Annealing is a process at high temperature which aim to soften the copper and make it more malleable.
The purpose of annealing is to make the conductor hardened by the lattice change during the mold stretching process to be heated at a certain temperature, so that the molecular lattice can be rearranged to restore the softness required by the process, and at the same time, the surface residue of the conductor during the stretching process can be removed. The lubricant, oil, etc., make the wire easy to paint and ensure the quality of the enameled wire. The most important thing is to ensure that the enameled wire has suitable softness and elongation during use as a winding, and at the same time helps to improve the conductivity.
The greater the degree of conductor deformation, the lower the elongation and the higher the tensile strength.
There are three commonly used methods for annealing copper wire: annealing in coils; continuous annealing on wire drawing machines; continuous annealing on enameling machines. The first two methods can not meet the requirements of the enameling process. Annealing in a coil can only soften the copper wire, but the degreasing is not complete. Since the wire is soft after annealing, the bending is increased when the wire is paid off. Continuous annealing on the wire drawing machine can soften the copper wire and remove the surface grease, but the soft copper wire after annealing is wound around the coil to form a lot of bends. Continuous annealing before painting on the enameling machine can not only achieve the purpose of softening and removing oil, but also the annealed wire is very straight and directly enters the painting device, which can apply a uniform paint film.
The temperature of the annealing furnace is determined according to the length of the annealing furnace, copper wire specifications, and line speed. Under the same temperature and speed, the longer the annealing furnace, the more fully the recovery of the conductor lattice. When the annealing temperature is low, the higher the furnace temperature, the better the elongation, but the opposite phenomenon occurs when the annealing temperature is high.
The temperature of the annealing furnace is too high, which not only affects the service life of the furnace, but also easily burns the wire when it is stopped and cleaned, and the wire is broken and threading. The maximum temperature of the annealing furnace is required to be controlled at about 500 °C. It is effective to use a two-stage temperature control form for the furnace, and it is effective to select a temperature control point at a position where the static and dynamic temperatures are similar.
Copper is easily oxidized at high temperature. Copper oxide is very loose, and the paint film cannot be firmly attached to the copper wire. Copper oxide has a catalytic effect on the aging of the paint film, and has adverse effects on the flexibility, thermal shock and thermal aging of the enameled wire. . In order not to oxidize the copper wire, it is necessary to keep the copper wire under high temperature from contacting with oxygen in the air, so a protective gas is required. Most annealing furnaces are water-sealed at one end and open at the other. The water in the water tank of the annealing furnace has three functions: closing the furnace mouth, cooling the wire, and generating steam as a protective gas. At the beginning of the drive, because the water vapor in the annealing tube is very small, and the air cannot be removed in time, a small amount of alcohol aqueous solution (1:1) can be poured into the annealing tube. (Be careful not to pour pure alcohol and control the amount of use)
The water quality in the annealing tank is very important. Impurities in the water will make the wire unclean and affect the painting, and a smooth paint film cannot be formed. The chlorine content of the used water should be less than 5mg/l, and the conductivity should be less than 50μΩ/cm. Chloride ions will corrode the copper wire and the paint film after a period of time attached to the surface of the copper wire, resulting in black spots on the surface of the wire in the enameled wire paint film. To ensure quality, the sink must be cleaned regularly.
The water temperature in the sink is also required. High water temperature is conducive to the generation of water vapor to protect the copper wire during annealing, and the wire leaving the water tank is not easy to carry water, but it is not good for the cooling of the wire. Although the water temperature is low, it has a cooling effect, but there is a lot of water on the wire, which is not good for painting. Generally, the water temperature for thicker lines is lower and the water temperature for thinner lines is higher. When the copper wire makes the sound of vaporizing and splashing when the copper wire leaves the water, it means that the water temperature is too high. Generally, the thick wire is controlled at 50~60℃, the middle wire is controlled at 60~70℃, and the thin wire is controlled at 70~80℃. Due to the fast speed and serious water-carrying problem, the thin wire should be dried with hot air.