US3154897A - Spliced coated abrasive belt - Google Patents

Description

1964 R. N. HOWARD SPLICED COATED ABRASIVE BELT Filed Nov. 27, 1961 INVENTOR. ROBERT N. HOWARD ,dz; Foam/, ATTORNEYS United States Patent 3,154,897 SPLECED (DATED ABRASIVE BELT Robert N. Howard, Maplewood, Minn, assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Nov. 27, 1961, Ser. No. 155,036 5 Claims. (U. 51399) This invention relates to endless coated abrasive belts, and it particularly relates to a novel splice therefor.

For many years coated abrasive belts have been made by joining together the two ends of an elongated strip of coated abrasive sheet material. The most common splice in commercial use today is the so-called lap splice, where one belt end is lapped over and adhered to the other belt end, the abrasive granules having first been removed from at least one portion of the lapped ends. No matter what variation in grinding technique or adhesives may be employed, such splices are always somewhat stitfer than the rest of the belt, a condition which both predisposes them to failure by delamination when they are placed around small contact rolls and causes a bump or chatter in many abrading operations. Such belts are recommended for running in only one direction to minimize the chance of snagging the upper layer of the splice.

Another means of joining coated abrasive belt ends is the so-called butt splice. In this type of splice the belt ends are abuttingly juxtaposed and a uniting means em ployed to hold them in this arrangement. Such a uniting means may be a thin piece of linen, a piece of material similar to the belt backing, or the like, adhered to the back of the belt ends in the area immediately adjacent the line of abutment. Although such belts can be run in either direction, they suifer from the other disadvantages inherent in lap splices.

Attempts have been made to improve the butt splice; for example, Miller and Riedesel US. Patent No. 2,391,- 731 discloses a butt splice in which the uniting means is a stranded material, such as wire screen, which is physically forced into the backing adjacent the juxtaposed belt ends. This product, although forming a smooth uniform caliper splice which is outstanding in a large number of abrading operations, tends to fail by fatigue of the stranded material when the belt is driven around a small contact wheel or when it is repeatedly flexed sharply. U.S. Patent No. 2,733,181 discloses a butt splice in which grooves or slots parallel to the length of the belt are formed in the juxtaposed belt ends, many fine strong lineally aligned filaments being forced into the grooves from the back and held in place by an adhesive. This splice is fatigueresistant and versatile when properly made, but rigorous control of temperature, humidity, and depth of grooving is necessary during its formation to avoid flaking off of the mineral layer during heavy duty sanding operations; further, the many lengthwise grooves may form the starting points for longitudinal splits. Like its predecessors,

this splice is substantially denser than the remainder of.

the belt, and sometimes hinges at either the line of abutment or one of the outboard edges of the splice, often when being mounted on an abrading machine.

I have now devised a novel splice for the butt-joining of coated abrasive belt ends to provide a belt which runs equally well in either direction. This splice is extremely easy to fabricate, lending itself to the use of automatic machinery, and is essentially universal in the coated abrasive materials to which it can be applied. The splice may be made of substantially the same thickness, density and flexibility as the remainder of the belt, and it is essentially free from the problems of hinging and bumping which have been characteristic of prior splices. It can be .entrained over small or extremely soft contact wheels With- 1 jacent the belt ends.

ice

out delaminating, splitting, or premature sand loss at the splice area. Other advantages of the invention will become apparent as the description proceeds.

In the formation of my novel splice, two coated abrasive belt ends which are to be spliced are juxtaposed and a splicing strip of a composition to be described hereinafter firmly adhered in place. Tapering of the belt ends may be accomplished by scuifing the backing with a coarse grit grinding wheel or coated abrasive. The splicing strip is a composite sheet comprising a multiplicity of lineally aligned strong, tough, synthetic filaments, a thin, strong, tough, tear-resistant non-woven mat formed from randomly disposed synthetic fibers, and a film-forming adhesive which, during the process of being heat-cured, passes first through a fluid stage and then quickly hardens to a heat-resistant water-resistant state. The splice is formed by adhering the reinforcing strip to the tapered belt ends in a heated splicing press, the heat causing the resinous material to flow between the belt ends and at least partially to overlie the abrasive-coated surface.

My invention will be better understood by referring to the attached drawing which is a view in perspective of a splice formed according to my invention.

