US3638364A - Guard device for machine tools - Google Patents

Abstract

An improved cutting tool guard system utilizing a deformable spacer as an energy dissipator. The deformable spacer is placed between a cutting tool guard and rigid structure by which the guard is secured to the machine base. In the event of a sudden energy release caused by cutting tool fracture, the deformable spacer dissipates excess energy during deformation by allowing displacement of the cutting tool guard.

Description

United States Patent Grove et al.

1 Feb. 1, 1972 [54] GUARD DEVICE FOR MACHINE TOOLS [72] Inventors: George L. Grove, Cincinnati; Irving J. Stewart, Montgomery; Lloyd W. Helson, Milford, all of Ohio [73] Assignee: Cincinnati Milacron Ine., Cincinnati, Ohio [22] Filed: Feb. 19, 1970 [21] Appl. No.: 12,619

521 05.0 ..51/269,143/159 511 mm ..B24b 55/04 [58] FieldofSearch ..51/269,268;29/454,413;

143/28, 159; 144/25] R; 220/85 B, 85 TC, 44 R; 285/2; 85/62, 61; 408/110; 188/1 C [56] References Cited UNITED STATES PATENTS 3,571,983 3/1971 Stewart et al. ..51/269 1,811,665 6/ 1931 Edsall .220/85 TC 3,174,386 3/1965 Lewis ..85/62 1,505,508 8/1924 Trager ..285/2 1,324,036 12/1919 DeLaval ..285/2 2,368,225 l/ l 945 Lebermann. ....51/268 3,129,537 4/ 1964 Backer ..51/269 FOREIGN PATENTS OR APPLICATIONS 181,314 3/1936 Switzerland ..51/268 57,381 1891 Germany ....51/268 399,851 2/1909 France ..51/268 Primary Examiner-William R. Armstrong Attorney-Howard T. Keiser and Jack J. Earl [57] ABSTRACT An improved cutting tool guard system utilizing a deformable spacer as an energy dissipator. The deformable spacer is placed between a cutting tool guard and rigid structure by which the guard is secured to the machine base. In the event of a sudden energy release caused by cutting tool fracture, the deformable spacer dissipates excess energy during deformation by allowing displacement of the cutting tool guard.

3 Claims, 8 Drawing Figures PATENTEU FEB I I972 SHEETIUFZ INVENTOR$ GEORGE. L. GROVE IRVING J. STEWART LLOYD W. HELSON PAIENTED FEB 1 19?:

same-M 2 GUARD DEVICE FOR MACHINE TOOLS BACKGROUND OF THE INVENTION This invention relates to cutting tool guards, and more particularly to a guard for grinding wheels.

With the advent of high-speed grinding, the energy of the grinding wheel, or any given fragment thereof, is much greater at high speeds, more exactly, it is 3.41 times as high at l2,000 f.p.m. (feet per minute) as at the conventional speed of 6,500 f;p.m. This, of course, implies greater danger to the operating personnel. Maximum personnel safety during wheel blowup can be achieved by adequate control of wheel fragments.

During the blowup of a grinding wheel, large amounts of energy are very rapidly transferred to the grinding machine wheelhead via the grinding wheel guard. Some means of absorbing this energy is desirable to assure maximum protection to both the operating personnel and the machine components. The critical requirement is that the dynamic force be reduced. During high-speed grinding the kinetic energy of a grinding wheel, for example, a 24" 20" l2 grinding wheel rotating at 12,000 f.p.m., can exceed 200,000 foot pounds, which energy a grinding machine must in some way absorb in the event of a wheel blowup if it is to operate in the safest manner. The bolts currently used to fasten the grinding wheel guard to the wheelhead cannot safely absorb the higher energy levels imposed by high-speed grinding.

In order to reduce the force Newtons second law {F=d/dt (mi) requires that the time during which energy is transmitted must be increased; i.e., the acceleration of the grinding wheel guard caused by impact of the broken wheel fragments must be reduced. One way to increase the time increment is to insert a flexible link in the chain of parts that transmits energy.

