Kistler updates sensor technology for injection moulding
Contact-free cavity pressure measurement with piezoelectric sensors is said to be the most sophisticated of the three measurement methods used in injection moulding, with the other two being direct and indirect measurement. The contact-free method is mainly used where high quality and process requirements have to be met (e.g., products for automobile interiors, high optical quality, or situations where very compact injection moulds are used).
Using a new PiezoStar crystal, the 9239B miniature longitudinal measuring pin from Kistler Group. Winterthur, Switzerland, is said to have achieved almost five times the sensitivity of its highly ranked predecessor. The company has also introduced the updated 2205B thermocouple amplifier to integrate temperature sensors more efficiently into the measuring chain for high-grade metal and plastic injection moulding.
The 9239B miniature longitudinal measuring pin is a cavity pressure sensor that is reported to take up 2.5 mm when installed and is able to perform its task without contacting the melt. It is mounted directly behind the cavity wall in the mould structure or the embossing die, where it measures the pressure-induced compression of the mould during the injection and holding pressure phases.
“Thanks to its compact dimensions for optimal installation, the 9239B gives mould makers more freedom when positioning it in smaller moulds or multi-cavity moulds with more complex structures,” stated Marko Marceta, Product Manager Plastics at Kistler.
The 9239B miniature longitudinal measuring pin is said to represent a major advance on its predecessor model: it features a PiezoStar crystal grown by Kistler, which reportedly increases the sensitivity many times over – to no less than 27 pC/N. Kistler has stated that this new measuring pin elevates contact-free cavity pressure measurement to an unprecedented level of accuracy. The mounting method is intended to eliminate the possibility of marks on the part, and the sensor is not exposed to abrasion or corrosion. And because the measuring pin is installed in the preloaded state, it is reported to capture both compression and tensile forces with very high accuracy.
The updated 2205B multichannel amplifier converts signals from temperature sensors installed in the injection mould into standardised voltage signals (thermocouples). Compared to the 2205A predecessor model, the improvements include channels for up to eight thermocouples. In addition, it is now possible to simultaneously connect different types (K,J,N). Type J thermocouples can now also be used at 400°C and the uniform measurement range (0-400°C) reduces the number of variants.
Measuring the mould temperature is intended to widen the scope for process monitoring & control of injection moulding with thermoplastics and other applications. The 2205B has a standard operating temperature range of 125-195°C with additional housing. The temperature sensors are connected using the cut-and-grip method to avoid the need for connectors and tools.
