US3699727A - Abrasive article and method of fabrication - Google Patents

Abstract

A continuous elongate flexible sheet bearing erect abrasive flaps, each held by an individual island of binder that is adherently bonded to the flexible support, can be formed into an abrasive flap wheel, endless belts, etc. The article is prepared by applying liquid binder to the sheet, inserting the flaps, isolating the islands, and hardening the binder.

Description

United States Patent McDonald Oct. 24, 1972 [54] ABRASIVE ARTICLE AND METHOD [56] References Cited 1 OF gz m i M Donald UNITED STATES PATENTS [72 inventor: W c Sti water Township county of washing, 2,948,090 8/1960 Klingspor ..51/337 Minn' Primary Examiner-0thell M. Simpson [73] Assignee: Minnesota Mining and Manufaetur- Attorney-Kinney, Alexander, Sell, Steldt & Delahunt ing Company, Saint Paul, Minn. v 221 Filed: April 30,1971 [57] l h A continuous eongate exib e s eet bearing erect [21] Appl' 139,088 abrasive flaps, each held by an individual island of binder that is adherently bonded to the flexible sup- 52 us. Cl 34 1 can be firmed abrasive flap wheel Int Cl Bub 7 endless belts, etc. The article is prepared by applying [58] Fie'm 51/33L337 358 liquid binder to the sheet, inserting the flaps, isolating 1 the islands, and hardening the binder.

13 Claims, 6 Drawing Figures PATENTED 0m 24 I972 SHEET 1 [IF 2 FIQZ INVENTOR. MLL/AM J MCDONALD BY MWAZJZ M ATTORNEYS PATENTEDncr 24 I972 3, 699- 727 sum 2 or 2 I N VEN TOR.

6 M L g M J MCDONALD MJWM ABRASIVE ARTICLE AND METHOD OF FABRICATION This invention relates to coated abrasives, more particularly to an elongate flap-bearing strip having a continuous array of firmly anchored, preferably erect, flexible abrasive flaps, and to a method of making the same. The invention also relates to the preparation of abrasive devices, such as abrasive flap wheels, from such strip materials.

Abrasive flap wheels, which comprise an annulus of juxtaposed radially extending abrasive flaps or leaves, have been known for a considerable period of time. One current method of assembling abrasive flap wheels involves notching opposite edges of the leaves near their base ends so that when the leaves are arranged in an annular array, the notches form concentric circular grooves on opposite sides of the array. Reinforcing rings are then seated in the grooves to provide positive anchorage of the leaves and to maintain the shape of the annulus. This method is primarily useful only for the assembly of narrow wheels, and without some other modification would not be suited for the assembly of wide wheels.

Rotatable cleaning and polishing brushes have been made without requiring side reinforcement. An early attempt disclosed in U.S. Pat. No. 449,239 involves attaching brush strips to a flexible support by stitching one end of each strip to the support. When mounted on a suitable core and rotated thereon the unattached ends of the strips are forced outwardly by centrifugal force causing flexing or bending of the strip near its point of attachment. This method however, is not adaptable for use with leaves of coated abrasive sheet materials. Repeated excessive flexing causes the abrasive leaves to weaken and to subsequently break off before they can be consumed by attrition against a workpiece, thereby decreasing the useful life of the device.

U.S. Pat. No. 3,468,642 discloses a series of erect abrasive flaps having one end bonded in a continuous adhesive layer, which may in turn be bonded to a flexible strip to form an integral structure that provides a convenient means of applying the flaps to a rotatable core. The structure as prepared is not capable of providing a flap wheel. It requires reinforcing side plates or flanges to complete the wheel.

The flap bearing strip of the invention is simple and easily assembled. It can be easily formed requiring no special skills, into inexpensive, versatile, useful products. Flap wheels formed of the strip require no reinforcing side flanges or plates to provide anchorage of the flaps or to maintain their shape. The flaps of the wheel are not restricted in width as is required by some prior art assembly methods; they can be prepared in any desired width.

