US3868793A

US3868793A - Internally safety reinforced cup grinding wheel

Info

Publication number: US3868793A
Application number: US370938A
Authority: US
Inventors: John J Corcoran; Paul W Kalinowski
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1973-06-18
Filing date: 1973-06-18
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04
Also published as: JPS5053989A; GB1459918A; ZA743553B; LU70354A1; FR2233142B1; DE2429051A1; FR2233142A1

Abstract

A resinoid bonded abrasive cup type grinding wheel with internal layers of safety reinforcing material integrally molded within, bonded to and tieing the central hub and sidewall portions of the wheel together. The safety reinforcement extends continuously, in a smoothly curved shape without sharp bends, generally radially outward through the central hub portion, and then generally axially and radially outward through the sidewall portion to an outer peripheral edge. The wheel is molded by supporting at least one layer of flexible reinforcing material between two layers of a curable mixture of abrasive and bond on a thin flexible supporting disk partially supported above a mold cavity by a fixed outer narrow top surface of a lower mold plate and an aligned movable support surface of a movable central hub support member resiliently biased into the mold cavity and slideable in the lower mold plate. During molding, the central hub forming portion of the mix is continuously held and slightly compacted between the central hub support member and an upper mold plate engaged by a platen of a press which forces them into and to a fixed stop at the bottom of the cavity. As the surrounding loose mix and layers of reinforcement, which are free to bend relative to the fixed outer annular surface, move into the cavity the abrasive mix shifts sufficiently to allow the reinforcement to assume a smoothly curved shape prior to being compressed to final size and shape.

Description

eat

States Corcoran et a1.

[451 Mar. 4, 1975 1 INTERNALLY SAFETY REINFORCED CUP GRKNDING WHEEL [75] Inventors: John J. Corcoran, Ashland; Paul W. Kalinow'ski, Boylston, both of .Mass.

[52] U.S. Cl 51/209 R' [51] Int. Cl 324d 7/04 [58] Field of Search 51/209 R, 206, 206 NF, 51/378,170 T, 170 PT [56] References Cited UNlTED STATES PATENTS 7 2,540,112 2/1951 Goepfert 51/206 2,997,820 8/1961 Skoog 1 1 51/209 R 3,041,797 7/1962 Moffly 51/378 3,121,981 2/1964 Hurst 51/209 X 3,136,100 6/1964 Robertson 51/209 R 3,431,687 3/1969 Fischer 51/206 NF Primary Examiner-Donald G. Kelly Attorney, Agent, or Firm-Walter Fred [57] ABSTRACT A resinoid bonded abrasive cup type grinding wheel with internal layers of safety reinforcing material integrally molded within, bonded to and tieing the central hub and sidewall portions of the wheel together. The safety reinforcement extends continuously, in a smoothly curved shape without sharp bends, generally radially outward through the central hub portion, and then generally axially and radially outward through the sidewall portion to an outer peripheral edge.

The wheel is molded by supporting at least one layer of flexible reinforcing material between two layers of a curable mixture of abrasive and bond on a thin flexible supporting disk partially supported above a mold cavity by a fixed outer narrow top surface of a lower mold plate and an aligned movable support surface of a movable central hub support member resiliently biased into the mold cavity and slideable in the lower mold plate. During molding, the central hub forming portion of the mix is continuously held and slightlycompacted between the central hub support member and an upper mold plate engaged by a platen of a press which forces them into and to a fixed stop at the bottom of the cavity. As the surrounding loose mix and layers of reinforcement, which are free to bend relative to the fixed outer annular surface, move into the cavity the abrasive mix shifts sufficiently to allow the reinforcement to assume a smoothly curved shape prior to being compressed to final size and shape.

8 Claims, 3 Drawing Figures INTERNALLY SAFETY REINFORCED CUP GRINDING WHEEL BACKGROUND OF THE INVENTION 1. Field of Invention The invention relates to cup shaped grinding wheels and particularly to an internally safety reinforced resinoid bonded abrasive cup type grinding wheel, apparatus and method of making it.

2. Description of the Prior Art Although cup shaped grinding wheels are used with different types of grinding apparatus and for various purposes, the resinoid cup shaped wheel is normally attached to hand operated high speed portable snagging grinders for heavy duty rough grinding off unwanted portions of castings, forgings, weldments and the like. Since various abrasive surfaces of the wheel may be used to grind with, it is obvious that those portions must be left unprotected and subjected to possible fracture resulting from accidental impact with another object. Thus when a fractured wheel is rotated at relatively high speed, one or more fragments of the wheel are likely to be hurled at great force and cause personal injury to the operator or others in the vicinity as well as damage the work and or equipment. Various procedures, devices and materials have been devised in an attempt to safety reinforce the wheel and prevent fragments of a fractured wheel from being hurled therefrom. However, some of the devices are unpopular with the operators and others obstruct or interfere with the grinding action.

