Automation technology of the hottest powder sprayi

2022-07-30
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This paper discusses the use of plc+pc to control the powder spraying production line. The control principles of surface treatment, drying furnace, curing furnace and powder spraying are described. The realization of plc+pc control system is introduced

our company mainly produces white household appliances (refrigerators, washing machines, electric water heaters and some small household appliances). The company has four automatic powder spraying production lines. The refrigerator company adopts the friction gun spraying system of Nordson, which is the largest and only flat plate spraying line in China; The washing machine and water heater adopt the vertical electrostatic powder spraying system of Nordson, and the water heater is equipped with a metal powder spraying system. The powder room is controlled by PC, which has the functions of powder recovery and air stabilization; The surface treatment adopts spray type treatment, and the control of water pumps at all levels adopts AC contactor control; The drying and curing furnace adopts electric heating and hot air circulation system, and the control part adopts PLC control. Due to the separate decentralized control, the production efficiency is low, the key process parameters are difficult to control, and the product quality is difficult to be improved. In order to meet the requirements of the company's development, we used PLC + PC control mode to burn out the components

the production line adopts the circulating conveyor chain, and the motor drive is controlled by the frequency converter. The system can adopt independent manual control and cyclic automatic control

2. Control mode

2.1 the knob on the main control cabinet is set to manual, and the working states of the three processes are as follows:

(1) press the button of the surface treatment line, the steam control valve is opened, and the degreasing tank and phosphating tank are heated respectively. The temperature controller displays the set temperature value, and the heating solenoid valve is automatically closed. After the workpiece is in place, spray at all levels in turn

(2) press the oven drying button, the drying and curing oven circulating air motor starts (the motor is started by the step-down of the autotransformer). After the motor is started, the PLC detects the signal, starts the heater (the heater is controlled by the solid-state relay), the drying and curing oven temperature controller displays the temperature to the set value, six groups of heaters in the drying and curing oven are disconnected, four groups are reserved, and two groups are reserved to maintain the temperature in the oven. The workbench operates on the y-axis

(3) press the powder room button, the PC in the powder room starts, the PC detects the pressure and dew point temperature of compressed air, the flame detector is normal, the powder level in the powder supply bucket is normal, and the PC starts the circulating fan. After PC recognizes the workpiece position switch signal, turn on the spray gun sequence controller, and the spray gun will spray and stop in turn

2.2 the knob on the main control cabinet is set to the automatic position, and the full-automatic state of the whole production line is as follows:

press the start button, the PLC detects the switching value of the temperature controllers of the surface treatment degreasing tank, phosphorous multimeter, oscilloscope and other chemical tanks, drying furnace and curing furnace, turns on the air supply solenoid valve of the degreasing tank and phosphorization tank, and heats the tank liquid; Start the drying and curing furnace circulating fan, PLC detects the fan startup completion switch signal, and starts six groups of heaters in sequence. When the temperature of each temperature indicator reaches the set value, the PLC sends a command to turn on the power supply of the frequency converter of the conveying chain. The six sprays of the conveying chain are equipped with photoelectric switches to detect the workpiece. After receiving the signal, the PLC starts the spray pumps at all levels in sequence. At the same time, the PLC turns on the power supply of the air compressor and the compressed air static system. The photoelectric switch in front of the powder room sends the workpiece in place signal to the PLC, the PLC turns on the power supply of the powder room PC, and the powder room PC runs according to the manual program

3. Technical realization

3.1. PLC selection

on the basis of the original control, according to the requirements of the production process. The control system has 43 analog inputs in total: 12 button switches SB1 ~ sb12; Two selection switches SA1 ~ SA2; 10 contactor input switching values KM1 ~ km10; 4 emergency stop buttons PB1 ~ PB4; Input switching value of temperature controller: 8 RS1 ~ rs8; There are 7 photoelectric switches SE1 ~ SE7. The electric control system requires a total of 44 output signals: 2 solenoid valves yv1 ~ yv2; 6 intermediate relays KA1 ~ ka6; 6 motor control contactors KM1 ~ KM6; Control the frequency converter to output 1 Fv1; Solid state relay 15 sCR1 ~ scr15; Buzzer 2 HA1 ~ HA2; There are 12 signal lamps HL1 ~ hl12. We selected omrom, one cpm1a-40cdr-a programmable controller and two cpm1a-20edr-a programmable controller extenders. There are 51 input nodes and 46 output nodes, which can meet the requirements

3.3. Software programming implementation

adopt ladder diagram statement programming and use computer application software sysmac-cpt for programming; Input through computer and PLC interface. Commissioning and maintenance shall be carried out by using the on-site handle programmer

summary: plc+pc sequence control is adopted to overcome the shortcomings of dead wiring, large volume, disordered wiring and high fault frequency of the relay. The ladder diagram is simple, precise and convenient; It can be programmed by computer interface or programmed by the programmer provided with the fuselage. The installation and commissioning are convenient, easy to learn and easy to maintain, and the operation and maintenance personnel do not need very professional technicians. Using plc+pc control system can realize powerful intelligent control. After more than half a year of operation, the first pass rate of the product offline has increased from 93% to 95%; The production cost of the product has also decreased to a certain extent, which has achieved the effect of energy saving and consumption reduction. And it lays a good foundation for realizing the whole process control of production process in the future

References:

[1] fundamentals and programming skills of programmable controllers, edited by Chen Yu and Duanxin

[2] zhaoshuguang, duantingrui, zhaomingying, chenliping, principle development and application of programmable analog devices

[3] Xude, suntongjing, chenguiyou, application technology of programmable controller

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