Galvanizing Air Knife & Coating Masking Vector Guide
Master the fluid mechanics, air knife stripping equations, vector edge baffle design, and thermal spray masking stencil prepress for continuous coil and structural steel manufacturing.
1. Air Knife Stripping Hydraulics in Continuous Galvanizing Lines (CGL)
In continuous hot-dip galvanizing lines (HDG) and thermal spray cladding, a steel strip exits a molten zinc pot (450°C - 465°C) dragging an excessive liquid film. Opposing linear air knives blow high-pressure compressed air or nitrogen across the strip width to wipe off excess liquid, establishing precise micrometer-level barrier coatings (Z100 to Z600 / G30 to G90).
W_coating = 2 * t_Zn * rho_Zn [g/m2]
2. Edge Overcoating & Aerodynamic Vector Baffles
At the edges of the traveling coil, high-velocity air streams wrap around the sheet corners, creating low-pressure aerodynamic vortices. This causes severe edge build-up (dog-bone defect) and zinc wiper serration. To ensure uniform coil winding:
- Dynamic Vector Edge Baffles: CNC-guided ceramic/stainless steel edge baffles are profile-cut with matching strip edge chamfers and tracked in real-time within ±1.5 mm of the moving sheet edge.
- Masking Stencil Templates: In selective thermal spray, laser-cut high-temperature molybdenum or stainless steel stencils (DXF cut paths) shield non-coated grounding zones with crisp zero-overspray step transitions.
- Nozzle Header Lip Flatness: The air knife slot must be machined with ±10 μm flatness over a 2.0-meter span to eliminate longitudinal coating striping.
3. Gas Wiping Medium: Air vs. Pure Nitrogen (N2)
For high-end automotive exposed panels (GI/GA), compressed dry air causes rapid surface oxidation and zinc dross flaking. Pure nitrogen (N2) gas wiping prevents zinc ash formation, suppresses nozzle clogging, and produces mirror-smooth paintable surfaces with Ra < 0.8 μm.