US3130087A - Composition and method for coating stainless steel articles - Google Patents

Description

United States Patent 3,130,087 COMPOSITION AND METHOD FOR COATING STAINLESS STEEL ARTICLES Ira 3'. Duncan, Atlanta, Ga., assignmto Detrex Chemical Industries, Inc, Detroit, Mich, a corporation of Michigan No Drawing. Filed May 1, 1961, Ser. No. 155,223 (Filed under Rule 47(1)) and 35 U.S.C. 118) 8 Claims. (Cl. 1486.24)

This invention relates to an improved composition and method for forming tightly adherent coatings on metal articles which are to be subjected to plastic deformation. More particularly, it relates to the formation, on ferrousbased stainless metal articles of tightly adherent oxalate coatings on the surfaces thereof.

It is known to coat ferrous-based stainless metals such as stainless steel and the like with an adherent surface coating of an oxalate compound prior to plastically deforming such articles by such methods as drawing and stamping. However, all of the effective known prior art treatments require either the utilization of a complex pre-treatment of the stainless surfaces, or the use in the treating bath of expensive and/ or dangerous compounds. For example, one prior art process involves a pro-treatment comprising an acid pickle and alkaline rinse. This incidentally requires the use of additional water rinses, and in the event that the alkaline rinse contains the conventional alkali metalcyanide, a further water rinse is required to obviate the liberation of hydrogen cyanide from the hot oxalate treating bath. Another prior art process discloses the use of a combination of a silico-fluoride compound and an organic nitro compound as activators or accelerators in an oxalate treating bath.

It is therefore an object of this invention to provide an oxalate treating composition and method for use in the coating of stainless surfaces that is greatly simplified over the above prior art processes.

It is another object of this invention to provide an oxalate treating composition and method which effectively coats stainless surfaces without the necessity of pro-treatment modification of the surfaces to be treated.

It is another object of this invention to provide an oxalate treating composition and method which does not require the use of expensive or dangerous compounds.

Other objects and advantages of the composition and method of this invention will readily become apparent from a reading of the following description and claims.

It has surprisingly been discovered that clean ferrousbased stainless metal surfaces may be effectively coated with an adherent oxalate coating by contacting said surfaces with a single aqueous solution consisting essentially of oxalic acid, ferric ions, bisulfate ions, silicofluoride ions and thiosulfate ions. While the exact mechanism of the present invention is not known, it is believed that the use of the silicofluon'de ion together with the ferric ion results in an effective balance between the pickling, or coating-dissolving, action of the bisulfate-silicofluoride complex, and the inhibition of this pickling action by a common ion effect due to the presence of the ferric ion in a large proportion. The resulting balance gives an accelerated coating action without the metal surface passivation effect usually associated therewith, particularly in the presence of the stronger oxidizing agents. Utilization of the composition and method of this invention results in the rapid formation on stainless metal surfaces of uniform, densely crystalline adherent coatings having coating weights in the range of from about 700-3000 mgm. per square foot.

Examples of composition suitable for use in accordance with this invention preferably have an analysis falling Patented Apr. 21, 1964 within the following ranges (parts being expressed as percent by weight of a dry composition) Percent Oxalic acid 50-89 Ferric sulfate 6-18 Sodium bisulfate 2-14 Sodium silicofiuoride 2-14 Sodium thiosulfate 1.0-4.0

Example 1 A processing tank is cleaned, filled with a quantity of water and heated to from -130 F. For each one hundred gallons of Water in the tank there is added 28.6 pounds of oxalic acid, 5 pounds of ferric sulfate, 3.2 pounds of sodium bisulfate, and 3.2 pounds of sodium silicofluoride. The contents of the tank are stirred to effect complete solution, and the temperature of the bath then raised to F. Just prior to the processing of the stainless articles to be treated, one pound of sodium thiosulfate for each 100 gallons of solution is added to the the bath. The stainless articles are then immersed in the bath for about 10 to 15 minutes while ensuring complete contact of the treating solution with all parts of the work. When the articles have received the desired coating density, they are removed from the bath, drained, rinsed in water, dried, and lubricated.

