Design Of Automatic Control System For Chemical Production Of Electronic Silver Powders

Electronic silver powders are the key material for high performance conductivepastes. The properties of conductive pastes are directly influenced by the size and densityof silver powders. The front silver paste is new conductive pastes and lead to higherperformance requirements on electronic silver powders.Chemical reduction is a main method for ultrafine silver powders preparation. Thismethod usually use ascorbic acid as reducer to reduce silver nitrate andpolyvinylpyrrolidone(PVP) as dispersant. The technological parameters have animportant effect on the properties of silver powders, such as concentration of silvernitrate and ascorbic acid, dosage of PVP, stirring rate, solution pH value, reactiontemperature.In this paper, the principle of chemical reduction was analyzed, and an automaticcontrol system for electronic silver powders production based on PLC and HMI wasdesigned. The asynchronous serial communication mode was used for thecommunication between PLC and secondary instruments. Stirring rate, solution pH valueand reaction temperature in the chemical reaction was automatically controlled.The hardware design of the system mainly includes three parts, PLC and MM440using USS protocol communication composes control part of stirring rate; PLC, pHmeter, pH electrode, magnetic valve using PID algorithm composes control part ofsolution pH value; Temperature controller, thermocouple, SCR, strip heater using PIDalgorithm composes control part of reaction temperature. HMI as the upper controller canrealize data communication with PLC and secondary instruments by PPI protocol andModbus RTU protocol.The system operation software and operation interface was designed by using STEP7-Micro/WIN and EasyBuilder8000. The system has the function of parameter setup, timing, data recording and querying, password protection and easy operation, stableperformance, reasonable structure.After finished, the system was tested for silver powders, three groups. The silverpowders were characterized by SEM and granulometer. Picked the best group, and madefor silver pastes, used to form front silver electrodes of silicon solar cells, tested. Theresult indicated the silver powders can fulfill the requirement of the solar cells.Through the actual test, the system has high reliability, simple operation and goodeffect. High performance electronic silver powders can be produced by the system.