Furnace atmospheres play a vital role in the success of the heat-treating process. It is important to understand why we use them and what the best atmosphere for a specific application is. There are many different types of atmospheres being used, and it is necessary to understand how a particular atmosphere was chosen and how to control them safely as well as its advantages and disadvantages.
The purpose of a furnace atmosphere varies with the desired end result of the heat-treating process. The atmospheres used in the heat-treating industry have one of two common purposes:
- To protect the material being processed from surface reactions; that is, to be chemically inert (or protective).
- To allow the surface of the material being processed to change; that is, to be chemically active (or reactive).
Some atmospheres, such as argon and helium, are often associated with vacuum furnaces and are used at partial pressure (pressure below atmospheric pressure). Others, such as sulfur dioxide, are used for very special applications.
Generated atmospheres produce combinations of gases of specific composition prepared on site by use of gas generators that are designed for this purpose. The atmospheric “feed” stock (hydrocarbon fuel gas used in combination with air to create the atmosphere) is typically natural gas or propane.