1. Problems caused by improper selection of working cone angle
When the wire is pulled, the working cone angle is too large (corresponding to the compression ratio is too small), so that the contact point of the wire into the drawing die is too close to the sizing tape. In this example, the deformation zone is relatively short, which accelerates the deformation rate of the wire and generates a large amount of heat and easily leads to lubrication failure. If the cooling is poor, it will affect the structure of the wire and increase the consumption of the mold. If the mold angle is larger or the compression ratio is smaller, the contact point will be closer to the sizing belt.
During the flow of the wire to the sizing belt, due to the influence of the taper angle, the wire is difficult to smoothly transition to the sizing area, which easily causes the wire to be concave and causes the diameter to decrease. If the material strength is too low, it will also cause a diameter reduction or elliptical phenomenon. Although the lubrication zone is relatively long and provides good lubrication at the beginning, it reduces the lubrication pressure on the contact surface and creates a vortex effect, causing the lubricant to flow back out of the die hole and weaken the lubrication.
In addition, various adverse effects caused by deformation eventually lead to lubrication failure and surface cracks and scratches, and the mold consumption is intensified, and the wire diameter is difficult to control. The working cone angle is too small, causing the incoming line contact point to be close to the upper end of the working cone, so that the deformation area is relatively lengthened, and the residual work generated by the wire drawing machine on the steel wire is increased, generating a large amount of heat, and increasing the power consumption of the wire drawing machine.
In addition, the lubrication zone is reduced, the lubrication effect is weakened, and the lubricating powder on the surface of the residual wire is exhausted at a certain point in the deformation zone. When the tensile stress is too large, axial elongation is likely to occur in the sizing area, and the diameter reduction and elliptic problems occur, which will eventually lead to poor lubrication, metal chipping, broken wire, overheating, and shrinkage.
2. Center break and herringbone crack
The central fracture and the herringbone crack phenomenon have been considered to be problems caused by raw materials after discovery. However, it was not until 1930 that Fenhi-SOIl pointed out that the central fault and the "human" crack were caused by the unreasonable arrangement of the drawing process (pass compression ratio, drawing pass).
During the drawing of the wire, the internal structure of the wire extends along the axial direction, and the velocity of the tissue on the surface of the wire is greater than the flow of the internal tissue, and the tensile stress in the axial direction is generated in the core. When the axial tensile stress exceeds the tensile strength of the drawn material, a "human" crack will occur in the core of the material, and in the severe case, a cup cone fracture (columnar) will occur. Therefore, in the development of the drawing process, the drawing process should be reasonably arranged according to the type of drawing material and wire drawing dies
3. Residual stress and surface work hardening
Residual stress and work hardening are caused by residual work. The residual work hardens the hardening of the material, which seriously causes the surface of the wire to crack and peel, which is difficult to draw. If the process arrangement is unreasonable, the residual work will increase, and the energy consumption of the equipment will be increased, so that the production cost will increase. Using Wistriech's (determined by the compression ratio and the mold cone angle) parameters to guide the process arrangement, it can avoid generating more residual work.
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