Surface Combustion - Belt Furnace

Surface Combustion’s belt furnaces start with an insulated hot zone which typically includes a 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 forms the base gas necessary for through hardening or carburizing. The belt style is either a woven mesh belt of a high-grade alloy construction for lighter loaded product types, a cast link belt with alloy link pins for heavier loaded product types, or a slat conveyor for specific gears or other shapes that lend themselves to this type of a large contact area style of belt. The belts are roll or skid supported (top and bottom) and the belt returns for higher temperature models are within the furnace for better fuel efficiency. Belt drives are electrical motor driven via drive drums or drive sprockets. These are continuous style furnaces and so products enter and exit through opposite ends. At the exit, an oil, polymer, high temperature salt, or water quench can be incorporated for the hardening process. For tempering, there is no quench involved. Traditional and boost diffuse carburizing–where zone separation is necessary for different process step temperatures or carbon potentials–can be performed in this type of furnace. Typical widths are 3.5 to 6 ft. but can be engineered up to 75 ft. in length. The operating temperature of higher temperature furnaces is typically 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.

Cascade quenching where small quantities of parts are dropped into the quench at one time is used. Separation of the oil from the furnace atmosphere is done via oil cascades which create a wall. Typical agitation in theses style of quenches are via pumps and nozzles pointed at the surface of the belt which retrieves the free falling parts and brings them up to the surface where they may be passed to a washing system prior to tempering. The oil can be heated via electric bayonet style heating elements and is cooled after quenching to return the oil temperature to the setpoint.