US3141271A

US3141271A - Grinding wheels with reinforcing elements

Info

Publication number: US3141271A
Application number: US230080A
Authority: US
Inventors: Herbert C Fischer; Jr Herbert C Fischer
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-10-12
Filing date: 1962-10-12
Publication date: 1964-07-21
Anticipated expiration: 1981-07-21

Description

y 21, 1964 H. c. FISCHER ETAL 3,141,271

GRINDING WHEELS WITH REINFORCING ELEMENTS Filed Oct. 12, 1962 United States Patent O 3,141,271 GRINDING WHEELS WlTI-I REINFORCING ELEMENTS Herbert C. Fischer and Herbert (J. Fischer, Jr., both of 3 Sawyer Road, Wellesley, Mass. Filed Oct. 12, 1962, Ser. No. 230,089 4 Claims. (Cl. 51-2496) This invention relates to the reinforcing of rotative abrasive articles such as grinding wheels and the like, and more particularly to novel reinforcing elements which may be pre-formed and thereafter embedded in a grinding wheel such that the wheel when accidentally cracked or weakened will not fly apart during high speed rotation.

Grinding wheels, under normal operative conditions, are rotated at extremely high angular velocities while being subjected to severe stresses during grinding operations. Since such wheels are not immune from structural failure, grinding operations are often looked upon as being inherently dangerous. Pieces thrown out from a broken grinding wheel, which has cracked during rotation, have tremendous momentum, have been known to cause exten sive damage and have even been lethal. Therefore, means for preventing the breaking up of wheels during rotation are necessary to the confident, safe operation thereof.

Rigid rotative abrasive articles, employed for most high-speed heavy-duty grinding operations, such as cut off wheels, snagging wheels and cup-shaped wheels, generally comprise essentially abrasive mineral grains rigidly and compactly bonded together by a cured bonding agent. The strength of these abrasive wheels depends on a high degree of adhesion between the mineral grains and the bonding agent. The articles are often brittle and highly inelastic. Upon localized failure of the adhesive bond within the wheel, cracks appear which tend to enlarge in a radial direction. As the radial cracks enlarge, additional stresses are applied to other sections of the wheel with progressive appearance of additional fractures and, unless restrained, the wheel eventually breaks up or bursts and flies apart during rotation.

According to the present invention, means are provided for producing improved abrasive wheels with reinforcing elements therefor which make possible the highly desirable safety feature of reinforcement against bursting or breaking up and flying apart during rotation even though partial failures and cracks should occur in the wheel. The novel reinforcing means provided by the present invention may be preformed for embedding in the grinding wheel and the like so that the latter may be manufactured economically and competitively. Furthermore the reinforcing means may be conveniently positioned wherever desired in the wheel, for example, in the outer portion of the wheel, where centrifugal forces are highest and thus where the need for reinforcement is greatest, as well as near the center. The reinforcement is accomplished without substantial reduction in abrading rate and total abrasive cut, without reduction in wheel life, and without replacement of a comparatively large volume of abrasive mineral by the reinforcing.

These and other advantages may be obtained according to the present invention by incorporating into the wheel one or more pre-formed reinforcing elements which comprises a glass fabric tape element of substantially greater width than thickness positioned around the central axis of rotation of the grinding wheel, said tape element having a plurality of portions thereof in the cross section of said wheel extending in both the circumferential and radial directions around the axis of the wheel and with its widthwise dimension parallel to the axis of the wheel. Preferably, the tape is stiffened and convoluted with the convolutions of the tape extending for a substantial radial distance relatively to the thickness of the tape, forming a convoluted annular band or zone of substantial radial extent around the axis of the wheel. It is also preferable that the tape not extend directly radially for any substantial distance, as an aid in avoiding radial cracking of the wheel. The band so formed may be either generally circular, spiral, or the like, and may extend throughout a zone from close to the axis of the wheel to closely adjacent its outer rim. Preferably, too, the widthwise dimension of the tape constitutes a substantial proportion of the thickness of the wheel and may even extend to the surface thereof since the glass fibers thereof are readily abraded during use of the wheel and hence do not interfere with its operation.

In the practice of the present invention, it is particularly important that a relatively bulky tape be provided and include a large number of glass fibers. This is accomplished by utilizing in the construction of the tape, strands, such as glass roving, composed of a multiplicity of glass fibers with the strand being disposed in over and under intercrossing relationship providing an interlaced structure having a multiplicity of strand crossings in a predetermined pattern with a surface pattern of strand projections and depressions. This latter effect is provided by utilizing a fabric tape such as a woven, braided or knitted tape made up of a plurality of relatively bulky strands so that the large mass of glass fibers may be provided as reinforcement for the wheel, the roughened surface of the tape being an important. feature which results in improved bonding to the finished product. Further in this regard, an open mesh tape may be utilized, if desired, for direct grain to grain bonding of the wheel through the mesh of the tape.

Preferably, too, the tape is pre-formed and impregnated with an adherent stiffening coating which should be compatible with the bonding agent utilized with suitable abrasive grains to form the grinding wheel or the like.

