US 3595634 A
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United States Patent O fice US. Cl. 51-298 6 Claims ABSTRACT OF THE DISCLOSURE A method for producing a grindstone characterized by molding an epoxy resin binder with a hardening agent, active sulphur and sodium nitrite. The novel grindstone is used to prevent rust and uneven finishing of a treated metal surface. The grindstone replenishes the loss due to hydrolysis of the grinding solution, thereby enabling the grinding solution to maintain its lubricating and anticorrosive properties.
This application is a continuation-in-part of copending application Ser. No. 650,662, filed June 22, 1967 and now abandoned.
BACKGROUND OF THE INVENTION The object of the present invention consists of preparing a grindstone with lubricating anticorrosive properties so as to prevent rust on the treated metal surface by uniformly distributing powerful lubricating anti-corrosive materials in the grindstone to be used for grinding metal. The specific lubricating anticorrosives which are contained in the grindstone gradually dissolve into the grinding solution and act upon the surface of the metal to be ground as the grinding operation proceeds and as the grindstone is abraded. The mixed lubricating anticorrosives are effective throughout the entire use of the grindstone, displaying a distinguished effectiveness in obtaining sufiicient grinding and in preventing rust on the metal products to be treated. The present invention relates to the method for producing such a lubricating and anticorrosive grindstone.
DESCRIPTION OF THE PRIOR ART When metal products are finished in the presence of a water-soluble grinding solution, there has very often occurred the problem of rust on the finished metal surface. This problem frequently arises prior to the anticorrosive treatment of the finished products owing to the deterioration and hydrolytic loss of efficiency of the grinding solution with lapse of time. To avoid such problems, it is necessary that the anticorrosive and lubricating properties of the grinding solution itself should be reinforced and replenished, even when the finished articles are exposed to moisture, which is the cause of rust prior to the anticorrosive treatment. The residual grinding solution should be powerful enough to form its primary anticorrosive function by enveloping the metal surface with a film.
The methods for improving the anticorrosive properties of the grinding solution have so far been limited to the improvement of the primary efiiciency of the grinding solution, for example, to make the pH of the solution higher than 8.5 or to use an ion blocking agent or the like. There has been no method to prevent the loss of etficiency due to hydrolysis of the water soluble grinding solution which is the key source of the above discussed problems. The rate of hydrolysis of anticorrosive and lubricating materials in the grinding solution is referred to as the 3,595,634 Patented July 27, 1971 secondary eificiency of the solution. Since there has been no method to improve this secondary efficiency in preventing rust, loss of grinding properties and the like, a technical bottleneck has remained until broken by the present invention. This has been a great disadvantage to the grinding operation on a mass production system, resulting in a serious hinderance to industrial advancement.
In the grinding operation of metal, lack of precision in grinding and the development of rust are serious problems which call for an immediate solution. Very important in this connection is the fact that the grinding efiiciency is greatly impaired by hydrolysis arising with the lapse of time irrespective of whether a water soluble grinding solution is employed or not. The problem of this loss has not been solved nor has it been fully recognized by those skilled in the art.
Special attention must be paid to the fact that the anticorrosive property of a fresh grinding solution, however excellent it may be, is merely the function of the primary etficiency of the grinding solution. It must be noted that the important problem is how to minimize the loss of efficiency due to hydrolysis and how to retain this efiiciency. With respect to the anticorrosive property of the grinding solution, great emphasis should be placed upon the secondary eiiiciency, that is resistance to decomposition, in view of the fact that all grinding solutions are susceptible to hydrolytic loss in the course of use. Consequently, it is clear that the hydrolytic loss of anticorrosive efliciency is fatal to the precision of the grinding process as well as to the mass production of metal articles.
PARTICULARS OF THE INVENTION The deterioration of the lubricating and anticorrosive efficiency of the water soluble grinding solution has so far been attributed only to (1) the nature of water used for the dilution of the grinding solution, for instance, the effect of hard water containing metals, such as calcium and the like and (2) the problems due to calcium, sulfur, pulverized grindstone and metal waste resulting from the grinding operation. Consequently whenever deterioration of grinding efiiciency arises due to rust or other such problems, the only counter-measure taken by the prior art has been to add fresh grinding solution to compensate for that loss or to replace the entire solution with fresh material.
