Research results of cooling speed influence on structure and properties lead tin bronze are given in this article. Cooling speed changed by casting mold heating to various temperatures. Following the researches results it is shown that cooling speed growth leads to growth of hardness, strength on samples stretching. Decrease in cooling speed gives decrease in hardness and strength on stretching, but at the same time the impact strength of samples increases. Results of metalgraphic researches showed that such properties changes are connected with phase structure change of cast samples.
The influence of crystallization conditions of leaded tin bronze on the obtained microstructure parameters is examined in the paper. Modification of crystallization conditions was realised by varying the cooling rate of the melt with preheating of the casting molds. Quantitative regularities of the influence of the cooling rate of bronze on its phase composition are presented. Data on mechanical properties of the material under investigation are also reported in the paper. It is demonstrated that high cooling rates (casting into mold at ambient temperature) enable obtaining higher mechanical properties in comparison with low cooling rates (casting into mold heated up to 800 °С).
In work are submitted data of casting mold coverings with nanopowders application for molding lead bronze. Influence of a structure of used protective - separating coating of a foundry core on a microstructure of castings was investigated. For experimental work following coverings (the patent No 2297300) a mix dioxide zirconium nanopowder with industrial oil, and the same structure, but already on a basis on oxide aluminum nanopowder have been chosen. It is shown that these coverings application leads to decrease in quantity of surface defects, the roughness of a cast surface decreases. At the same time penetration of particles of a powder from a foundry covering in casting doesn't occur.
The article presents the cooling curves of the tin-leaded bronze melt (consists of 10% of lead, 10% of tin, and 80% of copper) being poured in the moulds of various thermal conductivities: massive cast iron chill mould (with the 1:8 cast mass to mould mass ratio) and graphite mould. The curves were plotted for the moulds previously heated to the temperatures of 20; 200; 400; 600; 800 °С. Plotting of the curves was performed with the use of the device Thermograph designed at Tomsk Polytechnic University. The device records thermal electromotive force values of the chromel-alumel thermocouple and converts them into temperature values. The cooling curves are used to determine melt cooling rates within the temperature range involving the crystallization range. It is shown that under similar conditions the cooling rate when casting in cast iron mould is 30-40% higher than in the case of casting in graphite mould. The data given in the paper indicate that preheating of the mould enables us to considerably reduce the cast cooling rate and prolong the period of the melt being in liquid state. It is worth mentioning that cooling rate values of the preheated and non-heated casting moulds are most vividly observed at the initial moments after the melt pouring. When decreasing the casts’ cooling to 300-400 °С the cooling rates tend to be identical. In the article, the numerical data of cooling rates for various mould heating temperatures are presented.
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