Taking process monitoring on-line

It sounds like the opening line to a schoolyard joke: what do ultrasound technicians and plastic operators have in common?

Researchers at National Research Council Canada’s Industrial Materials Institute (NRC-IMI) in Boucherville, Que., have developed an on-line diagnostic tool that allows processors to monitor their parts using ultrasonic technology.

“Medical ultrasonography is used to look at babies inside the womb, to do imaging to see if the baby is healthy… it’s a non-intrusive and non-destructive process,” explained project leader and Ultrasonic Diagnostics of Materials group leader Dr. Cheng-Kuei Jen. “Similarly, we use ultrasonic technology to monitor molten plastic inside a steel barrel, mold or die.”

And much like the ultrasounds used in prenatal care, this new tool alerts operators to any problems during the process. Data collected by the system can provide information such as polymer viscosity, molecular weight, filler and blend concentration, and if the part has hardened or the polymer has degraded while being processed.

“Manual inspection is no longer sufficient, and if the process is affected by a defective screw heater or feeder you will produce a lot of parts that do not meet the specs,” noted Dr. Jen. “The advantage of our ultrasonic technique is that it operates in real-time. When a defective part is produced, the operator can make corrections right away.”

In addition to helping processors troubleshoot defective motors, screws or feeders, the ultrasonic diagnostic system can also help them adjust their process characteristics to suit their materials. For instance, if a processor is sourcing the same material from two different suppliers, they can use the diagnostic tool to minimize the impact of any slight differences in feedstock properties or processing characteristics.

Essentially, manufacturers can instruct their machine to change its screw rotation rate, pressure or temperature if necessary. This will result in a reduced number of defective parts and downtime, with a maximization of the production rate.

Probes and sensors are installed directly onto the extruder or molding machine, generating ultrasonic waves and receiving the reflective signals passing through the plastic melt. Monitoring can be carried out anywhere from the feed hopper down to the exit, for the extruders, and injection molding machines including nozzles and dies. The signal is then relayed to a beside-the- press ultrasonic instrument.

“We are not showing a complete plastic part image, though; rather different critical locations in the extruder or injection molding machine,” said Dr. Jen. “We can digitize the signal, store it in memory, and then use software to interpret the results real-time.”

NRC currently possesses four patent protections for the technology, and Dr. Jen notes that the ultrasonic technology at the centre of the innovation performs better than available commercial sensors and techniques. For example, he noted that optical techniques couldn’t see through opaque materials, even though they cost the same as ultrasonic sensors. X-ray and other radiation technologies may be expensive as well as impose a health hazard.

NRC-IMI has licensed this technology to two companies, and the diagnostic is available for Canadian processors. The Canadian licensee is PACE Simulation, of Boucherville, Que. They currently supply a $55,000 general-purpose system for research institutes which features simultaneous two-channel monitoring. In May 2008, PACE began production on a new special diagnostic system aimed at processors, which provides one-channel monitoring and retails for approximately $15,000. CPL

Dr. Cheng-Kuei Jen (Boucherville, Que.); www.imi.cnrc-nrc.gc.ca; 450-641-5085