Laser Cut Galvanized Steel

Choosing galvanized steel

Galvanized sheet is mild steel with a hot-dip zinc coating on both faces. G90 is the common designation for outdoor and HVAC work; the number tracks how much zinc is on the sheet, counting both faces. The zinc weathers slowly in place of the steel, and near a scratch or a cut edge it corrodes first, which shields the bare steel beside it.

Choose galvanized for parts that live outside or in damp spaces and don't need a show face: duct and plenum parts, flashings, utility box parts, covers and brackets. The faces can carry spangle, a frosty crystalline pattern that varies from sheet to sheet, so for a decorative face, paint it or choose stainless or aluminum. Parts that will be welded heavily are often simpler in mild steel, painted afterward.

Galvanized parts and their thickness

Galvanized sheet is made on continuous coil lines, so it comes in sheet gauges, and its usual work suits sheet: HVAC duct flanges, plenum and register boxes, roof and wall flashings, electrical and irrigation box parts, equipment covers, farm and livestock parts, and raised garden bed panels and corner brackets.

For duct work, the gauge is usually set by the project's duct construction standard or the mechanical drawings. Match that, and confirm the decimal in the sheet metal gauge chart.

Heavier parts that need zinc — base plates, heavy brackets, gate hardware — are usually cut from bare steel and hot-dip galvanized after fabrication, which coats the cut edges and welds too. Cut those from mild steel, add any hanging or drain holes your galvanizer asks for, and take the finished parts to them.

Designing for the laser

The laser cuts all the way through the sheet, so draw outlines, cutouts, holes and slots — not pockets or partial-depth holes. Keep holes at least about half the material thickness across so they cut cleanly; the quote flags anything smaller before you order.

Lines you set to engrave are etched on the surface instead of cut through — handy for part numbers, logos and bend or layout marks.

Edges, bends and welds in galvanized

The laser burns the zinc back a little from every cut edge, leaving a narrow band of bare steel, and an etched line takes some zinc off along its path too. Outdoors, edges and etched marks are where light rust shows first, so put etched part numbers on a face that will be hidden or painted; the laser file prep guide covers setting lines to etch.

Hot-dip zinc takes ordinary bends, but very tight bends can crack or flake the coating on the outside of the bend. Where the coating matters, use an inside radius at least as large as the sheet's thickness, add relief where bend lines meet an edge, and keep etched bend lines on the inside of the bend, where they'll be hidden.

Fasten galvanized parts with galvanized or zinc-plated hardware; in wet spots, stainless screws and copper or brass fittings make the zinc around them corrode faster. To weld it, grind the zinc back from the joint, weld with good ventilation — zinc fumes cause metal fume fever — and brush a zinc-rich cold-galvanizing paint over the weld and the ground area afterward.

Paint, powder coat and desert weather

Galvanized steel takes paint or powder coat over the zinc, and the pairing, often called a duplex coating, outlasts either one alone. The zinc needs its own prep first; the powder coat question below covers what to tell your coater.

Dry desert air is easy on zinc, so bare galvanized parts can last a long time in the valley. What wears the coating faster is water that sits: drip-irrigated planters and soil contact, sprinkler overspray, pool and spa water, and puddles left by monsoon storms. Lift galvanized parts off the soil where you can, and use 316 stainless for hardware that sits in pool water.

Store galvanized parts dry and spaced apart until they're installed. Parts stacked while damp grow white rust, a powdery white zinc corrosion that's mostly cosmetic when light; heavy deposits mean zinc has been lost.

What a galvanized order includes

Galvanized parts ship flat and as cut, with zinc on both faces and a bare band at each cut edge. Bending, welding, deburring, edge touch-up, paint and powder coat happen after the parts leave the shop, with your sheet metal shop, HVAC crew or coater. For a whole installation rather than parts, describe it in a custom fabrication inquiry. Galvanized tube and pipe are covered in the questions below.

How it's priced

Each part is priced on its cut length, each hole by its size, its pierces and any etched lines, plus setup and programming once per design, handling for each piece and loading for each sheet the job uses. Metal is billed by the area your parts use — each part's outer size plus a little cutting space — never more than the sheets they're cut from, and identical parts get automatic quantity discounts on the cutting.