A fog spray test chamber—also known as a salt spray or salt fog test chamber—is an essential tool for evaluating how well products withstand corrosive or humid environments. These chambers simulate harsh atmospheric conditions by exposing materials to a fine, atomized mist of saline or water-based solutions. They're widely used across automotive, aerospace, marine, electronics, and industrial sectors for corrosion testing, moisture resistance, and quality assurance.
Purpose of a Fog Spray Test Chamber
Corrosion Resistance Testing
Fog spray chambers accelerate the corrosion process by subjecting metallic or coated samples to continuous exposure in a controlled fog. This helps predict long-term behavior under real-world conditions.
Ingress or Moisture Protection
Chambers also evaluate sealing effectiveness of enclosures and electronic housings. A dense mist simulates humid or wet conditions, revealing points of moisture intrusion.
Quality Comparisons
Multiple samples—coated or treated differently—can be tested side-by-side to compare performance under identical stress conditions.
Common Testing Standards
ASTM B117 (Neutral Salt Spray)
- 5% sodium chloride solution
- pH: 6.5–7.2
- Chamber temp: 35°C (95°F)
- Spray rate: 1–2 ml/hr per 80 cm²
ISO 9227
Expands on ASTM B117 with variations like:
- AASS (Acetic Acid Salt Spray)
- CASS (Copper-Accelerated Acetic Acid Salt Spray)
Other Variations
Acetic Acid Salt Spray (AASS) and Copper-Accelerated Acetic Acid Salt Spray (CASS): These introduce acetic acid or copper chloride to the salt solution, intensifying corrosive effects—often used for high-performance coatings or applications requiring a harsher test.
- Cyclic Corrosion Testing: Instead of continuously spraying, these methods alternate between fog, dry, and humidity phases to mimic more realistic atmospheric conditions.
Key Chamber Components
- Atomizing Nozzle: Creates uniform mist using compressed air.
- Heater & Thermostat: Maintains set temperatures (e.g., 35°C).
- Solution Reservoir: Contains the prepared test solution.
- Spray Collection Funnels: Verify deposition rates.
- Sample Racks: Angle samples (15–30°) to standard exposure specs.
- Exhaust System: Controls internal pressure and prevents lab contamination.
Test Procedure Overview
- Solution Prep: Mix 5% NaCl with distilled water. Adjust pH as needed.
- Sample Prep: Clean and document all specimens.
- Chamber Loading: Position samples per standard guidelines.
- Start-Up: Heat chamber and initiate fog generation.
- Monitoring: Record pH, temperature, and deposition rate daily.
- Inspection: Evaluate samples at defined intervals or post-test
Result Evaluation
- Visual Grading: Rate rust, blistering, or coating failure (per ASTM D1654)
- Weight Loss: For uncoated metals, track corrosion via mass reduction.
- Adhesion Testing: Use cross-hatch or tape pull tests post-exposure.
- Functional Checks: Test electronic or mechanical parts for performance degradation.
Real-World Applications
- Automotive: Validate performance of wheels, fasteners, and body panels.
- Marine: Assess durability of boat parts, docks, and rigging hardware.
- Electronics: Verify housing seals and board conformal coatings.
- Aerospace: Evaluate aluminum alloys and coatings under stress.
- Industrial Equipment: Simulate harsh environments for painted components or enclosures.
Limitations & Best Practices
- Not Real-Life Replicas: Salt spray is aggressive and linear—unlike fluctuating natural conditions.
- Reproducibility Demands: Keep solution pH and temperature tightly controlled.
- Interpretation Challenges: Slight procedural differences can skew results.
- Safety First: Use PPE, good ventilation, and handle corrosive mist carefully.