US3777443A - Segmented griding wheel - Google Patents

Abstract

A segmented grinding wheel assembly particularly suited for high speed operation. The disclosed embodiments comprise wheel members having an outer peripheral recess in which grinding segments are positioned to define the grinding or working portion of the assembly. The recess and segments are related so that the segments are held in the recess by compressive reaction forces produced during wheel rotation. Additionally, the specification discloses an arrangement particularly adapted for supplying cooling or lubricating fluid to the wheel periphery. The arrangement comprises an inwardly open, circumferentially extending fluid receiving trough carried by the wheel. The trough is connected to the recess by generally radially extending passages such that during wheel rotation fluid moves outwardly to the recess and between the segments under the influence of centrifugal force.

Description

United States Patent [1 1 Shaw [ SEGMENTED GRIDING WHEEL [76] Inventor: Milton C. Shaw, 132 Maple Heights Rd., Pittsburgh, Pa. 15232 221 Filed: Jan. 24, 1972 [21] Appl. No.: 220,521

Related U.S. Application Data [62] Division of Ser. No. 28,721, April 15, 1970, Pat. No.

[56] t References Cited UNITED STATES PATENTS 3,144,739 8/1964 Brutvan et a1. 51/206.5

Primary Examiner-Othell M. Simpson Attorney-Fay, Sharpe & Mulholland Ill Dec. 11,1973

5 71 ABSTRACT A segmented grinding wheel assembly particularly suited for high speed operation. The disclosed embodiments comprise wheel members having an outer peripheral recess in which grinding segments are positioned to define the grinding or working portion of the assembly. The recess and segments are related so that the segments are held in the recess by compressive reaction forces produced during wheel rotation. Additionally, the specification discloses an arrangement particularly adapted for supplying cooling or lubricating fluid to the wheel periphery. The arrangement comprises an inwardly open, circumferentially extending fluid receiving trough carried by the wheel. The trough is connected to the recess by generally radially extending passages such that during wheel rotation fluid moves outwardly to the recess and between the segments under the influence of centrifugal force.

4 Claims, 8 Drawing Figures Coolant PAIENIED DEC 1 1 I973 SHEET 2 OF 2 SEGMENTED GRIDING WHEEL This is a continuation, division, of application Ser. No. 28,721, filed 4/15/70, now US. Pat. No. 3,636,665.

The present invention is directed toward the grinding art and, more particularly, to an improved grinding wheel assembly.

The invention is especially suited for wheels for use in high speed grinding operations and will be described with particular reference thereto; however, it will be the grinding operation decreases.

Equipment which can rotate a wheel and move the work at substantially any desired velocities is available or can readily be built with current technology. The problem, however, is providing a grinding wheel which can withstand the forces generated during high speed rotation.

Normally, failure of the wheels results from radial tensile cracks which run from the bore to the periphery of the wheel. With conventional solid grinding wheels, increased wheel speed results in increases in circumferential tensile stress. It can be shown that this stress varies as the square of the velocity.

As of consequence of the above, the speed of the wheels has generally been limited to the range of approximately 6,000 surface feet per minute for vitrified wheels, and 9000 surface feet per minute for resinoid wheels. Recently, improved bonding materials, more dense materials obtained by hot pressing, new types of abrasives, and steel and fiber glass reinforcements have allowed the speeds of resin bonded wheels to be increased to the range of 16,000 sfpm, and vitrified bonded wheels to 12,000 fpm.

While the fore going solutions have provided an increase in allowable wheel speed, they are still far short from an adequate answer. For example, most grinding wheels capable of 16,000 sfpm are available only in fine grain size and high'hardness. Additionally, for many grinding operations much higher speeds would yield greater efficiencies than can be achieved with the best wheels currently available.

The present. invention provides a grinding wheel assembly which allows wheels to be constructed for operation at speeds well above 25,000 sfpm. Additionally, wheels constructed in accordance with the invention can be used for many different types of grinding operations and provide savings in terms of increased grinding efficiency and reduced manufacturing and shipping cost.

Broadly, one aspect of the invention concerns a grinding wheel assembly in which the outer grinding or working portion of the wheel is constructed from discrete grinding segments in the-form of sectors of a ring.

The sectors are mounted in a wheel member in a manner such that centrifugal force generated during wheel operation gives rise to compressive rather than tensile stresses. Since the circumference of the wheel is made up of discrete segments circumferential tensile stresses are also avoided.

