GB561498A - The manufacture of moulded articles - Google Patents

Abstract

Coal is comminuted until at least 30 per cent thereof by weight has a particle size not exceeding 10m and is then moulded under high pressure at a temperature which lies between the temperature at which the coal begins to soften and that at which it ceases to be plastic, and lies below the temperature of onset of intumescence. In general, the pressure may be 250-600 atmospheres, and the temperature 345-375 DEG C., different coals requiring different treatment. The temperature of onset of intumescence may be raised (a) by adding to the coal an absorbent filler which assimilates the volatiles, e.g. powdered coke, powdered anthracite coal, colloidal silica or colloidal alumina; or (b) by pressing the coal relatively lightly (50-150 atmospheres) whilst the coal is being heated to the moulding temperature (e.g. 345-375 DEG C.) and then subjecting it, at the moulding temperature, to the full moulding pressure (e.g. 300-450 atmospheres). During moulding, the pressure may be lowered at least once, to release gases. Prior to moulding, the coal may be "de-gassed" by heating at subatmospheric pressure and at a temperature below the moulding temperature range. The mould may be heated electrically or by the vapour of an organic liquid. The coal may contain fillers, e.g. asbestos fibre or powder, powdered alumina, powdered aluminium, powdered coke or electrode carbon, powdered ferro-silicon, quartz meal, steel filings or fine steel wool. The filler may be such that at least 30 per cent by weight does not exceed 10m in particle size. The coal, with or without filler, may be compressed into preforms at atmospheric temperature before moulding.