US2913857A - Rotative abrasive structure - Google Patents

Description

Nov. 24, 1959 R. W. REED ETAL ROTATIVE ABRASIVE STRUCTURE Filed June 26, 1957 ATTORNEYS pan/m 2,913,857 7 ROTATIVE ABRASIVE STRUCTURE Ralph W. Reed, White Bear Township, Ramsey County, and Walter James Rankin and Barry F. iungseth, both of St., Paul, Minin, assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware 1 Application June 26, 1957, Serial No. 668,138

12 Claims. c1. 51-1935 The present invention relates to a novel type of reinforced rotative abrasive structure. In particular, our invention concerns new and improved rotative abrasive structures wherein an annulus of radially extending juxta posed abrasive flap members is provided with surfacef riable reinforcing, spacing and/or stiffening means adhered to the abrasively-active portions. of the flap members. A preferred example of such reinforcing, spacing and/or stiffening means is a cohesive surface-friable foamed resinous composition disposed between the several abrasive flap members and adhered thereto.

Abrasive flap wheels, that is rotative abrasive articles comprised of an annulus of radially extending flexible juxtaposed abrasive flaps retained together at their radially inner ends such that the outer ends of the flaps freely extend, have many known advantages. They are extremely light in weight as compared to conventional grinding wheels of corresponding site. The rate of stock removal of. such flap wheel structures is very high. Very little chattering against the workpiece occurs with these types of wheels.

When employed in continuous grinding and/or polishing operations, for example in the surface grinding of automobile bumper blanks, the surfaces of flap wheel structures tend to take or conform to the configuration of the surfaces being ground. Although, this feature is desirable in many abrading operations, in other operations, particularly in stock-removal operations, it is required that the workpiece surface be ground to conform to the surface of the abrasive article. Further there are practical limitations on the abrasive pressure under which abrasive flap wheels can operate. Under extremely severe abrading pressures flap wheels have been known to temporarily collapse whereby the wheel structures correspondingly temporarily become unbalanced and diflicult, indeed sometimes dangerous, to

manage.

Thus in many abrading operations, e.g., in portable abrading operations, it is desirable that rotative abrasive structures employed have surfaces harder and thus less conformable to the workpiece surface than those of the aforementioned abrasive flap wheels. To an. extent the well known molded hard grinding wheels meet these requirements, but these have numerous disadvantages. Grinding wheels generally are heavy and hence wearisome to manipulate in manual and portable abrading operations. They tend to chatter against the workpiece. Hard grinding wheels therefore, although being useful, do not provide a complete and optimum solution.

The present invention therefore is directed to the pro-' vision of, and does provide, relatively lightweight rotative abrasive structures which are highly efiicient as abrasive articles, i.e., which have a high rate of stock removal, lengthy useful abrading, life, etc. Where our structures are employed chatter .against workpiece surfaces is largely absent. They do 'not unduly deform under high abrasive pressures or under the rapidlyapplied shock-type pressures encountered in automatic 2,913,857 .Patented Nov. 24, 1959 commercial abrading operations. Our novel articles further tend to cause workpiece surfaces to conform to the configuration of the abrasive surface rather than vice versa. In brief, our invenion provides rotative abrasive structures in which inhere advantageous characteristics complementary to those of both the flap wheel type structures and the grinding wheel structures referred to above, while disadvantages of each of these are largely obviated.

Primarily,'our invention includes in novel combination a rotative abrasive article comprised of an annulus of many uniformly positioned radially extending flaps of abrasive material. The several flap sections are united and retained together at the radially inner ends thereof. Reinforcing means strongly adhered to the flap sections extend across the wedge-shaped spaces defined by and between adjacent abrasive sections. The reinforcing extends about the annulus in the abrasive portion thereof.

The reinforcing means are coherent and thus reinforcing in character, but readily surface-friable so as to be disintegrated and worn away at the surface upon subjection thereof to the rubbing action which occurs when the reinforcing comes into contact with a workpiece being abraded. The surface-friability of the reinforcing means continues in areas thereof successively exposed through gradual wearing away of previously overlying portions of the reinforcing. Throughthe reinforcing and stiffening action of the reinforcing means the flaps extend firmly radially outwardly even under conditions of high abra-.

sive pressures.

