Carburizing Atmosphere Exchanges 1

[induction31]

Can anyone tell me what the recommended atmosphere exchanges per hour should be during a carburizing cycle. We are using endothermic and enriching with methane. Thanks in advance.

 

[unclesyd]

I would get with the manufacturer of your furnace or the gas supplier as to their recommendations. Any book on heat treating will give the number of gas turn overs needed to maintain an atmosphere for each condition and size of furnace. In your case the composition will change rapidly at the start and then the rate of change in the gas mixture will slowly taper off.

We had two Lindberg Box furnaces using just endo gas and it was regulated by the vent flame. I don't have the numbers, but I remember the Heat Treater set his flow to the furnace by the flame height not by the installed rotometer. The vent nozzle was no more that 3/8" NPT and he kept about a 3" high flame. I don't recall any change when going from one operation to another, in other words this was a universal indicator that the proper amount of gas was in the furnace. There was a gas igniter to relight the vent when the door was in use.

 

[Carburize]

I have always worked on 3 changes per hour as a minimum with the additional constraint in Nitrogen -Methanol systems of at 100 cu ft per hour of methane.

 

[Carburize]

Missed out the word "least" before the 100 cu ft!!

 

[induction31]

Thanks for the help everyone. We have a customer who insisted that four exchanges per hour was not enough. I think I have enough information to change his mind.