745 Welding, Cutting, and Brazing Safety

The Basics

Welding, Cutting, and Brazing

Heat metal parts to a temperature that is high enough to join the metal parts by coalescence.

Coalescence

Coalescence occurs when two metals seem to pull together, or grow into one body, of the base metal parts when there is the slightest contact. There are two basic requirements for coalescence: heat and intimacy of contact.

Heat

Welding processes differ depending on the source of heat, the manner in which heat is applied or generated, and the intensity of the heat. The fuel used as a heat force may be:

• acetylene or hydrogen in air or in oxygen;
• an electric arc;
• an electric, gas, or oil furnace;
• the resistance of metal to the flow of electric current; or
• a chemical reaction between a metal oxide and finely divided aluminum.

The intensity of heat applied or generated at the joint varies according to the metals being joined and to the welding process being used. All welding processes, except brazing, use temperatures high enough to melt the base metals.

Intimacy of Contact

In the second basic requirement for coalescence, intimacy of contact, you can divide the welding processes into two groups: pressure processes and non-pressure processes.

• Pressure Processes: In pressure processes, there should not be any space between the surfaces being joined. Welders apply pressure while the contact surfaces are at a high enough temperature to allow plastic flow of the metal.
• Non-pressure Processes: In non-pressure processes, leave space between the joined surfaces. Fill this space, either progressively or all at once, with molten metal. The molten metal may be produced by:
• a filler metal (welding rod or electrode),
• melting the surfaces to be joined, or
• combining a filler metal and melted base metal.

Knowledge Check Choose the best answer for the question.