Investigation of linear shrinkage of model compounds and interaction mechanisms in the «lost wax pattern – refractory ceramic mold» system

The study covers the free linear shrinkage of non-filled (PS50-50, MVS3-T, Romocast 105, Romocast 152) and filled (Romocast 252, Romocast 325) model compounds depending on the ambient temperature. Research results revealed the following main features in the change of this technological parameter. It is found that the greatest free linear shrinkage is typical for non-filled model compounds, while filled model compounds have a minimum linear shrinkage. At the same time, processes associated with free linear shrinkage occurred in samples for a long time (up to 24 hours). This is probably due to the duration of polymerization processes and low thermal conductivity of model compounds. Changes in the ambient temperature within –5...+35 °C have a significant impact on the degree of changes in linear dimensions of the studied model compound samples. The length of samples changed within +0.3...–0.4 % for non-filled model compounds and within +0.2...–0.15 % for filled compounds. At the same time, non-filled compound samples cooled to –5 °C and then heated to +20 °C reduce their length by 0.2 mm on average. When non-filled compound samples are heated to +35 °C and then cooled to +20 °C, the initial length increases by 0.2÷0.3 mm on average. With similar ambient temperature changes in filled model compound samples, their change in length is not more than 0.1 mm. To eliminate refractory ceramic mould cracking, it is proposed to cool the «lost wax patter –refractory ceramic mold» system to ensure a guaranteed gap between the pattern and the mold and eliminate the negative impact of the expanding pattern composition.

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