Effect of polishing process on contact resistance of flat and spherical rivet electrical contacts

With the rapid development of the electrical industry, various power devices such as high and low voltage circuit breakers, disconnectors, contactors, relays, etc. that control power transmission and distribution have also been widely developed. Custom Electrical Contacts are responsible for connecting, disconnecting and transmitting current in electrical and electronic equipment. They are the main actuators of electrical switch actions, so electrical contacts are called "heart parts". The contact resistance of rivet electrical contacts is an important parameter to measure the performance of rivets. One of the main criteria for electrical contact failure is that the contact resistance exceeds the specified value. The main factors affecting the contact resistance of rivet electrical contacts include the roughness of the rivet working surface, foreign matter on the working surface, copper adhesion on the working surface, etc. These influencing factors are closely related to the post-processing polishing process. Therefore, this study analyzes the influence of two post-processing polishing processes on the contact resistance of plane and spherical electrical contacts during the production of electrical contacts, and discusses the relationship between the two polishing processes and contact resistance.

The steel needle grinding and polishing process uses steel needles and Electrical Contact manufacturers to perform full all-round and multi-angle grinding to achieve the effects of rapid rust removal, burr removal, oxide film and sintered foreign matter. And the steel needle polishing process does not damage the surface of the workpiece, does not affect the dimensional accuracy of the workpiece, and makes the rivet instantly bright and tidy.

The ball milling and polishing process uses polishing beads and rivet contacts for multi-angle grinding to quickly remove surface foreign matter, oxide film and sintering marks, etc., which can effectively solve the problems of workpiece overlap and uneven grinding that occur in the grinding and polishing machine during work. This process also does not damage the rivet surface and does not affect the dimensional accuracy. Make the rivet surface smoother.

The electrical contact performance of the rivet electrical contact when it is put into production mainly depends on the state of its working surface, and its surface state depends on the post-processing polishing process of the rivet electrical contact. The post-processing polishing process is directly related to the roughness and cleanliness of the contact surface, which has a lot to do with the resistance stability of the contact resistance. Therefore, it is very meaningful to study the influence of the post-processing polishing process of the rivet electrical contact on the contact resistance.

In order to further understand the effect of post-processing polishing process on the contact resistance of Electrical Contact Silver Point, this test observed and recorded 4 groups of samples, two of which were flat rivets and two were spherical rivets. The purpose is to compare the contact resistance and surface roughness of flat and spherical samples treated with different polishing processes, and to explore the effect of polishing process on the contact resistance of flat and spherical rivet electrical contacts.

AgSnO2 wire and copper wire were processed into spherical composite rivets with dimensions of R6×1.85 (0.6) + 3×2.5, and AgNi wire and copper wire were processed into flat composite rivets with dimensions of F6×1.85 (0.6) + 3×1.6. Four batches of rivets were tested, one batch of spherical and flat surfaces of two batches of rivets were ball-milled and polished, and one batch of spherical and flat surfaces of two batches of rivets were steel-needle-polished. They were numbered R1, F1, R2, and F2, and were processed according to different polishing processes. The polishing process of each batch number is shown in Table 1. The roughness of the working surface of the rivet contact was measured using the Keyence 400X; the contact resistance simulation measurement of the rivet contacts of different processes was performed using the CRS-4000 contact material contact resistance test analyzer. The principle of the equipment is that a certain pressure is applied to the two contacts, and the resistance value data is obtained through a fixed current and voltage. The principle is shown in Figure 1. The test conditions are: test voltage 1000 mV, test current 100 mA, contact pressure 200 g.

Figure 2 shows the appearance of the Silver Coated Electrical Contacts, where (a) is the ball-milled polished plane F1, (b) is the ball-milled polished spherical surface R1, (c) is the steel needle polished plane F2, and (d) is the steel needle polished spherical surface R2. The appearance of the plane and spherical rivet contacts under the two polishing processes was observed under an optical microscope. It can be clearly seen that the ball-milled polished plane and spherical surface have a matte appearance, while the steel needle polished surface has a pockmarked surface, but the color is brighter.

