- Type and size of furnace
- Presence or absence of doors and/or curtains
- Environment (especially drafts)
- Size, loading, orientation and nature of the work being processed
- Metallurgical process involved
Generated atmospheres are classified according to the relative amounts of the individual gases produced. Table 4 provides a list of these classifications according to the American Gas Association (AGA). The gases are divided into six main classes.
Exothermic reactions are heat-producing, while endothermic reactions require heat to promote the reaction. The composition of the atmospheres produced can be changed in a number of ways. Varying the gas/air ratio or using a different “feed” stock (natural gas or propane, for example) will cause the chemistry of the gas to change.