Internal cracks in rods, structured in a steam microwave environment

Abstract

The aim of the study is to elucidate the mechanism of the occurrence of internal cracks in casting molds and rods, structured by the process of steam-microwave hardening (SMH), with sand clad with water glass. The studies used quartz sand of grade 1K₁O₁02, which was clad with soda sodium water glass with a silicate modulus of 2.9 and a specific density of 1440 kg/m³ at 20 °C. Dilatometric measurements were carried out in a chamber of a specially adapted microwave oven with a magnetron power of 700 W and a frequency of 2.45 GHz. The linear change in the height of the sand in the container was recorded by video recording of the readings of the dial indicator in time. The sands were tested in both microwave and steam-microwave radiation with the previous sifting of dry clad sand through a sieve with a mesh of 0.4 mm and 0.63 mm. The article presents the results of dilatometric studies of changes in the size of samples from pure sand and sand clad with liquid glass, during their processing by microwave radiation in air and in a water vapor environment. It is shown that the reason for the appearance of internal cracks in casting molds and cores, which are made by the SMH-process, is the temporary cessation of microwave action on the mixture during its structuring. As a result, due to the difference in the nature and magnitude of the change in the size of the structured and unstructured mixture in the flask (core box), a layer with a weak mechanical bond between adjacent grains of sand appears at the structuring front, and, as a result, an internal crack. The scientific novelty of the work lies in the elucidation of the causes and mechanism of the occurrence of internal cracks in casting molds and rods, structured by the SMH-process with sand clad with liquid glass.