packaging | PET preforms
in the vent areas,” Rivollet says. “Then we flash the mould and the escaping PET sticks to the dust. We are using the preform itself to clean the vents.” The self-cleaning routine requires no more
than a press of a button on the machine control and is completed within one moulding cycle. Because production is not interrupted there is no need to stop and restart the dryer, which in itself can be a contributor to quality problems. Flashed preforms - complete with captured dirt – are diverted away from the production feed. “You can run the cleaning process as many times
as you want because there is almost zero impact on production time,” Rivollet says. While some more intensive cleaning will be required, he estimates this to amount to no more than 10 times a year for a system running a 5.5s cycle. The automated self-cleaning process relies on a
combination of mould features and – critically – hot runner design to achieve a fully controlled flash. While it is the opening of the mould that creates the flashing space, Rivollet explains it is the improved balance within the hot runner and the precise regulation of the flow into each of the 96 cavities that is key to the self-cleaning. “You have to be sure that every cavity gets exactly the right amount of material otherwise you will not clean all of the cavities,” he says. The improved flow balance in the latest HyPET HPP5 hot runner is also said to pay benefits in normal production, where the reduced variation across the mould allows part weights to be reduced further without risk of fill problems. Other elements within the new reduced mould
maintenance package include extending the periods between lubrication and automating mould alignment checks. “Mould misalignment is one of the main causes of mould wear and loss of part quality. We are using six sensors in the mould to detect the relative positions of the cavity plate and core plate – the two components that make the preforms – and to warn the operator of any problems,” says Rivollet. The system is able to detect an
Left: Husky’s
HyPET HPP5 machine is the basis for its new
preform coinjection system
offset of as little as 0.003mm and displays the appropri- ate correction process on the machine control panel. Husky is also using the HyPET HPP5 platform as the
base for its new – and first own-developed – coinjection barrier technology. In the past, Husky worked with US-based Kortec, supplying the machines and moulds for use with Kortec’s hot runner. Milacron’s acquisition of Kortec early last year brought that arrangement to an end. Husky claims its new coinjection system provides
unrivalled levels of fill consistency between cavities due to a new patented manifold design feature that minimises the “splitting” of the melt that creates imbalance in conventional systems. “Regardless of the cavitation we only split the melt twice,” says Rivollet. “Typically in a standard manifold the melt is split four or five times – every split of the melt makes it more challenging to control shear heat and thermal imbal- ance that follows through the channels.”
Right: Husky’s
new coinjection system provides complete barrier
protection at the base and control of core
layer placement in the wall
16 INJECTION WORLD | April 2015
Controlling barrier Rivollet claims that across the cavities in a shot the distribution of barrier material weight as a percentage of the total preform weight comes with a bandwidth of ±0.5% for a nominal weight as low as 2%. That is two to three times narrower than the current industry standard, he says, and is important because the volume of material in the barrier layer controls the shelf life performance – and ultimately the cost – of the final preform. The narrower the variation, the closer to the optimum the process can be set and the less of the costly barrier material is required. “What is new here is having this level of control. If you need 4% barrier but have to dose 6% to be sure of having the right amount in every preform it’s too expensive. But if you need 4% and can dose only slightly above 4% it becomes possible,” Rivollet says. Aside from the new balanced manifold design,
Husky’s coinjection systems also feature complete thermal isolation of the PET and barrier melt stream
www.injectionworld.com
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