson, Worcester, Mass., assig'nor to Norton Company,vWorcester, Mass., a corporation o f Massachusetts Application December 28, 1943, Serial No. 515,907

4 Claims. (Cl. 51-296) This invention relates to abrasive articles, such as grinding wheels, particularly abrasive articles utilizing diamond particles as the abrasive and to a method of producing the same.

One of the objects of this invention is to provide an abrasive article of the above-mentioned character that will be strong and efficient in action, long-lasting, and capable of facility of manufacture with facility of control of its structural characteristics. Another object is to provide a practical and dependable method for producing abrasive articles of the just-mentioned character.

Another object is to provide an abrasive article, particularly a grinding wheel, in which the abrasive portion and its supporting portion are structurally and functionally so inter-related to each other as to facilitate shaping, or facilitate change in shaping of, particularly the backing or supporting portion, by the user of the grinding wheel, to meet varying requirements of practical use, all without impairment of the structural and functional integrity of the abrasive article or grinding wheel as an entity. Another object is to provide an vabrasive article, particularly a, grinding wheel, of the just-mentioned character which can be efciently and reliably produced out of materials, such as resins of the phenolic type, in a manner and by a practical and emcient method that dependably avoid difliculties, such as swelling during curing, that are met with if the structure is attempted to be made by heretofore known methods. Another object is to provide a grinding wheel comprising an abrasive annulus and a resinoid type of backing or support, in which there may be achieved 'such distribution of stress from the relatively small abrasive annulus to the relatively larger mass of the support or backing, during grinding action, as will make for longer life of the wheel,

better eiicency of grinding, and greater strength f of structure to stand up to the reactions from the stresses exerted at the grinding line.

Another object is to provide a method of constructing a grinding wheel of the above-mentioned character in which an improved and stronger junction between the abrasive annulus and the backing or support can be achieved in an economical, efficient and thoroughly practical manner. Another object is to provide a method of the just-mentioned character in which detrimental eifects caused by change in volume or shape of the resinoid may be eliminated in a simple and dependable manner or maybe prevented from impairing the strength, durability K or uniformity of the junction between the abrasive annulus and the resinoid backing or support. Another object is to provide a method and construction for dependably overcoming the defects of swelling, shrinking or the like in effecting the junction between the abrasive .annulus and its vresinoid backing or support. Another object is to provide a grinding wheel, particularly one employing diamond as the abrasive, in which the junction between the abrasive annulus and its resinoid support or backing is of such a structural and functional character that it remains substantially unimpaired when both abrasive annulus and support are turned down or trued to different shapes or conformations as, for example,` is frequently required in certain grinding operations to shape not only the annulus but also its support to cope with a different or a particular grinding operation. Another object is in general to provide an improved grinding wheel and an improved method of achieving the same. 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 each of the same to one or more of the others, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of tne various embodiments o1' the mechanical features of my invention,

Figure l is a central transverse sectional view, as seen along a diameten, of a grinding wheel made according to my invention, illustrating a possible conformation which it may be given as a final step in the method or, in the eld, to suit it to a particular grinding requirement;

Figure 2 is a central transverse sectional view as seen along the diameter of a grinding wheel as it appears at the conclusion of other, and if desired, steps of my process;

Figure 3 is a diametrical transverse sectional view of a possible mold, showing it charged with certain ingredients, ready for a pressing operation;

Figure 4 shows the mold and certain parts of the wheel construction at the conclusion of the pressing operation; y

.Figure shows the mold and the wheel part of Figure 4 prepared for having the abrasive annulus molded in position;

Figure 6 is a central transverse sectional view as seen along the diameter of another form oi grinding wheel as it appears at the conclusion of other, and if desired final, steps of another form of my process;

Figure 7 is a central transverse sectional view, as seen along a diameter, of a grinding wheel illustrating a shape or configuration which may be .given the structure of Figure 6, by following certain other steps of my process; and

