QUESTION: I have a customer who wants to use ammonia in a belt furnace for their brazing. I was wondering what the health aspects of this would be for staff, and what environmental impact it has on nature. Are there any other downsides to the method it self?
ANSWER: When people refer to brazing with ammonia, they usually are not talking about brazing with raw ammonia itself but rather with the hydrogen and nitrogen components of the ammonia. An ammonia generator is often used to chemically heat liquid ammonia to a high temperature (in the presence of a catalyst) so that the ammonia molecules break up into one part nitrogen and three parts hydrogen. The nitrogen and hydrogen are then piped into the brazing furnace so that the actual brazing atmosphere is a blend of hydrogen/nitrogen gases – never just raw ammonia! This breaking-apart of the ammonia atoms is commonly referred to as “cracking ammonia.”
Thus, cracked ammonia is a term often used for the brazing atmosphere of hydrogen and nitrogen that is created by breaking apart the ammonia atoms. You are never actually brazing in raw ammonia. Therefore, there should never be any smells/odors of ammonia in the shop at all. If anyone can smell ammonia, then the equipment is not working correctly and needs to be repaired.
Cracked ammonia (hydrogen and nitrogen atmosphere) is a safe brazing atmosphere when used correctly. Obviously, you must be sure that the hydrogen is consumed, and the continuous belt furnace has gas-burner pipes at each end of the furnace so that any raw hydrogen is completely consumed before it can possibly escape from the furnace and enter into the work area where people are located. This type of brazing furnace must be treated just as if it were a regular hydrogen-atmosphere furnace. The only difference is that the hydrogen is being created from ammonia rather than being piped in from a liquid hydrogen tank or from hydrogen bottles.
As with any atmosphere gas used for brazing, it is also very important to measure the dew point of the gas at the furnace to be sure that you have the appropriate level of “dryness” for the required brazing. If you are brazing carbon-steel parts with copper BFM, then the dew point is not important. But if you are brazing stainless steel parts, dew-point control is essential!