Self-tapping screws Surface treatment: most of the self-tapping screws of the exterior coating using galvanized or zinc phosphate coating. Cadmium plating because of its high cost and toxicity and therefore the use of very little, if the appearance is very important, you can pick nickel or chromium. Appearance treatment will issue two questions: one is, the appearance of disposal will not only increase the scale (such as the hole to reduce, etc.) and not the same appearance will affect the torque, tightness, strength of the link, so the attack Into the experiment must be in accordance with galvanized, cadmium or phosphate treatment do not the same rules. In the test for drilling hole diameter, the use of the screws must be the same appearance of the screw. The second is, high hardness, small-scale self-tapping screws often result in the use of hydrogen embrittlement failure. Self-tapping screws have to be carburized in order to attack the iron plate. In the carburizing treatment will occur after the high hardness and high carbon content, when the situation to do electroplating or pickling treatment occurs when the embrittlement of hydrogen. B) the temperature of 375 ~ 425 oF (190 ~ 220 oC). At least 4 hours at a time. A) electroplating or pickling within 1 hour after the implementation of baking.
Hydrogen embrittlement test: hydrogen embrittlement test is to test the self-tapping screw is not residual hydrogen in the screw arrangement and will not make the self-tapping screw attack brittle, (usually brittle fracture is not a moment to attack, and must be given Of the stress will show up) plating or coated with screws should be included in the table 3 rules of the test iron and steel in the Pingshuaxi, outstanding head screw head under the surface of the use of standard Pingshuaxi, buried Type (Oval) the use of a screw with a chamfer distance from the steel. Under the surface of the bearing surface of the Division or the thickness of the film should be able to fit the maximum length of the screw invalid teeth. In the case of half-length screws, the shank can be supported by a longer distance piece of cold-rolled steel or a flattened blade to ensure that the complete tooth portion can be retained in the test plate thickness. The screw should be locked to 80% of the maximum breaking torque, break the torque is to lock the 5 screws to break with its average resolution, continue to insist on locking after 24 hours, then screw and then spin to the original lock Tight torque, the screw should be no significant loss.