PETpla.net Insider 12 / 2020

PREFORM PRODUCTION PETplanet Insider Vol. 21 No. 12/20 www.petpla.net 18 XActive-Cleaning cuts dust in hot runner systems Sipa has taken an innovative approach to tackling the problem of recycling used PET bottles in the development with Erema of the Xtreme Renew system. But this is not the only route that Sipa is pursuing: XForm systems too can produce high-quality preforms in rPET. Special measures need to be adopted to make this possible, how- ever, since rPET does have special characteristics. One of these relates to fine PET particulates – powder, dust– and how it can accumulate in hot runner systems. These are a concern in any preform processing system, but when it comes to rPET, the concern is greater. Over time, PET dust builds up on the inside the cylinders of the actuators. Initially, this powder does not cause any problems, but as it accumulates, it inhibits the movement of the pis- tons, eventually severely compro- mising the quality of the preforms. If not treated, this accumulation can cause the system to seize up completely. Cost-effective solution Important producers of hot run- ners have known about this problem for a long time, and a lot of work has gone into developing ways to counter it. Sipa has developed solu- tions that keep production of dust to very low levels. With the growing use of rPET, Sipa decided to take a new look at dust, and to devise an easier and more cost-effective solution to the problem. Simplic- ity is key to ensuring that the risk of malfunction is minimised. Sipa aimed for a system that could run continuously for five million cycles before those moving parts subject to wear – piston seals, valves, and so on – needed to be replaced. In a system running with a cycle time of 7 s, that means it would be able to work continuously for 10,000 h. Guided by this vision, Sipa’s en- gineers came up with a system, which the company has since pat- ented, which adapts the compressed air flows, normally used to move the hot runner valves, to also blow out the very few plastic particles that deposit inside the actuators each cycle. Sipa calls the system XActive- Cleaning. XActive-Cleaning principles The hot runner system is equipped with a supplementary circuit incor- porating a series of valves which, controlled with appropriate logic, govern the entry and discharge of air from the cylinders, making sure that any PET dust particles created in the system are evacuated every cycle. This solution should on its own be sufficient to keep the system clean. To be absolutely sure, there is also a “boost” function that can be activated to perform a forced cleaning cycle, at intervals that can be set by the user (every 40,000 cycles for example). This process lasts for a few tens of seconds, so it has no impact on pro- ductivity. High cavitation moulds Sipa has engineering expertise in moulds and hot runners, as well as machines for PET preform injec- tion moulding systems. As an illustra- tion of this prowess, Sipa conceived, designed, built, and delivered preform mould hot runner system with 192 cavities for one of the world’s leading PET container makers, based in North America. This presented an impor- tant challenge in ensuring even and consistent filling of all cavities, at high speed, without excessive force. Sipa met the challenge with the help of its XFlow melt distribution system. XFlow incorporates an innovative hot runner manifold design that Sipa believes provides the best balance of melt distribution in the industry. In fact, it exhibits the lowest pressure drop ever measured. That is one reason why the maintenance interval – five million cycles – is so long, since wear and tear are considerably reduced. XFlow makes high-cavitation systems pos- sible, without having to compromise on balance, pressure losses, and the formation of acetaldehyde due to polymer degradation. XFlow can be applied to moulds with more modest levels of cavitation with equally impressive results. XFlow applies as an advanced concepts of polymer fluid dynamics to hot runner engineering. By taking melt rheology aspects into account, it is possible to obtain balancing results quite beyond those of traditional sys- tems. Sipa has been implementing XFlow in its hot runner systems for several years now. www.sipa.it