METHOD OF APPLYING AN INTERMETALLIC ANTI-CORROSION COATING BY THERMAL DIFFUSION GALVANIZATION

Abstract

A method is proposed for applying a zinc coating to metal articles by thermal diffusion galvanizing. The articles to be treated and a two-component zinc mixture are loaded into a hermetically sealed container. The container cavity is filled with an inert gas, and heating is carried out. The first component of the mixture, in the form of acicular zinc powder with a size of 3–5 µm, is loaded directly into the container. The second component, in the form of spherical zinc powder with a size of 20–25 µm, is loaded into a capsule with walls that 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 are supplied to enhance the adhesion process.The galvanizing process is carried out in two steps, first under heating to a temperature of 350-380°?, allowing the formation of an inner layer of zinc by the adhesion of acicular zinc to the surface of the article to be treated, and then after heating to the disintegration temperature of the capsule material 400±20°? and the release of the spherical zinc powder, which allows the formation of an outer coating layer.

Description

METHOD OF APPLYING AN INTERMETALLIC ANTI-CORROSION COATING BY THERMAL DIFFUSION GALVANIZATION TECHNICAL FIELD OF THE INVENTION The invention relates to the chemical-thermal treatment of metal articles, particularly diffusion galvanizing, and can be used in machine building, instrument making, aviation and other industries. nczznn / zznz / E / viAi BACKGROUND OF THE INVENTION Currently, there are several methods for diffusion galvanizing. UK patent 2386723 describes a method for diffusion galvanizing, which includes preparing the surface of an article, loading articles into a working chamber together with powder components containing zinc powder, evacuating the working chamber and pumping in an inert gas, heating the working chamber to a working temperature of 350-450°C, which ensures the formation of a film of a given thickness. UK patent 2180018 describes a method for manufacturing a powder mixture for thermal diffusion galvanizing. The powder mixture consists of a zinc blend containing acicular and spherical fractions with a size smaller than 63 pm. Thermal diffusion galvanizing is carried out in the presence of zinc chloride (in the claimed invention, a flux), an inert process gas, and an activating agent. In this case, the process temperature is 300–450°C. US documents 20180016482 Al and US 20090266454 Al also describe a galvanizing process in which a destructible capsule is used, as in the claimed method. UK patent 2500833 describes an invention relating to the chemical-thermal treatment of metal articles, in particular diffusion galvanizing. The articles to be treated are arranged in a container in a regular fashion on fixtures with support surfaces, which secure them and prevent direct contact with each other and relative movement between them when the container is moved, such that the minimum distance between the treated surfaces of the articles is 3-5 mm. During the galvanizing process, the articles to be treated may move relative to the support surfaces of the fixtures in the container by no more than 5-10 mm. A saturated mixture contains zinc crystals with a purity of 0.97-0.99% and an acicular shape.The saturation mixture has a particle size distribution within the range of 3-7 pm, and its weight is 1-4% of the weight of the items to be treated or 130-140% of the weight of the coating required on the surface of the items to be treated. nczznn / zznz / E / viAi SUMMARY OF THE INVENTION The technical result of the invention is to increase the useful life of an article by eliminating its corrosion and to increase the productivity of a furnace in which diffusion galvanizing is carried out, as well as to reduce the consumption of zinc per unit of surface area of ​​the article to be treated. The claimed technical result is achieved by implementing a method for applying a zinc coating to metal articles by thermal diffusion galvanizing. The method comprises loading the articles to be treated into a hermetically sealed container, loading a saturated zinc-containing mixture into the container, filling a cavity of the container with an inert gas, and heating. According to the patented solution, a two-component zinc mixture is loaded into the container. The first component of the mixture is in the form of acicular zinc powder with a size of 3-5 µm and is loaded directly into the container, while the second component of the mixture is in the form of spherical zinc powder with a size of 20-25 µm and is loaded into a capsule with walls that disintegrate at a temperature of 400 ± 20°C. The capsule is placed in the container at the same time as the articles to be treated.The quantity of the first component is 80% of the theoretical weight required to cover the surface of the items to be treated with an inner layer and 60% of the theoretical weight required to cover the surface of the items to be treated with an outer layer. Afterward, a flux is added to the container, and an inert process gas and an activating agent are supplied to enhance the adhesion process. The galvanizing process is carried out in two steps: first, heating to a temperature of 350–380°C to form the inner zinc layer due to the adhesion of acicular zinc particles to the surface of the item to be treated; then, after further heating, the capsule material is heated to the disintegration temperature of 400 ± 20°C, releasing spherical zinc powder to form the outer coating layer. nczznn / zznz / E / viAi nczznn / zznz / E / YiAi DETAILED DESCRIPTION OF THE INVENTION One method for applying a zinc coating to metal articles by thermal diffusion galvanizing is carried out as follows: The items to be treated are loaded into a hermetically sealed container on support surfaces that prevent direct contact and provide a minimum distance between items within the range of 3-5 pm, ensuring the possibility of their movement in relation to the support surfaces by no more than 5-10 mm; Simultaneously, a two-component mixture is loaded into the same container. The first component is zinc powder with a purity of 0.97–0.99%, an acicular shape, and a crystal size of 3–7 µm (preferably 35 µm). The second component is zinc powder with a spherical shape and a crystal size of 20–25 µm. The second component is loaded into a capsule with walls that disintegrate at a temperature of 400 ± 20°C. In this case, the quantity of the first component is 80% of the theoretical weight required to cover the surface of the items to be treated, and 60% of the theoretical weight required to cover the surface of the items to be treated with an outer layer. - Next, a flux is loaded into the container and an inert process gas and an activating agent are supplied to intensify an adhesion process. The galvanizing process is carried out in two steps: first, it is heated to a temperature of 350-380°C to form an inner layer of zinc due to the adhesion of 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. Thus, the claimed invention is characterized in that it uses a mixture of two components, in which only one of the components is introduced into the capsule, and in that spherical zinc particles, which constitute the second component of the mixture, are applied to the inner layer formed by acicular zinc particles.

Claims

1. A method for applying a zinc coating to metal articles by thermal diffusion galvanizing, comprising: load items to be treated into a hermetically sealed container; load a saturated mixture containing zinc into the container; fill a cavity of the container with an inert gas; and heating; in which a two-component zinc mixture is loaded as a zinc-containing mixture; where the two-component zinc mixture has a first component as acicular zinc powder having a size of 3-5 pm and is loaded directly into the container, and a second component as spherical zinc powder having a size of 20-25 pm and loaded into a capsule having walls that disintegrate at a temperature of 400 + 20°C, the capsule being placed in the container at the same time as the items to be treated; wherein the first component is provided in an amount of 80% of the theoretical weight value required to cover a surface of the articles to be treated with an inner layer and 60% of the theoretical weight value required to cover the surface of the articles to be treated with an outer layer; in which a flux is loaded into the vessel and an inert process gas and an activating agent are supplied to intensify an adhesion process; where the galvanizing process is carried out in two steps: first, heating to a temperature of 350-380°C to form the inner layer of zinc due to the adhesion of acicular zinc to the surface of the article to be treated, and then heating a capsule material to the disintegration temperature of 400±20°C and releasing the spherical zinc powder to form the outer layer of the coating.