Siemens S7 - 400 PLC in cold rolling of continuous annealing furnace application - rapid cooling section

1, cold-rolled continuous annealing furnace of the fast cooling process introduction

in continuous annealing line for cold rolled, rapid cooling technology is the core technology, because the cooling speed of steel strip material influence is very important. To produce bake hardening steel, dual phase steel, and other products, the unit needs to have high speed cooling capacity, cooling speed requirements up to 50 ℃ / s or higher. So far, the development of cooling technology mainly include jet cooling ( GJC) And the high-speed jet cooling ( HGJC) , cold roll ( 中移动) , water quenching ( WQ) , hot water cooling, HOWAC） And flash of cold ( flash冷却) Cooling ways, such as baosteel, a unit has adopted the latest flash cooling control technology. The fast cooling section is composed of a circular furnace, 3 bellows, roller, 2 of 2 sets of sealing device, and electric heating equipment and equipment, including radiation pyrometer. The furnace structure is shown in figure 1. Figure 1

fast cooling furnace structure diagram of the control system of

2

2. 1 hardware

fast cooling section no separate PLC control system, it is controlled and the whole annealing furnace body, the time of a single process to complete the strip annealing technology of rapid cooling. Using the Siemens S7 - PLC system 400 series of hardware equipment, instrumentation PLC hardware system as shown in table 1.

table 1: instrument PLC hardware system

instrument based automation PLC and PLC, industrial Ethernet communication ways between upper machine communication between HMI and the PLC also adopt this way of communication. Automation system network configuration diagram as shown in the figure 2. Control system is divided into three levels:

site level ( L1 level, also known as basic automation level) , the control level ( L2 level) , management level ( L3) 。

figure 2 automation system network configuration diagram

2. 2 software platform

computer operating system is Microsoft Windows XP Professional English version operating system. PLC controller software development adopts Siemens PCS7 development programming software, choose Siemens Wincc6 L1 level automatic monitoring system. 0 development version. English version history database using Microsoft SQL 2000 database software.

3 functions of the control system of

3. 1

fast cooling temperature control function through three jet cooling fan cycle protecting gas blowing nitrogen hydrogen, bellows is decorated in the uplink pass fast cooling section, and in the two rollers room to provide electric heating radiant tube, prevent cold when heated in low yield. In RCS export temperature measurement at the same time, provides feedback for temperature control. Downward pass also provides an electric heating radiant tube, points three heating zone, the goal is to prevent the temperature is too low. Control, heater and cooling fan speed curve according to a certain proportion.

3。 2 furnace pressure control

cooling rate according to the annealing curve, can choose bellows in quantity, the location of the bellows can be moved, the export bellows by VF motor control respectively, bellows mobile position feedback, completed by the encoder, forward and backward limit position is set at the same time have a sensor to protect, prevent the bellows mobile too. Nitrogen hydrogen furnace protective gas circulation control circuit, a gas temperature detection, fan into the export a pressure testing, to ensure the control accuracy. Control circuit is shown in figure 3.

figure 3 control circuit diagram

recycling atmosphere temperature change is having a direct effect on the stability of the furnace pressure, for the furnace, will lead to dangerous situations, for a given production efficiency, can maintain the temperature of the blowing to avoid the above situation.

strip and protective gas heat can cause gas temperature rise, furnace pressure, to reduce the gas temperature, the controller will increase protection of gas flow, this will lead to the gas temperature is reduced, therefore, lower pressure in the hearth.

in order to avoid the low fan speed will affect the lower limit of stable operation, with a minimum power is used to control the minimum speed fan.

minimum motor power calculation formula is as follows:

,

Pmin. SP: motor power (minimum Based on the gas density nitrogen: 1. 250 kg/m3, hydrogen: 0. 089 kg/m3）

N: fan speed

N1: biggest fan actual speed ( Speed set point)

Pmin: fan stable before the minimum power ( Based on the maximum fan speed by 35% and nitrogen hydrogen gas H2)

rho 2: the current protection of gas density

rho 3:50 p. m % H2 hydrogen nitrogen protection gas density 0. 67公斤/立方米

3。 3 safety purging

this flash cold process segments is the biggest characteristic of high hydrogen ( Maximum 50% hydrogen content) , so the security is very important. Before the high hydrogen products, need safety tests on high hydrogen control circuit, so that after a failure in high hydrogen production, can rapid loss of hydrogen, preventing further failure. 4 conclusion

with the further development of annealing process, especially on the stability of the control system, advanced and scalability to ask for a higher level. Siemens S7 - 400 series PLC with the debugging is simple, easy to operate, the use of safe, stable and reliable running, characteristics of scalability, can satisfy the requirement of process.

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