Today, obello is here to teach you some knowledge about the surface way out and inspection methods of screw fasteners. It's just the so-called expert who looks at the door, while the layman watches the fun. Let's have a look at the fun!
Surface treatment and inspection of fasteners, surface treatment refers to the process of forming a covering layer on the surface of fasteners by some methods. After surface treatment, fasteners can present a more beautiful appearance, and the corrosion resistance of fasteners will also be improved. The surface treatment methods of fasteners are as follows:
Mechanical plating of fasteners refers to that the surface of fasteners is impacted by the powder of coated metal by specific physical and chemical means. In this way, coating metal forms coating on the surface of fastener in the form of cold welding to achieve the effect of surface treatment. Mechanical plating of fasteners is mainly applicable to screws, nuts and gaskets and other spare parts.
The hot-dip galvanizing of fasteners is to immerse the fasteners with carbon steel composition into the bath of molten zinc with a heat of about 510 ℃. In this way, the iron zinc alloy on the fastener surface will be transformed into passivated zinc, so as to obtain the surface treatment effect. The price of hot-dip galvanizing of fasteners is higher than that of electroplating, which is about 1.5 to 2 yuan per kilogram.
Electroplating of fasteners refers to immersing the parts of fasteners that need to be electroplated into a specific aqueous solution. The aqueous solution will contain some deposited metal compounds. In this way, after the current passes through the aqueous solution, the metal substances in the solution will precipitate and adhere to the immersion part of the fastener. Electroplating of fasteners generally includes zinc plating, copper, nickel, chromium, copper nickel alloy, etc.
The main purpose of the surface treatment of fasteners is to make the fasteners obtain corrosion resistance, so as to increase the reliability and adaptability of fasteners. Therefore, the quality judgment of fastener surface treatment is to check whether the corrosion resistance of fasteners is effectively increased and whether the increase range meets the expected requirements.
Appearance quality requirements: stainless steel screw appearance inspection is from the appearance, electroplating and other aspects of inspection.
Inspection of plating thickness of screws
1. Measuring tool method: the amount of micrometer, vernier caliper, plug gauge, etc.
2. Magnetic method: the magnetic method is used to measure the thickness of the coating layer, which is a non-destructive measurement of the non-magnetic coating layer on the magnetic substrate with the magnetic thickness gauge.
3. Microscope method: microscope method is called metallographic method. It is to enlarge the etched fasteners on the metallographic microscope with micrometer eyepiece to measure the thickness of coating on the section.
4. Chronoamperometry
The time flow method is to use the solution that can dissolve the coating to flow on the local surface of the coating, and calculate the thickness of the coating according to the time required for the completion of the local coating dissolution. There are coating drop method, anodic dissolution coulometry method and so on.
There are many ways to evaluate the adhesion of the coating to the substrate.
1. Friction polishing test;
2. File method test;
3. Scratch method;
4. Bending test;
5. Thermal shock test;
6. Extrusion method.
Stainless steel screw coating corrosion resistance inspection, coating corrosion test methods are: atmospheric explosion test; neutral salt spray test (NSS test); acetate spray test (ASS test), copper accelerated acetate spray test (CASS test); corrosion paste corrosion test (CORR test) and solution drop corrosion test; immersion test, intermittent corrosion test and so on.
