Drawing principle and matching

In the wire drawing field, people commonly use sliding water tank wire drawing machines, that is, there is a gap between the wire speed of the reel and the steel wire, so that the steel wire can slip at the contact surface with the reel drum, thereby generating sliding friction force. This force drives the steel wire in each mold. Before and after drawing.

The first is the efficiency of drawing production. With reference to the calculation of steel wire production efficiency, the most critical factors are the utilization rate of the machine, the size of the outlet, and the speed of the fastest take-up. If the production efficiency is calculated in terms of kilograms per hour, then the production efficiency = line speed * cross section area of ​​copper clad steel * density of copper clad steel * machine utilization rate. Machine utilization refers to the time during which the machine actually runs at full speed within 24 hours. If statistics are obtained, the maximum and minimum utilization error can be obtained on the premise of 100% utilization, or classification statistics can be made. Then we can get the average error. To determine the efficiency of wire drawing production.

Followed by the mechanism of drawing, with reference to the sliding process of the composite wire, we know that the metal plastic deformation is generally achieved by the movement of dislocations on the sliding surface. When the multi-crystals are deformed, they must also coordinate the grains. To proceed. Due to the complexity and inhomogeneity of the grain boundaries and the inhomogeneity of the original crystal grains, the plastic deformation will not be absolutely uniform within the metal. This non-uniformity of deformation will affect the subsequent deformation of the copper clad steel wire. .

In the cold deformation, the metal will have a strain-strengthening effect. Because the strain hardening index of the copper layer is larger than that of the steel core, during the drawing process, the strain hardening of the copper layer is more obvious (as the saying goes, the hardening becomes faster), ie The stress required to continue deformation is higher. Therefore, the copper layer is not destroyed under the action of a large stress during the drawing process of the copper clad steel. At the same time, due to the existence of strain hardening, the amount of deformation increases. The deformation will gradually become even. Korean scientific and technical workers discovered through research that from the perspective of the work area, the total deformation will lead to different changes in the proportion of copper layer, which is directly related to the strain enhancement. In our company's conventional production, through analysis and statistics found that the copper layer changes almost Can be ignored.

Once again, it is a working problem of the mold. Learning from the cutaway drawings provided by the mold supplier's sample, it can be known that the internal structure of the mold is mainly divided into six areas, entrance area, lubrication area, compression area, calibrating area, safety angle, exit area, and the most critical It is the stress of the yield compression of the compression zone and the friction force of the sizing zone. The drawing stress through the die and the yield stress of the copper clad steel itself, the compression ratio, the working area angle, the material friction coefficient, and the post-tension stress are determined. The yield stress of copper-clad steel itself is also based on the principle of addition. The yield stress of copper and the yield stress of steel are cumulatively calculated as the contribution ratio.

The final step is to complete the drawing by working on the tower wheel on the equipment. As mentioned above, sliding wire drawing basically relies on sliding friction, which means that the movement speed of copper-clad steel on the tower wheel is smaller than the rotation speed of the tower wheel, so that it is always in the relaxed state at the entry end (the rear tension is 0 ), on the other hand, if the cable end is tightened, it will increase the back tension so as to increase the front tension and easily lead to disconnection. The specific calculation process participated in Xuan Tianpeng's thesis on the basic conditions of sliding wire drawing. The final result is that the elongation factor of the drawing die wire should be greater than the gradient of the adjacent tower wheel, expressed as μ/ε>1, so that the wire rod is drawn. The process is sometimes tightly wound around the tower wheel to advance synchronously, sometimes loosening and slipping. Of course, this will cause wear on the surface of the tower wheel and increase power loss.

The ratio of the line speed of the tower wheel to the speed at which the wire is drawn is called the slip coefficient; the difference between the speed at which the tower wheel rotates and the speed at which the wire is drawn is the absolute slip; the absolute slip and the tower wheel The ratio of the linear speed of rotation is called the slip rate; the cumulative slip coefficient is the multiplication of each pass slip coefficient, and the cumulative slip rate is 1-1/accumulated slip coefficient.

The data shows that the sliding coefficient is generally between 1.02-1.10. The copper-clad steel and the mold have a good lubrication effect, and the relative wear with the tower wheel is also small. Therefore, some scholars suggest that the sliding coefficient should be within 1.01-1.04. We tend to 1.02.

In the actual drawing process, because the slide is preset for each pass, the farther the pass from the finished mold, the greater the slippage between the tower wheel and the copper clad steel wire, and the more serious the surface wear of the tower wheel, This non-uniformity of sliding will shorten the service life of the tower wheel. Therefore, a cumulative sliding effect must be considered. It is propagated and accumulate in a continuous manner from the start of the finished die to the incoming direction. The greater the slip, the more the wear is. The more serious, the earlier the pass, the thicker the wire diameter, the greater the pull-out load, the greater the power loss, and the more severe the damage between the wire and the tower wheel, causing the tower wheel to grind the groove, or the wire during drawing. Throw up and drive the mold to shake, the wire is not evenly stressed, bamboo-like or broken.

Generally, the sliding mode method is used to match the mold. From the 1/3 of the exit point, the sliding rate is maintained at 1.04-1.05. From the 1/3 of the exit point to the entrance, the sliding rate is gradually reduced, and finally it is reduced to 1.01. The arrow diagram is represented as :

1.01-1.01-1.01-1.02-1.03-1.04-1.04-1.04-1.05

At the time of mold matching, there is a concept of surface area reduction corresponding to the elongation, that is, the ratio of area reduction. For example, from 1.1 to 1.02, the area ratio is 1.1*1.1:1.02*1.02=1.163, the incoming line is 1.1, the outgoing line is 1.02, but the time flow is the same, the change in the area is the change in length, and the incoming line area is 1.163 times of the outlet area, then the length of the outlet line is 1.163 times the length of the line, 16.3% is the elongation rate, and the reduction rate is 14.02%. The accurate matching method is the elongation rate, and sometimes it also refers to the reduction rate. Matching, because the reduction rate is based on the entry line, and the elongation rate is based on the exit line, the reduction rate must be greater than the elongation rate, and the slip factor is greater. The distribution law of the elongation of each pass is generally the lower first, because the strength of the joint of the wire blank is low, the wire rod is not straight, the surface is rough, and the thickness is not uniform, so the safety factor should be larger. The second and third tracks can be higher, because after the first drawing, various factors affecting the safety factor are greatly reduced. At the same time, the degree of deformation hardening of the metal is also very small. At this time, the plasticity of the metal can be fully utilized. In each subsequent pass, the elongation can decrease one by one. This is because the degree of deformation hardening increases, the wire diameter decreases, and the metal plasticity decreases. The influence of internal defects and external conditions on the safety factor also gradually increases.

The tower wheel gradient (also known as the tower pole ratio) of our ordinary wire drawing machine is approximately 10-12%, plus the sliding rate, generally the ratio is set to 13-15%, according to the outlet diameter of the adjacent mold. Size, we can directly calculate the reduction rate or elongation, or, in turn, know the size of a mold, known elongation, you can calculate the size of the previous mold. It is worth mentioning that, when drawing the cord, the partial compression of the registration cord mold must not be too large. Otherwise, the tension of the constant speed wheel is too large to pull the cord, causing the cord diameter to shrink and the elongation to decrease.