D. Serikbayev East Kazakhstan State Technical University, Ust-Kamenogorsk, Kazakhstan:

O. O. Maslennikov, Senior Researcher, e-mail: ol-maslo@mail.ru
B. V. Syrnev, Professor
N. A. Kulenova, Head of a Chair “Chemistry, Metallurgy and Concentration”

The Kazakhstan Mint of the National Bank of the Republic of Kazakhstan, Ust-Kamenogorsk, Kazakhstan:

F. S. Tuganbaev, Executive Officer

Some surface defects (floating fibres, excessive grainsize and “orange peel”) relating to the metal macrostructure can occur in the manufacture of noble metal coins with the mass of more than 300 grams. To eliminate these defects in the result of thermomechanical processing, it is necessary to obtain cast ingots of large cross-section. It is possible to produce ingots with a coarse-grained macrostructure in the process of continuous horizontal casting of precious metals. The technological parameters of melting and casting affect the formation of a cast macrostructure. Non-optimal parameters of melting and casting (melt overheating, the mold cooling water temperature reduction, the increase of the speed of casting, the increase of an ingot drawing-down speed, the increase of the stop time, etc.) contribute to the increase of the columnar crystal area. The optimization of the ingot structure due to temperature of mold cooling water and/or the drawing-down speed is limited by the resulting ingot properties. The ingot discontinuity or separation can occur at sub-optimal technological parameters of casting. Determination of the optimal parameters for melting and casting in a continuous horizontal casting has individual character. It is primarily related to the processing rate and the composition of used equipment. This article presents the results of industrial tests of melting and casting ingots from Au 99.99 with 12040 mm section in a continuous horizontal casting AG Wertli A-3301 machine. During the tests there were some problems with the casting start and the ingot discontinuity. The article describes the probable causes of these problems and the methods of their elimination.

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