US2398408A - Abrasive article - Google Patents

Description

pril 16, 1946. H. w. BUELL ABRASIVE ARTICLE Filed Aug. 25, 1945 INVENTOR A ORNEY Patented Apr. 16, 1946- ABRASIVE ARTICLE Halsey w. Buell, Niagara Falls, N. Y.,

The Carborundum Company, Niagara assignor to Falls,

N. Y., a corporation of Delaware V Application August 25, 1943, Serial No. 499,879

4 Claims.

This invention relates to abrasive articles and methods for their manufacture. More particularly, it relates to resilient abrasive articles of the bonded type such as grinding and polishing wheels and shapes, mounted abrasive points, wheels, tools and the like, formed from small pieces of an abrasive-containing, felted fibrous sheet material. The arti-.es of the present invention are characterized by having a non-stratified structure, and a mild or soft abrading action which combines an effective cutting rate with an efficient and satisfactory polishing action. The invention further pertains to methods of making such abrading devices of soft" cutting and polishing action whereby the articles are made in various sizes and shapes without the presence of laminations or stratifications within the body of the article.

There has always been a need for abrasive articles of the bonded type which would combine an effective cutting action with satisfactory finishing or polishing whereby a reasonable amount of material would be removed from the work being abraded and at the same time the article would be left with a desirable surface finish or polish. Abrasiv articles heretofore provided for such dual purposes have failed to be completely satisfactory in accomplishing both goals and have been found to be defective in one respect or another. Among the reasons for their unsatisfactoriness have been the failure to combine an been formed from disc-shaped plies of similar fibrous sheet material of the size and shape of the final abrasive articles, which plies have been superimposed on one another and compacted to appreciable degree of cutting ability with a resilience or softness" of cutting action, non-homogeneity of the abrasive article, lack of permanency of their abrasive content (i. e., failure of the abrasive wheel structure to retain the abrasive particles within the abrading body),

non-uniformity of abrasive action, inflexibility,

etc. Provision of satisfactory properties in one respect has usually been at a sacrifice of one or more of the other characteristics desirable in such products.

Ordinary bonded abrasive articles of the prior art consisting of abrasive grains and a binder therefor in which various fibers have been incorporated for reinforcing means or for other purposes, on account of their harsh, hard cut- Y ting behavior, have never been found suitable for the purposes herein set forth. They do not provide an action equivalent or comparable to the combined "soft cutting and polishing action of the present articles.

Recently, abrasive articles have been made from abrasive-included, fibrous sheet material by proceses in which fibrous sheet material has been form abrasive wheels, discs and the like or a layered construction. While these articles have shown a resilient cutting action of the desired type they have retained as a defect thereof a layered or convoluted structure which it is desirable to avoid. Moreover, the process of making such articles by the said methods results in the convoluted articles having flash markings along the sides, i. e., an area on opposite sides of the article after it has been compacted where the convolutions of sheet material have been compressed toa higher degree than the rest of the body, leaving that part of the article one or more grades harder in grinding action than the remainder of the article. Similarly, the presence of plies of material in the laminated discor wheel-shaped articles to some extent tends to produce a striated peripheral surface which it is likewise desirable to avoid. Furthermore, such methods are economically impractical for the making of abrasive articles of smaller size such as mounted polishing points and the like because of the inconvenience and awkwardness of handling and assembling the small pieces which would be required.

