US3772831A

US3772831A - Grinding wheel

Info

Publication number: US3772831A
Application number: US00219683A
Authority: US
Inventors: M Shaw
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-01-21
Filing date: 1972-01-21
Publication date: 1973-11-20
Anticipated expiration: 1990-11-20

Abstract

A grinding wheel assembly particularly suited for high speed operation, comprising a solid wheel mounted in an outer peripheral recess of a wheel clamping mechanism, and a plurality of tapered wedges adapted to fit between the wheel surface and a complementarily tapered wall of the recess. The wedges move radially outward by centrifugal force as the wheel is rotated and thereby apply compressive reactive forces to the solid wheel to contain any fragments or pieces of the wheel in the event of wheel failure.

Description

ties

[ cmnnmcwiimi [76] Inventor:

M. Simpson Milton C. Shaw, 132 Maple Heights Primary Examiner-0thell Att0rneyDav1d S Urey Rd., Pittsburgh, Pa. 15232 T C A R T s B A 7 5 2 m 9 3 1 n9 1 m2 0 N L n w FA 1 21 22 [IL A grinding wheel assembly particularly suited for high speed operation, comprising a solid wheel mounted in an outer peripheral recess of a wheel clamping mechanism, and a plurality of tapered wedges adapted to fit between the wheel surface and a complementarily ta- 90 9 60 6 11 l /16 14m .b ,6 nm A 68 M VOO 2 6 l 9 1/ 7 55 0 "d N E 6 "0 mmm mnm6 0 "Th m Mmr mmeN m mmw i c fl .l MM UHF 1]] 218 555 [[l pered wall of the recess. The wedges move radially outward by centrifugal force as the wheel is rotated [56] lReierences Cited UNITED STATES PATENTS 226,013 3/1880 Allen,.......

and thereby apply compressive reactive forces to the solid wheel to contain any fragments or pieces of the wheel in the event of wheel failure.

51 206 R 51 206 R 6/1936 Offenbacher 51 206 R mums, Drawing e 1,735,891 11 1929 Bryant............. 2,044,442

in high speed grinding operations and will be described with particular reference thereto; however, it will beappreciated that the invention is capable of broader application and could be used in many types'of grinding machines without regard to their speed of operation or use.

Increasing the speed of grinding wheels has long been a matter of continued interest. This is because it has 7 been known that attritious wear, as well as grinding wheel costs, decreases with increased wheel speed provided that the ratio of wheel speed to work speed is maintained relatively constant. Generally, if the ratio is not maintained somewhat constant, excessive rubbing results with increased wheel speed, and the efficiency of 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 thw 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 (sfpm) for vitrified wheels, and 9,000 sfpm for resinoid wheels.

Recently, improved bonding materials, more dense materials obtained by hot pressing, new types of abrasives, and steel and fiber glassreinforcements 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 sfpm.

While the foregoing solutions have provided an increase in allowable wheel speed, they are still far short of 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 operated at these high speeds with greater safety in the event of wheel fractures. It has been known in the past that a taper or dovetail can be placed on the inner peripheral portion .of the wheel and held by a complementarily shaped clamping ring or holder which applies compressive forces to the wheel, as shown in US. Pat. No. 226,013, US. Pat. No. 1,735,891, and U.S. Pat. No. 2,044,442. However, at no time to my knowledge has it been suggested that movable wedges can be used to apply the compressive forces.

7 SUMMARY OF THE INVENTION In the preferred embodiment, the invention includes a grinding wheelassembly in which the outer grinding or working portion of the wheel is held in a peripheral groove of a wheel clamping mechanism under compressive reactive forces, provided by a plurality of tapered wedges which move radially outwardly as rotative speed of the wheel increases.

The advantages of wheels formed in accordance with this invention are many. First, it is not necessary to place a taper or dovetail on the grinding wheel, but instead the wedging action is achieved through tapered metal wedges, thereby providing a more economical wheel mount, and one which can be used with standard cylindrical grinding wheels.

Secondly, it is believed that greater clamping forces can be achieved in this manner since the wedges are free to move radially outwardly as the speed of the wheel increases. In the prior art where the taper was provided on the wheel, the only compressive forces, beyond those obtained at initial installation, are the forces which result from the minimal growth of the wheel.