Heretofore cup shaped grinding wheels have been reinforced internally by imbedding, one or more preformed rings, straps or bands of various high strength materials, in specific regions of the wheel in the manner disclosed in U.S. Pat. Nos. 2,250,580, 3,141,271 and 3,716,951. Others are reinforced by molding combination mounting inserts or backing plates with bent up flanges embedded only in the hub or mounting portion of the wheel as disclosed in U.S. Pat. Nos. 3,135,999, 3,278,301 and 3,204,371. Still others are safety reinforced externally by one or more separate bands or layers of high strength material bonded to or adjacent to the outer peripheral surfaces of the wheel as taught in U.S. Pat. Nos. 2,800,754, 3,121,981 and 3,171,236.

However, unlike the applicant the prior art does not provide an internally safety reinforced cup shaped wheel wherein the reinforcement or safety web extends continuously through the deeply recessed central hub portion and into the annular sidewall portion whereby substantially all portions of the wheel are tied together. Hence the wheel of the invention can be rotated safely at the higher speeds required in this day and age. Should the wheel become fractured, the reinforcement will hold the fragments which are likely to cause injury, together and thereby prevent serious injury.

Applicant is also aware of the various resin bonded, reinforced, depressed or raised hub type portable wheels disclosed in U.S. Pat. Nos. 2,540,112, 2,808,688, 2,997,820, 3,041,797 and 3,121,981. Molded within some of them are one or more parallel layers of continuous reinforcing material which extends through the raised or depressed central hub portion, then bending slightly and continuing radially out through a relatively thin larger annular portion to the peripheral edge of the wheel. However, depressed cen ter wheels differ from the more deeply recessed shape wheels in that they are more flexible, relatively much thinner, much easier to manufacture and reinforce due to the shallow recess and the slight axialdisplacement of the central hub portion which is of substantially the same thickness as the larger outer annular portion.

Heretofore, attempts have been made to manufac-,

ture and safety reinforce the relatively deeper cup type wheels by the same method used to make the depressed center wheel. However due to the deeper recess and mold cavity required to mold the cup wheel the reinforcement was bent sharply and fractured by the abrasive forced into contact therewith. Hence, the reinforcement was ineffective since it did not tie all portions of the wheel together, and the required quality, specifications and safety factor of the wheels varied widely and could not be consistently repeated.

Likewise multi-step molding methods of uniformly spreading abrasive mix, accurately placing and centering preformed safety reinforcing member therein, and uniformly filling the deep cavity around it with additional abrasive mix have not been entirely satisfactory, are more costly, and complicate the molding process. The applicants method and apparatus for molding the cup wheel of the invention differs from the prior art disclosed in the above mentioned patents and in the additional following U.S. Pat. Nos. Re. 20,460 and 3,705,248 in that the alternate layers of abrasive bond mix and flexible safety reinforcement for each wheel are placed and supported by a separate nonreusable thin flexible preformed support member supported within a mold band and above a mold cavity, by a narrow fixed outer ledge or surface and a movable support surface of a movable upwardly resiliently biased slideable central hub forming member in a lower female die or mold plate. During molding the central portion of the layers are continuously compressed and held between the moving central hub forming portions of the upper mold plate and the movable central hub member while the surrounding outer portion of the layers, which form the sidewall portion of the wheel, are free to shift relative to each other and thereby allow the reinforcement to bend smoothly about and from the fixed outer surface and assume a smoothly curved shape in the mixture as they move into the cavity prior to being trapped and finally compressed to final form. Each thin preformed support member being molded to the wheel and its shape, may be left on, but, preferably is removed from the molded wheel and disposed of.

SUMMARY OF THE INVENTION According to the invention cup shape grinding wheel has one or more layers of high strength safety reinforcing material situated in, integrally molded and bonded within molded curable resinoid bonded abrasive mixture. Each layer of safety reinforcement extends or has elements which extend continuously, in a smoothly curved shape, from an inner edge about the central hole radially outward through the central hyb portion, then generally axially and radially outward through the annular sidewall portion to an outer peripheral edge located initially at or adjacent a peripheral abrasive surface of the wheel. The safety reinforcement ties or connects the mounting or central hub and annular sidewall portions of the wheel together so that broken fragments thereof are held together and prevented for causing personal injury. Also the curvature or curvilinear shape of the reinforcement is such that, it is without sharp bends at which breaks are likely to occur, the radial position of its outer peripheral edge varies continuously as the axial length of the annular sidewall portion is re duced during grinding and does not materially interfere with grinding.

The invention also includes a method and apparatus for making the internally safety reinforced resinoid bonded abrasive cup type grinding wheel. Essentially the method and apparatus comprises: supporting alternate layers of a suitable resin bond abrasive mix and flexible reinforcing material on a thin flexible disk situated and supported above a lower portion of a mold cavity, by a fixed narrow outer annular top surface of a lower female mold plate having a cavity adapted to shape the lowerouter peripheral surface of the cup shape wheel and an inner annular top surface of a central hub forming member slideably mounted, about a central hole, arbor, in the lower mold plate and resiliently biased upwardly within the cavity to the plane of the fixed narrow outer annular top surface. Thereafter, an upper male mold plate adapted to form the interior and the exterior radial grinding surface of the cup shape wheel is forced initially into engagement with only the central hub forming portion of the layers.