It has been considered until the present invention, that the deterioration of the lubricating and anticorrosive efliciency of the water soluble grinding solution is due to foreign elements produced in the course of the grinding operation. In reality, the loss of efficiency is chiefly due to hydrolysis and it has never been recognized that there will be no fundamental improvement unless the foregoing disadvantage is avoided.
In the present invention, to remove the aforementioned technical defects, a binder having powerful lubricating and anticorrosive properties is uniformly distributed in the grindstone, said binder slowly dissolving in the grind ing solution in the course of the grinding operation, thereby effectively replenishing the efliciency of the grinding solution as it is deteriorated by hydrolysis. The binder composite will dissolve into the grinding solution throughout the entire period of use of the grindstone and problems arising from the loss of lubricating and anticorrosive properties of the grindstone will be prevented. The invention therefore enables the obtention of an excellent grindstone which can transform the grinding solution into that of an efficient non-degrading type, greatly contributing to the technical development of the metal grinding process.
More specifically, abrasives can be chosen from among materials such as Alundum, Carborundum and the like.
An epoxy resin is employed as the binder. The most significant property of the epoxy resin consists of the fact that this type of resin can be readily changed even at room temperature, from a liquid or thermoplastic state into a solid mass of thermosetting resin characterized by toughness. This phenomenon of changing the plastic or semiplastic mass into a solid mass is called hardening or curing. A suitable epoxy resin to be employed in the present invention is a diepoxide of the epichlorohydrinbisphenol A type such as Epikote 828 (Shell Chemical) (equivalent weight based on epoxide groups 182-194) having epoxide groups at both terminal positions of its molecular chain. It exists in the form of a viscous liquid, its molecular weight being 360 to 560 and its equivalent weight based on epoxide groups being 180 to 260.
For hardening, the addition of a hardening agent (or curing agent) is indispensible. As a hardening agent, a chemical compound which is capable of readily reacting with epoxide groups is employed. Such compounds are primarily amines, secondary amines, dicarbonic acid and its anhydride, and the like. Primary and secondary amines are used most widely. Among suitable amines are diethylentriamine, triethylentetramine and the like.
Although the hardening of the epoxy resin begins with the addition of the hardening agent, the curing time required largely depends on the temperature. When an amine is used as a hardening agent, the hardening may take place even at room temperature, but the curing time can be remarkably shortened by elevating the temperature. The optimal temperature for hardening ranges between normal room temperature and 90 C. Active sulfur (alpha or sublimed sulfur) is mixed with the amine and sodium nitrite to obtain sodium amine nitrite sulfide, which is in turn mixed with the epoxy resin to obtain a molding agent for the preferred abrasive. The amines and sodium nitrite in essence act as anticorrosives while the sulfur acts as a lubricant. In practice, however, these compounds exist in the form of reaction products; the amine nitrite acting as the effective anticorrosive and the amine sulfide as a lubricant.
The molding can be affected either at normal temperature or by heating. When sulfur, sodium nitrite and amine in excess of the equivalent quantity of epoxide, are added, the epoxy resin starts a hardening reaction, and various reactions simultaneously arise from the amine, sulfur and sodium nitrite. For instance, diethylenetri'amine and sulfur react as follows:
Amine and sodium nitrite react as follows:
resulting in production of the amine sulfide and amine nitrite, respectively. Furthermore, sodiumamine nitrite sulfide is obtainable by mixing active amine sulfide, sodium nitrite and amine nitrite sulfide by mixing amine nitrite and sulfur, the products having a powerful anticorrosive and lubricating effect. These products display a far greater anticorrosive property when produced in the presence of epoxy resin, and far greater rust-proof property is obtainable when the anticorrosives, such as amine, sodium nitrite and the like, are compounded with epoxy resin as compared with the case wherein such anticorrosives are simply added to the grindstone as ingredients thereof. Among the suitable epoxy resins is the diepoxide of epichlorohydrin-bisphenol A type, having epoxide groups at both terminal positions of its molecular chain. It exists in the form of viscous liquid, its molecular weight being 360-560 and its equivalent weight (based on epoxide groups) being 180-260.
Preferred ranges of epoxy resin are 30 to 50% by weight of the entire composition; preferred ranges of amine are 120 to 250% of the equivalent amount of epoxide; preferred ranges of sulfur are 0.3 to 1.0% of the entire composition and preferred ranges of sodium nitrite are 3 to 10% of the entire composition. Preferred molding temperatures are room temperature to C. and preferred pressures for molding are 50 to 300 kg./cm.
