The surface reaction layer is the main factor affecting the physical and chemical properties of titanium castings. Before the titanium castings are ground and polished, the surface contamination layer must be completely removed to achieve a satisfactory polishing effect. The surface reaction layer of titanium can be completely removed by pickling after sandblasting.
1. Sandblasting: For the sandblasting of titanium castings, rough blasting of white corundum is generally better. The pressure of sandblasting is smaller than that of non-precious metals, and it is generally controlled below 0.45Mpa. Because, when the spray pressure is too high, the sand particles impact the titanium surface to produce intense sparks, and the temperature rise can react with the titanium surface to form secondary pollution and affect the surface quality. The time is 15~30 seconds, and only the sticky sand, surface sintered layer and part and oxide layer on the surface of the casting can be removed. The remaining surface reaction layer structure should be quickly removed by chemical pickling.
2. Pickling: Pickling can quickly and completely remove the surface reaction layer, and the surface will not be polluted by other elements. Both HF-HCl series and HF-HNO3 series pickling liquids can be used for pickling of titanium, but HF-HCl series pickling liquids have a large hydrogen absorption capacity, while HF-HNO3 series pickling liquids have small hydrogen absorption and can control HNO3 The concentration of HNO3 can reduce hydrogen absorption, and the surface can be brightened. Generally, the concentration of HF is about 3% to 5%, and the concentration of HNO3 is about 15% to 30%.