In the drawing juxtaposed belt ends 10 and 10a, comprising backing 11 coated with mineral particles 12 and adhesive 13 are shown tapered and juxtaposed, the tapered ends defining a hollowed out space which is occupied by strong, thin, tear-resistant backup strip 14, which in turn is made up of a randomly laid mat 15 of oriented fibers 16, a multiplicity of lineally aligned strong synthetic fibers 17, and film forming resinous material 18] The longitudinal tensile strength of backup strip 14 when separately formed and cured is preferably such that it exceeds the corresponding lengthwise tensile strength of the belt ends 10 and 10a. Random mat 15 reduces any tendency to lengthwise or crosswise snagging which might occur in unsupported abrading operations and/ or when the workpiece is sharp or irregular.

It will be observed from the drawing that the resinous material 18 extends between the belt ends, despite the fact that they are in substantial contact throughout their line of abutment, uniting the belt ends, reducing the opportunity for accidentally gouging or lifting the trailing belt end during abrading operations, minimizing any tendency to hinge or gap at the line of abutment, and greatly enhancing the strength of the finished splice. The etfectiveness of this construction is particularly surprising in View of Riedesels teaching that reinforcing filaments should penetrate the backing and lie as close to the abrasive surface of the belt as possible. Since it is difficult to tell whether the resin has flowed only between the closely positioned belt ends, it has been found convenient to note whether the resin extends slightly over the abrasive coated surface in the area immediatelyad- The resin'in this location serves to indicate the degree of success obtained in having the resin flow between the belt ends. Microscopic examination of splies exhibiting suitable resin flow reveals that the resin:fiber ratio is higher along the line'of' abutment 19 than at the outer edges 20 of the splice; it'is believed that this readjustment may render more gradual the transition from the body of the belt to the splice during abrading operations, insure firm adhesion between the belt ends, and hence contribute to the'life of the belt.

This-invention has proved equally successful in splicing paper-backed, film-backed, or cloth-backed coated abrasive belts. For purposes of illustration but not of limitation, the invention will now be described with respect to an example in which the belt is fabricated from abrasive sheet material having an impregnated cloth base.

.to .005" and weighing about 20 grains per 24 square inches was formed on a garnett machine from a blend of equal partsby weight of S-denicr l /z-inch undrawn staple polyethylene terephthalate fibers having a melting point of about 400 F. and l /z-denier l /z-inch semi-dull polyethylene terephthalate fibers having a melting point .ofabout 500 F. The mat was unified by passing it over a hot can at a temperature sufficient to fuse the S-denier fibers, the tensile strength of the finished mat being about 20 lbs. per inch of width in the machine direction and about lbs. per inch of width in the cross direction.

;;Tear-resistance was excellent.

-,ments such as Dacron polyethylene terephthalate or Orion acrylic polymer may be used in place of the nylon. The laminating adhesive was a resinous composition consisting of a blend of approximately equal weights of polyvinyl butyral such as Vinylite XYSG and a heatadvancing phenol-formaldehyde resin compatible therewith and having a phenol:formaldehyde molar ratio of 5:9, dissolved in ethylene glycol monoethyl ether to a solids content of 2730%. Lamination was effected by positioning the nylon yarns above the random mat and passing both under a roller While simultaneously applying about 75 grains (wet) of the laminating adhesive per 24 square inches. The composite structure was then passed through a ft. long drying tunnel maintained at 225- 250 F. at a rate of about 5 ft. per minute, after which it .was suificiently tackfree to be wound into a roll. At this point, the condition of the resin was such that it existed as a readily deformable self-supporting film lwhichupon being subjected to heat and pressure exhibited extensive flow characteristics but, which was capable of being quickly cured to a tough hardened condition. The composite product weighed about 52 grains per 24 square inches.

, A sample of the composite splicing sheet was heated for 30 minutes at 200 F. and thereafter cured by being pressed between heated platens maintained at 350 F. and 2,000 lbs. per square inch pressure for 30 seconds. Upon being removed the strip was found to have a tensile strength parallel to the direction of the nylon filaments of about l50 lbs. per inch of width.

Scufiing and Tapering the Belt Stock ofthe coated abrasive belt stock was about 0.029 inch. -At eachof the markings scufling was now accomplished inthe followingmanner:

.A Az-inch x 5-inch Grade 46 aluminum oxide grinding ,wheelgwas adjustably positioned above a rigid steel plate and driven at 1,800 surface feet per minute.

