Electroplating is a common method for the surface treatment of fasteners such as hardware screws. Usually, the quality of electroplating is mainly measured by its corrosion resistance, followed by appearance. Corrosion resistance is to imitate the working environment of the product, set it to test conditions, and subject it to corrosion tests. Hardware Screw Product Plating Quality is Controlled from the Following
1, appearance
The surface of the hardware screw product shall not be allowed to have local non-plating, scorch, rough, gray, peeling, crusting, and obvious streaks. It is not allowed to have pinhole pits, black plating slag, loose passivation film, cracking, shedding, and Severe passivation traces
2, hydrogen embrittlement
Metal Screws Fasteners During processing and processing, especially during the pickling and caustic washing before plating, and subsequent plating, the surface absorbs hydrogen atoms and the deposited metal coating traps hydrogen. When the fasteners are tightened, hydrogen is transferred toward the most concentrated part of the stress, causing the pressure to increase beyond the strength of the base metal and create a tiny surface crack. Hydrogen is particularly active and penetrates quickly into newly formed fractures.
3, plating thickness
The working life of a hardware screw fastener in a corrosive atmosphere is directly proportional to the thickness of its coating. The general recommended economical plating thickness is 0.00015 to 0.0005 in (4 to 12 um). Hot-dip galvanizing: The standard average thickness is 54 um (claim diameter ≤ 3/8 is 43 um), and the minimum thickness is 43 um (call diameter ≤ 3 /8 is 37um).
4, plating distribution
With different deposition methods, the coating is also concentrated on the surface of the fastener. Metal Screws Fasteners Plating metals are not uniformly deposited on the peripheral edges during plating, and thicker coatings are obtained at the corners. In the threaded part of the fastener, the thickest coating is located on the crest of the thread, gradually thinning along the side of the thread, and depositing thinnest at the bottom of the tooth, whereas hot dip galvanizing is the opposite, with thicker deposits deposited on the inner corners and At the bottom of the thread, the mechanically deposited plating metal tends to deposit the same as the hot dip, but it is smoother and the thickness is much more uniform over the entire surface.