Alumina content is the quickest guide to a fire brick’s limits. In general, more alumina means a higher temperature capability, better strength under load and better resistance to wear and many slags. It also means a higher price.
Where 40% alumina fits
40% alumina bricks are an all-round choice for furnaces, kilns and boilers running at moderate temperatures without severe chemical attack. If the duty is steady and conditions are not extreme, they usually give good value.
When to step up to 70% alumina
Move up where temperatures peak higher, where the lining carries load or is scraped by material, or where slag and dust attack the surface. Using it only in those hot zones, and a cheaper brick elsewhere, is a common way to control cost.
What to tell us
The operating and peak temperature, the atmosphere, what touches the lining, and how often the furnace cycles. With those four things we can recommend a grade and a backup layer to match.
General guidance. Always confirm limits against the product data sheet.