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15. August 2019

KraussMaffei: Expandable graphite as a filler in PU foam systems

K 2019
KraussMaffei Hall 15 Stand C24 – C27

According to KraussMaffei, flame protection requirements for polyurethane foam components are increasing worldwide, both in the automotive and industrial applications sectors and also due to regulatory requirements. At K 2019, the company will present a complete system for the high-pressure processing of expandable graphite for high material and process efficiency and clean production.

Component made of polyurethane foam with expandable graphite as filler (Source: KraussMaffei)

Component made of polyurethane foam with expandable graphite as filler (Source: KraussMaffei)

"Expandable graphite is an economical filler that offers clear advantages for many automation tasks," explained Nicolas Beyl, President of KraussMaffei's Reaction Process Machinery Segment. "Unfortunately, the material is sensitive to mechanical stress during processing“. A newly developed high pressure mixing head with low pressure bypass and a special premixing station for expandable graphite metering make its use as a flame retardant a particularly efficient alternative or addition to liquid admixtures. The fully automated process chain ensures short cycle times and high overall system efficiency in component manufacture, said KraussMaffei.

The advantages of high pressure counter-current injection mixing in the precise processing of highly reactive PU foam systems can thus be put to use in applications with expandable graphite as a filler. This forms the basis for short cycle times and leads to efficiency in production. In this process, unlike processing in the low pressure range, the self-cleaning mixing head eliminates the need for a flushing process after each shot. This saves material, production time and ensures consistent product quality, while also eliminating costs for the provision and disposal of flushing material. In the high-pressure mixing process, a higher mixing energy is also achieved. This can be used to implement shorter cycle times.

A special expandable graphite mixing head is at the heart of the technology. This is based on the highly efficient high pressure mixing heads from KraussMaffei. The system has been equipped with a low pressure bypass with an enlarged cross-section, specifically for the processing of expandable graphite. The mechanical stress imposed on the expandable graphite particles between the cycles during which the charged polyol is continuously circulated is thus minimised. The material circulates through the nozzle to build up pressure only just before pouring starts. The filler is therefore subject to minimum mechanical stress. With this technology, high filling levels are possible, according to requirements and depending on the raw material system of up to over 30 % by weight in the polymer. The high flame retardant classes UL94-V0 can therefore be achieved, said KraussMaffei.

The polyol-expandable graphite mixture is prepared in a special premixing station. A special agitator mixes the filler homogeneously with the liquid component. This is done in a gentle manner such that the structure and size of the expandable graphite particles are preserved. Metering takes place automatically and can be increased to 80 % by weight in the polyol. Consistent quality is therefore always provided. In addition, production is made cleaner and more efficient because the steps of manual handling, weighing and filling are eliminated. In addition, the weight and volume of the component parts can be optimised using the mixing proportions of expandable graphite and other components during pre-mixing, without sacrificing the flame retardant characteristics.

According to the company, its expertise in the area of processing of expandable graphite goes far beyond mixers and metering machines. Customers can obtain a fully automated process chain, from semi-finished product/raw material storage to metering, mixing and plant technology (foam moulds, mould carriers, deflashing etc.), including the necessary process technology, from a single supplier. This not only saves time in the planning and installation of production chains, but also makes service and maintenance tasks easier, said the company.


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