Silicone injection moulding
Moulded 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.
Assembly within the injection moulding cycle
ARBURG will demonstrate its expertise in multi-component injection moulding 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 moulding cycle.
An electric two-component ALLROUNDER 570 A with a clamping force of 2,000 kN and size 400 and 70 injection units in an L-configuration uses a 2+2-cavity mould to produce two two-coloured 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 moulded 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.
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 moulding 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 mould 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.
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 moulds 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 mould technology because thermal isolation is required within the mould. The coupling cushion is produced from PBT and LSR on a fully-electric two-component ALLROUNDER 570 A with a clamping force of 2,000 kN. The four pre-moulded parts and four finished components with a part weight of 4.53 g are produced in a cycle time of 38 s.
Combined thermoplastic and LSR processing
For the production of a dishwasher keypad, thermoplastic and silicone are processed on an electric ALLDRIVE series injection moulding 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 mould: the PA must be cooled, while the LSR cross-links at a high temperature. The relevant sections in the mould are consequently separated from one another by means of thermal insulation. This is why transfer technology is particularly suitable here. The moulded parts are transferred in the mould via a MULTILIFT robotic system.