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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. Riveting nut electroplating is the process of plating a thin layer of other metals or alloys on some metal surfaces using the principle of electrolysis. 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:
The surface of riveted fastener products is not allowed to have local uncoated, scorched, rough, dark, peeling, crusted and obvious streaks, pinhole pitting, black slag plating, loose passivation film, cracks are not allowed , peeling and severe passivation marks.
The service life of pressure riveting fasteners in corrosive atmosphere is proportional to the thickness of its coating. The general recommended thickness of the economical electroplating coating is 0.00015in～0.0005in(4～12um). Hot dip galvanizing: the standard average thickness is 54 um (43 um when the diameter is less than or equal to 3/8), and the minimum thickness is 43 um (when the name is less than 3/8). diameter ≤ 3/8 is 37 um).
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. In the threaded portion of the fastener, the thickest coating is located on the thread crest, gradually thinning along the flank of the thread, and the thinnest deposit is at the bottom of the thread, while hot dip galvanizing is just the opposite, the thicker coating is deposited on the inside corners and On the bottom of the thread, mechanical plating has the same tendency to deposit metal as hot dip plating, but is smoother and has a much more uniform thickness over the entire surface.
During the processing and handling of press riveted fasteners, especially in the acid and alkali cleaning 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 most stressed parts, 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 after the first stress application. To eliminate the threat of hydrogen embrittlement, riveted fasteners should be heated and baked as soon as possible after plating to allow hydrogen to seep out of the coating, typically at 375-4000F (176-190°C) for 3-24 hours. Mechanical galvanizing is non-electrolytic, virtually eliminating the threat of hydrogen embrittlement.