The'belt stock was placed with the mineral side in contact with the steel plate and "held firmly positioned beneath the at the middle thereof.

. ber wheel, having a diameter of 8 inches with Wide lands alternating with ,45" wide grooves,'while theedge grinding wheel so thatthe axis of the wheel was at right angles to the edge of the stock. The Wheel was then urged against the backing of the belt stock to be scuffed, so as to remove in a shallow double-tapered groove approximately .003 inch of cloth along the /2-inch of the marked line and a gradually decreasing amount up to i inch on each side of the line. The grindhig wheel was repeatedly laterally repositioned so as to remove Splicing of the Scufied Belt Ends The splicing sheet material was now out at 45 to the lineally aligned nylon filaments to form /2" x 6" 45 parallelogram-shaped splicing strips in which the nylon fibers were approximately /z-inch long. The belt ends were next positioned, abrasive side up, over a rigid steel plate coated with polytetralluoroethylene, and a splicing strip centered under the line of abutment with the lineally aligned fibers parallel to the length of the belt strip and in contact with the back surface thereof. A strip of unsized canvas cloth was then laid over the abrasive side, again covering the line of abutment. The entire assembly was then placed in a conventional coated abrasive splicing press having platens heated to 350 F. The bars were closed and contact pressure applied for 5 seconds, after which .the pressure was increased to approximately 2,000 lbs. per square inch for 25 seconds. The spliced belt was then removed from the press and the excess splicing strip trimmed from the sides of the belt. Visual observation revealed that the resin had flowed between the juxtaposed belt ends and over the top of the abrasive grains for about A -inch on each side of the line of abutment. The caliper of the splice was found to be .029 inch, the same thickness as the rest of the belt. The splice felt slightly stilfer than the remainder of the belt but upon being gently manipulated by hand it softened and could not be tactilely distinguished therefrom.

Performance ofSpliced Belt rolled steel bar stock having a A" x A" cross section.

was urged against it, the dimension extending at right angles to the direction of belt travel, under a total force of 4 /2 lbs. The three belts averaged a total running time of 6 /2 minutes before failure by separation of one belt end from the splicing film and subsequent breakage. Splices made in the same way with the same splicing film, the only difference being that the belt ends were slotted as taught in Riedesel US. Patent No. 2,733,- 181, performed equally welland failed in the same way. Belts spliced according to Miller and Riedesel US. Patent No. 2,391,731, however, failed after only ll/z minutes, the wire screen fatiguing and breaking across the splice Belts made with the best commercially available overlap splice failed by delamination after two minutes.

,A 3 x84" Grade 60 aluminum oxide belt made in accordance with this example was used in a test simulating the sanding off of gateson castings. In this test, the belt was entrained over an SO-durometer. serrated rubof a cold-rolled steel ring Vs-inchthick and 9 inches in diameter was urged against it with a forceof 14 lbs; In this test the belt functioned successfully for 7 minutes and removed 142 grams of metal before failing by sand loss at the splice. A. splice prepared according to Riedesel 2,733,181, i.e., Where the belt ends were slotted and a'film substantially identical to the one employed in the splice of this example forced thereinto, showed severe sand loss at the splice after 2 minutes of running" andfailed by wearing a hole through the backing at the splice in less than 4 minutes after cutting only 88 grams of metal. It is thus apparent that the novel splice of the present invention is not only easy to make but also extremely versatile. It runs smoothly and performs at least as well as the best previously known splices both when subjected to severe flexing and when used in heavy duty sanding operations. No previously known splice, insofar as I am aware, could be so universally employed.

Although the manner of splice preparation described in the preceding example is, I believe, suflicient to enable anyone skilled in the art to produce satisfactory splices on any known coated abrasive sheet material from which belts are fabricated, including paper, cloth, polymeric films, nonwoven mats, and the like, certain recommendations may be profitably observed. For example, paper belts, which are somewhat less compressible than cloth belts, should probably be scuffed deeper than the otherwise identical cloth product if caliper control is of great significance. Caliper control is ordinarily not critical for Grade 60 or coarser grits, but, on the other hand, adhesion of the splicing strip to coarse grit belts is of increased significance. Accordingly, I find it generally desirable to scuff all belts prior to joining them. Where, however, increased density of the splice area and/or decreased adhesion is not a deterring factor, the hollowed out area may be created in effect by compressing the splicing backup strip into the portion of the belt ends immediately adjacent the line of abutment.