Figure 8 shows successive transverse sectional views, as seen along the diameter, of the successive structures corresponding to successive steps which may be pursued according to another form of my method.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Certain features of my invention are better illustrated in connection with the construction, and the method of making it, of a so-called cupshaped wheel which as shown in Figure 1 or Figure 2 comprises an abrasive annulus III carried by a backing or center that has a hole I I by which the wheel can be mounted onto a driving shaft,

i the abrasive annulus ID being of relatively small dimensions, for example, 1/8" in thickness along a radius and 1/8 in thickness in the direction of the axis of the wheel; this type of wheel, utilizing diamond grain as the abrasive in the grinding annulus I is intended primarily to perform a grinding operation by way of its side face Il)m but in practice may be called upon to perform a grinding operation by way of another exposed face, such as the outer or peripheral face IIIb which, illustratively, can be cylindrical. Diamond grinding wheels are usually employed in grinding very hard materials, such as cemented carbldes, and are subjected to extremely severe reactions and stresses during the grinding operations. The reactions and stresses are ultimately absorbed by or dissipated in the backing or center which may be made sufciently large and strong for that purpose but, because of the relatively very small dimensions of the abrasive annulus itself, these reactions and stresses can become exceedingly concentrated, particularly in the small area of the junction between the abrasive annulus and the backing or support. As a result failures, such as breakage of the abrasive annulus, separation thereof from the center or backing, and the like can occur and, moreover, the attempt to provide a wheel devoid of the above-mentioned shortcomings by the use ofheretofore known methods of wheel manufacture has but emphasized the inadequacy of such methods for it has been found that factors such as swelling during curing of the material of the backing can make impossible the production of a grinding wheel capable of Withstanding even a modest grinding load. Furthermore, all of these factors are aggravated by the requirement, to meet certain particular grinding needs, that the backing ,itself has to be shaped, with or Without also shaping the abrasive annulus, by the grinding wheel user to meet requirements of certain subsequent grinding jobs or of some succeeding stage o f grinding. To provide a practical, efficient and long-lasting grinding wheel, and a method of making it, that will overcome such disadvantages and defects as have just been noted is one of the dominant aims of this invention.

Referring flrst to Figure 3. I provide a mold which may comprise an outer mold ring I 2 having a bottom plate I3 and a top plate I4 provided with central holes I5 and I6 for receiving a central arbor I1, all constructed in known manner to be receivable within a suitable pressure-applying apparatus, such as an hydraulic press; thus the press may have a lower plater.'` I8 upon which rest the bottom plate I3 with its arbor I 5 and the mold ring I2, and an upper platen I9 which engages the top plate I4.

In such a mold, with the platens adequately separated and the top plate I4 removed, I place a suitable mixture of uncured resinoid with a suitable ller, and an illustrative mixture may comprise powdered uncured phenolic aldehyde resin, such as Bakelite, more specifically uncured Bakelite powder, known as BM 261. The powdered resin is preferably of fine size, for example, 220 grit size, and illustratively may be used in an amount about 86.3% by weight and thoroughly mixed with 13.7% by weight of a pigment (which may, incidentally, function aslo as a ller) such as manganese oxide (MnOz), 2.3 cc. of furfural per 100 grams of the Bakelite powder, 2.3 cc. of Carbosota per 100 grams of the Bak-elite powder, and 1.6 grams of CaO per 100 grams of the Bakelite powder.

The just-mentioned proportions are illustrative and may be varied according to circumstances, and the ingredients mentioned are also illustrative. For example, I may use pyrolusite which is 90% manganese oxide and 10% impurities of various kinds.

The furfural, which is a plasticizer and hardening agent for the resin, is first mixed with the manganese oxide and that mixture is then added to, and mixed with, a mixture of CaO and the powdered uncured resin, and finally the Carbosota is added; the latter is a neutral creosote oil which aids in giving good working consistency to the resultant mix. This sequence'of steps is preferred, for the manganese oxide thns out the furfural and there is avoided the difliculty and other disadvantages that would result if the furfural were added directly to the powdered resin, this latter procedure usually resulting in a sticky, lumpy mix. The resultant mix has uniformity of consistency and wetness and is sufciently pourable for charging the molds. Also, such a mix when suitably molded and cured to form a back or center is substantially non-porous, is strong and of the right kind of rigidity, and moreover, can be turned or trued, as with an abrasive stick or other suitable tool, with comparative ease or facility, leaving a nice finish and it also takes a nice polish; it may, however, have porosity, illustratively a porosity on the order of 10%. In making up the mix, suitable screening may be resorted to, if desired, and is preferred, particularly for cold-pressing of the mix.