Atcom'plete understanding of the present invention.

, will be facilitated uponreference to the following descriptions of preferred illustrative embodiments, taken in con.

nection with the accompany drawings, wherein like character references refer to corresponding parts in the several views, and in which:

Figure, 1 is a view in perspective of a rotative abrasive structure of the present invention;

Figure 2 is an enlarged partially cut-away perspective view of a portion taken from the rotative abrasive structure of Figure 1 along two radial planes; and

Figure 3 is an enlarged partially cut-away view in.

perspective similar to the view of Figure 2, but of a portion of an abrasive article of' alternative structure.

, The dimensions of the components shown in Figures 2 and 3, particularly the thickness thereof relative to their respective lengths and widths, are exaggerated for clarity of illustration. Thus it should be understood these views are intended to facilitate a description of our invention and not to portray the structures shown in accurate and exact proportion.

Referring now to Figures 1 and 2 a unitary abrasive wheel structure is comprised of an annulus of many radially extending juxtaposed flap sections 10 previously die-cut from flexible coated abrasive sheet material in the configuration shown in Figure 2. Said sections are positioned with respect to one another in the annulus such that the abrasive surfaces extend in the same direction around the wheel structure with the abrasive surface of one section facing the back surface of the next adjacent section. i

In a preferred abrasive flap wheel annulus, adjacent flap sections 10 in the annulus are firmly rigidified and adhesively bonded together over a substantial area at the radially inner end portions thereof'with hard strong unifying resin 11 which fills the radially'inner portion of the spaces between each of said sections 10. Such preferred abrasive flap wheel structures are specifically No. 710,837, filed as a continuation-in-part of Miller and Gothier-application-Serial Number 545,390, filed on November 7, 1955, now abandoned, said applications copending herewith.

Radially outwardly of the unifying resin 11 in each of the wedge-shaped spaces defined by and between adjacent radially extendingflaps are reinforcing or stiffening members 12,these members being of a shape corresponding to said wedge-shaped spaces. The wedge-shaped reinforcing members 12 are composed of a coherent material which is readily friable at its surfaces. The members 12 are retained in place in the structure through a firm adherent attachment to the face surfaces of the flaps 10. Where the wedge-shaped reinforcing members 12 are formed of preferred foamed surface-friable cohesive resin compositions the desired adhesion between the members 12 and the flaps is attained by forming the members in situ.

As can be seen from Figures 1 and 2, in the embodiment being described the members 12 substantially completely fill the spaces between the flaps 10, exclusive of the unifying resin 11, and thereby coextend radially as well as laterally, i.e., axially, with the flaps 10.

The generally rectangular flaps each have a pair of opposed notches extending inwardly from the lateral edges near the radially inner ends thereof. The notches of the many flaps in the annular structure align to define opposed circular grooves 13 and 13a in the lateral surfaces of the structure adjacent the inner periphery of the annular structure.

In use, the rotative abrasive structure just described is conveniently mounted for rotation on and with a shaft. A mounting assembly similar to that described in the aforesaid Miller and Gothier Patent No. 2,842,902 can be employed. Such assembly includes a cylindrical hub which fits snugly into the center hole 14 of the rotative abrasive structure. Circular side fianges, each having a ring extending laterally from the side surface adjacent the outer edge thereof, are afiixed one to each end of the hub, the flanges and rings being of such size and configuration that they fit into the lateral side of the article with the rings extending into and being snugly received by the grooves 13 and 13a ofthe structure. The ring serves to prevent orreduce radial expansion of the rotative structure during rotation due to centrifugal forces. The rotative structure containing the mounting assembly is then mounted on a shaft or arbor which is connected to a rotative power source. It may be desirable, particularly where wheels of relatively small or intermediate diameter are employed, e.g., 16 inches or less to eliminate the hub, and afiix the wheel to the shaft entirely through'the side flanges.

