Fastener screws must undergo full standard inspections before production, during processing, and after surface treatment. Only qualified products can be warehoused and delivered. Strict inspection procedures effectively ensure the dimensional accuracy, surface quality, mechanical performance and operational stability of fasteners. The routine inspection items for fastener screws are summarized as follows.
1. Plating Adhesion Strength Inspection
Plating adhesion strength is used to evaluate the bonding firmness between the electroplated coating and the screw substrate to prevent coating peeling and flaking. Common industrial testing methods include friction polishing test, file test, scratch test, bending test, thermal shock test and extrusion test.
2. Plating Corrosion Resistance Inspection
This inspection verifies the rust and corrosion resistance of fastener coatings to meet weather resistance requirements of different working conditions. Conventional testing methods include atmospheric exposure test, neutral salt spray test (NSS), acetic acid salt spray test (ASS), copper accelerated acetic acid salt spray test (CASS), corrosion paste test (CORR), solution drop corrosion test, immersion test and intermittent immersion corrosion test.
3. Screw Surface Quality Inspection
Fastener surface inspection covers the entire production process and is divided into two stages: the first is blank surface inspection after forming and heat treatment and before electroplating; the second is finished product surface inspection after electroplating and surface treatment, which comprehensively controls the surface quality of screws in each process.
4. Comprehensive Dimensional and Appearance Inspection
Before electroplating, strict inspections are carried out on key items such as product dimensions, tolerances, thread profiles and head appearances to ensure all parameters comply with national standards or customized customer requirements, eliminating defects such as dimensional out-of-tolerance, deformation, material shortage and thread damage.
After electroplating, inspectors mainly check the consistency of electroplating color and coating uniformity, and screen for appearance defects including damage, missing plating, blistering, peeling, black spots and color difference, so as to guarantee the overall appearance quality of finished products.
