Method of applying zinc-phosphate conversion crystal coating

Abstract

A modified zinc-phosphate conversion coating method, presented as the Absorbed Solution Layer Phosphating (ASLP) coating method. This modified zinc-phosphate conversion crystal coating (ZPCCC) method is carried out in a reactor, containing metal substrate, a quantity of phosphate solution and a quantity of inert, solid filler particles, the quantity of phosphate solution being dependent on the solid filler particle's solution absorption ability. The ASLP process is carried out in an interface layer between the substrate and the solid filler particles, with the reactor being constructed to provide movement of treated parts and filler particles relative to each other, continually exposing surfaces of the substrate to fresh phosphate solution.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method of applying phosphate conversion coating, and specifically zinc-phosphate conversion crystal coating (ZPCCC), on steel, cast iron, various metals and alloys, and on different types of Zinc coatings on metals.[0002]Phosphate conversion coating, and specifically zinc-phosphate conversion crystal coating, is used for improving paint coatings, rubber coatings, organic, and inorganic coatings to metal surfaces. In addition, zinc-phosphate coating is applied to increase corrosion protection for metals, where the coating works as a carrier for the specific oil or wax film that is applied over it.BACKGROUND OF THE INVENTION[0003]An excellent overview of the Zinc Phosphating processes is presented in the article by John Donofrio (Metal Finishing, v. 98, N 6, 2000, pp 57-73). For the reader's convenience, a portion of this article is presented here:[0004]“Zinc phosphate is a crystalline conversion coating that is formed on ...

AI Technical Summary

Benefits of technology

[0048]For the example, described previously, the required filler volume should be 140 L., and the filler particles are present as spheres having a 3 mm diameter. Experiments show that the phosphate solution volume, absorbed on this quantity of filler is approximately 3-5 L. This volume of phosphate liquid contains enough phosphate salts for providing the required thickness of ZPCCC. The ZPCCC reaction is carried out in a small volume of solution, in an interface layer between the treated substrate and the filler particle. The solution reacts rapidly not only on the border between the solution and the substrate, but also in all the interface layer volume. During the period of time when there is movement of treated parts relative to filler particles, fresh phosphate solution is introduced to the interface layer, enabling rapid coating layer creation and uniform coating thickness.

[0049]As a result, a thick, uniform ZPCCC layer may be created without having to add any special activators.

Problems solved by technology

This cleaning affects the adhesion of the coating to the base metal.

Due to free acid consumption in the liquid-metal interface, pH rises and the metal cations can't stay soluble in the solution.

There are a number of serious technical problems associated with the aforementioned coating application processes.

The coating process problems include the following:Applying uniform ZPCCC thickness on all areas of the substrate.Maintaining long-term bath solution reactivity.Controlling toxic material emissions.Removing precipitates from the coating immersion bath.Increasing the process cost, due to the addition of expensive process control components.Maintaining phosphate coating crystal size stability

Maintaining long-term bath solution reactivity is difficult.

Precipitation removal from the bath poses an additional problem.

The process problems, discussed above, are acute when dealing with corrosion resistance phosphate coatings that require 10 g / m2 and more.

Maintaining phosphate coating crystal size stability is an additional phosphate coating process problem.

It also disturbs the equilibrium of the bulk bath solution, resulting in the precipitation of insoluble phosphates in the bath solution, and its contamination.

Thick ZPCCC layer creation requires increasing the temperature and adding special activators, which in turn increase the bath solution contamination rate.

Using too much volume of solution results in increased cost due to loss of unusable chemicals and increased ZPCCC bath solution aging.

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