US2173461A

US2173461A - Grinding wheel and method of grinding

Info

Publication number: US2173461A
Application number: US48181A
Authority: US
Inventors: Herbert W Wagner; Kenneth F Whitcomb
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1935-11-04
Filing date: 1935-11-04
Publication date: 1939-09-19
Anticipated expiration: 1956-09-19

Description

p 19, 1939- H. w. WAGNER -r AL 2,173,461

GRINDING WHEEL AND METHOD OF GRINDING Filed Nov. 4, 1935 4 Shouts-Shoat 1 E 600- in H 4ooo i k i Distance from Center of Wheel, inches 5 e 2 16000- E a;

f-s a :0 17000 0) g 16000- 3 Q 2 .s 2 P15. 2-. 3 3 14000- 3 F13. 3. E

L 130 3 0 24 0010121410 62 Hole Diameter inWheeLinches g g grwmmfl 3 8 -HER8ERT W Mews/P urface Speed. f. .m KENNETH F. W-n-rcoma witness f P 19, 1939- H. w. WAGNER ET AL 2,

GRINDING WHEEL AND METHOD OF GRINDING Filed Nov. 4, 1935 4 Shasta-Spent 2 Fig. 4.

I For wheel with Thole :5 1100 For Wheel having holes 1360-- 0 a 0 1% 680 wheel having no hole ii i g, 210 Pg. 8 a in o II 1 2 U a 4" 5 II Distance between center ofwlml HERBERT l/V WAGNER and centers of mounting holes KENNETH WHITCDMB 4 Sheets-Sheet 3 H. W. WAGNER El AL GRINDING WHEEL AND METHOD OF GRINDING Filed Nov. 4, 1935 Fi g. 5.

a a J\ m 1 awe rm HERBERT W WAGNER KENNETH'F WHITCUMB 6/ mmy 0 2 $1 Sept. 19, 1939. H. w. WAGNER ET AL GRINDING WHEEL AND METHOD OF GRINDING 4 Sheets-Sheet 4 Filed NOV. 4, 1935 HERBERT W. WAGNER KENNETH I- WHITCOMB A A a 4 m w /7 1/ 4 1 I Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE GRINDING WHEEL AND LETHOD OI GRINDING ohuse to Application November 4,.1935, Serial No. 48,181

SCIaima.

This invention relates to a grinding wheel and methods of grinding, and particularly to grinding wheels made of abrasive grains bonded together by vitrified ceramic materials, rubber, shellac,

r resin, the artificial resinoids, etc.

When a grinding wheel of a.given mass is retated, each element of the wheel has a certain centrifugal force which acts outwardly. This force depends upon the speed at which the wheel 1 is rotating, the distance of the element from the center of the disk and the mass per unit of volume of the wheel. This centrifugal force sets up stresses in the rotating wheel and so causes strain and deformation which tend to break the 15 wheel when it is rotated at a certain maximum or breaking speed. Similarly. the act of grind ing on the periphery of the wheel causes frictional heat to be generated, and this results in a temperature gradient existing between the periphery go of the wheel and the center which also sets up disruptive stresses within the wheel. Hence. both the centrifugal force and the frictional heat combine to cause wheel breakage. Because of these two factors, each type of grinding wheel is limited in its use to a certain standard wheel speed. which should not be exceeded because of danger to the operator, although the emciency of a grinding operation is increased by raising the wheel speed.

so The primary objects of this invention are to increase the standard grinding speed for a given type of wheel by strengthening the wheel so that it will have the same factor of safety at the higher speeds, and to provide a grindlng wheel struc- 3 ture which may be rotated rapidly and subjected to a high frictional heat duringa grinding operation without danger of breakage of the wheel, to provide mountings for such a wheel which do not materially weaken the same; as well as to provide .1 a method of grinding which is more efficient than has been heretofore had by use of the standard grinding wheel speeds. Other objects will be apparent in the following disclosure.

The stresses within a grinding wheel due to the centrifugal force and to frictional heat are both maximum at the center of the wheel. The standard grinding wheel has a hole at its center for mounting the same on an arbor or spindle. The principal stresses within the wheel are in two ditn rections, radial and tangential; but at the edge of the hole of a rotating wheel, the radial stress is zero. Hence, the maximum stress occurring at the edge of the hole is tangential in direction. When this tangential tensional stress equals the tensile strength of the material, then a radial crack starts at the edge of the hole and grows until the periphery of the wheel is reached. This happens whether the stress be due to centrifugal force or to heat applied at the periphery of the wheel. and the stresses due to these two forces I combine by simple addition to cause wheel breakage.