The advantages of wheels formed in accordance with the invention are many. First, grinding materials have greater strength in compression than they do in tension. Hence, the elimination of tensile stresses allows the wheels to be safely operated at much higher velocities. Secondly, the relatively small size of the segments simplifies manufacture and reduces the possibility of thermal stresses. Additionally, should the wheel be damaged it is normally necessary to replace only one or two segments and the wheel does not have to be scrapped as in the case of a conventional wheel. Generally, wheels formed in accordance with the invention also provide higher efficiency of abrasive usage and present fewer safety problems at high speed.

A specific aspect of the invention contemplates that the wheel member of the assembly will include a circumferential recess having opposed radially extending side walls which are inclined toward one another in the radially outward direction. The arcuate segments are positioned in the recess and have side walls which are spaced and inclined to mate with the side walls of the recess. The segments are sized such that when they are positioned in the recess, they fit slightly loosely between the side walls of the recess. However, as the wheel is rotated, the segments move a short distance outwardly under the influence of centrifugal force until their side walls engage the sidewalls of the recess. Because of the relationship of the side walls, the segments are held in the recess. Most importantly, however, the holding forces generated on the segments are all compressive forces. This allows the wheels to operate at much higher velocities than conventional wheels formed from the same grinding material.

Another aspect of the invention concerns a cooling or lubricating system for wheels of the segmented type described. Particularly, the system includes at least one radially inwardly open trough or the like formed circumferentially about the wheel ata location spaced inwardly of the outer periphery. The trough is connected with the bottom of the segment receiving recess by small passages. Consequently, as the wheel is rotated, collant or lubricant can be supplied to the trough and it flows outwardly through the passages to the recess because of centrifugal force. The small spaces between adjacent segments permits the fluid to flow from the recess to the outer surface of the segments.

The invention also contemplates that rather than a cooling or lubricating liquid, air can be caused to move through the passages to the outer periphery of the segments. By the addition of fins, or the like at a positions adjacent the inner ends of the passages, the air flow can be greatly increased. For example, fins can be mounted in the trough or formed as a separate item and the trough omitted.

A primary object of the invention is the provision of an improved segmented-type grinding wheel which is particularly suited for high speed operation.

Another object of the invention is the provision of a grinding wheel assembly wherein the grinding periphery is formed from segments attached to a central wheel member in a manner which causes the forces on the segments to produce compressive stresses rather than the circumferential tensile stresses present in conventional wheels.

A further object is the provision of a grinding wheel assembly of the general type described wherein a coolant or lubricant can be supplied through the wheel to its outer periphery without special equipment.

Yet another object is the provision of a grinding wheel of the type discussed wherein the segments are mounted in a manner which eliminates any possibility of undue or irregular clamping forces being produced by improper installation of the segments.

A still further object is the provision of a grinding wheel assembly wherein individual segments can be rapidly replaced.

Still another object is the provision of a wheel of the type described which is simple to construct and safe to operate.

These and other objects and advantages will become apparent from the following description when read in conjunction with the accompanying drawings wherein;

FIG. 1 is a side elevation of a grinding wheel formed in accordance with the preferred embodiment of the invention;

FIG. 2 is a cross-sectional view taken on line 22 of FIG. 1;

FIG. 3 is an enlarged pictorial view of one of the grinding segments used in the embodiment of FIG. 1;

FIG. 4 is a side elevation of a grinding wheel assembly formed in accordance with a second embodiment of the invention;

FIG. 5 is a cross-sectional view taken on line 5-5 of FIG. 4;

FIG. 6 is an enlarged cross-sectional view taken on line 6-6 of FIG. 1 and used to show the forces acting on the grinding segment during operation of the wheel;

FIG. 7 is a pictorial view of the segments used in the FIG. 4 and 5 embodiment; and,

FIG. 8 shows a modified form of wedge biasing means. 1

Referring in particular to the drawings wherein the showings are for the purpose of illustrating preferred embodiments of the invention only and not for the purpose of limiting same, FIGS. 1 and 2 show a grinding wheel assembly which includes a support wheel portion 10 and a circumferentially extending segmented grind ing periphery portion 12. The wheel portion 10 is carried on a center shaft 12 which is mounted for rotation about axis 14 and is adapted to be driven at high speed by a drive assembly not shown. The wheel portion 10 could have a variety of specific constructions within the scope of the invention; however, in the embodiment under consideration, it is shown as a multiple component assembly including a first disc member 16 which is connected to shaft 12 in any convenient manner, such as by welding. The disc member 16 is suitably reinforced by angle plates or brackets 18 which extend between the shaft 12 and the left side of plate 16 as viewed inFIG. 2.

