Friday, March 11, 2011

PLC to Control Powder Recovery

Using a PLC to control the powder recovery portion of the system can improve performance in a number of ways. The recovery typically system uses a motor driven fan assembly to draw powder into the recovery system, whether it is a cyclone separator or cartridge collector. The PLC control the motor starter operation, on or off. The on/off status of the motor starter can be made dependent based on additional information collected by the PLC. For example, a roll online/offline booth can be programmed so that the recovery system is started only when in the online or offline position.

If the booth is between positions, the recovery system can not be started. Some recovery systems employ a variable speed drive control to run the fan motor. The PLC can be used to adjust automatically the fan speed of the motor under various conditions. For instance include reducing the fan speed during temporary idle production, or increasing the fan speed for maximum draw during booth cleaning. The fan speed also can also be adjusted automatically to provide a consistent airflow through the booth to compensate for changes in the static pressures of the collection equipment. This also eliminates the requirement for a mechanical airflow damper assembly on the recovery system.

Static pressures on the collection filters can be monitored using pressure transducers that are interfaced to the PLC. Filter pressures can be displayed in a digital format on an operator interface screen, which eliminates needle type gauges. The pulse-down filter cleaning cycle can be programmed to occur when the filters reach a pre -determined pressure level and/or when a certain amount of product has been coated. This increases the performance of the filter media by cleaning only when required.

The transfer of powder within the powder coating system can be controlled by the PLC to optimize powder utilization. Reclaimed powder from the recovery system can be transferred to the feed hopper based on the level of the powder in the hopper. In addition, virgin powder can be introduced to the feed hopper as required. By using the PLC to control the transfer, reclaim to virgin mixtures can be controlled to provide a consistent finish quality.

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