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What are the inspection methods for screws of precision hardware parts?

2022-10-10

What are the inspection methods for screws of precision hardware parts? There are two types of screw surface inspection. One is the inspection before electroplating after production, and the other is the inspection after electroplating, that is, the inspection after hardening and surface treatment. After the screws are produced and before electroplating, we will inspect the screws in terms of size, tolerance and other aspects.

See if they meet the 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 bad screws. In this way, when we deliver screw goods to customers, they can pass the customs smoothly when they receive 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 coating thickness of screws

1. Measuring tool method
The amount used includes micrometer, vernier caliper, plug gauge, etc.

2. Microscopic method
Microscopic method is called metallographic method, which is to put the etched fasteners on the metallographic microscope with micrometer eyepiece to magnify and measure the thickness of the coating on the section.

3. Magnetic method
The magnetic method for measuring the thickness of the coating layer is a nondestructive measurement of the non-magnetic coating layer on the magnetic substrate with a magnetic thickness gauge.

4. Timed liquid flow method
Chronometric flow method is to use the solution that can dissolve the coating to flow onto the local surface of the coating, and calculate the coating thickness according to the time required for the local coating to dissolve. There are also coating dropping method, anodic dissolution coulometry 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, including the following.

1. Scratch method; 2. Extrusion method; 3. Bending test; 4. Thermal shock test; 5. File method test; 6. Friction polishing test.

4、 Inspection of corrosion resistance of screw coating

The inspection methods for corrosion resistance of the coating include: atmospheric exposure 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 drip corrosion test; Immersion test, immersion corrosion test, etc.