PETpla.net Insider 04 / 2011

CAPPING / CLOSURES 40 PET planet insider Vol. 12 No. 04/11 www.petpla.net Injection moulds for the production of caps with a tamper-evident band (TE) are compact high-performance systems with exacting requirements in terms of output, production safety, quality, and reliability. The decision of a manufacturer for one concept is essentially influenced by the fact that they are familiar with one particu- lar mould concept. Regional safety requirements can also influence the decision for or against one particular removal concept. Traditional sliding split moulds Many cap producers use slider systems. This most traditional of removal methods is preferred by the majority of mould makers and widely used in many mould-operating facili- ties, numerous production sites and among most operators. Sliding split moulds remove the tamper-evident band by opening the sliders. Slider systems are available with different geometries and are pop- ularly used for demoulding undercuts of moulded parts. Removal with collet chucks Collet chuck moulds are con- sidered rare and they represent a smaller market segment, as only very few suppliers are able to manufac- ture them. Nonetheless, the market segment for this removal method is growing steadily. Schöttli claim that their collet chuck moulds offer to a high extent freedom in cap design and geometry combined with a particularly compact cavity arrangement in the mould and low space requirements. This method allows production on relatively small injection moulding machines. Collet chucks ensure that all bridges that connect to the tamper- evident band (TE) are demoulded in a geometrically identical manner because of the opening of the collet chuck in six directions. This approach is beneficial for contract bottling com- panies as well as for consumers. The constant and even geometry of bridges across the diameter of screw caps allows an uninterrupted capping operation at the bottling fill- ing line as the tamper-evident band is evenly distended during capping. During this process, all connecting bridges are subjected to an identical load, so that weak connections are not torn during capping. Schöttli claims a lifecycle guar- antee for its collet chucks of 5 million cycles, despite the fact that they are under high mechanical stress due to frequently changing loads. Pro- cessors using smaller collet chuck injection moulds have recently taken to ordering new moulds with a higher number of cavities. Accordingly, the Swiss company has built collet chuck moulds with a total of more than 8,000 cavities over the past years and almost all recently supplied moulds were equipped with 96 cavities. Post-slitting of the tamper-evident band Bottling specialists in the US, Europe and in China prefer caps with continuously gated tamper-evident bands that become operable by means of folding or slitting in downstream stations. These screw caps provide consumers with maximum safety from manipulation. This mould concept does not require any further movement for demoulding by sliders or collet chucks. Nonetheless, demoulding of small undercuts also has to be ensured. The core must withstand the forces applied during stripping. Schöttli adapts the forced ejection method to product and customer requirements. After injec- One-stop shop for cap moulds with various ejection systems A feather in their caps Schöttli AG is a manufacturer of injection moulds for the production of caps, offering all standard mould concepts from one single source. 96 bottle caps, the current maxi- mum number of caps produced in one single mould, can be removed by slider systems, collet chucks or without either of these two, in cases where the tamper-evident bands are slit after moulding. 32-cavity Schöttli cap mould with slider system