DE2552294A1 - PROCESS FOR PROTECTING TANKS OR CONTAINERS FOR MELTING METAL AGAINST CORROSION BY APPLYING CERAMIC COATINGS - Google Patents

Description

DR. BEKG DIPL.-ING. STAPF DIPL.-ING. SCHWABE DR. DR. SANDMAIR 9 ς ς 9 9 q Λ

PATENTANWÄLTE 8 MÜNCHEN 86, POSTFACH 860245

Dr. Bas Dipt-Ing. Stapfund Partner, 8 Munich 86, P.O. Box 860245

Your reference Our reference 26 582 8 MÜNCHEN SO η Α

Yourref. Ourref- Mauerktrcheistrasse 45 L. '-

Lawyer file-IIr .: 26 582

Patronato de Investigaeion Cientifiea y Tecnica

"Juan de la Cierva" del Consejo Superior de Investigaciones Cientlficas

150 Madrid / Spain

"Procedure for protecting tanks or containers

for metal melts against corrosion by applying ceramic coatings "

The present invention relates to a method for protecting tanks or containers for molten metal against corrosion by applying ceramic coatings.

609824/0910

X / R - 2 -

(089) 98 8272 Telegrams: BERGSTAPFPATENT Munich Banks: Bayerische Vereinsbank Munich 453100

987043 TELEX: 0524560 BERG d - Hypo-Banfc Manchen 3892623

983310 Postscheck Munich 65343-808

This process greatly improves the static and operational properties of tanks. The invention is applicable in all cases where an effective protection of the inner surfaces of hot-dip and galvanizing tanks and common containers for molten metal against corrosion by metals kept in a molten state, such as zinc, Aluminum, etc., is required.

The advantages result from the fact that the new, material properties obtained in this way lead to a greatly improved service life of the appropriately protected containers. This enables a reduction in the import of special hot-melt galvanizing tanks (Si-free mild steel) and Molten metal containers, and it may happen that such imports are stopped completely can. In the same way, the formation of slag and smear is avoided by the coatings, and it becomes one considerable savings in terms of consumption of molten metal (zinc, aluminum, etc.) as well as of maintenance the required temperature for the manufacturing process (galvanizing, injection, etc.) required thermal Energy achieved.

The materials or raw materials used in the process are of domestic origin so no imports are required. They are in general ^ / -

»8.2 4 / 0910- '■?'

ORIGINAL INSPECTED

Powders made from metals (e.g. Ni-Cr alloy) are produced, highly refractory inorganic oxides (for example ZrOp, AlpO,) or ceramic compounds (for example SiO2, Zr) that are suitable for good adhesion to ensure the surface of the container, while at the same time the aggressive attack of the molten metal, with which the surface is in contact with, and so the corrosion of the tank is eliminated.

The method of the present invention for protecting tanks or containers consists of the following process steps:

(1) Physical production of the materials used for the coatings.

(2) Preparation of the surface on which the plating should be applied.

(3) coating process, the materials in molten State using a plasma or gas spray gun.

(4) Appropriate treatment to ensure adhesion the over.pans under the appropriate working conditions.

(5) Leveling the coating and, if necessary, performing a final treatment, depending on the requirements of the application.

6U9824 / 0910

The first stage of the process consists of grinding and pelletizing and wet sieving the materials used for the coating to obtain powders having particles of rounded shape and a mesh size within closely spaced limits so that they are smooth in the spray nozzles of the spray guns used flow as described later. The aforementioned mesh size can vary by about 30 to 80 y, depending on the heat capacity and the density of the materials used. For example, a mesh size of 50 ί 5 μ for AIpO- suitable, whereas ZrO “with a higher Heat capacity and a greater density in a mesh size of 40 ± 5 μ is more suitable. These raw materials can also be in the form of rods ground to a suitable diameter for application by a suitable Plasma or gas torch.

The second stage of the process involves preparing the surface to be coated. This surface must not be polished and must be free from contamination, such as Be metal oxides or fat, so that the molten coating particles when they are as described later will be thrown onto the surface, find suitable key points and thus a firmly adhering protective layer form. If, contrary to these requirements, a polished or dirty metal surface is present, must

this using a ceramic blown sand from suitable hardness, such as brown corundum or electrically fused mullite, with a mesh size of not over 1.5 ram in diameter, be sandblasted.

