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Abstract

The paper presents a detailed description of one of the newest methods of vacuum saturation of reinforcing preforms in gypsum molds. As an appropriate selection of the infiltration time is a crucial problem during realization of this process, aim of the analysis shown in the paper is to present methods of selection of subatmospheric pressure application time, a sequence of lowering and increasing pressure, as well as examining influence of structure of reinforcing preforms on efficiency of this process. To realize the aim, studies on infiltration of reinforcing preforms made of a corundum sinter of various granulation of sintered particles with a model alloy were conducted. The infiltration process analysis was carried out in two stages. The first stage consisted in investigation of influence of lengthening of sucking off air from the reinforcing preforms on efficiency of this process. In the second stage, an analysis of influence of a two-staged infiltration process on saturation of the studied materials was conducted. Because the studied preforms were of similar porosity, the obtained differences of the saturation level of particular preforms have shown, that the saturation process is influenced mostly by size of pores present in the reinforcement. Because of these differences, each reinforcement type requires individual selection of time and sequence of the saturation process. For reinforcements of higher pore diameter, it is sufficient to simply increase air sucking off time to improve the saturation, while for reinforcement of smaller pore diameter, it is a better solution to apply the two-staged process of sucking off air. Application of the proposed analysis method allows not only obtaining composite castings of higher quality, but also economical optimization of the whole process.
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Abstract

Refinement is one of the most energy consuming technological process, aimed at obtaining mineral raw materials of the proper grain size. Cast structural elements such as jaws or hammers in crushing machines operate under conditions of an intensive wear. The data indicate that 80 % of failures of machines and devices is caused by wearing of rubbing surfaces. This problem became the subject of several scientific and industrial investigations carried out in the whole world in order to produce materials ultra- wear resistant. Methods allowing to obtain wear resistant composite castings are discussed in the hereby paper. Within the performed research microstructures of the produced composite zones were presented and the comparative analysis with regard to mechanical and functional properties of local composite reinforcements in relation to the commercial alloys of increased wear resistance was performed. The results show almost twenty five times increase in wear resistance compared to manganese cast steel containing 18 % Mn.
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Abstract

In order to increase wear resistance cast steel casting the TiC-Fe-Cr type composite zones were fabricated. These zones were obtained by means of in situ synthesis of substrates of the reaction TiC with a moderator of a chemical composition of white cast iron with nickel of the Ni-Hard type 4. The synthesis was carried out directly in the mould cavity. The moderator was applied to control the reactive infiltration occurring during the TiC synthesis. The microstructure of composite zones was investigated by electron scanning microscopy, using the backscattered electron mode. The structure of composite zones was verified by the X-ray diffraction method. The hardness of composite zones, cast steel base alloy and the reference samples such as white chromium cast iron with 14 % Cr and 20 % Cr, manganese cast steel 18 % Mn was measured by Vickers test. The wear resistance of the composite zone and the reference samples examined by ballon-disc wear test. Dimensionally stable composite zones were obtained containing submicron sizes TiC particles uniformly distributed in the matrix. The macro and microstructure of the composite zone ensured three times hardness increase in comparison to the cast steel base alloy and one and a half times increase in comparison to the white chromium cast iron 20 % Cr. Finally ball-on-disc wear rate of the composite zone was five times lower than chromium white cast iron containing 20 % Cr.
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