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ArticleName Elimination of the consequences of sticking the platinum group metals and alloys to the casting mould
ArticleAuthor Vershinina E. N., Levchenko S. D.

OJSC Scientific and Industrial Complex “Supermetall”

E. N. Vershinina, Engineer of Fusion Department, e-mail:
S. D. Levchenko, Chief Metallurgist

The quality of the semifinished products, obtained by the plastic working, depends essentially, and in many cases completely, on the quality of ingots. The method of the plastic working does not eliminate or locate the metallurgical defects; in many respects, it just helps to detect them. With the certain temperature-rate modes, there could be obtained the dense ingots without any non-metallic inclusions, shrink and gas friable areas, having no coarse cold shuts. These ingots can be produced by the method of moulding with directional crystallization, the feature of which is a one-way movement of the crystallization front. 10 years ago, the OJSC “SIC “Supermetal”, which manufactures the products of various platinum metals and alloys, tested one of the methods of moulding with directional crystallization, i. e. the low-rate moulding in a horizontal copper mould. This method is succesfully used until present. Sometimes, as a result of the crude errors, a stably high quality of ingots, occurs the sticking of the over-heated melt to the casting mould and the melting of the casting mould, which results to the contamination with copper. One of such ingots was used to study the copper content near the area of sticking. The copper content was determined by the method of the spectral analysis. At first, from the surface of the ingot, and then from a depth of 2.5 mm after milling. It has been found that in given case of such strong sticking with a penetration to a depth, up to 3 mm, the area of contamination concentrates exclusively near the area of sticking. It happens in a layer, up to 2.5 mm, in a vicinity formed by the external border of the 10–12 mm zone surrounding the sticking trace. This means that if the dimension of the trace after sticking is 18–19 mm across, the volume of the contaminated metal is less than 3 cm3. It follows that the sticking defect can be easily reworked by milling of the contaminated area of the ingot with subsequent pyrometallurgical refining of an insignificant amount of the scobs.

keywords Ingot, directional crystallization, low-rate moulding, horizontal mould, sticking, pyrometallurgical refining

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