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Liquid silicone rubber processing at its best.

Arburg's medical technology sector was presented with a requirement for a machine docked to a clean room and with precise LSR metering. Said to be an ISO GMP ISO 6-7 compliant solution, the 470 A operates docked to a clean room. It produces disposable hoses for use on infusion pumps. For a chance to read about it and watch the video, see http://www. arburg.com/en/gb/media-centre/videos/processes/silicone-in-jection-moulding/.

Particularly in the field of medical technology, the requirements set by the OEMs and users must be precisely met. Here, the modular product range from Arburg has distinct advantages, as it renders production cells configurable and allows them to be precisely tailored to customers' production requirements. Further benefits include the various clean-room concepts and Arburg's comprehensive expertise in the area of medical technology and LSR processing, as well as the opportunity to work with competent cooperation partners. This means that customer support is fully ensured from the outset through to commissioning of the appropriate systems.

Electric machines are fast and precise

The molding machine selected for the project was a fast, precise Allrounder 470 A electric machine with a clamping force of 1,000 kN. With its planetary gear liquid cooled drives, it proved ideal for the customer's demands on cleanliness and shot-to-shot repeatability. A de-ionizing clean air hood generates slight overpressure in the area of the clamping unit, preventing foreign matter in the ambient air from entering the production area, enabling ISO class 6 manufacturing to be achieved. A specially housed conveyor belt is used to transport the parts directly from the machine housed in the gray area into a clean room without further contamination. The parts are then further processed in the clean room. Due to the through-the-wall approach, the clean-room is now considerably smaller and more manageable than otherwise would have been the case.

[FIGURE 1 OMITTED]

Individual machine equipment

The eight-cavity mold was built by Austrian LSR specialist Rico, and the electric Allrounder was specially configured for LSR processing. An LSR cylinder module with special screw geometry and additional interfaces, for example for dosage systems, this machine also has a number of important LSR-specific options. These include, for example, additional mold heating circuits and an interface for external brushing and demolding devices that can be driven either pneumatically or servo-electrically. The equipment is rounded off by the option for controlling different needle shut-off systems and a fully-integrated vacuum system with graphical display and monitoring via the Selogica machine control system.

2KM dosage system

The servo-electrically-driven SilcoStar e-Flow from 2KM, which is equipped with a drive system that actuates the pumps centrally, operates with extreme precision. This means that the familiar problems with four-pump systems can be effectively avoided. A modern PLC control system with display enables the machine and production parameters to be entered using a keypad. The servo-electric axes of the system can be adjusted and positioned precisely, leading to an energy-efficient, highly reproducible dosing process without loss of material.

Mold technology

One of the special features of LSR processing is the fact that the two material components are only mixed directly upstream of the machine's cylinder module. The cold runner system in the mold transports the already mixed, as yet not vulcanized material directly to the hot mold cavity. The liquid silicone reaches a temperature of approximately 20-25[degrees]C. As well as saving material at a defined material injection point, the advantages of this process include improved automation and shorter cycle times.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The cold runner system can be relied upon to prevent the crosslinking of the silicone. However, the reaction in the cavities is very rapid after this. LSR molds have a complex structure because the cold sprue channels need to be insulated against the hot mold, but the "cooled" areas must actually be maintained at a very particular, narrowly limited temperature level. If this is not successful, the removal of the hardened material from the sprue channels and mold is a time-consuming task. To avoid this, very sensitive and precisely controlled dosage and cold runner components are now used. For example, Rico cold runner technology allows the parts to be injected directly without any loss of quality.

The mold concept includes a core bar that holds the parts inside the cavities, then demolds them as they drop from the opened mold using a stripper plate. The stripper plate functions can be programmed via the Selogica machine control system. The cycle time is 18 seconds.

LSR hose with a wide range of applications in medical technology

The special properties of liquid silicone mean that LSR molded parts are particularly suitable for medical technology applications. The silicone hoses produced are used on peristaltic pumps for transporting sensitive fluids in sterile environments. These include infusion and dialysis pumps, as well as cardiopulmonary machines. Disposable articles like the silicone hoses are used to ensure maximum hygiene.

LSR is extremely heat resistant, flexible, and offers excellent resilience. For medical technology, a good degree of resistance is essential for both standard and multiple sterilization procedures. Simple dyeing as well as suitability for combination with a variety of metals and plastics make liquid silicones ideal for a wide range of applications. Because it is recognized as physiologically safe, LSR is ideal for use in medical technology. The market for LSR applications is expected to continue growing in the coming years, partly due to the increasingly wide range of materials available.

by Sven Kitzlinger, Arburg
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Author:Kitzlinger, Sven
Publication:Rubber World
Date:Jun 1, 2015
Words:913
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