Figure 3 shows the surface morphology of the contact, where (a) is the ball-milled polished plane F1, (b) is the ball-milled polished spherical surface R1, (c) is the steel needle polished plane F2, and (d) is the steel needle polished spherical surface R2. The contact surface morphology of the two processes was observed by Keyence 400X. From (a) and (b), it can be seen that there is no obvious copper powder and foreign matter on the ball-milled surface, while (c) and (d) show that there is a small amount of copper powder residue on the steel needle polished surface. By comparing the appearance, it can be seen that the surface of the ball-milled polished process is relatively smooth. From (a) and (c), it can be seen that the steel needle polishing has a greater impact on the morphology of the flat and spherical rivets. The flat surface has more pits and appears rougher.

Figure 4 is a scanning electron microscope of the contact, where (a) is the ball-milled polished plane F1, (b) is the ball-milled polished spherical surface R1, (c) is the steel needle polished plane F2, and (d) is the steel needle polished spherical surface R2. Through the scanning electron microscope, the samples under the two polishing processes were scanned for foreign matter and compared and analyzed. It was found that the surface morphology after polishing by the two processes was similar, there was no obvious foreign matter, and the polishing effect was similar.

The morphology of the flat and spherical rivet working surfaces under the two polishing processes was observed from macro to micro. The analysis found that the rivet contact working surface under the ball milling polishing process was smoother than that under the steel needle polishing process, and the influence of the steel needle polishing on the morphology of the flat rivet was greater than that of the spherical rivet, and the surface was relatively rough.

The roughness test results of the four batches of samples are shown in Table 2, and the roughness measurement values ​​are plotted in a graph as shown in Figure 5.

As can be seen from Table 2, ten rivets were measured for each process. The roughness of the rivets under the F2 steel needle polishing process is significantly greater than that under the F1 ball milling polishing process, and the roughness of the rivets under the R2 steel needle polishing process is slightly greater than that under the R1 ball milling polishing process, indicating that the two polishing processes have little effect on the roughness of the spherical AgSnO2 material rivets. It can be clearly seen from the curves F1 and F2 in Figure 5 that the roughness of F2 is about twice that of F1, so the two polishing processes have a greater effect on the roughness of the planar AgNi material rivets.

The contact resistance test results of the four batches of samples are shown in Table 3, and the contact resistance measurement values ​​are plotted as shown in Figure 6.

From the average value of the data in Table 3, it can be seen that the contact resistance of the rivet under the F2 steel needle polishing process is significantly greater than that under the F1 ball milling polishing process, indicating that the two polishing processes have a greater impact on the contact resistance of the planar AgNi material rivet. The contact resistance of the rivet under the R2 steel needle polishing process is slightly greater than that under the R1 ball milling polishing process, indicating that the two polishing processes have little impact on the contact resistance of the spherical AgSnO2 material rivet. The contact resistance of the rivet with the R1 ball milling polishing spherical surface is the smallest, with an average value of 0.29 mΩ and a maximum value of 0.34 mΩ. The contact resistance of the F2 steel needle polishing plane is the largest, with an average value of 0.69 mΩ and a maximum value of 0.81 mΩ.

From the curves F1 and F2 in Figure 6, it can be clearly seen that the average contact resistance of F2 is 0.69 mΩ, which is about twice the contact resistance of F1, so the two polishing processes have a greater impact on the contact resistance of the planar AgNi material rivet. According to the comparison between Figure 5 and Figure 6, it is found that the curve is similar to the roughness result, which also shows that the contact resistance is closely related to the roughness. The greater the roughness, the greater the contact resistance, which is related to the contact area when the Contactor Electrical Silver Contacts are in contact.

The polishing process used two processes, steel needle grinding and ball milling. The color of the rivets made by ball milling is matte, while the color of the rivets made by steel needle grinding is brighter, but it has a rough surface; the surface foreign matter removal of both processes is relatively clean; the roughness of the spherical and flat rivets of both materials by ball milling is lower than that of the steel needle grinding process, but the polishing process has less effect on the roughness of the spherical AgSnO2 material rivets and a greater effect on the roughness of the flat AgNi material rivets; the contact resistance of the spherical and flat rivets of both materials by ball milling is better than that of steel needle grinding, but the polishing process has less effect on the contact resistance of the spherical AgSnO2 material rivets and a greater effect on the contact resistance of the flat AgNi material rivets. This is mainly related to the influence of the polishing process on the surface roughness and the electrical contact area.

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