Besides their chamber counterparts,car bottom preheating furnaces are most frequently used to heat up ingots and semi-finished items in forges. Temperatures up to 1,350 °C can be achieved in their working spaces. Their advantage is easy access for loading and emptying the contents, the possibility to use an over-head crane in the hall and independence of any other handling equipment.
Car bottom furnaces are mainly irreplaceable in the processing of very large forgings, such as steam turbine rotors, wind power plant shafts, ship engine crankshafts, and similar parts of large power generating and machinery equipment. As for their designs, size and capacity of their working spaces and the heating system setup, these furnaces will always reflect customer requirements regarding the weight and dimensions of loads and other requirements for material heating and furnace operation.
Let’s take as an example the car bottom preheating furnace we have supplied, with a 22 m long working space, used to forge long rotors and shafts up to 450 tonnes in total charge load. This furnace is the only one in the plant which allows handling of such long forgings and from this reason it has been conceived as multipurpose, allowing not only preheating for forging, but also the quality heat treatment of ready-made forgings, including controlled cooling and intense final cooling of the charge directly in the furnace.
Taking into account commonly high capacity, heavy conditions of operation and high plant factor, the following objectives were predominately followed in the engineering and construction of car bottom forging furnaces:
·high-level reliability and service durability, long service life of equipment
·uniform heating and prevention of local overheating of the charge
·highest possible level of reutilization of the exhaust fumes’ thermal capacity
In addition to systems with combustion air preheating in the central recuperator, it has proved convenient to use mainly regenerative burners for the utilization of heat contained in the outgoing waste gases.Regenerative heating systems are also used in the reconstruction of older furnaces. Here, in connection with additional measures,heating gas savings are up to 50 % when compared to the situation prior to reconstruction.