There are two types of screw surface inspections, one is the inspection before the screw is produced and not plated, and the other is the inspection after the screw is plated, that is to say, after the screw is hardened and the surface of the screw is treated.
After the screws are produced and before electroplating, we inspect the screws in various aspects such as size and tolerance. See if there are national standards or customer requirements. After the surface treatment of the screws, we will inspect the plated screws, mainly to check the color of the plating and whether there are any broken screws. In this way, when we deliver screw goods to customers, customers can successfully pass the customs when they receive the goods. Inspection after screw processing:
Appearance quality requirements
The inspection of the appearance of the screw is to inspect the appearance, electroplating layer and other aspects.
The inspection of the thickness of the screw coating
1. Measuring method
The amount used has a micrometer, a vernier caliper, a plug gauge, and the like.
2. Magnetic method
The magnetic method to measure the thickness of the coating layer is a non-destructive measurement of the non-magnetic coating layer on the magnetic substrate with a magnetic thickness gauge.
3. Microscopy
Microscopy is called metallography, which is to magnify the etched fasteners on a metallographic microscope with a micrometer eyepiece to measure the thickness of the coating on the cross-section.
4. Time flow method
The timing liquid flow method uses a solution that can dissolve the coating to flow on the local surface of the coating, and calculates the thickness of the coating according to the time required for the local coating to dissolve. There are also coating drop method, anodic dissolution Coulomb method, etc.
Inspection of the adhesion strength of screw coating
There are many methods for evaluating the adhesion between the coating and the base metal, usually the following.
1. Friction polishing test; 2. File method test; 3. Scratch method; 4. Bending test; 5. Thermal shock test; 6. Extrusion method.
Inspection of corrosion resistance of screw coating
The test methods for corrosion resistance of coatings are: atmospheric exposure test; neutral salt spray test (NSS test); acetate salt spray test (ASS test), copper accelerated acetate spray test (CASS test); and corrosion paste corrosion test (CORR test) and solution spotting corrosion test; immersion test, inter-dipping corrosion test, etc.
