The Oak Creek facility is a chemical batch manufacturing plant that creates industrial-strength finishes for automotive OEMs. Each order is custom-mixed to the customers' specifications, relying on controllers throughout the process to ensure the batch meets strict quality standards.
When a salesperson enters an order, it is automatically scheduled based on the materials required and the length of production. Depending on the request, it can take as little as an hour or as long as a few days to process a single batch. Raw materials stored at the plant are weighed, measured and mixed to create the coating, and for some orders, PPG must heat the batch to generate the proper chemical reaction.
"Each batch weighs around 70,000 pounds," said Joe Szul, resin plant operation manager, PPG Industries. "And if the weight is off by a few pounds or the temperature is a degree too hot, the entire batch must be reprocessed or discarded. Either scenario could dilute our profit margin."
Besides the need for precision, the plant's centralized control system had grown old and increasingly unreliable. In addition, replacement parts for the loop controllers were hard to find because the system was antiquated. This meant any equipment failure could lead to prolonged downtime as engineers waited for replacement parts to arrive.
For a plant that operates on a tight production schedule, the cost of downtime might be felt both in production backlog and dissatisfied customers. It also hampered the continuous improvement program the plant had started.
With tighter integration and greater accuracy available, PPG wanted to replace the aging control system. So the company decided to make a change and set out to meet the following goals: boost production efficiency, reduce operating costs and increase reliability. As a means to these ends, PPG enlisted the help of Rockwell Automation.
Together, the companies decided to build the control system on five distributed Allen-Bradley® PLC5/80™ controllers. PPG would then link each controller to an Allen-Bradley FLEX™ I/O module via ControlNet™, which would relay system data back to the plant's HMI. Using FLEX I/O, a compact, modular I/O assembly that is flexible in physical configurations, provided a number of choices in control platforms, networks and mounting capabilities. This architecture would be ideal for connecting new components like the PLC5/80s with existing technology platforms being used in other parts of the PPG plant.
But there was one major obstacle when it came to implementing the design. Because the plant operates on a 24-hour schedule, there were no opportunities to install the new control system while the plant was "closed." The solution: engineers worked through the plant during scheduled breaks in the process, replacing individual sections of the line at a time.
In all, PPG mounted and networked more than 1,000 I/O modules. And due to the fact that ControlNet terminals are built into the easy-to-install FLEX I/O, the company saw massive savings - around $2 million - in wiring and labor costs.
Another benefit is that moving from centralized equipment to a distributed control platform made room for an operator control room. PPG uses this space to run its HMI system, which consolidates process data like temperatures, pressures, weight and raw material status to give plant operators real-time production data. With this information, engineers can troubleshoot production events, order raw materials, schedule preventive maintenance and keep the plant running smoothly.
"We have at least 10 times more process data than we did before the upgrade," Szul said. "This makes problem solving much faster and efficient. Plus, the information is in one database - not spread across the plant floor - which has helped our Sigma Logic methodology efforts."
Even more monumental is what has happened on the plant floor. Since PPG installed the new system, downtime due to control equipment failures has dropped to near zero. Plant operators also have used the increased precision and reliability to eliminate substandard batches. As a result, the company is getting the most out of every hour of operation, every order. Ultimately, this will help PPG create a bottom line that will paint other companies green with envy.
For more information, contact Heidi Wight at Padilla Speer Beardsley, Inc., 612/455.1700, e-mail hwight@psbpr.com.
