Expandable graphite in PUR
03.07.2019 | Gerhard Konrad

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

Complete, automated process chain

"Expandable graphite is an economical filler that offers clear advantages for many automation tasks," explains 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.

Short cycles and self-cleaning mixing head

The advantages of high pressure countercurrent injection mixing in the precise processing of highly reactive PUR 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.

Low pressure bypass for the core of the process

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 minimized. 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.  

Gentle material mixing and high load factors

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 optimized using the mixing proportions of expandable graphite and other components during pre-mixing, without sacrificing the flame retardant characteristics.

One-stop shopping

KraussMaffei's expertise in the area of processing of expandable graphite goes far beyond mixers and metering machines. You can obtain a fully automated process chain, from semifinished product/raw material storage to metering, mixing and plant technology (foam molds, mold carriers, deflashing etc.), including the necessary process technology, from a single supplier. This not only saves time and headaches in the planning and installation of production chains, but also makes service and maintenance tasks easier.