Study of the Impact of External Influences on the Protective Coating Applied to Moulding Sand

Obtaining a good casting surface without defects requires proper preparation of the mould for the given metal alloy. It is important to select the appropriate moulding sand, which consists of a grain matrix and a binder. Due to the temperature and dynamics of the poured alloy, it is also important to apply a suitably selected protective coating to the surface of the mould. Depending on its chemical composition, the carrier used (water or alcohol), and the method of application, it is possible to create the most favourable conditions for obtaining a flawless casting. This article presents the impact of various protective coatings applied to moulding sand on a chromite matrix, comparing their technological parameters and selecting the best one for the given application conditions. During commonly used tests on moulding sand with a protective coating, its permeability, abrasion, and adhesion were determined. To verify the results obtained, microscopic photographs of the prepared surface layers of the moulding sand with a protective coating were also taken. It was found that, despite the same viscosity, the same carrier, and the same application method, the quality of the protective coating is determined by its appropriate composition developed by the manufacturers. The permeability of Pu moulding blocks after coating was found to be significantly reduced, from 255 to 37 [×10−8 m2/Pa × s]. The use of protective coatings significantly increased the moulding sand’s abrasion resistance, reducing the loss value from 0.826% to 0.330% for the weakest coating. In the group of protective coatings tested, the coating marked PC1M in the tests had the highest adhesion Np and its value, depending on the application method, ranged from 0.30 MPa to 0.37 MPa.