Stainless steel screw plating is a common surface treatment method in the production of screw fasteners. In general, the main reason and purpose of electroplating is to change the corrosion resistance, rust resistance and appearance color of stainless steel screws. Corrosion resistance, anti-rust performance is to imitate the use environment of stainless steel screws, to do salt spray test, to judge the anti-rust and corrosion resistance of stainless steel screws. In addition to rust and corrosion resistance, we have to judge the plating quality of stainless steel screws from the following four points:
1, appearance
When the stainless steel screw is plated, the surface is not allowed to be partially uncoated, burnt, rough, gray, peeling, crust, and obvious streaks. Pinhole pitting, black plating, loose passivation, cracking, shedding are not allowed. And severe passivation marks.
2, hydrogen brittle
During the processing and handling of stainless steel screws, especially during pickling and caustic washing before plating and subsequent electroplating, the surface absorbs hydrogen atoms, and the deposited metal coating then captures hydrogen. When the fastener is tightened, hydrogen is transferred to the most concentrated portion of the stress, causing the pressure to increase beyond the strength of the base metal and creating a slight surface crack. Hydrogen is particularly active and quickly penetrates into newly formed fissures.
3, plating thickness
The operating life of stainless steel screw fasteners in corrosive atmospheres is proportional to the thickness of the coating. The recommended economical plating thickness is 0.00015 in to 0.0005 in. (4 to 12 um). Hot dip galvanizing: the standard average thickness is 54 um (the nominal diameter is ≤ 3/8 is 43 um), and the minimum thickness is 43 um (the nominal diameter ≤ 3) /8 is 37um).
4, coating distribution
Stainless steel screws use different deposition methods, and the coatings are concentrated on the surface of the fasteners. When the metal screw fastener product is plated, the plated metal is not uniformly deposited on the peripheral edge, and a thicker coating is obtained at the corner. In the threaded portion of the fastener, the thickest coating is located on the crest of the thread, gradually thinning along the side of the thread, depositing the thinnest at the bottom of the tooth, while hot dip galvanizing is just the opposite, thicker coating is deposited inside the corner and At the bottom of the thread, the mechanical plating of the plated metal tends to be the same as that of hot dip coating, but is smoother and much more uniform over the entire surface.