Briefly, the preferred article of the present invention comprises a continuous elongate flexible backing sheet or. strip bearing erect transversely oriented closely spaced abrasive leaves, or flaps. Each abrasive flap is firmly adherently bonded to a separatesimilarly oriented narrow elongate island of binder. The islands form what appears to be a continuous layer of binder when the elongate flap-bearing strip is not flexed or bent, but bending reveals the discontinuities between the segments. The binder islands are closely spaced and adherently bonded to one major surface of of abrasive leaves. This strip, in any desired length, can be easily formed into various shapes, e.g., into a circle to provide an annulus of abrasive leaves. The flapbearing strip can be suitably adhered to a reinforcing member to provide a flap wheel or belt that is ready for use.

Surprisingly, the islands of binder hold the abrasive leaves in place on the flap wheel without requiring any supplemental reinforcement means. Even after considerable use the abrasive leaves are tenaciously held and erectly supported by the islands. Moreover, the islands appear to reduce adverse flexing or bending within the abrasive leaves that would otherwise cause them to prematurely break or tear off. The spaces between islands supporting the abrasive leaves permit the flexible support sheet to flex rather than requiring the abrasive leaves themselves to be severely flexed thereby substantially reducing the above mentioned flexing and breaking problem.

Articles of the invention can be prepared by applying a continuous coating of liquid hardenable binder to one surface of the flexible support sheet, inserting the abrasive flaps, isolating corresponding portions of the binder layer to form the islands, and hardening the binder. Of particular advantage is that the method is adaptable to continuous production.

The invention can best be understood and appreciated by reference to the accompanying drawings wherein like numbers refer to like parts in the several views and wherein:

FIG. 1 is a view in perspective showing a segment of a flap-bearing strip having 'a plurality of erect abrasive leaves or flaps according to the present invention;

FIGS. 2-4 are fragmentary side views of flap-bearing strips showing various ways in which the abrasive leaves can be supported by binder islands;

FIG. 5 is a side view of an abrasive flap wheel embodying the invention; and

FIG. 6 is a side plan view showing a spirally wound abrasive flap wheel also embodying the invention.

As shown in FIG. 1 the flap-bearing strip 10 of the invention is comprised of a tough flexible support sheet 15 to which is bonded elongated binder islands 14, each of which holds an abrasive leaf or flap 11 in erect position. The abrasive flaps 11 are held in place by the binder islands 14 in a face-to-back relation with their abrasive covered surfaces 13 facing toward the same the flexible sheet, providing an elongated resilient strip end of sheet 15. The strip 10 has a high degree of bending flexibility, permitting it to be easily formed into an annulus, and a limited degree of twisting flexibility, permitting it to be spirally wound about a core.

In the embodiment shown in FIG. 1, the islands 14 are bonded to one major surface of elongate sheet 15 and extend from side to side. The islands which support the abrasive flaps have significant thickness and are separate throughout most of the thickness but may be connected by a thin binder layer adjacent the flexible support sheet 15.

Each island 14 extends at least the full length of the flap edge which it is to hold. The island is of sufficient thickness to provide an area which will adequately hold the abrasive flap under the most strenuous operating conditions that may be encountered for use of the flap wheel. Useful for such purpose are islands that are at least one-sixteenth inch in thickness, with the preferred thickness range being from one-sixteenth to one-fourth inch. The width of island 14, also sufficient to provide an adequate bonding area, should be at least one-sixteenth inch, but this may vary upwards depending upon the desired number and the thickness of the flaps for each length of the flap-bearing article. Additionally, the islands should not be so wide as to unduly restrict the flexibility of the strip. The islands are normally made in uniform width to provide uniform spacing of the flaps. For some purposes it may be advantageous to space the islands apart from each other, and to have more than one flap per island.

