Abrasive disc of polyurethane bonded metallic wool

A soft abrasive tool is disclosed as comprising a solid molded mixture of edetermined quantities of an aluminum wool material and a catalyst setting elastomeric polyurethane binder material, the unique combination of which has been mixed, molded under pressure, and cured at room temperature in such manner as to have a disc-like, cup-like, or other predetermined geometrical configuration. A power source -- such as a motor or the like -- may be used to mechanically drive the aforesaid soft abrasive tool, so that it will cut, grind, and remove polyurethane paint, polysulfide sealant, and other soft coatings from aluminum aircraft skin without damaging the substrate aluminum thereof when held thereagainst.

FIELD OF THE INVENTION 
The present invention, in general, relates to abrasives and, in particular, 
is a soft abrasive disc. In even greater particularity it is an abrasive 
disc which will remove cured polyurethane paint and polysulfide sealant 
from a predetermined metallic surface without damaging the metal thereof. 
Description of the Prior Art 
Heretofore, numerous abrasive papers and discs have been employed for 
removing various and sundry materials from numerous other various and 
sundry materials. As a matter of fact, so many abrasive materials are 
available that the art including them is crowded, indeed. However, 
although each thereof may be satisfactory for some intended purpose, to 
date, insofar as is known, none thereof adequately performs the function 
of removing polyurethane paint and polysulfide sealant from aluminum 
aircraft surfaces without damaging the metal thereof. Ordinarily, the 
abrasive discs which have been used for such purposes include abrasive 
materials which are harder than the aluminum of aircraft skin and, 
moreover, the abrasives involved are usually in particulate form, thereby 
causing problems of controlling the density or consistency of the mixture 
in which they are included. As a matter of fact, it has been found that 
paint and sealant removal by the known prior art abrasive devices, and 
especially abrasive discs, can result in an aircraft surface being made 
more sensitive to corrosion, cracking, and fatigue, as a result of the 
physical damage done thereto thereby. In addition, the uneven surfaces 
produced by hard abrasive discs make it difficult, if not impossible, to 
accomplish ultrasonic inspections thereof. Accordingly, most of the prior 
art abrasive discs leave something to be desired, as far as the cleaning 
of aluminum aircraft skin is concerned, and sometimes in other situations, 
too. 
Summary of the Invention 
The subject invention overcomes some of the disadvantages of the prior art 
devices, in that it removes paint and sealant from aluminum aircraft skin 
without damaging the skin. 
Briefly, the invention comprises a soft abrasive tool that is constructed 
of a compressed mixture of aluminum wool and elastomeric polyurethane and 
a method for the making thereof. 
Therefore, it is an object of this invention to provide a new and unique 
abrasive tool. 
Another object of this invention is to provide a new and unique method of 
making a new and unique soft abrasive disc. 
Still another object of this invention is to provide an improved method and 
means for removing paint, sealant, and other elements from the aluminum 
surface of an aircraft and other materials without damaging them.

