US3014319A

US3014319A - Moulded back-up pad

Info

Publication number: US3014319A
Application number: US44193A
Authority: US
Inventors: Dirck J Olton
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1960-07-20
Filing date: 1960-07-20
Publication date: 1961-12-26
Anticipated expiration: 1978-12-26

Description

Dec. 26, 1961 D. J. OLTON 3,014,319

MOULDED BACK-UP PAD Filed July 20, 1960 FIG .4

INVENTOR DIRCK J. OLTON ATTORNEY United States Patent Ofiice Patented Dec. 26, 1961 The present invention relates in general to supporting devices for coated abrasive discs and more particularly to a resilient back-up pad having improved wear and other operating characteristics.

It has heretofore been proposed to utilize back-up pads for supporting devices for coated abrasive discs wherein the surface of the pad in contact with the uncoated side of the abrasive disc is resilient in nature, i.e., is formed of foam rubber or the like. Such soft-surfaced pads have generally had a relatively short wear life due to the tendency of the material to tear and therefore a common practice is to interpose a canvas face between the soft pad material and the abrasive disc to be mounted thereon. The resulting combination has found wide-spread usage 111 industry but is still subject to poor life, snagging, etc. An improved pad of this type is described and claimed in my copending application, Serial No. 29,985, filed May 18, 1960, and the present invention represents a still further improvement in pads of this kind.

Accordingly, it is an object of the present invention to provide an improved coated abrasive back-up pad.

Another object of the invention is to provide an improved working surface for a resilient coated abrasive back-up pad.

A' further object is to provide a coated abrasive backup pad capable of easy replacement and possessing improved ability to be driven by the machine upon which it is mounted.

Additional objects if not specifically, set forth herein will be readily apparent to one skilled in the art from the following detailed description of the invention.

In the drawings: I

FIGURE 1 is a top plan view of a coated abrasive back-up pad of the present invention.

FIGURE 2 is a bottom plan View of a replacement pad of the present invention.

FIGURE 3 is a side elevation of the pads illustrated in FIGURES 1 and 2.

FIGURE 4 is a side elevation of a modification of a pad incorporating the present invention.

Generally, as described and claimed in my aforesaid application, Serial No. 29,985, the present invention contemplates a back-up pad for coated abrasive discs wherein the body of the pad is made up chiefly of a tough cellular, resilient material such as polyurethane foam. Foam rubber or other materials of a like nature may be used and will form an improved product when the features of the present invention are incorporated into pads made therewith, but preferably the material utilized for the body of the pad is polyurethane foam. This material is tougher and more tear-resistant than foam rubber for example.

Specifically, the tough cellular resilient material is recessed at its working surface to receive a planar canvas insert. The canvas or similar material must be substantially flush with the non-recessed'portions of the working surface of the cellular, resilient material. Preferably this structure is achieved by placing the canvas insert into the base of the mold used in theformation of the cellular main portion of the back-up pad. The material to be used is poured into the mold over the canvas disc, foamed in situ and the composite structure removed from the mold. This construction produces a pad having many advantages including that of not marring the workpiece to applied. The rim of cellular material around the periphery of the pad protects the work from the edge of the relatively stiif canvas and prevents snagging or scoring of the work. Also, by being recessed the canvas insert will resist to a marked degree any separation from the cellular. back-up material. Tests indicate a life of two or three times that of a similar pad having the canvas face secured in non-recessed fashion to the cellular material.

A further innovation has been utilized to permit easy replacement of the cellular, resilient portion of the pad. Heretofore such portions have generally been held to the stiff, hard rubber back-up plate member by means of an adhesive. Replacement elements have been glued on or have been furnished with a stiff plastic or rubber plate glued to the base of the cellular member with a center hole adapted to permit the assembly to be held to the hard rubber back-up plate with a threaded shaft. In the case of the direct adhesive attachment of the cellular body to the back-up member, the disadvantages are obvious-cleaning the old adhesive and remnants of the old pad preparatory to applying the new pad to the supporting surface make this impractical. With a plastic face applied to the base of the cellular member, difficulty in preventing slippage of the plastic upon the face of the back-up member occurs. This can be corrected by tightening the threaded shaft to an extreme degree, but such measures result in early destruction of the cellular body through shearing between the body and the plastic at the interface between the two. The problem was to some extent overcome in the case of the invention described and claimed in Serial No. 29,985 by again recessing the base of the cellular body to receive the stiffening insert. The insert of plastic, hard rubber, thin steel, or the like, 'waspreferably applied byinsertion into the foamed cellular material while in the mold. With a rim of cellular material left flush with the surface of the periphery of the insert, the device when placed upon the driving backup plate had substantially no slippage.

