Munich, Germany — KraussMaffei has introduced three new mix heads allowing polyurethane processors to quickly change colours in coatings, foams and composite systems.
The first development, called linear mixing head MK5-2+1K, is designed for the firm’s ColorForm process. This allows for a ‘very fast die change,’ the company said. To do this an easy-to-replace module is mounted on the mixing head and injects dye directly into the mixing chamber.
Dye is not carried over from part to part because the dye circulates in a closed system in the dye module and does not run through the mixing head until needed, KM added. It continued, that the dye nozzle opens only when material is discharged. In the ColorForm process a thermoplastic base is moulded and then in the second cycle it is flow-coated with polyurethane or polyurea as a surface material.
KM said that the MK5-2+1K mixing head is ‘lightweight and compact, which reduces space requirements’. It added that the new mixing head is suited for smaller PU quantities. ‘This is a critical factor in the ColorForm process, because the applied PU layers are very thin,’ said Sebastian Schmidhuber, head of RPM Research and Development at KM.
The second development, designated MK 10/15 ULP-2K +4, is a transfer mixing head developed to simplify dye changes during the production of semi-rigid, rigid or flexible foams, the firm said.
The new mixing head makes it possible to feed up to 4 dyes directly and independently into the mixing chamber.
‘The mixing head is suitable for all applications in which PU processes face the challenge of providing components in relatively small quantities and in numerous colours,’ said Schmidhuber. The new mixing head makes it possible to change the die in continuous production from shot to shot, KM added.
Schmidhuber continued that ‘because production does not have to be interrupted for a dye change, machine availability increases.’
The mixing head works by splitting the polyol component into two sub-streams and introducing them through two nozzles to the mixing chamber. This means that different dies may be added at either polyol nozzle, KM said. The firm continues that metering occurs between the polyol nozzle and mixing chamber so that there is no die carryover part to part.
The third developments are mixing heads for use in structural component spraying. In this process, a layer is made up of fibre mats and honeycomb cores which are sprayed with unreinforced PU. These are then inserted into a mould and pressed into shape. This gives components which are lightweight and strong, KM added.
The newly developed nozzle-changing component, makes it possible to equip spray mixing heads with flat-fan nozzles to coat large areas and air-assisted circular jets for components with challenging geometry.
KM said that the development makes it possible to fit spray mixing head with both types of nozzle increasing their flexibility and reducing cycle times. Schmidhuber added that ‘investment costs are reduced because only one mixing head is required and there is no need for a hydraulic switchover unit’ which would be used before.