From screw forming to electroplating, a comprehensive explanation of fastener surface inspection technology

In the manufacturing industry, fasteners are important components for connecting and fixing parts. They are of various types and have different functions. From bolts, nuts, screws, to rivets, washers, retaining rings, pins, etc., each fastener plays an indispensable role. However, in the face of such a wide range of choices, it is particularly important to ensure that the selected fasteners can meet the needs of specific working conditions.

The selection of fasteners is not only based on their shape and function, but also on key factors such as their materials, specifications and surface treatment processes. The selection of these factors directly determines the performance of fasteners in actual use. For example, fasteners working in high temperature or corrosive environments need to choose high temperature and corrosion resistant materials and surface treatment processes.

The surface treatment of fasteners is particularly critical. It is directly related to the service life, wear resistance and corrosion resistance of fasteners. Therefore, fasteners need to undergo strict surface inspection before leaving the factory. However, the surface inspection here is not the "appearance inspection" in our traditional sense, but includes more in-depth and detailed inspection.

The first inspection is after the screw is formed and before electroplating. The inspection at this stage mainly focuses on whether the size and tolerance of the screw meet the relevant national standards or user requirements. Through precise measuring tools such as vernier calipers and thread plug gauges, the dimensions of the screws are strictly tested to ensure that they are within the error range.

However, the inspection after electroplating is more complicated and detailed. Electroplating not only changes the appearance of the screw, but also forms a protective film on its surface, which enhances its corrosion resistance. Therefore, the inspection after electroplating needs to be carried out from both the appearance and the electroplating layer.

In terms of appearance, the main inspection is whether the color of the screw is uniform, whether there are flaws, rust, etc. These will affect the beauty and service life of the screw. The inspection of the electroplating layer is more critical, which directly determines the corrosion resistance and wear resistance of the screw.

In the inspection of the thickness of the electroplating layer, there are many methods to choose from. The first is X-ray fluorescence (XRF), which works by analyzing the characteristic X-rays emitted from the material when exposed to X-rays, providing information about the thickness and composition of the plating layer. The second is Magnetic Induction, which uses the principle of electromagnetic induction to measure the thickness of non-magnetic coatings (including electroplating layers) on conductive substrates. This method has high accuracy, but it is only applicable to magnetic substrates.

The thickness of the electroplating layer can also be inspected by Cross-section Microscopy, which requires preparing a sample of the electroplated material, cutting it, and then examining the cross-section under a microscope to measure the thickness of the plating layer. The result is obtained by measuring the thickness of the coating on the cross section. Although this method is complicated, it is relatively accurate.

In addition, there are many methods such as Eddy Current Testing and Beta Backscatter Gauges that can be used to detect the thickness of the electroplating layer. Each method has its own unique advantages and scope of application. Which method to choose depends on the specific detection needs and conditions.

In summary, the surface inspection of fasteners is a complex and important task. It requires careful inspection and analysis from multiple aspects to ensure that the quality and performance of the fasteners meet the requirements. Only in this way can we ensure that the fasteners play their due role in actual use.

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