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Home / News / Industry Encyclopedia / Why should copper wire be tinned and the production process

Why should copper wire be tinned and the production process

Views: 71     Author: Site Editor     Publish Time: 2023-08-24      Origin: Site

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Tinned copper refers to copper coated with a thin layer of metal tin on the surface, such as tinned copper wire, which has certain applications in the cable manufacturing process.

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Reasons for tinning copper wire:


1. The main purpose of tinning copper wires is to prevent copper from being oxidized to form a film—patina (chemical formula CU2(OH)2CO3) when exposed to air. 

Patina, on the other hand, is a poor conductor of electricity and increases electrical resistance. Tinned copper wire can prevent oxidation-reduction reaction and produce patina; it can increase heat dissipation; it can improve electrical conductivity and improve wire performance. .


2. In addition, tinning the copper wire can also prevent the insulating rubber from sticking

The wire core will become black and brittle, and improve its solderability. Tinned copper wire is mainly used for rubber insulated mining cables, flexible wires, flexible cables and marine cables as conductive cores, as well as outer shielding braids and brush wires for cables.


Tinned copper wire production process:


1.Laying out

Pay-off is the key to production. The surface of the copper wire used for plating should be as smooth and round as possible, meeting the requirements of national standards. Due to the lubricating liquid on the surface of the thin copper wire that has just been pulled out, the surface of the copper wire is easily oxidized, so it should be tinned as soon as possible. It is recommended to use a φ300 reel (capable of holding copper wire 50 kg ) for the take-up, and require the copper wire to be evenly arranged, moderately tight, and smooth along the reel. The over-end type (without pay-off device) should be used for pay-off, because the wire diameter is relatively thin, the pay-off speed is fast, and the wire is easily broken during the production process. After trial and error, we used felt to block the wires on the disk, preventing the wires from hitting the edge of the disk. At the same time, the height between the pay-off reel and the pay-off guide wheel is increased, improving the reliability of pay-off, and reducing the probability 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 reheated 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 0. 2 mm or less, it should be controlled at 400~ 550 °C. Here I want to emphasize that the annealing furnaces of tin-plated annealing machines produced by many equipment companies are different in length and temperature control. , some are electric heating tubes, some are electric furnace wires, and the temperature can be adjusted according to the equipment. Make its elongation reach the national 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 uses tin-plating flux, and its ratio is 1:3. In order to ensure cleanness, felt pressing method should be adopted, felt width is 20 cm, regularly pouring felt with pickling solution. Special emphasis: please use according to the principle that the larger the wire diameter, the higher the concentration, and the effect of mixing with industrial soft water is better. Please pour the prepared flux flux into the flux tank and put it into the felt to slowly dilute it. Do not pour the flux directly on the felt. During the production process, the startup speed is too fast, you should put more water The cloth should be replaced frequently to prevent too much water in the sink from being brought to the copper wire, which will affect the flux concentration and cause other problems. The less the water belt, the less tin slag, and it will not cause tin frying.


4.Tin stove

The tin furnace equipment and the temperature of the tin furnace play a key role in the quality of the product. At present, there are three types of tin furnaces. One is that the entire tin furnace material is formed by two cast iron pots, and the bottom of the pot is formed into a triangular row, and the temperature is controlled by an electric heating tube. It is easy to produce large-scale flat wires, and the tin slag is more difficult to operate. The second is that the whole is Stainless steel pot body, the temperature control is electric furnace wire, the tin pot is easy to operate, the temperature is evenly controlled, and there is less tin slag. The third is the Japanese stainless steel tin pot with three-stage temperature control, which is better and more scientific. The surface of the wire is rough, and the surface of the wire is prone to tin bumps; the furnace temperature is too high, the tinned copper wire is prone to yellowing. It is easy to break the wire. After repeated tests, the melting point of tin is 231°C, and the temperature of the tin furnace should be 250--260°C (appropriately adjust the temperature of the tin furnace according to the production specifications). The elongation rate also reaches the national standard.


When the tin in the tin furnace is heated, the surface oxidizes quickly, causing waste. To prevent this, cover the surface of the molten tin with a layer of mica, charcoal powder, etc., but it will not cause mess in management, so as to isolate the contact between the air and the surface of the tin. It is best not to scratch the surface of the tin liquid frequently. Whether the combination of tin and copper wire is good or not, in addition to the need for pickling on 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 every 1.2 months, the copper content should not exceed 1%, if it exceeds 1%, it should be regenerated or replaced with tin.


5.Block the tin mold 

At present, many companies do not recommend to install the tin-blocking mold device in the take-up part of the tinning machine. The use of tin blocking molds is mainly to prevent tin particles and improper operation from being brought to the copper wire to affect the production of the next process. Generally, there are wire drawing molds and ceramic molds. Using wire drawing tin blocking mold, tinned copper wire surface quality is good, but the price is high. Generally, waste wire drawing dies are used, and attention should be paid to the adjustment of the angle of the die base during production to ensure that the crimping fulcrum in the tin furnace, the center point of the tin scraping die and the support point on the guide wheel are in a straight line. Avoid scratches on the surface of the wire The hole diameter of the tinning mold is also a key factor affecting the quality of the tinned copper wire. If the hole diameter is too small, the disconnection will be frequent. If the hole diameter is too large, the tin layer is too thick, affecting the quality of the coating, and the tin consumption increases, and the cost increases. After production test and product performance test, it is better that the hole diameter of the tin-plating die should be 0.05 mm larger than the outer diameter of the copper wire.


6.Cooling method

For tinned copper wires with a wire diameter less than 0.2 mm, air cooling should be used, and the distance between the pulling and the tinned copper wire coming out of the furnace should be well controlled during production. For tinned copper wires with a wire diameter of 0.2~ 0.6 mm, it is better to use air cooling, which can effectively avoid tinned copper wires from sticking tin between wires due to insufficient cooling, and ensure tinning Surface quality of copper wire.


7.Adding guide shaft oil should be a relatively important process

 Tinned copper wires are more or less produced with tin dust, such as 7/0.127, 7/0.16, 11/0.16, 11/0.127, 17/0.178, 41/0.16, 41/0.15 have strict twist lengths. If there is tin dust on the tinned wire, it will cause the entire strand to be broken. You should add guide shaft oil to prevent tin dust.


8.Take-up and traction speed

 The wire take-up and pulling speed should be determined according to the diameter of the wire. Also consider the annealing (and the time of the copper wire in the tin furnace) If the drawing speed is too fast, Insufficient annealing will affect the elongation, Also increase the probability of wire breakage ; If the speed is too slow, the copper wire will stay in the annealing furnace for too long, and the wire will become hard.


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