The production process of hot-dip tinned fine copper wire is: pay-off → annealing → pickling → tinning → cooling → pulling → winding and arranging wire, etc. The following describes the key points and precautions of the process 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, meeting the requirements of the standard. The surface of the newly drawn fine copper wire is very easy to oxidize due to the lubricant on the surface, so it should be tinned as soon as possible. The author recommends using a φ160 wire reel (which can hold 7 kg of copper wire) for winding, and requires the copper wire to be arranged evenly, with moderate tightness and a smooth reel edge. Pay-off should be done by over-the-end method (without a pay-off device) because the wire diameter is relatively thin and the pay-off speed is fast, which makes it very easy to break the wire during production. After repeated experiments, we used a pay-off felt on the reel to block the wire, which effectively avoided the wire from hitting the reel edge. At the same time, the height between the pay-off reel and the pay-off guide wheel is increased, which improves the pay-off reliability and reduces the chance of wire breakage.

(2) Annealing. The annealing temperature of the copper wire is a key factor affecting the elongation of the finished wire. Since it needs to be heated again in the tin furnace, the annealing temperature should not be too high (slightly lower than the normal annealing temperature). For thin wires with a diameter of less than 0.2 mm, it is advisable to control it at 300-330 °C to make its elongation slightly lower than the standard.

(3) Pickling. Before the copper wire enters the tin furnace, it must be cleaned with an appropriate pickling solution to ensure good adhesion between the tin layer and the copper wire. The pickling solution is a mixture of zinc chloride, ammonium chloride, sodium chloride and water in a ratio of 1:5:10:100. To ensure clean cleaning, a felt pressing method should be used, with a felt width of 20 cm, and the felt should be poured with pickling solution regularly.

(4) Tin furnace. The temperature of the tinning furnace plays a critical role in product quality. A low furnace temperature results in a rough surface and easy breakage of the tinned copper wire; a high temperature results in a yellowing tendency. After repeated testing, a tinning furnace temperature of 320°C was found to be optimal (the temperature was intentionally raised here because the annealing temperature of the copper wire used was relatively low). This results in a smooth, continuous coating on the finished wire, and the elongation also meets optimal standards.

When heated in the tinning furnace, the tin rapidly oxidizes, resulting in waste. To prevent this, the molten tin can be covered with a layer of mica, charcoal powder, or other materials to isolate the tin from air.

The quality of the tin-copper bond depends not only on the pickling of the copper wire surface but also on the purity of the tin itself. Therefore, the composition of the tin solution should be tested biweekly. The copper content must not exceed 1%. If it exceeds 1%, the tin should be regenerated or replaced. The specific method of regeneration is to put 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 released. In this way, the copper contained in the tin liquid will become copper sulfide and float up, which can be removed. When operating, please note that the product is toxic.

(5) Tin scraping mold. The tin scraping molds currently on the market mainly include diamond molds and rubber molds. The diamond tin scraping mold has good surface quality of tinned copper wire, but the price is high. For the production of fine tinned copper wire, due to the high speed, the operation and control of the rubber mold is difficult, which easily causes wire breakage. Moreover, each time the production is restarted, a section of copper wire will be used as a traction line, resulting in more than ten meters of untinned copper wire, causing unnecessary waste. The diamond mold is easy to operate and the surface quality of the tinned copper wire is good, so it is better to use the diamond mold for the production of fine wire. During production, pay attention to the adjustment of the mold frame angle to ensure that the wire pressing support point in the tin furnace, the center point of the tin scraping mold and the support point on the guide wheel are in a straight line. The aperture of the tin scraping die is also a key factor affecting the quality of tinned copper wire. If the aperture is too small, the wire will break frequently. If the aperture is too large, the tin layer will be too thick, which will affect the quality of the coating, increase the tin consumption and increase the cost. After production trials and product performance tests, the aperture of the tin scraping die should be 0.05 mm larger than the outer diameter of the copper wire.

(6) Cooling method. For tinned copper wire with a wire diameter less than 0.2 mm, air cooling is recommended. During production, the distance between the traction and the tinned copper wire leaving the furnace should be controlled. For tinned copper wire with a wire diameter of 0.2 to 0.6 mm, water cooling is better. It can effectively avoid the phenomenon of tin sticking between the wires after the tinned copper wire is wound due to insufficient cooling, and ensure the surface quality of the tinned copper wire.

(7) Winding and pulling speed. The winding and pulling speeds should be determined based on the wire diameter, taking into account the annealing time (≥10 seconds) and the time the wire spends in the tinning pot (≥0.03 seconds). For thin wires with a diameter of 0.2 mm or less, the pulling speed should be controlled at 130 m/min. Too fast a pulling speed will result in incomplete annealing, affecting elongation and increasing the chance of wire breakage. Too slow a speed will cause the wire to spend too long in the annealing pot, causing it to harden.