-However, I have now found that still further improvement is possible by extending the cellular material beyond the plane of the insert member, i.e. either forming a a raised rim around the periphery of the insert member or extending the cellular material at least partially over the surface of such insert member. I

Referring now to the drawings, FIGURE 1 illustrates the pad 10 of the present invention in top plan view,

which the pad and its associated coated abrasive disc is showingthe canvas insert 11 and therim of cellular, resilient material 12 surrounding insert 11. 7

FIGURE 2 illustrates the base of a cellular pad 20 adapted for use as a replacement pad to be used with a permanent, recessed center hard rubber back-up plate. The outer periphery of the working surface is shown at 21. This would correspond to the outer periphery of the rim 12 shown in FIGURE 1. The outer periphery at the base of the cellular member 20 is shown at 22. The plastic insert is shown at 23 with a raised center portion 24 and center hole (threaded) 25 adapted to conform to the permanent back-up plate (not shown). The area defined by

lines

22 and 26 is the raised rim of cellular material referred to above.

FIGURE 3 illustrates in detail a side view of the pad of FIGURES 1 and 2. The body of cellular resilient material is shown at 30 with the canvas insert illustrated in dotted lines at 31. The plastic face or insert in the base is identified by reference numeral 32, showing the raised central portion 33 and threaded center hole 34. The raised rim of cellular material at the base of the pad is identified by reference numeral 35.

FIGURE 4 shows a side view of a pad similar to that of FIGURES 1 and 2 except that the cellular material, instead of extending in rim form beyond the plane of the base insert, actually covers a portion of such insert. The

cellular body of the pad is shown at 40 with the canvas insert in the face at 41. The plastic or other relatively rigid base insert is shown at 42 with the raised central portion 43 and threaded center hole 44. The portion of cellular material extending beyond the plane of insert 42 and over the outer face thereof is shown at 45. This layer may be quite thin and preferably should not exceed about A1" in thickness.

In both modifications described above, the extension of the cellular material beyond the plane of the base insert provides a much firmer non-skid bond between the pad and the drive pad to which it is affixed in use than Where the cellular material is flush with the insert as described and claimed in my aforesaid earlier application. In the case of the rim, as illustrated most clearly in FIG- URE 3, pressure on the outer face of the plastic insert will cause such rim to fold over the edge of the insert and grip the same for improved drive. In the case of the actual coverage of the insert as shown in FIGURE 4, the frictional contact between the face of the driving pad (not shown) and the base of the back-up pad is substantially increased due to the nature of the cellular material.

be of a woven or non-woven nature, preferably canvas,

capable of providing an adhesive-receiving surface to which coated abrasive discs may be held adhesively and then stripped therefrom without marked deterioration of such surface. Frequently, pads of this type are used with open mesh abrasive products and in such instances adhesive is not required to hold the disc to the pad. The insert must be capable, however, of resisting the abrading action of such a disc to a greater degree than the cellular material. The top insert may therefore be described as a material of higher internal strength than the cellular material in which it is embedded. Likewise, the base insert, which is used for replaceable pads, may be made of any suitable material such as fabric, steel, plastic, etc. Again, it must be of higher internal strength than the cellular material in which it is embedded and preferably is substantially rigid in nature as compared to the cellular material. The cellular material should be tough and resilient and the body formed thereof should be relatively thick compared to the thickness of the inserts. A typical commercial pad uses a thickness of cellular material of 1%" with a plastic insert of A thickness and a canvas insert of thickness. Approximately A" of cellular material should be left around the periphery of each insert for best results.

The term substantially planar as used in the appended claims is intended to cover both planar inserts 4 and inserts having a raised or depressed centerportion such as is illustrated at 33 in FIGURE 3 and at 43 in FIGURE 4 of the drawingshereof.

I claim:

l. A back-up pad for use with a coated abrasive disc characterized by a relatively thick body portion of tough, resilient, cellular material having a relatively stiff, thin, substantially planar insert of a material having a higher internal strength than said cellular material embedded in the lower face of said body portion, said cellular material extending outwardly at least partially beyond the planar surface of said insert.

2. A pad as in claim 1 wherein the body portion has a fabric insert in the upper face thereof adapted to support the coated abrasive disc.

3. A back-up pad for use with a coated abrasive disc comprising: a relatively thick body portion of tough, resilient, cellular material having a circular upper face and a circular lower face; a relatively thin circular canvas insert of lesser diameter than said circular upper face embedded in such face with the outer surface of said insert substantially fiush with the upper surface of the periphery of such face; and a relatively thin, rigid circular insert member of lesser diameter than said circular lower face embedded in such face with the cellular material of such face extending outwardly at least partially beyond the plane of said rigid insert.

4. A back-up pad for use with a coated abrasive disc comprising a relatively thick body portion of a tough, resilient, cellular material having circular upper and lower faces; a canvas insert moulded flush into said upper face and a second insert of more rigid material moulded into said lower face so that each of said inserts is surrounded by a rim of said tough, resilient cellular material; said lower rim of tough, resilient cellular material extending outwardly beyond the plane of the outer surface of said References Cited in the file of this patent UNITED STATES PATENTS Newcomb June 16, 1931 Welch Aug. 30, 1960