US 2243049 A
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Patented May 20, 1941 I I GRINDING WHEEL Samuel S. Kistler, West Boylston, and Carl E. Barnes, Worcester, Mass., assignors to Norton Company, Worcester, Mass., a corporation of Massachusetts No Drawing. Application August 19, 1939, Serial No. 291,008
The invention relates to abrasive articles. This application is a continuation in part of our-copending application Serial No. 217,020.
One object of the invention is to increase the cutting efiiciency of a grinding wheel. Another object of the invention is to provide a filler in a grinding wheel which has a chemical action on metal work pieces. Another object of the invention is to provide at the cutting zone in a grinding operation an acid, without covering the work piece generally with acid. Another object of the invention is to provide a wheel containing an acid filler without detrimentally affecting the wheel. Another object of the invention is to provide a filler which shall prevent the wheel from loading. Another object of the invention is to set up. in a grinding wheel a chemical reaction between metal chips removed from a work piece and lodged in the portion thereof which shall loosen such chips, thus eliminating loading. Another object of the invention is to provide a filler for a grinding wheel which reacts on the hot metal chips removed from a work piece in the grinding action so as to prevent such chips from sticking to the wheel, thus preventing loading in the first place. Other objects will be in part obvious or in part pointed out hereinafter.
The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.
We have discovered that the efliciency and cut. ting ability of a grinding wheel may be materially improved by incorporating in the wheel a finely divided, strongly acidic inorganic compound, or one which decomposes under heat to a strongly acid substance, which should be in the solid as distinguished from the liquid state. Our invention may be carried out by using the anhydrides of strong inorganic acids and the acid salts of strong inorganic acids, for example the acid salts of strong polybasic acids especially with alkaline earth and alkali metals and ammonium. As an example of the acid anhydrides, we may use phosphorus pentoxide (P205). Examples of the strong polybasic acids are sulphuric and phosphoric acid. The acid salts of sulphuric acid may be the various bisulphates and pyrosulphates of the alkali metals and alkaline earth metals, and particularly ammonium, sodium, potassium, calcium andbarium. We may also use the acid phosphates and pyrophosphates of these alkali metals and alkaline earth metals.
Grinding wheels and also other abrasive bodies may be made from any of the usual abrasives, for example silicon carbide or other hard carbides, alumina in any of its forms including electric furnace fused alumina, corundum and emery, also diamonds, and these may be bonded with any desired type of bond, for example ceramic bond including all types oi? bond made by vitrifying ceramic or glassy constituents, rubber and the various resins, both natural and synthetic, including shellac and phenol formaldehyde resin. We have found that the incorporation of these strongly acidic solids, or substances which decompose under heat to form strong acids, into a wheel has advantageous eflect where the wheel is made from abrasive grains bonded with natural resins such as shellac, and with the alkyds (polymers of polybasic acids and polyhydric alcohols), the
a vinyl type of resins (such as polystyrene, polyvinyl acetate and polymethyl vinyl ketone), and others such as polymethyl methacrylate and other methacrylates.
As examples of the preferred bond compositions, we may employ sodium bisulphate with a resin bond of copolymerized methyl methacrylate and methacrylic acid; or this same filling material may be employed with a shellac bond or with phthalic anhydride-glycerol resin. We may make a grinding wheel, for example, of a copolymerized bond comprising by volume of methyl methacrylate and 25% of methacrylic acid and a suitable abrasive, such as crystalline alumina or silicon carbide abrasive of required grit size. We may incorporate sodium bisulphate directly into that bond or initially mix it with the abrasive grains. We may use sodium bisulphate in any desired proportions, but ordinarily we prefer that this filler comprise from 1 'to 10% by volume of the total wheel structure. We may make a wheel of this composition by mixing the abrasive grains with the dry sodium bisulphate powder, and the liquid mixture of the monomeric methyl methacrylate and methacrylic acid may be poured into a mold containing the mixture of abrasive grains and the bisulphate. The liquid monomers may contain 0.02% of benzoyl peroxide as a catalyst. The mold containing the abrasive grains wet with the liquid monomers may then be heated at about 10 C. for two days, thus causing the bonding substances to be copolymerized in the presence of the grains in an intimate association withthe sodium bisulphate. in order to provide an abrasive volume percent- We may proportion the materialsage of 43.9%, a bond volume of 46.6%, and a pore volume of 9.5%. The 46.6% 01' bond of the total wheel volume in this particular wheel may be made up 01' 43.4% of the copolymerized resin and 3.2% of sodium acid sulphate. We may use any 01 the resins mentioned above with this acid substance, or with the other acidic agents.
