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Updated: Article originally published in September 2018 has been amended with new details
In standard elevator furnaces – also known as bottom loader furnaces – a mechanism is used to elevate the load platform or kiln car into the furnace body. As the heating chamber itself doesn’t move, all the internal elements (heating coils, rods, wires, etc.) and insulation are protected from vibration.
Top hat furnaces differ from this in that an apparatus is used to lower the furnace body over the load platform. As the body is subjected to motion, there is a risk that sensitive elements inside the heating chamber could succumb to damage from vibration. However, this risk can be mitigated with a well-designed lift system and a light lining of high-temperature insulation that facilitates easy manipulation.
The base of a top hat furnace should be abrasion and fire-resistant, with a sophisticated sealing system between the hood and the base. This ensures maximum thermal efficiency. The bottom element of the furnace which can be movable or stationary and mounted on the floor is built up by insulating and fire-resistant brick or monolith plates.
Motion-related disturbances of workpieces are eliminated as the load platform doesn’t move throughout processing. Additionally, this means the weight of product loads is not an issue for lift mechanisms, unlike standard elevator furnaces requiring high-duty lift mechanisms for heavy workpieces.
Top hat furnaces are also easier to maintain as element replacement does not typically require the use of a ladder and is readily accessible. However, large production-scale furnaces may still need manual access of this caliber.
Top hat furnaces are used for all standard heat treatments of steel products, including tempering, hardening, annealing, normalizing, soft annealing, and stress relieving. At Deltech, we most commonly design top hat furnaces for ceramic processing, for example. They are also often used for heavy components which are loaded with an overhead crane or hoist.
Top hat furnaces are ideal for applications like the manufacture of gradient glass or applications in which there are multiple layers of kiln furniture.
At Deltech, our top hat furnaces can provide optimum temperature uniformity due to the heating elements being evenly spaced out across the four sides. Our furnace linings are made of the very best quality board and blanket, which results in rapid heating and cooling.
In our production size top hat furnaces, our unique pin-and-washer anchoring system preserves structural integrity through high fires and rapid cycling. They are also customizable, with an option of pneumatic (100 psi facility air required) or electric actuation systems. The pneumatic system features variable travel speed; the electric has a fixed rate of around 88cm per minute.
Our durable fiberboard exterior panels are offset from the furnace shell to enable convection cooling, keeping the furnace skin temperatures at safe levels without needing to use cooling fans. We also have forced air and vent flap choices to enable binder burnout and speed cooling rates as required.