The horizontal electric retort furnace, type GASCON K2, has been designed for thermal and thermochemical treatment in atmospheres of ammonia as well as the neutral gas atmosphere, e.g. nitrogen, in the temperature range from 560 to 650-degree C. The system design permits the furnace owner to perform heat treatment processes.
In particular, the furnace is intended for nitration and nitrocarburization. The atmosphere is created from ammonia. Carbon dioxide is used as carburizing agent. The use of suitable additives at different process stages, depending on the batch and furnace size, ensures that the right microstructure and high-level mechanical properties will be achieved. The furnace housing is made from rolled and welded sheet steel and profiled steel.
The furnace base is a structure of multiple steel profiles welded together that supports the cylindrical part of the furnace housing. The heating chamber of the furnace is a gas-tight retort consisting of the cylindrical part made from INCONEL 600 sheet steel welded to the INCONEL 600 bottom plate that seals the cylindrical part.
The insulating lining of the furnace is made from lightweight, fire-based, fire-resistant insulating materials with low thermal conductivity. The heating chamber includes the batch racks on which the batch for processing is fitted during the heating-up stage for heat treatment. This solution allows the regulated atmosphere to fully penetrate the batch from all sides. All elements of the furnace insulation ensure the adequate design of strength over the entire working temperature range of the furnace and all regulated atmospheres.
The electrical heating elements of the furnace are located in sealed, heat-resistant, horizontally arranged steel pipes that are fastened around the retort. The steel pipes are suspended on the collars fastened to the rear furnace wall. The power supply to the elements is from the switch cabinet via a thyristor system. The atmosphere mixer is located in the central section of the rear wall of the furnace heating chamber. The fan rotor with a suitable profile is made from high-alloy heat-resistant materials.
The rear part of the retort is also where all pass-throughs are located that are needed as inlets and outlets of the atmosphere and for measuring the atmospheric composition. The rear part of the furnace also contains a pass-through for connecting the vacuum extraction system. The furnace chamber is closed with a round door with a rotating ring that provides for tight sealing. This ring is operated by means of a hydraulic cylinder. The furnace also comes with a system for quick cooling of the batch.
This system consists of an external module – the cooling unit – that comes with a water-cooled heat exchanger as well as a rotor with an electric motor with a set of gas baffles. A pipe passes the hot gas from the furnace through the pass-through in the retort into the cooling unit. A second pipe passes the cooled-down gas through the pass-through in the retort, back into the retort. High performance flushing of the furnace retort starts automatically after the nitration process has ended. After the retort has been flushed, the shut-off valves of the gas inlet, gas outlet and cooling unit outlet open. The motors of the fan and the water system start up, which feeds the cold water into the heat exchangers.
The nitrogen circulates in a closed circuit and directly cools the batch inside the retort. Working in conjunction with the cooling unit, the indirect cooling system is started at the beginning of retort flushing the ammonia and hydrogen. This system consists of a high powered fan that injects the cold air from underneath the furnace after first opening the inlet flap; the air then flushes the retort surface and exits through the top furnace section that has a similar opening/closing flap as the bottom section. The furnace is also equipped.
The used atmosphere exiting from the furnace is burned by a pilot burner built into the end of the cracking system. A PLC provides the automatic control and monitoring of the nitration based on a preprogrammed recipe. The control of the nitration atmosphere is based on analyses measurements of the hydrogen content and a continuous regulation of the nitrogen potential KN via modification of the flow of added ammonia into the nitration atmosphere. The nitrogen is used to flush the atmosphere of the air and the nitration in the retort as well as for cooling after nitration. Nitration is monitored via the STANGE probe.