A rotative abrasive structure having a construction like that just described, namely, one wherein the spaces between adjacent flaps are substantially completely filled both radially and axially with the cohesively strong surface-friable wedge-shaped reinforcing members, is particularly suitable in abrading operations where a substantially non-conformable wheel structure is desired. The structure is smooth-running; the friable reinforcing members disposed between the abrasively active flap components dampen or reduce the tendency of the structure to chatter in .use. Yet by virtue of their surface-friable characteristic these resin-forcing members do not mar or otherwise damage the abraded surface even though it is the action of the latter which causes the said members to wear away.

Under normal abrading conditions the entire abrasive structure wears slowly and uniformly during use. The flaps are retained by the reinforcing in their radial position. Thus abrasion occurs virtually only on the edges (as distinguished from the face surfaces) of the abrasive flaps. As the flaps wear away through use, the reinforcing members wear away due to disintegration at their surfaces at about the same rate.' This is generally true even though .the reinforcing by itself wears 'away much more readily thanthe-abrasiveelements. =Apparently the presence of the latter in the structure effectively retards wear of the reinforcing to a rate similar to that of the abrasive elements.

The peripheral Wheel surface is not the only useful abrasive surface in our structures. The lateral generally flat surfaces are also extremely useful in abrading operations. The lateral surfaces can be employed apart from or in conjunction with the peripheral abrading surface. For example, the lateral surfaces are useful in conjunction with the use of the peripheral abrading surface in the grinding and polishing of difiicultly accessible areas where two or more surfaces to be abraded converge, such as occurs in the abrading of corner areas in stoves, automobile bodies, etc. Or in the grinding of sheets where a true fiat surface is required, the lateral fiat surface alone advantageously will be utilized. Where our structures are to be employed in such a manner that the lateral surfaces are utilized as abrasive surfaces, the flap sections from which the flap wheel annulus is formed preferably are shaped such that the hub area of the annulus is recessed a substantial distance laterally inwardly of the lateral surface. The wheel is then mounted on a cantilevered shaft. Due to the recessed hub portion of the structure the mounting assembly will not protrude on the lateral abrasive surface and inadvertently catch or mar the workpiece.

Advantages are also derived with rotatable abrasive structures of the present invention where the wedgeshaped spaces between adjacent flaps are not completely filled by the surface-friable reinforcing members. For example it may be advantageous to have the abrasive sheet flaps extend radially for some relatively short distance beyond the extent to which the reinforcing members extend. This may occur where a wheel initially completely filled with the reinforcing members is used under conditions of extremely high abrading pressures, or where a particularly friable reinforcing material is used. In such instance the reinforcing members under the rgorous conditions, may initially abrade or wear away somewhat more rapidly than the abrasive flap elements, baring the end portions of the flap elements. It should be borne in mind, however, that the farther the abrasive sheet elements extend beyond the reinforcing the less support or reinforcing for the elements will be present. We prefer to have no more than a relatively short portion of the abrasive sheet extend unsupported radially beyond the reinforcing. In another structure wherein the spaces between adjacent flap sections are incompletely filled with reinforcing, the surface-friable reinforcing members coextend radially with the abrasive flaps but not in the axial or lateral direction. An example of this latter mentioned structure is depicted in Figure 3, to be described shortly.

Before proceeding to describe the article shown in Figure 3 it is to be notei that, though preferable, it is not essential to the present invention that the abrasive sheet flaps be rigidly adhered together at the center ,of the wheel in the manner .of the structure shown inFigures 1 and '2. Nor are the lateral grooves contained in such structure absolutely necessary. The abrasive fiaps can beretained together at their radially inner ends by any appropriate and operable fashion. For example, theymay be retained together with a strip of cloth or tape adhered to the end edges of the individual flaps and extending about the inner wheel periphery as disclosed in Leggett Patent No. 2,651,894, granted September 5, 1953,.onapplicationfiled'March 13, 19,52, and Leggett Reissue Patent No, 24,143, granted April 17, 1956, on original applicationfiled May 18, 1954.