Adhesion between the belt ends themselves, as well as between the belt ends and the splicing strip, and consequently belt performance, can be still further improved by priming with flexible, heat-resistant, water-resistant polymers which can be applied from a highly penetrating low viscosity solution and thereafter cured to form an additive thermosetting resin, e.g., polyurethanes, bisamide polyesters, epoxy polyesters, epoxy polyamides, bis-ketenes, di-acrylates, styrene-polyesters, and the like. A preferred priming procedure involves coating the belt ends with a 200:9 polyester urethaneztriisocyanate blend (solids basis) and allowing the blend to penetrate and dry to a tacky condition (about 10 minutes), after which splicing is effected as previously indicated. A suitable polyester urethane may be prepared by reacting at 75 C. for 18 hours 1,000 parts of dry hydroxyl-terminated ethylene glycol adipate of molecular weight 2,000 with 87 parts of toluene diisocyanate. A suitable triisocyanate is the reaction product of 3 mols of toluene diisocyanate and 1 mol of trimethylolpropane diluted with ethyl acetate to a solids content of 75%. Grade 150 aluminum oxide belts primed in this way before joining showed no signs of failure after 17 minutes of sanding on the simulated jet blade test previously described.

Care should be exercised in scuffing cloth belts, probably more than is necessary with other types of backing, to avoid excessive scuffing, e.g., deeper than half the thickness of the backing. The reason lies in the fact that, although many of the woof yarns of the cloth may be removed without serious impairment of the splice, excessive removal of the Warp yarns tends to result in a product which fails in tension under operating conditions. The method of sending parallel to the Warp yarns, as disclosed in the preceding example, minimizes injury to them.

The technique of scuffing the belt stock before cutting it into belt strips is convenient and readily controllable; it also minimizes the number of preparation steps required and lends itself to automatic or semi-automatic opera tions. Where desired, however, a belt strip may be cut to size and the ends thereafter scuffed individually.

In addition to the polyvinylbutyral:phenol formaldehyde resin disclosed in the preceding example, various other adhesives may prove suitable. Among these are phenol-aldehyde and polyvinyl butyral resins, polyamide and phenol-aldehyde resins, polyamide and epoxy resins, polyester-isocyanate resins, and polyamide-resorcinolphenol aldehyde resins.

Having disclosed my invention with the aid of a detailed illustrative example, what I claim is:

1. A spliced strip of flexible abrasive-coated sheet material comprising a backing sheet having first and second surfaces and abrasive grains firmly affixed to the first surface thereof by a binder adhesive, and having a joint uniting two complementary abuttingly juxtaposed ends, the sheet material immediately adjacent each of said ends being contoured in such a manner that said first surface is essentially undisturbed and that said second surface is tapered toward each of said ends to define a single hollowed-out space across the entire width of said strip, said space being occupied by a thin, strong flexible tearresistant composite backup strip, said strip comprising a layer of strong synthetic fibers at least a substantial number of which extend across the line of abutment and lie generally crosswise of the belt, and a layer of fine strong synthetic fibers aligned parallel to the length of the belt, said layers being impregnated and firmly adhered to each other and to said ends by a flexible cured, hardened film-forming material extending between and firmly adhered to said ends.

2. An endless belt of flexible abrasive-coated sheet material comprising a backing sheet having first and second surfaces and abrasive grains firmly aflixed to the first surface thereof by a binder adhesive, and having a joint uniting two complementary abuttingly juxtaposed ends, the sheet material immediately adjacent each of said ends being contoured in such a manner that said first surface is essentially undisturbed and that said second surface is tapered toward each of said ends to define a single hollowed-out space across the entire width of said strip, said space being occupied by a thin, strong flexible tear-resistant composite backup strip, said strip comprising a layer of strong synthetic fibers at least a substantial number of which extend across the line of abutment and lie generally crosswise of the belt and other fine strong synthetic fibers aligned parallel to the length of the belt, said fibers being impregnated and firmly adhered to each other and to said ends by a flexible cured, hardened film-forming material extending between and firmly adhered to said ends.

