US3125475A - Method of producing a bright finish - Google Patents

Description

United States Patent METHOD OF PRODUCING A BRIGHT FINISH ON STAINLESS STEEL Sidney Livingston, Beechhurst, and Leonard Mackles,

New York, N.Y., assignors to Chemclean Products Corporation, College Point, N.Y., a corporation of New York No Drawing. Filed Aug. 24, 1960, Ser. No. 51,498

1 Claim. (Cl. 156-20) This invention relates to a method of producing a bright mirror-like finish on stainless steel by chemical means.

Various methods are now available for polishing stainless steel by the use of chemical preparations in combination with electric current. These methods are commonly designated by the term electropolishing and are fully covered in patent and trade literature. Also known and used are mechanical polishing methods, either alone or in combination with chemical or electrochemical means.

The principal object of the invention is the provision of a purely chemical method of producing a bright mirrorlike finish on stainless steel, said method involving the use of chemical means alone, producing a purely chemical action, and without the use of electric current.

Microscopic inspection of a typical stainless steel surface prior to polishing will show it to be most irregular and consisting of a plurality of high spots or projections interspersed among a plurality of low spots or depressions. Even the high spots may themselves be formed with depressed points or areas and similarly the low spots may themselves be peppered with high spots or projections. It is the function of the method herein described and claimed and of the chemical means involved therein to eliminate or at least soften these irregularities by selectively dissolving and removing the high spots, while at the same time inhibiting or preventing a corresponding attack upon the low spots, thereby leveling and smoothing the metal surface undergoing treatment and producing a bright mirror-like finish.

More specifically, the polishing method herein described and claimed involves the use of a chemical composition consisting of dilute phosphoric, hydrochloric and nitric acid combined with an inhibiting agent or restrainer and an activator or catalyst. When stainless steel is exposed to a heated bath consisting of such chemical composition, the result is a mirror-like finish which is at least as bright as that produced by electropolishing. The term stainless steel as used herein is intended to refer to austenitic stainless steel as described, for example, in the Mechanical Engineers Handbook, fourth edition, edited by Lionel S. Marks, page 587.

It has been found that a chemical composition of the following formula and within the following range of proportions will best perform the function and produce the best results herein described:

Percent by weight Phosphoric acid, approximately 15-50 Hydrochloric acid, approximately 2-25 Nitric acid, approximately 1-17 Water, approximately 30-80 Inhibitor, approximately .05-6 Activator, approximately .05-6

Total 100 3,125,475 Patented Mar. 17, 1964 'ice The phosphoric, hydrochloric and nitric acids in dilute form will dissolve the high spots or projections on the stainless steel surface. The inhibitor will prevent or at least inhibit corresponding reaction with the low spots or depressions in the metal surface. In order to activate the above combination and hasten the results, an activator or catalyst is added as above indicated.

More specifically, an inhibitor of the chemical classification known as acetylene alcohols will function effectively in the combination above described. An activator of the chemical configuration of formate selected from the aldehyde and acid groups functions effectively as a catalyst in the above combination.

To be even more specific, a suitable inhibiting agent may be selected from the class consisting of monoand poly-hydric acetylene alcohols. Effective inhibiting agents have been found to be 2-butyne-1,4-diol and 2-propynl-ol. Suitable activator or catalysts may be selected from the organic aldehydes and acids of the formic group. Specifically, activators which effectively serve as catalysts in the combination herein described and claimed are formaldehyde and formic acid.

A specific formula found to be highly suitable for purposes of the present invention is the following:

Water, approximately 65 Inhibiting agent, approximately .05 Activator catalyst, approximately .05

In the foregoing formula the preferred inhibiting agents are selected from the class consisting of the monoand poly-hydric acetylene alcohols and particularly 2-butyne- 1,4-diol and 2-propyn-l-ol. Also in said formula the preferred activator catalyst is selected from the organic aldehydes and acids of the formic group and especially formaldehyde and formic acid.

When the combination of materials above described is put in the form of a bath and heated to a temperature of approximately -212 degrees Fahrenheit, it may be used to produce a bright mirror-like surface on stainless steel. This may be accomplished by immersing the stainless steel in said bath for a period of approximately one to thirty minutes. When removed from the bath following such immersion, the stainless steel exhibits the desired finish. Optimum results are attained, however, Within a temperature range of approximately -200 degrees Fahrenheit and with an immersion period of approximate- 1y one to five minutes.

The foregoing represents preferred embodiments of the present invention and it will be understood that variations and modifications may be incorporated therein within the broad principles of the invention and the scope of the claim.

We claim:

A method of treating austenitic stainless steel to produce a bright mirror-like surface thereon, which comprises immersing a stainless steel surface in a bath consisting of approximately 25 parts by weight of phosphoric acid, approximately 7.5 parts by weight of hydrochloric acid, approximately 2.5 parts by weight of nitric acid, approximately 65 parts by weight of water, approximately A 3 4 .05-6 parts by Weight of an inhibiting agent consisting of References Cited in the file of this patent 2-butyne-L4-diol combined With 2-propyn-1-0l, and ap- UNITED STATES PATENTS proximately .05-6 parts by weight of an activator catalyst selected from the formates, said bath being heated to 2493327 Y 32 and maintained at an elevated temperature of approxi- 5 2662814 Wlhart 1 mately 190200 degrees Fahrenheit, and said stainless 2993862 Monroe et a y 19 1 steel surface being immersed in said heated bath for 9. OTHER REFERENCES Period of approxlmately one to five mmutes' Forster et a1.: Acetylenic Corrosion Inhibitors, Ind. &

Eng. Chem., vol. 51, No. 7, July 1959, pp. 825828.