Where our structures are to be employed at advanced rotative speeds, fowever, e.g.,'at rotative speeds in the order of about 5000 surface feet per minute at the Wheel [periphery (1600.r.p.m. inthe case of a 12 inch diameter wheel) or greater, orwhere Wide wheels, ,e.g., 34 PFhFs or wider, are. being used, -a flap wheel anfiul'us' such as that described'infthe aforesaid Miller. and Gothier Patent No. 2,842,902 isprfeferably employedin the practice of our'invention'. In such flap wheel an? nuli the abrasive flap sections are disposed in uniformly densely packed relationship with adjacent flaps being rigidified .and firmly adhesively bonded together over an inner end area extending radially outwardly from the inner end of the flaps for a substantial distance and extending across theeritire width th'ereof. Wheels of this type, which serve as preferred flap wheels form which we form'our structures, are-presently being marketed by the Minnesota Miningand Manufacturing Company of St; Paul, Minnesota, under the trade designation PG wheels. i

Reference is now made to Figure 3. Radially extending flexible coatedabrasive sheet flaps 20, retained together at their radially inner ends (by means not shown), are reinforced and/or stiffened at their respective lateral edge portions with adherently attached radially coextensive surface-friable reinforcing members 21 and 21a, each member'having a wedge-shape corresponding to thewedge-shaped spaces between adjacent flaps 201 The members 21 are in peripheral alignment .and, together with the edge portions of the flap sections 20 to which they are adherently attached, form a lateral'reinforcing and stiffening disc section. Wedge-shaped reinforcing members 21a are similarly positioned at the opposite lateral edge portion of the structure and together with the flaps 20 define another reinforcing and stiffening disc section. The reinforcing members each coextend in the radial direction with the flaps 20.

The abrasive structure just described in connection with Figure 3 demonstrates a highrate of stock removal. Useful abrasive life of the wheel is long. f The reinforced lateral edges support and effectively stiffen the flap surfaces all across theirwidth and thus promote rigidity throughout the entire wheel. This type of structure, wherein the Wedge-shaped reinforcing surfacefriable members are disposed only at the lateral edges provides .an abrasive surface which is somewhatmore conformable to theaworkpiece surface than the completely filled structure described in connection with Figures l and 2. r

If desired the lateral thickness of the wedge-shaped reinforcing members 21 and 21a can be increased, or decreased within limits. Or it may be advantageous to eliminate the members 2 1a so as to provide a structure having only one lateral reinforcing and stiffening disc section. By increasing the lateral thickness of members 21 and/or2'1a, a greater portion of the entire spaces between flaps will be filled. Hence, increased support for the flaps provides a corresponding increase inhardness and non-conformability of the resultant abrasive structures. It will thus be seen that a distinct advantage of the present invention resides in being able to control within broad limits the hardness of the resultant abrasive structures by controlling the extent-to, whichthe spaces between the flapsiin the abrasive portion of the wheel are filled by the surface-friable reinforcing members.

. Instead of positioning the reinforcing members inward ly of the lateral extremities of the flap sections such as is the case in the structure shown in Figure 3, it may be desirable to have the surface-friable reinforcing members otherwise extend about the annular structure and across the wedge-shaped spaces between the flap sections. For example, the surface-friable reinforcing means can be pre-formed in the shape of annuli of dimension corresponding to the respective lateral surfaces. These annuli can then be attached through adhesion to the lateral edges of the several flap sections with a suitable adhesive. v i

Alternatively, one edge of the wheel can be reinforced wi1h..c.ohr.ent surface-friable members. disposed -,inwar.d y of the lateral extremities of the flap sections, while the otheredge is reinforced with an exteriorly attached reinforcing annulus. Where only one lateral surface of such a structure is to be utilized as the abrading surface, the lateral wheel surface defined in part by the inwardly disposed reinforcing members will serve as such abrading surface. The reinforcing annulus affixed to the opposite or non-abrading lateral surface, or its equivalent for retaining the flap sections in radially disposed arrangement, may then be composed of a reinforcing material not surface-friable in character.

