Production of moulding cores and waterglass mixtures using “dry ice” for steel and iron casting

Abstract

Increased interest of industrial enterprises to manufacture of moulding cores and moulds of mixtures based on waterglass binder is connected with acceptability and high ecological safety of this material. It stipulated more active work for searching technical solutions that can decrease or exclude deficiencies of such technologies as carbon dioxide blowing and thermal effect that are mostly popular at Russian enterprises. Among these deficiencies, the following can be mentioned for example: low setting rates during blowing of waterglass mixtures in the normal temperature conditions as well as the effect of noncontrolled moisture migration in a moulding core of mould body during heating. Their appearances lead to deterioration of operation parameters of core or mould, such as lowering of surface strength, increase of friability, elevation of strength of internal parts of core or mould, what enlarges the risk of their poor knock-out ability from steel and iron castings. Analytical survey of accessible information data was conducted by the authors of this paper; they revealed two directions in searching the solution of the a.m. problem that were supported by overwhelming majority of the researchers. These directions include directed vacuum treatment of technological accessories for increase of control abilities of moisture migration in a body of core or mould, as well as technological additives of different origination in the mixture composition for provision of timely softening of core or mould during knock-out operation out of casting. However, their use does not guarantee always the stable positive effect, thereby this task is still not solved. The authors of this paper concentrated their attention on the problem of development and testing the innovative technology of production of moulding cores and moulds of waterglass mixtures in the conditions of operating enterprise. This technology allows to improve their operating properties and parameters, to lower the mentioned deficiencies and as a result to stabilize the quality of cast metallic billets of steel and iron at the high level. Solving of this task is based on well-known combination of chemical and physical mechanisms of setting of waterglass mixtures together with directed vacuum treatment of technological accessories during acquiring of the required geometrical shape by a moulding core or mould. In this case the following consequent operations tale place: filling of moulding core or moulding box accessories by mixture; its compacting and strengthening via passing of heated setting gas through the mixture from the one side of core or mould with simultaneous its consumption from the other side due to adjustable exhausting. The authors substantiated scientifically and proved experimentally expedience of introduction of small amount of solid carbon dioxide ("dry ice") in the form of particles with preset size and compensation of inevitably occurring undesirable endothermic effect of setting gas heating (air in this case) up to higher temperature in comparison...

Forming of the structure of binder film in waterglass mixtures depending on the setting method

“…It is known that this parameter depends on several factors that have influence on forming a sodium silicate film on the surface of refractory filling agent. Among these factors the following can be mentioned: relationship between basic mixture components [5][6][7], thermal physical parameters of the system "mould (moulding core) -casting" [1,2], influence of technological additives which provide softening of the mixture [8][9][10][11], methods of mixture preliminary preparation [12][13][14] etc. At the same time the setting method is very important; it also provides a mould (moulding core) with initial conditions for forming of the binder film structure and properties of waterglass mixture during interaction with melts [15][16][17].…”