US2394326A - Thin abrasive wheel - Google Patents

Description

Feb. 5, 1946'. E. N. NE' NHAM 2,394,326

THIN ABRASIVE WHEEL Filed Aug. 9, I945 2 Sheets-Sheet 1 fig-J J inventor Eu /Ene N-Ne wrzh an:

.M itty Feb; 5, 1946. E..N. NEWNHAM 2,394,326 I THIN ABRASIVE WHEEL Filed Aug. 9, 1945 2 Sheets-Sheet 2 112v err-01" u. ens N..NE'wnh.cL1u

Patented Feb. 5, 1946 THIN ABRASIVE WHEEL Eugene N. Newnham, Los Angeles, Calif., assignor to Max N. Felker, doing business as Felker Manufacturing 00., Torrance, Calif.

Application August 9, 1943, Serial No. 497,931

2 Claims. (01. 51206) It is a general purpose of this invention to provide an abrasive wheel structure which, although applicable to abrasive wheels of various sizes and thicknesses, is particularly applicable to thin wheels of the saw or cut-01f type. As applied to the thin type of wheel, it is the purpose of the invention to provide a structure which is simple in form and in manufacture, and which has a maximum strength to resist rupture, and maximum life in use.

The invention relates more particularly to that type of thin wheel which comprises a central disk of a suitable material such as metal, and a thin abrasive rim bonded with a non-metallic bond such as synthetic resin. In my improved wheel I utilize a central disk-preferably made up of a single piece of suitable metal, thereby to obtain a structure having a maximum of lateral stiffness. To the periphery of that stifi metal disk I attach a continuous thin annulus of bonded abrasive in such a manner that the thin abrasive rim also has good lateral strength in itself, and is attached to the disk in such a manner as to be given good lateral support from the laterally stifi disk. One of the more serious difi'iculties encountered in thin wheels of the type here under consideration has been due to lack of sufficient lateral stiffness, resulting in frequent fracture of the abrasive rim either by careless handling, or by subjection to pressures while in use. For instance, in one known type of thin wheel which employs metal and/or fabric disks to make up the central body of the wheel, there is difficulty in obtaining good adherence of phenolic bonds to the metal, and if a fabric disk is extended into the abrasive rim to bond it securely to the central disk the useful life of .the rim is shortened.

The manner in which I accomplish the desired objectives will be best understood from consideration of the following detailed specification wherein preferred and illustrative embodiments of the invention are explained, and reference for that purpose is had to the accompanying drawings in which Fig. 1 is a fragmentary side elevation of a peripherally notched disk showing the general configuration and spacing of notches. As compared with an average wheel size contempla'tedat present, Fig. 1 is enlarged.

Fig. 2 is a further enlarged diagrammatic view showing a preferred method of notching the periphery of the metal disk; i

Fig. 3 is a still further enlarged fragmentary view showing the raised edges which surround the notches as the result of notch formation;-

been laterally and peripherally pressed or rolled on a lathe;

Fig. 7 is a further magnified perspective showing the nature of the notch walls in the stage of operations shown in Figs. 5 and 6;

Fig. 8 is a diagram illustrating the operation by which the abrasive rim is molded upon the notched periphery of the metal plate, the scale of this figure being the same as that of Fig. 2;

Fig. 9 is a fragmentary side elevation of a finished wheel to the same scale as that of Fig. 8; and

Figs. 10 and 11 are sections, respectively, on lines I0|0 and [1-H of Fig. 9, to the same scale.

In Fig. 1 a portion of the notched edge of the central metal disk is shown, showing the general relative shapes of the peripheral 'notches and their spacing. The metal disk is designated and the notches 2|. The notches are relatively wide open, and although any relatively wide-open or broad mouthed notch formation will suiiice, I have found by extensive trials and tests that angular notches having included angles of from 30 to 45 are suitable, spaced apart along the periphery by spaces about equal to the peripheral dimension of the notch openings. However, although I do not regard size as being a limitation upon my invention, I will give typical dimensions which are based upon wheels of a typical size. Thus, for a finished wheel of about 3" diameter and a finished rim thickness of about .040", disk 20 may be about .030" thick, notches 2| may have an angle of from 30 to 45, a radial depth of about 1%" and a spacing between notches about 3 The axes of the notches may either be radial of the disk, as here illustrated, or may be tangential to a concentric circle smaller than the disk.

