1. Appearance quality requirements
The appearance of screws is inspected from the appearance, plating layer and other aspects.
Second, the inspection of the thickness of the screw coating
1. Measuring tool method
The amount used includes micrometer, vernier caliper, plug gauge and so on.
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
The microscopy method is called the metallographic method, which is to magnify the etched fasteners on a metallographic microscope with a micrometer eyepiece to measure the thickness of the coating on the section.
4. Timing sap flow method
The chronograph flow method is to flow a solution that can dissolve the coating on a local surface of the coating, and calculate the thickness of the coating according to the time required for the partial dissolution of the coating. There are also plating spot method, anode dissolution coulometric method and so on.
3. Inspection of the adhesion strength of the screw coating
There are many ways to evaluate the adhesion of the coating to the base metal, and there are usually the following.
1. Friction polishing test;
2. File method test;
3. Scratch method;
4. Bending test;
5. Thermal shock test;
6. Extrusion method.
4. Inspection of corrosion resistance of screw coating
The coating corrosion test methods include: atmospheric exposure test; neutral salt spray test (NSS test); acetic acid salt spray test (ASS test), copper accelerated acetic acid salt spray test (CASS test); and corrosion paste corrosion test (CORR test) and solution spot corrosion test; immersion test, inter-immersion corrosion test, etc.
