Process for surface treatment of metals

Abstract

An environmentally acceptable and comparatively safe acid cleaning solution containing sulfuric acid, water and amine containing inhibitors that adequately remove oxidation or contaminants from surfaces without excessively damaging equipment. The sulfuric acid is effective in removing impurities and contaminants, while the amine moieties or amine salts reduce the otherwise damaging effect of sulfuric acid on equipment and on human skin and tissue.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation-in-part of and claims priority to U.S. Application Ser. No. 12 / 335,072, filed Dec. 15, 2008 and entitled PROCESS FOR SURFACE TREATMENT OF METALS, which is a continuation-in-part and claims priority to U.S. application Ser. No. 11 / 679,997, filed Feb. 28, 2007 and is entitled PROCESS FOR SURFACE TREATMENT OF METALS, both documents are hereby incorporated by reference herein to the extent permitted by law.FIELD OF INVENTION[0002]The present invention relates generally to a process for the use of a modified sulfuric acid agent for the purpose of cleaning, deoxidizing, descaling, polishing, and / or brightening surfaces. These modified sulfuric acid agents prevent the attack on metal equipment used in their application and reduce or eliminate the release of hazardous or harmful metals to industrial waste water streams and prevent detrimental environmental release of harmful metals such as chromium, nickel and m...

AI Technical Summary

Benefits of technology

[0017]The present invention is a unique acid solution that contains components that limit or eliminate the removal of undesirable metals from the equipment used to contain, transfer, spray and pump these aggressive acid cleaners. The solution disclosed herein and method for employing the same prevent the attack on metal equipment while reducing or eliminate the release of hazardous or harmful metals as industrial waste. In addition, the solution disclosed herein and method for employing the same are generally not aggressive to human skin.

[0022]The second approach, mild acids are used in cleaning applications. Acids such as phosphoric or organic acids such as citric acid have replaced the more aggressive sulfuric acid. Unfortunately, use of these relatively mild acids requires increased production times, elevation of the acid solution temperatures, or increased acid concentrations or some combination of increased temperature and / or processing time. All of these requirements significantly increase the costs of cleaning an article or manufacturing operation.

[0023]There are definite environmental drawbacks for employing these milder acids for industrial cleaning. Phosphoric acid has come under increased EPA regulation and is being regulated since release into the environment can result in increased algae growth in lakes and streams. Citric and other organic acids are known to chelate or bond metal ions and make it costly and difficult to remove chelated metal ions such as chromium, nickel, manganese from industrial waste water. To prevent environmental release of these detrimental metal ions, it would be of advantage to find a method of using sulfuric acid or other acids for industrial acid cleaning purposes.

[0025]To overcome these difficulties with the use of mild acids for cleaning and also to avoid the use of hazardous acids such as hydrochloric and nitric acids, in the present invention a modified sulfuric acid is used as one component in an acid cleaning solution. To further enhance the modified sulfuric acid various additional compounds may be added as accelerators, inhibitors, and / or buffers and / or surfactants, to mitigate, control, eliminate acid attack (etch) on metals and / or enhance the removal of soils, scales, metal tarnish, or oxidation present on the metal surface, or the improvement of a final finish on the metal such as with anodizing processes. By the use of a modified sulfuric acid, the attack on the tanks, transfer pipes, spray nozzles and pumping equipment is greatly reduced or eliminated. By mitigating the attack on equipment, the release of undesirable and / or toxic metals to wastewater, city sewers, or the environment is reduced or eliminated. The modified sulfuric acid is formulated by combining sulfuric acid with water and with amines or amine salts. Although many amines will meet the requirements of this invention, a preferred amine or amine salt is an ammonia and / or sulfate salt of ammonia. Ammonia in many cases is preferred due to its cost and / or performance profile when compared to other additions to sulfuric acid to prevent attack on equipment used for its containment, application and transfer during the cleaning process.

Problems solved by technology

The removal of these impurities are of particular importance for metal surfaces since the surface may be subsequently conversion coated, anodized, and / or painted and without complete removal of impurities, the function and appearance of the metal surface would be negatively effected.

Although sulfuric acid solutions provide an excellent solvent media for the cleaning applications described above, they have the disadvantage of being too aggressive to metal surfaces and even when stainless steel equipment is employed to contain, transport and spray these aggressive solutions, some attack on the metal surface results that, over time, damages the equipment and can result in release of hazardous metal ions into the industrial waste water and / or into the environment.

Sulfuric acid is also known to be aggressive to human skin, particularly at higher concentrations, and this property makes it an extremely dangerous compound to transport, store and handle from a safety standpoint.

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