The Effect of Molding-Sand Mixture Properties on the Quality of Freight- Wagon Side-Frame Castings Made of Grade 20gl Steel

This article studies how the composition of the molding-sand mixture and the cleanliness of the molding sand affect casting quality in the production of freight-wagon side frames made of grade 20GL steel. The aim was to relate the properties of the clay-bonded (green) sand, namely its grain-size distribution, gas permeability and strength, to the formation of porosity, burn-on and surface defects, and to recommend an improved mixture. The clay-bonded mixture used at the Casting-Mechanical Plant (silica sand with 11.5% bentonite, 3.5–4.0% water and 1.0–1.5% Krakhmalit) was analyzed, and its behavior was interpreted through Darcy's law and the Kozeny–Carman relation for the permeability of granular media. The analysis showed that an increase in dust and fine fractions sharply lowers the gas permeability and degrades casting quality, whereas cleaner, better-graded sand raises both permeability and strength. Improving the cleanliness of the sand and optimizing the mixture reduced porosity by 16–18% and surface defects by 6–7%, and lowered the incidence of burn-on.