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Production practice of improving bar cut-to-length
Abstract: This paper introduces the production practice of improving the sizing rate of the bar production line of Pangang Metal Products Co., Ltd., through the control of the oxidation burning loss of the heating furnace, the negative deviation accuracy and the control of the line difference of the cutting specification, the improvement of the shearing accuracy of the double ruler, Through measures such as road improvement and billet length determination of various specifications, the bar sizing rate has gradually increased from an average of about 96% to 97% at the beginning to 99.2% to 99.3%.
The bar production line of Panzhihua Metal Products Co., Ltd. of Panzhihua Iron and Steel Group was relocated from Chengdu to Panzhihua. The price difference between non-fixed-length steel and fixed-length steel is large, and it is difficult to sell in the non-fixed-length market. Therefore, it has become one of the key issues to improve the fixed-length rate to a large extent. By comprehensively sorting out the rolling process that affects the fixed-length ratio, analyzing the reasons for non-sizing Through a series of measures such as process control and fixed length of casting billets, the fixed-length rate has gradually increased to 99.2% to 99.3%, and the finished product rate has also been improved.
1. Introduction of bar production line
According to the structural adjustment needs of Panzhihua Iron and Steel Group's production line, Panzhihua Iron and Steel Group relocated idle equipment and built a bar production line with an annual output of 600,000 tons in Panzhihua headquarters. The bar production line was commissioned on March 1, 2017 under thermal load. The bar product specifications are C>12 mm~C>40 mm ribbed steel bars, of which 012 mm specifications are rolled in three cuts, ①14mm~©18 mm specifications are rolled in two cuts, and the rest of the specifications are single-strand rolling. The main equipment consists of 1 regenerative push-steel heating furnace, 18 rolling mills, 3 flying shears, 1 cold shearing machine, 1 stepping tooth cooling bed, inspection and collection equipment, etc. The schematic diagram of the related process plane layout is shown in Figure 1.
2. Factors affecting the sizing rate and improvement measures
2.1, 3 times the shearing precision
The No. 3 double-foot flying shear of the bar production line is installed behind the 18 # finishing rolling unit. The shearing accuracy of the No. 3 flying shear is an important factor that directly affects the sizing rate. Since the speed of the finished bar passing through the No. 3 flying shear is about 16 m/s, the control of the No. 3 flying shear must be fast, timely and accurate. In actual production, it was found that the length of the No. 3 flying shears was unstable in shearing. The same multi-length length, the length of each steel changed greatly, resulting in a large waste of cutting heads and tails, which seriously affected the sizing rate.
The shearing accuracy of No. 3 flying shears is controlled and started by the hot metal detector, and the length of the double ruler is cut according to the set rolling speed, and the actual speed of the rolling piece is not measured. At the same time, the flying shear starting detection element is restricted by the on-site environment, and has poor anti-interference ability. To this end, modify the control logic, calculate the linear speed of the rolling piece through the actual speed of the final rolling motor and the working diameter of the rolling spoke, and use this as the actual linear speed E of the rolling piece, and then assign a manual correction window for correction to complete the calculation of the actual fixed-length length. Double ruler action to measure length requirements. To improve the start-stop time error of flying shears, a professional high-speed model proximity switch is used to ensure that the position of the shearing edge can achieve the purpose of accurate positioning and reduce the length change of the cutting head caused by the start and stop of the shearing edge. A camera is added at the end of the cooling bed to observe the length of the end of the steel after the cooling bed is flush with the spokes, and a warning is marked on the monitoring to monitor the double-scale length of the finished product to avoid non-scale expansion caused by equipment failures.
2.2. Improvement of cooling bed and spokes
At the beginning of production, the effect of the bars on the flush and spokes is not good, especially the splitting of small-sized ribbed steel bars is not good. When there are many active spokes in the aligned spokes, due to the poor rigidity of the small gauge bar, the double-length bar will bend after hitting the baffle; when there are few active spokes in the aligned spokes, the bar on the aligned spokes that hits the baffle first will immediately Stop, the bars that have not hit the baffle cannot move together due to lack of power. Improper setting of the alignment spoke speed will also result in bowing or inability to align. An important mechanism of the head-to-head spokes is: when the double-sized bar hits the baffle plate, it must slip reliably to ensure that the frictional force between the double-sized bar and the head-to-head spokes will not be too large.
The original flush spoke adopts a groove structure, the left side of the spoke is at an oblique angle of 60 degrees, the right side of the spoke is 34 degrees, and the horizontal section of the bottom spoke is very narrow. The two ribbed steel bars overlap, and the frictional resistance increases, making it difficult to achieve reliable slippage. To this end, change the left 60-degree oblique angle to vertical, increase the length of the straight section at the bottom of the spoke, increase the gap between the steel bars, and reduce the frictional resistance between the steel bars and the spokes. The schematic diagrams before and after the modification are shown in Figure 2 and Figure 3 shown. After the head-to-spoke structure is improved, the head-to-head effect is greatly improved. In addition, the HMI monitoring screen of the operating room is optimized, and a dialog box for speed control of the head and spoke is added. The main operator can timely modify the running speed of the head and spoke on the HMI monitoring screen, so as to realize the control of the speed of the spoke between bars of different specifications. , to ensure that the forward power of the active spokes can be adjusted, which basically eliminates the phenomenon that the steel bars cannot be aligned.
