Manufacturing products for health-care applications is a process subject to stringent standards and requirements regarding the acquisition, compliance with and documentation of process data. While liquid silicone rubber (LSR) injection molding (LIM) has long been a well-known and commonly used technique in this area, a potential source of problems has always been achieving a precise metering of additives and colorants.

Until now, sufficiently sensitive control and associated data acquisition capabilities have simply not been standardly available. Now, Austria-based Elmet, an internationally successful developer and manufacturer of LSR dosing systems, has launched a high-precision, automatically controlled multicomponent dosing system that enables processors to overcome these obstacles.

The key element of the new system is a high-resolution flow meter. Integrated as a closed-loop control instrument into the colorant and additive feeding system, it determines the dispensed volume with a resolution of 640,000 increments per liter. On the basis of these very precise measurements, the system accurately controls the supply of colorants and additives, in line with the set point defined on the touch display. At the same time, the corresponding values are made available for documentation.

In particular, processors using colorless functional additives, including certain active ingredients, will benefit from such precision-controlled metering. Optically imperceptible and hence potentially undetected deviations from the set point—due to wear, clogging strainers or changing properties (viscosity) of the additive charge—can result in significant extra costs and, in the worst case, may even have an impact on the health of the end-user.

The Elmet system is based on exact volume measurement. Metering accuracy is maintained throughout by continually readjusting the feed rate to the originally acquired and stored reference value. As long as these readjustments remain within a certain tolerance range, the operator is informed of this situation so that action can be taken in good time. However, if tolerances are exceeded, the system will automatically discontinue the production process to prevent rejects before they occur, thereby saving costs.

The new flow meter is part of ELMET's TOP 3000 S multicomponent dosing system for LSR injection molding applications, which comes equipped with particularly rugged and energy-efficient pneumatic drives and supports the use of both 20-liter and 200-liter drums. The system maintains a fixed 1:1 mixing ratio of the LSR A and B components over the entre drum content, ensuring a material utilization rate of over 99%. Its maximum discharge rate is 2.5 l/min, with a rate of colorant addition of up to 10%. The associated process data for each individual shot can be exported via an USB, LAN or WLAN interface.