The abrasive leaves or flaps can be any of a multitude of known abrasive manufactures. Flap 11 comprises a thin rectangular flexible support 12, such as paper, film, or cloth that has abrasive covering one of its major surfaces 13, the abrasive normally being held on the support 12 by a binding medium. Other conventional sheet-like abrasive manufactures can also provide abra sive flaps; one such material is a sheet-like abrasive web of randomly oriented polymeric fibers having adjacent fibers bonded together and abrasive particles held thereon by a thin coating of an adhesive material. It is to be noted that although the abrasive flaps 11 are shown in the drawings as being planar, they may be somewhat bowed, due to the curling nature of some abrasive sheets, or they may be flexible and bent over when not in use. The flaps may also have a plurality of parallel slits extending inwardly from their outer edge transforming a single wide flap into rows of finger-like flaps which more easily conform to the surface of a workpiece. Additionally, it may be desirable to replace some of the abrasive flaps with non-abrasive flaps to produce special effects such as lubrication of the abrasive flaps, e.g., using a lubricant saturated porous sheet.

The placement of the end of flap 11 with respect to its supporting binder island can vary in a number of ways. The flap may be bonded to either of the long edges of the island as shown in FIGS. 2 and 3, or may actually be embedded within the island and thereby supported on two surfaces as shown in FIG. 4. The presently preferred method of bonding is that shown in FIG. 2, wherein an area of the surface of flap 11 opposite the side coated with abrasive is bonded to binder island 14 and the entire abrasive coated face 13 of flap 11 is free of such bonding, leaving space 16 between it and the next island. Also useful is the bonding method shown in FIG. 3, wherein the binder is bonded to the abrasive coating leaving space 17 between the opposite surface and the next island. With this method, however, the bonding of the leaf depends upon the adhesion of the abrasive coating to the backing, which may not be sufficient in some cases. Flap 11 may also be held within binder island 14 as shown in FIG. 4, leaving spaces 18 between islands. Although the method of bonding shown in FIG. 4 produces a superior bond, since flap 11 is bonded on both faces, it requires an additional process step to prepare, as will be hereinafter described.

Islands 14 can be formed from a number of materials which possess the required physical properties. The binder must be capable of achieving a liquid state, to permit its application to the surface of sheet 15, and it must be capable of hardening to provide a material that is solid at room temperature. The binder should adhere to both sheet and flap 11 to provide an adherent bond between the surfaces. The cured binder should have sufficient internal strength to resist separation when subjected to the forces encountered in rotation I and use, and sufficient shock resistance to resist fracture upon stopping, starting and encounter with a workpiece. Because flap wheels and other articles of the invention may be used over an extended period of time while exposed to high working temperatures, and because they may be stored in hot warehouses prior to use, it is generally desirable for the binder to retain the aforementioned physical characteristics after being subjected to elevated temperatures, e.g., 150 F. for 24 hours or more.

Suitable binders which provide the aforementioned physical characteristics include those commonly used as bonding resins for coated abrasive sheet material, such as epoxy resins, hide glue, and phenolic resins, and other known binder materials such as hot melts, polyurethane resin, polyamide resins, silicone resins, etc.

Flap-bearing strips of the invention can be prepared by placing a support sheet smoothly along the flat bottom of a trough-like form with rectangular floor and walls that are .capable of holding liquid binder in a depth at least equal to the desired thickness of the binder islands being formed. Liquid hardenable binder is then poured into the form to the desired depth, flaps inserted thereinto and the binder hardened.

The individual binder islands can be formed in several ways. The preferred way involves applying a release coating over one of the major surfaces of the flap to prevent adhesion between that surface and the binder; most preferably the non-adherent material is coated over the abrasive-coated surface. This method will inherently produce islands such as are shown in FIGS. 2 and 3, the most preferred producing that shown in FIG. 2. Upon removal from the form, the finished strip is initially somewhat rigid clue to slight adherence of the binder to both surfaces of the flap. However, flexibility and separation of individual islands is easily accomplished by flexing the strip over a curved surface while applying tension to both of its ends.