Ferrous-based stainless articles treated in this manner are ready to be plastically deformed in the conventional manner.

During the treatment in accordance with the process of this invention the treating solution should be kept at a titration of 40-45 ml. of 0.1 N NaOH to a phenolphthalein end point per 5 ml. of solution, and at an iodine equivalent of 1.0-2.0 ml. of 0.1 N iodine solution per 25 ml. of solution. The acidity is adjusted by the addition of proper quantities of the oxalic acid, ferric sulfate, sodium bisulfate and sodium silicofluoride mixture. The iodine equivalent is adjusted by addition of sodium thiosulfate.

The following examples are illustrative of further specific dry compositions which are eifective in accordance with this invention, parts being expressed as percent by weight:

Example 2 Percent Oxalic acid 75.8 Ferric sulfate 12.2 Sodium bisulfate 7.8 Sodium silicofluoride 3.8 Sodium thiosulfate 2.4

Example 3 Oxalic acid 50 Ferric sulfate 18 Sodium bisulfate 14 Sodium silicofluoride 14 Sodium thiosulfate 4 Example 4 Oxalic acid 60 Ferric sulfate 15 Sodium bisulfate 11 Sodium silicofluoride 11 Sodium thiosulfate 3 Example Oxalic acid 80 Ferric sulfate Y Sodium bisulfate 4 Sodium silicofluoride 4 Sodium thiosulfate 2 Example .6

Oxalic 'acid 89 Ferric sulfate 6 Sodium bisulfate 2 Sodium silicofluoride Q 2 Sodium thiosulfate 1 Having thus described my invention, I claim:

1. A process for treating the surface of stainless steel based metals which comprises the step of contacting the clean metal surface with an aqueous bath containing from about 30 to about 50 pounds per each one hundred gallons of water of a dry composition consisting essentially of:

Percent by weight Oxalic acid 50.0 to 89.0 Ferric sulfate 6.0 to 18.0 Sodium bisulfate 2.0 to 14.0 Sodium silicofiuoride 2.0 to 14.0 Sodium thiosulfate 1.0 to 4.0

2. The process of claim 1 wherein said aqueous bath is maintained at a titration of 4045 ml. of 0.1 N NaOH to a phenolphthalein end point per 5 ml. of solution, and at an iodine equivalent of 1.0-2.0 ml. of 0.1 N iodine solution per 25 ml. of solution.

3. The process of claim 2 wherein said aqueous bath is maintained at a temperature in the range of from room temperature to about 155 F.

4. The process of claim 2 wherein said aqueous bath is maintained-at a temperature in the range of from about 145 F. to 155 F.

5. The-process of claim 1 wherein said aqueous bath is maintained at a temperature in the range of from room temperature to about 155 F.

Percent by weight Oxalic acid 50.0 to 89.0 Ferric sulfate 6.0 to 18.0 Sodium bisulfate 2.0 to 14.0 Sodium silicofluoride 2.0 to 14.0

(2) adding to said solution just prior to said treatment an amount of sodium thiosulfate in the range of from about one to about four pounds per each one hundred gallons of water in the solution, and

I (3) then immersing a stainless steel based metal article in said solution resulting from step (2), Whereby there is formed on the surface of said article a uniform, dense, adherent, crystalline oxalate coating. 8. A composition for producing a uniform, dense, adherent, crystalline oxalate coating on the surface of stainless steel based metal articles having a composition consisting essentially of:

Water to make 100.0.

References Cited in the file of this patent UNITED STATES PATENTS 2,550,660 Amundsen et al May 1, 1951 2,809,138 Wagner et al. Oct. 8, 1957 2,976,193 Pimbley Mar. 21, 1961

Claims (1)

1. A PROCESS FOR TREATING THE SURFACE OF STAINLESS STEEL BASED METALS WHICH COMPRISES THE STEP OF CONTACTING THE CLEAN METAL SURFACE WITH AN AQUEOUS BATH CONTAINING FROM ABOUT 30 TO ABOUT 50 POUNDS PER EACH ONE HUNDRED GALLONS OF WATER OF A DRY COMPOSITION CONSISTING ESSENTIALLY OF: