US1525502A - Method of treating metal articles - Google Patents

Description

Patented Feb. 10, 1925. I

UNITED STATES PATENT OFFICE.

WILLIAM H. GRAVES, JR., OF DETR OIT, MICHIGAN, ASSIGNOR TO PACKARD MOTOR CAR COMPANY, 015 DETROIT, MICHIGAN, ACORPQRATION OF MICHIGAN.

METHOD OF TREATING METAL ARTICLES.

No Drawing.

To all whom it may. concern-.-

Be it known that I, WILLIAM H. GRAVES, J12, a citizen of the United States, and resident of Detroit, WVayne County, State of Michigan, have invented certain new and useful Improvements in Methods of Treating MetalvArticlcs, of which the following is a specification.

This invention or discovery relates to the treatment of metal articles and it is particularly directed to the cleaning and removal of scale from hardened steel articles such as gears without injuring the articles or materially changing the physical properties thereof.

The invention or discovery will be described in connection with the treatment of hardenedsteel gears such as are used in the transmission or gear box of an automobile, though it is, of course, applicable to other gears and to other metal articles.

In the manufacture of steel gears for such uses as suggested above, the gears are, after being cut, hardened by heating to a temperature of around 1500 F. and then quenched in liquid such as oil. This operation produces a scale on the surface ofthe articles and they are unfit for use until such scale has been removed and the surface of the gear, particularly the teeth, is left clean. The scale is a hard abrasive substance which would soon wear bearing surfaces and would, therefore, quickly destroy the gears if they were used without having the scale removed from them.

In usual practice the scale is removed by the use of rapidly Evolving wire brushes and in some cases by a file or' the scraping action of a hard instrument. This requires considerable time and the brushes wear rapidly so that this method is expensive. This is also a difficult method where the gear or article has small teeth or interstices or where teeth or key-ways are cut inside of the gear hub.

Attempts have been made to clean such gears or remove the scale therefrom by the use of an electricallv operated acid bath but it has been found that subjecting a hardened gear to such bath greatly changes the physical properties of the material as by reducing its strength or ductility and such cleaning operations have not, therefore, been found practicable where maximum strength of material is important.

Application filed June 10, 1922. semi No. 567,432.

from which the hardening strains have not been removed, it results in greatly reducing the strength of the hardened gear and while drawing the temper thereafter restores the strength somewhat yet the gear is still far from its original strength. The present invention or discovery permits the use of an electrically operated acid bath in removing the scale from hardened gears without materially changing the physical properties of the metal.

The present invention or discovery consists principally of somewhat drawing the temper from the hardened steel articl'esbefore subjecting them to the acid bath and thus the strains in the metal are removed before the acid is permitted to act upon the articles. More specifically, the invention or discovery may be described as follows: The metal artieleis heated to a suitable temperature above its critical point, say 1500 F., and quenched in oil, thus hardening it. Sometimes this hardening step is repeated by a second heating and quenching. This hardening operation leaves a scale on the gear or article and it is then heated again, preferably to a lesser degree than in the hardening operation, say 7009 F., so that a part of the temper is drawn from the gear. The gear is then cooled. Some of the scale still remains on the gear and it is then subjected to an acid cleaning operation. This acid cleaning operation, in full, preferably consists of, first, washing the gears in an alkaline solution to clean the oil from the surface, next, washing them in cool water to remove the solution and cool the gears so that they will not heat the next bath, next, subjecting the gears to an electrically operated acid bath, next, again washing the gears in cold water, and then washing the gearsin a solution of sal soda (about one ound of sal soda to-ten or fifteengallons of water) to remove the acid. After drying, the ears are sometimes brushed with a fibre brus .to remove the slight deposit that is sometimes present on the surface and which may interfere with inspecting the gears.

The electrically operated acid bath above referred to is preferably a solution of approximately nine parts (by Volume) of water and one part of acid, the acid content consisting of two parts of commercial muriatic acid (specific gravity 1.15) and one part of commercial sulphuric acid (66 Baum). This acid bath should be kept cool in order to prevent pitting of the gears and its acid content may be varied somewhat to suit the particular case; Also; the length of time that the gears or other articles are subjected to this acid bath may be varied somewhat, the usual time-being from eight to twelve minutes. In a two hundred gallon lead lined tank ten carbon plates 10 "x 5"x 1% may be used and the electrical connections are so made that these plates will operate as the anode and the work (that is the metal articles) as the cathode. This tank when loaded may be run with say five volts to produce good results, and the amperage varies with the amount of work in the tank. Although the invention or discovery has been described rather specifically as to particular methods or processes that have been practiced under it, it will be understood that it is not thus limited in its application.

Having thus described the invention or discovery, what is claimed as new and desired to be secured by Letters Patent is:

1. The process of treating hardened steel articles consisting in partly drawing the temper from the article and then subjecting the article to an electrically operated acid bath to remove the scale.

2. The process of treating hardened steel articles consisting in partly drawing the temper from the article, then cleaning the oil from the article, and then subjecting the article to an electrically operated acid bath to remove the scale.

3. The process of treating hardened-steel articles consisting in partly drawing the temper from the article, then subjecting the article to an alkaline solution to clean the oil from the surface, and then subjecting the article to an electrically operated acid bath to remove the scale.

4. The process of treating metal articles such as gears consisting in hardening the article as by heating and quenching, then heating the article to a lesser degree than when hardening to thus partly draw the temper, and then subjecting the article to an electrically operated acid bath to remove the scale.

5. The process of treating metal articles consisting in heating the article and quenching in oil to harden it, then heating the article to partly draw the temper and cooling it, then subjecting the article to an oil cleaning bath, and then to an electrically operated acid bath to remove the scale.

In testimony whereof I aifix my signature.

WILLIAM H. GRAVES, JR.