Carbon steel rivet nuts and cold heading rivet nuts usually require electroplating. Because the pier of cold heading rivet nut is punched with oil and impurities. For customer needs, it is electroplated surface treatment. Electroplating is the process of plating a thin layer of other metals or alloys on the surface of certain metals using the principle of electrolysis. It can prevent corrosion, improve wear resistance, electrical conductivity, reflectivity and enhance aesthetics.

The following factors need to be controlled during the electroplating surface treatment of the rivet nut:

Appearance of the rivet nut

The surface of the rivet nut fastener product is not allowed to have local uncoated, scorched, rough, dark, peeling, crusted and obvious streaks, pinhole pitting, black slag plating, loose passivation film, tortoise cracking, peeling and severe passivation marks.

Plating thickness of rivet nuts

The service life of a rivet nut fastener in a corrosive atmosphere 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).

Plating distribution of rivet nuts

With different deposition methods, the way the coating gathers on the fastener surface is also different. During electroplating, the coating 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.

Hydrogen embrittlement of rivet nuts

During the processing and processing of the rivet nut fastener, especially during the pickling and alkali washing before plating and the subsequent electroplating process, the surface absorbs hydrogen atoms, and the deposited metal layer then traps 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. This pressure-rupture-penetration cycle continues until the fastener breaks. Usually occurs within a few hours of a stress application. To eliminate the threat of hydrogen embrittlement, rivet nut fasteners are heated and baked as soon as possible after plating to allow hydrogen to seep out of the plating, typically at 375-4000F (176-190°C) for 3-24 hours .Mechanical galvanizing is non-electrolytic, virtually eliminating the threat of hydrogen embrittlement.

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