US3571980A

US3571980A - Abrasive structures having a compression-producing reinforcing ring

Info

Publication number: US3571980A
Application number: US829950A
Authority: US
Inventors: Robert C Fisher
Original assignee: Milacron Inc
Current assignee: Milacron Inc
Priority date: 1969-06-03
Filing date: 1969-06-03
Publication date: 1971-03-23
Anticipated expiration: 1988-03-23
Also published as: DE2026266A1; GB1238145A; NL7007890A; FR2049823A5

Abstract

As an article and a method for making a reinforced grinding wheel wherein either (a) an in-tension ring is inserted into the grinding wheel central aperture or (b) an untensioned ring is inserted into the grinding wheel central aperture, and tensioned or (c) an annular disc formed of abrasive grains and a binder is molded around the periphery of an in-tension ring, with maintenance of the ring in its in-tension state until at least full attachment thereof to the peripheral surface of the grinding wheel central aperture. Reducing the tension induces a compressive stress on the peripheral surface of the grinding wheel central aperture which offsets a certain amount of the tensile stresses of rotation, thus allowing operation at higher speed and in greater safety.

Description

United States Patent Inventor Robert C. Fisher Milford, Ohio Appl. No. 829,950

Filed June 3, 1969 Patented Mar. 23, 1971 Assignee Cincinnati Milacron Inc.

Cincinnati, Ohio ABRASIVE STRUCTURES HAVING A COMPRESSION-PRODUCING REINFORCING RING [56] References Cited UNITED STATES PATENTS 2,004.630 6/1935 Krug 51/206 3,210,892 l0/l965 Perham 51/206 Primary Examiner-William R. Armstrong Attorneys-Jack 1. Earl and Ernst H. Ruf

ABSTRACT: As an article and a method for making a reinforced grinding wheel wherein either (a) an in-tension ring is inserted into the grinding wheel central aperture or (b) an untensioned ring is inserted into the grinding wheel central aperture. and tensioned or (c) an annular disc formed of abrasive grains and a binder is molded around the periphery of an intension ring, with maintenance of the ring in its in-tension state until at least full attachment thereof to the peripheral surface of the grinding wheel central aperture. Reducing the tension induces a compressive stress on the peripheral surface of the grinding wheel central aperture which offsets a certain amount of the tensile stresses of rotation, thus allowing operation at higher speed and in greater safety.

PATENTEnmzslsn I 8,571,980

3K1 INVENTOR.

ROBERT c. FISHER I I a ATTO B N [-315 ABRASIVE STRUCTURES HAVING A COMPRESSION- PRODUCING REINFORCING RING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to grinding wheels and more particularly to the installation of in-tension reinforcing rings, or rings which are put in tension upon their insertion, into the center holes of centrally apertured grinding wheels, and keeping the rings in tension until full attachment thereof to the peripheral surface of the grinding wheel aperture.

2. Description of the Prior Art 7 Generally, the behavior of grinding wheels materials can be assumed to be almost elastic until fracture and, therefore, the

stresses, and for a known strength, the circumferential speed at which a grinding wheel bursts, can be determined by using the laws of elastomechanics.

It is an acknowledged fact that the thermal and centrifugal stresses which limit higher grinding wheel speeds (those in excess of 8,500 s.f.p.m.) have a greater concentration at the central hole or bore of a grinding wheel than anywhere else in the wheel. Thus, the tensile stresses at the bore are greater than on the outside diameter. Vitrified grinding wheels especially, are very strong in compression, but very weak in tension. When a grinding wheel breaks from thermal and centrifugal stresses, the break or fracture normally first occurs at the bore and migrates toward the outside diameter.

Radial and tangential stresses in a rotating grinding wheel are necessary values in attaining the resistance against rupture or destructive disintegration at high speeds. The tangential stress is very high at the peripheral wall of the hold and readily acts on the notches and crevices of the rough grinding wheel material. Thus, at a certain speed the tangential stress equals the strength of the grinding wheel material and rupture may occur. The bigger the hole, the lower is the circumferential speed which leads to rupture.

