Materials, Tools, and Equipment
What this domain tests
The exam expects you to pick the right alloy and gauge for the service, and to know the capacity limits of the machine you are about to use. Items pair a service condition (pool air, kitchen grease duct, exterior coping) with a material, or a forming job with a machine rating.
Ferrous materials
- Galvanized steel is the HVAC default. G90 means 0.90 oz/ft2 of zinc coating and is the standard for most ductwork. Cut edges are unprotected, so they are primed or sealed in corrosive service.
- Gauge numbers are not thickness. Each material family has its own gauge table, so verify by micrometer or mill certificate before setting up a machine.
- Stainless: 304 general purpose, 316/316L for chlorides and marine, 430 for dry indoor trim. It work-hardens, so use sharp tooling, slower speeds, and dedicated stainless brushes.
- Black iron (uncoated steel) for welded grease duct and some exhaust, always coated afterwards.
Non-ferrous and non-metallic
- Aluminum 3003 for formable trim, 5052 for structural and marine, 6061 for extrusions. Aluminum is ordered by decimal thickness, not gauge number.
- Copper roofing is sold by weight, 16 oz and 20 oz per ft2. It solders, patinates, and must be isolated from steel and aluminum.
- Duct board, flexible duct with a listed jacket and R-value, and spiral pipe round out the inventory.
Tools and capacity
- Snips: aviation style, colour-coded left (red), right (green), straight (yellow). Never cut hardened wire with them.
- Machines: squaring shear, box-and-pan brake, bar folder, slip roll, Pittsburgh lock former, rotary machine (crimp, bead, turn, flange), plasma and laser cutters.
- Never exceed a rated capacity, and derate for stainless and aluminum.
Worked example: brake capacity
A brake is rated 16 ga (0.060 in.) mild steel. The job calls for 0.048 in. type 304 stainless. Stainless needs roughly 1.5 times the force of mild steel, so the equivalent mild thickness is 0.048 x 1.5 = 0.072 in., which exceeds 0.060 in. The brake is overloaded. Options: a heavier machine, a shorter bend length, or thinner material. Also confirm the bend length is inside the rated width, because capacity drops at the ends of the bed.
Traps that cost marks
- Using one gauge table for galvanized, stainless, and aluminum.
- Cutting stainless with a carbon steel blade or brushing it with a carbon brush; contamination rusts.
- Storing galvanized sheet flat in a damp stack, causing white rust.
- Direct metal-to-metal contact between aluminum and steel or copper, causing galvanic corrosion.