RX® Endothermic Atmosphere Gas Generators for Heat Treating

Surface® Combustion RX® Endothermic Atmosphere Gas Generators provide onsite generation of endothermic gas for controlled atmosphere furnaces performing metallurgical heat treatments such as carburizing, carbonitriding, ferritic nitrocarburizing (FNC), hardening, and annealing.  Industries using RX gas include Automotive, Energy, Mining, Agricultural, and Commercial Heat Treating.

Surface Combustion pioneered the development of RX gas to be used as the atmosphere for modern gas carburizing.  RX gas is produced by converting the incoming supply of natural gas[1] and air by catalyst and heat to a composition of 40% N2, 40% H2, and 20% CO.  The RX gas generator’s reliable production of consistent atmosphere chemistry with low oxidation, decarburization and soot potential revolutionized the heat-treating industry by enabling boost/diffuse carburizing, as well as atmosphere carbon control.

Our standard modular RX generator designs range from one (1) to five (5) tubes.  Surface offers short and tall tube designs.  Depending on the height of the tube, maximum flow rates of 2000 cfh or 3000 cfh can be produced in each tube.  As furnace demand for RX gas changes, our generators can produce quality gas through a 6:1 turndown range.

Our standard RX generators are 100% assembled and pre-tested at our facility, and are supported by a large inventory of critical and consumable spare parts like RX alloy retorts, catalyst, and refractory.   Surface Combustion has the largest installed base of RX endothermic atmosphere generators in North America. Many have been in operation for decades, proving the ruggedness of the product. 

Our customers find Surface Combustion RX generators so reliable, and the need to shutdown the generator so infrequent, that they consider them a public utility.  To improve uptime, we offer on-line burnout. A tube can be taken offline and reconditioned by passing air through the retort while at temperature.  A backup mixture pump allows for routine maintenance on the primary pump without impacting production.  Oxygen sensors can be replaced without shutting down the generator. 

Control features include our ESATM Dew Point Sensor system which employs dual, commercially available automotive oxygen probes to control the dewpoint (e.g., carbon potential) of the RX endothermic atmosphere.  Our proprietary flow control system, with our reliable air/gas mixer and positive displacement mixture pumps, allows consistent product gas chemistry and sufficient outlet pressure through the entire turndown range.  Temperature controls maintain proper retort temperature for efficient RX production.  ENDOQUENCH® air cooling locks the atmosphere chemistry and prevents carbon drop-out in piping headers.   

We now offer AP™ Endo series of tools for predictive maintenance of RX generators.  These expanding online diagnostic capabilities monitor each retort for equalized flow, pressure, temperatures, and utilization.  When action is suggested, the system alarms and offers possible solutions.

Typical enriching gases added to RX gas at the furnace are natural gas, air and ammonia.  Furnace types include Allcase® Batch Integral Quench furnaces, radiant tube box (RTB) furnaces, belt type furnaces, pusher tray, roller hearths, rotary hearths, rotary retort, and pit furnaces, which are all products designed and built by Surface Combustion. 

Surface supports our products with dedicated customer service, field service, and aftermarket parts personnel.  From equipment and process troubleshooting to rebuilds Surface is ready to assist.  Contact Surface for our expertise and proven performance providing consistent and reliable protective atmospheres. 


[1] Other hydrocarbon feedstock gases (e.g. propane, LPG or acetone) can be used.  Slightly different gas compositions would result.

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