Atmosphere control is critical to the success of heat-treat practices, especially with the carburizing process. It is also necessary that the furnace operator has an understanding of the process, its control features, and the cause and effect of corrective and non-corrective actions. There are many aspects to the control of the endothermically generated gas as well as the blended process gas both for hardening and carburizing. The endothermic gas generator is a simple unit to both operate and maintain. However, maintenance is often overlooked, particularly the burnout procedure.
When an atmosphere problem is present and the question "When did you burn out the generator?” is asked, the answer is usually, "We don’t need to," or “What do you mean?” It is a necessary maintenance procedure, and the recommended frequency of burnout can be seen in the operation and maintenance manual supplied by the equipment manufacturer. It is also necessary to do the procedure on the process furnace, particularly when operating with high carbon potentials. The high carbon potentials will very quickly load up the refractory brick with carbon, making it difficult to control the process and the final product quality.
Troubleshooting the Exothermic Gas Generator
The exothermic gas generator is a unit that is designed as a lower-cost atmosphere-producing generator and has been used for many years. The rich exothermic generator is a combustion chamber that is usually filled with a catalyst. The chamber is usually constructed with a gas combustion burner supplied with a gas air mixture for combustion. The important part of the unit is the combustion burner, which must ensure a close tolerance ratio of air to combustion gas. The general problem that occurs with the exothermic generator can usually be traced back to the air-to-gas mixing system or to the gas cooler on the reacted gas discharge side.
In some instances, depending on the gas quality required, the exothermically generated gas may pass through a refrigerant dryer. The refrigerant dryer will require the periodic recommended preventive maintenance as directed in the manufacturer's operating and maintenance manual. Without maintenance, one can expect problems to arise.
The troubleshooting of furnace atmospheres can be dramatically reduced if standard operating procedures are written for incoming material inspection as well as for the furnace equipment. The material for heat treatment can cause considerable atmosphere problems if the incoming material is not prepared and pre-cleaned prior to the process treatment. In addition, any residual surface contaminant can cause surface problems on the steel being processed in terms of corrosion, pitting, appearance and quality. Oils, greases, lapping compounds, marker ink, paint and cutting fluids should be removed by washing or degreasing.
The standard operating procedures for the generators and furnaces should include the burnout procedures as well as the method of furnace operation. If the operator/furnace technician understands both the process and operational procedures, they would become as valuable an asset as the equipment. Their practice will ultimately protect management’s capital investment.