1 Problems caused by improper selection of working cone angle
When drawing the wire, the working taper angle is too large (equivalent to too small compression rate), so that the contact point of the wire entering the drawing die is too close to the sizing belt (for example, a 14% die produces a 16% compression rate). In this example, the relatively short deformation zone will speed up the wire deformation rate and generate a lot of heat, which will easily lead 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 die angle is larger or the compression rate is smaller, the contact point will be closer to the sizing belt. When the wire flows to the sizing belt, it is difficult for the wire to smoothly transition to the sizing area due to the influence of the taper angle, which is easy to cause the wire to be inside Concave, resulting in diameter reduction, if the material strength is too low, it will also cause diameter reduction or ellipse. Although the lubrication zone is relatively longer and can provide good lubrication at the beginning, it will reduce the lubrication pressure of the contact surface and produce a vortex effect, causing the lubricating powder to flow out of the die hole in the opposite direction, weakening the lubrication effect, and all kinds of deformation caused by deformation The undesirable effect will eventually lead to lubrication failure, surface cracks, scratches, increased mold consumption, and difficulty in controlling the wire diameter. The working cone angle is too small, which leads to the contact point of the incoming line close to the upper end of the working cone, which makes the deformation zone relatively longer, which increases the residual work generated by the wire drawing machine on the steel wire, generates a lot of heat, and increases the power consumption of the wire drawing machine. In addition, the lubrication area is reduced and the lubrication effect is weakened. At a certain point in the deformation area, the remaining lubricating powder on the surface of the wire will be exhausted. When the tensile stress is too large, it is easy to cause axial elongation in the sizing area, resulting in diameter reduction and ellipse problems, which will eventually lead to poor lubrication, metal chips, wire breakage, overheating, and wire shrinkage.
2 Center fracture and herringbone crack phenomenon
The central fracture and "herringbone" cracks have been considered to be caused by raw materials after they were discovered, but it was not until 1930 that Fenhi-SOIl pointed out that the central fracture and "herringbone" cracks were caused by the drawing process (pass compression rate). , Drawing passes) caused by unreasonable arrangements. In the process of wire drawing, the internal tissue of the wire extends along the axial direction, and the flow rate of the tissue on the surface of the wire is greater than the flow of the internal tissue, and the axial tensile stress is generated in the core. When the axial tensile stress exceeds the drawn material
When the tensile strength is high, a "herringbone" crack will occur in the core of the material, and in severe cases, a cup-cone fracture (columnar) will occur. Therefore, the drawing process should be reasonably arranged according to the drawing material and the type of drawing die when formulating the drawing process.
3 Residual stress and surface work hardening phenomenon
Residual stress and work hardening are caused by residual work. Residual work aggravates the hardening of the material, which can severely cause the surface of the wire to crack and peel, making it difficult to draw. If the process arrangement is unreasonable, the residual work will increase, and the energy consumption of the equipment will be increased, which will increase the production cost. Use Wistreich to obtain the △ (determined by the compression rate and the mold cone angle) parameters to guide the process arrangement, which can avoid generating more residual work. The △ data is shown in Table 1.
In the past, it has been thought that the △ value for steel wire drawing is generally between 2 and 3. If △ is too large (that is, the die angle is too large or the compression rate is too small), more residual work will be generated and greater uneven deformation will occur; If △ is too small (that is, the die angle is small or the compression rate is too large), more frictional heat will be generated, so if △ is too large or too small, it means that the drawing process arrangement is unreasonable. In recent years, the foreign drawing process arrangement △ generally tends to be 1.5 or less (decreasing the die angle or increasing the compression rate will reduce the value of △). Thomas Maxwell believes that the contact length between the working cone of the mold and the steel wire should be 72% to 100% of the diameter of the sizing belt. At this time, the range of △ is between 1 and 1.5, which also tends to be too small for the value of △ Give a strong proof, because a small △ can minimize the residual work, and reduce the degree of uneven deformation and core fracture, and when the lubricant performance is very good, it will reduce the friction coefficient, that is, reduce the friction work produce.
Summary: As the basic tool for metal product deformation, no matter how its shape and structure change, its purpose is to ensure production efficiency and product quality. Therefore, product manufacturers should establish strict mold repair and inspection methods, and formulate reasonable drawing The quality of the products can only be guaranteed by drawing craftsmanship and strict quality control.