The foregoing describes the general disposition of the disk notches. .The individual notches have certain peculiarities of form which I will explain, first explaining a presently preferred method of producing a suitable and typical notch formation.

A preferred method of forming the notches'is illustrated in-Fig. 2. The, notches are preferably cut with a sharply beveled chisel 22 whose edge angle is considerably lessthan the notch angle. In forming a notch a cut is first made with the chisel as illustrated in Fig. 2 to form one edge wall of the notch. Then, in a subsequent operation, another cut is taken as indicated at 23, at such an angle as to form the opposite edge wall of the notch, the central part 24 of the material in each notch being removed. This method of formation builds up ridges 25 at the edges of the opposite notch walls 26 and also a ridge 21 around the bottom of the notch. This ridge formation is shownin the enlarged Figs. 3. and 4. Alsoa slight ridge formation 28 is formed" at the peripheral edges of the notch walls although that does not seem to be of any great importance.

While the notch might be formed by a. single cut of a chisel having an edge bevel at an angle equal to the notch angle, and with resulting edgeridges like those illustrated, that method of for-- mation does not seem so desirable as it may tend too much to compact and harden the material of the disk at the notch walls. It also. makes the steel flow and swedges it; it is better to remove some of the: material of the: notch; Operations which I will. subsequently describe have the result: of shaping the notch walls to give maxi.- mum lateral support to the appiiedabrasive rim; and for the. purpose of those operations it seems desirable not to; overly harden or densify'the: ma-- terial of the notch walls at this stageoff the: operations. It isclesirable. that the notches be rather wide angled; and the: best method which I have so far discovered of forming the: wide angled notches and. at. the same time: to achieve the other formations of thernotch. walls which. I will describe, is the method which: I. have described in connection with Fig; 2.. And I may remark at this pointv that I have. found that" perlpheral notches formed by an ordinary diepunching operation which removes all of the matcrial and leaves substantially no ridges. 25 for subsequent operations are unsatisractory;

The next operation in the preparation of the disk is that of applying lateral pressure tothe notched periphery to press the ridged periphery downtothe thicknessdimension which is desired for the rim portion of the finished wheel and to shape thenotch walls 25; to the formsshown in Figs. 5, 6 and 7'. The lateral pressure may be applied either by rolling the rim portion of the disk, or by pl'ungenpressingthe whole rim at one operation. The peripheral edge of the disk may which cuts the, peripheral ridges 28 down. It is simpler however to true it up by a pressure operation.

The results of the pressure operations are shown in. Figs. 5, Band; 7.. As a result of the lateral pressure the. ridges 25 are pressed down to form widened ridges 2511 with flat faces. As an instance of dimensions corresponding with the dimensions previously given, the. overall thickness through the ridges 25a may then be approximately .034". This. lateral pressing of the ridges results. in. a change in the. shape. of notch walls 26'. As originally formed, the wall faces 26 are substantially flat, assuming. that a chisel 22. with a. fiat cutting face. has. been. used. As will be mentioned, a cutting. chisel with a curved cutting face may be used, but. the method here described seems preferable. The original fiat faced walls. 26 are changed to. the. shapes shown at 1.601. in- Fig. 6; a shape. that-may be designated as concave, or with inwardly overhanging edge portions 25a at the side edges of the notch walls. The material of the notch walls which is forced inwardly by the pressing operation to form the overhangs 26a is also roughened or wrinkled as shown at 26b in Fig. 7.

If the disk periphery is also pressed for trueing, the peripheral notch edges may be pressed in to form slight overhangs 26c (inside the normal surfaces 26.) as illustrated in: Figs. 5 and 7 and whichmay also be slightly wrinkled as shown at 26d. (The showing of this overhang at 26c in Fig. 5 is exaggerated.) Those overhangs and wrinklings do not however seem to be of any great importance to the radial strength and durability of a wheel. which is run at about 5000 surface: feet per" minute, although they may be advantageous at higher speeds. Continued tests of various wheel structures at about the stated speedhave indicated that radial bonding of the rim to the central disk is not so important as lateral bonding. The resinoid. bonded; rim. seems to. have sufilcient tensile strength. to withstand the rupturing. strains. generated: by, centrifugal action. The thin rim however does not have in itself sufficient strength to withstand any-substantial lateral pressures, and for that reason the widemouthed and: closely spaced notches, with the described wall formations having overhangs at their side edges, are important.