A grindstone of excellent quality is obtainable by mixing and molding the foregoing materials, the anticorrosives and hardening materials while the epoxy resin hardens, the lubricating and anticorrosive materials being uniformly distributed throughout the grindstone simultaneously. If the metal grinding operation is conducted with such a grindstone, the ingredients gradually dissolve into the grinding solution as the grindstone is abraded, giving the grinding solution enhanced lubricating and anticorrosive properties. Moreover, as the dissolution continuously occurs throughout the period of use of the grindstone, problems arising from the deterioration of the efficiency of the grinding solution can be prevented, displaying the eifect of transforming the grinding solution into an efiicient nondegrading type.
The present invention is useful with grinding solutions which degrade either by hydrolysis or other phenomena. A grinding solution uesful in the present invention is, for example, one containing sodium nitrite, amine and surfactant. Another suitable solution is, for example, one containing amine derivatives. The present invention is most useful with grinding solutions containing anticorrosive lubricants such as amine sodium nitrite, amine nitrite, and amine sulfides, etc.
The term sodium amine nitrite sulfide denotes a mixture composed of an amine sulfide and sodium nitrite which mixture has both anticorrosive and lubricating properties.
All percentages set forth herein are by weight.
The preferred embodiments are disclosed hereunder.
EXAMPLE 1 Abrasives: Parts Alundum 1 60 Corundum 1 40 Lubricating and anticorrosive binders? Fluid epoxy resin (Epikote 828 Shell Chemical equivalent 182-194) 2 Diethylenetriamine 2 15 Sulfur 2 1 Sodium nitrite 2 10 1 Admixture 60 parts.
2 Admixturo 40 parts.
The lubricating anticorrosives are fully incorporated, to 40 parts thereof being added 60 parts of the abrasive, the resultant admixture being fully incorporated and then granulated, the grains thus obtained being heated at 40 to 80 C. and then molded into a grindstone with a pressure of 200 kg./cm.
1 Admixlture 55 parts.
2 Admlxture 45 parts.
The lubricating anticorrosives are fully incorporated, to 55 parts thereof 45 parts of the abrasives being added, the resultant admixture being fully incorporated and then granulated, the grains thus obtained being heated at 70 C. and then molded into a grindstone with a pressure of 200 kg./cm.
METAL SURFACE Rust appearing time, Kind of grindstone Grinding solution min.
Ordinary grindstone Water D0 Water soluble grinding 70 solution. Anticorroslve grindstone Water 2 120 1 Of the invention.
2 Or more.
What is claimed is:
1. A process for producing a grindstone comprising: (a) preparaing a grindstone composition by admixing (l) epoxy resin30 to 50% by weight of said composition,
(2) a hardening agent for said epoxide selected from the group consisting of primary and secondary amines-420 to 250% of the equivalent weight of said epoxide,
(3) sodium nitrite-3 to by weight of said composition,
(4) active sulphur-0.3 to 1% by weight of said composition, (5) abrasive grainsthe balance of said composition;
(b) molding said grindstone composition into a grindstone at temperatures between room temperature and 90 C. under a pressure of to 300 kg./cm.
2. A process according to claim 1, wherein the epoxy resin is a diepoxide of epichlororhydrin-bisphenol A condensate having epoxide groups at both terminal positions of its molecular chain and having a molecular weight of about 360-560 and equivalent Weight based on epoxide groups of about 180 to 260.
3. A process according to claim 1 wherein the amine hardener is diethylenetriamine.
4. A process according to claim 1 wherein the abrasive grains are selected from the group consisting of Alundu-m, Carborundum and mixtures thereof.
5. A process according to claim 4 wherein the alundum and corrundum are employed in admixture in the ratio of to Alundum to 30 to 40% Carborundum.
6. A grindstone produced by the process of claim 1.
References Cited UNITED STATES PATENTS 2,448,985 9/1948 Kuzmick 51-298 2,462,480 2/1949 Eppler 51308 2,779,668 1/ 1957 Daniels 5l-298 3,020,140 2/1962 Bluth 51-308 DONALD J. ARNOLD, Primary Examiner UJS. Cl. X.R.