an industrial furnace in which stacked items are heated in an insulated car that is rolled out of the furnace on rollers or chutes, guided by rails or a grooved way.
A crane is used to load and unload items for processing on the car, or roller hearth. Sand or water are used to seal gaps between the roller hearth and the walls in order to decrease the intake of air into the furnace.
Classified by their mode of operation, roller-hearth furnaces belong to the category of chamber furnaces. Roller-hearth furnaces are from 1.2 m to 6.4 m wide and from 2.5 m to 40 m long. They are heated by gas or liquid fuels, using burners or nozzles attached along the length of the walls in one or two rows at the height of the furnace. Roller-hearth furnaces work at operating temperatures ranging from 500°C to 1150°C. They are used to heat-treat items before forging or rolling.