In fact my investigations and. tests indicate that, in thinwheels, the; lateral stiffening and support of the abrasive rimis of much greater importance than: any radial bonding or locking of the rim to the central disk; and it is that lateral support which my invention provides. To provide the-maximum of lateral support-andstiifness. it is. important that: the: closely spaced notches be formed. without. any substantial constrictions at their mouths. Consequently, in forming the notches I take care that the. peripheral rolling (if used) does not: produce. anysubstantial overhang at 2.6c,.sothat the matches. remain substantially or wholly V-shaped. clear to the disk periphery;

As indicated before, the concave wall formation shown in. Fig. 6 might. be; obtained initially by using a chisel 22. or other cutting took with: a correspondingly shaped cutting edge, and the lateral pressing operation dispensedwith: except for any necessary trueing. of the notched disk. However, the described pressing operations develop the, wrinkles 26bwhich I consider advantageous.

Disk materials suitable for my purposes. are such metals as copper. soft steel, or; aluminum or other alloys. Materials of about. the hardness of rolled copper are suitable for the specifically preferred operations; although harder materials may be used, particularly if the notches be cut initially to the. desired wall shapes without lateral' pressing. Using the softer materials, the disks can be. hardened as desired after the desired notch formations are made, to increase the lateral stiffness of the finished wheel. However, for all ordinary purposes, I find a. copper or steel wheel to. be satisfactory.

The operation of applying thev abrasive annulus to the peripheryof the disk is. indicated in Fig. 8; A typical molding die. for. the purpose has. an outer cylindric: wall 35 and. upper: and lower plungers 34 and 3-3, 34-. The lowerplunger may be recessed at 31 to form a part of an an nular moldingcavity 38 which takes in the notched and thickened rim portion oi the disk, that being generallydcsignated in Fig. 8. by the numeral 39. The upper plunger may include a central plunger 33 and a surrounding pressure ring 34. When the plungers are pressed home to completely compress the plastic rim mixture, their central parts bear upon disk In. In this closed position of the mold the molding cavity 38 may have transverse dimension somewhat greater than the thickness dimension of rim 39; for instance the transverse dimension of the molding cavity may be .040" in comparison with a rim thickness of .035. That is'however not necessary as will be pointed out; the finished abrasive rim may have a thickness either equal to or greater than the thickness of the disk rim.

The molded abrasive rim, set on the metal disk, is shown in Figs. 9, 10 and 11. Typically, for the wheel sizes previously given, the body of the rim, designated by numeral 40, may be of the thickness previously stated and have a radial depth of approximately /8" outside the periphery of the metal disk. In the molding operations the disk notches 2| are completely filled with the compressed and set substances of the abrasive rim, the applied pressure compressing and flowing the plastic mixture tightly into the notches and in pressure bonding engagement with notch walls 26a and their wrinkled formations 26b. In the molding operations a suitable amount of the initial plastic mixture is placed in recess 31 of the lower plunger, then disk l and plunger 33 are placed in position and more of the mixture is added until the disk rim 39 is covered by an adequate mass of the plastic charge. Upon subsequent pressing and curing, the inner portions of the rim (indicated at 4| in Figs. and 11) may or may not inwardly overhang the innermost portions of the ridges a. It seems to be immaterial whether the overhanging rim portions 4| do or do not overhang inwardly to that extent; and in the drawings the portions 4| are shown extending inwardly to about the bottoms of notches 2|. It is only important that the notches be completely and tightly filled, under pressure, with the plastic mixture and that the mixture be forced into intimate contact with the non-fiat walls 26a.