Various cohesive yet readily surface-friable reinforcing materials can be employed as components in our novel structures. Preferably we employ cellular cured resinous compositions of such character that they are readily surface-friable. Although, for the most part the reinforcing members are formed in situ byfoaming the reactants of such compositions in place, they may be pre- Example I One hundred parts Bakelite ERL-2774 epoxide resin (the reaction product of bisphenol A and epichlorhydrin, having an epoxy number of about 192 and a hydroxy number of about 2 5 parts of Bakelite ERL- 2793 partially cured epoxy resin (similar to the reaction product of 10 parts of diethylene triamine and 12 parts of the said Bakelite ERL-2774), and 5 parts of powdered ammonium carbonate blowing agent, all by weight, are hand stirred together at room temperature. The syrupy liquid thus obtained, having a useful pot-life of about 45 minutes, is then poured to a depth of 7 inch into a circular flat-bottomed container, previously coated on the inside surfaces with a release agent. Preferably to avoid waste the diameter of the container is just slightly greater than the diameter of the structure being prepared. In the present example, a 6 inch diameter flap-type abrasive wheel consisting of an annulus of 165 radially extending juxtaposed flap sections of grit coated abrasive sheet material retained together at their radially inner ends, each flap section having 'a radial length of 2 /8 inches and a width of 2 /2 inches, is laid on one of its lateral surfaces in the container.

The container and its contents are then placed in a 193 F. oven for about 20 minutes, wherein the resin composition foams to a depth of about inch and cures to a firm state in its thus foamed condition. Upon expiration of this period the container and its contents are removed from the oven, cooled, and the wheel is lifted out of the container. The partially foam filled wheel is then inverted and the same procedure is repeated whereby the opposite side of the wheel is filled with foamed resin and the resin cured. Any excess resinous composition contained on the lateral surfaces and about the periphery is removed from about the surface of the structure with the aid of a suitable dressing tool.

In the resulting structure the in-place foamed and in situ formed wedge-shaped reinforcing members, having a uniform lateral thickness of about /8 inch, are

firmly adherently attached to the surfaces of the several abrasive flaps. Thus the reinforcing members disposed at'the respective lateral edges of the wheel align peripherally, and with the edge portions of the flaps to which they adhere, form reinforcing andstiffening disc sections on each side of the wheel.

The foamed product of which the reinforcing members are composed is readily surface-friable, that is, upon being abraded the surface portions readily break up into fi particles rrow r; and y tuitis. ufli ie t hc herent that substantial reinforcing is imparted thereby and the. breaking down of the reinforcingmembers, is confined to the surface portions. The foamed product is ratherv rigid and difficulty compressible. Abrasive structures reinforced with this composition are thus quite hard and firm. Further the resulting structure of the present example is not much heavier than was the original flap wheel annulus prior to the addition of the reinforcing; for when foamed unconfined the foamed composition has a cellular density. of only about 8 lbs./ft.

Example II A rotative abrasive structure wherein the spaces between the abrasive flaps are substantially completely filled, i.e., a structure similar to that described in connection with Figures 1 and 2 hereof, and formed of an abrasive flap wheel and a foamable resin composition like htose described above in Example I, is formed by procedures similar .to those described in the Example I. A deeper resin container having a depth of about 4 /2 inches is employed and the syrupy resinous composition is poured into the container to the depth of /2 inch. The 6 inch diameter flap-type abrasive structure is then inserted into the container and laid on one of its lateral surfaces partially immersed in the syrupy resinous composition. The container and its contents are then heated in a 210 F. oven for about 20 minutes, wherein the resinous composition foams to a depth of about 4 inches, thus entirely surrounding the flap sections and filling the spaces between the several flap sections. The foamed resin also cures to a firm state. The container and the contents thereof are then removed from the oven and cooled followed by removal of the resulting structure, as before, from the container. The excess foam composition is then removed with a dressing tool.

By employing the procedures of the preceding examples the resulting rotative structures are uniformly reinforced about their rotative axes. They are balanced to substantially the same degree as the initial flap-type wheel structures to which the reinforcing components are attached. Excellent abrasive properties are exhibited by these structures.

