Технические науки

Металлургия

Zhiguts Yu.Yu., Dragula Je.Yu., Pylypko P.V.

Uzhgorod National university, Ukraine

ADDITIONAL HEATING OF COPPER CASTING BY USE THE EXOTHERMIC REACTIONS

Introduction. Since 70-s thermit ways of synthesis of materials have received "the second breath" due to the discovery of self-propagating high-temperature synthesis (SHS). The idea advanced by the author lies in combining SHS and metallothermy, which allows using the hybrid method in producing metals and alloys. The additional ingredients of metallothermic charge were: sodium and potassium saltpeter and powder aluminum. Further on we have succeeded to carry using the metallothermic processes.

The given technology has enabled to produce heating casting alloys by “non-traditional method” [1,2]. The essence of this technology is rather simple: powder–like ingredients of slag are being charged into a metallothermic reactor and are being using a special kind of ignition. When combustion is over an ingot is being formed on the lover part of the reactor. The scheme of this process has suggested a new technology under which we were able to overlap an instrumental plate directly on the base of metal – chamber from of the metallothermic reactor with a plate – gasket made of aluminum [3]. This "hybrid" technology has proved to be universal because it helped to decide the production problem – the synthesis of copper alloys of bronzes (“Бр АЖ 10-4” аnd “Бр ОЦС 5-5-5”) for the technology of high temperature.

Theoretical and experimental investigations. The calculated composition of metallothermic charge for copper alloys took into consideration activity coefficients of separate components of the reaction. On the basis of this we have stated adiabatic burning temperature of the mixture and have corrected chemical composition of the charge. In order to get metallothermic samples microstructure, grain member and mechanical properties (hardness, strength) and porosity have been investigated. The compositions of exothermic charges have been worked out theoretically and then there have been experiments in the conditions of laboratories in industry. This composition is an exothermic mixture for additional heating up of molding addition, which releases heat but does not form metal as the result of its burning. It consists of ~20 % aluminum powder and 80% of potassium or sodium saltpeter (КNO₃ or NaNO₃).

Deviation of this relationship from stoichiometric (Al – 34,6%, NaNO₃ – 65,4%) is caused by the fact that when there is some excess of aluminum, the have its relationship with saltpeter without clamp and activity coefficient of aluminum powder decreases to 0,96% when being dried. As the result the undesirable influence of Al on alloyed Al is being removed. The reaction of this composition charge relationship is the following:

, (1)

. (2)

The products of the reaction K₂O and Al₂O₃ interact and form potassium acuminate will a little heat release. Similarly,

, (3)

.

Introducing Si into charge composition we shall get Al₂O₃ and K₂SiO₃ according to the (4):

, (4)

form potassium aluminosilicate, which being liquid is good slag and improves technical–economic properties of synthesis reaction.

The technology of exothermic additions will for bronze melting was successfully used in experimental–industrial conditions. Two types of the above–mentioned exothermic additions passed the test while melting the cock body (of “P6 010401–Б”) with the mass 2,55 kg (“БрОСЦ 5-5-5”). The exothermic mixture made from Al sodium saltpeter (in 20% to 80%) was inserted into addition opening: as a stack, a metallothermic core. While using this type of mixture in the result of its hightemperature burning heating up of neighboring to exothermic charge bronze formations takes place. The contraction cavity is filled up with overheated liquid melt. The dander of overheating of zone alloy under melt addition and changes due to its physics-mechanical properties has been averted thanks to further operation of the metallothermic charge (approximately 1–1,5 minutes after casting), which defined the heating up of the upper part of the melt addition when under its influence began the process of crystallization.

As the result we have succeeded to decrease the mass of bronze alloy going for addition. The technology of metallothermic cores production consists in adding 4,5% pulverbakelite, 0,2% sulphanol and 5,5% water to the mixture with further drying at a temperature 150–200°C.

By this technology it is possible to produce casting from copper alloys in for away regions, non-specialized plants and in the fields without "usual" smelling equipment and sources of electricity. As the result of burning of special metallothermic mixture liquid overheated copper alloy is formed in the melting addition. Then after catching slag it is being poured into the carting form.

Conclusion. In general it should be noted that, in spite of the increased price of mixture components, the above–described technology has considerable advantages: the absence of complex and expensive equipment (melting furnaces, powerful sources and generators of electricity), full autonomy, high productivity and speed of response (it takes only some minute to get alloy at mixture combustion). These advantages make it possible to widely use this technology in the conditions of no specialized production.

Literature:

1. Zhiguts Yu. Špeciálna termitova liatina//Výrobné inžinierstvo. Košice. − 2007. − N 2. − s. 45−48.

2. Zhiguts Yu.Yu. Thermit smelting of copper alloys//Acta Metallurgica Slovaca. Special issue. − 1999. − No. 2. − Р. 418−421.

3. Патент України №70176 А МПК: 7С21С1/08. Екзотермічна суміш для металотермічних ливарних додатків бронзових виливків/ Ю.Ю. Жигуц, Ю.Ю. Скиба. Опубл. 15.09.2004.; − Бюл. №9.