The above-mentioned resin BM 261 comprises essentially a mixture of phenol formaldehyde resin (about by volume) which is in a partially cured state, clay or asbestos or other suitable filler (about 40% by volume), and a suitable amount of black dye; it is intended as a hot-molding material, but I am enabled to employ it for cold-molding or cold-pressing. It is less reactive than Bakelite 2417. Other suitable resins as later mentioned may, however, be employed. Such an uncured mix is placed into the mold of Figure 3, as indicated at 2|, that is, in the annular space above the bottom plate I3 and between the arbor I1 and the mold ring I2 to a depth about twice the thickness of the intimate center or backing. the amount thus depending upon how thick it is desired to have the ultimate center or backing of the wheel. Where BM 261 resin is employed as in the above illustration, it is preferable. to charge it into the mold within a short time after making up the mix, for example, within one or two hours. to avoid the effects of drying out and other possible undesirable actions. With a suitable template the top surface is levelled H throughout the major portion of its radial extent from the center outwardly, as indicated at 22. the template being shaped, however, to give the outer top portion of the uncured resinoid charge 2i a frusto-conioal surface as indicated at 23.

This operation is carried on. of course, with the top plate lil removed and any suitable means (not shown) may be used to aid the operator in swinging and guiding the template about the axis oi the arbor Il so that it will leave the top surface 22 and the frusta-conical surface 2t oi' the resinoid charge 2i iree from material irregularities or undulations, make them both concentric with each other and with the mold, the top face 22 thereby falling in a plane that is transverse to the axis of the mold. The mix, though wet and pourable as above described. is however not of such fluidity as will cause such ilow of the upper portions of the charge 2i as would materially alter the shape given the charge by the abovementioned template; in other words. the consistency of the mix 2l is sutllciently thick, though plastic. for the charge to maintain its shape at least until the annular tri-angularly-cross-sectioned space S between the surface 2l and the mold ring 121s iilled up.

Into the space S I now place an uncured mix which, from the viewpoint of curing and union therewith, is compatible with the uncured ingredient or ingredients of the charge 2| in the mold and where, as in the above-described illustration the charge 2i is also an uncured phenolic reslnoid mix, I make up a resinoid mix with which to charge the space S that comprises also an uncured phenolic resin, but this mix- I make up to have, when cured, a suitable porosity, for reasons later explained in greater detail. This second mix is, however, also related as to various of its attributes to the later-described mix out of which I make up the abrasive annulus i0.

The mix to iill into the space B of Figure 3 illustratively comprises 30.48% by weight oi powdered uncured phenolic'resin or Bakelite, more specifically, Bakelite resin known as "BR 9727," a. suitable ller, preferably a mineral ller in particle form such as feldspar of. for example. 220 grit size, or ground quartz, or the like, and where feldspar is used its amount is 63.80% by weight, 3.60% by weight of CaO, 2.12% of carbon black (to function as a pigment, the manganese oxide used in the charge 2| being a black pigment), furfural in the proportion o! 50 cc. per pound of uncured powdered resin, and Carbosota in the proportion of 30 cc. per pound of the above-mentioned uncured powdered resin. This mix is poured into the space S which by way of illustration in Figure 3, assuming that the outside diameter of the chargev 2i is 6", is in cross-section a right-angled triangle whose vertical leg and horizontal leg are each about t" in length. Actually, in one embodiment of my invention forv a 6" wheel. the charge 2i consisted of 625 grams and the charge indicated in Figure 3at 2l of the lustdescribed mix for the annular space S consisted of 30 grams. The charge 24 is. oi course, levelled oi! at the top. as with a template, to bring its top fece 2l into the same plane with the top tace 22 of the charge Il.

'I'he operations thus far described may be and preferably are carried on with the mold parts and platens cold. that is, at about room temperature. the top plate I4 is put in position about the upper end of the arbor i'l and within the upper end of the moldnring i8. whence the pressure-applying apparatus is actuated. as by moving the platens Il and il one toward the other to telescope the top plate il toward the bottom plate Il to reduce the axial dimension of the charge 2i to about one-halt, and this may require a pressure on the order of 5 tons per square inch. This pressing operation may be and prei'- erably is carried on with the mold parts and platens cold.