I have found that abrasive articles such as grinding and polishing wheels and shapes, mounted abrasive points, etc., having a "soft or resilient combined cutting and polishing action can be made in any shape or size, regardless of how small, which not only have the advantages of the abrasive articles heretofore made from plies proved abrasive articles of the resilient or soft" acting type and of non-stratiiied structure are made by a process in which an abrasive material in the form of a felted fibrous web having abrasive grains and an adhesive binder included internally thereof, is chopped, minced, cut or otherwise broken down into a number of relatively small pieces of fibrousmaterial containing abrasive grain and binder securedtherein... Th e abraslve and adhesive content of the fibrous mate rial is incorporated and distributed throughout th fibrous web at the time of its manufacture andconstitutes an integral part thereof. This fibrous abrasive web material can be satisfactorilymade in a number of ways, as will be set forth later. Although the abrasive-containing fibrous sheet material has some adhesive included therein which may suiilce for the making of certain abrasive articles, an additional adhesive usually, and preferably, is incorporated with the fibrous sheet materiaLeither as a sizing. applied to the sheet material before it is reduced to small pieces and/or as a separate'ingredient mixed with the abrasive-containing sheet material after it has been chopped or cut up. After the fibrous web material has, been broken down to a number of small pieces, as for example, pieces 1 inch square, and an adhesive binder incorporated therewith, the materials are placed in a mold and compacted, as by the application of heat and/or pressure, to the desired shape, size and density. Anadditional oven cure for the adhesive may follow the pressing operation, if desired. 1

In order to better understand the nature of the terial internally of the fibrous sheet material during its manufacture may be employed. For example, the abrasive particles can be thoroughly admixed with the adhesive binder and the mixture applied to the web by the usual adhesiveapplying rolls. This method has been found to be particularly satisfactory for the inclusion of the finer abrasive materials of the size employed in bufiing and polishing operations.

Another method is to project the abrasive material into the web or sheet afterit has been built up to the desired thickness and immediately prior to consolidating the web. The projection of grain is suitably carried out by means of a blast of air or gas against one or both surfaces of the fibrous web, the air stream being laden with the abrasive material to be included internally of the web.

. The other steps in the formation and consolidainvention, reference is made to the accompanying drawing, in which:

Figure 1 shows a vertical cross-sectionthrough a mold for forming'the mounted abrasivepolishing point shown in Figure 2, including a scl-ematic picturization of the nature of the mold contents in uncompacted condition; and

. Figure 2 shows a finished mounted abrasive pol. ishing point made in accordance with the present invention. a

The abrasive -included fibrous web material used in making the products of the present invention can be manufactured in several ways. A very satisfactory method of making included abrasive sheet materialof the herein required type is that set forth and fully described in U. S. Patents Nos. 2,284,715 and 2,284,716. Briefly, the felted fibrous web is formed by feeding a plurality of thin carded fibrous membranes from a number of carding assemblies onto a moving endless support so that each membrane. is deposited or superimposed upon the preceding membranes until a web of loosely felted fibrous materialof the desired thickness is built up on the traveling support. A number of abrasive grain hoppers are also disposed between the carding assemblies and above the traveling conveyor. Abrasive grain is fed from the hoppers onto the fibrous membranes at various stages in the building up of the final web, so that, as a result, the abrasive material is applied between the individual membranes making up the web and s0 is internally distributed throughout the fibrous web or sheet. A suitable adhesive binder is then incorporated within the fibrous-abrasive web and the web is consolidated 'to a desired density and passed to a curing zone,

particles may vary from the finest polishing or bufling powders to the coarser grit sizes used in rinding.

Other methods of incorporating abrasive mation of the web are carried out in a manner similar to that used in the previous procedures.

Felted fibrous web's having abrasive material included within the web and which are suitable for use in the fabrication of the herein described products can also be made by a modification of the above processes in which the individual fibers are interwoven and interlocked by a gentle air or gaseous agitation of the thin carded membranes during their deposition. This process is termed aerodynamic weaving" and is used to promote the strength and eliminate any laminations from the web. For a more complete description of such a process and product, reference is made to U. S. Patent Nos'. 2,284,738 and 2,284,739 in which further details are also given of the above procedures for including abrasive materials within the fibrous structures.

In claiming my invention I have used the term abrasive-included felted fibrous sheet material" or abrasive-containing felted fibrous sheet material to mean products made by any of the methods just described.

