Flexible production with faster neck changes on the stretch blow molder
Greater line efficiency thanks to shorter changeovers/ In-built magazine for easier replacement of change parts/ Newly developed mandrel heads can be removed more quicklyDortmund, )
It is usual to try to only manufacture and fill bottles with an identical neck on one line. If a water bottler wants to produce a still and a carbonated product alternately, until now it had to decide whether to use the higher and heavier neck really only necessary for carbonated water for both products or not. The bottler would then save time but waste material and money in the filling of the still water. The alternative would be to live with the long intermittent downtimes caused by a neck changeover. Besides these considerations, marketing often plays a role in a decision like this, calling for a bottle adapted to suit the various products. Combined lines such as these that require neck changes are very often found in Japan.
Complex process made simple
In order to gain an idea of just how complex the exchange of parts for the above process is on the stretch blow molder alone, it is worth taking a closer look at the individual steps involved. First, the preform infeed needs to be adjusted and what are known as the mandrel heads replaced that are wedged into the preform necks to guide these safely through the heating module. The grippers that transport the preforms by their necks to the blow wheel are then exchanged on the star wheel. Finally, the molds in the blow stations, the blow nozzles and often the stretch rods and further grippers downstream that feed the finished containers to the subsequent filler need to be changed over. Here, the number of parts that need replacing depends on the size of the machine. The mandrels and shields especially are of particular importance: the higher the machine output, the longer the heater, as the containers may move faster but always need the same amount of time to heat up. On an InnoPET Blomax 16 stretch blow molder with a capacity of up to 48,000 bottles per hour, around 170 mandrel heads and shields have to be changed by hand, for instance. This means that this part of the neck change is particularly relevant when it comes to the amount of time needed – unlike the exchange of the just 20 grippers that is quick in comparison.
Thought through to the end
In order to considerably speed up the conversion process as a whole, KHS has not just simplified the individual work steps involved but also the concept governing the entire procedure. “We started out by analyzing how the operators work,” says Arne Andersen, stretch blow molding product manager. “On this basis we then considered how all tasks could be made easier and organized as perfectly as possible – paying particular attention to the ergonomics. Magazines were thus installed that stop the operator having to repeatedly abandon the machine to fetch and carry change parts, for example. We also replaced the grippers to reduce the number of screws that need to be loosened. At the same time, newly developed mandrel heads are now used that can be simply removed by pressing a release spring. This process used to be much more complex.”
In this case, KHS consciously went for an approach that thought all of the specific processes through to the end based on actual customer requirements, Andersen emphasizes. “We aimed to achieve the best possible improvement within the shortest possible time.” KHS managed both: thanks to the simple neck change, the time needed for two operators to convert the KHS InnoPET Blomax16 stretch blow molder, for instance, has now been cut by a good two thirds to approximately just 86 minutes – including the preform infeed. As the PET bottles in a block like the KHS InnoPET BloFill are held and conveyed by their necks throughout the entire machine, not only the stretch blow molder but also the filler has been developed further in order to shorten conversion times. The capper was one particular area of focus, where the cone responsible for lifting and closing the bottles needs to be replaced manually. No conversion is required regarding the screw cap, however, as there are two cap feeds – one for each neck diameter in the respective format.
Greater flexibility, less storage space
Andersen is convinced that the new neck change option will give beverage producers much greater flexibility, as they can now also run much shorter production cycles for bottles with different necks and therefore reduce their warehousing effort accordingly. “Some of our customers produce just in time; this means that the finished containers are loaded straight onto the truck without any interim storage. The drastically reduced conversion time will now enable filling operations like these to change necks more frequently; they thus profit from totally new options in their production planning.” The same goes for converters who can now produce the generally smaller batches for their customers – often in very different bottles – on a single line much more efficiently. The first customers in Asia who are already using the quick neck change developed by KHS are extremely pleased with the amount of time and effort they save. This retrofittable option has thus earned plenty of praise from KHS’ clients in this region.