Brief Description of the Preferred Embodiments 
Referring now to FIGS. 1 and 2, there is shown a soft abrasive disc 11 
which contains a metallic wool matrix 13 impregnated with an elastomeric 
polyurethane binder 15, both of which have been effectively mixed in such 
manner as to have a substantially uniform consistency and/or density. 
As a general rule, the metal of the aforesaid metallic wool matrix should 
be selected to be substantially identical to the metal which is to be 
cleaned or polished by the subject disc 11; however, it should be 
understood that other metals may be substituted therefor, too. For 
example, the metal of metallic wool matrix 13 could be harder or softer 
than the metal of the surface being polished, and, of course, abrasive 
disc 11 may be used to clean, polish, grind, or the like, any other 
surface material as necessitated by operational circumstances. Obviously, 
the harder the metal of metallic wool matrix 13, the more effective it is 
as a cutting agent. Therefore, it would perhaps be noteworthy that the 
selection thereof is without limitation and would be well within the 
purview of the artisan having the benefit of the teachings presented 
herewith. 
The foregoing notwithstanding, since one of the preferred embodiments of 
the invention is a method and means for removing paint, sealant, and other 
coatings from the aluminum skin of an aircraft, metallic wool matrix 13 
would be an aluminum wool matrix -- the aluminum of which is preferably of 
commercial medium grade with hard temper -- which is thoroughly mixed with 
a polyether type elastomeric polyurethane binder 15 -- the elastomeric 
polyurethane of which is a very abrasion resistant, tough, long-lived 
material -- with the mixture thereof preferably containing (but not 
limited to) approximately 55 percent aluminum wool and 45 percent 
elastomeric polyurethane binder by weight. 
As previously suggested, because other metallic wool matrixes may be 
incorporated in the instant invention, metallic wool matrix 13 may, in 
fact, be a stainless steel wool, while binder 15 may be a polyether type 
polyurethane material such as, for instance, elastomeric polyurethane, two 
component ether type catalytic or polyol, air cured. Of course, being 
harder than aluminum wool, stainless steel wool would be incorporated in 
abrasive disc 11 when it is desired to polish harder materials, such as 
steel, for example. 
For simplicity of disclosure purposes, FIGS. 1 and 2 both depict abrasive 
disc 11 cutting a polyurethane paint 17 and a polysulfide sealant 19, and 
cleaning an aluminum substrate material 21. Obviously, as previously 
indicated, other materials may be cut and polished thereby, if so desired. 
As best seen in FIG. 1, disc 11 has a hole 23 extending therethrough, 
through which a shaft 25 of a drive motor 27 extends; as best seen in FIG. 
2, the latter of which may be, in actuality, an electric, pneumatic drive 
or other motor, as desired. Disc 11 may, of course, be connected to shaft 
25 in any convenient, conventional manner; accordingly, it may be 
connected thereto by means of a pair of nuts 29 and 31 screwed on threads 
33 of the threaded end of shaft 25 in such manner that disc 11 is 
effectively clamped therebetween and, thus, will be rotated with said 
shaft 25. 
Because it is not intended that the geometrical configuration of the 
subject invention be limited to the aforementioned disc form 11, a 
cup-shaped species 31 thereof is illustrated in FIG. 3. Although tailored 
or configured differently than disc 11, abrasive cup 31 contains the same 
metallic wool and polyurethane binder in the structure thereof; however, 
in order to distinguish between the two species, the metallic wool and 
polyurethane binder thereof have been referenced by numerals 33 and 35, 
respectively. 
At this time, it would appear to be noteworthy that regardless of the 
geometrical configuration of the subject abrasive device, a key element 
therein is the matrix or wool configuration of the aluminum or other metal 
incorporated therein; and when such key abrasive matrix of aluminum 
material is uniquely combined with the aforesaid polyether type 
elastomeric polyurethane binder material, a new and highly effective 
combination of materials comes into existence which constitutes a superior 
cutting, abrasive, polishing device, indeed, and which certainly 
facilitates the removal of various types of soils and coatings from 
various and sundry substrate materials, such as, for example, paint and 
sealant from aluminum and other metals, tarnish from silver, and barnacles 
from metals and other materials. 
Referring now to FIG. 4, there is disclosed, in representative block form, 
the preferred steps to be performed in the making of the aforesaid disc 11 
or cup 31, as the case may be. Because only the molds will be different, 
only the method of making soft abrasive disc 11 will be discussed, so as 
to keep this disclosure as simple as possible. 
Hence, the subject abrasive disc 11 may be manufactured by using the 
following steps: 
First, place a commercial medium grade, hard tempered aluminum wool matrix 
in the bottom of a suitable mold, as indicated in block 41; 
Second, compress said aluminum wool matrix against the bottom of said mold 
at a pressure of, say, 3,000 to 4,000 pounds per square inch gauge, as 
indicated in block 43; 
Third, bring the polyether elastomeric polyurethane binder material to room 
temperature of approximately 75.degree. F, as indicated in block 45; 
Fourth, mix said elastomeric polyurethane binder material with a setting 
catalyst of the amine catalyst type, as indicated in block 47; 
Fifth, pour said elastomeric polyurethane binder and catalyst mixture into 
the mold on the aluminum wool matrix already deployed therein, as 
indicated in block 49; 
Sixth, compress said elastomeric polyurethane and catalyst mixture at, say, 
300 to 400 pounds per square inch gauge, so as to cause the former to 
impregnate the latter with a substantially uniform consistency and/or 
density, as indicated in block 51; 
Seventh, cure said polyurethane binder and aluminum wool mixture at room 
temperature until it becomes a solid disc (or other shape) having 
approximately a "Shore hardness A" of 90, as indicated in block 53; and 
Eighth, remove the cured elastomeric polyurethane and aluminum wool matrix 
disc from the aforesaid mold, as indicated in block 55. 
As best seen in FIG. 5, which, of course, is representative only, there is 
shown a press 61 of any appropriate conventional type which is connected 
to a suitable piston 63 adapted for traveling within the cylinder portion 
65 of a suitable mold 67. Hence, those method steps of FIG. 4 requiring 
compression -- as indicated in blocks 43 and 51 -- may be implemented by 
using such arrangement, if so desired. Thus, disc 11 (comprising aluminum 
wool 13 and polyurethane binder 15) is formed therein. But, in the 
particular configuration of disc 11 shown in FIGS. 1 and 2, a hole 23 
extends therethrough; therefore, mold 67 contains a center post 69 which 
causes said hole 23 to be made during the compression and curing process. 
Preferably, the length of post 69 should be equal to the width desired for 
disc 11, so that said hole 23 will extend therethrough when disc 11 is in 
its finished form. 
MODE OF OPERATION 
The operation of the subject invention will now be discussed briefly in 
conjunction with all of the figures of the drawing. 
When disc 11 is removed from its mold, as referenced in FIGS. 4 and 5, 
respectively, it is ordinarily connected to the shaft of drive motor 27 in 
the manner shown in FIG. 2. Then, while being rotatably driven by motor 
27, abrasive disc 11 is held (by hand or otherwise) against the material 
or materials desired to be cut, removed, and/or polished. In this 
particular case, as best seen in FIGS. 1 and 2, paint 17 and sealant 19 
are ground away -- since the cohesive strength thereof is less than that 
of aluminum -- while aluminum 21 -- that is, the aluminum skin of an 
aircraft -- becomes polished. And because the cutting element of disc 11 
is a matrix of aluminum wool, the aforesaid substrate aluminum 21 is 
polished without any significant damage thereto, as far as loss of 
strength, cracking, fatigue, or the like, are concerned. Hence, said 
substrate aluminum (or other material) is put into a condition which 
facilitates inspection, rework, refinishing, or other operations to be 
performed thereon. 
Again, for purpose of emphasis, it is hereby mentioned that the metal of 
the wool matrix should preferably be the same as the substrate metal to be 
polished if said substrate metal is to be polished or have the coatings 
thereon, if any, removed therefrom without damage thereto. Nevertheless, 
other metals or materials in matrix form may be substituted therefor by 
the artisan without violating the spirit or scope of this invention. 
In view of the foregoing, it may readily be seen that an improved soft 
abrasive tool and a unique method for making same have been invented 
which, as a consequence of the improved results produced thereby, 
constitute an advancement in the abrasives art. 
Obviously many modifications and variations of the present invention are 
possible in the light of the above teachings. It is, therefore, to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.