The quality of hot rolled wire rod produced by high speed wire mill usually includes two aspects: one is the dimension and shape of wire rod, that is, dimension accuracy and appearance appearance; 2 it is the immanent quality of wire rod, namely chemical composition, microcosmic organization and all sorts of performance. The former is mainly controlled by strip rolling technology, while the latter is seriously affected by upstream process besides rolling technology.
Any quality control must rely on strict and complete quality assurance system, on the guarantee ability of factory processes, on the scientific, accurate and timely measurement, analysis and feedback of the quality control system. High-speed wire rolling mill is a highly automated modern rolling equipment, and its quality control concept must focus on all the quality links of the whole system. In order to accurately judge and control defects, it is necessary to analyze the causes of defects clearly and try to eliminate them in the initial process. The sooner the defects are cleaned up or the steel discarded, the less the loss.
rolling mill,The precision of finishing mill is very high, and the quality of roll is very good. When the speed control system is sensitive, the pass rolling system is reasonable, and the adjustment technology is skilled, the precision of the wire rod produced by it can greatly exceed the precision of the old wire rod.
Higher dimensional accuracy is one of the most effective ways to save steel, and it is particularly important to use the wire rod of high grade steel as the raw material for deep processing. If calculated according to the nominal size, the first deformation of the design drawing process, if delivered according to the allowable diameter positive deviation limit of the past standard, the first deformation exceeds the design value of more than 1/3, for high carbon steel, this will reach its fracture limit. For the manufacture of non – tempered high strength standard parts, it will cause serious difficulties to the cold pier process, produce a lot of waste products and damage to the mold. Rolling to the negative limit allowed by past standards also poses problems for these customers. According to this, YB4027-91 also stipulates that raw materials for manufacturing standard parts must be delivered with grade B and C precision. Some famous manufacturers in the world stipulate that the diameter deviation of the “equivalent circle” of the wire rod is less than the nominal diameter ±0.15mm, so as to limit the fluctuation of the cross-sectional area.
Another index of dimensional accuracy is the difference between the maximum diameter and the minimum diameter of the same section, which is generally defined as 80% of the sum of the absolute values of the allowable positive and negative deviations. When the roundness exceeds a certain limit, it will do great harm to the drawing process. In the same section of the mutual vertical direction of the deformation is different, will cause the mold pressure difference, which not only damage the lubrication effect, but also cause the straight section of the mold in the direction of uneven wear, which has a serious impact on the product yield and die life.rolling mill
There is no problem when the product precision of high-speed wire mill reaches ±0.15mm. It is generally considered that the flexible wire precision reaches ±0.25mm, which can completely meet the requirements. Although high-speed wire products can reach ±0.1mm, but this is not economical. In addition to the regular roll change, but also in the guide and guard, pass, rolling mill, transmission, electric control and other aspects to do a lot of work, can only make the wire in a period of time to maintain the accuracy of ±0.1mm.
Rolling process is the main link to control dimensional accuracy. The main factors that affect the accuracy are temperature, tension, pass design, machining accuracy of roller and technological equipment, wear of hole and guide, guide installation and adjustment of rolling mill, stiffness and adjustment accuracy of rolling mill, reliability of roller bearing and the level and accuracy of fly-by control, etc.
The change of temperature will affect the deformation resistance and width of the rolled parts, resulting in the fluctuation of the rolled parts size. The change of rolling temperature is related to mill process design, layout and cold control equipment. The high speed wire mill does not have a large number of long loggers like the horizontal mill. The serious temperature drop of these loggers is the main reason for the head and tail temperature difference of the horizontal wire mill. In order to realize tension-free rolling in high speed wire mill, some adjusting loggers are set up, which do not constitute temperature drop. Therefore, the temperature change of high-speed wire mill is mainly caused by operating factors, such as uneven heating, controlled cooling change, and the stop of rolling parts, so the rolling temperature of high-speed wire mill must be strictly controlled to make the rolling temperature of the same strip and batch as consistent as possible.
Tension is the main factor affecting the dimensional accuracy of hot rolled wire. But tension is inevitable in high speed continuous rolling of small rolling parts. It is impossible to pile up looper in rough rolling because the distance between rolling mills is not large. The purpose of continuous wire rolling is to realize the micro-tension or tension-free rolling as much as possible. The size fluctuation of rough-rolling parts can only be eliminated by 4/5 to the finished product, and the elimination ability of finishing rolling is only 50%. So the tension control in the whole rolling line in every link can not be ignored. In general, a continuous rolling mill, such as rough rolling or rolling as a design unit, the design value of each unit should not be more than 1%, in order to smooth rolling, and draw steel is placed between the first and second continuous rolling mill
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