The Batch Management Control System (BMCS) is the heart of PPG’s ‘Envirobase’ automotive paint process, monitoring and controlling the batching and blending of deionized water, bulk latex and various ‘hand add’ ingredients to produce high grade automotive colours and clear coat finishes..
The BMCS was retrofitted onto an existing manual batching system comprised of 10 large batch tanks on Mettler Toledo load cells and two floor scales for preweigh/hand add preparation, all equipped with 8042 indicators. An Allen Bradley PLC5 provides complete control of the batch process retrofit. A 1771-DMC control co-processor installed in the main PLC rack polls the 8042 indicator for weight information via a multiport ‘smart switch’. Since the indicators are located in a hazardous area 12 RS232 to fibre optic converters are employed to provide an intrinsically safe fibre optic connection to each weighing point.
Operator interface is provided by three PC based workstations housed in purged stainless steel enclosures with sealed mylar keyboards. A fourth workstation, located in the manager’s office ties to the in house network. The batch process is fully automated and driven from user developed recipe screens. All operator interaction and prompts are via full colour interactive graphic displays. Any out of spec conditions are alarmed and adjusted before bad product can be produced.
All batch data is stored to an Excel file complete with all weights, setpoints, operator actions, alarms, trends etc. for traceability and continuous improvement purposes. The BMCS has been expanded twice since it’s initial installation and payback is being realized daily with improved batch consistency, conformity to spec (as part of the ISO9000) and minimized rework and scrap. |
