Refractory castables consist of suitably graded aggregates and hydraulic cements in proportions formulated to achieve certain desired properties for the particular end use. They require only the addition of clean water either by hand or mechanical mixing or during pneumatic gunning to form a heat resistant concrete piece or structure.
Fireclay is a silica rich clay used to make firebricks. Containing only small amounts of lime, iron and alkali, it is able to withstand intense heat without fusing.
Darley Refractories have been manufacturing fire bricks and other refractory materials for over 100 years and as such, are part of the rich history of Bacchus Marsh, Victoria.
Refractory Fireclay and Castables
The general method of making firebricks has altered little over a hundred years although the grinding, extruding and pressing equipment has become much more sophisticated. Clays are still ground and mixed with crushed fired aggregate called grog, to stop excessive shrinkage in the material as it is mixed with water and extruded into a soft lump to be pressed into the desired shape. Right up to the 1960’s, many of the larger and special brick shapes were hand moulded. This involved throwing hand sized soft pieces of clay mixture into wooden moulds which had detachable bottom and side inserts shaped to suit the characteristics of the firebrick. A typical full gasworks setting would contain up to 1500 tonnes of firebricks with over 100 different shapes. Many of these contained tongues and grooves to provide a gas tight seal and were hand moulded, as were large “D” shaped pipe retorts up to 5 meters in length also used in these settings.
After shaping and drying, green bricks are fired in a kiln up to 1350ºC to form a ceramic bond giving them strength and integrity. Coke and black coal were used as a fuel to fire the kilns up to 1965 when they were converted to use heavy fuel oil. Probably the most significant improvement to firing was made in 1974, when the change to natural gas occurred. Quality was improved and rejects reduced with the even control of burning temperatures. After 72 years there was no more landmark black smoke from the chimneys, only the occasional wisp of steam.
The most recent improvement in production was the introduction of a 500 tonne Laeis dry press, giving the ability to make precision shaped high quality bricks.