Application of PLC in electric control plywood hot-pressing

Hot press is the key equipment for the production of plywood, directly determine plywood production output and quality of the product. Traditional plywood hot-pressing machine control system based on relay as the master control component, it is difficult to meet the hot pressing process for pressure and flow control, also directly affect the reliability and security of the hot press. To this end, the author puts forward using programmable controller ( PLC) Replace the existing control circuit, try to simplify the system design, meet the needs of enterprise production. 1 application of PLC in the control system of the hot-press domestic plywood production generally use multilayer frame type hot press, for the suppression of plywood board face level off, even thickness, hot press plate should be used more than oil cylinder to ascend, the closing of the platen process, pressure, pressure, and the rise and fall of loading plate, are all through the oil cylinder and hydraulic system, makes the increase in the number of solenoid valve control oil; Equipment of temperature, pressure, flow adopt intermediate relay, contactor, time relay, such as control, the control circuit is more complex. Due to the hot platen adopts steam heating plywood, hard to avoid has the steam leakage, make the workshop humidity increases, cause high failure rate in control circuit. In order to improve the production efficiency, guarantee the quality of plywood, must demand the control system of hot press high degree of automation, good reliability, safety. In the hot-pressing machine control system adopts PLC controller control, can save almost all of the time relay, intermediate relay, contactor contact between interlocking can also be used by PLC internal implementation. Modern large scale integrated circuit and the PLC was adopted, and strict production process, the internal circuit adopts the advanced anti-interference technology, has the very high reliability, mean time between failures of 300000 h. The use of PLC, make the reliability of the control system of hot press greatly improved. 2 PLC control system design ideas to meet the reliability of equipment in the production in the first place. By the size of the original equipment control section components, the control line is complex, the fault is very difficult, therefore, can consider thermal control part adopts the PLC control of the oil cylinder lifting, in meet the requirements of the situation, try to reduce the input and output points, the overall equipment reliability; In addition, considering the equipment repair, maintenance and trial production of the new board, need to add manual and automatic switch control circuit; During maintenance, to prevent the rising pressure plate displacement occurred for wrong operation, equipped with the protection switch, when the switch in the protection state, even if the wrong operation, due to electrical interlock, also not to clamp down. Based on the above design idea, according to the compressor working process, identified the output input of 17 points and 14 points, a total of 31 points, adopts omron C40P products ( This type of products has 24 input points, 16 output points) Ez3。 Figure 1 shows the PLC input plywood hot press in output point distribution. Combining with the characteristics of this series of machine and control circuit was designed, and document control procedures; Addressing input and the output are shown in table 1. 3 working principle and control process to rapidly cover press as an example. This series of hot press is equipped with four cylinder, cylinder overhead, electromagnetic valve control hydraulic circuit need 6, due to the design of hot press different specifications, the oil pump motor power range from 10 to 22 kW, to reduce motor starting current, design for Y/delta starter. Plywood slab used car load, wagon bearing parts can be single direction, the car exits the slab automatic slide on the pressure plate. The car drive motor controlled by frequency converter, which can realize the car fast and slow. Figure 2 for rapid plywood hot press process, figure 3 for PLC control of a part of the ladder diagram. Control six of the solenoid valve in the cylinder, only one 1 dt for the filling valve; Oil cylinder in two upper and lower oil respectively in parallel, in 2 groups, each group has one upper filling valve 3 dt, 1 only lower suction valve 5 dt and 2, 4, dt, dt and a total oil return valve 6 dt. Oil cylinder bottom feed, column inserting move; The upper feed, the piston moves down. As 1, 2, 4, dt dt dt work, linking piece rise, 1, 3, 5 dt dt dt work, clamp down and pressure; 6 dt work, oil cylinder unloading. Hydraulic oil pump, is driven by three-phase ac asynchronous motor to reduce the starting current need to buck, adopts Y/delta starting, conversion time is 2 ~ 5 s. Oil pump work normal 3 s, linking piece rise in place ( Set a limit switch) After, linking piece stop rising; This fashion plate slab rapidly into the small car, the arrived at the set position, the car unloading slab and began to retreat, retreat after the limit switch to stop. Around the back of the car unloading, at the same time, linking piece begin to decline, when touching the lower limit position switch, stop down, pressure and time, with the increase of oil pressure, moving, or between the clamp pressure, when reach the cap, the limit switch contact monometers, stop the pressure. Required by each solenoid valve automatic control of hot pressing pressure, realize the holding until the end of the hot pressing, start unloading, linking piece rise after 3 s. Completed by artificial plate.
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