A planned space in brickwork or a monolithic lining that takes up thermal expansion, filled with ceramic fiber, or with cardboard and other combustible spacers that burn away. Too little allowance causes pinch spalling, bulged walls and crowns that lift off their skewbacks; too much leaves open joints for slag and metal to run into. Silica and magnesia, which expand more than 1 percent on heating, need the most careful layout.
Put the cardboard in every fourth expansion joint like the drawing says, mag grows and that ring will pinch without it.
Also heard as
- expansion allowance
- expansion gap
Related terms
Spalling
Cracking off of pieces or layers from the hot face of a refractory lining.
Skewback
Angled brick or support course from which a sprung arch springs and pushes its thrust into the steelwork.
Silica brick
Brick of over 93 percent silica with high hot strength but sharp volume changes when cooled below red heat.
Magnesia-carbon brick
Resin-bonded brick of magnesia and graphite, the workhorse lining of BOFs, electric arc furnaces and ladle slag lines.