For a given speed of wheel rotation. as the side of the hole at the center of the wheel is increased in diameter. the tangential stress at the edge of the hole increases. Hence, the larger the hole, the more likely the wheel is to break at a given speed. As the hole size decreases, the tangential stress at the edge decreases until, when the hole size becomes zero, this tangential stress becomes equal to the radial stress at the center of the wheel. The tangential stress in a no-hole wheel is one half of that present at the edge of a small central hole. The resultant of combining the radial and tangential stresses at the center of a so wheel of a homogeneous isotropic structure which has no central hole is about 71% of the stress at the edge of the hole in a wheel having a very small central hole; or the tangential'stress at the edge of the small central hole is about 41% greater than the resultant stress at the center of a wheel having no central hole. Thus, since the stress varies with the square of the speed, such a wheel of homogeneous isotropic structure which has no central hole will theoretically stand an 80 increase of about 19% in breaking speed above that of a wheel having a small central hole. In actual grinding practice. the real increase in breaking speed is however dependent upon various non-homogeneous structural features of the as wheel, as aflected by the type of bond, the type and size of the grain, the spacing of the grains or wheel porosity and the physical condition of the bonded structure. Hence. as discussed below, the breaking speed of a grinding wheel may be increased 30 or more per cent by leaving out the central hole.

This invention therefore contemplates fortifying the grinding wheel by omitting the central hole thereof and providing bonded abrasive ma- 45 terial in that position of maximum stress. and of rotating such a wheel at a speed which exceeds the fastest rate formerly considered safe for a wheel having a central hole and thereby grinding more efllclently and rapidly. Furthermore, structures have been provided which enable such a wheel to be satisfactorily mounted for a high speed grinding operation. The invention also contemplates a multiple zone wheel having a strong central zone adapted to provide strength as where it is needed in the wheel and which is so mounted that the mounting structure does not materially weaken the grinding wheel. A wheel satisfying the various features of this invention may have no perforations therethrough but have a uniform abrasive structure in its central zone, or it may have small holes arranged concentric of the axis but remote from the center of the wheel which are of such size and so located that the wheel is not materially weakened in its structure by the presence thereof.

Referring to the drawings. which illustrate various embodiments of this invention:

Fig. 1 shows various curves which serve to compare the stresses within two rotating wheels, one of which has a central mounting hole and the other none;

Fig. 2 shows curves illustrating the wheel breakage speeds of a given type of grinding wheel as compared with a wheel of an isotropic homogeneous structure;

Fig. 3 shows by means of a curve how the rate of grinding a piece of work increases with the wheel speed;

Fig. 4 is a vertical and partly broken away which illustrates a grinding wheel having no central hole but small mounting holes located remote from the center. together with a structure designed for mounting the same on a grinding spindle;

Fig. 5 shows a side view of a grinding wheel and the relative locations and sizes of the mounting holes;

Fig. 6 shows a curve which indicates the manner of determining the locations of the mounting holes;

Fig. 'i is a side view of a two-zone wheel having no center hole but a series of mounting holes concentric with its axis;

Fig. 8 shows in a fragmentary vertical elevation, partly in section, one manner of mounting a wheel having no hole therethrough;

Fig. 9 shows in fragmentary section the shape of a grinding wheel having beveled clamping shoulders on opposite sides thereof, but no perforations therethrough, together with a diagrammatic showing of clamping flanges adapted to wedgingly engage and support the clamping shoulders of the wheel;

Fig. 10 is a sectional view showing another manner of mounting a no-hole wheel;

Fig. 11 is a similar view of a modified form of wheel;

Fig. 12 is a fragmentary section showing a wheel cemented to a supporting member;

Fig. 13 is a plan view, broken away, of a wheel reinforced at its center by a supplemental bond;

Fig. 14 is a sectional view showing how the supplemental bond may be applied to the wheel of Fig. 13; and

Fig. 15 shows how a vitrified wheel may be strengthened during the firing operation.

