US3477180A - Reinforced grinding wheels and reinforcement network therefor - Google Patents

Description

N 1969 J. ROBERTSON, JR 7, 8 REINFORCED GRINDING WHEELS AND REINFORCEMENT NETWORK THEREFOR Filed June .14, 1965 3 Sheets-Sheet 1 an A.

N 11, 1969 J. ROBERTSONyJR 3,477,180

REINFORCED GRINDING WHEELS AND REINFORCEMENT NETWORK THEREFOR Filed June 14, 1965 3 Sheets-Sheet 2.

INVENTOR. JOHN ROBERTSON, JR.

" Filed June 14, 1965 Nov. 11, 1969 BER 5 JR 3,477,180

REINFORCED GRINDING WHEELS AND RHiNFORCEMENT NETWORK THEREFOR v 3 Sheets-Sheet 3 INVENTOR.

JOHN ROBERTSON, JR N BY United States Patent US. Cl. 51-206 2 Claims ABSTRACT OF THE DISCLOSURE A rotatable abrasive article having a reinforcing network formed of a yarn made from continuous fiber glass filaments, the yarn being spirally wound about the axis of rotation of the article and including a plurality of circumferentially spaced radially extending bands of high tensile strength material disposed across the spaced spiral turns and bonded thereto to complete the network.

The present invention relates to the improvement of rotatable molded articles, such as abrasive grinding wheels and the like by incorporating therein one or more networks of a special configuration which may be manufactured economically and which provides strength even when the wheel is worn and subjected to normal operating conditions.

Grinding wheels of the resinoid bonded type are in widespread use as cutoff and snagging wheels. They are generally used without any coolant and rotated at relatively high speeds. The operating conditions to which these grinding wheels are subjected frequently cause the development of radial cracks in the wheels which materially reduce the strength of the wheels and create a safety hazard to operating personnel and to the machine itself in the event of breakage or disintegration of the grinding wheels.

Several reinforcing techniques have heretofore been proposed to strengthen the abrasive structure against likelihood of breaking due to centrifugal forces. These techniques include imbedding, woven cloth or screen-like discs, rings, polygons, and short or elongated fibers in the grinding wheel during the forming process. The materials used have included hard and soft metals and glass, nylon and other fibers.

Abrasive wheels are commonly manufactured by bonding abrasive particles or grains with resin or comparable material which is otherwise inert and can be dissipated as the abrading material is progressively worn. A major problem encountered in the attempted reinforcement of such articles is that of securely integrating the reinforcing elements with the composite material of the wheel without at the same time sacrificing strength. For example, a closely woven cloth mesh used to develop more powerful restraining forces will not be as well penetrated by and locked with the composite abrasive material as a looser weave mesh particularly in cases where the particle sizes are large. On the other hand a looser weave mesh tends to reduce the strength available from the reinforcing fabric or network.

Alternate layers of fiber glass cloth have been employed but the use of such cloth in alternate layers in order to increase the strength of the grinding wheel to any acceptable degree results in impairment of the grinding eificiency of the wheel and increases the cost of the wheel materially.

In accordance with the present invention, these difliculties are avoided and significant improvements in wheel strengths and in the ease and economy of abrasive wheel manufacture are realized by forming a reinforcement web from a band of a plurality of substantially continuous 3,477,180 Patented Nov. 11, 1969 glass or other high tensile strength filaments into a generally spiral formation by a substantially continuous forming process, thereafter incorporating one or more of such reinforcement webs into the binder and abrasive mix in the mold and then baking or curing the combination to form a solid wheel. This provides an advantageous distribution of bands interlocked with the molded abrasive material, the distribution of which promotes substantial increases in strength and freer cutting action without interference by the material of the web.

One object of this invention is to provide a novel reinforcing network which, when imbedded in a rotatable molded article, such as a grinding wheel, substantially increases the strength thereof.

Another object is to provide a reinforcement web for such articles which is economical to manufacture.

A further object is to provide a novel method for the manufacture of reinforcement webs for rotatable molded articles such as abrasive wheels.

Yet another object is to provide a geometrical pattern for a reinforcing network that extends to a point near the periphery of the grinding wheel to reinforce the wheel but which does not detract from the grinding efficiency of the wheel as the diameter thereof decreases exposing portions of the reinforcing network.

A still further object of the present invention is to provide an improved rotatable reinforced molded abrasive wheel incorporating therein a reinforcing web to provide a wheel of high strength, safe operation, high durability, high grinding efficiency and of economical manufacture.

