By Bruce Adams
Trexel's technology places tiny cells of gas in plastic parts to create lighter, more dimensionally stable parts that can be produced on smaller, more energy-efficient injection molding machines. The company offers MuCell physical foaming and TecoCell chemical foaming products.
The injection molding machine needs to be outfitted with a plasticizing system that is compatible with MuCell.
“With MuCell, you are adding supercritical gas directly into the melt, so you need a plasticizing system that can properly disperse the gas and prevent the gas from escaping before it gets into the part,” he said. “That requires a special screw.”
At K 2019, Trexel introduced a new screw tip dosing module, designed to make it easier for machine makers and processors to incorporate the MuCell physical foaming process. Instead of having to use a different screw specifically to handle MuCell, processors now can use a screw tip insert that goes over an existing screw.
“We designed our new screw tip dosing module to be paired with a standard, off-the-shelf screw,” Bechard said. “It allows the injection molding machine producer to use MuCell less expensively because they are using more standard equipment.”
In addition to the screw tip dosing module, plastic processors also will need an injector and a gas system for MuCell physical foaming.
“The injector threads into the barrel of the machine and injects the gas,” Bechard said. “The purpose is to compress nitrogen into a supercritical form and accurately dose the gas into the barrel of the machine.”
Trexel offers four gas-dosing units, the T-100, T-200, T-300 and T-400. Each is intended to work with presses of a different size range, with the T-100 for a smaller machine and T-400 for a larger one.
“We have a control panel on the gas system that allows the user to set up their process,” he said. “In most cases, the control system is controlled from our touch screen on our gas system. We have a few injection molding machine suppliers that have integrated our control into their control, so they can run our gas system from their machine controller.”
Controlling the gas process from the machine controller is slightly less expensive because it does the same work using only one screen, instead of two.
“About 80 percent of our implementations we sell directly to the injection molding machine manufacturer,” Bechard said. “Their customer is ordering a MuCell-equipped machine. The other 20 percent we are upgrading an existing machine to be compatible with our MuCell process.”
When upgrading an existing machine, Trexel often does the upgrade, but other times, the machine manufacturer will do the upgrade. “Some machine manufacturers want to upgrade their own machines,” he said.
MuCell physical foaming can be used with a wider range of resins and a wider range of processes than TecoCell chemical foaming.
“In chemical foaming, you are blending the chemical foaming pellets into the material mix and running it through a standard injection molding machine,” Bechard said. “It is temperature-activated. Once the pellets reach a certain temperature, they begin to emit gas. You have a more limited process because you don’t want to gas it too early or too late. You have to control that through your injection molding process to make sure you get the gas at the right point.
“MuCell is not temperature-dependent. You are adding the gas into the melted plastic. It starts to form bubbles once it sees the pressure drop. With chemical foaming, there is a chemical additive that is added to the material.”
Bruce Adams, senior staff reporter
Contact:
Trexel Inc., Wilmington, Mass., 781-932-0202, www.trexel.com
