Special screw plating product quality control method

Special screw plating is a very common surface treatment of screws. Presumably, everyone has seen screw fasteners of various colors, such as silver, black, gold, etc., so how are these screws made so colorful? These colored screws are achieved thanks to the plating surface treatment. But we will also find that the screws of the same batch of screws, some of the screws have a very beautiful surface, and some of the screws are not satisfactory after plating, so how should the special screws control the quality when plating?

1.The special thickness of the hot-dip galvanizing specification for special screwis 54μm, (the nominal diameter is ≤3/8 is 43μm) and the minimum thickness is 43μm (the nominal diameter is ≤3/8 is 37μm).

2.pinhole pitting, black plating slag, passivation film looseness, cracking, shedding and severe passivation marks are not allowed. The exterior of the product is not allowed to be partially uncoated, charred, rough, dull, peeled, crusted and markedly streaked.、

3.the thickness of the coating, the working life of the metal screw in the corrosive atmosphere is proportional to the thickness of its coating. The recommended economical plating thickness is generally 0.00015 in-0.0005 in (4-12 μm).

4.The plating has different ways of gathering on the outer surface of the fastener. The plating metal is not uniformly deposited on the outer peripheral edge during electroplating. Different deposition methods are adopted, and a thicker coating is obtained at the corner. Part of the thread of the screw, the thickest coating is located on the top of the thread, gradually thinning along the front of the thread, the thinnest deposit at the bottom of the tooth, and the hot dip galvanizing is just the opposite, the thicker coating is deposited on the inner corner and the bottom of the thread, mechanical Plated metal plating tends to be the same as hot dip coating, but is smoother and much more uniform throughout the exterior.

5.especially the special screw in the pickling and caustic washing before plating and the subsequent plating process, the screws in the processing and disposal process. The surface absorbs hydrogen atoms, and the deposited metal plating then traps hydrogen. When the screw is tightened, hydrogen is transferred to the most concentrated part of the stress, causing the pressure to increase beyond the strength of the base metal and causing a slight surface crack. Hydrogen is particularly active and quickly penetrates into newly formed fissures.

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