Automotive Fastener Trivia

Specialized knowledge of automotive fasteners. Today, Aobiao will teach you some small knowledge about the surface treatment and inspection methods of screw fasteners. As the saying goes, insiders look at the doorway, outsiders look at the excitement, so let's take a look at the excitement as insiders!

Surface treatment and fastener inspection. Surface treatment refers to the process of forming a covering layer on the surface of fasteners through certain methods. After surface treatment, fasteners can have a more beautiful appearance, and the corrosion resistance of the fasteners themselves will also be improved. The surface treatment methods for fasteners include the following:

Mechanical plating of fasteners refers to using specific physical and chemical methods to impact the surface of fasteners with powder of plating metal. In this way, the plating metal forms a coating on the surface of the fastener through cold welding, achieving the surface treatment effect. Mechanical plating of fasteners is mainly suitable for screws, nuts, and washers.

Hot-dip galvanizing of fasteners involves immersing carbon steel fasteners into a molten zinc plating tank at approximately 510℃. This causes the iron-zinc alloy on the surface of the fasteners to transform into passivated zinc, thus achieving a surface treatment effect. The Price of hot-dip galvanizing of fasteners is higher than electroplating, approximately 1.5 to 2 yuan per kilogram.

Electroplating of fasteners involves immersing the parts of the fasteners that need to be electroplated into a specific aqueous solution. This solution contains some deposited metal compounds. When current passes through the solution, the metal in the solution precipitates and adheres to the immersed parts of the fasteners. Electroplating of fasteners generally includes zinc, copper, nickel, chromium, and copper-nickel alloy plating.

The main purpose of surface treatment of fasteners is to provide the fasteners with corrosion resistance, thus increasing the reliability and adaptability of the fasteners. Therefore, the quality judgment of the surface treatment of fasteners mainly checks whether the corrosion resistance of the fasteners has been effectively increased, and whether the increase is in line with expectations.

Appearance quality requirements: The inspection of the appearance of stainless steel screws is carried out from aspects such as appearance and electroplating layer.

Inspection of screw plating thickness

1. Gauge method: The gauges used include micrometers, vernier calipers, and plug gauges.

2. Magnetic method: Magnetic method for measuring plating film thickness is a non-destructive measurement using a magnetic thickness gauge on non-magnetic plating layers on a magnetic substrate.

3. Microscopic method: The microscopic method, also known as metallographic method, is to place the etched fastener under a metallographic microscope with a micrometer eyepiece to magnify and measure the thickness of the plating layer on the cross-section.

4. Chronometric liquid flow method

The chronometric liquid flow method uses a solution that can dissolve the plating layer to flow onto the local surface of the plating layer. The thickness of the plating layer is calculated based on the time required for the local plating layer to dissolve completely. There are also plating drop method, anodic dissolution coulometry, etc.

Inspection of the adhesion strength of screw plating. There are many methods for evaluating the adhesion of the plating layer to the base metal. The following are some common methods:

1. Friction polishing test;

2. File test;

3. Scratch test;

4. Bending test;

5. Thermal shock test;

6. Extrusion method.

Corrosion resistance test of stainless steel screw plating. The corrosion resistance test methods include: atmospheric exposure test; neutral salt spray test (NSS test); acetic acid salt spray test (ASS test); copper-accelerated acetic acid salt spray test (CASS test); corrosion paste corrosion test (CORR test) and solution drop corrosion test; immersion test, intermittent immersion corrosion test, etc.