Improved graphite filler processing

Cannon Afros, which makes mixing equipment and dosing systems, has improved its mixing head system to make it easier to process expandable graphite.

The graphite can be used in molded foam sandwich and board panels.

The company’s EG-AX system consists of a mixing head with four streams – one for the polyol and expandable graphite slurry with an injection pressure of 120-160 bar, two consisting of an isocyanate stream fed by a single pump and split into two by a flow divider and mainly used for discontinuous molded flexible foams, and a fourth stream as an optional input depending on the application. For sandwich and board panels requiring a continuous process, a proportion of the polyol is drawn from the slurry and injected via the fourth stream which allows injection pressures as low as 80-90 bar, the company said.

“Expandable graphite is probably one of the best inorganic and physical fire retardants for versatile molded flexible open cell PU foams used for seating, arm and headrests in public transport and automotives, where it is also used under-the-hood to provide protection from the heat and noise of the engine,” said Stefano Andreolli, sales manager. “It is considered as an eco-friendly, highly effective intumescent char-forming fire retardant with low smoke and toxicity however, it’s very sensitive to mechanical stress when incorporated into a PU formulation and therefore requires expertise when processed.”

According the company, expandable graphite is derived by treating flake graphite with reversible intercalation reagents such as nitric acid and sulphuric acid. Maintaining the integrity of flakes during processing is important because normal high-pressure recycling times, of up to seven seconds, can disintegrate the flakes releasing sulphuric acid, destroying the polyol catalyst, and may also corrode equipment. The improved mixing head system reduces the high-pressure recycling time to under one second before the shot, Cannon said. This minimizes damage to the graphite flakes and preserves the formulation intact for much longer processing times.

The Cannon EG-AX system is available with three different mixing heads, providing mass flow rates ranging from 100 g/s to 1100 g/s. Cannon says that it also provides all upstream equipment to prepare and process expandable graphite in high pressure including batch slurry premixing, metering, and dosing machines.