Electrolytic polishing

Jan. 8, 1952 s. B. emery , ELECTROLYTIC POLISHING

Filed July 15, 1947 2 SHEETS—SHEET 1

2,582,020

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Jan. 8, 1952

S. B. EMERY

ELECTROLYTIC POLISHING

2,582,020

Filed July 15, 1947

SHEETS—SHEET 2

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INVENTOR.

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Patented Jan. 8, 1952

2,582,020

UNITED STATES PATENT OFFICE

2,582,020

ELECTROLYTIC POLISHING

Sheldon B. Emery, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware

Application July 15,1947, Serial No. 760,951

Claims. (Cl. 204—140.5)

This invention relates to electrolytic polishing and deburring and is particularly concerned with operations on cupreous metals and the like.

It is therefore a primary object of this invention to provide a method and apparatus for electrolytically polishing and deburring cupreous articles.

In carrying out this object, it is another object of the invention to utilize alternating current as a power source for the electrolytic bath.

A still further object of the invention is to provide an apparatus for carrying out the method wherein a cathode is utilized which has a dual function of acting as a cathode in the electrolytic polishing bath and simultaneously acting as a rectifier for changing the alternating current to effective direct current.

In carrying out the above object, it is another object to utilize a film-forming metal as a cathode, for example, aluminum, tantalum or magnesium.

A still further object of the invention is to provide an electrolyte for use in the method which has a low factor of dissociation and which does not attack the film on the cathode. In some cases, it may be desirable to add a brightener to the bath, such as a polyhydric alcohol.

Another object of the invention is to provide a method for electrically connecting several polishing baths to a single transformer wherein the efficiency of the setup is improved by utilizing both half waves of the alternating current.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

Fig. 1 shows a sine wave indicating an A. C. current, the shaded portions having similar polarity, being that part of the current that is used in the cell hookup shown in Fig. 2.

Fig. 3 shows a sine wave indicating an A. C. current wherein the shaded portions above the axis are used in one cell and the shaded portions below the line are used in the other cell hookup shown in Fig. 4.

Fig. 5 shows two sine waves superimposed wherein the shaded portions of the A, C, current are alternately used in the two cells shown in the hookup, Fig. 6.

Electrolytic polishing and deburring is a well known expedient for use with various metals. 5 In the usual type of apparatus, a cathode is utilized as one electrode in the electrolytic bath and the work to be polished is connected in the circuit as the anode. An electrolyte is provided which will suitably polish and debur the mate10 rial being operated upon and in most cases, contains phosphoric acid together with desired quantities of sulphuric acid. The current source for such operations is direct current, provided by a motor-generator set or other suitable appara15 tus. The necessity of direct current is one of the expensive items in electrolytic polishing procedures since this type of current is not usually available and requires a motor-generator set for its production.

This invention is directed to a method and apparatus for electrolytically polishing cupreous materials, for example, brass, bronze, berylliumcopper and in fact any copper alloy wherein the copper predominates. In this respect, stainless •25 steel and the like may be polished if sufficiently high current densities are utilized. The main advantage of the apparatus and method is that alternating current is used as the power source and in this manner current may be taken from 30 any alternating current source.

In use, the A. C. current must be rectified and this is accomplished by providing a cathode in the electrolytic polishing bath which may be filmed or anodized. The cathode may be filmed 35 prior to its introduction into the bath, or the film may be formed during the first polishing operation. This film or anodized coating permits current flow in one direction but not in the other whereby in a single cell setup, as shown in 40 Fig. 2, the half waves of the current (those of the same polarity as shown In Fig. 1) only are utilized. Thus it is possible to merely connect a transformer to an alternating current power line and utilize the current from this transformer in 45 the polishing cell.

I have found that it is important to utilize electrolytes that do not attack the film on the aluminum or other anodized metal. For this reason, I prefer to use as a base for the electrolyte, acid having a very low factor of dissociation

2,582,020 such as citric acid, tartaric acid, etc. To this acid or salt thereof is added a salt of a strong acid and a weak base for example, ammonium phosphate or the like. A brightener in the form of glycerine, ethylene glycol or other polyhydric alcohol may be added if desired together with a large quantity of water. Several specific formulas for the electrolyte are as follows:

#1. A saturated solution of ammonium phosphate.

#2. A saturated solution of ammonium phosphate and 5% phosphoric acid.

#3. A saturated solution of ammonium phosphate and 5% to 50% citric acid.

#4. A saturated solution of ammonium phosphate and 5% to 50% tartaric acid.

#5. Ammonium citrate in saturated solution with 5% phosphoric acid.

#6. 100 grams ammonium phosphate

100 grams citric acid grams potassium phosphate 1000 cc. water

Current densities from one-half ampere to four amperes per square inch have been found to be satisfactory and it is noted that the time of polishing is inversely proportional to. the; current density, for example, at one-half ampere satisfactory polishing occurs in about two minutes whereas at four amperes, a thirty second immersion is satisfactory. In all· instances, the voltage used must be varied in accordance with the distances between the electrode for best results and I have found that from six to twenty-five volts gives very satisfactory results.

When polishing cupreous alloys, a deposition of loose copper is sometimes noted oh the aluminum cathode during periods of bath idleness. This may be brushed off if desired or the cathode may be removed from the bath during periods of idleness, in any event the deposit has no deleterious effect on the operation. In all cases, the electrolyte has a dual purpose of acting as a polishing medium by a slight dissolution of the metal to be polished and simultaneously acting as an anodizing means for the aluminum or other cathode metal provided.

Various electrical hookups may be resorted to for obtaining different efficiencies of operation and these will be noted by referring to the drawings, wherein, in all drawings, 20 indicates a transformer connected to an A. C. power source. The output of the transformer is lead to electrodes 26 and 28. In all cases, 26 is a filmed electrode such as aluminum and 28 is the work to be polished. The electrodes 26 and 28 are contained in cells 22 which are substantially filled with suitable electrolyte.

The sine wave preceding each cell hookup indicates the portion of the current used in the particular setup as noted by shaded lines.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.