Wheels without center holes can be used at higher speeds than wheels with center holes. It is known that a ring glued into the inner periphery of the grinding wheel central aperture reduces its tangential stress by exercising radial tensile stresses on the wheel glue or wheel-adhesive layer.

In order to properly describe the stresses involved, both the wheel and reinforcing ring materials have to be considered separately. In addition, the radial tensile stress in the joint between the two materials is quite critical because it is supported by the glue or adhesive which in turn is also influenced by the thickness of its layer.

For example, in the case of steel reinforcing rings, the tangential stress drops from the inner to the outer peripheral surface of the steel ring and changes to a noticeably smaller value at thehole of the grinding wheel. In this example, this drop is due to the differences of Youngs modulus of elasticity (E) of the two materials (for steel, E---30 10 p,s.i.; for a vitrified grinding wheel body, E approximately 8 l0 psi). The radial stress in the glue layer increases, however, a small amount when a bigger reinforcing ring is used, this being explainable by the fact that under a higher centrifugal force, the steel ring is strained less than the grinding wheel due to the differences in Youngs modulus. It is also known that for a grinding wheel of a given size (grinding wheel O.D.: grinding wheel l.D. the ratio of the reinforcing interior ring (ring O.D.: ring I.D.) may be chosen in a manner that at a surface speed normally leading to rupture, the tangential stresses in the central bore peripheral surface become generally equal to the ulti mate tensile strength of the grinding wheel and to the radial stress in the glue or adhesive layer.

SUMMARY OF THE INVENTION The preceding information shows that reinforcing the central bore portion of the grinding wheel by bonding in situ, for example, steel rings, will allow higher surface speeds accompanied by an increase in safety.

This invention allows even higher speeds and greater safety by disclosing a design, structure and process for tensioning or expanding a reinforcing ring means and maintaining it in an intension state with an expanding means at least until full attachment thereof to the periphery of the grinding wheel cen tral aperture. Subsequent removal of the expansion means reduces the tension in the rings, thereby inducing a compressive force on the periphery of the grinding wheel central aperture. This induced compressive stress will then offset a certain amount of tensile stresses of rotation and allow operation at higher speeds and in greater safety.

One embodiment of this invention includes an in-tension ring which is inserted into the periphery of the grinding wheel aperture. The ring may be coated with adhesive either before or after tensioning. As an alternative, either the periphery of the grinding wheel central aperture only, or both the periphery and the ring may be coated prior to the insertion of the in-tension ring.

Another embodimentof this invention utilizes an untensioned ring which is inserted into the grinding wheel central aperture prior to putting it in tension. The ring may be coated with adhesive prior to insertion, or only the periphery of the grinding wheel aperture may be coated, with the alternative that both the ring andthe. periphery of the grinding wheel aperture may be coated prior to insertion and subsequent tensioning of the ring.

In addition, this invention includes an in-tension ring around and in contact with the outer periphery to which there is molded an annular disc formed of abrasive grains held by a curable binder. The ring is maintained in tension until the binder of the in-tension ring and molded disc assembly is fully cured by the application of heat, thereby providing retention of the abrasive grains and attachment of the ring to the inner periphery of the disc.

Furthermore, this invention discloses the manufacture of a ring-reinforced grinding wheel including the method steps of applying a curable adhesive means on at least one surface of the interface existing between the outer periphery of the ring and the periphery defining the central aperture of the grinding wheel, and expanding the ring as of its'insertion thereof into the grinding wheel central aperture, this expansion being cluding a ring-shaped reinforcing means around the central axis of rotation of the article concentric to the axis as well as being attached to the periphery defining the central aperture of the article, the improvement therewith which comprises expansion of the reinforcing means as of the insertion thereof into the central aperture, with maintenance of the expansion at least until the full attachment thereof to the abrasive article.

Other features and advantages of the present invention should be readily apparent by reference to the following specification, considered in conjunction with the accompanying drawings forming a part thereof, and it is to be understood that any modifications may be made in the exact structural details thereshown and described, within the scope of the appended claims, without departing from or exceeding the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a grinding wheel, composed of abrasive grains held by a curable binder, molded around the outer periphery of a reinforcing ring, which in accordance with the present invention, is maintained in an intension state at least until full adherence of the ring to the grinding wheel.

