US 3092476 A
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United Sites 3,092,476 METHOD OF MANUFACTURING A GRINDER OR HONE HAVING FINE CUSHIONY SURFACES Yoshio Yatabe, 1 l-chome Jujo-nakahara Kita-ku, Tokyo, Japan No Drawing. Filed Sept. 25, 1959, Ser. No. 842,361 Claims priority, application Japan Sept. 27, 1958 2 Claims. (Cl. 51-293) This invention relates to a high finish grinder or hone characterized by numerous fine cushiony surfaces of polymeric materials distributed around the uniformly bound abrasives and to the manufacturing method thereof. The object of the invention is to oifer such a grinder or hone that the shocks or impulses against the work surface to be ground due to the mechanical vibrations during grinding can be prevented to produce an extremely smooth and accurate surface, and also to provide an easy and simple method to manufacture such a grinder or hone.
Extreme smoothness and accuracy like an optical flat is generally most desirable in a grinding operation. However, such a surface is very difiicult to obtain even by the modern super-finishing, lapping, honing, polishing, etc. The only method to realize this is so-called precision lens-polishing process by means of a .pitch lap which is applied for polishing optical glass or crystal. However, such a lapping method is confined to the special materials as aforementioned, and it is not applicable for common metals which are strong enough and useful for energy transmissions. The only processing for such a high finish for metals is the method applied for finishing block gauges, for which extreme skill and patience are required, of course. The basic idea of the processing for block gauges is to copy the smoothness and flatness of the highly finished surface of the lap onto the work surface. However, generating such a lap surface and maintaining its accuracy are almost impossible except by an expert of more than ten years experience.
By the grinder or hone of the present invention, any metal can be finished to the extreme extent of smoothness and accuracy without high skill or long experience. By the grinder or hone of the invention, contrary to the aforementioned method for block gauges, both smoothness and flatness can be attained simultaneously by means of the discontinuously spaced abrasives of O.51,u. to several hundreds mesh size.
In the conventional mechanical working processes wheel or hone, scraper, lap, etc. are actuated with relative displacements or motions with regard to the work materials. Therefore, periodic or non-periodic vibration cannot be avoided during the operations. In other words, not only the tangential motion along the work surface which is essential to machining, grinding, lapping or polishing action, but the vertical motion harmful to the work surface also takes place in usual finishing operations. The vertical motion to the work surface is conspicuously detrimental to accuracy or smoothness of the work surface. For example, in a grinding machine, the perfect revolution of the wheel spindle (5000-6000 rpm.) entirely free from any vibration cannot be expected by the best fit between the wheel spindle and the hearing as well as by the best balance of the rotating system. So that, a conventional grinder or hone of vitrifide, silicate, resinoid, rubber, synthetic resin or the like bond directly contacts the work surface with the hard abrasives and grinds the work surface with the above mentioned inevitable vibrations to cause the vertical shocks or impulses against the work surface.
In the conventional grinder or hone, the function of bond such as vitrifide, rubber, synthetic resin or the 3,092,47fi Patented June 4, 1963 like is merely to bind numerous abrasives, and it does not imply the aforementioned cushiony action of abrasives against the vibratory shock.
As widely known, if the bonding strength of a bond, which is expressed by the term of hardness or grade, is adequate, the abrasives having worn out or dull edges due to the numerous grinding actions are destined to drop off or to cause cleavage automatically to expose the new and sharp cutting edges which are essential to the efficient grinding action. This is called self-dressing action of a grinder or hone.
Although the above explanation is very reasonable as far as normal or conventional grinders or homes are concerned, the other type of grinder or hone than the conventional must be required for a better performance in the case where metal removal is very slight, so that the grinding actions of the abrasives are confined to the extremely thin layer of the work surface as in a precision fine grinding operation.
Generally speaking, grinding abrasives are much harder than usual work materials, so that abrasives will not be scratched or abraded by work materials through the same process as that the materials are scratched or ploughed by the abrasives. Nevertheless, the abrasives of grinder or hone actually drop off during the grinding action. This seems to be because of that the abrasives plunged into the work material have a tendency to be captured and broken by the material or fractured by the vibratory shocks or impulses due to the rotation of the grinder. Thus, the surface layer of the grinder or bone drops off one after another and at the same time the work surface is seriously damaged or scratched due to the reaction. Apparently this is detrimental to a precision surface finish.