In one embodiment, the foregoing objects and advantages are achieved by employing a reinforcing network, preferably made from a multifilament substantially continuous strands of glass fibers which are arranged in a generally spiral formation having a plurality of turns which progressively increase in size from the interior toward the periphery of the web and eventually the rotatable molded article or grinding wheel. According to a preferred embodiment, the generally spiral turns are secured together in predetermined spaced relationships by a plurality of radially extending bands which are bonded to the turns at their crossover sites by a resinous material which also imparts stiffness to the web when it cures or sets thereby to provide a reinforcement web which is self-sustaining and may be incorporated into the mix for the molded abrasive wheel easily and economically.

In one aspect the method comprises forming a band of glass or other high-tensile-strength filaments into a generally spiral formation by mechanical means, thereafter extending another band of glass or other high-tensile-strength filaments diametrically of the web of generally spiral turns from a first point near the periphery of the web to a second point near the opposite side of the periphery, thence substantially peripherally of the web for a short distance from said second point, thence diametrically of the web again, and thence peripherally of the web, and repeating these steps until the desired number of radially extending bands have been provided, and thereafter bonding said radial bands to the generally spiral bands at their cross-over sites thereby to provide a reinforcement web which is self-sustaining and stiffened for ease and economy of use in the manufacture of grinding wheels.

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, wherem:

FIG. 1 is a plan view of a cutoff grinding wheel embodying this invention;

FIG. 2 is a section taken on the lines 2-2 of FIG. 1;

FIG. 3 is a perspective of apparatus suitable for forming a band of high-tensile-strength filaments into generally sprial formation;

FIG. 4 is an enlarged vplan view of certain of the elements of the apparatus of FIG. 3;

FIG. 5 is a side elevation of the elements of FIG. 4;

FIG. 6 is a plan view of the elements of a reinforcement web and certain apparatus elements at a further stage in the method of manufacturing it; and

FIG. 7 is a side elevation of the web and apparatus elements of FIG. 6.

Referring to FIGURES 1 and 2, the grinding wheel, indicated by the numeral 8, is shown in dot dash and the reinforcement web is shown in full lines. The grinding wheel has a hole 9 at the center and it is made of abrasive particles and a binder which comprises resin with the web imbedded therein. The web consists of a band or yarn 10 of substantially continuous filaments of fiberglass arranged in a generally spiral formation having a plurality of turns which progressively increase in size from the central hole to the periphery of the web. A plurality of radially extending elements 11 formed of yarn, also preferably made of substantially continuous fiber glass filaments, extend from the central orifice nearly to the periphery of the wheel.

The grinding wheel is made by any conventional method, for example by mixing abrasive particles with a dry powdered binder such as a resin, placing the mixture and one or more webs in a suitable mold pressing the contents of the mold and heating and curing the combination to form a solid annular article.

The apparatus shown in FIGS. 3 to 5 may be used to form a substantially continuous band of high tensile strength material into a generally spiral formation having a plurality of turns which progressively increase in size from the interior toward the periphery of the web.

Continuous lengths of glass fibers, or other suitable high tensile-strength-filaments, are wound on supply rolls 13 and 14 which are rotatably supported on the bench extension 16. In one embodiment of this invention making use of glass fiber material to make a reinforcing web for a snagging wheel, 204 continuous individual glass filaments may constitute a single end or strand for example, with 72 of such ends or strands constituting a single band. In the embodiment illustrated two bands are shown, 10A and 10B, and as they are drawn towards the spiral forming assembly they are merged into a single yarn 10 by their passage partly around a guide pulley 17 which is rotatably mounted on the vertical bracket 18.

A second pulley 19 is mounted below the first pulley and it forces the band 10 to travel through a pool of bonding resin 20 within the container 21. The adjustable platform 23 supports the resin container at the desired position for impregnation of the glass fiber yarn with the resln.

The impregnated yarn is brought out of the resin pool over a third pulley 24 and the excess resin is removed by a wiper 25 through which the band passes. The wiper comprises a bracket mounted holder lined with felt or similar material to exert a gentle squeezing action causing the excess resin to fall back into the container. Preferably the resin used is the same as that used for bonding the abrasive particles in the ultimate grinding wheel structure, one example comprising a phenol formaldehyde resin, in powder form, which has been dissolved in alcohol.

The apparatus for arranging the yarn 10 into a generally spiral formation comprises a circular table 31 slid ably keyed to the upper end of shaft 32 (FIG. 5) which is rotated by a variable speed reduction drive unit 34 supported by the bench 15.

The workholder 35 is detachably supported on the table 31 by a pair of pins 36 secured to the table and passing through orifices in the workholder 35, thereby insuring that the workholder will be rotated by the table.

