After sandblasting, the titanium alloy castings must be pickled before surface quality inspection. Before delivery, it is also best to carry out a pickling process so that the surface of the casting is clean and bright, which is convenient for judging the appearance quality and level of the casting.
Hydrofluoric acid is the main component of the pickling solution. It is one of the few chemical substances that can effectively corrode titanium. Adding nitric acid to the pickling solution of hydrofluoric acid promotes the uniformity and stability of this chemical process.
The operation process of pickling is as follows: the titanium castings loaded into the plastic net basket are lifted by a lift and immersed in the pickling tank for pickling. The pickling time is about 3-5 minutes, and the humidity of the pickling tank should be controlled at 20-25 ° C. After pickling, the casting must be cleaned in water and then dried in a stream of hot air to maintain a uniform and shiny surface. In industrial production, plastic drums can be used instead of net baskets to load castings, immersed in bath towels for pickling. The slow rotation of the ten rollers drives the casting to continuously stir during the pickling process, to avoid the formation of bubbles from the gas generated by the reaction, and to adhere to the surface of the casting, so that the pickling process of the casting can be carried out evenly and efficiently.
Corrosive pickling can be used to adjust the dimensional accuracy of casting wall thickness. The corrosion rate of the new bath is generally o. oo 5-0.0077mm / min, the ability of titanium casting to corrode and cut, the maximum can reach 0.2-0.4mm. Therefore, during the time corrosive pickling process, we must pay attention to the problem of hydrogen permeation to avoid hydrogen embrittlement fracture of titanium alloy castings during use. Therefore, the precision titanium alloy castings after corrosive pickling generally need to be subjected to vacuum annealing.