Referring to Fig. l, the curves show the locations of the stresses within a no-hole wheel and a wheel with a central hole which are set up by centrifugal force. The stresses due to heating the wheel at the periphery follow the same principles. These curves are plotted on a u-axisgiving the stress in pounds per square inch and an :r-axis showing the distance from the center of a wheel in inches. The wheels tested each had diameters'of inches and were rotated at 3720 revolutions per minute. The stress distribution curve A shows the distribution of the tangential stress within a wheel which has a central mountelevation partly in section ing hole of 1;. inches diameter. The curve B shows the distribution of the radial stress within the same wheel. The curve C shows the vectoral sum of the curves A and B and thus indicates the distribution of all of the stress found in the wheel having a central hole. Similarly, the curve D shows the tangential stress distribution within a wheel which has no central hole, while the curve E shows the radial stress within that same nohole wheel. The curve 1'' shows the vectoral sum of the tangential and radial stresses in the nohole wheel. Considering the curves C and F, it will be readily apparent that the no-hole wheel has a total stress at its center of approximately 1200 pounds, while the wheel with a small central hole has a stress of about 1700 pounds at the edge of the hole. It will also be noted that the curve C slopes steeply near the hole in the wheel, thus showing that the hole is a dangerous factor in wheel breakage. These curves give the distribution of stress within a homogeneous isotropic substance, such as Celluloid, used for an experimental wheel.

The speed at which a wheel breaks varies wideiy, depending upon the structure of the wheel as well as such other factors as the hole size. For example, a series of Alundum wheels of 4611! grade, as made by the puddled wheel process to a structure of about 9, were tested to determine the variation in breaking speed with the hole diameter, and these results were compared with those for another wheel which followed the theoretical values above discussed. As shown in Fig. 2, a wheel structure which conforms in its behavior substantially with an isotropic homogeneous Celluloid wheel may have the breaking speeds indicated by curve A for difierent central hole sizes. The curve has been plotted on a u-axis showing the speeds in surface feet per minute at which breakage occurs for the wheels of diflerent hole diameters, indicated on the :r-axis. The nonhomogeneous 48M wheels of 20 inches diameter however followed the curve B and so departed widely from the theoretical values of curve 3.. The no-hole wheel will have a breaking speed of at least 50% more than that of the 46M whee having a 16" hole.

Fig. 3 shows how the rate of grinding is increased with the rotational speed of the wheel. The curve represents the results of grinding with an Alundum vitrified grinding wheel 16 inches in diameter and 2 inches thick. The wheel had a grade of Q and a grain size of 16 on the Norton scale. The operation was that of snagging cast steel. It is readily apparent from the drawing that as the wheel speed increased from about 5000 surface feet per minute to 10,000. the number of pounds of steel removed per hour from the test bar increased from 3.7 to 7. This represents an increase of about 89% in the rate of production. Hence, an increase of grinding wheel speed is highly desirable. if a safe grinding wheel structure can be provided for the pu p se.

The structure of the grinding wheel may be made in accordance with the standard methods of manufacture. except as regards leaving out the central hole of the wheel. The wheel comprises abrasive grains. such as crystalline alumina, silicon carbide, boron carbide or diamond of suitable grit sizes, which are cemented or bonded together by standard bonds. such as vitrified ceramic materials, vulcanized rubber, heat set resinoid, shellac. resin, sodium silicate, etc. The invention is particularly applicable to the vitrified wheels because of their being relatively fragile although of great commercial value. The vitrlflable materials comprise ball clay, slip clay, feldspar, kaolin, flint and various other materials compounded in suitable proportions which are intermixed with the abrasive grains in a plastic condition for moldng the wheel shape. The molded wheel is fired in a ceramic kiln at a suitable temperature to mature the bond to a glassy or porcelanlc condition. Rubber and resinoid wheels are heated at lower temperatures to vulcanize the rubber or to convert the plastic resinoid to a hard infusible body. Various well known procedures are adopted for the purpose of setting the particular bond chosen. The primary difference over the prior art lies in so shaping the wheels as to omit from such wheels the central spindle hole. If outer mounting holes are provided, these may be made either in the plastic moldable mass prior to heat setting the bond or by drilling the hole in the final wheel structure after the bond has been metured or heat set. Various expedients may be adopted for this purpose.

By such methods, we provide a wheel having no central hole i. e.. having a continuous imperforate structure throughout the central zone of high stress, without regard to the natural porosity of the wheel. It may be mounted on a grinding wheel spindle in various ways. As shown in Figs. 4 and B, the wheel ll of bonded abrasive grains is clamped between two supporting plates i I and If. These are in turn mounted for rotation with the grinding wheel spindle it which is driven by the pulley i8 secured thereon by means of the key It. flange on a sleeve II which is keyed on the tapered end of the spindle II and secured thereon by the nuts ll, in accordance with standard procedure. The spindle mount may be of any suitable structure and arrangement, as is well understood. In the present case, the spindle H is mounted in bearings located in the boxes 20 arranged on opposite sides of the pulley and which are in turn supported on the wheel slide ll of a standard Norton grinding machine.

