Module 3: Finishing & Protection 

Surface Preparation

Proper surface preparation is the critical first step in ensuring long-lasting metal finishes. This process creates the ideal foundation for coatings while removing imperfections that could compromise durability.

Mechanical Preparation Methods

• Grinding: Uses abrasive wheels to remove weld seams, burrs, and surface irregularities. Angle grinders with flap discs create smooth transitions between metal components.

• Sanding: Progressive grit sanding (from coarse 60-grit to fine 220-grit) prepares surfaces for high-end finishes. Orbital sanders ensure uniform texture without visible scratch patterns.

• Polishing: Buffing wheels with progressively finer compounds (from tripoli to rouge) create mirror finishes on stainless steel and brass. This is essential for decorative architectural elements where reflectivity matters.

Chemical Treatments

• Pickling: Acid baths (typically nitric-hydrofluoric blends for stainless steel) remove oxidation and weld scale. This treatment restores corrosion resistance in welded areas.

• Passivation: A nitric acid soak enhances stainless steel's chromium oxide layer, dramatically improving rust resistance. Critical for exterior applications in coastal environments.

Protective Coatings

Selecting the right protective system balances durability requirements with aesthetic goals and environmental conditions.

Coating Application Methods

• Powder Coating: Electrostatic application of dry polymer particles that cure under heat (typically 200°C). Provides superior impact resistance and color retention compared to liquid paints. Thickness ranges from 60-120 microns.

• Liquid Paint Systems: Multi-layer approaches including:

• Epoxy primers for adhesion

• Polyurethane topcoats for UV resistance

• Fluoropolymer finishes (like PVDF) for extreme weather performance

Metallurgical Protection Processes

• Hot-Dip Galvanizing: Immersion in molten zinc (450°C) creates a metallurgical bond. The zinc layer (85-140 microns) provides sacrificial protection, ideal for structural steel in corrosive environments.

• Anodizing: Electrochemical process growing aluminum oxide layers (5-25 microns). Hard anodizing (Type III) reaches Rockwell C 60 hardness for high-wear applications.

Patina & Aesthetic Finishes

These specialized finishes combine artistic expression with functional benefits, particularly for architectural features.

Chemical Patination

• Copper Patinas: Controlled application of ammonium sulfide creates classic verde green, while liver of sulfur produces rich browns. Accelerated patination systems mimic decades of natural weathering in weeks.

• Bronze Effects: Ferric nitrate solutions create dramatic black finishes on bronze sculptures and architectural details. Wax sealing preserves the desired patina stage.

Mechanical Finishes

• Brushed Finishes: Directional abrasion (typically with Scotch-Brite belts) creates satin sheens that hide fingerprints. Common grits range from #120 to #240 for varying texture depths.

• Mirror Polishing: Sequential buffing with increasingly fine compounds (up to diamond paste) achieves <0.05μm Ra surface roughness for high-reflectivity applications.

• Textured Surfaces: Bead blasting (glass or ceramic media) creates uniform matte finishes. CNC-controlled laser texturing allows precise patterning for decorative panels.

This module provides comprehensive training in transforming raw metal into durable, visually striking architectural elements through scientifically-proven finishing techniques. Students will gain hands-on experience with both industrial-scale processes and artisanal finishing methods.