At the conclusionijii| this pressing operation the parts are in the relative positions shown in Figure 4 from which the .change in shape ot the charges 2i and 2l can also be seen. the charge 2i of Figure 3 being. now compressed axially to the proportions shown at 2 if* in Figure 4 while the charge 24 in the space S of Figure. 3-'is compressed axially into the shape shown at 24e, but vwill be seen not to be materially altered insofar es the shape and area of its upper face Il are concerned, the. .pressing operation. oi course. neatly merging thatnpper face 2l into the, upper race l2 of the compressed charge 2|.. a similar nicety of merging taking place between the outer cylindrical faces ot the two charges 2i* and 2 4 in Figure 4. Also the two compatible uncured mixes are. .under this relatively high pressing together. brought into intimate inter-minglins'in the region. indicated by the inclinedline orv plane .20 'in Figure 4,. of .their mutua l oontact. all in a manner that is conducive, during the curing or heat treatment. for the two portions 2|. and Il. to cure and harden into a single entity devoid of any material line or plane of cleavage 'therebetween. y

The top plate I4 is now removed whence it is replaced by a top plate il* as shown in Figure 5 top plate I4l being or lesser radius the radius o f the mold ring i! by an amount equal to the radial dimension which the abrasive annulus il (Figures l and 2) is to have .`and in the illustrative embodiment here selected for description. that dimension is 'to be Sigoi' an. inch. Accordingly. I may now charge the annular space 21 (Figure 5) above the portion 2 4* and between the mold ring I2 and the top plate M l 'with an abrasive and bondmix. yindicatediii Figure 5 at It. Here it is to be noted that I prefer. in shaping the space S during the steps "destgribed above in connection with Figure 3. to make the dimension ot the upper face 2l oi' the charge .2l several times greater than the radial dimension which the abrasive annulus Il is to-liave: in the il/lustration the former is t" andthe latter is The mix represented by the charge. yinliflgure 5 is in turncompatibles 10A-cillin .and certain other characteristics.l with the mix oiwhich 'the charge 2l of Figure 3 Ais made. lIn place oi' Ithe illustrative 63.80% of fcidspcr, I employ, where the abrasive annulus is to contain diamond as the abrasive. 41.00% byweight o f diamond. particles and 25.50% by weightr of particles. then 25.47% by weight of powdered uncuredfakelite. namely. BR9727, 2.97% by weight 0 1 Cao, 3.26% by weight of iurtural. and 1.80% oi Carbosota. the furi'ural and Carboeots. though being set forth in percentages by weight, are nevertheless in amounts equivalent to 50 cc. of i'urfural per pound of the powdered resin and 30 cc. oi.' Carbosota per pound oi' the powdered resin.

This abrasive and bond mixture I pour into the annular space 21 oi.' Figure 5 and level off as by a template to a height about twice the axial dimension which the abrasive annulus I of Figures 1 and 2 is to have in the ilnal product and where the latterA dimension is to be the charge 28 in Figure 5 may have a height or depth of about M4.

Bearing in mind that the portion 24. in Figure 5 is still uncured, I now place into the annular space 21 and above the charge 28 a mold ring 28 and bring the pressing apparatus into action, as by suitably actuating the platens I8 and I9 as before, thus pressing the lcharge 28 downwardly in the annular space 21 of the mold and against the upper face 25 of the compressed but uncured portion 24,

Here a pressure on the order of 5 tons per square inch may be employed, bringing the axial dimension of the charge 2B down to about 1/2, illustratively to about 1/8 of an inch; at the same time the mutually engaging parts of the portions 28 and 24 are forced, under this substantial pressure, into an intimacy of inter-mingling and inter-engagement throughout the area 30 of their respective potentially-reactive and compatible resinous constituents as is effective, during the subsequent curing, to cause these parts to join and harden and cure together as though they were a single entity, somewhat the same as takes place when the charges 24 and 2| of Figure 3 are compressed as was above described.

Having completed this last-described pressing operation, the uncured wheel structure is stripped from the mold and is then heat-treated to cure the resinoid and harden the three portions of the wheel into a single unitary strong entity. As stripped from the mold the structure has dimensions or shapes substantially like that shown in Figure 2. Heat treatment may take place in an oven and is suited to the particular characteristics of the resin employed in the mixes and with the resins and mixes illustratively set forth above, a suitable heat treatment comprises heat treatment of the structure at about 100 C. for a period of about 5 hours followed by treatment at about 175 C. for about 24 hours.