The abrasive-containing, felted fibrous sheet material is chopped, minced, cut or otherwise reduced in size to relatively small pieces which still retain the shape and composition characteristics of the original sheet material. Small squares 1% inch on a side have been found to be a highly suitable size to usein practicing the present invention, although pieces somewhat larger or smaller can be made without departing from the spirit or scope of the invention. A suitable adhesive binder is incorporated with the pieces of fibrous, abrasive-containing material and thoroughly admixed therewith. One method for introducing the adhesive binder with a surety that it will be thoroughly disseminated throughout the molding mixture is to apply the adhesive to one or both sides of the abrasive-containing felted fibrous sheet material prior to shredding or cutting it to the desired small pieces. The chopped or minced abrasive-containing fibrous material to which the adhesive has been added is placed in a suitable mold and'compacted to form the desired abrasive article. The molding is usually performed by subjecting the mold contents to sufficient heat and/or pressure to compact the article to the desired density. After removal from the mold the formed article, which may be further oven cured if the nature of the adhesive requires it, is dressed or edged to remove any mold flashes or the like, whereupon it is ready for use.

It has been found that the character of the abrasive articles produced by the herein-described process, as for example the grade of hardness, can be altered by variations in the quantit and character of the adhesive binder employed in making the abrasive-containing, fibrous sheet materi '1, and also by the choice of auxiliary or supplemental adhesivesubstance which is admixed with the sheet material as a size thereto or as an additional ingredient of the molding mix. It is desirable that the adhesive binders selected for making the aforesaid articles do not smear during grinding operations. This is especially true in polishing wheels and devices where smearing of the bond tends to produce a .hot cutting or burning action which is ruinous to the finish being produced.

Among those substances which can be satisfactorily used as bonding materials herein and which are non-smearing, are included glue adhesives, particularly when treated with plasticizing agents such as ethylene glycol, dibutyl phthalate, glycerine and the like. The plasticizer may amount to as much as 40% by weight of the total adhesive binder. Other non-smearing adhesives which can be used are casein glues, natural or synthetic rubber latices, urea resins, phenol aldehyde resins and other natural or synthetic resins, or mixtures of twoor more of such adhesives.

As a specific example of the manner in which the present process has been carried out and abrasive articles made in accordance with the teachings of the present invention, the following procedure is given.

A flexible, felted fibrous sheet material made in accordance with the teachings of U. S. Patents Nos. 2,234,738 and 2,284,739, and containing approximately 75% of fused alumina particles of 80 mesh grit size, 15% cotton fibers and 10% natural rubber derived from latex was sized with a 20% aqueous solution of Casco glue (which is a casein glue marketed and sold by Casein Corporation of America) to provide about 10% casein by weight based on the fibrous sheet material. This sized material was dried and run through scoring rolls both lengthwise and crosswise to score it into squares approximately 6 inch on a side and was then broken up by forcing it through a wire screen havin 3%. inch openings to produce a mass of material composed of individual 1 inch square ieces of sized, abrasive-containing, felted fibrous material. Enough of the material to make a finished article having a density of aproximately 0.8 pound per cubic inch wa then tamped in a mold and subjected to a pressure of 1500 pounds per square inch and a temperature of 260 F. for 12 minutes, after which the molded article was removed from the mold and placed in an oven for 5 hours at 260 F. to complete the curing of the bond. The article was then dressed and edged according to usual procedures.

Referring further to the drawing, Figure 1 shows a diametrical, vertical cross-section through a mold 3 containing an uncompacted mix 4, and suitable for making a mounted polishing point such as that shown in Figure 2. The mold contents t are made up of small s inch square pieces ll of felted fibrous abrasive-in-' eluded sheet material having an adhesive sizing applied to their surfaces. For convenience in depicting the mold contents these pieces are all presented edgewise to view, although it is to be understood that they lie haphazardly in all directions in the mold. The mold consists of a barrel 5 which is provided with a slight inner wall taper from bottom to top, a top plunger 6 and a split bushing i. As the mold is set up for reception of the mold mixture the split bushing I is provided with a steel spindle 8 having a knurled portion 8 for embedding and strongly gripping the surrounding mixture 4 when the mix has been compacted under pressure.

