Electroplating is a common method for surface treatment of fasteners such as hardware screws. Generally, the quality of electroplating is mainly measured by its corrosion resistance, followed by its appearance. Corrosion resistance is to simulate the working environment of the product, set it as the test condition, and conduct corrosion test on it. How to Control the Quality of Metal Screw Electroplating in Hardware Processing Factory?
Hardware processing factory
1. Appearance: The surface of hardware screw products shall be free from local non plating, scorching, roughness, grayness, peeling, skinning and obvious stripes, pinhole pitting, black plating slag, loose passivation film, cracking, falling off and serious passivation traces.
2. Hydrogen embrittlement: During the processing and treatment of hardware screw fasteners, especially in the pickling and alkaline cleaning before plating and the subsequent electroplating process, the surface absorbs hydrogen atoms, and the deposited metal coating then captures hydrogen. When the fastener is tightened, the hydrogen turns to the part with the most concentrated stress, causing the pressure to increase beyond the strength of the base metal and causing minor surface cracking. Hydrogen is particularly active and soon seeps into newly formed fissures.
3. Plating distribution: different deposition methods will lead to different aggregation modes of the coating on the fastener surface. When metal screws and fasteners are plated, the plated metal is not uniformly deposited on the peripheral edges, and thicker plating is obtained at the corners. In the thread part of the fastener, the thickest coating is located at the top of the thread, gradually thinning along the side of the thread, and the thinnest coating is deposited at the bottom of the thread. On the contrary, the thicker coating is deposited at the inner corner and the bottom of the thread. The metal deposition tendency of the mechanical coating is the same as that of the hot dip coating, but it is smoother and the thickness is much more uniform on the entire surface.
4. Plating thickness: the working life of hardware screw fasteners in corrosive atmosphere is proportional to its coating thickness. Generally, the recommended economic plating thickness is 0.00015in~0.0005in (4~12um) Hot dip galvanizing: the average thickness of the standard is 54um (43um for nominal diameter ≤ 3/8), and the minimum thickness is 43um (37um for nominal diameter ≤ 3/8).