Over the years various forms of energy dissipators have been suggested for interposing between the grinding wheel and the inner surface of the grinding wheel guard. More recent developments in this area include a rigid closed cell foam liner such as described in the copending application of l. J. Stewart and L. W. Helson, entitled Guard System, Ser. No. 822,120, filed May 6, 1969, now US. Pat. No. 3,571,983, and owned by the assignee of the present invention. This liner adds one flexible element.

The present invention contributes to the solution of the previously mentioned problems by interposing expendable energy dissipators in the region between the wheelguard and the mounting bolts. These dissipators may be permanently secured to the mounting bolts so that machine assembly is impossible without their utilization.

When the present invention is used in conjunction with a liner such as that of aforementioned application Ser. No. 822,120, the liner becomes the primary dissipator, absorbing the shock of impact of the broken wheel fragments. The deformable dissipators of the invention are secondary, absorbing a fraction of energy not readily absorbed by the liner. These secondary dissipators tend to prevent shearing of the mounting bolts and possible deformation of the wheelguard. These dissipators allow the wheelguard to move relative to the wheelhead without shearing the mounting bolts or damaging the wheelguard or wheelhead.

SUMMARY OF THE INVENTION This invention provides expendable energy dissipators for a machine tool, for example a grinding machine having a wheelhead with a spindle carried therein for securing a rotatable grinding wheel and a wheelguard mounted thereon partially enclosing the grinding wheel. The expendable energy dissipators are inserted between the cutting tool guard and the means securing the guard to the rigid structure of the machine tool. In the event of cutting fracture during rotation, the energy released is dissipated by the expendable energy dissipator through deformation. The deformation provides space for the cutting tool guard to move relative to the rigid structure of the machine tool while still controlling fragments of the broken cutting tool, thus providing better protection for both operating personnel and machine components.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary end view of a grinding machine embodying the elements of this invention.

FIG. 2 is an enlarged section view taken along line 22 of FIG. 1.

FIG. 3 is an enlarged section view taken along line 3-3 of FIG. 1 and showing the deformable spacer assembly.

FIG. 4 is a sectional end view of a grinding machine embodying the elements of this invention after wheel blowup has occurred.

FIG. 5 is an enlarged section view taken along line 5-5 of FIG. 4 and showing the deformable spacer assembly after blowup of the grinding wheel.

FIG. 6 is the preferred embodiment of the deformable spacer.

FIG. 7 is the first alternative embodiment of the deformable spacer.

FIG. Sis another alternative embodiment of the deformable spacer.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings in detail, FIGS. 1 and 2 depict a portion of a grinding machine wheelhead 10. The wheelhead 10 has mounted in it on suitable bearings (not shown) a grinding spindle 12 on which is fixedly mounted a grinding wheel 14. One of the ends of the spindle 12 extends through the wheelhead l0 and is suitably connected in any of the ways well known in the art to a drive motor (not shown) for rotating the spindle I2 and the grinding wheel 14 at high speeds. This invention is illustrated on a centerless-type grinding machine; however, it is applicable to all types of cutting tools or grinders.

Rigidly attached to the wheelhead l0 and partially enclosing the grinding wheel 14 is wheelguard 16. Attached in the same manner to the wheelguard 16 is frontpiece 18 which covers a portion of the grinding wheel 14 leaving exposed only a small segment of the grinding wheel 14 to provide a work zone. The wheelguard l6 and the frontpiece l8 retain metal chips and coolant spray during normal machining and in the event of wheel blowup, as depicted in FIG. 4, control wheel fragments 20.

The wheelguard 16 is secured to the wheelhead 10 by mounting bolts 22. The size of the bolt 22 is selected to provide slack space 28 of predetermined size between the lower annular face 24 of the head 26 of the bolts 22 and the surface 27 of wheelguard l6. Placed in and designed to fill the slack space is a deformable spacer 30 to form a semirigid connection between the wheelhead l0 and the wheelguard 16. The frontpiece 18 is secured to the wheelguard 16 in the same manner. The deformable spacer 30 is permanently secured to the bolt 22 by placing a retaining means 32 on the bolt shank of 36.