A threaded rod 37 has one end mounted for rotation in a bearing 38 and its other end mounted for rotation by the reversible variable speed reduction drive unit 39.

The guide rod 40 is rigidly mounted in horizontal position by means of the tubular member 41 and the vertical strut 42 which is secured to the bench 15.

A pulley supporting bracket 45 has an interiorly threaded passage which receives the threaded rod 37 and a second passage which slidably receives the guide rod 40. It carries a guide roller or pulley 48 which is rotatably mounted by means of a spindle 49.

The helical spring 33 presses upwardly against the driven table 31 and provides moderate friction between the workholder 35 and the guide roller 48. As the table 31 and the threaded rod 37 are rotated, the pulley 48 is caused to rotate and friction between the pulley 48, yarn 10 and the surface of the workholder 35, draw the yarn 10 forwardly from the spools l3 and 14. The combination of the rotary movement of the work support 35 and the rotation of the driven rod 37 cause the guide 45 and guide roller 48 to move from left to right looking at FIG. 5 and thus to form the yarn 10 into a generally spiral formation on the surface of the workholder 35 having turns which progressively increase in size.

The somewhat tacky resin causes the yarn to remain in the position on the surface of the workholder where it is applied by the guide roller 48.

After the spiral pattern has been formed on the surface of the workholder, the yarn 10 is cut and the workholder is removed from the table 31 and placed on the stationary table 50 as shown in FIGURES 6 and 7. The stationary table 50 is provided with a plurality of pins 51 which project upwardly from its surface. The radial yarn elements 11 are then formed by extending a single band of substantially continuous glass filaments, or other hightensile-strength material, from a first point 55 near the periphery of the web of the spiral turns diametrically to a second point 56 near the opposite side of the periphery of the web, thence substantially peripherally of the web to a third point 57 and thence diametrically of the web to a fourth point 58 near the Opposite periphery thereof and thence peripherally to a fifth point 59. This operation is repeated until the desired number of radial yarn elements 11 have been formed and laid in engagement with the yarn 10 forming the spiral element; see for example the complete pattern of FIG. 6. During this operation the pins 51 serve to retain the radial yarn elements in the desired positions and also to form the short circumferential stretches 60 of yarn.

The continuous yarn which forms the radial yarn elements 11 may be impregnated with resin prior to application to the spiral turns or it may constitute an untreated yarn of fiberglass filaments. In the latter case, a suitable adhesive, such as phenolic varnish, may be applied to the radial yarn elements 11 especially at the cross-over points of the radial and spiral yarn elements.

After the network of FIG. 6 has been completed, the phenolic varnish or the resin impregnant is partially set or cured so the yarn will be joined together at the crossover points and the yarn stiffened. This may be accomplished by placing the assembly of FIG. 6 in an oven, or alternatively the web may be set or cured with the aid of a hot air jet.

After the web has been partially set and stiffened, it may be removed from the pins 51, a central hole may be cut to suit the hub of the wheel which is to be formed and the circumferential portions 60 of the band cut away so that the radial yarn elements project only slightly beyond the outermost spiral turn as shown in FIG. 1.

The reinforcement web then is in condition for placement in the mold with the binder-abrasive mix and a composite grinding wheel made in the manner described above.

It should be understood that it is unnecessary to use two pieces of yarn 10A-10B to form the single yarn element 10, and that either a single supply such as 13 may be used or two or more supplies may be used.

Furthermore, the yarn and the yarn 11 may be formed of a plurality of glass fiber yarn, for example 3, which are twisted or braided to form the yarn utilized for making the spiral turns and the radial elements.

It is also unnecessary to impregnate the yarn 10 with resin prior to its application to the surface of the workholder 35. Instead of impregnating the yarn, it may be surface treated with an adhesive such as phenolic varnish and the varnish partially dried or set before the yarn 10 is applied to the surface of the workholder so it will remain in the position where it is applied.

While the grinding wheel shown in the drawing utilizes only one reinforcing web, the invention contemplates that a plurality of spaced substantially parallel webs may be used, depending upon the thickness of the wheel and the amount of reinforcement desired.

While the spiral turns are spaced a uniform distance apart in the embodiment which is illustrated, it is within the scope of this invention to vary such spacing, for example the turns at the center may be closer together where the stresses in the wheel are higher.

