New mixhead offers faster changeovers

By David Reed, UT EditorMunich, Germany-Krauss-Maffei Kunststofftechnik GmbH has introduced a six-component mixhead which, it claims, allows component changeover times "in the millisecond range." This makes it possible for moulded flexible polyurethane foam makers to accommodate the current trend to shorter cycle times and smaller batch sizes, the firm explained, in a 2 Feb press announcement.Many conventional mixing heads are at their performance limits, Krauss continues, so processors often experience bottlenecks caused by slow component change-over, coupled with the inability to achieve precise control over the material flow into the mixing chamber, the announcement says.The new six-component transfer mixing head, designated MK 18/22ULP-6CN-G, has been redesigned in order to overcome these problems. At the heart of the compact heads are six hydraulically controlled needle shut-off valves which control the component mixing. These are arranged in star formation around the mixing chamber and incorporate a sophisticated bypass system so that only very small volumes of fluid have to be moved during changeover, Krauss explains. These means that processors using the new mixing head can change component blends rapidly. The time needed to change from 100 to 400 g per second is only 0.5 seconds, making the new head almost twice as fast as mixing heads previously developed by Krauss-Maffei. When two identical formulations are being output (without a cleaning stroke) the waiting time between two shots is only 0.2 seconds. Even with a cleaning stroke and a complete component switch, the time between shots is only 0.8 seconds, the Munich-based firm claims.The head's operation is extremely precise, thanks to the retention of the proven control-piston principle and the fact, that the cleaning plunger position can be reset from shot to shot, the Krauss-Maffei statement concludes."