Thirdly, greater control over the amount of compressive clamping force can be obtained since various sizes of wedges and wedges of varying density can be used to obtain different amounts of compressive force without necessarily changing the grinding wheel that is being used.

Four'thly, it is believed that more evenly distributed compressive forces can be obtained with the movable wedges since there is no reliance upon manually applied clamping forces around the circumference of the wheel mount at the time of wheel installation. Instead, the wedges are freely positioned in the peripheral groove, and there is reliance upon the wheel rotation to build up the compressive forces. Since the wheel must rotate at the same speed throughout its entire circumference, the centrifugal forces to move the wedges outwardly, and the compressive reactive forces applied to the wheel should be uniform.

Lastly, in the event of wheel failure the compressive forces applied by the wedges hold the wheel together and greatly minimize the possibility of an injury to opcrating personnel by reason of flying wheel fragments.

A specific aspect of the invention contemplates that the wheel member of the assembly will include a circumferential recess having opposed radially extending sidewalls which are inclined toward one another in the radially outward direction. The wheel is positioned in the recess and the wedges have sidewalls which are spaced and inclined to mate with the sidewalls of the recess. The wedges are sized such that when they are positioned in the recess, they tit slightly loosely be tween the sidewalls of the recess. However, as the wheel is rotated, the wedges move a short distance outwardly under the influence of centrifugal force until their sidewalls engage the sidewalls of the recess and the grinding wheel. Because of the relationship of the sidewalls, the wedges are held in the recess. Most importantly, however, the holding forces generated on the grinding wheel are all compressive forces. This may permit the wheel to operate at higher velocities, and assuredly provides a safer condition in the event of wheel wedges in this embodiment are positioned circurnferentially around the wheel only on that one side, and the other side of the wheel is flush with the wall of wheel support. The wedges may be larger and/or of more dense material in order to obtain the desired compressive reactive forces on the wheel.

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

Another object of the invention is the provision of a grinding wheel assembly wherein a plurality of circumferentially positioned wedges apply compressive reactive forces to the grinding wheel to hold the wheel together in the event of wheel fracture.

A further object of the invention is to provide evenly distributed compressive forces around the circumference of the grinding wheel resulting from the outward movement of tapered wedges by reason of centrifugal forces thereon.

Yet another object is the provision of a grinding wheel support of the type discussed which can be used with conventional cylindrical grinding wheels.

A still further object is the provision of a grinding wheel assembly wherein the individual tapered wedges can be rapidly replaced with wedges of a different density.

Still another object is the provision of a wheel support 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 drawing.

BRIEF DESCRIPTION OF THE DRAWING 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 2-2 of FIG. 1;

FIG. 3 is an enlarged cross-sectional view with portions removed of a second embodiment of the invention; and

FIG. 4 is an enlarged cross-sectional view with portions removed of a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring in particular to the drawing 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 wheel support member 70 and a circumferentially extending conventional, solid wheel W.

The invention permits the grinding wheel W to have the normal shape, which is an annulus generated by a rectangle rotated about an axis with one of its sides parallel to the axis. That is, the wheel W of the FIGS. 1 and 2 can be of generally rectangular cross-section with parallel sidewalls. The wheel member 70 is connected to a rotatably mounted shaft 72, and the shaft 72 is adapted to be driven at a relatively high number of RPMs by a drive assembly (not shown). The wheel member 70 is preferably of two piece construction and, for example, can be a forging or the like. As shown, wheel member 70 is affixed to shaft 72 by

flanges

74 and 76.

The outer perimeter of the wheel member 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 sidewalls

82 and 84 which extend radially and circumferentially of the wheel. The

walls

82, 84 are inclined slightly toward one another in the radially outward direction so that the recess 78 is of trapezoidal cross-section.

In all of the embodiments, it is advantageous that the outer rim of the wheel be massive not only to withstand the substantial forces exerted on the sides of the recess, but also to provide a large polar moment of inertia relative to whe wheel axis. The large polar moment of inertia will tend to minimize the tendency for imbalance due to inhomogeneity or nonuniformity in the wheel W. The grinding wheel W is mounted in the recess 78 and has opposed

parallel sidewalls

88 and 90. In order to apply compressive reactive forces to the wheel W, there are provided a series of wedge members 92-92 and 94-94 which extend about the wheel on opposite sides of the wheel. The wedge members 92-92 and 94-94 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 grinding wheel face, as shown in FIG. 3.

