Mechanical descaling and chemical pickling two methods
Shelling descaling cold heading steel strip removal of iron oxide plate process stripping light, descaling, mechanical descaling and chemical pickling two methods. Mechanical descaling wire rod to replace the chemical pickling process, both to improve productivity, but also reduce environmental pollution. This descaling process, including bending method (commonly used round groove with triangular groove repeatedly curved rod), such as nine spray method, descaling better, but can not make the residual iron scale to clean (iron oxide scale removal rate was 97% ), Especially in the case of strong scale adherence, mechanical scale removal is subject to the use of carbon steel wire rod for low-strength fasteners (grade 6.8 or less) due to the influence of the thickness, the structure and the stress state of the scale. High-strength fasteners (greater than or equal to 8.8) with wire rod in the mechanical descaling, in addition to net all the iron oxide skin, and then through the chemical pickling process composite descaling. For low carbon steel wire rod, the mechanical descaling residual iron easily lead to uneven wear die grading. When the die hole pull due to the wire rod friction outer temperature when the metal adhesion, so that the wire rod surface longitudinal grain marks, wire rod cold heading flange bolts or cylindrical head screws, the head microcrack causes, Over 95% is caused by scratches on the wire surface during drawing. Therefore, the mechanical descaling method should not be used for high-speed drawing.
Fourth, the drawing and drawing process has two purposes, one is the size of the restructuring of raw materials; the second is through the role of deformation to make fasteners to obtain basic mechanical properties, for medium carbon steel, carbon steel also has a purpose, namely Is controlled by the wire rod cooling obtained flake cementite in the process of drawing as much as possible Crack, for the subsequent ball (softening) annealing granular cementite get ready, however, some manufacturers to reduce costs, Any reduction in drawing pass, excessive reduction rate increases the work hardening tendency of the wire rod, a direct impact on the wire rod cold heading performance. If the reduction of the rate of distribution of each channel is inappropriate, but also make the wire rod in the drawing process to produce torsion cracks, which along the longitudinal distribution of the steel, the cycle of certain cracks exposed in the cold wire during heading. In addition, the drawing process, such as lubrication is not good, can also cause cold-drawn wire rod regularly appear horizontal cracks. Wire rod out of the wire rod die at the same time the tangential direction and the drawing die is not the same heart, will lead to drawing die unilateral hole type of wear and tear increase, so that the hole out of round, resulting in uneven circumferential drawing wire deformation, so that Out of roundness of the steel wire in the cold heading process of cross-sectional stress unevenly affect the rate of cold heading. Wire rod drawing process, the excessive part of the rate of reduction of the surface quality of steel wire deterioration, and too low reduction rate is not conducive to flake cementite crushing, it is difficult to obtain as much granular cementite , That is, the rate of cementite is low, and the cold heading performance of the steel wire is extremely unfavorable. The bar and wire rod produced by the drawing method are partially controlled in the range of 10% -15%.
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