Automatic control system for heat treatment produc

2022-08-18
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Automatic control system of PC steel bar heat treatment production line

[Abstract]: This paper introduces the composition and operation principle of the steel bar heat treatment production line, and expounds the composition of the control system and the control means adopted. The adaptive ability of the system is discussed and explained in detail, and the derivation formula and conclusion are given. The software design and flow chart of the control system are given. Finally, the mechanical properties of PC steel bars produced by this system are analyzed, and the conclusion is given

[Key words]: steel bar heat treatment PLC

PC steel bar is a kind of low-carbon alloy steel heat treatment high-strength prestressed concrete reinforcement, which is mainly used to make port concrete pipe piles, high-rise building foundation concrete pipe piles, pier concrete pipe piles, etc. With the rapid growth of the national economy, the market of PC steel bars is constantly expanding, and the varieties and specifications of PC steel bars are becoming more and more abundant. Due to the limitations of the traditional PC steel bar production line, it can not adapt to this change. In order to improve the current situation of PC steel bar production line, this paper systematically expounds a new automatic control system of steel bar heat treatment production line, which integrates flexibility and reliability. This set of automatic control was developed by Zhejiang University Sanyi company and has been put into operation

1 Composition of steel bar heat treatment production line

1.1 system structure the market team supporting market development is the entrepreneurial "accelerator" into

the steel bar heat treatment production line described in this paper is a pipeline system. The system block diagram is shown in figure (1). The system can be divided into four parts: electric drive, induction heating, console, data acquisition and other auxiliary equipment. The electrical transmission part is composed of five motors (two press feeders, one traction machine and two take-up machines), and each motor is driven by the frequency converter provided by ABB; The induction heating part is composed of four induction heating machines (two intermediate frequency power supplies, of which the power of 1 # intermediate frequency power supply is p1=250kw, and the power of 4 # intermediate frequency power supply is p4=160kw. The power of 2 # power supply and 3 # ultra audio power supply is p2=100kw and p3=160kw respectively). 1 # thermometer is used to measure quenching temperature, 2 # thermometer is used to measure tempering temperature, tension detector is used to detect the tension of PC steel bar, and finally the shearing and splitting of PC steel bar. The console is the main control console of the whole production line. Simens series PLC and touch screen (tp27) jointly monitor the production line

1.2 operation principle

during normal operation, the steel bar starts from the wire feeding point, and under the traction of the tractor at a certain linear speed, from the press 1, straightener 1, straightener 2, and press 2, it is sent to the first three power supplies in Figure 1 to complete the quenching treatment of PC steel bar to a certain quenching temperature. After water cooling, the tempering treatment of PC steel bar is completed to a certain tempering temperature by the last power supply, and then after water cooling, It is sent to the corresponding take-up machine for take-up by the take-up distributor. In take-up, the angular velocity of the take-up decreases with the increase of the diameter of the take-up reel. All the signals collected and sent by the system are sent to the console and controlled after corresponding processing by PLC

2 control system

2.1 speed control of electric drive

this system should complete the speed control of five motors and the speed coordination control between five motors. The speed regulation of 5 motors adopts frequency converter, and the speed is given by PLC, and the speed stability and accuracy are met. In order to coordinate the operation of the five motors, the rollers driven by the five motors must have the same linear speed. There is a proportional relationship between the speed of the motor and the linear speed of the roller, that is, vm=kvgl (where VM is the speed of the motor and VGL is the speed of the roller). Adjusting the corresponding speed coefficient K on the touch screen can make the roller driven by each motor have the same linear speed, so that the five motors can operate in coordination

2.2 temperature closed-loop control

temperature closed-loop control is mainly to ensure the quenching temperature and tempering temperature of PC steel bar during normal operation of the system. The data measured by 1 # thermometer and 2 # thermometer are sent back to PLC and compared with the given quenching temperature and tempering temperature. According to the difference between the actual temperature and the given temperature, the control quantity is calculated through the PI control link, and the power of 3 # ultrasonic power supply is adjusted to meet the quenching temperature, Adjust the power of 4 × intermediate frequency power supply to meet the tempering temperature

2.3 tension closed-loop control

tension closed-loop control is the same as temperature closed-loop control. The tension signal detected by the tension detector is sent to PLC to compare with the given tension. According to the difference between the actual tension and the given tension, the control quantity is calculated through the PI control link, and the speed of the tractor is adjusted to meet the PC steel bar tension between the tractor and the straightener

2.4 automatic splitting

the automatic splitting system completes the automatic take-up of the PC steel bar heat treatment production line. When the line of the take-up machine 1 is full, the shearer cuts off the steel bar wire. When the PLC detects the cutting signal, because the take-up machine 2 is in a static state at that time, the PLC controls the frequency converter to speed up the take-up machine 2, so that it can reach the line speed of the whole production line, and the cash collection surcharge is 25%. The line machine 1 stops rotating, and sends a signal to make the take-up distributor act, and the line produced later is distributed to the take-up machine 2 for take-up, Thus, an automatic line separation process is completed, and the cycle is repeated

