Tips for colour changing Hot Runners

The cleaning of a hot runner should always be carried out one step at a time in the correct order: housekeeping, screw and barrel, manifold and finally tips. Housekeeping Always start from the beginning and it always starts with housekeeping; ensure hoppers, granulators and conveying systems are immaculately clean. This should never be taken lightly especially when using purging compounds. The faster results expected from a purging compound can be seriously hampered by reintroducing colour from poor housekeeping. Screw and Barrel The screw and barrel are sometimes mistaken as being clean when colour changing hot runners because purging the screw and barrel is done at low and constant pressure and low speed (Fig 2). This can give a purging that looks clean yet can show up in your mouldings as is depicted in c, d and e (Fig 1). Aquapurge’s mechanical purging compounds like Barrel Blitz Universal that use the natural compression of the screw to clean can be effective to clean under low pressure and speed conditions especially when encountering colour plate-out (Fig 2) or carbon.