| Hot sand is the critical problem for green sand molding process. Return sand in the temperature range of 50℃to 70℃is hot enough to demonstrate inconsistent properties during mixing and is very difficult to control. The Multi-cooler, through strong agitation, water spraying, air blowing and exhausting, can enhance the water evaporation and therefore lower the sand temperature.This project investigated the domestic and international method and trend for multi-cooler water-cooling control systems, and established the following components for the water spraying and air blowing control system: A SIEMENS S7-300PLC as lower machine to achieve integral control of the temperature and moisture of the return sand, an industrial computer as upper machine to monitor the cooling process, and an electrical linear proportional valve to continuously regulate the spraying water flow.After field test and data analysis, a mathematical model of moisture set point was established based on the process requirements. The PID algorithm was designed based on the moisture deviation, and was programmed into the S7-300PLC system. The fuzzy control algorithm was researched based on the relation among air blowing flow rate, sand temperature and moisture, and was programmed into the S7-300PLC system as well. The human-machine interface of multi-cooler water spraying cooling control system was developed using the WinCC configuration software.The control system has been running reliably. The return sand meets the temperature and moisture requirements after cooling process. The performance of molding sand has been improved. All of above established a foundation for improving the casting surface finish and further reducing the casting failure rate.This control system replaced the traditional single-chip microcomputer with PLC, and adopted advanced PID, fuzzy control and high-accuracy sensing technology. This system is simple to operate, highly reliable and stable, and easy to maintain, thus has substantial practical value.
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