2.5 system adaptability

the whole PC steel bar heat treatment production line needs to process steel bars with different specifications of 7~13mm. Different products have the same process parameter requirements that do not remember to save the experimental data, which requires different induction heating power supply power settings and electrical transmission speed. When we know the operating parameters of one type of PC steel bar, we can calculate the operating parameters of other types of PC steel bars. For example, when we know Φ When the 9.0mm PC steel bar runs at the speed of V (m/min) and the given power P (kw), if it runs next time Φ When the PC steel bar is 7.1mm, the system will give the appropriate Φ The operating parameters of 7.1mm are calculated as follows

when taking the operating speed V as the independent variable (keeping the power unchanged), where l - the length of the induction heating furnace

Φ — Diameter of PC steel bar

p - given power of power supply P = c1p1 + c2p2 + c3p3 (C1, C2, C3 are distribution coefficients of power supply)

c - specific heat coefficient of steel bar

η — Efficiency of induction heating power supply (it can be regarded as a constant when the power changes little)

t - the difference between the final temperature and the initial temperature of PC steel bar at the outlet of 3 # ultrasonic power supply during normal operation

ρ — Density of steel bars

from formula (2), when the power of induction heating power supply is given and t is constant, the running speed is inversely proportional to the square of the diameter of PC steel rod, so it can be obtained from formula (2) Φ Running speed V of 7.1mmpc steel bar Φ 7.1。

it is known from formula (3) that under the condition of constant running speed and T, the given power of induction heating power supply is proportional to the square of the diameter of PC steel bar, so it can be obtained from formula (3) Φ Operating power P required for 7.1mm PC steel bar Φ 7.1。

in order to change the running speed of PC steel bars of the same model, the given power must be changed at the same time, that is, from formula (1):

from the above formula, it can be seen that the given power of PC steel bars of the same model is directly proportional to the running speed

various operating parameters can be calculated from equations (2), (3), (4) or the combination of these three formulas. The same method is also used to control the power of 4 intermediate frequency power supply and the temperature at the outlet. For the errors existing in the system, for example, the efficiency of induction heating power supply when the power changes greatly η It cannot be regarded as a constant, and other errors caused by ambient temperature can be compensated by the temperature closed-loop control and induction heating power self closing loop described in Section 2.2. If you are dissatisfied with the operating parameters during operation, you can also modify them on the touch screen. At the same time, this system also provides the archiving of the operating parameters required for steel bars with different specifications and process parameters. When a steel bar of the same kind is to be produced, it is only necessary to call the corresponding operating parameters

2.6 system reliability

the system monitors the whole production line. When the system fails (such as transmission failure or induction heating power failure), the fault signal is sent to the PLC for processing and gives a real-time alarm. At the same time, the fault type of the system is recorded and archived, which can be viewed on the touch screen. This effectively ensures the reliability of the system and can handle the faults in time

3 software design and process

program according to the design idea. The program is divided into two parts: inching and automatic. S7-300 series PLC has rich functional instructions and symbolic addressing mode, which greatly facilitates programming. In the program, the functions of digital filtering of a/d conversion, PI control, function block, function, high hardness of data block, good wear resistance, and communication interface with tp-27 are applied, which fully reflects the characteristics of PLC function control and makes the program of the whole system simple and intuitive. The automatic program flow chart is shown in Figure 2

Figure 2 automatic program flow chart

4 result analysis of PC steel bars

in order to test the quality of the produced PC steel bars, we sampled and analyzed 1570mpa high-strength PC steel bars. From the test results (shown in Table 1), it can be seen that the mechanical properties of the PC steel bars produced by this system meet and exceed the national standards, indicating that the control system can meet the quality requirements of PC steel bars

5 conclusion

this system has been successfully applied and achieved good benefits. At the same time, this production line is also the first self-produced automatic control production line for heat treatment of PC steel bars in China, which fills the gap in China and enables the automatic control of the heat treatment production line of PC steel bars from the original manual state. The practice also proves that the automatic control system has good adaptability and reliability

[References]:

[1] Research on heat treatment process of PC steel bar by Zhou hemin [j] metal heat treatment, 2000, (10):

author profile:

Bao Hui (1979 -), male, master of national power electronics engineering research center of Zhejiang University, mainly engaged in the research and development of power electronic transmission and motion control. Tutor

Professor Zhao Rongxiang (1962 -), doctoral tutor, director of the national power electronics engineering research center of Zhejiang University, mainly engaged in the research and development of power electronic transmission and motion control, induction heating power supply. (end)

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