The thicknesses of cutoff wheels are considerably smaller than of snagging wheels but webs embodying this invention are suitable for use in both types of wheels. The cutoif wheel shown in FIGURES 1 and 2 may for example be one that is 8 in diameter, 0.158" thick and has a central hole 1 in diameter, whereas one example of a snagging wheel consists of a wheel 24" in diameter, 3" thick with a central hole 12" in diameter. Accordingly, to adequately reinforce a snagging wheel it would be necessary to use a plurality of reinforcing webs and the pulley 48 would commence laying the spiral band outwardly from the center of the workholder 35 to provide a central orifice. It is contemplated that more than one web may be used in making cutoff wheels also.

As one particular example of the use of my invention, cutoff wheels were made by cold pressing a mixture consisting of 48% by volume of 24 grit alumina abrasive and 42% by volume of phenolic resin bonding materials together in a mold at 160 tons of pressure. The pressed wheels before curing had a porosity of 10% by volume, and were 8 7 in diameter by .145 thick with 1" diameter center holes.

Spiral reinforcing webs as disclosed herein, each consisting of 168%" of glass yarn having 44 strands of 204 continuous filaments per strand twisted together, Specification ECG 150 4/11, commercially available from Owens Corning Fiber Glass Corporation, were placed one on each side of the pressed green wheels. The wheels each with a spiral web on each of its sides, were placed between pressure plates and cured in an oven for four hours at 175 C.

After curing, the wheels were trued to 8- /6" in diameter and coated on both sides with a resin binder consisting of 100 parts of Bakelite BRL3794 epoxy resin and 37 parts of ZZL 0803 or other suitable hardener, such as are available from Union Carbide. The resin binder further penetrated the remaining loose glass filaments and was cured in an oven for one hour at 125 C. Upon curing of the binder the glass filaments were securely bound together and the yarn of each web was secured more firmly to the bonded abrasive mass. The wheels then average .161 of an inch in thickness.

Wheels made in the above manner were tested and were found to be much safer and stronger than non-reinforced wheels of comparable size. The spiral web reinforced wheels were speed tested to destruction and averaged 13,900 r.p.m. which is an average increase of 1,400 r.p.m. above the speed at which comparable non-reinforced wheels are destroyed. The spiral web reinforcing not only enables the wheels to be run safely at higher speeds but also provides a higher factor of safety at normal operating speeds.

It should be noted that the method of this invention does not involve forming the fiberglass yarn in any relatively sharp acute angles and consequently there is no possibility that the filaments will be cracked or broken and their strength impaired either by the formation of the spiral turns or in forming the radial yarn elements.

From the foregoing description, it will be apparent to persons skilled in the art that this invention provides a novel reinforcing network which when imbedded in a rotatable molded article, such as a grinding wheel, substantially increases the strength thereof, that the resultant article has high grinding efficiency and is economical to manufacture. It will also be apparent to persons skilled in the art that this invention provides a novel method for the manufacture of reinforcement webs which is economical and which produces webs which are easy to use during the manufacture of grinding wheels embodying them.

It should be understood that the specific embodiments and methods herein described have been presented by way of disclosure rather than limitation and that various modifications, substitutions and combinations may be effected without departure in spirit or scope from this invention in its broader aspects.

I claim:

1. A reinforced molded abrasive wheel comprising: a substantially annular body of abrasive particles secured together by a binder material; at least one reinforcement web embedded within said body, said web comprising a substantially continuous band of high-tensile-strength fiber glass material arranged in a generally spiral formation, in substantially a single plane, having a plurality of spaced turns which progressively increase in size from the interior towards the periphery of the wheel; a plurality of spaced radially extending elements of high tensile strength fiber glass material disposed in substantially a single plane across the turns and bonded to the continuous spiral band at a plurality of crossover sites.

2. A reinforcement web for a molded article intended to be rotated about a center, comprising: a substantially continuous band of high-tensile-strength fiber glass material arranged in a generally spiral formation in substantially a single plane, having a plurality of spaced turns which progressively increase in size from the interior towards the periphery of the web; a plurality of spaced radially extending bands of high-tensile-strength fiber glass material disposed in substantially a single plane across the turns and bonded to the continuous spiral band at a plurality of crossover sites.

References Cited UNITED STATES PATENTS 228,257 6/ 1880 Hart 51-206 699,302 5/ 1902 Fowler 51206 1,860,224 5/ 1932 'Schumacher 51-206 3,123,948 4/1964 Kistler 5 l-204 3,141,271 7/1964 Fischer 51-206 3,208,838 9/ 1965 Fischer 51206 3,262,230 7/ 1966 Seymour 51-206 3,315,418 4/ 1967 Zawodni 51-206 ROBERT C. RIORDON, Primary Examiner D. G. KELLY, Assistant Examiner

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