2.3. Strict negative deviation precision control
Ribbed steel bars of the same finished product specification and size, the same billet length, due to different dimensional accuracy, the length of the rolled finished product will be different, which will also affect the sizing rate. Combined with the market user needs of bar ribbed steel bars, our factory implements negative deviation control on ribbed steel bars. From pass design, rolling groove processing, rolling mill assembly accuracy, material type standardization operation, negative deviation target value, fixed bundle and fixed support, Carry out work in various aspects such as bale weight warning, so as to strictly control the accuracy of negative deviation.
The main control of negative deviation is to control the inner diameter and implement negative deviation design for the entire base circle of the finished product. In order to ensure the service life of the rolling groove, the processing depth of the transverse rib of the rolling groove is processed according to the large positive tolerance of 0.1~0.2 mm. Standardized operations are carried out on the material types of each pass, and the material type display panels and record display panels are made. Team members are required to strictly control the standard material types, conduct random inspections on the material types in each shift, and record the size of the material types randomly checked on the display panels. The assembly precision of the rolling mill is strictly controlled, and 12 new rolling mills with short stress are ordered. The new rolling mill can ensure that the radial clearance of the rolling mill is controlled within 0.2 mm, and the axial clearance is controlled within 0.1 mm. within. In terms of sampling, it is equipped with special sample measurement and weighing tools, and the sampling frequency and measurement methods are standardized. The bundles and supports are determined for each specification, and the upper and lower limits of the internal control of the deviation of the bundle weight are specified. Each post can monitor the bundle weight in a timely manner through the MES system, which plays a role in the early warning of the bundle weight, which is convenient for the rolling mill to adjust the size of the finished product in time and ensure the accuracy of the size. Stablize.
2.4. Strictly control the difference of cutting line
Rolled ribbed steel bar cutting specifications ①12 mm ~ ©18 mm, when there is a large line difference in the finished product geometry, it will not only affect the stability of the product quality, but also increase the length of the cutting head and tail when cutting to a fixed length, resulting in non-fixed length. increase in volume. In the strict control of the difference between the cutting lines, in addition to strengthening the processing accuracy of the rolling spokes, the service life of the rolling grooves, the quality of the rolling mill assembly and the alignment of the guides. Optimize the cutting specifications of 14 vertical box passes, increase the convexity of the groove bottom, and reduce the wear degree of the rolling groove. The splitting guide and the splitting wheel are changed from the original one-side fixed to the two-sided fixed, which reduces the failure caused by the axial movement of the splitting wheel. Before rolling, use iron wire to pass through the spoke slits on both sides of the rolling spoke to ensure that the deviation of the spoke slits on both sides is controlled within 0.1 mm. When controlling the difference between the spoke gaps on both sides, the employees ignored the 13 flat spokes at the beginning. After a period of production, it was found that the rolling stock was freely spread among the 13 flat spokes, and it was the key to ensure that the north and south spoke gaps of the rolled spokes were consistent. The rolling stock will appear wedge-shaped, which affects the filling degree of the 14 box-shaped holes. Through a series of technical improvements and strengthened management, the line difference of the cutting specification can be basically controlled within 100 mm.
2.5. Strictly control the length of the cutting head and tail
Under the condition of ensuring that the defects are clean and does not cause steel stacking in the rolling line, the lengths of the flying shearing head of Well 1, the flying shearing head and tail of Well 2 and the cold shearing head and tail of different specifications are formulated. The operator sets the leading coefficient and shearing length of the corresponding flying shears according to the linear speed and material size of the front rolling mill of Well 1 and No. 2 flying shears, and sets the shear compensation of the flying shears according to the actual situation. The length is reduced to the required range, the loss of metal in the process is reduced, and the control of the length of the double ruler is stable. See Table 1 for the head and tail lengths of the 1-well and 2-well flying shears and cold shears of various specifications of the bar.
2.6. Reduce heating and oxidation burning loss
In order to reduce the oxidative burning loss of the billet, reduce the heating temperature of the billet as much as possible, implement rapid heating, shorten the time of the billet in the furnace, and control the oxidizing atmosphere. At the same time, considering the load capacity of the equipment, the billet is burnt through, the temperature of the section is uniform, and the temperature of the tail of the billet is slightly higher than that of the head by 30 °C to ensure the temperature uniformity during the rolling process and lay the foundation for obtaining a higher finished product sizing rate.
2.7. Fixed length of billet
Since there is no weighing device for the slab in the steelmaking process, only the length can be controlled. On the basis of equipment optimization and improvement, precise control of size and specification, precise control of cutting head, and calculation of single weight in different casting periods of steelmaking, etc., the length of the billet is continuously optimized. After multiple rounds of continuous optimization and adjustment, the lengths of billets of different specifications are fixed to achieve a better billet weight.
3. Conclusion
Through measures such as improving the shearing accuracy of the double ruler, improving the alignment of the head and the spoke, the negative deviation accuracy and the control of the line difference of the cutting specifications, the length of the cutting head and the tail and the control of the oxidation burning loss, and the fixed length of each specification of the billet, the fixed length ratio of the bar has been improved from the rigid one. At the beginning, the average of about 96% to 97% was gradually increased to 99.2% to 99.3%, and the yield was also improved, and good economic benefits were achieved.
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15358968703
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15358968703