Another method of forming the flap-bearing strip involves alternately placing non-adherent spacers between abrasive flaps supporting the spacers and flaps in closely adjacent arrangement in a jig, and immersing one end of each into liquid binder contained in the aforementioned form. Upon hardening of the binder and removal of the non-adherent spacers, there results a flap bearing strip having binder islands such as is shown in FIG. 4. A flap-bearing strip can be made continuously by moving a strip of the flexible support between adjacent side dams moving at the same rate as the support, continuously coating liquid, hardenable binder on the support, positioning on the side dams closely spaced flap holding structures, inserting abrasive flaps into the holding structures from a continuous source, e.g., a

Flap-bearing strip 10 can be formed into various useful abrasive devices such as flap wheels 20 or 30 shown in FIGS. 5 and 6 respectively, endless belts, etc. Flap wheel 20 is prepared by forming strip 10 into a circle to produce an annulus of radially extending flaps. The abutted ends of strip 10 are joined by adhesively applying a suitable sheet 21 of tough flexible material over the inner surfaces adjacent the edges. Thereafter the annulus is attached to a suitable strong stretch-resistant support member 22. A suitable support member can be prepared by cutting a sheet of stretch-resistant material such as glass fabric, fabric made of glass and strong polymeric fibers (i.e., polyester), metal mesh, etc., to fit with overlapping ends within the inner curved surface of the annulus, and adhesively applying it therein. Another suitable support member can be provided by a strong tube made of such materials as metal, wood, or cardboard. Generally, wood and cardboard cores are weaker and heavier than the glass fabric core; therefore, they are used for small (i.e., less than two inch inner diameter) flap wheels.

Flap wheel 30 shown in FIG. 6 has an elongated cylindrical support member 31 having spirally wound over and attached to its outer surface a sufficient length of the flap-bearing strip of the invention to cover the entire periphery. This type flap wheel is advantageous for many applications because it does not have the edges of its flaps aligned in a perpendicular plane about the axis of the wheel and hence will not produce streaking or edge marks on workpieces, even when used by the most inexperienced operators.

Another use for the elongate flap-bearing strip includes forming of a flap wheel having inwardly projecting flaps which is useful for finishing the exteriors of round workpieces such as pipes. Additionally, the strip can be attached to the interior surface of a drum with its flaps projecting inwardly to provide a tumbling drum thereby eliminating the need for loose abrasive particles in such a drum.

To better illustrate the invention, the following nonlimiting examples are provided wherein all parts and percentages are by weight unless otherwise stated.

Example 1 A 3-inch wide, approximately 2-inch high, 6-foot long flap-bearing strip having six erect flaps per inch was formed using flaps of coated abrasive sheet material having glue-starch treated drills cloth backing, phenolic make and sandsize adhesive, and Grade 80 aluminum oxide mineral (sold as 3 Mite coated abrasive sheet). The flaps had been previously roll coated over their abrasive surfaces with a 1.8 percent solution of silane resin in organic solvent (Ram Chem. No. 225) to deposit about 0.016 grain of solids per 24 square inches and dried. The flaps were set into a jig having six individual compartments per inch, each compartment being capable of receiving and loosely holding one flap with its ends exposed. A 4-inch wide, 72-inch long drills cloth sheet saturated with a cured mixture of phenolic resin and elastomer (Vinylite XYHL), back-sized with the same mixture filled with powdered calcium carbonate, and flocked over the front surface with 25 grains/24 square inches of 5 denier, 0.055 inch long (ave.) rayon fibers held thereon by a 12 grain/24 square inches of coating of a phenolzformaldehyde resin, provided the support sheet.

The support sheet was placed with the flocked side up in a previously heated aluminum mold assembly having a base part that was 6 feet long and 6 inches wide, having therein a cavity containing a heating element that extended its full length. Side dams, 1% inch wide, /fi inch high, and extending the length and width of the base, were placed over the edges of the sheet to hold it smoothly in place, and fastened to the base portions with screws to provide a trough-like liquid-tight cavity. The inner walls of the side dams were previously coated with a release coating.

Fifty grams poly-(oxytetramethylene) glycol endcapped with 2,4-toluene diisocyanate having an equivalent weight of 1,000 (Adiprene" was hand mixed in an open container with 8] parts polymethylene polyphenyl isocyanate having an equivalent weight of (Mondur MRS), to produce a first mixture. To the first mixture was added, with stirring, 214 parts of a second mixture consisting essentially of 30 percent 4,4'-methylene-bis(2- chloroaniline) (MOCA) in 69.7 percent polyoxypropylene glycol having an equivalent weight of 1,000 (PPG-2025) and 0.3 percent phenyl mercuric acetate catalyst, to produce a liquid hardenable binder composition.

