Method of applying an intermetallic anticorrosion coating by thermal diffusion galvanization

Abstract

Proposed is a method of applying a zinc coating to metallic articles by thermal diffusion galvanization. Articles to be treated and a two-component zinc mixture are loaded into a hermetically sealed container, the cavity of the container is filled with an inert gas, and heating is carried out. The first component of the mixture, in the form of a powder of acicular zinc having a size of 3-5 μm, is loaded directly into the container, and the second component, in the form of a powder of spherical zinc having a size of 20-25 μm, is loaded into a capsule having walls which disintegrate at a temperature of 400±20° C., which is placed in the container at the same time as the articles to be treated. A flux is loaded into the container, and an inert process gas and an activating agent for intensifying the adhesion process are supplied.

Claims

1. A method for applying a zinc coating to metallic articles by thermal diffusion galvanization, comprising: loading articles to be treated into a hermetically sealed container; loading a saturating zinc-containing mixture into the container; filling a cavity of the container with an inert gas; and heating; wherein a two-component zinc mixture is loaded as the zinc-containing mixture; wherein the two-component zinc mixture has a first component as a powder of acicular zinc having a size of 3-5 μm and loaded directly into the container, and a second component as a powder of spherical zinc having a size of 20-25 μm and loaded into a capsule having walls which disintegrate at a temperature of 400±20° C., the capsule being placed in the container concurrently with the articles to be treated; wherein the first component is provided in an amount of 80% of a theoretical value of a weight required to cover a surface of the articles to be treated with an inner layer and 60% of a theoretical value of a weight required to cover the surface of the articles to be treated with an outer layer; wherein a flux is loaded into the container, and an inert process gas and an activating agent for intensifying an adhesion process are supplied; wherein the galvanization process is performed in two steps: first, heating to a temperature of 350-380° C. to form the inner layer of zinc due to an adhesion of the acicular zinc to the surface of the article to be treated, and then after heating a material of the capsule to the disintegration temperature of 400±20° C. and releasing the powder of spherical zinc to form the outer layer of the coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) A method for applying a zinc coating to metallic articles by thermal diffusion galvanization is performed as follows: The articles to be treated are loaded into a hermitically sealed container on supporting surfaces which prevent their direct contact and provide a minimum distance between the articles within the range of 3-5 urn, while ensuring the possibility of their movement relative to the supporting surfaces by no more than 5-10 mm; At the same time, a two-component mixture is loaded into the same container, which has a first component as a powder of zinc having a purity of 0.97-0.99%, an acicular shape and a crystal size of 3-7 μm (preferably 3-5 μm) and a second component as a powder of zinc having a spherical shape with a size of 20-25 μm. The second component is loaded into a capsule having walls which disintegrate at a temperature of 400±20° C. In this case, the amount of the first component is 80% of the theoretical value of a weight required to cover the surface of the articles to be treated and 60% of the theoretical value of the weight required to cover the surface of the articles to be treated with an outer layer; Then, a flux is loaded into the container, and an inert process gas and an activating agent for intensifying an adhesion process are supplied.

(2) The galvanization process is performed in two steps: first, heating to a temperature of 350-380° C. to form an inner layer of zinc due to the adhesion of the acicular zinc to the surface of the article to be treated, and then after heating the capsule material to the disintegration temperature of 400±20° C. and releasing the spherical zinc to form the outer layer of the coating.

(3) Thus, the claimed invention is characterized in that the two-component mixture is used, in which only one of the components is placed into the capsule, and in that spherical zinc particles constituting the second component of the mixture are applied to the inner layer formed by acicular zinc particles.