The resultant wheel structure appears as shown in Figure 2. It is characterized by substantial strength throughout, by freedom from detrimental or material warping, shrinkage or swelling, and by uniformity of strength particularly in the rather concentrated region where the three portions 2I, 211a and lli (Figure 2) are merged into a single solid entity. It has heretofore been impracticable or dimcult to achieve satisfactory union between such a small or concentrated abrasive annulus asthe annulus I0 and a backing or support, and this has been due principally to the fact that change in volume, as by swelling, during curing, causes such distortion or relative shift as to preclude uniformity of strength of the union between the abrasive annulus and its support; accordingly, the abrasive ring or annulus would fail because of failure at a weak spot or region in the annular area throughout which the two parts are supposed to be in union. This defect became aggravated when the wheel structure, particularly the resinoid backing or center, was turned down or trued to a different shape such as, for example. the general type oi' configuration shown in Figure 1, and here it is to be noted that such change in shape was irequently eiiected by the user. Such limitations and deficiencies of prior practices and constructions have also imposed a limitation upon the hardness that could be given the abrasive annulus itself or the backing or center or both, because, in the effort to overcome such deiiciencies lesser pressures have been employed in the pressing operations, and curing temperatures and periods have been employed which, while tending to mitigate such deficiencies, precluded the achievement oi' a hardness that is desirable from structural and operating viewpoints.

Such and other denciencies, limitations and disadvantages my invention overcomes, and for various reasons. For example, the portion 24* in Figure 2, compounded and proportioned in relation to the other parts of the wheel as illustratively above set forth has a porosity which, during curing, coacts to prevent distortion, as by swelling, of the abrasive annulus portion in that gases or vapors that might be evolved as the abrasive mix cures, instead of blistering or raising the abrasive mix away from the portion 24, nd egress across the plane of contact between the two and into and'through the pores of the part 24a. As a result, the abrasive mix and the portion 24 can undergo curing virtually as a single homogeneous mix would undergo curing and hence the union between the two is strong and uniform throughout. A similar action can take place in effecting a like, strong and uniform union between the portions 2l and 24, but due to the preferred congurations or relative contact areas employed in assembling the several mixes, the union between the portion 24B and the portion 2 I* is over an area of inter-mingling or engagement between the two mixes that is greatly in excess of the area throughout which the abrasive mix and the portion 24a are inter-mingled at their region of contact; in the illustrative embodiment, the former area is about four times as great as the latter area, and desirably an angularity, like that indicated in Figure 2, is provided between the two.

Furthermore, because of this divergence in areas the mix employed in making up the backing or center 2 I may differ considerably from the mix employed in making up the part 24a, though preferably maintaining compatibility of the uncured resins employed so as to facilitate what is practically a curing of the two as a single mix. Thereby the mix for the center or back 2 Izl may be compounded, illustratively as above set forth, and cured, to give it the desired hardness, rigidity, strength and other mechanical properties desired, for the larger area of inner engagement, as at 26 inFigure 4, can still form in the aggregate an adequately strong union while the porosity in the portion 248 provides egress for such gases or vapors as are evolved in the mix 2|a undergoing curing, thus preventing change in volume with accompanying distortion or other phenomena as might disrupt the uniformity of the union between the two. An illustrative porosity for the portion 24n is l5 percent; another is 4 percent.

Preferably also, and as the above illustrative compositions of the mixes for the parts l0 and 24 indicate, the two mixes have substantially identical or closely similar compositions structurally; that is to say, in each are present substantially the same proportions of resin, furfural, Carbosota, CaO and of feldspar (with carbon black) illler on the one hand and diamond grain plus quartz grain' on the other hand. As a result there is excellent compatibility between the two as to curing characteristics and phenomena that transpire during curing. and in the resultant in-4 tegral cured final structure, the two portions l and 24 have substantially the same structuralv to dependablv and reliably transmit and distribute to the center or backingr 2|*3L such strains and stresses. in effect substantially relieving, and certainly lessening, a too direct concentration of strains or stresses in the region of the area 30 throughout which the uncured mixes 28 and 24* of Figure 5 became engaged and intermingled. These substantial similarities of the above-mentioned characteristics of the mixes 28 and 24a in Figure 5 also coact toward giving these two mixes, during curing. similar or substantially identical change of volume characteristics whereby also curing of the two into an integral or single entity, without material risk of cleavage, shear, rupture or the like along the annular area 30 is avoided or lessened. Preferably the compounding of the several mixes includes. as in the illustrations given above, an ingredient such as CaO which coacts with water or water vapor evolved during the curing to chemically take it up and thus counteract material change in volume by shrinkage. The wheel may be used in the form shown in Figure 2 but more usually, before shipment, the wheel is mounted in a suitable apparatus and rotated and the hardened cured back or center' 2| I turned down to change its shape, as by use of an abrasive stick, though the user of the wheel may himself in a similar way change the shape of the wheel. In Figure 1 I have indicated at 2|b and at 24b an illustrative change in conformation which may be given the parts 2| and 2l!a of Figure 2, the turning down or truing being in a direction to emphasize the dish or cup shape oi' the wheel as might be necessary to suit it to some particular grinding operation. The cured portion 24b lends itself readily to such a turning down operation and the shape initially given it as in Figure 2 will be seen to be such as to make it possible to maintain the now diminished annular area 2li#l in Figure 1 as compared to the area 26 in Figure 2 (still greater than the annular area 30). In the shape shown in Figure 1 the abrasive annulus i0 may be made to operate by way of any of its three exposed faces and by suitable truing tools, such as an abrasive stick, these or any of them may be changed in shape or configuration to suit particular grinding needs.

