Surface^® Combustion’s pusher furnaces start with an insulated hot zone, typically with bricked floor and walls and a fiber-lined roof. The heating source can be direct or indirect gas fired or electric elements. For those products requiring an internal atmosphere, only indirect gas firing and electric heating may be used. Endothermic (RX^®) gas or exothermic (DX^®) gas forms the base gas necessary for through hardening, carburizing, annealing or normalizing. The internal alloy rolls, rails and trays are a high-grade alloy construction. Pusher mechanisms are traditionally electrically actuated ball screws or can, in certain instances, be hydraulic cylinders. These are continuous style furnaces and so products enter and exit through separate charge and discharge ends. There are typically vestibules which are separate chambers to preserve internal atmosphere integrity. At the exit, an oil, polymer or water quench can be incorporated for hardening or carburizing processes. For annealing or normalizing, an atmosphere cooling chamber is used to slowly cool the load or it can be discharged into air. Traditional and boost diffuse carburizing (where zone separation is necessary for different process step temperatures or carbon potentials) can be performed in this style of furnace. Typical tray width is 2 to 5 ft. and furnace lengths are generally limited to a calculated tray column length. The operating temperature of higher temperature furnaces is typically from 1400°F to 1950°F as this is a radiant/conduction style of heat transfer to the load. Lower temperature styles for tempering or stress relieving are from 350°F to 1400°F and typically incorporate convection fans.

The conveyance method changes based upon tray load weight. Light loads use a pusher tray skid type where the basket supporting the tray is horizontally pushed tray on tray over the top of an alloy or silicon carbide rail set. There are two other alternatives variations. Pusher roller rail furnaces operate in a fashion where the trays are pushed tray on tray on top of conveyor rollers located in trunnions and run throughout the heated length of the furnace. This type is used for heavier loading as the rollers significantly reduce the frictional factors. Finally, pusher roller trays have the rollers incorporated on the bottom of the trays, and these trays roll through the furnace on guide tracks. This style is used for the heaviest of loads and allows for the rollers to be maintained when the trays exit the furnace.

Each product being processed will require a different type of pusher tray set up. Surface has a complete selection of pusher tray type furnaces and will help you select the best option for your process.