The grinding wheel I! is held between the clamping plate Ii and the outer face of the clamping plate I! by means of screw threaded bolts passing therethrough. The clamping plates are preferably cut away at their central portions so as to engage the wheel at points remote from its center and preferably as near the grinding zone as is possible, so as to grip between them a large portion of the wheel and thus hold it in position in the event that the wheel breaks under the stresses of the grinding. Soft paper blotters 22 are preferably located between the clamping plates and the comparatively fragile material making up the grinding wheel structure. Strips of soft metal, such as lead, or rubber may be used there instead. and they may be fastened either to the wheel or to the inner faces of the clamping plates as desired. In order that the plates may be drawn'towards the wheel, the latter is provided with a series of mounting holes 24, and the clamping bolts 20 pass through these and suitably arranged holes in the plates. It is preferred that the mounting holes 24 within the wheel be somewhat larger than the bolts 25 so as to avoid any lateral strain on the edges of the holes in the wheel. The nuts 21 on the ends of the bolts I! serve to draw the plate H tightly against the outer face of the wheel and in turn clamping the wheel firmly and rigidly against the outer face of the clamping plate I! as will be readily apparent by inspection of the drawings.

The mounting member I! is shaped as a.

A suitable number of the mounting bolts are emplayed, and it is desirable that they be located at points remote from the wheel center.

A primary feature of this invention involves the size, the number and the locations of these mounting holes 24. It is desirable to satisfy insofar as possible the following conditions: Each of these holes should be so located and of such a size that the stress within the grinding wheel material at the edge of each hole is less than the stress would be at the edge of a small central hole in a standard type of grinding wheel. This stress at the holes edge should be no greater than the maximum stress to be found at the center of a wheel which has no hole. The mounting holes are preferably located inside of what may be termed the discarding zone of the wheel. The holes should be of sumcient size to take bolts of adequate strength; but they should be so small that the stresses around them will be localized to small zones. These localized zones should a not overlap nor extend to the periphery of a single zone wheel or the boundary between the zones of a composite wheel. If these holes are therefore so spaced that the localized zones of stress do not overlap, then any reasonable number required for mounting may be employed. There are usually from two to eight of these holes, depending largely upon the size of the wheel and the strength of the bolts. For example, as shown in Fig. 2, eight steel bolts may be mounted in inch holes in a wheel over 16 inches in diameter without changing the stress conditions materially within the wheel. These holes are each preferably equidistant from the adjacent holes and arranged concentric with the wheel axis.

One manner of locating these mounting holes may be accomplished by what is termed the photoelastic method of analysis of a similarly shaped wheel of transparent material. For instance, if the grinding wheel is to be made 20 inches in diameter and two inches thick, then a model is made of Celluloid of twenty inches in diameter and V inch in thickness and its stress characteristics are analyzed. This photoeiastic analysis of stresses is an optical method based upon the double refraction of the transparent material. When the transparent Celluloid model is rotated in beams of plane and circularly polarized light and is thus stressed by the centrifugal force of rotation, the directions as well as the magnitudes of the two principal stresses within the wheel can be determined. By making due allowance for the respective diametrical dimensions and the weights per unit of volume of the Celluloid model and of the particular grinding wheel considered, the photoelastic results may be translated into experimental values for the grinding wheel. As shown in Fig. 6, curves are plotted on an aw xis giving the distance from the wheel center to the cenfers of mounting holes located at various points and a g-axis giving the stress in pounds per square inch for a Celluloid wheel of 20 inches diameter revolving at 3720 revolutions per minute. The values thus obtained show that the stress is 1440 pounds per square inch at the edge of a central hole one half inch in diameter. The theoretical value for a wheel having a 2 inch hole is about 1700 pounds. L kewise. it is found that the stress is 1200 pounds per square inch at the center of a wheel having no central hole therein, this stress being approximately 83% of that of the wheel having a hole of k inch size. This experimental 83% compares with the 71% calculated by theory and obtained by actual tests of a fairly homogeneous wheel. Actual speed tests of plaster wheels 12" in diameter without a central hole as compared with similar wheels having 2 holes show that the breaking speeds were increased 19% by leaving out the hole. This difference in breaking speed shows that for the same speed the maximum stress in the no-hole wheel was 71% of that in the wheel having a central hole. The curve gives approximately the value of the stress to be found at the edge of a small mounting hole of ti inch diameter for the various locations of the hole as measured on the :r-axis.

