Запобігання появи поверхневих дефектів на внутрішніх порожнинах корпусних чавунних виливків

Abstract

The insufficiently high quality of the surface of metal castings, which are made in sand molds, is due to the formation of various surface defects, of which galling is the most common. Cleaning castings from scorch leads to additional costs of material and labor resources, which can reach 40-60% of the total labor intensity of production. The process of increasing the strength of the non-stick coating of casting molds and rods can be implemented by optimizing its composition. According to the result of the analysis of thermochemical reactions at the contact interface "melt - mold" in the process of heat exchange between the casting and the casting mold and related physical processes, as well as hydrodynamic processes of interaction in the contact zone, in particular, specific for graphitized cast iron, in order to prevent surface defects on the internal cavities of body cast iron castings, after experimental and industrial work, non-stick coatings of increased resistance were developed and applied in foundry production for sand molds and rods. Coating compositions were completed according to the concept of partially directing the energy of the high-temperature exposure of the metal to chemical transformations in the non-stick coating and the contact zone of the sand mold with the formation of compounds that would contribute to the sintering of the particles of the surface layer of the mold at the temperature of its heating from the contacting metal. This served as a means of preventing cracks in such a layer and avoiding cracks and mechanical burning on the surface of castings. A method of reducing the metal pressure from the pre-shrinkage expansion of graphitized cast irons during its action on the surface of the walls of the casting cavities by the timely partial weakening of the vacuumed casting mold without disturbing the given geometry of the casting when applying the method of casting according to gasifying patterns has also been developed.