of retractable roller hearth 40 despite the lifting the mass of the hearth and the work and the thermal expansion or distortion which the hearth and furnace chamber 30 are exposed to the primary aspect of the invention can be appreciated by reference to fig4 multi chambered industrial heat treat furnaces are principally designed as such so that the temperature of furnace chamber 30 is maintained at an elevated state during the charging and discharging stages although some temperature drop must occur a normal heat treat cycle is generally about four hours in duration if the conventional roller hearth must support the load during the entire cycle the thermal stress over the four hour cycles shortens the life of the roller rails as shown by the dotted line thus to maintain the hearth life the loading of the hearth and thus the capacity of the furnace was reduced in accordance with the present invention the rollers are only loaded for about 1 of the heat treat cycle and only during the discharge or charging stages before the initial high temperature heating stage of the cycle is actuated during that high heating stage i e in excess of 2 000 u00b0 f rollers 25 are not under load and the thermal stress induced by the high temperatures does not exceed the elastic limit when the rollers are actuated the furnace temperature may be at its lower value where higher work tray.