Another cellular resinous composition which is highly suited for use as the surface-friable reinforcing component in the novel structures hereof, but which is considerably more resilient and depressible and much less rigid than the cellular epoxide composition previously described, consists of a flexible foamed cellular product of a diisocyanate prepolymer, an isocyanate foaming agent and an amine catalyst. Generally the prepolymer comprises the reaction product of a hydrocarbon diisocyanate and a polyhydroxylated polyester of low acid number, said polyester being the condensation product of castor oil or equivalent and a dibasic carboxylic acid. The following example describes an abrasive structure which is reinforced with a specific such diisocyanate cel lular, surface-friable composition.

Example 111 'Eighteen hundredand fifty parts by weight of #3 castor oil, 135 parts diglycollic acid, 18.5 parts of xylene solvent and 3 parts anthraquinone (to lighten the color of the product) are azeotropically distilled together at about 425 F. until about 38 parts of water are removed. The resulting composition is then vacuum distilled at about 400 F. (two inches mercury pressure) to remove the solvent. The resulting diglycollic acid modified castor oil alkyd resin, having a viscosity of about 2700 centiposes -at 25 C. -and;an acid number of '5 as measured by end group determination, is then mixed with tolylene diisocyanate, in weight proportions ofabout 30 parts of the latter to 70 parts of the alkyd resin, for about 1 hour at 135C. The thus prepared prepolymer is then foamed by mixing about 50 parts thereof with'6 parts of a3 1 mixture of water and diethyl ethanol amine. Ifhisviscousliqu'id has a useful pot-life of aboutmin- 8 utes .and, when allowed tofoam unconfined, foams to, a densityof about 4 lb./ft.

A structure like that described in connection with Figure 3, wherein the surface-friable reinforcing members have a lateral width of about /8 inch, can be prepared by applying or trowelling the viscous foamable, not yet fully foamed diisocyanate composition, as soon as practicable after mixing the several resin components together, to the lateral surfaces of the wheel structure to a depth of about 43 inch. The structure is then heated in a 200 F. oven for about 10 minutes. An abrasive structure having excellent abrasive properties, and a hardness intermediate that of the structure described in Example I and the initial flap wheel structure without the friable reinforcing components results.

The wheel is light in weight and runs smooth against a workpiece substantially without chatter. Where the surfaces between the abrasive flap sections are to be completely filled by the diisocyanate composition, the same trowelling procedure can be used. Since this foamable composition foams to a depth of about three times its initial unfoamed depth, the foamable resin composition is applied to each lateral surface to a lateral depth of about at least one-sixth of the Wheel depth.

Various other suitable surface-friable coherent reinforcing materials undoubtedly will suggest themselves to the man skilled in the art. Those compositions specifically shown above merely represent preferredfexamples of materials which are coherent, i.e., of sufficient strength internally as to exhibit reinforcing or stiffening qualities, and yet which are surface-friable, i.e., readily break down at the surface upon abrading contact with the surface being abraded without deleteriously marring the latter.

The degree of coherency required on the one hand and the surface-friability required on the other hand for optimum results will vary, within limitationsfwith the type of abrading operation being performed and with the type and composition of articles being abraded. Asan indication of the direction to proceed in selecting a suitable and optimum coherent surface-friable material for a given operation and article, it is suggested that a more readily friable less strongly coherent composition would be required in a wood abrading operation than in the case of a steel strip-scouring operation. Likewise a more readily friable less strongly coherent composition would be required in an abrading operation wherein rather low abrading pressures are employed than in the case of an operation where very high abrading pressures are employed.

Herein we have described our invention with the aid of various specific embodiments. It is not our intention to be limited to such embodiments. Rather, we intend to be limited only by the scope of this application taken as a whole including appended claims and the range of equivalents to which the latter are entitled.

What we claim is:

1. A rotative abrasive article comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof, said annulus having a hub portion and a radially outer abrading portion, adjacent sections being separated in said abrading portion by wedge-shaped spaces defined therebetween, said sections having firmly adhered thereto coherent reinforcing means substantially uniformly disposed about said annulus across said wedge-shaped spaces, said reinforcing means upon subjection thereof to abrasion further being readily surface-friable at areas successively exposed at the article surface through a gradual wearing away of said reinforcing means.