FIG. 2 is a fragmentary end view of a centrally apertured grinding wheel showing an in-tension ring maintained in that state in accordance with the present invention by an expanding means until full adherence of the ring to the peripheral surface of the grinding wheel central aperture.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2 showing the details of one type of expanding means.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, FIG. 1 is a perspective view of a disc-type grinding wheel 10, composed of abrasive grains 12 held by curable binder 14 and having sides 16, outer peripheral surface 18, centrally aperture and aperture peripheral surface 22. Located within aperture 20 and in intimate contact with peripheral surface 22 is a reinforcing ring 24 having outer peripheral surface 26, central aperture 28, inner peripheral surface 30 and sides 32. Numeral ll denotes the ring-reinforced grinding wheel assembly.

FIG. 2 is a fragmentary end view of the same type of grinding wheel 10 and reinforcing ring 24 shown in FIG. 1 with the addition of curable adhesive means 34 located in interface 36, the latter defining the space between grinding wheel aperture peripheral surface 22 and outer peripheral surface 26 of reinforcing ring 24.

FIG. 3, which is a sectional view taken along line 3-3 of FIG. 2, best shows expanding mandrel assembly 40 located within central aperture 28 or ring 24. Expanding mandrel assembly 40 is composed of split expander ring 42 having a substantially cylindrical and concentric or coaxial outer surface 44 abutting inner peripheral surface 30 or ring 24 and a tapered inner surface 46 engaging tapered outer surface 50 of centrally apertured and threaded collet 48; apertured retainer plate 52 abutting one side 16 of wheel [0, one side 32 of ring 24 and large end 47 of ring 42; and a bolt 56 having a head 58 restrained by plate 52 with threaded portion 60 retained in collet 48. Clockwise turning of bolt 56 forces tapered outer surface 50 of collet 48 to slide inside split ring 42 on its tapered inner surface 46 thereby expanding split ring 42 and consequently causing expansion or tensioning of reinforcing ring 24.

In FIG. I reinforcing ring 24, which may be made of any suitable material such as steel, fiber glass, or even exotic hightemperature alloys for example, having greater tensile strength than grinding wheel 10 itself, is tensioned or expanded by any expanding means, such as expanding mandrel assembly 40 shown in FIGS. 2 and 3. Once ring 24 is expanded, wheel 10 composed of abrasive grains I2 suspended in for instance, a curable binder 14 of a type generally used for resinoid-bonded grinding wheels, is molded around in-tension ring 24. Several examples only, of a curable binder 14, which could be utilized here, are disclosed in US. Pat. No. 3,098,730 issued to Rowse on Jul. 23, I963. This in-tension ring and disc assembly 11 is then inserted into a kiln or furnace wherein binder 14 is fully cured by the application of heat, thereby providing both for the retention of abrasive grains l2 and for the attachment of ring 24 to aperture peripheral surface 22 of grinding wheel 10. Subsequent to cooling, the reinforcing ring expanding means, such as expanding mandrel assembly 40, is removed, which reduces the 'ension in reinforcing ring 24, thereby inducing a compressive stress or force on aperture peripheral surface 22 now joined 1y cured binder 14 to outer peripheral surface 26 of reinforcng ring 24. This induced compressive stress or force will then offset a certain amount of the tensile stresses of rotation and pennit operation both at higher speeds and in greater safety. "The induced compressive stress or force, of course, depends on the degree of tension or expansion initially imparted to reinforcing ring 24, with this degree of tension being determined by both the amount of resultant compressive force tesired and the ultimate tensile strength of binder 14. The a mount of tension of the in-tension reinforcing ring 24 may i :adily be calculated by using the values obtained by measuring ring 24 in both its untensioned (free) and subsequent intmsion states. Thus, for a grinding wheel 10 of a given size (grinding wheel O,D.: grinding wheel [.D.), the amount or ext :nt of tensioning and the ratio of the reinforcing ring 24 (ring O.D.: ring [.D.) may be chosen in a manner that at a surface speed normally leading to rupture, the tangential stresses in grinding wheel aperture peripheral surface 22 become generally equal to the ultimate tensile strength of grinding wheel I0 and to the radial stresses in binder 14 at the junction of grinding wheel aperture peripheral surface 22 and outer peripheral surface 26 of ring 24.