The liquid hardenable binder composition was uniformly spread in the trough to a depth of three-sixteenth inch. The jig bearing the flaps was placed above the surface of the liquid and supported by its ends on the end side dams, allowing one end of the flaps to fall into the liquid binder. The immersed ends of the flaps were caused to come into contact with the support sheet by pressing on their free ends extending above the jig. The mold assembly which had been previously heated to F. was maintained at that temperature for 30 minutes, causing the binder to harden.

Thereafter the jig was removed and a 6 foot long rigid flap-bearing strip removed from the mold. The strip was then flexed over a A inch diameter rod, the islands separating between the silane-coated abrasive surface and the cured resin to impart flexibility.

A 4 inch inner diameter abrasive flap wheel was prepared by first cutting a 25.1 inch length of the above described 6 foot strip, trimming excess support sheet .from the edges, forming on annulus by abutting its ends, and butt splicing the ends by pressing a 1 inch long, 3 inch wide piece of glass-polyester cloth impregnated with heat curable epoxy adhesive (Epon 828: Versamide 125, 50:50) over the abutted edges and heating to cure the resin. A stretch-resistant core was prepared by first cutting a 3 X 27-inch piece of glass-polyester cloth (20 mils thick) and knife coating it with the above-mentioned curable epoxy resin to give a total thickness of 30 mils. The resin-impregnated cloth was pressed against the inner surface of the annulus, held in place on an inflatable core under pressure of 25 psi, and the assembly heated in an air oven at 200 F. for 30 minutes to cure the epoxy resin and produce the completed flap wheel.

The flap wheel was placed on a 4 inch outer diameter expanding mandrel and evaluated in a simulated heavy duty grinding operation in which it was rotated at 4,000 rpm. while being urged at a constant pressure of 5 pounds against the surface of a mild steel workpiece. Rotation was maintained for a period of 5% hours producing atotal cut of 1,206 grams of steel (average cut 3.65 grams per minute) with flap wear of 1% inch (average). The wheel performed successfully during the test with no flap loss or excessive vibration. The test was voluntarily terminated after the 5% hour period.

EXAMPLE 2-2l To compare a variety of binder materials and flap constructions, a series of flap wheels was formed from the materials shown in the table below. Unless otherwise specified the forming steps, the dimensions and the testing of these examples were the same as those described in Example 1.

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3. The article of claim 1 wherein said binder is polyurethane.

4. The article of claim 1 wherein said abrasive flap comprises a sheet having abrasive covering one face thereof and said flaps are arranged on said abrasive sheet with their abrasive covered faces facing in one direction.

5. The article of claim 1 wherein said abrasive flap comprises an open porous sheet of randomly oriented polymeric fibers having adjacent fibers bonded together and abrasive particles held therein by a coat ing of adhesive material.

6. An abrasive flap wheel including a length of the abrasive article of claim 1 having its ends joined to form an annulus with the flaps radially arranged therefrom, and a tough stretch-resistant support member firmly adhesively bonded to the inner surface of said annulus.

7. The abrasive flap wheel of claim 6 wherein said tough stretch-resistant support member is fabric comprised of glass and polyester fibers.

8. The abrasive flap wheel of claim 6 wherein said support member is a rigid tube.

9. The abrasive flap wheel of claim 6 wherein each of said flaps has a plurality of parallel slits starting at the outer end thereof and perpendicular to the axis of rotation of said wheel.

10. A flap wheel including an elongate core having firmly attached to the outer surface thereof a spirally wound cover comprised of a segment of the abrasive article of claim 1.