The wedges 92-92 and 94-94 each have a first planar face 96 which engages the side of the wheel W. The opposite side of the wedge is inclined an amount corresponding to the

surfaces

82 and 84. As the wheel W is rotated, centrifugal force causes the wedges to be moved outwardly and apply an axially directed clamping force to the wheel W to prevent the wheel W from flying apart in the event of fracture. It should be noted that the clamping force is strictly compressive and produces no tensile loading of the wheel.

In the embodiment shown in FIG. 1, there are twelve wedges 92-92 provided on one side of the wheel W, and a like number of wedges 94-94 provided on the other side. It is to be understood that more or less wedges may be provided, and the number is not critical.

As can be appreciated, since the clamping produced by centrifugal force is not present when the wheel is stationary, means may be provided to maintain the wheel W concentric with the shaft 72. In this 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 support 70. As shown, there are three O-

rings

97, 98 and 100. The O-rings are sized so that when the wheel W and wedge members 92-92 and 94-94 are assembled into the recess, the O-rings may be compressed slightly. Only a light force is required because of the rapid buildup of clamping forces 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. 4 which is an enlarged view of the lower portion of FIG. 2. A single jack screw 112 in threaded engagement with each wedge 92-92 and 94-94 at its center is forced against the bottom of recess 113 thus causing the wedge to move radially outward against the wheel W and the inclined surface 1 14. 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 clmaping action that is operative when the wheel is in use. Jack screws 112-112 will then normally leave contact with surface 113 in FIG. 4. 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 grinding, and thus if the wheel W fractured, the pieces would be held together.

Clearly, other modifications to the arrangements shown in the three embodiments could be provided. As previously mentioned,'the wheel could have only a single set of wedge members 92-92 (W6. 3) positioned on one side of the wheel W. In such case, the opposite surface 116 of the recess has no incline or an incline to correspond to the orientation of the opposite face of the wheel. Also, a pair of flange members 102 and 1041 may be mounted on opposite sides of the enlarged outer portion of the wheel support 70, if desired.

It is to be understood that the wedges 92-92 and 94-94 may be made of various materials, but preferably would be made of steel. Since the specific gravity of steel is over two and one half times that of the norrnal abrasive grinding material, it is possible to develop substantially higher compressive reactive forces on the grinding wheel when the instant invention is utilized, rather than the prior art devices which relied upon growth of the wheel. Also, lead or other metals heavier than steel can be used to fabricate the wedges if still further compressive forces are necessary.

The wedges 92-92 and 94-94 are loosely fitted into the groove 78 when the wheel W is stationary, and, therefore, no operator controlled clamping forces are applied to the wheel. Instead, all the forces result from the outward radial movement of the wedges which should be constant throughout the circumference of the wheel support since the centrifugal forces are constant at any given speed. This eliminates the difficulty of manually applying an equal clamping force to clamping screws positioned around the circumference of the wheel.

An additional advantage resides in the fact that the invention permits grinding wheels of a variety of thicknesses to be used. For example, a thin wheel for-cut-off operations can be used in the same wheel support by providing wider wedges.

It is believed that the instant invention prevents the vast majority of the wheel from becoming dangerous missiles in the event of wheel failure. While a piece or two may still break loose, the danger to personnel is substantially reduced. It is also believed that the compressive reactive forces applied by the wedges may even reduce the likelihood of wheel failure by reducing the tensile forces on the wheel, but this is only a theory at this time.

' 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 embodiments 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 ivention insofar as they come within the scope of the appended claims.

Having thus described my invention I claim:

1. A grinding wheel assembly, which comprises:

a cylindrical wheel support for rotation about its axis, said support having a peripheral groove extending therearound with at least one inclined surface thereon;

a grinding wheel supported in said groove, said wheel being of less thickness than the width of said groove; and

a plurality of movable wedges circumferentially positioned around said groove and interposed between the wheel and at least said one inclined surface of the groove, said wedges having an inclined surface complementary to the surface of the groove, and said wedges being designed to move radially outwardly under centrifugal force as said grinding wheel support is rotated to apply compressive reactive forces to said wheel so that in the event of wheel failure the wheel fragments are contained in said groove.

