Which type of flame is preferred for heating parts to be brazed?

The preferred type of flame for heating parts to be brazed is a neutral flame. A neutral flame is characterized by an equal supply of acetylene and oxygen, leading to a balanced mixture that achieves the optimal temperature for brazing without introducing harmful chemical reactions. This flame provides sufficient heat to melt the filler metal while preventing oxidation of the metals being joined.

Using a neutral flame is advantageous because it minimizes the risk of carbide formation and other unwanted surface issues that can occur when using a reducing atmosphere, such as a carburizing flame, or when the flame is too oxidizing. Properly controlling the flame to maintain neutrality is key to achieving a clean and effective brazing joint, ensuring that the joint is strong and corrosion-resistant.

The other types of flames, while they have their applications, do not suit brazing as effectively due to potential adverse effects on the materials being joined. Therefore, a neutral flame is the best choice for proper brazing practices.