11. A method of fabricating an article having a tough fl 'b1 1 t he tha 'n fi dherentl bonded 03 o n 23%;)? urfiace t l'ieiedf z i glurality 0 f closely spaced parallel transversely oriented narrow islands of room-temperature solid binder each of which hold in erect position a like oriented abrasive flap, comprising the steps of:

applying a continuous layer at least one-sixteenth inch in thickness of liquid hardenable binder upon said one major surface of said sheet; placing erectly supported closely spaced parallel abrasive flaps into contact with said liquid binder layer; isolating elongate portions of said binder layer to form elongate islands of liquid binder corresponding to said flaps; and hardening said resin. 12. The method of claim 11 wherein said abrasive flaps have a release coating over one major. surface.

13. The method of claim 11 wherein said portions of said binder layer are isolated by non-abrasive sheets having releaseable major surfaces.

UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3'699'727 p g d October 4,1972

i Invent0r(s) William J- McDonald It is certified that error appears in the above-identified patent: and that said Letters Patent are hereby corrected as shown below:

Following the Abstract "13 claims should be "14 claims Col. 6 line 37 "on" should be "en" Col'. 7, Example 11. "Sic" should .be "SiC" Example 14 end of last column "flao wear" should be "flap wear" Footnote 6 l4" should be "140K The following claim inserted 312 Amendment of July 2'7, 1972 should be included:

"14. The article of claim 1 wherein each island is firmly adherent'ly bonded to and holds in erect position a plurality of like oriented abrasive flaps."

and sealed this let day of May 1973.

QLTLLLLJ if, FLQTCHER, ROBERT GOTTSCI-IAIK Attesbing Officer Commissioner of Patents CRM PO-lOSO (10-69) USCOMM-DC 60376-P69 U.S. GOVERNMENT PRINHNG OFFICE: l9! 0-366-334

Claims (13)

1. An elongate flap-bearing strip comprised of a tough, flexible, elongate support sheet having firmly adherently bonded to and covering one major surface thereof a plurality of closely spaced, parallel, transversely oriented narrow islands of strong room temperature-solid binder each of which is firmly adherently bonded to and holds in erect position, a like oriented abrasive flap.

2. The article of claim 1 wherein said sheet of tough flexible material is a fibrous sheet.

3. The article of claim 1 wherein said binder is polyurethane.

4. The article of claim 1 wherein said abrasive flap comprises a sheet having abrasive covering one face thereof and said flaps are arranged on said abrasive sheet with their abrasive covered faces facing in one direction.

5. The article of claim 1 wherein said abrasive flap comprises an open porous sheet of randomly oriented polymeric fibers having adjacent fibers bonded together and abrasive particles held therein by a coating of adhesive material.

6. An abrasive flap wheel including a length of the abrasive article of claim 1 having its ends joined to form an annulus with the flaps radially arranged therefrom, and a tough stretch-resistant support member firmly adhesively bonded to the inner surface of said annulus.

7. The abrasive flap wheel of claim 6 wherein said tough stretch-resistant support member is fabric comprised of glass and polyester fibers.

8. The abrasive flap wheel of claim 6 wherein said support member is a rigid tube.

9. The abrasive flap wheel of claim 6 wherein each of said flaps has a plurality of parallel slits starting at the outer end thereof and perpendicular to the axis of rotation of said wheel.

10. A flap wheel including an elongate core having firmly attached to the outer surface thereof a spirally wound cover comprised of a segment of the abrasive article of claim 1.

11. A method of fabricating an article having a tough flexible elongate sheet having firmly adherently bonded over one major surface thereof a plurality of closely spaced parallel transversely oriented narrow islands of room-temperature solid binder each of which hold in erect position a like oriented abrasive flap, comprising the steps of: applying a continuous layer at least one-sixteenth inch in thickness of liquid hardenable binder upon said one major surface of said sheet; placing erectly supported closely spaced parallel abrasive flaps into contact with said liquid binder layer; isolating elongate portions of said binder layer to form elongate islands of liquid binder corresponding to said flaps; and hardening said resin.

12. The method of claim 11 wherein said abrasive flaps have a release coating over one major surface.

13. The method of claim 11 wherein said portions of said binder layer are isolated by non-abrasive sheets having releaseable major surfaces.

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