Solution to the problem of oxidation, discoloration and blackening of copper wire drawing oil during wire drawing
October 30, 2022
In the process of copper wire drawing in China's cable industry, copper material and enamelled wire industry, oxidation discoloration and blackening are common, especially in spring and summer. With the popularization of the existing high-speed machine, the wire drawing speed has been greatly improved, and the contradiction has become increasingly prominent. This paper focuses on the analysis of the temperature produced during copper wire drawing, which affects the oxidation and lubrication. The temperature of wire rod and the friction between wire rod and die during wire drawing directly affect the lubrication effect.
Therefore, the following aspects can be analyzed: First, the fat content of lubricating oil; Second, stretching speed and use temperature; The third is the stretching force; Fourth, how to prevent oxidation and blackening. 1. Fat volume The grease content of drawing oil produced by almost every manufacturer is different, and the grease content, viscosity and use temperature of drawing oil are the main reasons affecting the lubrication effect. It is further analyzed as follows: The so-called fat content can be simply understood as the thickness of the oil film formed in the deformation area during the wire drawing process. If the fat content of the drawing emulsion is too high, the oil film formed in the deformation area during the wire drawing process will be too thick, and the following adverse conditions will occur: A. The oil film is too thick, and the drawn copper wire loses its surface gloss B. This will cause uneven and incomplete oil film locally, increase the direct contact area, increase the friction force and make the surface of the product pulled out have oil spots. C. In addition, if the fat content of the emulsion is too high, some of it will be free, causing the emulsion to delaminate and adhere to the copper powder, suspend on the emulsion, stick to the mold hole, cause plugging of the mold hole, and then break the wire. In serious cases, it will directly lead to the deterioration of the lubricating oil, resulting in the replacement of the whole pool and loss. If the fat content of wire drawing fluid is too low, the oil film must be very thin or cannot form a complete oil film. In the process of wire drawing, it is easy to cause cracks, so that the drawn copper wire can not play the role of lubrication when contacting with the mold, and the friction force is increased, resulting in the following adverse conditions: A. Increased tensile force will lead to frequent wire breakage B. Friction increases, heat is generated, oil temperature increases, and oil consumption increases C. The surface quality of the drawn wire is reduced D. Rapid loss of moulds and tower wheels and increase of copper powder Therefore, when selecting copper wire drawing lubricant, we should determine the amount of fat content required according to the wire diameter of the specifications drawn by our factory. The concentration of copper wire drawing lubricant is different from the content of fat. Generally, the fat content of copper wire drawing lubricant is 70-80%, which means that the fat content in every 100kg wire drawing oil is only 70-80kg. Therefore, some users adjust the emulsified oil according to the concentration recommended in the user manual, It is wrong to assume that 10 kg of oil plus 90 kg of water is fat and has reached 10%. Actually, the fat content is only 7~8 kg, so it is necessary to use a saccharometer to detect the fat content. The method is as follows: at room temperature 24 ℃, add 10ml of drawing oil crude oil into a 100ml measuring cylinder with a plug, then add distilled water to the scale of 100ml, plug the cylinder cover, and shake it up and down about 20 times After the filling is even, take the saccharometer, wash the mirror surface with clean water and dry it with soft paper, drop a few drops of evenly prepared emulsion on the mirror surface, and wipe it off after cleaning once. Add another 1-2 drops onto the mirror of the saccharometer, and observe it against the light. The obtained reading multiplied by 10 times is the fat content of this copper wire drawing oil. 2. Temperature and tensile speed The use temperature of wire drawing oil and the lubrication effect are mutually dependent. If the temperature is too low, the newly added wire drawing oil is not easy to emulsify, and the particle mobility of the emulsion will decline, which is not conducive to lubrication. On the contrary, if the temperature is too high, the grease is easy to decompose, suspended on the emulsion, and the lubrication effect is reduced. If the temperature of the emulsion is further increased without taking effective measures to control its temperature, the oil film in the deformation zone may break, leading to the chemical chain breaking in the drawing oil process formula. In this way, the friction coefficient will inevitably increase greatly. Under the vicious cycle, not only the surface quality of the product will decline, but also the emulsion temperature will rise rapidly, leading to the increase of the scrap rate. Therefore, maintaining the cooling state of high-speed wire drawing emulsion cannot be ignored. The temperature shall be controlled below the oil film rupture point, and the cooling tower or heat exchanger shall be used for temperature stabilization. 3. Tensile force During the normal operation of wire drawing, the higher the wire drawing speed is, the easier it is to bring the emulsion into the die hole and increase the pressure of the lubricating fluid in the die. Therefore, the thickness of the lubricating film is increased, thereby reducing the friction coefficient. During stretching, the greater the load, the greater the pressure. As a result, the emulsion is easy to be squeezed out of the deformation zone, thus reducing the thickness of the lubricating oil film, increasing its actual contact area, and thus increasing the friction coefficient. The influence of tensile force on lubrication effect: the greater the tensile force, the greater the extreme pressure property generated when drawing wire rods of the same weight or length, and the more work converted into heat. At this time, the temperature rise of wire is also greater. Therefore, the factors affecting the tensile force will cause deformation resistance, and the tensile force will be increased if the die is damaged and the drawing continues. The greater the tensile force is, the greater the friction loss will be, and the friction loss will be converted into heat energy, which will increase the temperature of the wire surface and cause the emulsion oil temperature to increase, which cannot be ignored. 4. How to prevent oxidation and blackening
There are many reasons for copper wire blackening and oxidation: 1) The area of the drawing emulsified oil pool is small, the return pipe is short and sealed, resulting in slow heat dissipation and high emulsion oil temperature. 2) It is caused by copper wire annealing. First, tap water and groundwater are generally used as the cooling water for continuous withdrawal. Because the water quality varies from place to place, the PH value of the water quality in some areas is low, only 5.5-5.0. All the anti-oxidation oil film in the original emulsion has been cleaned, and the annealed copper wire is easy to be oxidized and blackened; Second, the finished copper wire drawn by an ordinary wire drawing machine is annealed on another annealing line, and the cooling water is also free of antioxidants. The oxygen resistance time is short, and oxidation and blackening will soon occur. 3) Some old factories still use annealing cylinders for annealing, and oxidation and blackening can also be caused by the following reasons: First, the nuts of the annealing cylinder are not tightened, and air leaks after flushing carbon dioxide or high-purity nitrogen; Second, the copper wire temperature at the cylinder outlet is too high, exceeding 30 ℃; Third, the maintenance of wire drawing emulsion is not enough, and the PH value is too low; These situations are common when the temperature is high in summer. The emulsion will be lost if it is used continuously, and the loss is fast when the temperature is high. If new crude oil is not replenished in time, the fat content is small at this time. In addition, the temperature of the emulsion may also exceed 45 ℃ when the temperature is high, which is easy to cause oxidation and blackening. 4) Another situation is that because high-speed wire drawing is widely used at present, its speed is increased, and the relative heat dissipation time is reduced, which brings a certain space and time for oxidation. Therefore, it is recommended that manufacturers pay more attention to the fat content of the emulsion, whether the use temperature, PH value, etc. are appropriate. In the yellow and rainy seasons of spring, bacteria breed rapidly, so bactericidal and antimycotic agents can be used, and in summer, antioxidant agents can be used to solve oxidation Blackening is not a problem.
