Effect of coatings viscosity on metal scaling at reheating it before rolling

Abstract

To protect metal from oxidation during reheating before rolling different kinds of coatings are used. Silicate enamel, presenting alloy of oxides from a mixture of sand, chalk, soda, alumina and other cheap components, are most widely used as such coatings. When applying coatings on a metal, it is important to take into consideration their viscosity, which determines the evenness of the coating distribution on the sample and its thickness. In the process of the experiments the following coatings were used: one -based on clay, soda, periclase, burnt sand, liquid soap and the other based on clay, activated charcoal, soda, graphite, brucite and liquid soap. In all the coatings the content of liquid soap and water was varied, the other components were not changes. To check the scaling while coating application and without it, samples of the same carbon steel were used. All the samples were divided for three groups for heating at different temperatures. Every group had a reference sample without coating for scaling comparative analysis. On the other samples different kinds of coatings of different viscosity were applied. After coating application, the samples were kept at room temperature within 1 hour for the coating complete drying. Next the samples were placed in a SNOL 7,2/1300 furnace. Each group was kept in the furnace at required temperature within 45 min. After cooling, the scale and the cleaned sample were weighted to determine the scaling percent. Based on the results of the study the range of a coating viscosity values to provide the minimal scale formation was determined. It was determined, that for magnesia-alumina coatings the optimal coefficient of kinematical viscosity is in the range of 0.450-0.501 m 2 /s.