Associated with plate 16 and adapted to cooperate therewith for clampingly engaging the peripherally extending segment holding portion 20, is a second plate member 22. Member 22 is removably connected to the shaft I2 by a large diameter nut 24 rotatably received on the threaded end 26 of shaft 12. Preferably, the member 22 is prevented from rotating relative to shaft 12 by keys 26 which are positioned between the shaft l2 and corresponding grooves or keyways formed in member 22.

In the embodiment in consideration, the segment holding portion 20 is gripped between the members 16 and 22. Note that member 16 is provided with an axially extending raised portion 28 which faces a correspondingly shaped raised portion 30 that extends axially from an outwardly extending flange 32 formed on member 22. The surfaces 34 and 36 of raised portions 28 and 30, respectively, are preferably circumferentially continuous about their respective members. Additionally, the surfaces are preferably parallel and lie in planes perpendicular to axis 14.

Although the segment holding portion 20 could be constructed in many ways, in the FIG. 1 embodiment, it is shown as comprised of three separable, generally annular shaped members 40, 42 and 44. Members 40 and 44 each have an outer peripheral portion which includes a circumferentially extending surface having both a radial and axial extent. Note that member 40 has an inclined surface 46 which is continuous about the member and faces a correspondingly inclined surface 48 formed on member 44.

The member 42 functions as a spacer and is of lesser outer diameter than the members 40 and 44. When positioned between members 40 and 44, it functions to cooperate therewith to define a continuous peripheral recess 50 which has a trapezoidal cross-section and extends circumferentially about the wheel assembly.

The three members 40, 42 and 44 are engaged and held tightly together by a plurality of high strength bolts 52 which pass through openings formed in members 42 and 44 and into threaded openings 54 formed in member 40.

Positioned within the circumferential recess 50 and forming the working or grinding periphery of the wheel assembly, are a plurality of grinding segments 56. Although the segments could be arranged to provide a discontinuous grinding surface about the outer periphery of the wheel, they are preferably shaped and positioned so as to form a relatively continuous grinding surface. As best shown in FIG. 3, each of the segments 56 is in the form of a sector of an annulus generated by a trapezoid rotated about an axis with the largest base of the trapezoid parallel to and a fixed distance from the axis. Note that the segment 56 has opposite side surfaces 58 and 60 which are inclined at the same angle as the previously mentioned surfaces 46 and 48. In the embodiment shown, there are 12 of the segments 56 each of identical size and shape. It should be recognized however, that the segments could vary in length and differ in the particular grinding material from which they are formed. Additionally, it may, for certain operations, be advantageous to provide alternate hard and soft segments or to provide segments having different grits. Additionally, although the segments 56 are shown as having a shape in cross-section of a trapezoid, it will become apparent hereafter that the particular shape could vary within the scope of the invention. The number of segments may be more or less than 12.

Of particular importance to the invention, is the relationship of the segments 56 to the recess 50. As can be appreciated, because the grinding periphery is discontinuous, there can be no generation of circumferential tensile stresses within the segments 56. Additionally, the size of the recess is controlled so as to prevent any application of clamping forces to the segments when the wheel assembly is being constructed or assembled. In the subject embodiment, this is accomplished by having the spacer 42 of a width such that tightening of the bolts 52 can never cause the surfaces 46, 48 to clampingly engage the segments 56. On rotation of the wheel; however, (see FIG. 6) the radially outwardly acting centrifugal force F, causes the segments 56 to move radially outwardly until their surfaces 58, 60 engage surfaces 48, 46. The restraining forces R act to maintain the segments locked in the recess 50. Additionally, it should be noted that the restraining forces R generate only compressive loads within the segments. That is, no tensile stresses are produced by the arrangement shown. when the segments are seated under the influence of centrifugal force, there is no contact between the bottom of the segments and the bottom of the recess 50.

The lack of any unknown clamping force being applied to the segments during assembly is particularly important to safety and high speed operation. In addition to the primary advantages provided by the invention i.e., the total elimination of tensile stresses in the grinding portion of the wheel, the subject invention also allows several other advantages to be obtained. Note, first, that merely by varying the width of the spacer 42 the wheel assembly can be used for a variety of different widths of segments. Additionally, if desired, the segments 56 can be alternately hard and soft or intermediate dummy segments can be inserted to provide an intermittant cutting or grinding operation. These last two features are particularly important when grinding temperatures are a problem. Also, if the wheel should accidentally be damaged, it is necessary only to replace one or two of the segments. In a conventional wheel, damage can require that the entire wheel be scrapped An additional feature of the subject invention is that there can be a high percentage of the grinding material actually used. Consider that with a conventional wheel formed entirely of grinding material only a small portion of the total amount of material can be used. With the subject device, up to one-half and more of the entire segment can be used.