It will be observed that each notch 2| comprises a pair of opposed walls or surfaces 26a,

the disc thus being provided with a series of pairs of opposed surfaces. mixture into the notches and against the walls 26a provides the. abrasive rim with a series of integral V-shaped inward extensions, each extension comprising the material which lies between a pair of opposed surfaces 26a. Each such extension thereby has a pair of surfaces, so that the abrasive rim includes a series of pairs of surfaces intimately engaged with the series of pairs of opposed surfaces formed by the walls of the disc notches.

Lateral stiffness and strength are given to the abrasive rim 49 from the metal disk through the portions of the plastic rim which fill notches 2|. Those filling portions, intimately engaging and bonding with the non-fiat notch walls 2611 are rigidly locked in the notches against any relative lateral displacement. The mouths of the notches being wide open and closely spaced, there is an integral connection of great strength between the notch fillings and the rim proper. The absence of any constrictions in the crosssections of the lugs at the notch mouthsat the section of juncture of the lugs with the rimprovides maximum lateral bending strength at that critical point. And, in general, the V- Forcing the abrasive shaped notches and lugs are superior in lateral strength to any other form because the increase in cross-sectional area from base to mouth is uniform and because the change in cross-sectional area at the unconstricted mouth has a minimum of abruptnes's. The lateral strength which is thus imparted to the rim is sufiicient' to make it unnecessary to employ any reinforcements in the rim proper. In fact, my tests have indicated that the finished wheel gives better performance without having in it any of the ordinarily used reinforcement material, such as glass wool, cotton fibre, fabric or the like. So far as the functions of my invention are con- .cerned in giving the abrasive rim its desired support, the particular composition of the rim is of no great importance. For certain types of cutting and grinding operations an abrasive bonded with a resin such as a phenolic synthetic resin is preferred. It is one of the features of my invention that it gives adequate support to a rim of that character which is, in itself, relatively fragile. Usingsuch a bond, the nature and proportion of abrasive, the nature and proportions of filler materials and of secondary abrasive fillers may be chosen to suit the performance desired. However, my invention performs its useful function with respect to a bonded rim of any character which needs lateral support and which cannot be integralized with the central disk.

It will be seen that the notch walls give rigid lateral support to the rim lugs because the surfaces of the notch Walls are not straight as viewed in any section such as that of Fig. 6-a section in a plane perpendicular to a radius through the notch. Although the concave formation is at present preferred and has advantages, any form of notch wall non-straight in such a plane, or transversely non-straight, will perform the lateral supporting function at least to some extent. For instance, they wrinklings 261) may suflice, or a general roughness of surface.

I have said that it is immaterial whether the abrasive rim thickness is made equal to or greater than the peripheral thickness of the metal disk. Although ordinarily I mold the abrasive rim to a slightly greater thickness as I have described, the rim in use wears down in thickness to the thickness of the disk periphery, and the performance of the wheel is not decreased in efficiency by that fact.

I claim:

1. A thin abrasive wheel of the type comprising a non-abrasive center structure and a peripheral abrasive rim of annular form supported thereon, characterized by the center structure being composed solely of a thin circular disc provided around its periphery with a spaced series of outwardly facing open-mouthed notches of substantially V-formation having an angle of not less than approximately thirty degrees and extending through the disc from side to side to provide a series of pairs of opposed surfaces, the annular rim being of bonded abrasive circumferentially surrounding the disc and having its greatest axial thickness not more than substantially one-and-a-third times that of the disc, at least the major radial portion of the abrasive being positioned outwardly of the disc periphery and its inner annular edge terminating at least at such point that the rim will not extend inwardly to any substantial distance-beyond the inner ends of the notches, the abrasive rim including integral V-shaped inward exten- 4 aeaeaze sinus t0 provide a settles Qi pairs of surfaces in.- timately engaged with: the series oi penis 012 cm surfaces formed by the walls of the. disc notches, the. pairs of surfaces of one of said series, being: concave between the radial faces of the disc. to. support the rim against lateral pressure. and all of the surfaces of said two series 01 surfaces being substantially symmetrical with respect to ev central plane biseeting the same and paraklel to. the. radial faces of the disc;

2;, A thin abrasive wheel of: the character defined in claim 1, wherein the series of. pairs: of opposed surfaces of the notch walls are concave between the radial faces of the disc.

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