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What are the key points of the inspection method of special screws?

There are two types of special screw surface inspection, one is the inspection before the screw is electroplated after the screw is produced, and the other is the inspection after the screw is electroplated, that is to say, the inspection after the screw is hardened and the surface of the screw is treated. So, let's talk about the special screw inspection method:


Appearance quality requirements
The inspection of screw appearance is carried out from various aspects such as appearance and electroplating layer.



Inspection of Screw Coating Thickness
1. Measuring tool method
The amount used has micrometers, vernier calipers, plug gauges, etc.
 
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 microscope method is called the metallographic method, which is to enlarge the etched fastener on a metallographic microscope with a micrometer eyepiece, and measure the thickness of the coating on the section.
4. Time flow method
The timing liquid flow method is to use a solution that can dissolve the coating to flow on the partial surface of the coating, and calculate the thickness of the coating according to the time required for the local coating to dissolve. There are also plating drop method, anodic dissolution coulometric method and so on.
 




Inspection of adhesion strength of screw plating
There are many ways to evaluate the adhesion between the coating and the base metal, usually as follows.
1. Friction and 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 Plating
The test methods for coating corrosion resistance include: atmospheric exposure test; neutral salt spray test (NSS test); acetic acid salt spray test (ASS test), copper accelerated acetate salt spray test (CASS test); and corrosion paste corrosion test (CORR test) and solution spot corrosion test; immersion test, interleaved corrosion test, etc.