PET preform injection molding is a highly competitive business, so production efficiency is critical to success. Systems needed to be up and running as much as possible, making preforms as perfect as possible. The hot runners in the mold are a fundamental element in the total system, so any anomaly in their operation can compromise output.
In addition to mechanical or electrical issues that can affect the efficiency of a hot runner system, there is also another problem that processors should be well aware of: dust. Over time, PET powder builds up on the actuators. Initially, this powder does not cause any problems, but as it accumulates, it inhibits the movement of the actuators, eventually severely compromising the quality of the preforms. If not treated, this accumulation can cause the system to seize up completely.
This is especially true when processing rPET. This trend, a response to growing concern about the scale of the global plastics waste problem, presents a significant challenge for the entire PET bottle production chain.
Producers of hot runners have known about this problem for a long time, and a lot of work has gone into developing ways to counter it. SIPA is among the leaders in this area. It has developed solutions that keep production of dust to very low levels. But increasing performance requirements and the growing use of recyclate – rPET – are complicating the issue. For this reason, SIPA decided to take a new look at dust, and to devise an easier and more cost-effective solution to the problem.
The target of the development was to find a solution that was smart and simple at the same time. Simplicity is key to ensuring that the risk of malfunction is minimized.
The highly ambitious goal was to have a complete hot runner system that needs maintenance only to carry out standard renovation operations – that is, to replace worn components. A system that could run continuously for several million cycles before those moving parts subject to wear – piston seals, valves, and so on – needed to be replaced that means it would be able to work continuously for several tens of thousands hours.
The hot runner system is equipped with a supplementary circuit incorporating a series of valves which govern the entry and discharge of air from the hot runner, 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. But just 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. This process has no impact on productivity.
A hot runner system incorporating XActive-Cleaning includes additional channels within the hot half themselves, so there are no obvious differences from a conventional hot runner system, apart from an additional air connection with the XActive-Cleaning device.
The XActive-Cleaning device was born for the Sipa Xform preform systems but is applicable to any injection machine in a very simple way and the only action the operator has to carry out is the regular cleaning of the easy-to-access filters installed on the external box.