| 摘要 |
PURPOSE:To form easily and exactly a hard film only on the head part of a piston which is harged electrostatically to positive and is exposed with only the head part faced downward by hanging the piston and ejecting a soln. contg. sulfuric acid charged electrostatically to negative and air thereto from below. CONSTITUTION:A piston 5 which has a head part 5a faced downward and is covered with masking rubber 6 is suspended in the air of the part upper than the top surface of a soln. contg. sulfuric acid 2 contained in a vessel 1 charged electrostatically to positive. The liquid 2 is vigrously sprayed together with discharging air to the head part 5a by a pump 4 through the hole 3a of an air pile 3 sunk near the top surface of the liquid 2 in this state. As a result, ionization is accelerated and a hard film a of alumite, etc. is quickly and efficiently formed only on the head part 5a. Since the rubber 6 is covered on the piston 5, the film (a) is not formed on the outside circumferential surface and the uniform product is formed without dimensional errors in the outside diameter of the piston 5.
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