2. The article of claim 1 wherein said reinforcing means comprises a coherent surface-friable foamed resin composition.

3. A rotative abrasive article comprising an: annulus 9 of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof with adjacent sections defining wedge-shaped spaces therebetween, said sections having firmly adhered thereto coherent cellular reinforcing means substantially uniformly disposed about said annulus across said wedge-shaped spaces, said reinforcing means upon subjection thereof to abrasion fur ther being readily surface-friable at areas successively exposed at the article surface through a gradual wearing away of said reinforcing means.

4. A rotative abrasive structure comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof, said annulus having a hub portion and a radially outer abrading por tion, and a coherent surface-friable material firmly adhered to and separating each of said sections in said abrading portion, said surface-friable material being disposed substantially uniformly about said annulus.

5. A rotative abrasive structure comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof, said annulus having a hub portion and a radially outer abrading portion, and a cellular coherent surface-friable material firmly adhered to and separating each of said sections in said abrading portion, said surface-friable material being disposed substantially uniformly about said annulus.

6. A rotative abrasive structure comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof, and a cellular coherent surface-friable material firmly adhered to and separating each of said sections substantially uniformly throughout the radial extent of the flaps about said annulus.

7. A rotative abrasive article comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof, said annulus having a hub portion and a radially outer abrading portion, adjacent flap sections being separated in said abrading portion by wedge-shaped spaces defined therebetween, and in each of said wedge-shaped spaces a coherent reinforcing member of corresponding wedge-shape, said reinforcing members being substantially uniformly disposed about said annulus and being firmly adherently attached along their opposed convergent surfaces to the face surface of the flap sections, said reinforcing members upon subjection thereof to abrasion further being readily surface-friable at areas successively exposed at the article surface through a gradual wearing away of said members.

8. A rotative abrasive article comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof, and in each of the wedge-shaped spaces defined by and between adjacent flap sections a cellular coherent reinforcing member of corresponding wedge-shape, said reinforcing members being substantially uniformly disposed about said annulus and being firmly adherently attached along their opposed convergent surfaces to the face surfaces of the flap sections, said reinforcing membsrs rpon subjection thereof to abrasion further being readily surface-friable at areas successively exposed at the article surface through a gradual wearing away of said members.

9. A rotative abrasive article comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the-radially inner ends thereof, each of the wedge-shaped spaces defined by and between adjacent flap sections being essentially completely filled by coherent reinforcing members of corresponding wedgeshape, said reinforcing members being substantially uniformly distributed about said annulus and firmly adherently attached along their opposed convergent surfaces to the face surfaces of the flap sections, said reinforcing members upon subjection thereof to abrasion further being readily surface-friable at areas successivelj exposed at the article surface through a gradual wearing away of said members.

10. The article of claim 9 wherein said reinforcing members comprise a cohesive surface-friable foamed resin composition.

11. A rotative abrasive article comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof, said annulus having a hub portion and a radially outer abrading portion, adjacent sections being separrted in said abrading portion by wedge-shaped areas defined therebetween, and coherent reinforcing members of substantially uniform lateral thickness and of wedge-shape corresponding to that of said spaces disposed at the lateral edges of each of said spaces, said reinforcing members being firmly adhered to face surfaces of said flap sections and therewith forming lateral reinforcing disc sections, said rein-' forcing members upon subjection thereof to abrasion further being readily surface-friable at areas successively exposed at the article srrface through a gradual wearing away of said members.

12. A rotative abrasive article comprising an annulus of many substantially uniformly positioned radially extending flap sections of abrasive sheet material retained together at the radially inner ends thereof with adjacent sections defining wedge-shaped spaces therebetween, and cellular coherent reinforcing members of substantially uniform lateral thickness and of wedge-shape corresponding to that of said spaces disposed at the lateral edges of each of said spaces, said reinforcing members being firmly adhered to face surfaces of said flap sections and therewith forming lateral reinforcing disc sections, said reinforcing members upon subjection thereof to abrasion further being readily surface-friable at areas successively exposed at the article surface through a gradual wearing away of said members.

Leggett May 18, 1954 Block June 5, 1956

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