RU2283368C1 - Method of manufacture of cylindrical articles provided with wear-resistant coats - Google Patents

Abstract

FIELD: foundry, centrifugal casting in particular; manufacture of multi-layer vessels, pipe lines, bottles, connecting parts and other articles.

SUBSTANCE: proposed method includes placing the thermit mixture in cavities of article, followed by rotation, initiating of exothermic reaction, melting of thermit mixture, cooling of external surface of article and crystallization of molten thermit mixture. Thermit mixture contains additionally fluid material. Cooling of external surface of article is continued till temperature of its internal surface gets equal to melting point of metal of article.

EFFECT: reduced thickness of coat; improved control of heat removal.

Description

The invention relates to foundry, in particular to the technology of centrifugal casting of products with wear-resistant inner coating, and can be used in the manufacture of multilayer vessels, pipelines, cylinders, connecting parts and other products.

A known method of manufacturing pipes with a wear-resistant inner coating (AS USSR No. 1678513, B 22 D 13/02, publ. 09/23/1991), in which the pipe is placed in a chill mold, shot is filled into the gap between the pipe and the chill mold, in the pipe cavity termite is poured (a mixture of aluminum aluminum powder and iron oxide Fe ₂ O ₃ ), the chill is placed in a centrifuge, the chill is rotated, an exothermic reaction is initiated, and the thermite mixture is molten, after crystallization of which a wear-resistant coating is formed.

The amount of termite required for surfacing is determined by the ratio

P _t = (0.9-1.1) P ₃ ,

where R _t is the mass of termite, kg;

P ₃ - the mass of the workpiece, kg

It was established by experiments that the upper limit of the mass of the termite mixture is limited by heat absorption by the pipe and shot, and the lower one is limited by the conditions for the exothermic reaction and the formation of a high-quality coating. To exclude local melting of the tube billet, the amount of heat (thermite mixture) should be reduced, but with a lack of heat (termite mixture), the coating is loose, fragmented, i.e. substandard.

The disadvantage of this method is the use of excess mass of the thermite mixture and, therefore, the need to use fractions for heat removal.

The closest technical solution adopted for the prototype is a method of manufacturing pipes with an internal wear-resistant coating (AS USSR No. 804191, 22 D 13/02, publ. 02/18/1981), in which the pipe is placed in the chill mold, in the gap between metal fraction is poured with a chill and a pipe and compacted additionally, a thermite mixture is poured into the pipe cavity, an exothermic reaction is performed when the chill is rotated, the outer surface of the chill is cooled.

The disadvantage of this method is the complexity of heat removal from the pipe with metal shot and cooling the outer surface of the chill mold. With a possible melting (burn-through) of the pipe, the pipe and shot are fused, which makes it difficult to remove it from the chill mold. Excessive mass of thermite mixture worsens the quality of the pipes and increases the cost of wear-resistant coating.

The technical problem solved by the invention is to reduce the complexity and cost of the method of manufacturing products, improving the regulation of heat dissipation and reducing the thickness of the coating.

The problem is solved due to the fact that in the method of manufacturing cylindrical products with an internal wear-resistant coating, comprising placing a thermite mixture in the cavity of the product, its rotation, initiating an exothermic reaction, melting the thermite mixture, cooling the outer surface of the product and crystallization of the molten thermite mixture, according to the invention in the thermite mixture is additionally injected with a fluid material, and the outer surface of the product is cooled when it reaches the inner surface awn melting temperature metal product.

Reducing the complexity and cost is achieved due to the fact that cylindrical products with a wear-resistant coating are made without chill mold and fractions.

Improving the quality of the coating is achieved by directly removing heat from the surface of the product by cooling it, in particular, by using an air-water mixture, reducing the mass of the thermite mixture, introducing into the thermite mixture a fusible (liquid-flowing) material (ЖМ), for example, magnesium, water glass, etc. .

The melting temperature of glass and its derivatives is two times lower than the temperature of the melt of the thermite mixture, therefore, the increased fluidity of the HMF improves the quality of the coating and allows to reduce the thickness of the wear-resistant coating.