It is to be understood that this invention is not restricted in use to resin-bonded (resinoid) grinding wheels, but may also be utilized for grinding wheels using other bonding media such as, for example, porcelain-bonded (vitrified) grinding wheels. Naturally the high firing temperatures (generally around 2.300" F.) used in the production of vitrified grinding wheels will require the utilization of high-temperature alloy reinforc ing rings 24 and expanding means as well as use ofa compatible binder [4, Le. that binder 14 will properly wet and adhere to both abrasive grains [2 and outer peripheral surface 26 of ring 24. An example only, of a binder 14, which could be utilized here, is disclosed in US. Pat. No. 2,680,895 issued to Sjogren on Jun. I5, 1954. Suitable nonoxidizing protective furnace atmospheres should also be considered.

FIGS. 2 and 3 disclose other embodiments of this invention different from that shown in FIG. 1 in that in FIGS. 2 and 3 reinforcing ring 24 is attached to grinding wheel aperture peripheral surface 22 of an already molded-and-fired grinding wheel 10. As already noted in relation to FIG. I, grinding wheel 10 may be made of any type of abrasive grains [2 suspended in any of the curable binders 14 as previously noted and reinforcing ring 24 may again be made of any suitable material, such as steel, for example, having greater tensile strength than grinding wheel 10 itself.

In one embodiment of this invention, ring 24 is put in tension with tensioning or expanding means, such as expanding mandrel assembly 40, prior to being inserted into grinding wheel aperture peripheral surface 22. The amount of tension is commensurate with values obtained by measuring ring 24 in both its free and in-tension states. The outer peripheral surface 26 of ring 24 may be coated with curable adhesive means 34 either before or after tensioning. As alternatives, either aperture peripheral surface 22 only, or both aperture peripheral surface 22 of grinding wheel [0 and outer peripheral surface 26 of reinforcing ring 24 may be coated with adhesive means 34 prior to the insertion of ring 24 into aperture 20 of grinding wheel [0. Adhesive means 34, after the insertion of ring 24 into aperture 20 of grinding wheel [0, occupies interface 36 located between outer peripheral surface 26 of ring 24 and aperture peripheral surface 22 of grinding wheel [0. Many types of adhesive means 34, with or without fillers, may be utilized, one example of which is a liquid epoxy glue of the cold-hardening type, commercially available as Agomet Vl made by the Atlas Ago Co. of Wolfgang near Hanan, West Germany. The strength of adhesive means 34 is not only influenced by its composition but also by the thickness of its layer, which should be kept to a minimum. Preferably, outer peripheral surface 26 of ring 24 is roughened and grinding wheel aperture peripheral surface 22 is solventcleaned prior to coating with adhesive means 34. In addition, there should be eoncentricity between grinding wheel aperture surface 22 and outer peripheral surface 26 of reinforcing ring 24. After proper curing of adhesive means 34, removal of the tensioning or expanding means, such as expanding mandrel assembly 40, again reduces the tension in ring 24, thereby inducing a compressive stress or force on aperture peripheral surface 22 of grinding wheel 10 now joined to outer peripheral surface 26 of reinforcing ring 24 by cured adhesive means 34 occupying interface 36 between them. This induced compressive stress will offset a certain amount of the tensile stresses of rotation as previously described. Of primary importance in this species of this invention is the ratio of the ultimate tensile strength of the grinding wheel to that of the adhesive. The higher this ratio, the higher the induced compressive force will be (since it will allow greater prestressing of ring 24).

Therefore having shown and described the nature of this invention, the following nonlimitative example will more specifically illustrate the same.

