The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before grinding and polishing titanium castings, it is necessary to completely remove the surface pollution layer in order to achieve satisfactory polishing results. The surface reaction layer of titanium can be completely removed by sandblasting and acid washing.

1. Sandblasting: For the sandblasting treatment of titanium castings, white corundum coarse spraying is generally preferred, and the sandblasting pressure is lower than that of non precious metals, generally controlled below 0.45Mpa. Because when the injection pressure is too high, the sand particles impact the titanium surface, generating intense sparks. The temperature rise can react with the titanium surface, forming secondary pollution and affecting the surface quality. The time is 15-30 seconds, and only the sticky sand, surface sintering layer, and partial oxidation layer on the casting surface need to be removed. The remaining surface reaction layer structure should be quickly removed by chemical acid washing.

2. Acid washing: Acid washing can quickly and completely remove the surface reaction layer without contaminating the surface with other elements. Both HF HCl and HF HNO3 acid wash solutions can be used for acid washing of titanium, but HF HCl acid wash solution has a higher hydrogen absorption capacity, while HF HNO3 acid wash solution has a lower hydrogen absorption capacity. The concentration of HNO3 can be controlled to reduce hydrogen absorption and the surface can be treated with brightness. Generally, the concentration of HF is around 3%~5%, and the concentration of HNO3 is around 15%~30%.