Silicone injection molding

System solutions for LSR and HTV

Molded parts made from liquid silicone (LSR) open up many fields of application thanks to their universal material and processing characteristics, e.g. when producing hard/soft combinations and in medical technology. Clean room applications are also possible, as the following films show.

Two-component LSR wristwatch

Assembly within the injection molding cycle
ARBURG will demonstrate its expertise in multi-component injection molding and the automation and processing of liquid silicone (LSR). An efficient turnkey system produces the wrist straps from two LSR components and assembles the watch mechanism fully automatically within the injection molding cycle.

An electric two-component ALLROUNDER 570 A with a clamping force of 230 tons and 13.8 oz. and 1.4 oz. injection units in an L-configuration uses a 2+2-cavity mold to produce two two-colored wrist straps from the liquid silicones (LSR) Silopren 2670 and 2620 in a cycle time of 60 seconds in a fully automated process. A linear MULTILIFT V 15 robotic system removes the molded parts and sets them down in a cooling station and then in an assembly station. Here, they are assembled into ready-to-wear wristwatches. For this purpose, the watch housings are supplied in the correct position on interchangeable trays and the buckles are provided by means of a conveyor system.

Drip tubes

LSR production in the clean room
One interesting application for medical technology, for example, is the manufacture of disposable silicone tubes for use on infusion pumps. The electric injection molding machine and the dosage system meet the highest standards for precision and cleanliness.

The electric ALLROUNDER 470 A with clean air hood is docked to a clean room and equipped with an 8-cavity mold with cold runner technology, an LSR package with software adaptations for the SELOGICA machine control system, an LSR cylinder module with special screw geometry and additional interfaces. A specially housed conveyor belt is used to transport the parts directly to the clean room, where they are further processed.

Rain/light sensor

LSR coupling cushion
Liquid silicone compensates for curvature: thanks to an LSR coupling cushion, a rain/light sensor can be optimally attached to a car windscreen. A multi-component machine molds a low-viscosity liquid silicone (5 Shore A) onto a PBT frame, in which the sensors are inserted.

The production of hard-soft combinations with a silicone component represents a significant challenge in terms of machine and mold technology because thermal isolation is required within the mold. The coupling cushion is produced from PBT and LSR on a fully-electric two-component ALLROUNDER 570 A with a clamping force of 225 tons. The four pre-molded parts and four finished components with a part weight of 4.53 g are produced in a cycle time of 38 s.

Button housing

Combined thermoplastic and LSR processing
For the production of a dishwasher keypad, thermoplastic and silicone are processed on an electric ALLDRIVE series injection molding machine to form a hard-soft combination. Here, various material properties can be brought together in a targeted manner and a single production step.

A particular challenge is the joint processing of “hot” and “cold” materials in a single cycle and one mold: the PA must be cooled, while the LSR cross-links at a high temperature. The relevant sections in the mold are consequently separated from one another by means of thermal insulation. This is why transfer technology is particularly suitable here. The molded parts are transferred in the mold via a MULTILIFT robotic system.