Study And Application Of Mill Pacing Control Technique In Plate Rolling Process

With the development of medium plate industry, the plate rolling with high quality, efficiency and low waste of energy has become dominant tendencies. On the basis of fine capability, surface quality and precision of dimensions, reduce the retention time in the production line as far as possible has been a urgent problem to be solved. Meanwhile, in order to implement optimum control of manufacturing procedure, harmonizing the processing speed of all the departments is also very important.In view of the problems above, the macroscopical and microcosmic mill pacing control technique has been fully expatiated in this paper. The macroscopical mill pacing includes the establishment and taxis for rolling assignment with considering of inventory and orders. The microcosmic mill pacing includes the selection of temperature-waiting mode, calculation of slab discharging time and strategy for self-adaption of microcosmic mill pacing. Establish the optimum mathematic models for distribution of rolling load and enactment of rolling speed. Furthermore, it is very necessary to obtain some original parameters for the time forecasting model and temperature-waiting mode model from these two models. The specific research contents were shown as follows:(1) Optimum mathetic model for distribution of rolling load with the purpose of optimizing mill pacing was established. Methods for calculating the turning thickness and rolling force self-adaption are founded. Equation for turning thickness was deduced and the mechanics for ratio of broadening β and lateral flowing coefficient kβ are discussed in both of little and large deformed conditions. The conventional pre-calculation of rolling force and its limitations were introduced. Use this as a foundation, a new strategy for self-adaption of rolling force was proposed. In this strategy, self-learning coefficients was classified according to the information of steel type, target thickness and initial rolling temperature, etc. In response to the method of using the mill capability maximumly, initial values for the subsequent optimum calculation were obtained. Furthermore, SQP and penalty function methods were adopted to make initial value approach optimum solution step by step. Algorithm for the coefficient of heat-transfer, heat-flow density and constant-pressure specific heat were discussed. In this condition, mathematic model for forecasting temperature-waiting time was established.(2) Optimum algorithm for rolling speed settings was developed. Originally, the shapes of curves for speed setting were enumerated, assumably including horizontal line, triangle and trapezia. Then the rules that can decide which curve to choose were analyzed. The influencing factors acting on speed settings were discussed adequately. Critical values for biting, stable rolling and throwing speed were obtained by analysing the restrictive conditions, such as biting and stable rolling condition, torsional oscillation of mill and minimum oil film thickness for bearing. The principle for gaining friction factor between roller and plate is studied emphatically when discussing the condition of bite and stable rolling.(3) Optimum temperature-waiting mode for single stand was presented. The waiting modes in the same specification were enumerated. Firstly, it is cursorily to sort for three kinds: single-slab waiting mode, group waiting mode and crossed waiting mode. Then, it can be divided into more categories according to the amount of blocks and different discharging time. This chapter takes a batch of blocks for fixed number, and it is necessary to assume that these slabs can satisfy all the waiting requirements. Based on this, the total rolling time, utilization and discharging time were calculated in order to screen for the optimum temperature-waiting mode. To sovle the case of variable specifications, it was translated into TSP problem for minimum processing route and its solving steps using ant colony algorithm was analyzed. The judgement for direction of travelling was developed by the strategy of priority invited in order to remove some possible routes and accelerate the convergence of the algorithm.(4) Strategy for the macroscopical mill pacing control with considering the slab inventory and orders was established. The complexity of plate production technology was introduced. Furthermore, some rules and constraints in technological process were discussed systematically. The slab allocation model was established with the purpose of gaining maximum profit. Meanwhile, this model has many other objective functions, users can select anyone which can satisfy the actual demand. This chapter has proved that the structure of production can decide only one structure of slab inventory from two aspects:the maximum yields and maximum total production values. Conventional taxis for rolling assignment, expert system and their limitations were introduced. Based on this, a new rolling assignment sorting method was developed which create a sequencing network using dynamic programming to solve the scheduling problem. (5) The self-adaption for microcosmic mill pacing was studied. The mathematical meaning and compositions of Petri Net were introduced firstly. Based on the condition of process arrangement on plate production line, the foundamental and necessity of self-adaption were analyzed. Then, figure of the model with double stands based on Petri Net was designed and the mathematic model was built consequently. According to the real-time feedback data from the monitoring library, states of all the buffers were restructured, so as to calculate the discharging time and pace of all the other equipment.Research findings above have been applied to some national plate mill, it solved several puzzles in production. Plate production mill pacing control technique is also an extensive research field, whose theory and method should be abundant, developed and sounded further, and many problems need be solved further.