Maximum rate of heating or cooling refractory?

[Sheeny]

We have a several refractory lined furnaces. Due to production pressures, we are often asked to cool them down and reheat them quickly to allow some remedial work to be done in the furnaces. A range of refractory materials are used including brick, castable, etc.

The concern is that heating or cooling the refractory too quickly will damage the refractory (or reduce it's operating life) due to thermal stresses.

What sort of rates of temperature change are too quick for cured refractory?

 

[nnjunger]

Sheeny,

I work with the same materials in another industry, and can speak from experience that the hardest thing you can do to refractory is the cycling of the heat load. I have seem systems with castable and brick last 30+ years, and others fail in a couple, and the only difference is the operation of the unit with regard to cycles and rate of heating and cooling. I would imagine that the refractory supplier could provide the information for maximum rate of heating and cooling for the materials. I have only been interested in this for cure out schedules, since I have no control once the unit is in operation, as business cycles dictate the rate the machines are fired at as well as their off cycles. Hope this helps, and I would be interested if you find any additional information.

 

[Dean78au]

During startup and shutdown of some refractory lined furnaces we had and high temperature storage bins the cooldown rate used for the furnace was from about 900C to 400C over a period of 5-6hours to allow the refractory some time to adjust. These times were recommended by our refractory engineer onsite. The heat up rates for the furnaces from cold was 12hours and similarily for the storage bins. Both had cured refractory.

However the longer the period you heat/cool over the better it is for the refractory and you will experience many happy years together.