US 2877103 A
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, abrasive art.
United States Patent Q ARTIFICIAL ABRASIVE ARTICLES Richard 0. Lane, Munith, Mich., assignor to M & M Research and Development Company, Jackson, Mich, a corporation of Michigan No Drawing. Application December 7, 1954 Serial No. 473,762
4 Claims. (Cl. 51-298) The present invention relates to improvements in abrasive articles and the manufacture thereof, being a continuation-in-part of copending application Serial No. 314,072, filed October 10, 1952.
It has heretofore been proposed, as disclosed in the Hartman Patent No. 1,830,757, granted November 10, 1931, to employ an additive material in the manufacture of abrasive articles to produce an abrasive wheel or the like having self dressing characteristics to control glazing. The additive material contemplated by Hartman was not comparable to the abrasive grain forming the body of the articles in any physical respects. According to Hartmans disclosure the additive functioned to provide ,voids by being more friable than the abrasive grains and by being of a less hardness yet capable of being broken out of the molded mass of abrasive grains to leave an irregular face. Thus, the self-dressing was effected by the bodily displacement of the additive to leave a void.
In contrast to the disclosure of the aforesaid Hartman patent, the present invention contemplates an additive material in the form of abrasive grains which are comparable in physical respects to the abrasive grains of the mother matrix.
In the form of loosely or weakly bonded abrasive grains dispersed Within the mother matrix, the additive, according to the present invention, is bodily dislodged by the action of the work piece presented to the working face of the abrasive article; the
. present theory being that the self-dressing results from the mechanical fracturing action of the additive upon the abrasive grains of the mother matrix taking place between the work piece and the working face of the abrasive article.
In practicing the present invention, only the form and manner of association of the additive in the mother matrix distinguishes the manufacture of abrasive articles made according to the invention over standard practices in the This holds true without regard to the form of bond of the mother matrix such as vitrified, resinoid, shellac, rubber, silicate, magnesium, oxychloride and metallic.
Being mechanical in nature, the action of the loosely or weakly bonded abrasive additive upon the firmly bonded abrasive body is relatively independent of the type of bonding so long as the bonding and/ or processing of the firmly bonded abrasive body does not destroy the functional characteristics of the dispersed loosely or weakly bonded abrasive additive.
Thus, an object of the invention is to provide an improved abrasive article having self-dressing characteristics in use in which a dispersed additive is present in the form of loosely or weakly bonded abrasive grains comparable in physical respects to the firmly bonded abrasive grains of the main body of the abrasive article.
Another object of the invention is to provide an improved abrasive article of the type described in the preceding paragraph in which the additive is in the form of pellets of loosely or weakly bonded abrasive grains dispersed in the firmly bonded matrix of the abrasive article ice and the grains of which are readily and bodily dislodged during use of the abrasive article to function as a freed fracturing agent of the firmly bonded abrasive grains of the matrix at the point of contact between the work piece and the abrasive article.
Another object is to provide, as a new article of manufacture, an improved additive for grinding wheels and the like to provide the same with self-dressing characteristics, in the form of pellets or loosely or weakly bonded grains comparable in physical respects to the abrasive grains making up the firmly bonded matrix.
These and other objects and advantages of the present invention will more fully appear from the following specification and appended claims.
In carrying out the present invention the additive for abrasive articles preferably comprises abrasive grains which are comparable in hardness and resistance to fracture to the abrasive grains of the firmly bonded body which make up and provide the structural mass of the abrasive article.
As it is the practice, for example, in the manufacture I of grinding Wheels to make wheels of many sizes of abrasive grains, it would not be practical to match the grain size of the additive with the grain size of each wheel in which the additive is used. It has been found in practice that it is not necessary to closely match the size of the abrasive grain of the additive with the abrasive grain of the firmly bonded matrix of the wheel in order to obtain good results. For example, with the additive having an abrasive grain size of 80, good results are obtained when the additive is used in grinding wheels having abrasive grain sizes ranging from 16 to 120. Likewise,
with a grain size of used inthe additive, good results have been obtained from this additive when used in grinding Wheels having grain sizes ranging from 150 to 500.
The additive is preferably molded or shaped into pellets by an SXlII'IlSlODPIOCESS which is facilitated by having the additive mix somewhat sticky and greasy. A typical additive mix would comprise 11,360 grams of 80,grain size green or black silicon carbide; cornstarch 675 grams; carboxyl methyl cellulose 575 grams; a colloidal type clay such as bentonite 350 grams; glycerin 1000 cc.; and water The cornstarch, clay and carboxyl methyl cellulose are first dry blended and then these are added to the water and glycerin to form a sticky mass. To this is slowly added the abrasive grains. Thereafter, the mix is agitated until a suitable consistency for extrusion is obtained. This mix is then introduced into a pug mill and extruded through holes and cut to A length to provide the pellets.
The extruded and cut to length pellets are then dried to remove substantially all moisture and thereafter subjected to a calcining operation to eliminate the volatile materials, leaving a complex magnesium aluminum silicate bond, holding the abrasive grains together with a degree of tenacity which may be characterized as loosely or weakly bonded as compared to the bonding of the abrasive grains in the matrix of the grinding wheel. After calcining the pellets may be screened and graded to provide a uniform product with the pellets ranging roughly in size from Me" to for use in grinding wheels of a diameter in the range of 4" and over. With smaller diameter wheels the pellet size should be proportionately reduced to permit uniform dispersion of the pellets with the matrix.
It is to be understood that the binding materials for the abrasive grains of the pellets may be numerous. In the example given only the bentonite will be present in the pellets after calcining as a functional residue of any consequence. The other ingredients provide wetting,
lubricating and filler rolesto enable the pellets to be exused in'making thepllets. As for example, in making the pellets the bonding material would be reduced to the order of 2% of the abrasive grain as compared to 15 of'the abrasive grain going to make upthe matrix.
