WEST WARWICK, R.I.—Battenfeld GmbH is taking gas-assisted injection molding in a whole new direction: gas pushing on the surface of a part, to eliminate sink marks.
Battenfeld is aiming its Airmould Contour technology at firms that mold large parts with ribs, including housings, covers and panels. The technology could open some major new markets to plastics, such as housings for washing machines and other large appliances.
With traditional gas-assisted molding, gas, usually nitrogen, is pumped inside the mold. The gas pushes melted plastic out in all directions against the mold. That creates a hollow space inside the part. The process is internal.
Airmould Contour is different.
``We call it an external gas-pressure process,'' said Helmut Eckardt, technical director of processing engineering at Battenfeld GmbH. ``It is a nice process for all moldings that need one-surface areas with a good visual exterior surface.''
Here's how it works: The mold is filled completely with melted plastic. Gas is injected between the mold surface and the melt on the rib side. Pressure is maintained during the cooling phase. Before the mold opens, the gas is vented out.
The German injection press maker released details about the technology during an April 15 press conference at its U.S. unit, Battenfeld of America Inc., in West Warwick. Battenfeld charges a onetime license fee of $3,000 per mold. Existing molds can be modified to run it.
So far, Battenfeld has sold 10 - 20 licenses, none in the United States.
Airmould Contour is designed for cosmetic parts with large surface areas, specifically, flat parts that require a high-gloss surface on one side. Ribs and bosses on the back side cause problems with sink marks and blemishes on the cosmetic side, a common injection molding problem caused when the plastic shrinks as it cools.
Converting those types of molds to regular gas-assisted molding is a costly undertaking, according to Battenfeld. Gas channels must be cut into in the ribs. But new channels are not necessary to convert a mold to Airmould Contour. Instead, the mold is hand-textured to create a rough surface that lets the gas pass through.
The license fee gives a molder Battenfeld's expertise in how a specific mold should be textured and prepared, and where the nozzle should be located.
Airmould Contour targets only problem areas.
``We treat it in the area where we want to compensate for the rib,'' Eckardt said.
The gas acts as a pressure cushion in lieu of pack-and-hold pressure used in conventional molding, to push the melt flat against the mold.
Battenfeld claims other benefits include shorter cycle times, the ability to use smaller-tonnage presses, and reduced part warping.
A research and development firm, Kontor Moulding Systems Ltd. of Oxford, England, invented the technology. Battenfeld of Meinerzhagen, Germany, bought worldwide patent rights through an exclusive license in 1997 and changed the spelling to Contour.
Battenfeld supplies the gas injection equipment for both Airmould Contour and Airmould, its traditional gas-assisted injection molding system introduced in 1987. Both systems can run on the same equipment.
Airmould has run into high-profile legal challenges from competitor Michael Ladney and his firm, Gain Technologies Inc. of Sterling Heights, Mich. But Battenfeld officials say they expect no problems from Ladney on Airmould Contour, because it is so different from regular gas-assisted molding, which uses gas inside the melt.
``That's the core idea of Ladney's patents all over the world. So we cannot see how we have any problems with Ladney on this technology,'' said Michael Gosdin, head of Battenfeld's patent and license department.
Battenfeld said it believes any patents from other firms that do deal with external gas-assisted molding have expired.