Then during further simultaneous movement of the upper mold plate and the slideable central hub forming member, the inner central hub forming portions of the layers are continually held and partially compacted between them while the free outer annular sidewall forming portions of the layers of loose resin bond abrasive mix and reinforcement are allowed to and do shift slightly from their original relative positions because the more rigid layers of flexible reinforcement have more resistance to being bent sharply as it is forced into the cavity prior to being trapped and compressed to final size and shape.

Therefore it is the primary object of the invention to provide an internally safety reinforced resinoid bonded abrasive cup shaped grinding wheel wherein the safety reinforcement extends, continuously, in a smoothly curved shape, between and ties the central hub and annular sidewall portions of the wheel together, apparatus and method for making the wheel.

BRIEFv DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective vertical sectional view through the cup shaped wheel of the invention;

FIG. 2 is a vertical sectional view showing the relative positions of the parts of a mold assembly filled with and supporting alternate layers of abrasive resin bond mix and safety reinforcement above the mold cavity prior to being molded into a cup shape wheel; and

FIG. 3 is another vertical sectional view of the mold assembly showing the relative positions of the abrasive layer and safety reinforcement and positions of the mold parts after the wheel has been molded.

DESCRIPTION OF THE PREFERRED EMBODIMENTS(S) Referring to FIG. 1 there is shown an internally safety reinforced cup shaped or type grinding wheel comprised of a deeply recessed central hub or mounting portion 12. On the hub portion 12 are mounting means such as, the central hole 12a with or without a bushing therein shown extending between an inner or recessed surface 12b and an outer or back surface 120 and through the hub portion about the central axis of the wheel. The mounting means may further comprise a suitable insert or threaded bushing in the center hole 12a adhesively or mechanically secured to the wheel as shown in phantom lines. The hub portion 12 has an exterior or outer tapered or frusto conical shape surface 12a extending axially from the back surface 120. Integrally molded with the central hub portion or mounting portion 12 is an annular sidewall portion 14 of predetermined axial length or depth and radial thickness extending around the central axis of the wheel. The annular sidewall portion has an internal or inner abrasive surface 14a projecting, generally in an axial direction, from the recessed surface 12b to a junction with the inner edge of a radial grinding face or surface 14b and an exterior peripheral grinding abrasive surface 14d tapering from the outer tapered surface 12d of the hub portion 12, to a junction with an outer or circumferential edge of the radial grinding surface 14b.

Preferably, the cup wheel 10 shown is what is known as a flared cup type wheel wherein the annular sidewall portion 14 tapers or flares outwardly in both axial and radial directions from the central hub portion 12 and has a central frusto conical shaped recess of predetermined depth therein.

Cup grinding wheels are also known as or designated by number which indicates its general shape and dimension. The flared cup shaped grinding wheel of the invention has what is generally known in the art as a type 1 1 shape, which the applicants have modified slightly to enhance the manufacture, and safety thereof without reducing its effectiveness.

One or more layers or disks 16 of safety reinforcing material may be provided for safety reinforcing the wheel against breakage at high speed increasing the safety factor of wheel and holding fragments of a broken or cracked wheel together to prevent personal injury. The safety reinforcing layer or disk 16 may be preformed or cut out of any suitable and well known flexible sheet, foil or fabric of high strength materials such as metal, nylon, rayon, cotton, glass or combinations thereof. Preferably the reinforcement disks 16 are made of woven, braided or knitted open mesh fiber glass fabrics containing a plurality of continuous strands or roving composed of a large number of continuous glass filaments. However, other types of high strength perforated sheet material may be used.

One preferably suitable fiber glass material which was used to safety reinforce the wheel 10 is designated as Lewcott Style No. 202, 2 X 2 mesh or two openings per inch, of mock leno woven substantially untwisted rovings of fiber glass fabric having a breaking strength of 1,600 lbs. per inch and weighing 30 oz. per square yard before being coated with a thin layer of uncured thermosetting liquid resin and commercially available from Lewcott Chemical and Plastics Corp., Millbury, Mass.

Initially the layers 16 of safety reinforcing material are preformed or cut into flexible disks of predetermined diameter prior to being molded or reformed to the smoothly bent curvature shown in FIGS. 1 and 3 during molding of the wheel 10.

As shown in FIG. 1 each reformed layer or safety disk 16 has a plurality of spaced strands, tapes, rovings or elements 16a each consisting of a plurality of filaments which may extend continuously from either the central axis or an inner edge about the central hole 12a radially outward through the central hub portion, then bending or curving smoothly therefrom into generally an axial direction through the annular sidewall portion and again bending or curving smoothly outwardly in generally a radial direction to an outer peripheral edge situated at or adjacent the exterior peripheral grinding surface 14d.

The composition of the molded and cured resin bonded abrasive mix used to make the wheel may comprise any of the suitable and well 'knonw natural or synthetic resins, abrasive particles, fillers, and grinding aids. For example, the abrasive particles may be of diamond, boron nitride, alumina, aluminazirconia, silicon carbide, garnet and mixtures thereof bonded to gether with the reinforcement 16 preferably by a thermosetting resin such as, phenolic, or phenolformaldehyde resin, urea formaldehyde resin, epoxy and combinations thereof in either the form of a liquid coating on the grains or powder mixed with the abrasive.