1 Figure 2 shows a finished abrasive tool or point as made in the mold set-up of Figure 1 and consists of compacted abrasive-containing, felted fibrous abrading body 10 mountedand secured on the steel spindle 8. The herein-described invention offers numerous improvements and advantages over the prior art. It provides a practical method of fabricating small sized abrasive articles, particularly of the mounted type such as grinding and polishingpoints, tools and the like, having a "soft or resilient combined cutting and polishing action. Furthermore, it provides bonded abrasive articles of the "soft .orresilien't type, regardless of size or shape, having allthe improved properties and enhanced grinding action resultingfrom a structure .which is homogeneous and without the laminated or stratified structure common to similar type abrasive products constructed f c mpac d layers or convolutions oi felted sheet material. These and other improvements and advantages accrue from the practice of the present invention.

The articles of the present invention have a relatively high rate of stock removal from the material being ground and at the same time produce a surface finish equal to that obtained by an ordinary bonded abrasive article embodying abrasive particles several grit sizes smaller. Abrasive wheels made as herein described but both emciently and effectively, with an accompanying polishing action, and are capable of high operating speeds without chattering, smaller A wheels operating smoothly to remove burrs and produce very high finishes on metal castings at speeds of 75-100,000 revolutions per minute. It is theorized that the soft cutting action of such abrasive articles is the result of the abrasive grains being cushioned by the surrounding felted fibers and binder so as to prevent gouging and scratching and to provide the abrasive grains with a yielding background by which they are caused to maintain individually more effective contact with the work and at the same time absorb and take up inequalities of surface so as not to scratch or mar the surface being finished.

Although I have set forth, in the specific example, certain specific conditions, it will be understood that my invention is not limited to the conditions there described. Generally speaking, I have found it to be desirable to mold the articles under pressures of the order of 1000-2000 pounds per square inch. The length of time that the article is subjected to heat and pressure is determined to some extent by the size of the article being molded but is usually in the range of 10-15 minutes. Likewise, articles of different grades can be made by varying the fiber, abrasive and adhesive content of the abrasivecontaining felted fibrous material, the amount and kind of adhesive applied thereto or mixed with the small pieces thereof, and by the density to which the articles are compacted as determined by the pressing pressure. In general the sheet material contains 5-20% adhesive, 5-20% fibers, usually cotton, and 65-90% abrasive. The densities of the articles are usually within the range 0.75-0.90 pound per cubic inch.

Having described-and set forth the invention in detail, the scope of the invention'is not to be 75 confined other than by the appended claims.

I claim:

1. An abrasive article, the abrading portion of which consists essentially of. an adhesive binder and pieces of felted fibrous sheet material containing substantial amounts of abrasive particles internally thereof, said abrasive-containing fibrous pieces being held together in non-stratifled, compacted form by the adhesive binder.

2. An abrasive article, the abrading portion of which comprises a major proportion of an adhesive binder and of piecesof felted fibrous sheet material containing substantial amounts of abrasive particles internally thereof, said abrasivecontaining fibrous pieces being held together in non-stratified, compacted form by the adhesive 15 binder.

3. An abrading tool comprising a metalspindle and an abrading body secured about .a portion thereof, said abrading body consisting essentially of an adhesive binder and pieces of felted fibrous sheet material containing substantial amounts'of abrasive particles internally thereof, said abrasive-containing fibrous pieces being held together in non-stratified, compacted form by the adhesive.

4. An abrasive article, the abrading portion of which consists essentially of pieces of felted fibrous sheet material containing substantial amounts of abrasive particles and an adhesive binder internally thereof, said abrasive-containing fibrous pieces being held together in nonstratified, compacted form by the adhesive binder contained in the said felted fibrous sheet material.

HALSEY W. BUELL.

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