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KraussMaffei at Swiss Plastics: High precision in silicone processing


The requirements of medical technology when it comes to product cleanliness and quality are high. At the Swiss Plastics Expo exhibition (January 24 to 26, 2017, Lucerne Trade Fair, Switzerland), KraussMaffei will be demonstrating how a PX 50-180 SilcoSet can satisfy these requirements with high precision and productivity in the growth market of silicone.

The new all-electric injection molding machine produces 0.03 g lightweight LSR (liquid silicone) diaphragms in a 32-cavity mold.
Flexibility is the key

The PX 50-180 SilcoSet is exemplary of the high degree of modularity and precision of KraussMaffei's new, all-electric PX series. "The modular concept of the PX is especially beneficial in the micro-injection of silicone, where extremely small shot weights, but also large platens are required," explains Bruno Schleiss, Managing Director KraussMaffei Schweiz AG. The ejector of the PX 50-180 SilcoSet is electric and encapsulated, so it corresponds with the strict clean room requirements of medical technology. The compact design provides lots of space for demolding and peripheral equipment and good accessibility.

Another highlight is a servo-hydraulically powered injection unit for the nozzle contact force, which guarantees reliable and leak-free injection of the low-viscosity LSR material through the open cold runner. The version with two pressure cylinders provides for even power transmission and high stability. Other equipment features of the SilcoSet machine at Swiss Plastics include a water-cooled cylinder, an electrically heated mold and a vacuum pump for mold ventilation.
High precision and greater stability

The production of LSR diaphragms weighing just 0.03 g and measuring just 0.2 mm thick in a 32-cavity mold requires particularly high precision. Unlike thermoplastics, LSR does not shrink in the cavity, but rather expands, meaning precision is primarily the result of accuracy during injection. Here, the PX series scores particularly well by being an all-electric injection molding machine. Another highlight is the plasticizing process, which has been specially configured for applications with silicone. It features a separate non-return valve with precise closing characteristics. The linear guidance of the moving platens also provides for precise, low-friction clamping movements, even with high mold weights.

KraussMaffei's new APC plus function takes on a particularly important task, for it compensates for the batch fluctuations commonly encountered when processing LSR. "LSR processing is especially demanding. The consistency varies from water to honey, and demands absolute platen parallelism to ensure that the mold closes extremely tightly, and an injection molding process that is refined to the finest detail, explains Schleiss. As the process progresses, APC plus monitors the viscosity of the material and corrects the filling volume even in the shot. The process as a whole is made even more precise; the part weight remains constant. APC plus is even able to compensate for any potential preliminary cross-linking of the silicone.

Partner and customer of the PX 50-180 at Swiss Plastics is the Swiss silicone injection molding specialist Trelleborg Sealing Solutions Stein am Rhein AG, from where the high-precision mold and the metering unit come. The mixing unit is an electrically powered scoop piston pump supplied by the company Reinhardt Technik. The end customer is the company Filtertek.
Optimized gripper concept

Automation with a 6-axis robot allows precise demolding of the micro components, which are then electrically discharged and filled into jars. "One particular challenge in this application is the handling of the delicate components. The geometry means that the 32 diaphragms have to be grasped at the same time and are carefully peeled from the mold, all at a mold temperature of around 190 °C and without contact with the mold," explains Schleiss. The task is performed by a specially designed gripper from KraussMaffei Automation.

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