By: Bill Bregar
October 7, 2013
Linde LLC is promoting carbon dioxide — the stuff that makes the bubbles in your soda — to cool down injection molds.
Linde is targeting the plastics industry, where pressure to cut cycle times has spawned several rapid-cooling technologies that use water or oil to heat and cool the mold. Linde has developed the system-level design.
Rick Ortwein, a Linde applications specialist, said liquid carbon dioxide can very quickly cool down hot spots in the mold, in some cases cutting cycle time in half.
Linde will exhibit at K 2013 in Düsseldorf, Germany (Hall 14/C56).
Ortwein said it is fairly simple to use liquid CO2 in a mold. The system uses solenoid valves to time the injection of the gas through small, stainless-steel “capillary tubes” and into the mold. The chambers can be either drilled into the mold, or they can be formed by hollow core pins, Linde said.
The tube goes to about a quarter of an inch from the part. The fast cooling is especially good for cooling long, thin areas, cores or other difficult-to-reach parts. “It’s for those hot spots that you can’t get water to go into,” Ortwein said.
Using controlled pulses, liquid carbon dioxide is fed under high pressure (about 60 bar) through the capillary tubes, directly to the area that needs cooled. The action takes place when it comes out of the tube.
“When that pressure drops quickly, a portion of the liquid CO2 turns to snow, or dry ice,” Ortwein said. The snow and gas mixture drops the temperature down to minus 109° F.
The CO2 pulls heat out of the mold, and then escapes as a gas.
In problem areas, such as long, thin sections, or long distances between cooling channels and molding surfaces, it can lead to surface defects like knit lines and warpage, and long cooling times.
Ortwein said the liquid carbon dioxide process has been used in Europe for mold cooling for six or seven years. “Our first venture in the U.S. market was at the NPE show in Orlando,” he said.
One example from Europe is using liquid CO2 cooling of a mold producing automotive headlamp housings. The design of the cooling system used a thermal image of the mold, which showed where the capillary tubes had to be placed.
Of course, carbon dioxide has other plastics industry uses. Linde supplies gas for enhanced gas-assisted injection molding, foaming and a process to clean injection molds, called Cryoclean.