Quite a large number of both captive and commercial plants have integral-quench furnaces, which are used for atmosphere heat-treatment procedures such as carburizing, carbonitriding and neutral hard-ening. More often than not, the furnaces are filled with combustible atmospheres and an internal quench tank of specialty quench oil. 

Fig. 2 is an integral-quench furnace. It can be likened to a “fire-breathing dragon” once the furnace is gassed up. The atmosphere concern also applies to continuous furnace systems, shaker-hearth furnaces and two- to four-row pusher furnaces. 

The safety rules are really quite simple. However, one should follow implicitly the furnace builder’s safety and atmosphere-handling introduction into the furnace. This will be found in the manufacturer’s operational and maintenance manual. The following should also be considered: 

  • Do not introduce the combustible atmosphere into the furnace below 1400°F (760°C).
  • Never stand directly in front of the furnace door once the furnace is gassed up with a combustible gas. If an explosion should occur, there is the potential for the explosion to blow off the furnace door.
  • The integral-quench furnace will have an internal oil quench built into the unit. Ensure that the quench-medium temperature setpoint is maintained. In other words, ensure that the oil quench agitators are functional and, most importantly, that the quench-oil heat exchanger is functional and operating within the quench-medium temperature setpoint.
  • Ensure that the oil quench filters (usually located on the external side of the furnace) are cleaned regularly. When the quenching procedure is in operation, fine particles resulting from microscopic debris quenching from both the workload and atmosphere are recirculating through the filters. It is recommended that a weekly filter clean is part of the maintenance routine.
  • Check the functionality of the explosion caps monthly.

It is suggested that the manufacturer’s operational and maintenance manuals are held in a secured location and that at least one copy is kept in the shop, maintenance department and engineering department. 

If operating an atmosphere generator, ensure that the air-to-gas is correct. Do not forget to consider potential variances in atmosphere moisture content, particularly during humid and rainy weather. 


Fig. 2. An integral-quench furnace filled with process gas.