Direct cooling of the outer surface of the product when its inner surface reaches the melting point of the metal allows more intensive heat removal from the surface of the product in a controlled manner, and the crystallization rate of the melt thermite mixture is regulated.

The regulation of heat generated during the exothermic reaction allows to reduce the mass of the thermite mixture.

To maintain heat in the melt, a fluid material is introduced into the thermite mixture, which screens the melt of the thermite mixture and provides a time interval for crystallization of the melt without crystallization cracks, pores, gas and non-metallic inclusions.

To ensure the quality of the coating, two conditions must be met: to obtain a thermite mixture melt and crystallize it (cooling to a certain temperature). To initiate an exothermic reaction, the more reducing agent (aluminum or magnesium) in the thermite mixture, the more intense the exothermic reaction. Therefore, to obtain a melt of the thermite mixture in the shortest possible period of time, it is necessary to increase the percentage of reducing agent in the thermite mixture.

Since the mass of the thermite mixture is reduced with respect to the mass of the product, a low-melting component is introduced, which shields the melt of the thermite mixture. The increase in the crystallization period of the thermite melt makes it possible to equalize the coating thickness along the entire length of the product and ensure its high-quality crystallization.

It is known that the combustion front of a thermite mixture propagates at a certain speed along the length of the product; therefore, it is necessary to obtain a melt of the thermite mixture along the entire length of the product (to ensure uniform coating thickness) and its simultaneous crystallization. Thus, the reduced weight of the thermite mixture allows to prevent the melt of the workpiece, to increase the content of the reducing agent, providing a more intensive passage of the exothermic reaction. Reducing heat dissipation into the cavity of the product, the fusible fluid material ensures uniform crystallization of the melt along the entire length of the product.

The amount of fluid material (MT) is determined from the following conditions. It was established by experiments that the thickness of the coating after crystallization of the thermite melt is approximately 9.2-10 times greater than the ratio of the mass of the thermite mixture to the mass of the workpiece. And for shielding the main thermite melt, a ZhTM melt layer with a thickness of about 0.1-2 mm should be

A method of manufacturing a cylindrical product with a wear-resistant inner coating is as follows.

The thermite mixture of the proposed composition (for example, Al or Mg reducing agent, Fe ₂ O ₃ , water glass) in a certain weight ratio is placed in the cavity of the product, in particular in the cavity of the pipe, the pipe is installed in the device for its rotation around the longitudinal axis. The pipe is rotated until the thermite mixture is evenly distributed on the inner surface of the rotating pipe, an exothermic reaction is excited, after the thermite mixture is melted, the outer surface of the pipe is cooled, for example, with an air-water mixture, when its inner surface reaches the melting temperature. The temperature control of the outer surface of the pipe is carried out by a pyrometer. The intensity of the heat sink is regulated by the pressure and composition of the supplied cooling mixture, therefore, melting (burn-through) of the pipe is excluded.

To conserve heat in the melt, a fusible material, for example, liquid glass, which during the crystallization process prevents heat from the melt to the pipe cavity, is used. After crystallization of the melt, the cooling of the pipe and its rotation are stopped.

Using the proposed method for the manufacture of cylindrical products can reduce the cost and thickness of the coating due to the lower mass of the thermite mixture and increase the fluidity of the melt, improve the properties of the coating by controlling the crystallization of the thermite melt, eliminate the melting of the pipe billet, reduce the complexity and time of surfacing.

Using the proposed method, it is possible to produce pipes with a wear-resistant coating for pipelines transporting abrasive and aggressive media, multilayer vessels, cylinders, and connecting parts.

Claims (1)

A method of manufacturing cylindrical products with an internal wear-resistant coating, comprising placing a thermite mixture in the cavity of the product, rotating it, initiating an exothermic reaction, melting the thermite mixture, cooling the outer surface of the product and crystallizing the molten thermite mixture, characterized in that a fluid material is additionally introduced into the thermite mixture, and the cooling of the outer surface of the product is carried out when its inner surface reaches the melting point of the metal of the product.