As above stated, the ideal wheel is one in which the stress at the edge of this A inch mounting hole is no greater than or is substantially equal to the stress to be found at the center of a no-hole wheel, so that the wheel will break at the center as soon as it breaks at the edge of a hole. Hence, the point D at which the curve intersects a horizontal line through the no-hole wheel stress of 1200 pounds gives the desired location for the mounting hole. This intersection D is located at about 40% of the distance outwardly from the center of a wheel of 10 inches radius. Hence, the holes in a grinding wheel of the same large diameter are to be similarly positioned at four inches from the center or 40% of the radial distance from the center. Similar analysis of the mounting hole sizes indicates the desirability of making the holes not over A inch in diameter in a wheel of at least 16 inches diameter. Test wheels were run with 2, 4 and 8 holes of b inch diameter arranged 4 /2 inches from the axis, the speed being 3720 R. P. M. The stress at the edge of the holes in each case measured 1100 lbs. per square inch or less than the stress at the center of a no-hole wheel. Tests with inch holes gave a stress of 1540 pounds per square inch. Hence, if the holes are increased to 3/ inch diameter, about half of the advantage over a central hole wheel is lost. The bolts may be inch or "A inch in diameter for a half inch hole.

If desired, the hole may be lined with a bushing, such as by casting Babbitt metal therein or vulcanizing a layer of rubber and sulfur thereon, of such a size that the bolts will slidingly fit therein and accurately center the wheel. The rubber will permeate the pores of the wheel and make a strong union therewith and so strengthen the wheel in the localized zone of stress. A wheel thus provided with small widely spaced mounting holes will break no sooner at the mounting holes than at the wheel center when subjected to centrifugal force. The some considerations apply to the breaking force resulting from heating the periphery of the wheel, and the mounting holes will likewise be located at about 40% of the radial distance from the center. Wide variations in this location are of course permissible, since tr e hole location may be governed by other fach rs involved in the use of the wheel.

We may further strengthen the wheel by other means which supplement the above described features. For example, the wheel may be provided with a central zone of stronger material, such as is disclosed in the application of Whitcomb and Wagner, Serial No. 678,816, flied July 3, 1933. The stronger inner zone may be formed by impregnating the pores in the central portion of a standard one zone wheel of uniform structure with a resinoid or other material which may be beat set in position within the wheel pores. Likewise, such a wheel may be made up of two annular zones of different structures, in which the outerv zone has a desired structure for the grinding operation, and preferably of uniform volume percentages of bond, grains and pores throughout, and the inner zone is made of such composition and structure that it has not only a higher strength, but such a ruptural deformation and modulus of elasticity that the composite wheel will withstand a greater stress due to rotation or frictional heat than will a wheel made wholly of the outer zone composition and structure. In such a wheel, the moduli of elasticity of the two zones may be substantially equal and the materials are so chosen as to quantity and kind that the drying and firing shrinkages do not cause detrimental strains or cracks at the Junction between the two zones. For example, as shown in Fig. '7, such a wheel may comprise an outer zone made of vitrified ceramic bonding material and suitable abrasive grains cemented together thereby and an inner zone I! likewise made of abrasive or other granular material cemented together by vitrified ceramic material, but in which the grains are much smaller or the bond is present in a larger amount in the inner than in the outer zone, so that the central zone I! is the stronger of the two. The outer zone may be made, for example, of crystalline alumina abrasive grains of 16 grit size bonded by means of 2% ounces of a standard ceramic bond per pound of the abrasive. The central zone may be made of similar abrasive grains of 36 grit size, and 3% ounces of the grain bond per pound of abrasive may be employed. when these two mixtures have been molded together into the annular shapes illustrated and fired in a ceramic kiln to mature the bond, the inner zone will be materially stronger than the outer.

As a further example, the outer zone may be made of crystalline alumina abrasive of between 30 and 36 grit size, and 3% ounces of bond to the pound of abrasive may be employed. In the inner zone, the abrasive may be made up of a mixture of one half of 60 grit, one quarter of '10 grit and one quarter of 80 grit size, and the ceramic bond may be used in the proportion of 3 /2 ounces per pound ,of abrasive.

The'lnner zone will be of such size radially that it will receive a considerable proportion 01 the stress within the wheel, and preferably extend to such distance from the center that the mounting holes may be located as above defined within this inner zone. That is, the mounting holes of the wheel, as above defined, will be located at approximately 40% of the distance outwardly from the center, and the material of this inner zone will extend sufficiently far beyond these holes so that the localized zones of stress around each of the mounting holes will be located substantially wholly within this inner zone material. It is satisfactory to locate these holes at least inch inside of the periphery of the inner zone. Thus, we may produce a wheel which is far stronger than either the one zone no-hole wheel or the two zone wheel having acentral mounting hole, whereby the wheel will stand a very high rate of rotation as well as a high temperature gradient from the periphery to the center of the wheel.

