Krones AG's ProShape process allows the blow molding of oval or unusually shaped, asymmetrical plastic containers on a Contiform stretch blow molding machine — by selectively taking heat out of a standard preform in specific areas, before blowing.
ProShape is custom-designed for each desired bottle shape, to give precisely defined temperature boundaries. The cooler part of the preform is the last to be stretched in blow molding, so that ProShape enables stable, thick-walled areas to go right next to thin-wall sections.
The process makes containers in non-round shapes and with off-center bottle necks.
ProShape is the company's answer to preferential heating, according to Adam Stowitts, technical manager for plastic technology at Krones Inc., the U.S. division of Krones AG of Neutraubling, Germany.
“It's much more accurate and much faster,” Stowitts said in an interview at Krones in Franklin, a suburb of Milwaukee.
Krones introduced ProShape to the U.S. market at Pack Expo, held in September in Las Vegas. The company showed the process on an eight-station blow molding machine.
Krones calls the technology “selective preform tempering.” Standard round preforms are heated evenly in an oven, in a traditional fashion. Then a star wheel transfers the preforms to the ProShape module.
“There are 20 stations of tempering plates. And these plates are heated to roughly half the temperature of the preform,” Stowitts said. “So they're actually colder than the preform. And they're contoured to match the shape of the preform.”
The plates come into contact with key points on the preform, drawing heat out of that area. The plates do not change the shape of the preform. “They just wick some of the heat on the surface of the preform, and then that plastic stretches differently,” Stowitts said.
Krones designs plates for each bottle shape, and the specific preform. The company makes the plates, and makes molds, at a major machining operation in Franklin.
“A round preform, heated uniformly, is going to blow round, and if you blow round into a flask or a rectangular bottle, you're going to get different thicknesses from one part to another,” he said. “What you do is cool the areas on the short side that have to stretch the longest. The idea is, that preform, that cold area, will stretch last.”
ProShape also can orient preforms, using a camera that takes an image of each preform while it is in the transfer star wheel. Software calculates the position the preform must be transferred to at the ProShape module and then to the blow mold.
Preferential heating generates alternating areas of hot and cold zones in the preform in the oven.