Many different arrangements can be provided within the terms of the invention. FIGS. 4 and 5 show a modified form of the invention which permits the grinding segments to have a shape which is a sector of an annulus generated by a rectangle rotated about an axis with one of its sides parallel to the axis. That is, the segment in the wheel of the FIG. 4 and 5 embodiment can be of generally rectangular cross-section with parallel side walls. Specifically, the FIG. 4 and 5 embodiment includes a wheel member 70 which is connected to a rotatably mounted shaft 72. The shaft 72 is, of course, adapted to be driven at a relatively high number of RPMs. The wheel member 70 is preferably of one piece construction and, for example, can be a forging or the like. As shown, wheel 80 is afixed to shaft 72 by flanges 74 and 76. l

The outer perimeter of the wheel section 70 is of substantial thickness and has a recess 78 formed circumferentially thereabout. Preferably, the recess 78 is located on the wheel center plane 80. As shown, recess 78 has a pair of opposed side walls 82 and 84 which extend radially and circumferentially of the wheel. The walls 82, 84 are inclined slightly toward one another is the radially outward direction so that the recess is of trapezoidal cross-section.

In both of the embodiments, it is advantageous that the outer rim of the wheel be massive not only to withstand the substanstial forces exerted on the sides of the recess, but also to provide a large polar moment of inertia relative to the wheel axis. The large polar moment of inertia will tend to minimize the tendency for unbalance of the segments due to inhomogeneity or nonuniform spacing from exciting lateral vibration of the spindle.

The grinding segments or sectors are mounted in the recess 78 and have the shape shown in FIG. 7. In this embodiment, each of the segments 86 has opposed parallel side walls 88 and 90. Rather than providing inclined body portions on the segments (as in the FIG. 1 through 3 embodiment), the subject arrangement provides a series of wedge members 92 and 94 which extend about the wheel on opposite sides of the segments 86. The wedge members 92 and 94 are shown as being of identical size and shape; however, it should be appreciated that it would be possible to use different size wedges on opposite sides or, to use wedges only on one side with the opposite side of the recess extending parallel to the radial segmental face. The wedges 92 and 94 each have a first planar face 96 which engages the side of the segment 86. The opposite side of the wedge is inclined an amount corresponding to the surfaces 82 and 84. Thus, with the wedges in position adjacent the segments 86, the wedges function in somewhat the same manner as the inclined body portions of the segments of the FIG. 1 through 3 embodiment. That is, as the wheel of FIG. 4 and 5 is rotated, centrifugal force causes the wedges to be moved outwardly and apply an axially directed clamping force to the associated segments to lock them or bind them firmly into the wheel. It should be noted that the clamping force is strictly compressive and produces no tensile loading of the segments.

As can be appreciated, since the clamping produced by centrifugal force is not present when the wheel is stationary means must be provided to maintain the sectors 86 in the wheel during this period. In the subject embodiment, a light clamping pressure is provided by resilient O-rings which are positioned in the bottom of the recess 78 and extend circumferentially about the wheel. As shown, there are three O- rings 96, 98 and 100. The O-rings are sized so that the segments and wedge members are assembled into the recess, the 0- rings must be compressed slightly. Thereafter, a light outward bias is maintained on the wedges to produce a very light controlled gripping force on the sectors. Only a light force is required because of the rapid buildup of clamping produced by centrifugal force generated as the wheel is brought up to speed.

An alternative way of providing the initial clamping force is shown in FIG. 8 which is an enlarged view of FIG. 5 in the vicinity of A. A single jack screw 112 in threaded engagement with each wedge at its center is forced against the bottom of recess 113 thus causing the wedge to move radially outward during assembly of the straight sided wheel segments. As soon as the assembly is rotated at high speed, centrifugal force causes the wedges to move outward a very small amount which provides the final clamping action that is operative when the wheel is in use. Jack screws 112 will then normally leave contact with surface 113 in FIG. 8. However, the friction force induced by centrifugal force on both sides of the wedge are far more than adequate to offset any radial force that arises during grindmg.

