Use of plasma spraying in the production of slide gate plates

Abstract

The protection of the working surfaces of refractory parts by the application of coatings is an effective method of increasing the life of refractories under the action of aggressive reactants and makes it possible to use less expensive and more available materials.Especially promising is the use of protective coatings for slide gate plates, in which primarily only the contact surfaces and the steel teeming channel to a comparatively shallow depth are subjected to wear.In recent years plasma spraying has obtained wide use. Its advantages include the possibility of spraying practically any materials on various bases including large ones, the comparatively low heating of the sprayed part, mechanization and automation of the process, simplicity of servicing of the equipment, and its high productivity [i]. The formation of the plasma coating as the result of rapid hardening of the individual molten particles deformed in impact on the base determines the stratification and controllable porosity and from this the high thermal insulation properties, elasticity, and thermal shock resistance of the coatings [2]. Therefore the interest in plasma coatings based on highly refractory oxides from the point of view of their use as protective layers on refractories is understandable.In contrast to the large number of publications devoted both to the techniques and technology of plasma spraying in general and to the properties of plasma coatings on parts of metals and graphite, there is only individual unsystematized information on the applicatian of plasma coatings on refractories (magnesite--chromite roof parts, chamotte parts for glassforming machines, slide gate plates, etc.) noting the promise of this direction [3][4][5].This determined the necessity of conducting a cycle of comprehensive investigations of plasma treatment of refractories, which were conducted by the State Institute for the Design of Nickel Industry Plants and the All-Union Institute for Refractories.This article presents theresults of investigations of the production of slide gate plates with the use of plasma spraying.The determination of the possibility in principle of application of protective coatings on the plates and development of the spraying conditions were done on a unit built in the State Institute for the Design of Nickel Industry Plants.The unit, the structural plan of which is shown in Fig. i, includes the plasmotron 1 connected through the manifold 2 with the electrical, gas, and water supply systems and also the feeder 3 for supplying the powder.The working tool determining all of the parameters of application of the coatings is the plasmoton.A comparative analysis of the capa-