3. An endless belt of flexible abrasive-coated sheet material comprising a backing sheet having first and second surfaces and abrasive grains firmly affixed to the first surface thereof by a binder adhesive, and having a joint uniting two complementary abuttingly juxtaposed ends, the sheet material immediately adjacent each of said ends being contoured in such a manner that said first surface is essentially undisturbed and that said second surface is tapered toward each of said ends to define a single hollowed-out space across the entire width of said strip, said space being occupied by a thin, strong flexible tear-resistant composite backup strip, said strip comprising a layer of nonwoven randomly disposed fine strong, tough fibers and a layer of fine strong fibers aligned parallel to the length of the belt, said layers being impregnated and firmly adhered to each other and to said belt ends by a flexible cured, hardened film-forming resinous material which in its uncured form was precurabie to a readily deform-able self-supporting film and thereafter quickly hardenable to a' heat-resistant waterresistant state, said resinous material extending between and being firmly adhered to said juxtaposed ends.

4. The method of preparing an endless belt from a roll of flexible coated abrasive sheet material including the steps of cutting a strip of the desired length, tapering the back of said strip immediately adjacent each of the ends thereof and across the entire width thereof with an abrasive grinder driven in the same direction as the long dimension of said strip, abuttingly juxtaposing the tapered ends, positioning in the single hollowed-out space defined by the juxtaposed ends a composite splicing strip comprising a layer of nonwoven randomly disposed fine strong tough synthetic fibers and a layer of fine strong lineally aligned synthetic fibers, said layers being impregnated and united by a flexible, precurable, readily deformable film-forming resinous composition which flows readily under heat and pressure and which is quickly curable to a hard heat-resistant water-resistant condition, said splicing strip being disposed with said lineally aligned fibers extending parallel to the length of the belt, placing the positioned splicing strip and belt ends in a heated splicing press, and applying heat and pressure to cause said resinous composition to fiow between said belt ends and thereafter harden, thereby firmly uniting said belt ends to each other and to said splicing strip.

5. The method of preparing an endless belt from a roll of flexible coated abrasive sheet material including the steps of cutting a strip of the desired length, tapering the back of said strip immediately adjacent each of the ends thereof and across the entire width thereof with an abrasive grinder driven in the same direction as the long dimension of said strip, abuttingly juxtaposing the tapered ends, positioning in the single hollowed-out space defined by the juxtaposed ends a composite splicing strip comprising a layer of nonwoven randomly disposed fine strong tough synthetic fibers and a layer of fine strong lineally aligned synthetic fibers, said layers being impregnated and united by a flexible, precurable, readily deformable film-forming resinous composition which flows readily under heat and pressure and which is quickly curable to a hard heat-resistant water-resistant condition, said splicing strip being disposed with said lineally aligned fibers ex tending parallel to the length of the belt, applying a priming layer to one of the strips between the splicing strip and tapered ends, placing the positioned splicing strip and belt ends in a heated splicing press, and applying heat and pressure to cause said resinous composition to flow between said belt ends and thereafter harden, thereby firmly uniting said belt ends to each other and to said splicing strip.

References Cited in the file of this patent UNITED STATES PATENTS 299,747 Coy June 3, 1884 756,220 Elstun Apr. 5, 1904 2,189,754 Cherrington Feb. 13, 1940 2,733,181 Reidesel Ian. 31, 1956

Claims (1)

1. A SPLICED STRIP OF FLEXIBLE ABRASIVE-COATED SHEET MATERIAL COMPRISING A BACKING SHEET HAVING FIRST AND SECOND SURFACES AND ABRASIVE GRAINS FIRMLY AFFIXED TO THE FIRST SURFACE THEREOF BY A BINDER ADHESIVE, AND HAVING A JOINT UNITING TWO COMPLEMENTARY ABUTTINGLY JUXTAPOSED ENDS, THE SHEET MATERIAL IMMEDIATELY ADJACENT EACH OF SAID ENDS BEING CONTOURED IN SUCH A MANNER THAT SAID FIRST SURFACE IS ESSENTIALLY UNDISTURBED AND THAT SAID SECOND SURFACE IS TAPERED TOWARD EACH OF SAID ENDS TO DEFINE A SINGLE HOLLOWED-OUT SPACE ACROSS THE ENTIRE WIDTH OF SAID STRIP, SAID SPACE BEING OCCUPIED BY A THIN, STRONG FLEXIBLE TEARRESISTANT COMPOSITE BACKUP STRIP, SAID STRIP COMPRISING

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