Electroplating hardware processing - screws, master four points to control the quality!

Electroplating is the processing of hardware products—a common method for surface treatment of fastener products such as screws. Usually, electroplating The quality of the product is mainly measured by its corrosion resistance, followed by appearance. Corrosion resistance is to imitate the working environment of the product, set it as the test condition, and perform a corrosion test on it. The quality of electroplating of hardware screw products is controlled from the following aspects:

1. Appearance

The surface of hardware screw products is not allowed to have partial uncoated, scorched, rough, dark, peeled, crusted Condition and obvious streaks, pinhole pitting, black slag plating, loose passivation film, cracking, peeling and serious passivation marks are not allowed.

2. Hydrogen embrittlement

Hardware screw fasteners in the process of processing and processing, especially in the pickling and alkali cleaning before plating and During the subsequent electroplating process, the surface absorbs hydrogen atoms, and the deposited metal layer then traps the hydrogen. When the fastener is tightened, the hydrogen swirls toward the stress-concentrated portion, causing the pressure to build up beyond the strength of the base metal and producing microscopic surface cracks. Hydrogen is particularly active and quickly seeps into the newly formed fissures.

3. Plating thickness

The service life of hardware screw fasteners in corrosive atmospheres is proportional to its coating thickness. The general recommended thickness of economical electroplating coating is 0.00015in～0.0005in (4～12um). Hot-dip galvanizing: the standard average thickness is 54um (named diameter≤3/8 is 43um), and the minimum thickness is 43um (named diameter≤3 /8 is 37um).

4. Plating distribution

Using different deposition methods, the coating gathers on the fastener surface differently. During electroplating of hardware screw fastener products, the plated metal is not uniformly deposited on the peripheral edge, and a thicker coating is obtained at the corners. On the threaded portion of the fastener, a thicker coating is located at the thread crest, tapering along the flank of the thread, and a thin deposit is deposited at the root, while hot dip galvanizing is the opposite, where a thicker coating is deposited on the inside corners and the bottom of the thread , mechanical plating has the same metal deposition tendency as hot dip plating, but is smoother and has a much more uniform thickness over the entire surface.