The wheels may be cold or hot pressed to form and cured in the conventional manner at prescribed temperatures for a period of time sufficient to fully cure the resin bond and further comprise an initially thin preformed flexible support member 50 molded to and forming a permanent backing on the

surfaces

12d and 12c of the wheel as shown in FIG. 3.

A method of and apparatus for molding the cup wheel in accordance with the invention will now be described in conjunction with FIGS. 2 and 3 of the drawings. Referring to FIG. 2. there is shown a molding apparatus or mold assembly 30 which is useable with and normally supported on the bed or lower platen P of either a hot or cold molding press of well known suitable and conventional design.

The mold assembly 30 comprises a mold band or hollow cylinder 32 supported on the platen P of pressing means not shown and having a central hole or cylindri cal aperture defined by and within the inner or internal molding surface 320 of the desired peripheral shape of the wheel to be molded. Mounted within the lower por tion of the mold band 32 and supported by the platen P is a lower female mold plate 34 extending axially and vertically within the central hole between a bottom surface 34a and an annular top surface 34b extending radially between an inner side molding surface 34c in the lower portion of a mold cavity 34d and an outer surface 34e of the lower mold plate 34 adjacent surface-32a of thgmold banci3 2 Alternatively the lower female mold plate 34 could be made an integral part of the mold band 32 and whereby the annular top surface 3412 would extend to the internal surface 329 defining the peripheral shape of the central hole or upper portion of the mold cavity M about the central axis of the mold assembly 36.

Slideably mounted with a central recess or counter bore 34f in the lower mold plate 34 is an adjustable central hub forming and/or support member or movable support cylinder 36 with a central aperture or arbor hold 36a extending axially between an upper top annular hub forming surface 36b and a lower or bottom surface 36c thereon. The central bore or recess 34f extends from the bottom of the mold cavity 34d to a recessed bottom stop surface 34g, an axial depth substantially equal to the axial length of the hub support member 36. Hence when the surface 360 engages the stop surface 34g the upper hub support and forming top surface 36b will be aligned to a horizontal plane with the bottom surface of the mold cavity 34d.

Biasing means, which may be of any suitable form and material, are provided for biasing the central support member 36 upwardly into the mold cavity 34d relative to the stop surface 343 and lower mold plate 34. The biasing means shown comprises at least one but preferably a plurality of resilient compressible coil springs 38. Each of the springs 38 has one end portion situated in and engaging the member 36 within a hole 36d and an opposite end portion engaging the lower mold plate 34 within a recess 34h in the stop surface 34g. Alternatively a larger single compression spring could be arranged around the central axis and recessed into a single central hole or counter bore in the bottom of the hub support member 36 or the counter bore could serve as an air cylinder into which compressible air is forced to raise the member 36.

Adjustable means are preferably provided for limiting the movement of the member 36, positioning and aligning the movable upper-annular or top surface 36b of the hub forming member 36 on the same plane as the fixed narrow outer annular top surface 34b on the lower mold plate 34. The adjustable means may be fixed but preferably comprise one or more adjustable threaded screws or bolts 40 each with a threaded portion threaded into a threaded hole in the lower portion of the member 36 and extending-therefrom through a clear counterbored hole 34h to a stop shoulder on the head portion of the screw 40 within the counterbore 341' of suitable depth. It can be seen that by adjusting the screw 40 the verticle position of the upper top surface 36b of the member can be aligned and maintained on the same plane with the outer annular surface 34b of the lower mold plate 34. Also, "the depth of counterbore 341' must be deep enough to'allow sufficient free unobstructed movement of the head 40 and the member 36 to bottom against stop surface 34g.

l-Iole forming means are provided and supported by the lower mold plate 34 for providing the cup shape wheels with any one of the desired conventional mounting or drive means by which it can be mounted and rotatably driven about its axis in the well known manner. The hole forming means shown comprises an elongated hole arbor 42 of the desired cross sectional size and shape of the central hole 12a to be formed in the wheel 16. The arbor 42 extends vertically and coaxially with the axis of the mold assembly 30 from a lower end or bottom surface 34a of the: lower mold plate 34 through a support hole therein, the central aperture 36a in the movable member 36 and the upper portion of the mold cavity to an upper or opposite end situated a sufficient distance above the top of the mold band 32 to receive an upper mold plate 44.

Obviously the mold assembly could be modified, for example, the arbor 42 could be fixed to or made an integral part of the central hub support member 36 and movable therewith. Also, the bolts 40 could be eliminated by making each spring 38 to the exact axial length sufficient to align the surfaces 36b and 34b on a single plane. When the wheel has no center hole the arbor 42 is eliminated and replaced with suitable drive means such as a threaded insert, bushing or another type of wheel mounting integrally molded therewith or adhesively secured thereto in the well known manner. Alternatively the center hole could be bored after the wheel has been molded or fully cured.