Deformable spacer 30 is employed in the manner best shown in FIG. 3. It should be understood that the deformable spacer 30 is composed of a material that deforms permanently when its deformation threshold is passed. The spacer 30 can be composed of surfaces of revolution. Such as the preferred embodiment depicted in FIG. 6. The shank 36 passes through the hollow portion 34 of the spacer 30. The lower annular face 24 of the head 26 of the bolt 22 rests against the upper bearing surface 38 of the spacer 30. A retaining means 32 is placed against the lower bearing surface 40 to hold the spacer 30 in place on the bolt 22, augmenting use of the spacer 30 when ever the wheelguard l6 and the frontpiece 18 are assembled. The clearance hole 44 is slightly larger than the bolt shank 36 to allow for slight lateral shift or rotation of the wheelguard 16. The bolt 22 is secured in tapped hole 46 of the wheelhead l0 bringing the lower bearing surface 38 of the spacer 30 in contact with spot face 42 of the wheelguard 16. The spotface 42 insures proper seating of the spacer 30 and proper alignment of the wheelguard 16 with respect to the wheelhead 10.

Alternative forms of the deformable spacer 30 are depicted in FIGS. 7 and 8. The center flange 48 added to the embodiment of FIG. 7 creates a more rigid embodiment with no change in material composition due to the added bulk of the spacer 30. However, the upward displacement of the wheelguard 16 is limited because of this added overall bulk. The simplest configuration is the tubular member 50 illustrated in FIG. 8. This allows for maximum movement of the wheelguard 16, however, the member 50 tends to shear at bearing surfaces 52 and 54 when tightening down bolt 22 during assembly, if made of the same material composition as the rest of the member 50. To prevent this shearing the bearing surfaces 52 and 54 must be made of a harder material composition than the rest of tubular member 50. Another solution to this problem is larger bearing surfaces 38 and 40 of the deformable spacer 30 as shown in the preferred embodiment depicted in FIG. 6. Bearing surfaces 38 and 40 can be of the same material composition as the rest of the deformable spacer 30. The increased area of the bearing surfaces 38 and 40 distribute the load while tightening down bolt 22, thus minimizing the chance of shear.

The control portion 56 of the deformable spacer 30 has a failure threshold which will cause permanent deformation of the spacer 30 when a predetermined energy level is reached, but will withstand normal loading forces used to secure the wheelguard 16 to the wheelhead l0, and the frontpiece 18 to the wheelguard 16.

Typically, the bolts 22 are tightened to a maximum torque of 60 foot pounds. The deformable spacer 30 is designed to fail at an energy level approximately 20 percent above the tightening down force of 60 foot pounds. In the preferred embodiment the deformable spacer 30 is made of a ductile material, usually aluminum, however, other materials such as plastics and metals with characteristics similar to aluminum may also be utilized.

The deformable element 30 is usually used in conjunction with an expendable, flexible liner 58 such as that described in the aforementioned copending application, Ser. No. 822,120. The liner 58 acts as a primary dissipator and after exhaustion of this link the deformable spacer 30 absorbs an additional increment of the excess energy that may remain.

OPERATION MODE During normal operation all elements are in the condition and position shown in FIG. 1. During grinding wheel blowup fragments 20 of grinding wheel 14 are thrown outward from the spindle 12 as depicted in FIG. 4. The fragments 20 may release a total energy in excess of 200,000 foot-pounds which must be absorbed by the grinding machine to assure maximum safety to operating personnel and machine components. The liner 58 absorbs a large fraction of this energy by increasing the time increment over which the energy is released by providing a flexible link in the chain of elements which have to absorb the released energy. A secondary dissipator, the deformable spacer 30, absorbs a remaining fraction of the released energy in applying the same principle by allowing displacement of the wheelguard 16 without any deformation of the rigid elements of the grinding machine. The control portion 56 of the spacer 30 deforms upon exhaustion of the liner 58 to provide the second flexible link in the chain of elements which must absorb the released energy. By employing these two flexible links, the fraction of energy which must be absorbed by the rigid structure of the grinding machine is greatly reduced.

