CHOICE OF THE OPTIMAL COMPOSITION OF NON-STICK COATINGS ACCORDING TO THE CONDITIONAL CRITERION OF FILLING MASS ACTIVATION

Abstract

Development of the technique for choice of the optimal composition of non-stick coatings based on the filling mass quality evaluation (taking into account the results of differential scanning calorimetry) is the aim of this research. Non-stick coating for iron casting based on filling mass and polyvinyl butyral lacquer was taken for investigations with the following relation – filling mass : polymer composition (2% polyvinyl butyral lacquer) = 1:1. The mixture of natural and mechanically activated graphite with their different correlation was used as a filling mass. Calculation of the conditional activation criterion displayed that the most optimal relation between selfdrying coatings of natural and mechanically activated graphite in a filling mass is 50:50. It was established in this case that increase of activated graphite in a filling mass of non-stick coatings leads to increase of density, toughness and reduced strength. The most essential improvement of the properties is observed if the content of activated graphite in a filling mass increased up to 50%. Additional increase of GLS-2A graphite content does not lead to substantial improvement of the properties. The developed non-stick coatings were tested during fabrication of the casting “Centrifugal soil pump. Internal pump shell” with mass 70 kg and size 510×615×128 mm, made of 320Kh20N (320Х20Н) iron. Use of non-stick coating on the base of the mixture of natural and mechanically activated graphite (with their relation 50:50) is characterized by decrease of burning-on thickness by 1.8 times (on the bottom surface of a casting) and by 1.9 times (on the side surface of a casting) in comparison with thickness values for non-painted castings. The obtained results can be explained in the following way: if we apply the coating containing 50% GLS-2 (ГЛС-2) and 50% GLS-2A (ГЛС-2А), large particles of natural graphite don’t penetrate in mould pores and remain on the surface, what leads to decrease of burning-on on the casting surface.