two of which incorporate an additional two integrated cores for the fork lift access elements. The ejector system comprises
four central block ejectors assisted by round ejectors at the periphery of the pallet and the cooling system for the core PP component is optimised for a 90s cycle time. The big challenge for Haidlmair was how to incorpo-
rate the relatively small volumes of TPE onto the required parts of the pallet. The design called for the incorporation of 2mm of TPE onto the top of each rib in the nine foot structures and onto the six ribs running across the full length of the upper and lower surfaces of the pallet. This called for placing just 129cm3 the top surface and 86cm3
of TPE on part with a total volume of 18,000cm3
on the bottom surface of a .
“This is the most complex project which we have
completed until now in pallet moulds,” says Haidlmair project manager Guenther Auer. “The mould system is ground breaking in my opinion, due to the size and the different movements in the mould. There is also a big difference in the weight of the different materials – close to 18 kg of PP material and only 200 grams for the TPE.” Feasibility studies carried out with Haidlmair’s machinery partner in the project, Engel, determined that a 3,200 tonne two platen machine from the Austrian firm’s Duo product line would accommodate the mould. Two large injection units arranged in parallel and directly connected to the hot runner system deliver the PP for the pallet main body. Auer says this arrange- ment was preferred to guarantee sufficient plasticising
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capacity would be available to further optimise the production cycle. Two small injection units deliver the TPE. One is positioned on the top of the fixed platen and the second on the rear of the moving platen where the hydraulic ejector system would normally be located. Each of the secondary injection units feeds the mould via a hot runner, one with nine nozzles and the other with 13 nozzles in a 9+4 arrangement. Even so, it was deter- mined that it would not be possible to fill the four corner areas of the pallet using simple injection, forcing a redesign of the mould to create a connecting route for the TPE. “A pallet design adaption and the addition of four
miniature side cores, which open and close the respective area at a length of about 10mm to 2mm rib width provided the solution,” says Auer. The complex hot runner system for the project was supplied by Husky Injection Molding Systems and is equipped with 96 zones of control. The moulding process is a two-
stage fully automated sequential routine. First the pallet body is moulded and cooled, then the mould is opened in two sequential steps. In the first step a 2mm gap is created on the fixed platen side and the
April 2012 | InjEcTIOn wOrlD 19
Main image: The moulding
process is fully automated
Integrated TPE anti-slip
elements in the Interpallet design help
provide optimal load security
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