In order to show the superiority of this two zone no-hole wheel over the standard wheel, two wheels were made as follows: A two zone wheel was made with the outer zone of crystalline alumina abrasive of 36 grit size and bonded to what is known as grade J on the Norton scale of hardness. This outer zone employed of an ounce of standard ceramic bond per pound of abrasive. The inner none without a central hole was made of 60 grit size of the same abrasive and with the same bond in the proportions at one ounce oi bond per pound of abrasive so that the grade of the central zone was grade K. In that wheel the inner zone had a radius oi 4% inches and the outer periphery of the wheel a radius of ten inches. I'bur ,i-inch holes were located four inches from the center and 95 inch bolts employed in mounting the wheel. l'br comparison. a single zone wheel with a 3-inch central hole was made to grade J of 38 grit else so as to correspond with the structure of the outer zone of the first wheel. This single sone wheel brohe at the speed of 11,890 surface feet per minute. while the two sone wheel broke at a speed of 18,850 surface feet per minute or approximately 58% higher breaking speed. An average increase of 40 to 50% in this breaking speed is thus easily obtained.

This no-hole wheel may also be made without any mounting hole. Such a wheel may be cemented or bolted to a supporting plate. or it may be mounted between clamping flanges which engage its opposite sides. As illustrated in Fig. 8, the wheel may have one iiat aide II and a tapered hub I! on its opposite side which are adapted to be engaged by the clamping plates M and I respectively. Although an intermediate layer of blotting paper may be used, each of these plates is shown as provided with an inner layer of soft Babbitt metal or bed. These layers 48 and 41 serve to transmit the thrust from the iron plate to the fragile wheel structure. The annular face or the gripping metal it on the plate It lies in one plane and thus engages the plane side of the wheel, while the clamping surface of the metal I! on the plate II is beveled to correspond with the bevel of the wheel hub 42. By forcing the two plates I4 and 4! towards each other. the wheel is wedgingly engaged between the clamping elements 44 and ll.

The plate 45 is suitably mounted on the grinding wheel spindle '0 which is rotated by means of a belt and pulley Ii keyed to the spindle or any other suitable mechanism. The-spindle Ill is in turn mounted in suitable bearings and the latter carried by means of the wheel slide 52 which may be or any suitable and standard construction. In order that the two plates may be thrust towards each other to grip the wheel therebetween; an arm II is pivotally mounted on the pin II carried by ears I6 projecting from the wheel slide 52. The arm 84 is suitably adjusted in position by means of the set screw II which projects through the lower short end SI of the lever arm and engages 9. depending portion ll of the wheel slide 52, whereby the arm may be suitably moved at its upper end inwardly towards the grinding wheel and there be locked in position by means of the adjusting screw 81.

The plate II is carried on a sleeve II which slides within a housing or outer sleeve 8!, the latter being pivotally mounted on a yoke BI on the upper end of the lever arm ll. A set of ball bearings 60 of standard construction are arranged within the housing It and held in place by means of the cap BI fixed thereto by means of suitable screws. The ball bearings comprise two annular races carrying the balls and surrounding a pin III which projects within the hollow sleeve and carries a helical spring 1! therearound. This spring presses at one end on the plate 44 and at the other end on the flange I! on the pin which in turn presses on the races of the bearings. A screw II in the housing I! having its inner and riding within a slot in the sleeve It holds the parts together but permits movement of the other member 02 and thus serves toimpose such force upon the spring as will hold the clamping plate 44 securely against the side of the wheel and in turn thrust the latter securely within the tapered seat of the clamping plate ll. The thrust thus imposed upon the wheel spindle III is taken up by another set of thrust bearings ll mounted upon a reduced end of the spindle and held against the shoulder II thereon by means of the cap plate II. The thrust of the plate ll is transmitted to the spindle It through the flange ll secured on the latter.

As shown in Fig. 9, the wheel may also be made with two tapered hubs, one on each side, whereby the clamping plate It may be the same as the plate above described. 'Ihe construction shown in Fig. 9 may otherwise be the same as indicated in Fig; 8.

Various other constructions may be adopted for the purpose of mounting a no-hole wheel on a spindle for rotating it at a high rate. This may take the form shown in Fig. 10 in which the wheel I! has an annular groove or a series of spaced holes 84 arranged concentrically of the wheel axis and preferably spaced therefrom in accordance with the principles above specified. These holes are so shaped and arranged that they may carry the heads of mounting bolts ll cemented therein, the bolts projecting laterally from the wheel parallel with the wheel axis. The holes in the wheel may be undercut as illustrated, so that when the bolts are imbedded in cement, such as sulfur, Lavasul, resinoid, Babbitt metal, etc.. which is hardened in place. they will be rigidly secured in position. These bolts may then be mounted on a suitable supporting plate such as the flange I! shown in Fig. 4 and secured thereto by suitable nuts. If the mounting holes .4 tend to weaken the given wheel structure too much. then the side 0! the wheel may have a central hub ll of suitable shape within which the bolts 85 may be mounted so that the bottoms of the mounting holes are not inside of the plane of the wheel face 81, as shown in Fig. 11.

