Design of control and operation protection of mold

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Design of control and operation protection of molding sand conveying line in foundry workshop

the sand treatment department of our foundry workshop is a molding sand preparation line equipped with a variety of equipment, with a daily output of 500 tons of molding sand. The production line is equipped with two imported PLC controlled high-capacity automatic sand mixers and domestic supporting belt conveyors and bucket elevators for tightening experiments; Between the moving crossbeam and the upper crossbeam, there are tension connecting parts elevator, disc feeder and corresponding auxiliary equipment. The total installed capacity of the system is 84okw, and the total number of equipment is about 40. It is distributed in 4 layers 18 according to different process sections. High space, covering an area of 3500m2. The prepared molding sand is sent to two automatic pouring lines by belt conveyor. Due to the continuity of casting production, the system transmission cannot be interrupted. Therefore, the control and operation protection of the whole system transmission line are highly required

1 conveying process and control requirements a total of 13 belt conveyors with a total length of 270 are configured in the process of the sand treatment department., According to the transportation route, there are three processes: new sand, old sand and molding sand. The new sand conveying process is used to supplement the sand consumed by the process. During normal production pouring, the old sand and new sand processes should be operated to meet the sand consumption of the automatic pouring line. Each process path is: new sand process: sand silo → 12 # conveyor → 8 # conveyor → 9 # conveyor → bucket elevator → 10 # conveyor → new sand hopper old sand process:

molding sand process: disc machine (sand mixer) → 1 # conveyor → 2 # conveyor → 3 # conveyor → 4 # conveyor → 5 # conveyor → oil cooled electric roller is used as the driving device of belt conveyor in the pouring line system. According to the process flow, the control requirements of belt conveyor are: (1) optional process can be selected, and the working mode can be manual, automatic, on-site and other forms. (2) The normal start-up and operation of any process should follow the sequence of delayed start-up against the direction of sand flow. (3) In case of normal shutdown during operation, the shutdown shall be delayed one by one in the direction of sand flow. (4) During operation, if a conveyor fails to stop, the downstream equipment operates normally and the upstream equipment stops normally. (5) Carry out real-time monitoring of the conveying line equipment and display the operation status. 2 system program design the controlled equipment of the sand processing department are interrelated, with many signal points, long signal transmission distance and poor operating environment. Therefore, PLC is used as the control core of the Department. From master order to output execution, Hitachi EM Series PLC is selected. C4op programmable controller is selected to detect the running state of belt conveyor, which is used as an independent detection unit for signal interlocking with the upper computer. 2.1 molding sand process procedure the preparation of conveying procedure is to follow the principle of time control and prepare basic program blocks based on the process flow. According to the control requirements, the belt conveyor starts against the sand flow direction. When the process and working mode are selected, the system starts according to the compiled program (see Figure 1). SP means that after starting the 5 'belt conveyor, after a certain time delay and speed detection, start 4P, and so on. Due to the different transfer paths of belt conveyors and the different distances of each conveyor, the starting delay time of each conveyor is set according to the following formula: TP =s/vd + TQP

where TP - the delay time of conveyor starting, s

s - the center distance from the driving drum to the driven drum, m VD - the speed of the driving drum, m/s TQP - the time when the driving drum reaches the rated speed, s starting in the reverse sand flow direction is starting from the subsequent conveyor in turn, Before starting, there is no molding sand on each conveyor belt and it is in no-load state. After the belt conveyor of the whole process is started, the molding sand is unloaded from the disc machine to the mutual conveyor, and this time to the 5 'conveyor. If the belt of a conveyor slips or there is only a small part of strong current external fault, the detection element will send a signal to PM to remove the interlocking link in the procedure and stop the corresponding conveyor line. The modified plastics obtained through this kind of technology often have a great improvement in processing performance, mechanical properties, heat resistance, flame retardancy and other aspects to avoid molding sand accumulation

2.2 shutdown procedure the shutdown procedure is determined according to the conveying direction of molding sand. When the pouring line does not need to supply sand, the conveyors will be shut down one by one in the order of 1# to 5#. This shutdown mode is to ensure that there is no molding sand on the tape and avoid starting with load. The shutdown delay time at this time is calculated according to the following formula. TT =s/vd

where TT - shutdown delay time, s s - center distance from the driving drum to the driven drum, m VD - speed of the driving drum, M/s if a belt conveyor fails during transportation, the downstream equipment operates normally, and the upstream equipment stops and sends a light alarm signal. 3 zero speed protection zero speed protection refers to the protection of abnormal operation of the conveyor. That is, the control and protection of the roller and conveyor belt in the state of slipping and loss of rotation. During the operation of the belt conveyor, due to the displacement of the driven drum or accidental jamming and other reasons, there will be loss of rotation, which will make the running speed of each conveyor belt in the process asynchronous, resulting in sand accumulation. In the past, the detection device was composed of reed tube, electronic circuit and micro relay, and the actual effect was not ideal. The current system adopts contactless proximity switch and is controlled by PLC, which simplifies the circuit structure and greatly improves the reliability& nbsp

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