2. A grinding wheel assembly, as recited in claim 1,

wherein:

said cylindrical wheel support peripheral groove has a pair of oppositely disposed, inclined surfaces which are inclined toward each other in a radially outward direction; and

said wedges are positioned on opposite sides of said wheel in said groove.

3. A grinding wheel assembly, as recited in claim 2, wherein said pair of surfaces are continuous about the periphery of said wheel assembly.

4. A grinding wheel assembly,as recited in claim 2, wherein the width of said peripheral groove is slightly greater than the thickness of said wheel and said wedges so that the wedges are loose fitting when the wheel assembly is stationary, and so that the wedges move radially outwardly as the wheel is brought up to speed.

5. A grinding wheel assembly, as recited in claim 2, wherein said pair of surfaces are continuous about the periphery of said wheel support and each is inclined toward the other to define a continuous recess of trapezoidal cross-section in a plane containing the axis of rotation of said wheel.

6. A grinding wheel as recited in claim ll, wherein the inner surfaces of said wedges which are in engagement with said wheel are in a plane which is perpendicular to the axis of rotation of said wheel.

7. A grinding wheel as recited in claim 1, which further comprises;

means for biasing said wedges radially outwardly when the wheel is stationary.

8. A grinding wheel assembly for supporting and rotating a one piece cylindrical grinding wheel, which comprises:

a cylindrical wheel support for rotation on its axis, said support having a peripheral groove extending around the outer circumferential surface thereof, said groove having at least one inclined surface which slopes toward the centerline of said support as the inclined surface progresses radially outwardly for receiving said grinding wheel; and

a plurality of movable wedges circumferentially positioned around said groove and interposed between said wheel and said inclined surface of the groove, said wedges having an inclined surface complementary to the surface of the groove, and said wedges being designed to move radially outwardly under centrifugal force as said grinding wheel support is rotated to apply compressive reactive forces to said wheel so that in the event of wheel failure the wheel fragments are contained in said groove.

10. A grinding wheel assembly, as recited in claim 9, wherein the width of said peripheral groove is slightly greater than the thickness of said wheel and said wedges so that the wedges are loose fitting when the wheel assembly is stationary, and so that the wedges move radially outwardly as the wheel is brought up to speed.

Claims

1. A grinding wheel assembly, which comprises: a cylindrical wheel support for rotation about its axis, said support having a peripheral groove extending therearound with at least one inclined surface thereon; a grinding wheel supported in said groove, said wheel being of less thickness than the width of said groove; and a plurality of movable wedges circumferentially positioned around said groove and interposed between the wheel and at least said one inclined surface of the groove, said wedges having an inclined surface complementary to the surface of the groove, and said wedges being designed to move radially outwardly under centrifugal force as said grinding wheel support is rotated to apply compressive reactive forces to said wheel so that in the event of wheel failure the wheel fragments are contained in said groove.

2. A grinding wheel assembly, as recited in claim 1, wherein: said cylindrical wheel support peripheral groove has a pair of oppositely disposed, inclined surfaces which are inclined toward each other in a radially outward direction; and said wedges are positioned on opposite sides of said wheel in said groove.

6. A grinding wheel as recited in claim 1, wherein the inner surfaces of said wedges which are in engagement with said wheel are in a plane which is perpendicular to the axis of rotation of said wheel.

7. A grinding wheel as recited in claim 1, which further comprises; means for biasing said wedges radially outwardly when the wheel is stationary.

8. A grinding wheel assembly for supporting and rotating a one piece cylindrical grinding wheel, which comprises: a cylindrical wheel support for rotation on its axis, Said support having a peripheral groove extending around the outer circumferential surface thereof, said groove having at least one inclined surface which slopes toward the centerline of said support as the inclined surface progresses radially outwardly for receiving said grinding wheel; and a plurality of movable wedges circumferentially positioned around said groove and interposed between said wheel and said inclined surface of the groove, said wedges having an inclined surface complementary to the surface of the groove, and said wedges being designed to move radially outwardly under centrifugal force as said grinding wheel support is rotated to apply compressive reactive forces to said wheel so that in the event of wheel failure the wheel fragments are contained in said groove.

9. A grinding wheel assembly, as recited in claim 8, wherein: said cylindrical wheel support peripheral groove has a pair of oppositely disposed, inclined surfaces which are inclined toward each other in a radially outward direction; and said wedges are positioned on opposite sides of said wheel in said groove.