The improved cutting ability oi a wheel containing sodium acid sulphate over-a wheel not containing the same is shown by the following data. Two wheels were made as above described except that the filler in one comprised the normal sodium sulphate (non-acidic), and in the other sodium bisulphate (strongly acidic) was used. These wheels were made of crystalline alumina abrasive grains of equal parts of 16, 20,
24 and 30 grit sizes. Each wheel had the dimensions 01' six inches in diameter and one inch thickness, with a hole of seven-eighths-inch diameter. These were tested in a grinding machine by grinding a test bar of stainless steel of a cross-section of 1.5 by 0.5 inches. Each barwas held against the wheel under a constant pressure of five kilograms for one set of tests and six kilograms for another. The grinding wheel was rotated at a constant speed oi 5500 surface feet per minute. The data obtained from this test was as follows:
The above table shows that the ratio of wheel wear to the amount of metal removed was 1.56 under a grinding pressure or 10 kilograms and 2.2 under a grinding pressure oi. 12 kilograms, where the filler consisted of normal sodium sulfate. The ratios for the filler of sodium bisulphate were respectively 3.06 and 3.13. This shows a material improvement in the cutting action due to the presence of the acid salt. In this test the normal sodium sulphate was employed as an inert filler in one wheel so. that the two wheels would have substantially the same structure and volume percentages of the different ingredients and thus give a closer comparison than would be the case if the acid filler were used in one wheel nd no filler at all were used in the other.
We may also make a grinding wheel with shellac bond, but in which the shellac in its dry powdered form is intermixed with the solid acidic substance used as the modifying agent. We may mix this bond mixture with the dry abrasive grains, then place the mixture in a mold and heat it to set the shellac and bond the grains. We may proceed similarly with the other types of resin bonds, and we may incorporate the acidic substance either in the bond or intermix it with the abrasive grains as desired. We may substitute any of the acid substances above specified for the sodium bisulphate in the example given, and we may employ any of the compatible resins as bonds in intermixture with these acidic solids. We may incorporate the vinyl resins in the abrasive article by pouring the liduid monomers over the mixture of abrasive grains and dry acidic agent, as above described. 11' desired, the low fusing resins may be first made as a molding powder and then intermixed in its polymerized condition with the grains and acid substance and then the article may be pressed at a high temperature to cause plastic flow of the resin into intimate association with the solid substances. Many other types 01 resins may be used in carrying out our invention, such as polymerized vinyl acetate or chloride, styrene, methacrylic acid, methyl methacrylate, or combinations 01 such substances.
Having thus given concrete embodiments oi. our invention, the same should not be limited by the theories which we have as to the reasons for improved efilciency of grinding wheels made in accordance therewith. Nevertheless for a clearer understnding oi the invention, we now give our views as to the underlying cause of the improved results. Every grinding wheel to some degree has a tendency to load, that is, to accumulate particles of the material which is being ground.