The upper mold plate 44 which may be attached to and supported by the upper platen of a press has a central hole 44a into which the arbor 42 extends and slideably engages the male mold plate 44 as it is forceably moved in an axial direction relative to the arbor 42. The central hole 44a extends coaxially with the axis of the arbor 42 between an upper press platen engaging top surface 44b and a lower or central recess hub forming surface 440 substantially parallel to the surface 36b. Extending upwardly and outwardly from the lower forming surface 440 is a frusto conical shape portion with a tapered exterior surface 44d extending to an intermediate or'annular radial surface 44e substantially parallel to the surfaces 440 and 44b. The substantially flat surface 44a extends radially outwardly to the circumferential or outer peripheral surface 44f of a diameter or size and shape adapted to allow sliding engagement with the surface 32a of the mold band 32.

Obviously the

exterior surfaces

44c, 44d, 44e and 44f of the upper male mold plate will determine the final shape and size of the respective interior surfaces 12b and 14a and the radial surface 14b of the cup wheel 10. Also, the interior surfaces 34c of the lower female mold plate 34 and exterior top surface 36b of member 36 will shape the respective surfaces 120 and 12d of the cup wheel 10. Molding surface 32a of the mold band 32 substantially parallel to the central axis and surface 34a of the lower mold plate 34 wil determine respectively the larger circumferential size or diameter and shape of the cup wheel and provide an additional triangular shaped portion l4e, shown in phantom lines in FIG. 1 and which is preferably removed to form the tapered peripheral surface 14d situated at an angle to the surface 12d.

The mold assembly 30 may further comprise flexible support means for supporting and containing a load consisting of the layers of thecurable mixture of abrasive and bond and reinforcing material to be molded above the cavity between the movable and fixed support surfaces 36b and 34b during the molding operation. Preferably the flexible means comprises a replaceable, nonreuseable and disposable thin flexible preformed member 50 molded to the wheel and its shape and which may be left as a part of the wheel or removed therefrom as desired. Initially, each preformed support member extends horizontally across the mold cavity and is supported at its outer peripheral edge portion by the fixed narrow outer surface 34b, at its inner central portion by the movable surface 36b and has an intermediate unsupported portion spanning the mold cavity below.

Preferably as shown in FIG. 2, a flexible support disks 50 of suitable flexibility, shape, strength and stiffness is preformed out of substantially imperforate sheet material or closely woven fabric sufficient to contain the abrasive mix and has a center hole allowing it to be slipped over the hole arbor 42, and supported by the relatively radially spaced top annular surfaces 36b and 34b. The support disk 50 may be cut out of any suitable flexible sheet material, such as paper, plastic, cotton, rayon, nylon, fiber glass, metal, foil and combinations thereof. However, either a single disk of crepe paper or a composite or laminated support disk of paper stick glass cloth consisting of a layer of thin paper attached to a layer of open mesh fiber glass cloth found to be satisfactory for supporting the alternate layers of abrasive resin mix 18 and reinforcement 16 without any appreciable sag into the cavity 34d. A suitable glass cloth for the composite disk and final backing secured to the wheel is designated a No. 955 consisting of woven low twist strands of glass fibers available from Eli Sandman Company, Worcester, Mass. When the disk 50 is a composite of paper and glass cloth it is placed in the mold with the thin paper side thereof in contact with the surfaces 34b and 36b and the open mesh glass cloth on top whereby the abrasive mix 18 is prevented from passing into the lower portion of the mold cavity 34d and the open mesh glass cloth becomes integrally molded to the exterior surfaces of the wheel 10 after which the paper may if desired be peeled off and removed therefrom. To load and prepare the mold assembly as shown in FIG. 2 for molding a cup wheel a new replaceable support disk 50 is slipped over the arbor and placed on the supporting surfaces 36b and 34b for each wheel molded. A first or bottom layer of the desired loose abrasive resin mix 18 is spread and leveled to a predetermined depth upon the support dish 50 followed by at least one or a first safety disk 16 and at least a second or top layer of the loose abrasive resin mix 18 if the wheel 10 is to have only one layer or disk of internal safety reinforcement 16. Obviously when the cup wheel 10 is to have more than one layer of in-' ternal reinforcement the depth of each layer of loose abrasive mix 18 spread on each layer of safety reinforcement 16 is reduced in proportion to the number of layers of safety reinforcement disks 16 desired. To provide the additional strength and a better safety factor the cup wheel 10 of the invention may have two but preferably three internal layers of safety reinforcement 16. Hence, second and third disks of reinforcement 16 are placed upon thinner second and third intermediate layers of abrasive mix 18 and followed by a final top layer of the abrasive mix 18.

Alternatively, each layer 18 of the abrasive mix may be preshaped, and lightly prepressed into an uncured or green self supporting preformed layer or disk of the abrasive bond mix. Each preformed layer or disk being lightly pressed and compressed to a thickness and degree which will allow handling and placing of the disks in the mold assembly and yet allow them to break up and crumble during the molding operation.

It can be seen that the horizontally extending layers of mix 18 and reinforcement disks 16 collectively provide a moldable load with an unpressed inner annular portion or central hub forming portion, around and adjacent to the hole arbor 42, resiliently supported by the inner annular movable surface 36b, an outer narrow annular portion thereof supported by the fixed top annular surface 34b of the lower mold plate 34 and between them an intermediate annular portion or annular sidewall forming portion supported by the flexible support disk 50 spanning the lower portion of the mold cavity 34d.

