308A Metal Types and Properties 2

Question 1

What is 'galvanic corrosion' and why must sheet metal workers be aware of it?

Accepted Answer

Accelerated corrosion that occurs when dissimilar metals are in contact in the presence of an electrolyte

Answer

Galvanic corrosion occurs when two different metals are in contact with each other and exposed to moisture. The more reactive (anodic) metal corrodes faster than it would alone. Sheet metal workers must isolate dissimilar metals.

Question 2

What is the thickness in inches of 24-gauge galvanized steel?

Accepted Answer

0.0239 inches

Answer

24-gauge galvanized steel has a thickness of approximately 0.0239 inches (0.607 mm). This is a common gauge used for residential and light commercial ductwork.

Question 3

What is copper sheet metal primarily used for in the sheet metal trade?

Accepted Answer

Roofing, flashing, gutters, and architectural features due to its durability and aesthetic patina

Answer

Copper is prized for architectural applications including roofing, flashings, gutters, downspouts, and decorative elements. It develops a distinctive green patina over time and has excellent corrosion resistance.

Question 4

What is 'work hardening' and how does it affect sheet metal during fabrication?

Accepted Answer

The metal becomes harder, stronger, and more brittle with repeated bending or forming, eventually cracking if overworked

Answer

Work hardening (strain hardening) occurs when metal is repeatedly deformed — bent, hammered, or formed. The crystal structure becomes distorted, making the metal harder but more brittle. Annealing reverses this process.

Question 5

What is the purpose of 'annealing' sheet metal?

Accepted Answer

To soften work-hardened metal by heating it to a specific temperature and cooling it slowly, restoring ductility

Answer

Annealing heats work-hardened metal to a temperature that allows the crystal structure to recrystallize, then cools it slowly. This restores the metal's ductility and formability, allowing further work without cracking.

Red Seal Sheet Metal 308A Practice Test

Red Seal Sheet Metal 308A Practice Test

308A Metal Types and Properties 2