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Analysis and control measures of buckle head in rolling process of wide and thick plate

Abstract: This paper mainly analyzes the reasons why the head and tail of the rolled piece often buckle in the production process of the 4300 wide and thick plate production line of Laiwu Iron and Steel Co., LTD., and gives adjustment measures according to the production practice, which has certain guiding significance for the actual production on site.

Since it was put into operation in 2010, Laigang Wide and thick plate plant has successfully produced construction machinery steel, ship plate steel, wear-resistant steel, high value-added pipeline steel and other products. Our factory from the commissioning to the production process, many times encountered the phenomenon of rolled buckle head, this phenomenon more appears in the finishing mill area, in the rolling process, once the rolled piece produced tilt or buckle head, it is easy to collide with the equipment, not only seriously damage the equipment, but also affect the mill operation rate, output and yield.

1、 The reason of buckle warping head of rolled piece

Rolling tip is a typical thermodynamic coupling problem in the rolling process of wide and thick plate. There are many influencing factors, such as rolling tip in thickness direction, uneven distribution of lower surface temperature, different reduction rate, inconsistent friction conditions of rolling piece, and different linear speed of roll surface caused by different diameter of upper and lower rolls. According to the actual production situation of wide and thick plate factory, the main influencing factors of buckle head are analyzed.

1.1 Effect of temperature

Theoretically, under normal circumstances, there are two rolls of the same diameter at the theoretical rolling height, and the flat head should be produced at the same rolling speed. However, in the production process, the difference between the upper and lower surface temperatures of the slab is one of the reasons that affect the buckle of the slab head. If the lower surface temperature is higher than the upper surface, other influencing factors will be ignored at this time. The metal on the lower surface of the slab is easy to deform and the metal flow speed is fast. Otherwise, it should be buttoned. The causes of the temperature deviation of the upper and lower surfaces of the slab include the temperature difference generated during the heating process of the slab, the temperature difference generated when the slab is exposed to the air, the temperature difference caused by the uneven cooling of the upper and lower surfaces of the slab when the slab is descaled, and the temperature difference generated during the transport of the slab on the roller table.

1.2 Effect of rolling line

According to the experience and rolling principle analysis, when the actual rolling line is higher than the theoretical rolling line, the plate passing through the rolling mill is easy to produce a buckle, because the lower roll of the upper roll is greater than the lower roll of the extension of the upper surface of the plate is greater than the lower surface of the extension, so the buckle is produced, and vice versa.

1.3 The influence of pass reduction rate of rolled piece

In the case of temperature difference between the upper and lower surfaces of the slab, the influence of the reduction rate on the upwarping of the slab must be considered. The reduction rate is one of the most important rolling parameters used to adjust the shape of slab rolling mill in asymmetric rolling. It has been proved by practice that it is very direct and effective to adjust the pass reduction rate and restrain the warping of rolled pieces in the production process. On the premise of meeting the requirements of rolling process, the phenomenon of warping of rolled parts can be reduced by making appropriate rolling schedule.

1.4 Influence of roller speed difference

In normal rolling process, the diameter of the upper and lower work rolls is usually not equal. Because the speed of the upper and lower surface of the rolled piece is related to the speed of the upper and lower rolls. When the diameter of the upper work roll is greater than the diameter of the lower work roll, and other deformation conditions are the same, the speed of the upper surface of the rolled piece must be greater than the speed of the lower surface, resulting in the rolled piece of the buckle, vice versa; The upper and lower work rolls of the finishing mill are driven separately by two main motors. Due to the different characteristics and speed control of the two main motors, the speed and torque of the upper and lower work rollers are different. Even if the speed control system parameters of the upper and lower roller main motor are the same, due to the difference in the natural mechanical characteristics of the two main motors, the speed difference of the upper and lower work rollers will cause warping of the rolled parts.

2、Control measures for buckle warping head of rolled piece

In the actual production, the reasons affecting the buckle of rolled pieces are complicated, and the interaction between many factors makes it difficult to restrain the buckle of a single factor. In view of this situation, it is necessary to comprehensively consider the process, equipment, electricity, model and other aspects to solve. In the actual production process, our factory mainly adopts the following methods to control the phenomenon of rolled buckle head.

1) Improve the uniformity of rolling temperature. First of all, the heating furnace adopts the two-stage mode to burn steel, which ensures the uniformity of the temperature of the rolled parts. Secondly, in the rolling process, the leakage of the cooling water of the upper work roll is reduced, especially for the control rolled steel plate, and the number of descaling passes is reduced as much as possible during the finishing rolling. In addition, as permitted by the equipment, the use ratio of the upper and lower roll cooling water is appropriately changed.

2) Reasonable development of rolling process regulations, optimization of rolling model, to ensure the flatness of the steel plate. In actual production, according to the existing rolling technology, summarize the shortcomings, constantly optimize the rolling model, make different rolling technology according to different steel grades, rationally distribute the rolling force and the reduction amount of each pass. Through discussions with Siemens technicians and automation personnel, control functions such as "minimum number of finishing passes", "maximum rolling force at last pass" and "maximum reduction amount of smoothing pass" have been added to the rolling model. The "minimum number of finishing passes" is mainly used to control the crown of the finished steel plate, the finishing rolling temperature and the wave shape of the steel plate. The "maximum rolling force of last pass" mainly controls the rolling force of finishing pass, controls the deformation zone of head and tail is too large, and ensures the flatness of the steel plate; "Last pass reduction amount" is to control the leveling pass value in 0~ 8mm, which plays a leveling role. At present, this procedure is mainly for steel plates with the target thickness of 30 mm and above. By optimizing the rolling model, the buckle head of rolled parts has been reduced to a great extent.

3) At the instant stage of biting, the buckle head is controlled by optimizing the SKI function. SKI is also known as sleigh rolling, that is, adjusting the speed difference of the upper and lower work rollers to control the buckle and tip of the steel plate. The main motor of the upper and lower work rollers in our factory adopts a separate drive. According to the rolling principle, allospeed rolling can effectively improve the shape of the head. If SKI is positive, increase the tilt of rolled parts or reduce the degree of buttoning. (V is the speed of the upper work roll in finishing rolling; Under V is the speed of the lower work roll); We optimize the SKI adjustable length, that is, the adjustable length can be selected for each roll pass. The SKI value is adjusted according to the actual shape of the steel plate on site, which greatly reduces the appearance of the buckle of the rolled piece.

4) Our factory's AGC hydraulic cylinder in the lower part of the rolling mill, can properly adjust the height of the rolling line to inhibit the phenomenon of buckling head in the rolling process.

3、Closing remarks

To sum up, Laixi Steel wide and thick plate factory in the production process of rolling buckle problem has been solved to a certain extent, the middle blank head and tail shape is better, reduce the production shutdown rate, greatly improve the production rate and product yield rate, for our factory to create good economic benefits.

2023/10/24 09:36:53 199 Number

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