After, the upper portion of mold cavity in the mold band 32 has the desired number of layers of mix and reinforcement, the upper mold plate 44 is slipped over the exposed upper end portion of the hole arbor 42 so that the inner or lower surface 44c engages only the inner annular portion of the top layer of abrasive mix 18.

The loaded mold assembly 30 if not on the lower platen P of a conventional molding press is transferred thereto and aligned with the upper platen of the press or the upper mold plate if attached thereto. Then the press is actuated which forces the upper and lower mold plates to move relative to and toward each other and partially compact the central annular portion of the mix 18 between surface 36b of the resiliently biased movable member 36 and surface 440 of upper mold plate prior to overcoming the total resistance of the springs 38 and movement of the member 36 thereby.

Depending on the total spring resistance, which is predetermined and can be varied by substituting springs made of lighter or heavier wire, the central annular portion of the mix 18 may be reduced to an axial depth or dimension up to one-third less than the initial total load thickness before the total resistance of the springs is overcome.

In FIG. 2 there is shown in phantom line the partially displaced position of the upper mold plate 44 and the partially compressed central portion of mix 18 and safety disks 16. It can be seen that the surrounding intermediate and outer annular portions of the layers of mix 18 and reinforcement 16 are free to shif relative to each other and the lower mold plate 34 until the surfaces 44e of the upper mold plate has moved down to entrap the mix and compress the outer annular portion of the mix between the fixed surfaces 34b and movable surface 44c sufficiently to prevent further relative movement in the outer annular portion only.

Further, downward movement of the upper mold plate 44 causes simultaneous movement of the partially compressed central portion of the mix 18 into the lower portion of the mold cavity 34d, and the movable member 36, in the counter bore 34f, which continuously compresses, increases the resistance and the force exerted by the springs 38 against the member 36 further compressing the central portion of the mix l8 prior to engaging the stop surface 343.

As the partially compressed central portion of the mix 18 and member 36 move together into the lower mold cavity relative to the fixed outer annular surface 34b the intermediate annular portion of the mix is trapped and forced by the tapered or conical surface 44d of the upper mold plate 44 to flow into the lower portion of the mold cavity 34d. The surrounding intermediate annular portion of the mix 18 remains substantially unpressed until it moves into engagement with the tapered surface 34c of the lower mold cavity 34d of frusto conical shape. Since the outer annular portion of mix 18 above the fixed top surface 34b is partially compressed before and to a greater degree than the adjacent intermediate portion, the narrow outer annular portion adjacent the outer peripheral edges of each disk 16 and of the support disk 50 is firmly gripped by the partially compressed mix therein. The inner or central annular portion adjacent the inner edge of each of the disks 16 around the central hole is also firmly gripped and substantially fixed against radial movement of the arbor 42 and the compressed and movable central annular portion of the mix 18 aroung the arbor is compressed to a greater degree than and prior to the outer annular portion of the mix 18.

During the downward movement the flexible disks 16, which have a greater resistance to bending than the relatively unpressed loose granular intermediate annular portion of the mix 18, move through and reposition themselves in the mix and bend gradually into a smoothly curved shape by displacing and allowing the abrasive mix 18 to pass through the openings therein prior to being reformed to the final shape of curvature.

Each of the flexible disks 16 are drawn inwardly and move radially relative to the intermediate and outer annular portion of the mix as they assume a smooth bending curvilinear shape or internal path'of curvature extending between their inner edge in the central portion to their outer peripheral edge in the outer annular portion of the mix. Obviously the length of the smoothly bending curvature of each reformed safety disk 16 is substantially equal to the initial radius or radial distance between the hole and the outer peripheral edge of the disk 16 prior to being reformed and molded in the wheel 10.

When the movable member 36 reaches and engages the stop surface 34g its upper top surface 36b will be aligned substantially with the surrounding fixed bottom surface of the lower mold cavity and which together provide a solid bottom surface against which the mix is pressed to final size and shape. As shown in FIG. 3 the mix 13 is further compressed and molded to the desired size and shape determined by the mold assembly at a pressure of between 1 and 4 tons per square inch applied thereto by the press.

If desired the mold assembly 30 may be constructed so that it can be heated in any suitable well known conventional manner or used in contact with and heated by the heatable platens of a conventional hot press to either partially or completely cure the resin and bond the mix 18 and the safety disks 16 together. The wheels after being pressed to shape are stripped from the mold in the conventional way such as by separating the mold plates whereupon the released compressed springs resiliently forces the member 36 and molded wheel upwardly out of the lower cavityfrom which it may be removed. Another method would be by axially displacing the upper and

lower mold plates

34 and 44 relative to and out of the mold band 32, the arbor 42 out of the upper mold plate 44 and the molded wheel 10, remo ving the upper mold plate 44 from the inner or central cavity of the wheel and the wheel from the cavity in the lower mold plate 34.

Next, the molded and reformed thin support diskSll, which may be left on, is preferably peeled off or re moved in any suitable manner from the-exterior surfaces of the wheel.