EXAMPLE- Two grinding wheels were speed tested to destruction to evaluate the merit of prestressing the wheels by means of prestressed steel reinforcing rings cemented to the wheel l.D.'s. Three standard. unbushed wheels were also speed tested to destruction to determine the normal bursting speed of the selected wheel grade. The wheel selected was graded 2A80l4-VFM, and the size was 12 inches CD. by 1. inch thick by 5 inch l.D.

The following procedure was prestressed wheels:

l. A 5 inches CD. by 1 inch thick by 5 inches l.D. steel reinforcing ring was placed on theexpanding mandrel and expanded (0.002 inch for first wheel and 0.003 inch- 0.004 inch for the second wheel).

2. The ID. of the grinding wheel was then enlarged to accomrnodate the expanded bushing. A clearance of about 0.001 inch-0.002 inch was allowed.

3. An epoxy cement composition was applied to the OD. of the bushing and the ID. of the wheel, and the wheel was then carefully slipped over the expanded bushing. The composition of the epoxy cement was as follows:

46 percent bisphenol-A epoxy resin 19 percent polysulfide liquid polymer 13 percent p, p methylenedianiline 22 percent asbestos fibers (7RF3-Johns Manville) 4. The assembly (wheel, reinforcing ring and expanding mandrel) was then cured for approximately 12 hours at 275 F.

. After cooling to room temperature, the expanding mandrel was released, thereby imposing a compressive stress in the ID. of the grinding wheel. 6. The prestressed wheel was then refinished to insure that the sides were parallel and the OD. and LB. were concentric. 7 The finished wheel was then speed tested to destruction.

Bursting speeds were as follows:

employed in preparing the Increase over standard,

R.p.m S.f.p.m 1 percent No. 1Standard 8, 400 26, 389 No. 2Standard.. 8, 000 5, 133 N0. 3Standard 7,800 24, 504 No. 4Pre-stressed 9, 600 30,159 19 N0. 5-Pre-stressed 6003-004)... 11,800 37,071 46 1 Surface feet per minute. 7 2 Average of three standard whee1s=25,342 s.f.p.rn.

In a variation of the previously described embodiments and in contrast thereto, ring 24 is tensioned or expanded only after its insertion into aperture 20 of grinding wheel 10. The outer peripheral surface 26 of ring 24 may be coated with curable adhesive means 34 prior to the insertion of ring 24 into grinding wheel aperture 20. As alternatives, either aperture peripheral surface 22 only, or both aperture peripheral surface 22 of grinding wheel and outer peripheral surface 26 of reinforcing ring 24 may be coated with adhesive means 34 prior. to the insertion of ring 24 into grinding wheel aperture 20. The amount of tension in ring 24 may be controlled by specifying the amount of torque applied to the expanding means, which amount is initially determined by tests, as previously described, by using the values obtained by measuring ring 24in bothits free and in-tension states prior to insertion. Except for the stated reversal of the insertion and tensioning with maintenance of this expansion at least until the full attachment of reinforcing ring 24 to grinding wheel 10, wherein subsequent termination of the expansion induces a compres sive stress on aperture peripheral surface 22 of grinding wheel central aperture 20.

In addition, this invention discloses the manufacture of a high-speed annular rotative centrally apertured grinding wheel 11 formed of abrasive grains 12 held together by curable binder l4 and having reinforcing ring 24 attached to grinding wheel aperture peripheral surface 22, including the steps of pretensioning ring 24 and maintaining this tension with an expanding means, such as expanding mandrel assembly 40; molding grinding wheel 10, formed of abrasive grains 12 held by curable binder 14, around and in abutting contact with outer peripheral surface 26 of in-tension ring 24; heating the molded grinding wheel in-tension ring assembly 11 until binder 14 is fully cured, thereby providing both proper retention of abrasive grains l2 and complete attachment of in-tension ring 24 to grinding wheel aperture peripheral surface 22; and removing the expanding means to reduce the tension in ring 24 thereby prestressing or inducing a compressive force on aperture peripheral surface 22 of grinding wheel central aperture 20. I

While the invention has been described in connection with possible forms or embodiments thereof, it is to be understood that the present disclosure is illustrative rather than restrictive and that changes or modifications may be resorted to without departing from the spirit of the invention.

