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, which is enhanced by the effective use of spray control systems that maintain consistent mist 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.