Electrocoating chrome-plated steel

Abstract

Steel cabinet parts and other steel objects are electrocoated in a cationic resin-containing bath. The steel objects are chromium-coated, free of phosphate and preferably free of chromium oxide. The products are not significantly subject to filiform corrosion, and the process is economically beneficial because throwpower is more easily controlled than in previous processes.

Description

RELATED APPLICATION [0001] This application is a Division of application Ser. No. 10 / 303,529 filed Nov, 25, 2002, claims the full benefit thereof under 35USC120, and also incorporates and claims the full benefit of Provisional Application 60 / 339,005 filed Dec. 7, 2001.TECHNICAL FIELD [0002] This invention relates to appliance housings and other shapes which are stamped or otherwise fabricated or formed from steel strip, and particularly to methods of making electrocoated steel appliance housing preforms and other types of preforms including automotive parts. More broadly, the invention comprises a method of depositing a resin-containing coating on a steel object by electrocoating the steel object having a chrome surface in a bath containing a cationic polymer. BACKGROUND OF THE INVENTION [0003] The manufacture of appliance cabinets and other parts from steel sheet or strip is a capital-intensive, multi-step process. A simplified recitation of the conventional steps would include for...

AI Technical Summary

Benefits of technology

This method significantly reduces the incidence of filiform corrosion, simplifies the manufacturing process, and maintains excellent adhesion characteristics, thereby improving productivity and reducing costs associated with quality control rejections.

Problems solved by technology

The manufacture of appliance cabinets and other parts from steel sheet or strip is a capital-intensive, multi-step process.

It should be remembered that housings and cabinet parts for laundry washers and dryers, for example, are large and cumbersome to move in and out of the various coating, drying, immersing and baking areas.

Quality control rejections of large parts such as appliance cabinets can be quite expensive.

Filiform corrosion too often appears between the metal and the final coating, forming iron oxides in thread-like lines emanating from an anodic nucleus where oxygen is able to penetrate through the paint or other coating.

To guard against filiform corrosion, phosphate treatment, usually in the form of zinc phosphate, is undertaken to place a phosphate coating on it for corrosion control, but is not entirely effective in that the parts are still undesirably subject to a risk of filiform corrosion.

Such a complicated and demanding process, having many steps and numerous conditions to maintain, necessarily provides many opportunities for error and mishap.