The so constructed reinforcing pre-form may be incorporated by embedding it into the grinding wheel structure during formation thereof, and the composite assembly may thereafter be pressed to form an integral abrasive wheel having a relatively large proportion of reinforcing glass fibers therein distributed throughout a zone thereof. The techniques of the actual construction of the wheel are conventional and well known in the art so that the utilization of the reinforcing pre-forms of the invention and grinding wheels incorporating them are readily carried out by known processes.

For the purpose of explaining further objects and features of the invention reference is now made to the following specification including detailed description of preferred embodiments of the invention, together With the accompanying drawings, wherein:

FIG. 1 is a plan view partly in section of a grinding wheel according to the present invention;

FIG. 2 is a side sectional view of the grinding wheel of FIG. 1;

FIG. 3 is a perspective view of a braided reinforcing tape of a relatively closed mesh pattern such as may be utilized in the wheel of FIGS. 1 and 2.

FIG. 4 is a perspective view of a tape having a relatively open mesh pattern such as may be utilized in the wheel of FIGS. 1 and 2;

FIG. 5 is a side view partly in section of a modification of the grinding wheel of FIG. 1, wherein two reinforcing means according to the invention are provided in a cupshaped wheel;

FIG. 6 is a plan view of a grinding wheel according to the invention having a spiral reinforcing means therein; and

FIG. 7 is a plan view of a wheel according to the in- .3 vention having a plurality ofradially spaced reinforcing means therein.

In FIGS. 1 and 2 is shown an abrasive wheel 10 of the disk type rotatable about its central axis 12 by means ofia'shaft 14, said shaft having,

suitable clamping elements

16, 18 contacting each sideof the wheel. In accordance with the present invention, such wheel has incorporated therein a convoluted reinforcing element 20 of fabric tape of substantially greater width than thickness positioned around the central axis of rotation of the wheel with the widthwise dimension of the tape parallel to. the axis. As shown in said drawing, the convolutions of said tape include inner and outer partially closed loops with radially inward bights 22 and outward bights 24 and connecting portions 26 therebetween so that the tape extends in a band or Zone 28 for a. substantial radial distance preferably of the order of /2 to /3 of the wheel radius, or even more. Preferablyjthe band far zone 28 extends relatively close to the outer periphery of the wheel wherein centrifugal forces will be the highest and extends as well for a major portion of the thickness of the wheel, that is, with the widthwise dimension of the tape 20 being a substantial proportion, say more than half, of the thickness of the wheel 10.

As best shown in FIGS. 3 and 4 the tape 20 itself consists of a braided structure, although knitted or woven might as well be used, with relatively bulky strands 30, each, composed of a multiplicity of glass fibers 32, the strands being disposed in over and under intercrossing relationship providing a multiplicity of interlaced strand crossings in a predetermined pattern with a surface pattern of strand projections and depressions as shown. The tape may be either a relatively closed mesh tape 20a as shown in FIG. 3 or an open mesh tape 26b as shown in FIG, 4, the former providing a somewhat greater bulk of glass fibers and the latter somewhat better bonding to the substance of the wheel itself because of a direct grain to grain bond through the mesh interstices. However, with either a closed mesh tape 20a or an open mesh tape 2012, the roughened surface composed of the strand projections and depressions provides highly effective bonding of the tape 20 to the substance of the wheel, both the abrasive grains and the bonding agent thereof. The tape utilized should have a relatively high ratio of width-to thickness, preferably about 1 to as shown, and is also preferably pre-impregnated with an adherent stiifening coating compatible with the bonding agent utilized for bonding together the abrasive grains of the wheel itself, By so doing, and by pre-forming the reinforcing element 20 into its desired pattern and thereafter curing the bonding agent thereof at least partially, the pre-forrned pattern is maintained during its assembly with the abrasive grains and their bonding agent in a suitable mold, as well as subsequently during heating and pressing therein to bond the completed wheel, including ts integral reinforcing element according to the present invention.

In FIGS. 5-7 are shown modifications of the invention wherein one or more reinforcing elements are incorporated into the wheel structure, that of FIG. 5 being a wheel of the cup type having two reinforcing elements 20" axially spaced therein; that of FIG. 6 being a disk wheel 10" having a reinforcing element 20" in a spiralpattern with a plurality of turns incorporated'therein; and that of FIG. 7 also being a wheel 10 of the disk type having three radially spaced reinforcing elements 20?", 20", 2t) incorporated therein. In each of these cases the reinforcing elements 20 may be either of the type shown in FIG. 3 or FIG. 4, for example, that is, a tape of substantially greater width than thickness, of convoluted form, with thewidthwise dimension of the tape extending parallel to the axis of the wheel, and of either closed or open mesh as may be desired.

In essence, the present invention is directed to the use as an integral grinding wheel reinforcing means bonded integrally within and as a part of the wheel structure, of a glass fiber tape of flat construction of substantially greater width than thickness of about the order of 1 to 5. Such tape is constructed as by braiding or weaving of a plurality of strands each composed of a multiplicity of glass fibers to provide an over and under intercrossing and interlacing relationship providing a multiplicity of strand crossings in a predetermined pattern with a surface pattern of strand projections and depressions to augment the rough surface of the strands themselves. This latter aspect of the invention is particularly important in providing adequate bonding between the tape and the substance of the wheel itself. Such a structure provides a relatively high mass of glass fibers within a limited cross-sectional area and yet in a configuration having a surface which is readily bondable to and within a grinding wheel. The tape itself is readily handled to be formed as desired and thereafter may be impregnated with an adherent stiffening coating to provide a completely finished reinforcing pre-form which may be placed in a mold with suitable bonding agent and abrasive grains, so that a wheel will be provided wherein the reinforcing means is embedded therewithin and extends throughout a substantial portion of the volume of such wheel. The convoluted form is particularly desirable since it makes possible the use of a radially extensive Zone or band of reinforcing wherein the fibers embedded within the wheel extend both radially and peripherally of the wheel. In this latter regard, it is noted that it is considered to be preferable that the fibers do not extend directly in a radial direction for any substantial distance, but rather as will be seen in FIG. 1, for example, the convolutions are generally in the form of closed loops wherein the portions 26 connecting the inner bights 22 and outer bights 24 extend along a chord at a substantial angle to the radius, while the bight portions themselves extend generally perpendicular to the radius. The direction of fiber alignment is thus at an angle to the probable direction of radial shear of a wheel upon damage thereof. Preferably, the strands themselves are of glass fiber roving, composed of many fine hairlike glass monofilaments, the roving being generally untwisted, with each of the monofilaments being substantially continuous. The bonding material of the tape serves to combine the monofilaments as well as the fabric structure into a stiffened unitary structure so that such structure may be handled as a pre-form during the manufacture of the wheel itself, and to produce a pre-forrn structure which is at least of a sufficient hardness and firmness to be incorporated into the wheel without becoming extensively damaged during the pressing operation by which the final grinding wheel structure is manufactured. Such bonding material should be compatible with that used in the wheel to bond the abrasive grains thereof together, and, further, may be but partially cured during the .manufacture, of the pre-form structure, with final curing taking place during manufacture of the final grinding wheel for optimum bonding of the pre-form structure within the grinding wheel.

In the operation of a grinding wheel of the invention, when the reinforcing element becomes exposed at the abrading surface, the abrasive cutting ability of the wheel is nevertheless substantially unimpaired since the glass filaments are easily abrasively removed by being ground into fine particles. The bonding agent originally coating and uniting the glass monofilaments is also easily abraded away. Thus the wheel may be safely operated during the time when the reinforcing element is exposed at the surface, whether the side or peripheral surface of the wheel, and this is due as well to the continuity of adhesion between the components of the wheel and the reinforcing elements, there being no separation or 5) loosening of the reinforcing element from the Wheel, the Whole, in effect, being an integral structure.

Thus it will be seen that the invention provides novel reinforcing elements for abrasive wheels and the like, as well as such wheels having the reinforcing elements of the invention incorporated therein. Thus there are provided means for economically reinforcing rotated structures against flying apart at advance rotative velocities Without reduction in abrasive characteristics and without shortening the effective abrading life of the article.

We claim:

1. An annular rotative abrasive article having a central axis of rotation, said article being formed of abrasive grains bonded together with a bonding agent, With integrally bonded reinforcing means imbedded in said article distributed throughout a major portion of the axial and radial dimensions of said article, said reinforcing means comprising fabric element means of substantially greater width than thickness and consisting of a plurality of strands each composed of a multiplicity of glass fibers With said strands being disposed in over and under intercrossing and interlacing relationship providing a multiplicity of strand crossings in a predetermined pattern with a surface pattern of strand projections and depressions, said element means being impregnated with an adherent coating compatible With the bonding agent of said article, and being positioned around the central axis of rotation of the article with its greater WidthWise dimension parallel to said axis, said fabric element means having a plurality of portions thereof in the cross section of said article extending in both the circumferential and radial directions around the axis of said article, the greater Widthwise dimension of said fabric element means extending for a substantial proportion of the axial dimension of said article, providing an annular rotative abrasive article integrally reinforced with a substantial proportion of glass fibers.

2. An annular abrasive article as claimed in claim 1 wherein said fabric element means has a closed mesh.

3. An annular abrasive article as claimed in claim 1 wherein said fabric element means has an open mesh, and the abrasive grains of said article are directly bonded through the openings in said tape.

4. An annular rotative abrasive article as claimed in claim 1 wherein said fabric element means is a tape having a Width of at least about five times its thickness.

References Cited in the file of this patent UNITED STATES PATENTS 228,257 Hart June 1, 1880 1,570,664 Amos Jan. 26, 1926 1,925,901 Leguillon Sept. 5, 1933 2,147,438 Hassler Feb. 14, 1939 2,814,918 Erickson Dec. 3, 1957 2,900,241 Kubsh et al. Aug. 18, 1959 2,988,860 Sohl June 20, 1961