The ease of change in conformation or shape makes it possible also for the user to vary the conformation to suit particular grinding needs, and though the abrasive annulus itself may be thus reduced to small radial dimension, the underlying portion 24b strengthens and reinforces it and gives it good and substantial support to and from the backing 2|b itself.

In making up the mix for the charge 24 in Figure 3, I may employ other llers and preferably I employ fillers that are relatively low on the scale of hardness; thus a preferred filler is cryolite which has a hardness on the order of 2.5, or pyrolusite which has a hardness on the order of 2.0, or powdered metal of which aluminum is a good illustration, the latter having a hardness` on the order of 2 or 3, and also I may employ certain clays. The fillers to employ are hence preferably soft, and preferably they do not react with the bond and preferably also they are not hygroscopic. By following these preferred characteristics for the filler, the final cured portion of the wheel, such as the part 24a of Figures 2 and 4, after curing, can be easily and readily turned down to give it any desired shape, by the use, for example, of an ordinary so-called "abrasive stick, and, for certain purposes, the hardness of the filler employed should be below that value which would cause that portion of the wheel to take the edge off of certain tools, such as a tool made of Carboloy.

Also it is preferred that certain relationships as to porosity be maintained as earlier above set forth and it is preferred also that the volume percentage of the bond in the mixes 24 and 28 be .substantially the same, these factors coacting to achieve good adhesion or a good union between the portions l0 and 24, as seen in Figure 2. The mix 2| may and preferably is given a suitable porosity, say, on the order of 10%, and the provision of suitable porosities in the several sections or portions aids in combatting swelling or tendencies toward swelling, for the porosity can provide sufficient egress for or accommodation of such gases or vapors as are evolved during curing, and thus detrimental or undesired changes in volume, particularly such as might have bad effects upon the union between adjacent portions, can be prevented or minimized.

With such relationships also, a greater range 0f variation or flexibility in the structural relationships and also in the method of making up the wheel are achieved. For example, it is possible to ilrst cure the structure as it appears in Figure 4, in any suitable'way, and after curing, mold thereon the abrasive mix or annulus l0, following steps substantially like those described above in connection with Figure 5, and then subjecting the now composite and complete structure, of which the parts 2 I and 24* are already cured or, if preferred, substantially cured, to suitable heat treatment to cure the bond of the abrasive annulus. By way of illustration, the two steps oi' curing can be and preferably are, as to heat treatment, the same and each curing step may comprise heat treatment at about C. for a period of about 5 hours followed yby treatment at about 175 C; for about 24 hours. The heat treatments preferably take place in an oven, the composite wheel center or back being restored to the mold apparatus after curing in' order to have the mix of the abrasive annulus molded and pressed thereon.

The securityy of union or of junction between the several parts achievable according to certain features of my invention and also the ease and facility with which shaping after curing, particularly of the part that corresponds to the mix 24, makes possible the carrying out of certain features of my invention in other forms. For example, instead of shaping or molding, pressing, and curing the wheel structure with its several portions shaped as shown in Figure 2 and as above described, the wheel structure may be made up as indicated in Figure 6 in 4which the backing.`

, portion 3i and to which l structure to which the joined and thus a number of practical 11 `molded and pressed together green, cured, and then the abrasive element I molded and pressed thereon and the resultant unit cured, as by baking; the latter method has advantages in that. `after curing the entity 30--3 I the ease with which `the parts may be turned down or trued, as by an abrasive stick, makes it possible to give that part or face of the portion 3i any desired configuration. shape or dimension as, for example, might be appropriate or suitable for the 'attachment thereto or union therewith of the abrasive annulus I0.

