Application and production technology of tinned flat copper wire

Tinned flat copper wire is mainly used for rubber insulated mining cables, rolling stock cables and Marine cables such as conductive wire core, as well as wire and cable external shielding braid layer. After the copper wire is tinned, it can effectively prevent the oxidation of the copper wire and the rubber contact caused by the rubber, the copper wire blackening and other problems, and improve the service life of the cable and the weldability of the wire core.

At present, the production of tinned copper wire in China's cable industry mainly includes two ways: chemical tinning (electroplating tin) and physical tinning (hot tin plating). Tin plating is a more advanced production method, its main advantage is that the coating thickness is uniform, and can be controlled arbitrarily, but its process is more complicated than hot tin plating, strict operation requirements, high equipment price. Hot tin plating process is simple, and the equipment price is low, so it is used by many manufacturers. Because of the different process of hot tin plating in each factory, the quality of tinned copper wire produced is also different. According to many years of production experience, the author believes that the following factors are the key to affect the quality of tinned copper wire, for reference only.

2 Quality of copper and tin

The raw materials of tinned copper wire are copper and tin. Since the diameter of tinned copper wire produced by our factory is below 0.2 mm, the requirements for copper wire are relatively high. This can effectively increase the single wire length of copper wire in the plating process and reduce the breaking rate of tinned copper wire. Some people believe that the copper wire must be pickled before tinning, so the quality requirements of the copper wire are not strict. The copper wire with serious surface oxidation or contamination cannot be cleaned in a short time during pickling, so that the tin layer and copper body of the tinned copper wire produced are not well combined, easy to fall off, and there are more pinholes. Because the quality of copper wire directly affects the quality of tinned copper wire, it is necessary to correct the bias that the quality of copper wire for tinned copper wire is not high. The author thinks that the quality of tinned copper wire should meet the technical requirements of enamelled copper wire.

The quality of tin also directly affects the quality of tinned copper wire. If the use of low purity tin ingots or impurities in the market, the temperature of the tin furnace is not easy to control during the production process, which can easily lead to the alloying of the tin layer of the finished line, affecting the continuity and adhesion of the tin layer. Moreover, due to excessive impurities, it is easy to block the die hole, resulting in frequent wire breakage and affecting the length of the finished single wire. Therefore, in order to ensure the quality of tinned copper wire, the tin ingot used should not be lower than the technical requirements of No. 2 tin in GB /T 728-1984.

3 Several problems that should be paid attention to in production

The production process of hot tinning fine copper wire is as follows: pay-off → annealing → pickling → tinning → cooling → traction → take-up wire and other seven processes. The process points and precautions are described below according to this process.

(1) Pay-off. Pay-off is the key in production. The surface of the copper wire used for plating should be as smooth and round as possible, in line with the requirements of national standards. Because of the lubricating fluid on the surface of the fine copper wire just pulled out, the surface of the copper wire is easily oxidized, and should be tinned as soon as possible. The author suggests that the use of φ160 wire reel (can be loaded with 7 kg copper wire), and requires the copper wire to be uniform, moderate tightness, and smooth disk edge. Pay-off should be used over the end type (without pay-off), because the line diameter is relatively thin, pay-off speed is fast, and it is easy to break the line in the production process. After repeated trials, we used to add wire felt on the disc to block the line, which avoided the line colliding with the edge of the disc. At the same time, the height between pay-off disc and pay-off guide wheel is increased, the reliability of pay-off is improved, and the probability of breaking is reduced.

(2) Annealing. The annealing temperature of copper wire is the key factor affecting the elongation of finished wire. Since it is necessary to enter the tin furnace for secondary heating, the annealing temperature should not be too high (slightly lower than the normal annealing temperature). For the thin line with a diameter below 0.2 mm, it should be controlled at 300 ~ 330 °C, so that its elongation is slightly lower than the national standard.

(3) pickling. Before the copper wire enters the tin furnace, it must be cleaned with appropriate acid washing solution to ensure that the tin layer and the copper wire have good adhesion. The pickling solution is a mixture of zinc chloride, ammonium chloride, ****** and water in a ratio of 1:5:10:100. In order to ensure clean cleaning, the felt line should be used, the felt width is 20 cm, and the felt is poured regularly with acid washing solution.

(4) Tin furnace. The temperature of the tin furnace plays a key role in the quality of the product. The furnace temperature is low, and the surface of tinned copper wire is rough and easy to break. If the furnace temperature is too high, tinned copper wire is easy to yellow. After repeated tests, the temperature of the tin furnace is 320 °C (because the selected annealing temperature of the copper wire is relatively low, the temperature of the tin furnace is intentionally increased). The finished wire surface coating is smooth and continuous, and the elongation reaches the national standard.

When the tin in the tin furnace is heated, the surface oxidation is rapid, which will cause waste. In order to prevent this, the surface of the molten tin liquid can be covered with a layer of mica, charcoal powder, etc., to isolate the contact between the air and the surface of the tin liquid.

The combination of tin and copper wire is good or bad, in addition to the pickling of the surface of the copper wire, the purity of the tin liquid itself is also an important factor. Therefore, the composition of the tin liquid should be tested once every half month, and the copper content should not exceed 1%, if more than 1% should be recycled or replaced. The specific method of regeneration is to put in a perforated metal cylinder filled with sulfur powder, and let the metal cylinder sink to the bottom of the tank until the sulfur dioxide is fully escaped. In this way, the copper contained in the tin liquid will float as copper sulfide and can be removed. It should be noted during operation that the product is toxic.

(5) Scraping tin mold. At present, the tin scraping molds on the market mainly include diamond molds and rubber molds. Using diamond scraping tin die, tinned copper wire surface quality is good, but the price is high. For the production of fine tinned copper wire, due to the relatively fast speed, the use of rubber mold operation and control is more difficult, easy to cause broken wire, and each time the production will use a section of copper wire as a traction line and produce more than ten meters of untinned copper wire, resulting in unnecessary waste. The use of diamond mold operation is simple and tinned copper wire surface quality is good, so the production of fine lines with diamond mold is better. In production, attention should be paid to the adjustment of the Angle of the mold frame to ensure that the fulcrum of the pressure line in the tin furnace, the center point of the scraping mold and the support point on the guide wheel are in a straight line.

The aperture of the scraping die is also a key factor affecting the quality of tinned copper wire. If the aperture is small, the line breaks frequently. If the aperture is larger, the tin layer is thicker, which affects the quality of the coating, and the tin consumption increases, and the cost increases. After the production test and the performance test of the product, the diameter of the tin scraping die should be larger than the outer diameter of the copper wire 0.05 mm.

(6) Cooling method. For tinned copper wire with wire diameter less than 0.2 mm, air cooling should be used, and the distance between traction and tinned copper wire can be controlled during production. For tinned copper wire with wire diameter of 0.2 ~ 0.6 mm, it is better to use water cooling method, which can effectively avoid the phenomenon of tin sticking between the wires after the wire is collected due to insufficient cooling, and ensure the surface quality of tinned copper wire.

(7) Take-up and traction speed. The take-up and traction speed should be determined according to the diameter of the wire, and also consider the annealing (≥ 10 s) and the time of the copper wire in the tin furnace (≥0. 03 s). For thin lines with a diameter below 0.2mm, the traction speed should be controlled at 130 m/min. If the traction speed is too fast, it will lead to insufficient annealing and affect the elongation, and also increase the probability of breaking. If the speed is too slow, the copper wire will be hard in the annealing furnace for too long.