Welding and Soldering for Sheet Metal Flashcards

What is 'oxy-fuel welding' and what fuel gas is most commonly used for sheet metal work?

Answer: A process using oxygen mixed with a fuel gas (typically acetylene) to produce a flame hot enough to melt and join metal

Oxy-fuel welding combines oxygen with a fuel gas (most commonly acetylene, producing oxy-acetylene) to create a flame reaching approximately 5,700°F (3,150°C), hot enough to melt and fuse sheet metal with or without filler rod.

What is a 'neutral flame' in oxy-acetylene welding and why is it important for sheet metal?

Answer: A balanced flame with equal burning of oxygen and acetylene that does not add carbon or oxygen to the weld

A neutral flame has a balanced mixture of oxygen and acetylene, producing a clean weld without adding excess carbon (carburizing) or oxygen (oxidizing) to the metal. It is the standard flame for most welding applications.

What is the 'capillary action' principle in soldering and brazing?

Answer: The natural flow of molten filler metal into tight-fitting joints due to surface tension between the liquid filler and the base metals

Capillary action draws molten solder or brazing alloy into the narrow gap between properly fitted and cleaned surfaces. The gap must be tight (typically 0.001-0.005 inches for brazing) for capillary action to work effectively.

When welding stainless steel sheet metal, what problem occurs if improper technique or filler metal is used?

Answer: Carbide precipitation (sensitization) in the heat-affected zone, leading to intergranular corrosion

Improper welding of stainless steel can cause carbide precipitation where chromium combines with carbon at grain boundaries, depleting chromium from the surrounding area. This creates zones susceptible to intergranular corrosion.

What is the correct gap for a brazed joint on sheet metal?

Answer: 0.001 to 0.005 inches (tight clearance) to promote capillary action

Brazed joints require a very tight clearance of 0.001 to 0.005 inches for optimal capillary action. Too tight prevents filler flow; too wide prevents capillary action and weakens the joint.

What is 'purging' and why is it done when TIG welding stainless steel duct?

Answer: Flooding the inside of the duct with argon gas to prevent oxidation (sugaring) on the back side of the weld

Back purging fills the inside of the duct with argon gas during welding. This prevents the back side of the weld from being exposed to air, which would cause heavy oxidation (sugaring) that weakens the joint and creates a rough surface.