The structure shown in Figure 6 may, like the structure shown in Figure 2, be shaped as by turning down its various surfaces or faces to the desired configuration as, for example, by truing or turning down along the broken lines 32-33 of Figure 6, giving an ultimate shape like that shown in Figure 7, or itV may be conformed by turning down to the shape of the wheel shown in Figure 1 and earlier above described. The turning down along the broken line 33, in Figure 6,

and particularly along that part of it that intersects the portion 3| may, if desired, be effected after the completion of curing of the entity 30- 3l and hence prior to the molding and curing i thereon of the abrasive annulus l0, Where it is preferred to make the wheel in two steps of curing, and in such case the surface 34 of the the abrasive annulus i3 is'to be joined may be shaped oryturned to its desired configuration and also the outer cylindrical face of the portion 3|, prior to the assemblage and curing thereon of the abrasive annulus I0.

' Such features as these also make it possible to give, by truing or turning down, geometric'accuracyto that face of the backing or support advantages may be achieved. For example, departures from abrasive annulus is to be.

geometric accuracy such as may be caused by uncontrollable or accidental swelling, shrinkage, warping, or other changes, particularly during curing when the structure is cured outside of the mold, may thus be quickly and inexpensively rectified. Also, in such case particularly, wastage or inemcient use of expensive diamond abrasive can be avoided forthe innermost boundary of the abrasive annulus Il) may thus be accurately determined with the result that uniformity of abrasive action by the abrasive annulus In con-v tinues down to and including the very last or innermost layer of diamonds thereof. These latter advantages are peculiarly practicable where the abrasive annulus is made up in the shape of a ring carried by the outer periphery of a disk-like or cylindrical center or 'backing and makes possible also construction of wheels of that type with 'simpler and less expensive molding equipment;

this can be illustrated by the successive steps indicated in Figure 8.

Thus, let it be assumed grinding wheel is to be made up to have an outside diameter D. In such case, by the use of any suitable molding apparatus, and hence in any known manner, I mold up two mixes, like the mixes 2l and 24 above described, to form a disklike or cylindrical center or backing 36 with a peripherally-extending annulus 31, the union and junction therebetween being just as secure and having other attributes as were described in connection with the junction between the parts 2|- and 24 of Figure 2; in Figure 8, the outside diameter of the outermost portion 31 is the dimension D. as indicated, and its radial dimension or that such a peripheral thickness is materially greater than the radial dimension or thickness of the ultimate abrasive annulus which the wheel is to have.' For example. if the latter is to be 1;/8", the thickness of the portion 31 can be 1A".

After curing, which is preferably achieved by baking as in an oven and hence outside of the mold, the structure 36-31 is mounted on an arbor for rotation, or supported in any suitable way to be rotated about its axis, and is turned down to remove a :substantial portion of the annulus 31, preferably in an amount to correspond to the radial dimension of the ultimate abrasive annulus which the wheel is to have. and the side faces of the structure may likewise be turned down and trued. The annulus 31 thus becomes in cross-section` an annulus 33 with its outer face 39 turned to substantial geometric accuracy, in the illustration, a true cylinder of revolution; due to the features above described, this truing operation is an easy one to carry out, the compositions of the parts permitting ease of cutting by the truing or turning tool.

The resultant structure is now returned to the same mold which has an inside diameter of D, thus leaving an annular space between the geometrically accurate internal cylindrical face of (diameter D) of the mold ring and the geometrically accurate face 39, and into this space an abrasive mix, like. that out of which the abrasive annulus IB above described is made, is injected in suitable quantity and under suitable pressure, as by the use of a mold structure substantially like that shown in Figure 5 and utilizing a mold ring 29 to act upon the abrasive mix which thus becomes neatly and accurately conformed to the concentric'cylindrical faces of the mold and the part 38. Heat'treatment then ensues, preferably outside of the mold as in an oven, thus to cure the abrasive annulus which in Figure 8 is indicated at 40. After curing, either or both' of the side faces of the composite backing 36-38 may be shaped as by turning or truing and, by way of illustration, turning down may take place along the broken lines 4I and 42 where the abrasive wheel is to have side clearance.

The plane of the junction or union between the portions 36 and 31 can beoblique or inclined, as by making it frusto-conical as indicated' at 43, thus to give the junction between the portions 36 and 38 in the final wheel a greater area than the junction between the abrasive annulus and the portion 38.