Iclaim:

1. A high-speed rotative abrasive article reinforced against destructive disintegration at advanced rotative velocities comprising:

a. an annular disc formed of abrasive grains held by a binder and having a central axial aperture;

b. a curable adhesive means; and

c. an in-tension ring which is inserted into said central aperture and held in the peripheral surface of said aperture by adhesive means, with maintenance of said ring in its intension state until the adhesive means is fully cured.

2. The high-speed rotative abrasive article of claim 1 wherein the in-tension ring is coated on at least one surface thereof with the adhesive means prior to being put in tension.

3. The high-speed rotative abrasive article of claim 1 wherein the in-tension ring is coated on at least one surface thereof with the adhesive means prior to being inserted into said central aperture.

4. The high-speed rotative abrasive article of claim .1 wherein the peripheral surface of said central aperture is coated with the adhesive means prior to the insertion of said in-tension ring into said aperture.

5. The high-speed rotative abrasive article of claim 1 wherein both at least one surface of the in-tension ring and the peripheral surface of said central aperture are coated with the adhesive means prior to the insertion of said in-tension ring into said aperture.

6. The high-speed rotative abrasive article of claim 1 wherein element (c) comprises a ring which is inserted into said central aperture and held on the peripheral surface of said aperture by the adhesive means, said ring immediately upon insertion being tensioned and maintained in a tensioned state until the adhesive means is fully cured.

7. In a rotatable annular centrally apertured abrasive article formed of abrasive grains held by a binder including a ringshaped reinforcing means around the central axis of rotation of said article concentric to said axis as well as being attached to the periphery defining the central aperture of said article, the improvement therewith which comprises expansion of said reinforcing means as of the insertion thereof into the central aperture, with maintenance of said expansion at least until the full attachment thereof to said abrasive article.

8. A high-speed rotative abrasive article reinforced against destructive disintegration at advanced rotative velocities comprising:

a. an in-tension ring; and

b. an annular disc formed of abrasive grains held by a curable binder which is molded around and in contact with the outer periphery of said ring, with maintenance of said ring in-tension until the binder is fully cured by the application of heat thereby providing proper retention of the abrasive grains and full attachment of said ring to the inner periphery of said disc.

9. In the manufacture of a high-speed rotative centrally apertured grinding wheel formed of abrasive grains held together by a binder including a reinforcing ring attached to the periphery defining the central aperture of said grinding wheel, combining the method steps of:

a; providing a curable adhesive means on at least one surface of the interface located between the outer periphery of said ring and the periphery defining the central aperture of said grinding wheel;

b. tensioning said ring and maintaining said tension with an expanding means;

c. inserting said ring into said central aperture;

d. fully curing said adhesive means; and

e. removing said expanding means to reduce the tension in said ring, thereby putting a compressive force on the peripheral surface of the grinding wheel central aperture.

10. The process of claim 9 wherein step (a) providing a curable adhesive means on at least one surface of the interface located between the outer periphery of said ring and the periphery defining the central aperture of said grinding wheel, is performed after step (b) tensioning said ring and maintaining said tension with an expanding means.

11. The process of claim 9 wherein step (b) tensioning said ring and maintaining said tension with an expanding means. is performed after step (c) inserting said ring into said central aperture.

12. ln the manufacture of a high-speed annular rotative centrally apertured grinding wheel formed of abrasive grains held together by a curable binder including a reinforcing ring attached to the periphery defining the central aperture of said grinding wheel, comprising the method steps of:

a. tensioning said ring and maintaining said tension with an expanding means;

b. molding the grinding wheel, formed of abrasive grains held by the curable binder, around and in abutting contact with the outer periphery of said in-tension ring;

c. heating said molded grinding wheel in-tcnsion ring assembly until the binder is fully cured thereby providing both proper retention of the abrasive grains and complete attachment of said in-tension ring to the inner periphery of said grinding wheel central aperture; and

d. removing said expanding means to reduce the tension in said ring, thereby inducing a compressive force on the peripheral surface of said' grinding wheel central aperture.