A further type of mounting for a no-hole wheel is illustrated in Fig. 12. In accordance therewith, the grinding wheel 80 is secured to a metal or other rigid plate ll by means of a layer of vulcanized hard or soft rubber 92. The plate 9i corresponds in diameter and location substantially with the mounting plates above described and indicated in the drawings. The plastic rubber may be placed between the side of the completed grinding wheel and the iron plate 0! and then subjected to heat and pressure to cause the rubber to stick to the iron plate and to permeate the surface pores of the wheel where it is vulcanized in position. Various expedients may be adopted for the purpose of increasing the cohesion of the rubber cement with the wheel face and the metal plate. The metal plate OI may be mounted on the flanges 83 oi a supporting hub Bl similar to that shown in Fig. 4. For this purpose, the bolts 06 may have their heads countersunk within the iron plate ill so that they will not interfere with the rubber cement which holds the wheel in place. Various other constructions may be adopted for the purpose. Likewise, a resinoid cement may be adopted for this purpose, such as the unconverted Bakelite phenol aldehyde condensation product which is applied in a plastic condition between the mounting plate and wheel and is set to a hard infusible condition by means of heat,

as is well understood in the art. It will also be appreciated that the various constructional features herein described will apply to the various types of no--hole wheels, whether of a single zone type or of a multiple zone type, and that the various types of abrasives and bonds may be used with every different type of no-hole wheel, as is determined by the particular needs of a given grinding operation.

Another way of strengthening the no-hole wheel involves impregnating the central portion of the wheel with a strengthening bond or cement. As indicated in the Fig. 13, a porous wheel of uniform structure which has no central hole may be made of desired grade and structure in accordance with the prior art methods but may be provided with mounting holes as indicated above. The central zone 98 of this wheel is then impregnated with a strengthening agent which is capable of filling the pores of the wheel sumciently and oi adhering to the surfaces there-. of so as to materially aid the wheel in withstanding the stresses of the grinding, but the outer zone 01 is left unfilled. f the various materials which may be employed for that purpose, vulcanizable rubber and a plastic unconverted resinoid of a type of the Bakelite phenolic condensation product are preferred, although other materials such as rosin, sodium silicate, and other well known cementitious materials or grinding wheel bonds may be employed for the purpose. The wheel may be impregnated with this material by any suitable procedure. For example, as indicated in Fig. 14, the wheel may have annular plates 98 and a ring 99 mounted so as to enclose the outer grinding zone 91 which is not to be impregnated to any material extent. Then the strengthening material may be flowed or forced into the pores of the wheel in the central zone thereof. For instance, melted rosin or a liquid resinoid or sodium silicate may be poured onto the two wheel sides and allowed to permeate the pores by the natural capillary action. A vacuum may be applied to the wheel face to cause the material to permeate the same. If rubber is used, a layer of the plastic rubber compounded with sulfur in the right proportions may be forced under pressure and heat into the wheel faces and thus caused to permeate the same. The rubber may also be employed as a solution or in any other suitable form for the purpose. After the strengthening material has filled the pores of the central zone sufhciently, it is caused to set to a hard condition, as by vulcanizing the rubber compound or converting the resinoid to the infusible condition by the application of suflicient heat for the purpose. The wheel may be preheated prior to the introduction of the filling material in order to cause it to flow more readily, or one may preheat only the inner zone by means of a flame or by heating the central zone within an oven while the outer zone is suitably insulated by thermal insulation. Other expedients may be adopted for the purpose. By this means, the vulcanized rubber or the resinoid or other medium employed is caused to grip the pore surfaces and to be sufficiently integral therewith so that it aids the wheel materially in resisting the stress set up by centrifugal force and the heat of grinding. Thus the wheel is strengthened in that imperforate continuous zone where the maximum stresses are present. This internal strengthening zone may be sufficiently wide so that it will receive the major portion of the stress, but the rosin, etc. should preferably not extend materially into the anaacr zone used for grinding. As shown in Fig. 13, the zone may extend throughout approximately 40% or the radial distance within the wheel.