As above set forth, reference to specific resins is to be interpreted as illustrative and other resins may be employed such as, for example, other forms or compoundings of phenol formaldehyde resins, also aniline formaldehyde, any one of the alkyd resins, shellac, rubber, methyl methacrylate, glyptal, styrene, and the like, or other suitable or equivalent resins, all of which I comprehend within the term resinoid or resin" or resin-bonded used in the claims.

It will thus be seen that there has been provided in this invention, an article, a composition and a method 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 hereinabove set forth is 13 to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A grinding wheel comprising a resinoid back presenting a ring-shaped securing face and a resin-bonded abrasive annulus spaced a short distance from the aforesaid securing face and having a ring-shaped securing face that is of lesser width than the width of the securing face of said resinoid back and a resinoid stress-distributing annulus interposed in the space between said first-mentioned securing face and said abrasive annulus and presenting annular faces respectively matching in width the different Widths of said two securing faces and being joined thereto and integrally united therewith and having a cross-section that varies substantially progressively from the lesser Width of said one of its securing faces to the greater width of the other securing face thereby to transmit the substantial grinding stresses exerted upon the abrasive annulus to 'said back and distribute them throughout the larger area of the securing face between the resinoid back and said resinoid annulus, and said resinoid annulus being cured to a porosity between about 4 and 15%.

2. A grinding wheel comprising a back made of a resinoid mix containing a filler that is relatively low in hardness and having a ring-shaped securing face, an abrasive annulus having a ringshaped face of less width than said securing face of said back, and an interposed securing and reinforcing annulus made of a resinoid mix containing a ller that is relatively low in hardness and compounded to have a porosity for the escape of gases therethrough, said interposed annulus having faces respectively integrally united to said securing face of said resinoid back and said ringshaped fa'ce of said abrasive annulus under conditions of heat and freed from deleterious blistering or disunion through the escape of evolved gases or vapors through the aforesaid porosity and being of substantially corresponding variation in crosssectional configuration from one of said faces to the other, and said resinoid annulus being cured to a porosity between about 4 and 15%.

3. A grinding wheel comprising a resinoid back havingr a substantially frusto-conical securing and thrust-receiving face and an abrasive annulus spaced a short distance fromA the aforesaid face and having a ring-shaped face of less Width than the width of said frusto-conical face and an annular resinoid member interposed in the space between said thrust-receiving face and said ring-shaped face for distributing, in lesser intensity throughout said thrust-receiving face, stresses from said abrasive annulus to said resinold back and, for that purpose, having a frustoconical face substantially matching in width said first-mentioned frusta-conical face and integrally united thereto and'having a face of lesser width to which said abrasive annulus is united throughout the ring-shaped securing face thereof, and said resinoid annulus being cured to a porosity between about 4% and 15 4. A grinding wheel4 comprising a disk-like truable resinoid back comprising a cured porous resinoid mix containing a soft ller and having a porosity on the order of 10%, said back presenting a peripheral substantially cylindrical face andv carrying a truable abrasive annulus having a peripheral substantially cylindrical face substantially aligned with said first-mentioned cylindrical face, said abrasive annulus being mounted upon and secured to a side face of said back by means of a truable annular layer of resinoid containing a soft filler and cured to a porosity on the order of from about 4% to about 15% and having a peripheral substantially cylindrical face substantially aligned with said first-mentioned face, said layer being of greater radial dimension than that of said abrasive annulus and tapering off inv thickness in a direction away from its said face to merge its exposed side face substantially with said side face of said back, thereby touistribute stresses from said annulus to and throughout a greater annular area of said back than the annular area of said annulus and whereby the lastmentioned relationship may be maintained even after truing the aligned cylindrical faces or the merged side faces of said layer and of said back to a shape, such as frusto-conical, to provide clearance for said abrasive annulus, said annular layer and said back being integrally joined together throughout said greater annular area freed from deleterious blistering or disunion through the escape of evolved gases or vapors, during curing, through the aforesaid porosity of said annular layer.

JOHN R. ERICKSON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,785,437 Doermann Dec. 16, 1930 1,826,300 Chapel] Oct. 6, 1931 1,832,515 Webster Nov. 17, 1931 2,070,734 Voegeli-Jaggi Feb. 16, 1937 2,073,590 Sanford Mar. 9, 1937 2,110,143 Ball et al. Mar. 8, 1938 2,150,886 Van der Py] Mar. 14, 1939 2,268,663 Kuzmick Jan. 6, 1942 FOREIGN PATENTS Number Country Date 166,869 Switzerland Apr. 16, 1934 178,296

Switzerland Sept. 16, 1935