In the stretching process of wire rod, the process conditions that affect the service life of the drawing die mainly include: the effect of reverse tension, the compressibility of passes, the lubricant and the surface quality of the wire. During the stretching process, the wire rod is subjected to a variety of forces, including positive pressure, friction, pull-out and anti-tension of the die wall. The mechanical reason for the frequent occurrence of annular wear grooves at the inlet of the wire drawing die is that the compressive stress on the die wall gradually decreases from the inlet to the outlet of the drawing die, and the maximum compressive stress occurs at the time of the inlet.
The effect of anti-tension force can reduce the compressive stress at the inlet of the drawing die, which is conducive to the lubricant entering the working area, reducing the friction between the wire rod and the die wall, slowing down the annular wear and die breakage, thereby prolonging the service life of the wire drawing die. However, excessive anti-tension will increase the pull-out stress when pulling the wire, which can easily lead to the shrinkage or breakage of the wire.
The pass compression ratio is another factor that affects the service life of the drawing die. All other tensile conditions being the same, the greater the compressive stress on the iw drawing die wall, the greater the frictional stress, resulting in more severe die wear. Therefore, under the allowable tensile conditions, increasing the compressive ratio of the passes and appropriately reducing the working cone angle can reduce the compressive stress on the die wall and help to improve the service life of the wire drawing die.
The quality and supply of lubricants also have an impact on the service life of the drawing dies. The lubricant should have oil-based stability and good emulsification, have excellent lubrication, cooling and cleaning properties, and be easy to filter and precipitate copper powder to maintain optimal lubrication. By forming a film that can withstand high pressures without being damaged, the friction in the work area is reduced, thereby increasing the service life of the wire drawing die. The pH stability of the lubricant has an important impact on the lubrication effect. Precipitation of copper powder in the emulsion reduces the amount of fat in the lubricant and increases the free alkali content, which reduces lubricating properties. When the emulsion is unstable and the fat content is too high, it will cause the emulsion to stratify, and the fat components with fine copper powder will float on the emulsion, making the copper powder difficult to precipitate and filter, causing the drawing die hole to be blocked, resulting in poor lubrication.
The surface quality of the wire rod also has an impact on the service life of the wire drawing die. If there is an oxide layer, sand or other impurities on the surface of the wire, it will adversely affect the service life of the drawing die. Therefore, the heavily oxidized wire needs to be pickled before stretching. In addition, when stacking blanks, pay attention to the cleanliness of the stacking site and avoid contact with sand and other impurities.
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