About the inspection method of screws

There are two types of screw surface inspection, one is the inspection before electroplating after the screw is produced, and the other is the inspection after electroplating, that is, the inspection after the screw is hardened and the screw surface is treated. After the screws are produced, we will inspect the dimensions, tolerances and other aspects of the screws before electroplating. See if it meets national standards or customer requirements. After the screw surface treatment, we will inspect the electroplated screws, mainly to inspect the color of the plating and whether there are bad screws. In this way, when we send the screws to the customer, the customer can pass the customs smoothly when receiving the goods. Inspection after screw treatment:
1、 Appearance quality requirements
The inspection of screw appearance is carried out from the aspects of appearance, electroplating and so on.
2、 Inspection of screw coating thickness
1. Measuring tool method
The quantity used includes micrometer, vernier caliper, plug gauge, etc.
2. Magnetic method
The magnetic method for measuring 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. Microscope method
Microscopic method is called metallographic method. It is to magnify the etched fastener on a metallographic microscope with a micrometer eyepiece to measure the thickness of the coating on the section.
4. Chronometry
Timed liquid flow method is to use the solution that can dissolve the coating to pour on the local surface of the coating, and calculate the thickness of the coating according to the time required to complete the dissolution of the local coating. There are also coating drop method, anodic dissolution coulomb method, etc.
3、 Inspection of adhesion strength of screw coating
There are many methods to evaluate the adhesion between the coating and the base metal, usually including 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 test methods for corrosion resistance of coating include: atmospheric explosion test; Neutral salt spray test (NSS test); Acetate spray test (ASS test), copper accelerated acetate spray test (CASS test); Corrosive paste corrosion test (CORR test) and solution drop corrosion test; Immersion test, immersion corrosion test, etc.