Even tighter tolerances than for bottle preforms

Sipa has spent several years developing new injection mould tooling solutions for medical applications sector. A special cold-half core-centring technology that it developed for blood collection tubes (BCTs) is already used successfully at a leading global supplier of these critical and widely-used items. The solution Sipa developed is claimed to be unique in the industry and the subject of a patent application. The development makes it possible to adjust the core alignment from the front face of the cold half, in contrast to competing solutions that require access the back of the core plate. This makes any adjustments easier and faster to carry out during production.

Time- and cost-saving core-centring feature is ideal for blood collection tube production

Production of high-quality blood collection tubes demands that wall thickness around the circumference is within very tight tolerances. This can only be guaranteed by precise design and especially accurate production of the various elements in the injection mould. While such criteria also apply to more common PET products like bottle preforms, consistently high performance over long-term production is more difficult to ensure with BCTs.

Why is this? There are two specific reasons. First, because BCTs have a diameter much smaller than regular preforms, the various components of the mould also have reduced dimensions. In the specific case of the cores, these obviously also have a small diameter, which means that their stiffness is lower than preform cores. As a result, they are more likely to flex under the pressure of the PET melt if the wave front during injection is not perfectly symmetrical.

The situation is made more critical by the fact that injection pressures used in BCT moulding need to be higher than in preform production, due to the higher length: thickness ratios of the tubes. This obviously puts the mould components under greater stress, increasing the potential for deflection of the cores.

The solution developed by Sipa is claimed to make it easier to fine-tune the positions of the cores, correcting any slightest deviation from the set value, and so enabling production of a product with optimal wall thickness.

“Our solution is unique because it allows the processor to make adjustments to the mould while it is still in the machine, simply via access to the front face of the cold, moving half,” says a Sipa spokesperson “No disassembly is necessary, providing the user with a considerable advantage in time taken for the execution of the operations.

“Obviously the task is also much simpler than in an adjustment operation requiring access to the back of the mould, where the mould, or at least part of it, has to be taken out of the injection moulding machine, dis-assembled, adjusted, reassembled, and then refitted to the machine.”

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