Grinding, Lapping, and Polishing Compounds

1. Field of the Invention

This invention relates to grinding, lapping, and polishing compounds whose residues can be removed from the workpiece with water and whose vehicles have good lubricating properties.

2. Description of Current Problems

Abrasive materials are often used in surface finishing as part of machining operations. Metals and other materials may be machined with abrasive materials which are solidly bonded together (whetstones, grinding wheels, cutting wheels, abrasive cloths and papers), loose abrasives are also conventionally used.

These loose abrasives are mixed with either liquids or greases and applied to the workpiece; the desired degree of material removal is achieved by movement relative to an abutting surface. The abutting surface can either be a different part of the workpiece itself or can be a special tool surface (ranging from lapping disks to lamb's wool).

In using such abrasives, the removal of oil- or grease-based abrasive compounds from the treated workpiece frequently causes problems, especially when the workpiece has recesses. In order to remove residual abrasive compounds, the workpiece must then be treated with a cleaning fluid. Aside from the danger of working with this solvent, there is the additional danger that some abrasive grains may remain on the workpiece or return to the workpiece from cleaning fluid which is not continually replaced.

Therefore, it has already been suggested that the workpiece be coated with a water-soluble film-forming or viscous material, so that the workpiece can be cleaned with water after the grinding or polishing process has been completed. However, this technique has the disadvantage that two operations are required.

In addition, grinding compounds with water or aqueous emulsions are known. These compounds, however, frequently have the applications-related disadvantage that their vehicles do not have sufficient lubricating properties and thus produce deep scratches.

Thus, the task was to find grinding, lapping, and polishing compounds which neither had the disadvantages of requiring washing with cleaning fluid nor requiring a two-step process and whose vehicles would exhibit good lubricating properties.

The above objectives are met with the grinding, lapping, and polishing compounds of this invention which contain

(a) a finely dispersed abrasive material

(b) a thickener, and

(c) a water-soluble alkylene oxide polymer as a paste vehicle.

Typical abrasive materials are Vienna polishing chalk, iron oxide red, diatomaceous earth, pumice powder, quartz sand, chromium trioxide, corundum, silicon carbide, boron carbide, boron nitride, and diamond powder, whereby particle sizes used in grinding generally range from about 1 to 1200 .mu.m. Preferably, standard commercial, closely graded grain size classes per DIN 848 and DIN 69 101 are used.

The thickeners which are primarily used are inorganic substances with large internal surface areas and particle sizes of less than 50 nm (nanometers). Finely dispersed silicic acid, in particular silicic acid obtained through the pyrolysis of silicon tetrachloride, is used. This latter silicic acid can be obtained commercially, for example, under the name Aerosil.RTM. silica. As used herein, the term "silica" includes silicic acids.

Typical alkylene oxide polymers are water-soluble polyglycols of ethylene oxide, propylene oxide or butylene oxide or their monoalkyl ethers with low-molecular weight alcohols. The polymers should, for greatest effectiveness, have a viscosity of from 22 to 1500 mm/s at 40.degree. C. Accordingly, the polymers have a molecular weight from 500 to 25,000, preferably from 2000 to 4000. Particularly preferred are the (statistical) addition products of ethylene oxide and propylene oxide on butanol, whereby the addition is performed at 40.degree. up to a viscosity of, e.g., 320 mm.sup.2 /s.

The grinding, lapping, and polishing compounds contain, as a rule, from 10 to 70, preferably from 2 to 50, weight percent abrasive material based on the compound.

The thickener content is most efficaciously from 5 to 15, preferably from 5 to 10 weight percent, based on the compound.

The remainder of the compound consists of the alkylene oxide polymer, whereby additional known additives such as colorants can be included in the compounds.

In particular, the compounds can also contain water to adjust the viscosity depending in the intended application.

The compounds of the invention are characterized by a multitude of applications-related advantages. The grinding, lapping, and polishing compounds can be washed off after the machining process has been completed. This eliminates the need to work with cleaning fluid, which is dangerous and is associated with other disadvantages.

The abrasive compounds of the invention exhibit improved lubrication properties through the use of the glycol etherols. These lubricating properties are very important for obtaining a uniform peak-to-valley depth and to assure that dry abrasion does not take place at any location. At such dry locations, the friction between the workpiece, the abrasive powder, and the surface abutting the workpiece would increase to such an extent that relatively large particles of material would separate from one of the two surfaces causing deep scratches. Such inadequate lubrication is very much feared in production: thus, the grinding time with standard commercial compounds is limited and the compounds must be replaced at relatively frequent intervals with a great loss in time, even though the actual abrasive components have not been consumed and the desired degree of machining has not yet been achieved. Said disadvantages are eliminated by the abrasive compounds of the invention.

Fifteen parts of an adduct obtained by reacting a mixture of 55 weight percent ethylene oxide and 45 weight percent propylene oxide on an n-butanol initiator up to a viscosity of 220 mm.sup.2 /sec. at 40.degree. C. and one part Aerosil.RTM.200 (Degussa) silica produced a glassy-clear, water-soluble, highly lubricating grease to which four parts grade 100 silicon carbide were added (DIN 69101).

The same procedure was used as in Example 1, however, employing four parts 600 grade silicon carbide.

The following Table describes additional compounds with the same vehicle. TABLE

All the compounds were mixed together in one operation at room temperature in a suitable, slow-turning mixer.