Billions of cell phone cases, laundry baskets, plastic totes, and storage bins are produced by a process known as plastic injection molding. That’s why there’s a lucrative, multi-billion-dollar plastics injection molding industry in the U.S. — and why they’re facing stiff competition from overseas producers. But one enterprising manufacturer based in Denver, Colo. — Intertech Plastics — illustrates the new trend in "reshoring" by re-energizing domestic plastics manufacturing with the help of innovative, energy-efficient Danfoss Turbocor® compressors.
"In a plastic injection molding machine, it is very important to cool the mold properly to get maximum productivity," says Mike Clavelli, west coast regional manager for Niles, Ill.-based Thermal Care, Intertech's process cooling system provider. As a manufacturer of process cooling equipment and systems for worldwide applications, Thermal Care recently installed for Intertech two centrifugal chillers using Danfoss Turbocor® variable speed compressors.
Clavelli explains: "When Intertech added two new Husky 1,100-ton high-speed molding presses, we implemented the chiller installation using an array of variable speed technologies. This solution delivers variable cooling capacity that is precise, reliable, and efficient, which is giving Intertech a huge domestic and global competitive advantage."
Handling the heat of plastic injection molding
An injection molding machine employs two basic components: a clamp unit to hold the mold, and an injection unit where plastic is heated and mixed before being injected into the mold. Time, speed, pressure, and temperature all have to be controlled to ensure proper operation and maximum throughput.
Depending on the resins, mold temperatures can range as high as 180° Fahrenheit. At the beginning of each production cycle, the clamp unit closes the mold, and a screw in the injection unit pushes forward to shoot molten material into the mold. Continual pressure is applied to hold the plastic in place until it solidifies. While the material in the mold cools, the screw rotates and retracts to draw in new material for the next shot. When the part reaches the precise temperature set point, the clamp opens to eject the finished part and start the next cycle. Depending on the part size and type of plastic, the entire cycle can take anywhere from a few seconds to over a minute.
"Productivity depends on cooling that mold properly," says Clavelli. "The difference in throughput can be huge. For example, with good temperature control you might be able to make 20 parts per hour instead of just three."
Energy-efficient cooling for injection molding machines
For efficient cooling, Thermal Care designed and manufactured a plant-wide central chiller cooling system to handle the unique requirements of Intertech Plastics’ two injection molding presses.
The system comprises two centrifugal chillers, a cooling tower, and condenser and evaporator circuits using variable frequency drive pumps. The piping was designed to scale up to add another chiller if needed.
To maximize the chillers’ efficiency, Clavelli applied Danfoss Turbocor® centrifugal compressors with an oil-free, magnetic-bearing design instead of rotary screw compressors commonly used in the industry.
"We've been successful using Danfoss Turbocor® centrifugal compressors in injection molding cooling for nearly a decade," says Clavelli. "In this case, a 140-ton chiller employs two Danfoss Turbocor® TT300 compressors, and a 70-ton chiller uses one TT300 compressor."