Normally, the forces released tend to push the wheelguard l6 upward and the frontpiece l8 outward in a direction parallel to the axis of their respective mounting bolts 22. However, in the cases where the wheelguard l6 and frontpiece 18 are not forced in this direction the oversize clearance hole 44 allows for the necessary limited rotation or shift in a direction not parallel to the axis of the bolt 22 without damaging the bolt 22 or any rigid structure.

While use of this invention is of special significance with respect to high-speed grinding, it will also provide significantly increased operator protection even at conventional cutting tool speeds. It should be understood that the embodiment of the instant invention described herein is illustrative only, and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

What is claimed is:

1. In a precision-grinding machine, having a wheel head, a spindle rotatably carried therein, and adopted for holding a grinding wheel and closure including a wheel guard partially enclosing said grinding wheel to maintain fragments of the grinding wheel within said closure in the event of wheel blowup, said closure comprising:

a. means including a slack space for securing said wheel guard to said wheel head; and

b. a permanently deformable element placed in and adapted to fill the slack space of said securing means for absorbing a portion of the energy supplied to said wheel guard when the grinding wheel fractures and fragments are thrown outward from the spindle, said element including:

1. a hollow body through which said securing means passes;

2. two bearing surfaces, one of said bearing surfaces adjoining said securing means, and the other of said bearing surfaces adjoining said wheel guard; and

3. a control portion determining the threshold of failure of said permanently deformable element.

2. The apparatus of claim I, wherein said securing means is a bolt loosely extending through said hollow body and an aperture in said wheel guard and secured to said wheel head the bolt comprising:

a. a head engaged with said hollow body; and

b. a shank extending from said hollow body and loosely passing through said hollow body and said aperture in said wheel guard to allow shifting of the wheel guard with respect to said support structure during blowup of said grinding wheel.

3. The apparatus of claim 1, wherein said permanently deformable element is a secondary energy dissipator absorbing a portion of energy not dissipated by a primary energy dissipator comprising a rigid closed cell absorption means placed between said grinding wheel and said wheel guard for dissipating a portion of the energy released during blowup of said grinding wheel. I

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Claims (5)

1. In a precision-grinding machine, having a wheel head, a spindle rotatably carried therein, and adopted for holding a grinding wheel and closure including a wheel guard partially enclosing said grinding wheel to maintain fragments of the grinding wheel within said closure in the event of wheel blowup, said closure comprising: a. means including a slack space for securing said wheel guard to said wheel head; and b. a permanently deformable element placed in and adapted to fill the slack space of said securing means for absorbing a portion of the energy supplied to said wheel guard when the grinding wheel fractures and fragments are thrown outward from the spindle, said element including: 1. a hollow body through which said securing means passes; 2. two bearing surfaces, one of said bearing surfaces adjoining said securing means, and the other of said bearing surfaces adjoining said wheel guard; and 3. a control portion determining the threshold of failure of said permanently deformable element.

2. two bearing surfaces, one of said bearing surfaces adjoining said securing means, and the other of said bearing surfaces adjoining said wheel guard; and

2. The apparatus of claim 1, wherein said securing means is a bolt loosely extending through said hollow body and an aperture in said wheel guard and secured to said wheel head the bolt comprising: a. a head engaged with said hollow body; and b. a shank extending from said hollow body and loosely passing through said hollow body and said aperture in said wheel guard to allow shifting of the wheel guard with respect to said support structure during blowup of said grinding wheel.

3. The apparatus of claim 1, wherein said permanently deformable element is a secondary energy dissipator absorbing a portion of energy not dissipated by a primary energy dissipator comprising a rigid closed cell absorption means placed between said grinding wheel and said wheel guard for dissipating a portion of the energy released during blowup of said grinding wheel.

3. a control portion determining the threshold of failure of said permanently deformable element.

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