Loading is widely variable, depending on the abrasive and the bond and the hardness of the structure of the wheel and the amount of pore space in the wheel and the grit size of the abrasive in the wheel and the material being ground and the peripheral velocity of the wheel and of the work piece and the area of contact and pressure between the wheel and workpiece. All these factors are, of course, widely variable so loading may be very much more of a problem in certain instances than in others. Loading may involve an actual deposit of material from the work piece into the pores of the grinding wheel or a sticking oi the material 01' the work piece to the abrasive grains or to the bond or combinations of these. Mostgrindlng operations involve the generationoi heat at the point of contact if the grinding is being performed efficiently. Tearing away of chips from the work piece, especially in grinding metal, creates a shower of sparks, each spark representing a red or white hot fragment or metal or other substance. These sparks are over 500 C. in temperature. We believe that the tendency of red or white hot metal, especially in finely divided particles, to weld itself to any adjacent surface is a primary factor in the loading phenomena. We believe that the presence, at the point of contact between the metal or other substance'being ground and the abraslve and bond, of a strongly acidic inorganic compound inhibits to a large degree the sticking of the red or white hot particles to the substance oi. the grinding wheel. Probably this action occurs more strongly in the case of grinding metals than in the case or grinding other substances, but at all events the great majority of grinding operations are performed on metal work pieces.
We believe the reaction of the strongly acidic solid substance is far greater with respect to hot particles than with respect to cold particles. Inorganic compounds are selected because organic compounds melt at too low a temperature, and also vaporize and dissociate at too low temperatures. It should be remembered that the white hot sparks may be as hot as 1400 0. Thus the chief effect 01' the incorporation of a strongly acidic substance into the wheel is to prevent loading in the first place although we believe there is some action in loosening any metal chips which may have become lodged in the pores of the wheel.
It will thus be seen that there has been provided by this invention an article and a method in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the aaaaoeo 3 mechanical features of the above invention and as the art herein described might be val-led in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbeiore set iorth is to be interpreted as illustrative and not in a limiting sense.
1. As a new article oi manufacture, an abrasive body comprising abrasive grains. bond holding the abrasive grains together, there being pore spaces in the :lieel, and a flnelydividedsolid compound whi is strongly acid in reaction at grinding temperatures above 500 C. uncombined with the abrasive or bond and available (or reaction with a metal work piece during grinding when the grinding line gives on sparks, via. sparks above 500 C. in temperature, and selected from the group consisting of the anbydrides and acid salts of sulphuric and phosphoric acids.
2. As a new article of manufacture, an abrasive body comprising abrasive grains. organic resin bond holding the abrasive grains together, there bein pore spaces in the wheel, and a iinely divided solid compound which is strongly acid in reaction at grinding temperatures above 500 0. uncombined with the abrasive or bond and available ior reaction with a metal work piece during grinding when the grinding line gives oi! sparks, viz. sparks above 500 C. in temperature, and selected irom the group consisting oi the anhydrides and acid salts o! sulphuric and phosphoric acids.
3. Method 0! grinding metal which consists in applyin to the cutting line between grinding wheel and metal work piece a iinely divided solid compound which is strongly acid in reaction at grinding temperatures above 500 C. and selected from the group consisting of the anhygiides and acid salts of sulphuric and phosphoric 4. As a new article of manufacture, a grinding wheel comprising abrasive grains, bond holding the abrasive grains together, and a filler of sodium bisulphate (NaHSOo 5. As a new article of manufacture, an abrasive body comprising abrasive grains, bond holding the abrasive grains together, and a finely divided solid compound which is strongly acid in reaction at grinding temperatures above 500 C. uncombined with the abrasive or bond and available for reaction with a metal work piece during grinding when the grinding line gives oi! sparks, viz. sparks above 500 C. in temperature, and selected from the group consisting of the anhydrides and acid salts of sulphuric and phosphoric acids.
6. As a new article of manuiacture, an abrasive body comprising abrasive grains, organic resin bond holding the abrasive grains together, and a finely divided solid compound which is strongly acid in reaction at grinding temperatures above 500 C. uncombined with the abrasive or bond and available for reaction with a metal work piece during grinding when the grinding line gives off sparks, viz. sparks above 500 C. in temperature. and selected from the group consisting of the anhydrides and acid salts of sulphuric and phosphoric acids.
8. KISTLER. CARL E. BARNES.