Special knowledge for automotive fasteners. Today, Aobiao will teach you some small knowledge about the surface and inspection methods of screw fasteners. As the saying goes, experts look at the tricks, outsiders look at the excitement. So let's also have an expert look at the excitement!
Surface treatment and inspection of fasteners. Surface treatment refers to the process of forming a covering layer on the surface of fasteners through certain methods. After surface treatment, fasteners can present a more beautiful appearance and improve their corrosion resistance. There are several methods for surface treatment of fasteners:
Mechanical plating of fasteners refers to the use of specific physical and chemical methods to impact the surface of fasteners with coated metal powder, so that the coated metal forms a coating on the surface of fasteners through cold welding, achieving surface treatment effect. Mechanical plating of fasteners is mainly applicable to spare parts such as screws, nuts, and washers.
Hot dip galvanizing of fasteners is the process of immersing carbon steel fasteners into a molten zinc plating bath at a temperature of approximately 510 ℃. This transforms the iron zinc alloy on the surface of the fasteners into passivated zinc, resulting in a surface treatment effect. The price of hot-dip galvanizing for fasteners is higher than electroplating, about 1.5 to 2 yuan per kilogram.
Electroplating of fasteners refers to immersing the part of the fastener that needs to be electroplated into a specific aqueous solution, which contains some deposited metal compounds. After passing current through the aqueous solution, the metal substances in the solution precipitate and adhere to the immersed part of the fastener. The electroplating of fasteners generally includes galvanizing, copper, nickel, chromium, copper nickel alloys, etc.
The main purpose of surface treatment of fasteners is to enhance their corrosion resistance, thereby increasing the reliability and adaptability of fastener use. Therefore, the quality assessment of fastener surface treatment is mainly to check whether the corrosion resistance of fasteners has been effectively increased and whether the increase meets the expected requirements.
Appearance quality requirements: The inspection of the appearance of stainless steel screws is carried out from various aspects such as appearance, plating layer, etc.
Inspection of Coating Thickness on Screws
1. Measuring method: The amount used includes micrometers, vernier calipers, plug gauges, etc.
2. Magnetic method: The magnetic method is used to measure the thickness of a coating layer, which is a non-destructive measurement of a non-magnetic coating layer on a magnetic substrate using a magnetic thickness gauge.
3. Microscopy method: Microscopy method, also known as metallographic method, involves magnifying etched fasteners on a metallographic microscope with a micrometer eyepiece to measure the thickness of the coating on the cross-section.
4. Timed flow method
The timed flow method is to pour a solution that can dissolve the coating onto the local surface of the coating, and calculate the thickness of the coating based on the time required for the local coating to dissolve completely. There are also plating drop method, anodic dissolution Coulomb method, etc.
There are many methods for testing the adhesion strength of screw coatings and evaluating the adhesion between coatings and base metals, usually including the following.
1. Friction polishing test;
2. Filing method test;
3. Scratch method;
4. Bending test;
5. Thermal shock test;
6. Squeezing method.