How to use the Salt Spray Tester

Salt Spray Tester

The Salt Spray Tester is used to create and maintain the salt spray (fog) test environment, and test the anti-corrosion quality of all the

materials surfaces after the rust-proof of painting, coating, electroplating, anodizing and rust-proof of greasing. Our salt spray testers

available in two capacities meet ASTM-B117. J1S-D0201. 1IS-H8502. J1S-H8610. 1s-Z2371 and other Interational Standards test methods.

Power supplied can be configured upon request.

Internal Physicochemical Principles

1. The corrosion of metal materials in a salt spray test chamber is actually caused by the conductive salt solution penetrating into the metal, where an electrochemical reaction occurs, forming a micro-battery system of "low-potential metal - electrolyte solution - high-potential impurities." During this process, electron transfer occurs, causing the metal acting as the anode to dissolve. The resulting compounds are the corrosive products.

2. Chloride ions play a primary role in the salt spray corrosion process. Due to their strong penetrating power, chloride ions easily penetrate the metal oxide layer and penetrate deep into the metal, destroying the metal's passivity. Furthermore, chloride ions have a low hydration energy and are easily adsorbed on the metal surface, replacing oxygen in the protective oxide layer and causing damage. In addition to chloride ions, oxygen in the salt solution also plays a significant role, causing depolarization on the metal surface and accelerating the dissolution of the anode metal.

During the salt spray test, the continuous spray and the salt solution film that continuously settles on the specimen surface keep the oxygen content in the chamber near saturation. The formation of corrosion products causes the volume of the salt solution that penetrates into the metal defects to expand, thereby increasing the internal stress of the metal, causing stress corrosion and resulting in bulging of the protective layer.

Operation method

1. First, connect the power supply to the salt spray tester and the air compressor, and connect the air compressor air line.

2. Pour purified or distilled water into the water inlet inside the chamber and at the back of the chamber until the low water level indicator on the panel turns off; otherwise, the chamber will not function properly.

3. Connect the drain and exhaust pipes, as shown on the previous page, with the indicator pointing left for open.

4. Fill the isolation tank with water up to the pad level to prevent salt spray leakage.

5. Preparation of the test solution:

A. Cover, Neutral Salt Spray Test (NSS Test)

a. Prepare the salt solution using sodium chloride (chemically pure, analytically pure) and distilled or deionized water to a concentration of (5% ± 0.1)% (mass percentage). The collected solution after atomization, except for the portion removed by the baffle, must not be reused.

b. The pH of the salt solution before atomization should be between 6.5 and 7.2 (at 35 ± 2°C). When preparing the salt solution, chemically pure dilute hydrochloric acid or sodium hydroxide solution may be used to adjust the pH, but the concentration must still meet the requirements in point a.

B. Metal Coating, Copper Accelerated Acetic Acid Salt Spray Test (CASS Test)

a. Dissolve sodium chloride in distilled or deionized water to a concentration of 50 ± 5 g/L.

b. Add copper chloride (CuCl2·2H2O) to solution a to a concentration of 0.26 ± 0.02 g/L (i.e., 0.205 ± 0.015 g/L anhydrous copper chloride).

c. Add an appropriate amount of glacial acetic acid to solution a to ensure that the pH of the salt spray collection solution in the test chamber is 3.1-3.3. If the pH of the solution before spraying is 3.0-3.1. the pH of the collection solution will generally be within the range of 3.1-3.3. Measure the pH of the solution with a pH meter. You can also use precision pH test paper calibrated with a pH meter that can read a 0.1 pH change for routine testing. The pH of the solution can be adjusted with glacial acetic acid or sodium hydroxide.

d. To prevent nozzle clogging, the solution must be filtered before use.

Note: For metal coatings, the acetic acid salt spray test (ASS test) omits step "b" in process "B."

6. Pour salt water into the salt solution refill bottle, which automatically fills the salt water into the laboratory spray tower, allowing the solution to flow into the salt water spray tower.

7. Fill the wet-bulb cup with water. Cover the wet-bulb thermometer with gauze, and place the end of the gauze in the wet-bulb cup.

8. Place the test piece or specimen on the rack: The angle should be based on the required standard. For example, a standard test piece 130×70 mm can be tilted at 15 or 30 degrees.

9. Set the test temperature: Set according to the required standard (press "▲" to increase, "▼" to decrease).

a. NSS and AASS tests: Test chamber temperature 35°C; saturated air chamber temperature 37°C (35°C to 40°C).

b. CASS test: Test chamber temperature 50°C; saturated air chamber temperature 55°C (50°C to 55°C).

10. Set the test time: 0 to 999 hours (hours; press "+" to increase, press "-" to decrease).

11. Press the power button on the salt spray tester and operate the preheating buttons to reach the set temperature. Note: Always close the test cover and handle with care to avoid damage.

12. Press the spray button:

a. Open the outlet valve on the front of the air compressor and adjust the pressure to 0.2-0.4 MPa.

b. Adjust the pressure regulating valve to 0.07-0.17 MPa. The pressure can be read on the pressure gauge (clockwise increases, counterclockwise decreases).

13. Press the timer button to start the timer.

14. After the test is complete, turn off all switches of the salt spray tester in order.

15. If any abnormalities occur during the test, refer to the functional abnormality diagnosis table for corrective action.