In Good Company

ControlDesign.com

Our 2008 Innovator Awards Winner, In the Tradition of Its Predecessors, Adapts Technology In Unique Ways to Bring Big Improvements In Product Quality and Consistency to Its Blow-Molding Machines

By Mike Bacidore, Managing Editor

If necessity is the mother of invention, then application must be the father of innovation. Without a practical application of a new idea, enhancement or improvement, its merits are fleeting at best. When Benjamin Franklin invented bifocals near the end of the 18th Century, they eliminated the need to keep switching between two pairs of glasses. The bifocals were put to use, and an innovation was born.

If not for the application or use of the invention, its benefits would have remained invalidated and largely unrealized.

So it goes with machine controls and automation. New components are created constantly, and those components often are combined in inventive ways. Some promise benefits to machine builders, and others over-deliver.

This year’s winner of Control Design’s Innovator Awards competition is one of the others. Graham Engineering of York, Pa., changed the controls on the Graham Wheel, a non-PET bottle-molding machine. The main component of the wheel spins around a horizontally mounted axis, where extruders feed plastic into a component known as a flow head to form bottles in virtually any type of thermoplastic to the perfect shape and highest quality available.

In a May 2007 case history, “PC Control Breaks Blow-Molding Mold,” we reported how Graham reinvigorated its 30-year-old rotary blow-molding machine with new PCs to boost I/O speed and flexibility. “We’d determined that our existing PC hardware platform wasn’t going to keep up with our machine design migration, so we needed to find a successor,” says Dave Fiorani, engineering manager at Graham.

Graham engineers test a new PC-controlled Graham Wheel before delivering it to a customer. Beckhoff Automation

One of Graham’s customers, Ring Container in Oakland, Tenn., has been using the Graham Wheel for years. Ring owns and operates several proprietary wheel blow mold machines designed in conjunction with Graham. Sam Kerley, controls engineering manager at Ring Container, explains the big benefit of Graham’s change in controls was realized largely in the ability to execute more precise parison programming. “In the past, a lot of what has been produced has been with a PLC system or a DCS with a dedicated card that handles the parison programming,” says Kerley. “There have always been faults with the parison setups. You either had low accessibility and flexibility or a lack of speed. It’s extruded through a mandrel, which controls the amount of plastic. The movement in our application is about 1 in. It’s done with a servo, and you have to have very precise movements in a very short time.”

This is where the speed of the new controls struts its stuff, but a little background on parison programming is necessary to understand the full implications.

We’ll Always Have Parison

The parison programmers control the thickness of the plastic, based on the height of the bottle, explains Kerley. Some plastic bottles have parison programming, and some don’t. “When a bottle is made, an extruded parison comes out, and the length of that parison is divided into 128 profile points,” says Kerley. “The operator programs the bottle by selecting where he wants each pin to be. He can put some master points down, and it interpolates set points in between. In the history of blow molding, parison programming is the key ingredient in making these bottles. It’s important and hard to accomplish well.”

Ring Container Maintenance Manager Brian Best looks at a control screen on the Graham Wheel.

Very few systems offer the speed and control necessary for precise parison programming, says Kerley. “Maybe a dozen are out there. Graham had one up until recently that was based on a large board that provided 40 pins of parison programming,” he says. “With the new control system, you can get up to 256 pins of parison programming. It’s all in the controller. This new wheel uses Beckhoff Automation’s TwinCat soft PLC  and InduSoft’s HMI. Their solution puts the entire control system, including the HMI and the parison programmer, in one computer. Closing the loop on the parison programmers increases the quality of the bottle. It can monitor, in closed-loop servo-type control, and adjust. We can make it faster and lighter. I can program any machine to do 1,000 points, but it may not be fast enough to actually do it. This machine is fast enough to hit those parison points.”

Ring Container’s blow molding wheel has two extruders, an inner and an outer layer, explains Kerley. “It extrudes them together as a single parison,” he says. “The parison extrudes up vertically. After a short amount of time, it blows a bottle inside the mold. As the wheel turns around, it maintains the blow pressure. When it reaches the bottom, the molds open, the pin holders retract, and the bottle falls out of the mold. The wheel is synchronous with the star wheel and the takeout conveyor. The star wheel will rotate and set the bottle down on a conveyor, which takes it to a trimmer.”