Clearly many modifications of the segment mounting arrangements shown in the two embodiments could be provided. As previously mentioned, the wheel could have only a single set of wedge members positioned on one side of the segments. In such case, the opposite surface of the recess would have no incline or an incline to correspond to the orientation of the opposite face of the segment. Similarly, a combination of wedges with segments of only a slight or a narrow trapezoidial configuration could be used.

In addition to the many advantages obtained by the described wheel arrangement many other advantageous features can easily be obtained. For example, in the FIG. 4 and 5 embodiment, a pair of flange members 102 and 104 extend circumferentially about the wheel on opposite sides of the enlarged outer end portion. The two flange members defined inwardly open troughs or recesses 106 and 108 respectively. Passages 110 and 112 extend inwardly from the troughs to the bottom of recess 78. When the wheel is rotating, a coolant or lubricant can be supplied to the trough portions 106 and 108. The rotation of the wheel causes the lubricant to be maintained in the trough and directed to the bottom of recess 78 by centrifugal force. Because of the segmented grinding periphery, slight crack-like gaps are present between each of the segments. The coolant can thsu flow through these gaps to the outer surface of the segments.

If it is not necessary to use a coolant or lubricant liquid, the presence of the passages 110 and 112 and their relationship to the wheel will induce air flow outwardly through the passages and the segments. Additionally, if desired, the amount of air flow can be increased by adding fins or vanes to the wheel adjacent to the passages.

When it is desired to change segments in the FIGS. 4 and 5 embodiment, it is simply necessary to force the wedges inwardly against the bias of their respective O- ring members. The segments can then be freely removed and new segments inserted. If desired, all segments can be rapidly changed by positioning bands about the upper ends of the segments and tightening the bands inwardly.

In the case of the jack screw arrangement, the screws need only to be slightly loosened and the segments The FIG. 4 and 5 embodiment also permits grinding segments of a variety of thicknesses to be used. For example, a thin segment for cut-off operations can be used in the same wheel merely by providing wider wedges.

The invention has been described in great detail sufficient to enable one of ordinary skill in grinding art to make and use the same. Obviously, modifications and alterations of the preferred embodiment will occur to others upon a reading and understanding of the specification, and it is my intention to include all such modifications and alterations as part of my invention insofar as they come within the scope of the appended claims.

Having thus described my invention I claim:

1. A grinding wheel assembly including:

a cylindrical wheel member mounted for rotation about its axis; a recess formed circumferentially about the outer periphery of said wheel;

a plurality of grinding segments positioned in said recess and extending outwardly of the outer periphery of said wheel, said segments spaced to one another to provide gaps which extend inwardly from the outer periphery to the inner portion of said recess;

means to supply cooling fluid to the inner portion of said recess to flow outwardly through said gaps under the influence of centrifugal force, said means including a circumferentially continuous trough forming member carried by said wheel and rotatable therewith, said trough being open to atmosphere in a radial inward direction continuously about its circumference and connected with said recess by generally radially extending passages; and,

supply pipe means having a discharge end spaced from said trough for discharging fluid through the atmosphere to said trough.

2. The grinding wheel of claim 1 wherein said grinding segments are positioned continuously about the periphery of said wheel and wherein said passages are relatively uniformly spaced about said wheel.

, 3. The grinding wheel of claim 1 wherein there are trough forming members on both sides of said wheel member.

4. The grinding wheel assembly of claim 1 wherein said segments are spaced outwardly from the bottom of said recess to provide a continuous circumferential space radially inwardly of the segments.

Claims (4)

1. A grinding wheel assembly including: a cylindrical wheel member mounted for rotation about its axis; a recess formed circumferentially about the outer periphery of said wheel; a plurality of grinding segments positioned in said recess and extending outwardly of the outer periphery of said wheel, said segments spaced to one another to provide gaps which extend inwardly from the outer periphery to the inner portion of said recess; means to supply cooling fluid to the inner portion of said recess to flow outwardly through said gaps under the influence of centrifugal force, said means including a circumferentially continuous trough forming member carried by said wheel and rotatable therewith, said trough being open to atmosphere in a radial inward direction continuously about its circumference and connected with said recess by generally radially extending passages; and, supply pipe means having a discharge end spaced from said trough for discharging fluid through the atmosphere to said trough.

2. The grinding wheel of claim 1 wherein said grinding segments are positioned continuously about the periphery of said wheel and wherein said passages are relatively uniformly spaced about said wheel.

3. The grinding wheel of claim 1 wherein there are trough forming members on both sides of said wheel member.

4. The grinding wheel assembly of claim 1 wherein said segments are spaced outwardly from the bottom of said recess to provide a continuous circumferential space radially inwardly of the segments.

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