The grinders or homes of the present invention can easily effect much superior finishes in smoothness, fiatness and accuracy to those obtained by conventional ones. In the grinder or hone of the present invention, the particles of synthetic resin polymer or copolymer are uniformly distributed in the structure of abrasives bound together tightly. Generally as a grinder or hone wears out very slowly by the relative motions between the grinder or hone and the work material while they are in contact, the tops of the distributed polymer particles are exposed to the grinder or hone surface, said exposed tops of the particles making an envelope surface as a whole, wherein the grinding abrasives are closely stuck around the polymer particles. It appears as if the mountains of polymer particles having the exposed flat tops are surrounded by the abrasives at the middle parts of the mountains. When such a grinding surface makes frictional contact with a work material to be ground or polished, the exposed tops of the polymer particles touch the work surface first, and then, when the grinding pressure is increased, the grinding abrasives located just behind the exposed fiat surfaces of the polymer particles come in contact with the work surface by the minute elastic deformations of the polymer particles so that a soft and desirable grinding action can be performed by the friction or abrasion of the grinder or hone. In this process, the exposed elastic tops of polymer particles act as a cushiony absorber of the inevitable vibratory impulses or shocks during grinding. As understood by the above explanation, the contact between the grinder or hone and the work surface is so soft and light that the hammering action resulting into a rough finish can be decreased considerably. Therefore, by the grinder or hone of the present invention, ultra-finish up to 0.002 (2 x 10-6 mm.) and extreme dimensional accuracy like that of an optical glass can be obtained.
In accordance with this invention, the precision of flatness attained by the ground surface being such that the roughness of the surface attained was 0.002; and the Newton rings became monochromatic. In other words, in accordance with this invention, a metallic surface can be finished to a degree comparable to that of an optical glass.
In accordance with this invention, grinding abrasives, of which grit size is to be selected in accordance with the objects of grinding in the range from (LS-1 to several hundreds mesh, are properly bound by a synthetic resin. Numerous polymer particles which are the same or larger in size as said abrasives, i.e., several tens to several hundreds mesh, are distributed in said structure consisting of the abrasives and the resin bond. The polymer particles are manufactured by such mechanical process as crushing and the like, or by emulsion or suspension polymerization.
And moreover, by the use of the grinder or hone of the present invention, a metallic surface was finished up to 0.002;.t in surface roughness and in flatness to such an extent that the Newton rings became almost monochromatic.
The manufacturing method of the grinder or hone of the invention is as follows:
Grinding abrasives and hue particles of a synthetic resin type polymer mixed in together in a specific ratio are put into a metallic mould and hot-pressed to be bound together into a shaped structure, one or more synthetic resin monomers different or the same as the said synthetic resin, which are mixed together into a single phase by adding a plasticizer or without adding it, or are somewhat polymerized to be a low grade polymer for each case above mentioned, being absorbed into said prosintered abrasives and polymer particles or not absorbed to be tempered, and finally the polymerization is completed by heating or other means to be tempered and stabilized.
The present invention has such merits as high productivity and low cost because of the speedy circulation of the metallic mould. Besides, according to the invention, one can control the properties of the grinder or hone or improve its quality freely by means of adding monomers, plasticizer, low grade polymer, polymerization accelerator, etc. after the preliminarily sintered grinder or hone is accurately machined or formed.
'In manufacturing conventional grinders or homes, a great amount of care has been required in mixing the abrasives and bonds uniformly, but in the present invention there is not such a trouble at all because the bonding process of the abrasives can be eflectively performed while maintaining the polymer particles distributed around the abrasives under a definite structure.
If higher grinding efliciency is desired, the amount of the abrasives should be as large as possible While keeping the amount of polymer particles to bind said abrasives as small as possible.
Even though the polymer particles are softened by heating to have the maximum fluidity, it cannot be expected that their bonding strength is exerted on the abrasives located Within the distance of two or three times diameter of said polymer particles, because there is a certain limit in the range of the bonding strength or ability of said polymer particles at the stage of pre-sintering. If such a grinder or hone insufiicient in bonding strength as a whole is applied to an actual operation, it will not be able to stand the grinding pressure and Will be broken down. Therefore, other treatments are often needed to increase the bonding strength enough to stand various grinding pressures after the hot-pressing process which is regarded as a kind of pre-sintering.