Likewise, a vitriiied grinding wheel made of abrasive grains cemented together by vitrified ceramic bonds may be so made as to have no hole in the central stress zone, but the wheel may be greatly strengthened in this central zone by applying what is termed a reversed strain with in the wheel structure during the act of cooling the wheel from the fluid or plastic condition of the bond produced by heat maturing the bond. This may be accomplished by various expedients and particularly by the method described and claimed in the U. S. patent of Wallace L. Howe 2,034,721 dated March 24, 1936. For example, the wheel may be mounted on a flat refractory plate and there supported while fired within a ceramic koln. The wheel may be covered with refractory clay or other suitable heat insulating material in the manner shown in Fig. so that the clay is increasingly deeper going from the center of a wheel outwardly towards its periphery. Thus the wheel will radiate heat more quickly at the central zone during the cooling operation than it will on the outer portion and the center will set first from a plastic to a solid condition and thereafter the still plastic outer zone will shrink as it sets and so impose a compressional strain upon the central zone of the wheel. This strained condition within the wheel material tends to resist the stresses set up by rotation and heat during use of the wheel.

It will now be appreciated that by means of this no-hole wheel structure, one may grind work at a far higher grinding speed than was heretofore attainable by means of standard grinding wheels having central holes and thus obtain greater economy in the grinding operation. That is, the wheel may be run safely without endangering the operator or spoiling the work and be cause of the higher peripheral speed, it will remove the material from the work at a more rapid rate. Hence, where wheels have been run at a standard rate of 6000 surface feet per minute in the past, that wheel speed may be now increased safely to as much as 50% or higher.

a It will also be understood that the structure of the wheel in the grinding zone will be made according to the requirements of any particular grinding operation. At the higher speed, the wheel tends to heat the work to a higher degree. If this heat is excessive, with a given grade and structure of a wheel, one may employ a wheel of softer grade or a more open structure. Also, if the higher wheel speed causes the wheel to dull more rapidly, one may increase the rate of feeding the wheel into the work, Oi he may use a softer grade of wheel or one of a more open structure, i. e. greater porosity. The various principles of a grinding wheel which are well known to those skilled in the art may otherwise be employed in the operation and use of a high speed no-hole wheel of the types here described. This invention therefore contemplates grinding a work piece with a wheel'having an imperforate center in its zone of maximum stress and which is rotated at a speed far in excess of the safe speed of a central hole wheel or the same size grade and structure, such as 15 to 50% 01- more above the old standard speed, and particularly by increasing the rate of feed over that used with the standard central hole wheel or by emplaying a wheel of a softer grade or more open structure.

In carrying out this method. the work may be mounted for rotation about its axis or it may be held non-rotatable and either reciprocated or revolved past the wheel face, or it may be otherwise held in grinding contact with the wheel face. Likewise the grinding wheel may be so shaped and mounted that it will grind on its peripheral lace or on a flat side race. The wheel may there- !ore be shaped as a disk or in any other form which is found best suited for a given grinding operation. The principles of this invention apply irrespective of the shape, kind. typ size or other physical characteristics of the wheel as well as to the various wheel structures made by using the diflerent type 01 abrasive and or bond in any suitable proportions and structural ar-' rangement.

We claim:

1. A grinding wheel comprising abrasive grains united by a bond into an integral wheel structure which is continuous and imperiorate at the wheel center, said wheel being over 16 inches in diameter and having a plurality small mounting holes arranged concentric with the wheel axis and remote therefrom, each or the molmtlng Patent uo. 2,175',h61.

holes being not over 56 inch in diameter and subfrom the center 01' the wheel towards the periphcry and not over eight in number. whereby the wheel may be secured to amounting plate by bolts which are so located that the mounting holes do not materially weaken the wheel structure.

2. A grinding wheel according to claim 1 in which the central acne oi the wheel is impregnoted with a material which gives it additional strength.

3. A grinding wheel comprising abrasive grains united by a bond into a required grinding structure and which is continuous and imperiorate wheel being impregnated with a strengthening material within the central zone of the wheel and said zone being provided with mounting holes of such sizes and locations that the stress throughout the central high stress zone, said due to centrliugal'torce is no greater at the edge or each hole than the stress at the wheel center.

:loa' in W. WAGNER. KENNETH F. WHITCOMB.

CERTIFICATE OF coRREcrIoN September 19, 1959.

HERBERT w. WAGNER, ET AL. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page'l, sec- 0nd column, line 20, claim}, strike out the words "throughout the central high stress zone, said" and insert the same after "imperforate" in line 15, same claim; andthat the said Letters Patent shouldbe readw ith this correction therein that the same may conform to tho record of the case .in

l the Patent Office.

Signed, and sealed this 5th day or December, A. D. 1959.