Pusher kilns, belt furnaces, tunnel kilns and lehrs are continuous heat treat furnaces designed for high production. The ware is placed on a conveyor or sagger manually or automatically and, while traveling through the furnace, it is exposed to different temperatures and atmospheres. This design is more energy-efficient as a batch furnace, since the furnace refractory doesn’t need to be heated and cooled for every load. On the other hand, firing ware with different heating profiles and atmosphere is more challenging since this is determined by the belt speed or pusher interval.
The term lehr refers to a long kiln where glass is annealed while sitting on a belt and transported through the temperature-controlled kiln. The general term for these types of continuous furnaces is belt furnace. The maximum temperature for fuel-fired or electric lehrs is determined by the material of the conveyor belt and the atmosphere in the furnace. For most applications, temperatures up to 1600°F are sufficient, but Inconel belts and ceramic belts can withstand higher temperatures.
We commonly build continuous heat treatment belt furnaces with added quench tanks.