title = "Thermal Spray Coatings: Flame and Arc Spray"

content = """
Thermal spray is a family of coating processes in which feedstock material (wire, rod, or powder) is melted or softened by a heat source and propelled onto the prepared substrate by a gas stream, forming a layered coating through impact and rapid solidification. At Ridgecrest Metalworks, thermal spray is used to restore worn dimensions, apply wear-resistant surfaces, and provide corrosion protection on large structures where other coating methods are impractical.

Flame spray (oxy-fuel wire or powder spray) is the simplest thermal spray method. Feedstock is fed through a flame produced by combustion of acetylene or propylene with oxygen. Particle velocities are relatively low (60–100 m/s), and coating densities are moderate, with higher porosity than more energetic processes. Flame spray is cost-effective for large-area zinc or aluminum anti-corrosion coatings on structural steel and for dimensional restoration of worn shafts and bores using mild steel or bronze wire.

Electric arc spray (wire arc spray) uses two electrically conducting wires as electrodes. An arc forms at the wire tips, melting the wire ends. Compressed air atomizes and propels the molten droplets onto the substrate. Arc spray is faster and more economical than flame spray for electrically conductive materials and is widely used for applying zinc and aluminum corrosion-protection coatings to structural steel (metallizing). Coating rates are high and the process is suitable for large outdoor structures and bridge components.

High-velocity oxy-fuel (HVOF) spray, while more specialized, is used for wear-resistant coatings of tungsten carbide-cobalt (WC-Co) and chromium carbide on high-wear components such as pump shafts, mixing paddles, and forming tools. HVOF achieves particle velocities above 600 m/s, producing very dense, low-porosity coatings with strong bond strength exceeding 70 MPa.

Surface preparation before thermal spray is critical. Parts must be grit blasted to Sa 3 (white metal) with a coarse angular profile (Rz 75–125 µm) immediately before coating. Any delay risks oxidation and reduces bond strength. Masking of adjacent areas uses specialized tape and tooling to keep coating boundaries precise.

Post-spray, coatings are measured for thickness (typically 100–500 µm depending on application), porosity is assessed by metallographic cross-section, and bond strength is tested by tensile pull-off per ASTM C633. Sealed thermal spray coatings receive a sealant infiltration step to close surface pores before service.
"""

version = "0.0.1"
