Hi everyone,

Came across a question regarding nitrogen atmosphere

Here is general guideline of current heat treat

1) Furnace ram up to 1400F
2) Parts austenite for 1 hour (nitrogen atmosphere)
3) Within 1 hour cool below 60F with freezer
4) Age part to TH1050 or TH1100 (nitrogen atmosphere)

From various observation, it seems that most people run the nitrogen at a rate of 25 SCF/Min.

However this source is telling me it should be the interior volume of furnace x 5 volume change/hr

Obviously the 2 calculation will greatly affect the nitrogen usage so wonder which is correct.

So far most facility I have seen run nitrogen or argon at 15 to 30 SCFM
however this engineer is saying it is based on volume of furnace and from his calculation I will be getting approximately 2 SCFM.
 

dchu,

It depends greatly upon the type of furnace (batch vs. continuous) and what the intended process is, is purging required, etc.  Here are two references on the subject, the first of which specifically describes the 5 volume changes/hour rule-of-thumb:

The Annealing Process Revealed (Part Two: Furnace Atmosphere Considerations)
http://www.industrialheating.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000896275

Linde Gas Furnace Atmosphere No. 2 Neutral Hardening and Annealing
http://heattreatment.linde.com/International/Web/LG/HT/like35lght.nsf/repositorybyalias/wp_anlghdng_11/$file/11.pdf

 

The furnace is going to be a batch furnace.

Intention is austenite and aging (heat treating to bring hardness up)