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The challenge at hand—to manufacture a sensor housings for flow metering with an integrated seal for medical device application in a cost-effective manner. The solution—an electric 120-tonne Engel e-victory 200H/80W/120 combi (two-shot) injection molding machine with an Engel viper 20 linear robot.

August 28, 2015

2 Min Read
Engel shows medical molding capabilities in two-shot molding of PBT, LSR

The challenge at hand—to manufacture a sensor housings for flow metering with an integrated seal for medical device application in a cost-effective manner. The solution—an electric 120-tonne Engel e-victory 200H/80W/120 combi (two-shot) injection molding machine with an Engel viper 20 linear robot.

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Medical device housing is two-shot molded using LSR (green) and PBT.

The first stage [of molding] involves housings being molded simultaneously from a 30% glass fiber-reinforced PBT material from Lanxess in a four-cavity mold. The robot then transfers the rigid housing components to a second set of cavities, where the seal made from liquid silicone rubber (LSR) is directly over-molded. While the soft components of one set of housings are being processed, the next housings are already in progress in the lower half of the mold.

Says Aram Tongurai, managing director of Engel Machinery (Thailand) Ltd.: “Having the seals molded directly onto the housings not only increases production efficiency, but also product safety. The thermoplastic and elastomer form an inseparable unit.” There are examples for this application in every sector, from the automotive industry to medical technology to packaging. Further, the LSR grade from Japan’s Shin-Etsu is a self-bonding material that does not require priming of the rigid surface prior to LSR injection.

The shot weight of the LSR components is just 0.04 grams per part, and a customized solution would normally be required for processing LSR when such a small injection volume is involved. Engel is able to use a standard unit, however. To meter the LSR, mini pumps with one-liter tanks are used that all fit within the safety housing of the injection molding machine, saving both space and costs.

The shot size for the rigid PBT component. is 21 g. Further, the tool, built by Hefner moulds, employs a hot runner for the thermoplastic injection and a cold runner for the LSR injection.

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