The third process stage comprises the application of the coatings. For this purpose the coating particles are applied to the nozzle of a plasma gun by means of a carrier gas (usually Argon), or brought to the spray nozzle of a gas torch (e.g. oxygen-acetylene) by means of suction. Coating rods can also be used in both cases, as in the first part of the description was explained. When the particles are blown by the electric arc of the plasma spray gun (15,000 ° C) or pass the gas torch flame (10,000 ° C), they melt and are ejected in the form of liquid droplets, which are spread flat when impacted on the surface to be coated and between the rough parts of the Surface remain in key position and thus form an increasing protective layer or an increasing coating, which adheres firmly to the surface.

The fourth procedural stage comprises the relevant procedures, which ensure the adhesion of the coatings to the mechanical forces caused by the stresses

25522S4

result from temperature-related expansion and contraction, according to the nature of the requirements and conditions of the industrial Working method. For this purpose, the surface is first covered with a Layer of an alloy or an oxide or a ceramic compound coated, capable of chemical Binding with any component part of the corresponding To form the surface and the coating, by way of solid-state reactions which suitably the Increase temperature. In this way the surface / plating bond, which is in principle of a physical nature, converted into a chemical bond, xtfor by a two-way reaction or diffusion layer is formed, and, as the case may be, ensures that the ceramic coating with the protected Surface remains connected. This first coat can in turn be covered with another coating capable of better resistance to the corrosive effects to ensure the molten metal. For example, if the inside of a hot dip galvanizing tank with a layer of Ni-Cr 80-20 followed by another Layer of clay that is coated and then the tank for that Hot-dip galvanizing is used, the Ni-Cr and clay layer lift off and the molten zinc will then be able to attack the steel surface of the tank. If on the other hand the Ni-Cr coating of a suitable heat treatment,

- 7 -BU9824 / 091G

which ensures an initial alloying between the Ni-Cr and the ■ steel, prior to the application of the alumina layer is subjected, an intermediate diffusion layer is formed, which at the same time has a gradient of the expansion coefficient (Steel / diffusion layer / Ni-Cr alloy / alumina) that protects against temperature changes and also ensures permanent bonding of the coating to the surface of the tank. That way you can too alternating layers can be applied according to the requirements that may exist.

The fifth and final stage of the process involves grinding and polishing the coating, in those cases where it is Location or purpose may require this, as is the case, for example, in the case of pressure pistons for injection molding of molten materials Metals is given. The grinding and finishing can be completed using normal methods if they only take into account the fact that the abrasives to be used in terms of hardness and technical properties of the coating to be processed must be suitable.

• - 8th -

6UU82W0910

Claims (4)

Claims 1. Method of protecting tanks or containers for molten metal against corrosion using ceramic Coatings, characterized in that the materials forming the coating are in the form of a powder with particles of rounded shape and suitable uniform size (between 30 and 80 μ) according to the heat capacity and density, such that they flow and melt as that for the nozzles to be protected the spray gun is required, the ground sticks of suitable diameter also for the Spin can be produced by means of suitable spray torches. 2. The method according to claim 1, characterized in that the surface to be coated by Sandblasting using a ceramic product of suitable hardness as an abrasive material such as brown corundum or electrically fused mullite of a mesh size below 1.5 µm in the case that the surface to be coated has insufficient roughness or is oxidized or dirty, is prepared in a suitable manner. 6U9824 / 0910 3. The method according to any one of claims 1 and 2, characterized in that the particles or rods of the material forming the coating in molten form (liquid droplets) by means of a plasma or gas torch onto the previously prepared metal surface to be coated are thrown and remain bound to the rough surface and a protective or coating layer through Form growth that adheres firmly to the correspondingly coated surface and this in an effective manner against the Protects against corrosion from molten metal. 4. The method according to any one of claims 1 to 3, characterized in that in the case where it is necessary to ensure the adhesion of the coating layer to mechanical stresses, for example as a result of expansion and contraction as a result of temperature changes, a first intermediate layer an alloy or an oxide or a ceramic compound which is able to chemically combine with a partial component of the coated surface to be protected by reaction in the solid state or by diffusion, suitably with an increase in temperature, the coating by numerous successive Layers can be formed with a view to ensuring a permanent bond and thus an increased level of corrosion protection - 10 6Uy824 / 0910 is obtained and one in a later stage the coating grinds and polishes in the normal manner as may be required for a given application. 600824/0910