Electroplating & Metal Coatings
Zinc Plating
| Type | Thickness | Corrosion Resistance | Applications | Notes |
|---|---|---|---|---|
| Clear Zinc | 5-12 μm | 96-200 hours SST | General indoor use | Bright silver finish |
| Yellow Zinc (Chromate) | 5-12 μm | 200-400 hours SST | Moderate outdoor exposure | Iridescent yellow/gold |
| Black Zinc | 5-12 μm | 96-200 hours SST | Aesthetic applications | Black oxide appearance |
| Zinc-Nickel (ZnNi) | 8-15 μm | 500-1000+ hours SST | Automotive, harsh environments | Superior corrosion resistance |
Hot-Dip Galvanizing
Process: Immersion in molten zinc at 450°C
Thickness: 45-85 μm (typical)
Corrosion Protection: 20-50+ years (depending on environment)
Standards: ASTM A153, ISO 1461, BS EN ISO 10684
Applications: Outdoor structures, marine environments, infrastructure
Advantages: Thick coating, excellent long-term protection, cathodic protection
Other Electroplated Finishes
| Finish | Thickness | Key Properties | Typical Uses |
|---|---|---|---|
| Cadmium Plating | 5-12 μm | Excellent corrosion resistance, no hydrogen embrittlement | Aerospace, military (restricted due to toxicity) |
| Nickel Plating | 12-25 μm | Hard, wear-resistant, decorative | Hydraulics, precision components |
| Chrome Plating | 2-10 μm | Very hard, low friction, decorative | Show chrome, wear surfaces |
| Tin Plating | 5-15 μm | Food safe, solderable | Food processing, electronics |
| Silver Plating | 5-25 μm | High conductivity, anti-galling | Electrical, high-temperature |
Mechanical & Conversion Coatings
Mechanical Plating (Peen Plating)
Process: Mechanical deposition using tumbling with glass beads and metal powder
Materials: Zinc, zinc-tin, cadmium
Advantages: No hydrogen embrittlement risk, uniform coverage on threads
Thickness: 12-50 μm
Best For: High-strength fasteners (Grade 10.9+), spring steel
Phosphate Coatings
| Type | Color | Purpose | Applications |
|---|---|---|---|
| Zinc Phosphate | Gray | Paint base, mild corrosion protection | Automotive, pre-paint treatment |
| Manganese Phosphate | Dark gray/black | Wear resistance, oil retention, break-in | Gears, military, break-in coatings |
| Iron Phosphate | Light gray | Light protection, paint adhesion | General manufacturing |
Black Oxide
Process: Hot alkaline chemical conversion (140°C)
Thickness: 0.25-1.5 μm (very thin)
Corrosion Protection: Minimal (must be oiled)
Advantages: No dimensional change, aesthetic black finish, reduces glare
Applications: Tools, firearms, decorative hardware
Organic Coatings & Dry Film Lubricants
PTFE (Teflon®) Coatings
| Product | Thickness | Temperature Range | Key Features |
|---|---|---|---|
| Pure PTFE | 15-25 μm | -200°C to +260°C | Lowest friction, chemical resistant |
| PTFE/Moly | 15-25 μm | -200°C to +260°C | Enhanced load capacity |
| Modified PTFE | 15-25 μm | -40°C to +180°C | Better adhesion, lower cost |
Xylan® Coatings (Fluoropolymer)
| Grade | Description | Temperature | Applications |
|---|---|---|---|
| Xylan 1010 | PTFE-based, high lubricity | -195°C to +260°C | General purpose dry lube |
| Xylan 1014 | PTFE/Moly, extreme pressure | -195°C to +260°C | High load, galling prevention |
| Xylan 1070 | Corrosion resistant | -195°C to +260°C | Marine, chemical environments |
| Xylan 1424 | NASA low outgassing | -195°C to +260°C | Aerospace, vacuum service |
Molykote® & MoS₂ Coatings
Composition: Molybdenum disulfide (MoS₂) in various binders
Coefficient of Friction: 0.04-0.08
Temperature Range: -185°C to +400°C (in vacuum/inert atmosphere)
Load Capacity: Very high
Applications: High torque fasteners, space applications, ultra-high vacuum
Geomet® / Dacromet® (Zinc Flake)
Process: Zinc/aluminum flake dispersion coating
Thickness: 8-15 μm
Corrosion Resistance: 1000+ hours salt spray
Advantages: No hydrogen embrittlement, excellent corrosion protection, thin coating
Temperature: Can withstand 300°C
Applications: Automotive chassis, high-strength fasteners, brake components
Specialty Coatings
Ceramic Coatings
| Type | Temperature Range | Key Properties | Applications |
|---|---|---|---|
| Alumina (Al₂O₃) | Up to 1650°C | Extreme hardness, electrical insulation | High temp fasteners, thermal barriers |
| Zirconia (ZrO₂) | Up to 2200°C | Thermal barrier, wear resistant | Turbine components, exhaust systems |
| Silicon Nitride | Up to 1400°C | Low friction, high strength | Precision components, bearings |
Specialized Lubricant Coatings
| Coating | Composition | Best For | Special Features |
|---|---|---|---|
| Xylar® 101 | Fluoropolymer primer | Corrosion + lubrication | Salt spray 1000+ hrs |
| Silver Plating + PTFE | Silver base + dry lube | High temp, anti-galling | Nuclear, aerospace |
| Copper Anti-Seize | Copper in grease base | High temp assembly | 1800°F service temp |
| Nickel Anti-Seize | Nickel in synthetic base | Stainless steel fasteners | Prevents galling |
Coating Selection Guide
| Environment/Requirement | Recommended Coatings | Not Recommended |
|---|---|---|
| Marine/Offshore | Hot-dip galvanizing, Geomet, Xylan 1070, Stainless Steel | Clear zinc, black oxide |
| High Temperature (>260°C) | Ceramic coatings, silver plating, uncoated alloy | PTFE, standard zinc, cadmium |
| High Strength (>150 ksi) | Mechanical plating, Geomet, baking after plating | Standard electroplating (hydrogen embrittlement risk) |
| Chemical Processing | PTFE, Xylan, Halar, stainless/exotic alloys | Zinc, cadmium |
| Food/Pharmaceutical | Stainless steel, PTFE, tin plating | Cadmium, lead-based |
| Electrical Conductivity | Silver, tin, nickel | Anodizing, ceramic, PTFE |
Important Considerations
Hydrogen Embrittlement
Risk Factors: Electroplating processes can introduce hydrogen into high-strength steels (>150 ksi / 1035 MPa)
Prevention: Baking at 190-200°C for 3-24 hours after plating, or use mechanical plating/Geomet
Critical Applications: Grade 10.9+ bolts, spring steel, heat-treated components
Torque & Preload Effects
• Lubricated coatings (PTFE, Xylan, Molykote) reduce friction coefficient
• K-factor changes from ~0.2 (dry) to 0.10-0.14 (lubricated)
• Must adjust torque values when using lubricated fasteners to achieve correct preload
• Over-torquing can strip threads on lubricated fasteners