17/02/2011

www.gupta-verlag.de/thermoplastic-elastomers

Effective combination of machine and mould

A two-component electric Allrounder 720 A produces 12 PP toothbrushes with moulded-on TPE elements per 20 s cycle and demoulds them with the mould closed.It involved a two-component version of an electric Allrounder 720 A (3,200 kN) and two injection units, one size 800 (horizontal) and one size 290 (vertical). 12 toothbrush bodies made from PP with moulded-on TPE ele­ments were produced per cycle.Main advantage of SCPS or paternoster technology is that the moulds are only slightly larger than standard moulds. The parts were demoulded with the mould closed and removed by a pneumatic removal device from Barth. The cycle time for production of the 12 toothbrush bodies is ca. 20 s. The proportionate weight of the two components is 10 g for the TPE and 6.15 g for the PP.Zahoransky's innovative SCPS (Servo Cavity Positioning System) technology guides the parts vertically through the mould. SCPS complements the mould systems used to date for multi-component injection moulding, such as rotating or stack-turning mould technology. Until now, the problem with these technologies was that the moulds needed to be very large. As a consequence, these large moulds necessitated machines with a high clamping force, even though the products themselves did not require this.With the SCPS technology, Zahoransky has developed a system that does not use the conventional rotating, interchangeable variants. The 12-cavity mould features special moulded part carriers on the ejector side, which are rolled vertically from station to station via a spindle drive. When the mould opens, the continuous system engages the part carriers in the cavities and transfers the preforms to the subsequent station. The preforms are injected at the first station. After opening of the mould, the preforms are transported into the final injection position by the moulded part carriers. Once the second component has been injected, the moulded part carrier conveys the finished article to the removal position and removal takes place automatically with the mould closed. The next injection takes place simultaneously. The empty moulded part carrier is transported back to the first station by means of a second spindle drive.The main advantage of the SCPS technology is that the moulds are only marginally larger than standard moulds. Therefore they can be used on standard machines with the optimum clamping force for the parts, without requiring any additional equipment. This means that the investment costs for the machines remain reasonable because it is no longer necessary to use oversized machines as a result of the mould sizes. Likewise, there is no need to enlarge the clamping platens or installation dimensions. All movements in the mould, including those of core pulls and needle shut-off nozzles, are driven servo-electrically, making them independent of the machine technology. In turn, this means that there are no restrictions with regard to simultaneous machine movements, ensuring optimised cycle times. Finally, the application of force in the mould is absolutely central, which results in high-quality parts.

www.gupta-verlag.de/thermoplastic-elastomers