[3. In the manufacture of a high-speed rotative centrally apertured grinding wheel including a reinforcing ring having its outer periphery attached to the periphery defining the central aperture of said grinding wheel. combining the method steps of:

a. providing a curable adhesive means on at least one surface of the interface located between the outer periphery of said ring and the periphery defining the central aperture of said grinding wheel; and

b. expanding said reinforcing ring as of the insertion thereof into the central aperture with maintenance of said expansion at least until the full attachment of said reinforcing ring to said grinding wheel, wherein subsequent termination of said expansion induces a compressive stress on the peripheral surface of said grinding wheel central aperture.

Claims

1. A high-speed rotative abrasive article reinforced against destructive disintegration at advanced rotative velocities comprising: a. an annular disc formed of abrasive grains held by a binder and having a central axial aperture; b. a curable adhesive means; and c. an in-tension ring which is inserted into said central aperture and held in the peripheral surface of said aperture by adhesive means, with maintenance of said ring in its in-tension state until the adhesive means is fully cured.

4. The high-speed rotative abrasive article of claim 1 wherein the peripheral surface of said central aperture is coated with the adhesive means prior to the insertion of said in-tension ring into said aperture.

7. In a rotatable annular centrally apertured abrasive article formed of abrasive grains held by a binder including a ring-shaped reinforcing means around the central axis of rotation of said article concentric to said axis as well as being attached to the periphery defining the central aperture of said article, the improvement therewith which comprises expansion of said reinforcing means as of the insertion thereof into the central aperture, with maintenance of said expansion at least until the full attachment thereof to said abrasive article.

8. A high-speed rotative abrasive article reinforced against destructive disintegration at advanced rotative velocities comprising: a. an in-tension ring; and b. an annular disc formed of abrasive grains held by a curable binder which is molded around and in contact with the outer periphery of said ring, with maintenance of said ring in-tension until the binder is fully cured by the application of heat thereby providing proper retention of the abrasive grains and full attachment of said ring to the inner periphery of said disc.

9. In the manufacture of a high-speed rotative centrally apertured grinding wheel formed of abrasive grains held together by a binder including a reinforcing ring attached to the periphery defining the central aperture of said grinding wheel, combining the method steps of: a. providing a curable adhesive means on at least one surface of the interface located between the outer periphery of said ring and the periphery defining the central aperture of said grinding wheel; b. tensioning said ring and maintaining said tension with an expanding means; c. inserting said ring into said central aperture; d. fully curing said adhesive means; and e. removing said expanding means to reduce the tension in said ring, thereby putting a compressive force on the peripheral surface of the grinding wheel central aperture.

11. The process of claim 9 wherein step (b) tensioning said ring and maintaining said tension with an expanding means, is performed after step (c) inserting said ring into said central aperture.

12. In the manufacture of a high-speed annular rotative centrally apertured grinding wheel formed of abrasive grains held together by a curable binder including a reinforcing ring attached to the periphery defining the central aperture of said grinding wheel, comprising the method steps of: a. tensioning said ring and maintaining said tension with an expanding means; b. molding the grinding wheel, formed of abrasive grains held by the curable binder, around and in abutting contact with the outer periphery of said in-tension ring; c. heating said molded grinding wheel in-tension ring assembly until the binder is fully cured thereby providing both proper retentioN of the abrasive grains and complete attachment of said in-tension ring to the inner periphery of said grinding wheel central aperture; and d. removing said expanding means to reduce the tension in said ring, thereby inducing a compressive force on the peripheral surface of said grinding wheel central aperture.

13. In the manufacture of a high-speed rotative centrally apertured grinding wheel including a reinforcing ring having its outer periphery attached to the periphery defining the central aperture of said grinding wheel, combining the method steps of: a. providing a curable adhesive means on at least one surface of the interface located between the outer periphery of said ring and the periphery defining the central aperture of said grinding wheel; and b. expanding said reinforcing ring as of the insertion thereof into the central aperture, with maintenance of said expansion at least until the full attachment of said reinforcing ring to said grinding wheel, wherein subsequent termination of said expansion induces a compressive stress on the peripheral surface of said grinding wheel central aperture.