In the past, sealing beads - also called Formed in Place Foam Gaskets (FIPFG) - were almost exclusively manufactured in a low-pressure process. Hennecke GmbH has now developed a special variant of highpressure technology that enables a highly reactive PU sealing foam system to be processed and applied to a car door module. The reactivity of the PU system has been accelerated so as to synchronize the manufacturing time of the door module in the injection moulding process with the sealing application and its curing.

Hennecke GmbH – a leading supplier of PU processing technology – invests considerable resources in research and development each year. This is beneficial for the user as the most recent example of gasketing under high pressure illustrates.

Low pressure systems prevail in the production of gaskets because very low outputs of under 5 g/s are usually required. The disadvantage of the low-pressure process is that the reactivity of the foam has to be slow enough to maintain the processability of the reaction mixture. In addition, the mixer needs to be cleaned with solvent or the mixing element has to be replaced after completion of each part while high-pressure mixheads are self-cleaning.

Further disadvantages of low-pressure technology are long curing and processing times.

The endeavour of many manufacturers to constantly increase efficiency is thus limited by the technical capability of the lowpressure process.

A successful method of making production more effective is the combination of manufacturing steps, i.e. manufacturing processes are linked and synchronized. An essential requirement for this is the synchronization of the cycle times of the individual production steps including the combination of thermoplastic injection moulding with polyurethane processing. The reactivity of the PU mixture has to be simultaneous with the curing of the injection moulded part that carries the gasket in this case. This means that new, highly reactive PU systems are required which can only be processed under high pressure. With a MICROLINE polyurethane high-pressure metering machine and the MT mixhead for very small outputs, Hennecke is able to process a highly reactive PU system that is especially suited for high pressure and to execute the application to a door module within the cycle time of injection moulding production. With outputs down to 2 g/s of reaction mixture,more complex part geometries can also be provided with gaskets. To this end, the mixhead is either handled by a 6-axis robot or an injection portal or the part is moved under the fixed mixhead - depending on the geometrical complexity of the part.

Applications are not restricted to door modules. According to Jürgen Wirth, Manager Application & Development Technology, „drum lids, control cabinet doors, body panels and case parts as well as extraction booth gaskets etc. are also possible.

Basically all applications in which the cord thickness of the gasket to be provided has a width of at least 3 mm.“

For an FIPFG mass production, the MICROLINE can be combined with automation equipment such as mould carrier systems.