To give a typical example of the use'of the additive pellets in the manufacture of grinding wheels, 134 lb. 7
oz. of green or black silicon carbideof 46 size grain is mixed with 1640 cc. of a solution of dry dextrine in water (50% dry dextrine and 50% water, approximate) until all 'the grain is uniformly wetted. Thereafter, 37 lb., 12 oz. of A3" to size pellets (previously calcined and graded) are carefully and uniformly dispersed in the wetted abrasive grains which make up the main body of the grinding wheels. This dispersion should be carried out with care to avoid any appreciable crushing or disintegration of the pellets.
The bond for the abrasive grain of the matrix of the grinding wheel in the example being given comprises 16 lb. '13 oz. of the following ingredients in the proportion given:
Percent Feldspar 57.35 Kentucky clay 17.50 Stoneware clay 17.50 Silica 7.65
With this bond is hand-blended 5 lb. 11 /2 oz. of dry dextrine and the blended bond and dextrine is then added to the mixture of the preceding paragraph and a final mixing takes place to provide a uniform blend with the pellets uniformly dispersed therein. This final mixture is then removed to the press room where 3,221 grams of the final mixture is placed in a steel mold of the proper shape to make a 10.250" by 2.250 by 7.025 wheel.
The wheel mold is then placed in av hydraulic press and pressure applied until the prescribed thickness is obtained, namely, 2.250"; the tonnage required to carry out this operation being in the order of 1000 to 2000 per square inch of pressing surface.
Following inspection, the pressed wheel is then placed in a humidity dryer to remove the moisture. After being thoroughly dried the vitrification cycle is then carried out for nine days in a tunnel kiln in a well known manner. Thereafter the wheel is sized to by 2" by 7 and mounted upon a steel backing disc and placed in use.
In the example given above it will be noted that the pellets constitute 20% by weight of the batch of the final mixture. Experimentation to date indicates that the per-- centage of the pellets used may be varied over a rather Wide range without materially effecting the improved performance of the grinding wheels. However, good practice would indicate that the range should be in the order of 15% to for best all around results.
It is to be understood that the bonding material for the 46 size abrasivegrain of the example given will firmly bond these grains into .the main mother matrix of the resulting grinding wheel in the conventional manner.
However, the bonding of the pellets in the matrix will be confined to a boundary'or skin bonding with the result that the interior abrasive grains of the pellets will retain their original'loosely or weakly bonded state. Thus, the 46 size abrasive grains of the mother matrix will all be firmly bonded together while the 80 size abrasive grains of the pellets will be loosely or weakly bonded in the wheel except for the boundary bonding that takes place between the mother matrix and the exterior grains of the pellets.
In the appended claims the term pellets is used to designate the small preformed objects made up of a relatively large. number of abrasive grainsor crystals 4 bonded together to provide the additive which is mixed into the batch from which the abrasive article 'is later molded and cured.
1. An abrasive article of the type in which the components thereof are batch mixed, molded into shape and cured to provide the structural form of the article consisting essentially of a main body portion constituting the mother matrix of the article, said main body portion being formed of abrasive grains and bonding'material therefor, said abrasive grains being firmly and independently bonded to each other to provide thernother matrix with said abrasive grains being the main abrasive grains of the abrasive article and providing in their bonded state the structural strength and wearing surface of the article, pellets of abrasive grain and bonding material, the abrasive grains of said pellets being of similar hardness and resistance to fracture as said main abrasive grains, said pellets being present in said matrix as a batchmixed dispersed additive, the abrasive grains of said pellets being weakly bonded to'each other, the bonding material and the amount thereof used in said pellets weakly retaining the abrasive grains of said pellets in bonded association with each other as compared to the firm bonding of said main abrasive grains to each other in said matrix, said abrasive grains of said pellets being of a size and being present in sufficient number in said pellets to provide exteriorly located as well as interiorly located grains,"the exteriorly located grains of said pellets having boundry bonding in said matrix with the interiorly located grains of said pellets being free from bonding with said matrix, said interiorly located grains in said pellets being subject to bodily dislodgment in the working surface of said article when in use more readily than said main abrasive grains in said matrix, the abrasive grains of said matrix and saidpellets having a hardness of 9 orhigher onjthe Mobs scale, said pellets being of a size substantially to in diameter, and said'pellets constituting in the order of 15% to 25% by weight of the mixture from which the article is molded.
2. An abrasive article as defined in claim 1 in which the main abrasive grains have a size in the range of 16 to and the size of the abrasive grains of the pellets are substantially 80.
3. An abrasive article as defined in claim 1 in which the main abrasive grains have a size in the range of'150 to 500 and the size of the abrasive grains .of the pellets are substantially 150.
4. An abrasive article as defined in claim 1 wherein the interior abrasive grains of the pellets are bonded to each other with a tenacity comparable to that resulting from a reduction in bonding material of 15% to 20% of the bonding material of the matrix to provide the weak bonding of the abrasive grains of the pelletsin contrast to the firm bonding of the abrasive grains of the matrix.
References Cited in the file of this patent UNITED STATES PATENTS 1,133,739 Morse Mar. 30, 1915 1,830,757 Hartman Nov. 10, 1931 2,162,600 Ball June '13, 1939 2,246,362 Kehoe et al June 17, 1941 2,334,266 Houchins Nov. 16, 1943 2,463,679 Buckey Mar. 8, 1949 FOREIGN PATENTS 163,179 Germany Dec. 7, 1902 172,813 Germany July 3, 1906 OTHER REFERENCES Websters New International Dictionary, 2nd edition, pp. 1715-1716, 1940.