The cold pressed green wheel is then placed in between a pair of pressure setting plates, batts, or supports preformed to the shape of the upper and

lower mold plates

34 and 44 and which :apply about 2 pounds per square inch of pressure to maintain the molded shape and baked in an oven for 15 hours at a temperature of C until the resin has completely cured and bonded the abrasive mix and the safety disks 16 into a rigid integral structure. After curing, the assembly of setting plates and the wheel are removed from the oven allowed to cool and the wheel separated therefrom.

The cured wheel which has substantially the same cross sectional shape as that shown in FIG. 3 can be left and used with that configuration which includes an upper sidewall portion with an outer cylindrical peripheral or circumferential surface 14f, sugstantially parallel to the central axis, formed by and to the same diam eter or size as the engaging surface 320. The surface 14f extends between the annular radial surface 14b formed by the engaging surface 44a and an intermediate narrow outer annular radial surface ll4g formed by the engaging fixed surface 34b. When compared with the preferred cross sectional shape of the wheel 10 ure. The results were as follows:

shown in FIG. 1, it can be seen that the cured wheel must be further processed to remove a triangular shaped portion l4e within the initial molded surfaces 14f and 14g as indicated by phantom lines and the desired outer tapered periphery abrasive surface 14d shown in FIG. 1. The triangular portion 14c is preferably removed by a truing or reshaping operation which reshapes the wheel to have the upper frusto conical shaped or tapered outer peripheral surface 14d around the flared annular sidewall portion 14 extending from the lower or adjacent the frusto conical shape or tapered outer peripheral surface 140 around the central hub portion 12. The surfaces 12d and 14d shown are situated at an angle to each other and inclined at different angles fromthe central vertical axis and the horizontal plane at bottom surface 120 normal to the gep t r2 1 l axis of the wheel.

A group of internally reinforced resinoid bonded abrasive flaring cup wheels of the invention were made, each purposely cracked at four places 90 apart and speed tested to failure. The cracked wheels tested had an annular sidewall peripheral surface 14d tapering from a mazimum outside diameter of 6 inches to inches diameter, a 1% inch diameter center hole 120 with a threaded bushing adhesively secured therein, a 1%. inch thick central hub portion 12 with the surface 12b recessed 1% inches from the radial surface 14b and a surface 12d tapering from the 5 inch diameter to the back surface 120 of approximately 3 inches in diameter all molded from the same premixed batch of mix but a with a different number of identical safety discs 16 therein of style No. 202 described above.

The premixed batch of abrasive mix from which the wheels were molded was comprised of the following percentage by weight of the ingredients listed below:

Ingredients by Wt.

16 grit aluminum oxide abrasive grain 77.53 Bakelite No. 5980 powdered thermosetting resin 9.26 325 mesh glass spheres (filler) 8.40 lime (CaO) 1.84 carbon black .20 (Carbosota) refined Creosote .99 furfural (plasticizer) 1.78

disks or webs are capable of being operated safely at' 14,000 surface feet per minute (s.f.p.m.) without any fear of failure and personal injury.

A series of 6 inch cup wheels of the invention each with three safety disks were also made in five different grades or degrees of hardness and speed tested to fail- Average Speed (s.f.p.m.)

Grade No. of Wheels At F allure Softer l 3 22,600 2 3 23,900 3 3 24,500 4 3 25,700

Harder 5 3 26,200

From the above data wheels of increasing hardness and grade indicated by the larger number failed at proportionately higher surface feet per minute (s.f.p.m.) than the softer grades and are likewise capable of being safely operated at proportionately higher operating speeds greater than 14,000 surface feet per minute.

It is to be understood that the disclosure hereinabove is for the purpose of illustration only and the the invention includes all modifications and equivalents which fall within the scope of the appended claims.

We aim; 1. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel comprisingz i a recessed central hub portion of predetermined axial thickness extending radially between a relatively deep recess in one side of the grinding wheel and an opposite side of the grinding wheel to an exterior peripheral surface of the hub portion and wheel and including substantially the entire opposite side of the grinding wheel; means in the central hub portion for mounting and rotating the wheel about a central axis; an annular sidewall portion of predetermined radial thickness and initial axial length reduceable during grinding, integrally molded with the hub portion, extending around the central axis and the recess and generally axially from the recessed central hub portion to the one side of the wheel and having a radial grinding surface on the one side of the grinding wheel and an external peripheral surface adjacent to and extending from the radial grinding surface to a junction with the exterior peripheral surface of the hub portion and wheel; and at least one internal layer of safety reinforcing material integrally molded within and bonded to the central hub and sidewall portions and having a smoothly curved shape extending continuously generally radially outward through the central hub portion, then generally both axially and radially outward in a continuously curving path through the annular sidewall portion to an outer peripheral edge;

whereby the continuous internal safety reinforcing material is bonded to and continuously interconnects the central hub and sidewall portions of the wheel, has no sharp bends at which breaks are likely to occur, permits the wheel to be operated safely at high speed, holds fragments of the wheel which may be accidentally broken together and thereby prevent them from being hurled at high speed and causing personal injury and the radial position of the outer peripheral edge once exposed at the radial grinding surface varies as the axial length of sidewall portion is reduced during grindmg.

3. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 2, further comprising:

a third internal layer of safety reinforcing material spaced from the second internal layer of safety reinforcing material, integrally molded within and bonded to the central hub and sidewall portions and having a smoothly curved shape extending continuously generally radially outward through the central hub portion, then generally axially and radially outward through the sidewall portion to an outer peripheral edge.

4. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 3 wherein each of the internal layers of safety reinforcing material comprises a layer of open mesh woven fiber glass fabric.

5. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 4 wherein the open mesh fiber glass fabric comprises:

a plurality of woven roving each having a plurality of continuous substantially untwisted glass filaments.

6. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 5 further comprising:

a frusto conical shaped recess situated within the annular sidewall portion and adjacent the central hub portion, and

wherein the recessed central hub portion further comprises:

LII

an inner surface located initially a predetermined axial depth from the radial grinding surface, and spaced from the opposite side of the wheel and a tapered exterior peripheral surface flaring radially outward from an outer peripheraledge of the opposite side of the wheel to a junction with the external peripheral surface of the annular sidewall portion.

7. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 6 wherein the annular sidewall portion further comprises:

a tapered external peripheral surface extending from a junction with the tapered exterior surface of the central hub portion and flaring radially outwardly relative to the central axis to a junction with an outer edge of the radial grinding surface.

8. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 6 wherein the annular sidewall portion has a straight external peripheral surface of predetermined axial length extending substantially parallel to the central axis from a junction with an outer edge of the radial grinding surface, and

a narrow intermediate radial surface spaced from the radial grinding surface and extending radially outward from the tapered exterior peripheral surface of the central hub portion to a junction with the straight external peripheral surface.

Claims

1. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel comprising: a recessed central hub portion of predetermined axial thickness extending radially between a relatively deep recess in one side of the grinding wheel and an opposite side of the grinding wheel to an exterior peripheral surface of the hub portion and wheel and including substantially the entire opposite side of the grinding wheel; means in the central hub portion for mounting and rotating the wheel about a central axis; an annular sidewall portion of predetermined radial thickness and initial axial length reduceable during grinding, integrally molded with the hub portion, extending around the central axis and the recess and generally axially from the recessed central hub portion to the one side of the wheel and having a radial grinding surface on the one side of the grinding wheel and an external peripheral surface adjacent to and extending from the radial grinding surface to a junction with the exterior peripheral surface of the hub portion and wheel; and at least one internal layer of safety reinforcing material integrally molded within and bonded to the central hub and sidewall portions and having a smoothly curved shape extending continuously generally radially outward through the central hub portion, then generally both axially and radially outward in a continuously curving path through the annular sidewall portion to an outer peripheral edge; whereby the continuous internal safety reinforcing material is bonded to and continuously interconnects the central hub and sidewall portions of the wheel, has no sharp bends at which breake are likely to occur, permits the wheel to be operated safely at high speed, holds fragments of the wheel which may be accidentally broken together and thereby prevent them from being hurled at high speed and causing personal injury and the radial position of the outer peripheral edge once exposed at the radial grinding surface varies as the axial length of sidewall portion is reduced during grinding.

2. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 1 further comprising: a second internal layer of safety reinforcing material spaced from the at least one internal layer of safety reinforcing material, integrally molded within and bonded to the central hub and sidwall portions and having a smoothly curved shape extending continuously generally radially outward through the central hub portion then generally axially and radially outward through the sidewall portion to an outer peripheral edge.

3. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 2, furthEr comprising: a third internal layer of safety reinforcing material spaced from the second internal layer of safety reinforcing material, integrally molded within and bonded to the central hub and sidewall portions and having a smoothly curved shape extending continuously generally radially outward through the central hub portion, then generally axially and radially outward through the sidewall portion to an outer peripheral edge.

5. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 4 wherein the open mesh fiber glass fabric comprises: a plurality of woven roving each having a plurality of continuous substantially untwisted glass filaments.

6. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 5 further comprising: a frusto conical shaped recess situated within the annular sidewall portion and adjacent the central hub portion, and wherein the recessed central hub portion further comprises: an inner surface located initially a predetermined axial depth from the radial grinding surface, and spaced from the opposite side of the wheel and a tapered exterior peripheral surface flaring radially outward from an outer peripheral edge of the opposite side of the wheel to a junction with the external peripheral surface of the annular sidewall portion.

7. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 6 wherein the annular sidewall portion further comprises: a tapered external peripheral surface extending from a junction with the tapered exterior surface of the central hub portion and flaring radially outwardly relative to the central axis to a junction with an outer edge of the radial grinding surface.

8. An internally safety reinforced cup type resinoid bonded abrasive grinding wheel according to claim 6 wherein the annular sidewall portion has a straight external peripheral surface of predetermined axial length extending substantially parallel to the central axis from a junction with an outer edge of the radial grinding surface, and a narrow intermediate radial surface spaced from the radial grinding surface and extending radially outward from the tapered exterior peripheral surface of the central hub portion to a junction with the straight external peripheral surface.