The self-tapping screw immerses the electroplated part in an aqueous solution containing the deposited metal compound, and passes an electric current through the plating solution, causing the electroplated metal to precipitate and deposit on the part. Jinjia hardware tell you the general electric galvanizing, copper, nickel, chromium, copper-nickel alloy, etc., sometimes boil black (blue), phosphating, etc., also included. The quality of self-tapping screw plating is mainly measured by its corrosion resistance, followed by appearance. Corrosion resistance is to imitate the working environment of the product, set as the test conditions, and perform corrosion tests on it. So the quality of self-tapping screw plating products should be how to control, the following Jinjia hardware for you to explain in detail: the quality of self-tapping screw plating products from the following aspects to be controlled:
1, appearance: the metal tells you that the surface of the product is not allowed to have local coating, burnt, rough, gray, peeling, skin conditions and obvious stripes, not allowed to have pinhole pitting, black plating slag, passivation film loose, cracked, falling off and serious passivation traces.
2, coating thickness: The working life of fastener self-tapping screws in corrosive atmosphere is proportional to its coating thickness. Jinjia hardware generally recommended economic plating coating thickness of 0.00015in ~ 0.0005
in(4 ~ 12um). Hot dip galvanizing: The average thickness of the standard is 54 um(43 um for the diameter ≤3/8), and the minimum thickness is 43 um(37 um for the diameter ≤3/8).
3, coating distribution: using different deposition methods, the coating on the surface of the fastener aggregation is also different. During electroplating, the coated metal is not uniformly deposited on the outer edge, and a thicker coating is obtained at the corner. The metal tells you that in the threaded part of the fastener self-tapping screw, the thickest coating is located at the top of the thread, gradually thinning along the side of the thread, and the thinnest deposit at the bottom of the tooth, and the hot dip galvanizing is the opposite, the thicker coating is deposited inside the corner and the bottom of the thread, the mechanical plating plating metal deposition tendency is the same as the hot dip plating. But it's smoother and much more uniform in thickness over the entire surface.
4, hydrogen embrittleness: The fastener tells you that in the processing and treatment process, especially in the pickling and alkali washing before the self-tapping screw plating and the subsequent electroplating process, the surface absorbs hydrogen atoms, and the deposited metal coating then captures hydrogen. When the fastener self-tapping screws are tightened, the hydrogen is diverted toward the most concentrated part of the stress, causing the pressure to increase beyond the strength of the base metal and produce a small surface rupture. The hydrogen moves around and soon seeps into the newly formed fissure. This pressure-crack-penetration cycle continues until the fastener breaks. It usually occurs within a few hours of the first stress application. In order to eliminate the threat of hydrogen embrittlement, fasteners should be heated and baked as quickly as possible after plating to allow hydrogen to seep out of the coating, and baking is usually carried out at 375-4000F(176-190 ° C) for 3-24 hours. Since mechanical galvanizing is non-electrolyte, this virtually eliminates the threat of hydrogen embrittlement.