In the case of the present invention, as an example the pre-sintered grinding Wheel or hone is dipped into a monomer, then taken out to be further heated for the purpose of polymerizing the monomer after removing of superfluous drops of the monomer. In this case, the
4 monomer enters into the deepest spots through the capillary gaps among the grinding abrasives while dissolving the surfaces of the polymer particles distributed to become one body or phase, and the bonding process of the abrasives is completed by being solidified as the polymerization progresses.
Although in the process of dip-tempering only one monomer is used in the foregoing example, two or more types of monomers may be used or plasticizer also may be added if desired. Furthermore, a polymerizing accelorator is effective to speed up the polymerization and to attain higher productivity.
Porous products can be easily obtained, if desired, by adding foam-forming agents, or. otherwise by rapidly raising up the temperature without adding the above.
The monomer can be used in the state of a low-grade polymer if low viscosity by being somewhat polymerized in advance is convenient for the tempering process.
For a better' understanding, the following examples shall be given as a more concrete illustration of the nature of this invention.
Example 1 5 gr. silicon carbide (#1000) and 2 gr. of particles of polymethyl methacrylate are mixed up uniformly, put into a metallic mould, heated up to 140 C., cooled down to room temperature under the pressure of about 100 kg./crn. and thereafter taken out of the metallic mould. The material thus pre-sintered is dipped into monomethyl methacrylate, taken out after impregnated with the monomer, from which the superfluous drops of the monomer are removed, and then polymerized and solidified in a thermostatically controlled bath of 50 to 100 C. to be the final product.
Example 2 6 gr. cerium oxide and 3 gr. copolymer particles of methyl methacrylate and butylmethacrylate are presinter'ed as in Example 1. Thus pre-sintered material is dipped into low grade polymer produced by mixing and dissolving 5 cc. of monomethyl methacrylate, 5 ,cc. of monobutylacrylate, 5 cc. of dibutyl phthalate and 0.1 gr. of benzoyl peroxide, and heated to be polymerized in a thermostatically controlled bath of C. after eliminating the superfluous drops of the low grade polymer. In this process, the desirable temper can be performed rather easily by controlling the dipping time, the viscosity of monomeric low-grade polymer, etc.
As to grinding abrasive, diamond powder, boron carbide, silicon carbide, aluminum oxide, other metallic oxides, etc. can be applied regardless of their grit size.
The polymer particles may be either spherical or formless, and both polymeric synthetic resins such as a methacrylate resin, styrol resin, vinyl resin, etc. and condensation synthetic resins such as polyester resin, phenol formaldehyde resin, urea formaldehyde resin, etc. are applicable as the material.
The compatibility between the polymer particles and monomeric low-grade polymer used in tempering is not necessarily essential, but the poor compatibility can yield a special effect upon the product.
The compatibility of the plasticizer is also not so important; Therefore, the ranges for selecting polymer, monomer and pl-asticiz'er, the latter two of which are used for tempering, are so wide that almost any of synthetic resins can be used.
Since it is apparent that many changes and modifications can be made in the above described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited thereto except as set forth in the appended claims.
What is claimed is:
1. Method of preparing a grinder or bone having a cushiony surface, which comprises mixing abrasive particles and particles of a synthetic resin selected from the group consisting of vinyl resins, polyester resins, and urea formaldehyde resins, putting said mixture into a mould, heating said mixture under pressure in said mould in order to obtain a pre-sintered moulded article, dipping said pre sintered, moulded article into a mixture of a liquid monomeric material selected from the group consisting of vinyl monomers, polyester monomers nad urea formaldehyde monomers and polymerization catalyst therefore, and then heating said dipped article to completely polymerize said monomeric resin.
2. Method according to claim 1 wherein said synthetic resin is selected from the group consisting of polymethyl methacrylate and a copolymer of methyl methacrylate and butyl methacrylate; and said monomeric synthetic resin is an alkyl methacrylate.
References Cited in the file of this patent UNITED STATES PATENTS 2,117,513 Scutt May 17, 1938 2,246,898 Sayre June 24, 1941 2,256,618 Kistler et al. Sept. 23, 1941 2,308,854 Barnes Jan. 19, 1943 2,377,995 Coes June 12, 1945 2,774,108 Wyllie Dec. 18, 11956