When testing salt spray test chambers, corrosion results vary greatly between batches. If uneven spraying is suspected, how should it be troubled?

1. Analysis of the Cause of the Problem

The "large differences in corrosion results at different locations within the same box" you encounter are usually not core equipment faults, but are caused by the following three easily overlooked links:

• Poor nozzle condition: The glass nozzle is the core atomization component of the salt spray test chamber. After long-term use, saltwater crystallization may clog the nozzle micro-holes, causing the spray to concentrate in a specific area; It may also be due to tiny cracks in the glass nozzle, causing uneven spray pressure and increased atomized particle size. Some literature points out that glass nozzle rupture is one of the common causes of abnormally low settlement.

• Mist collection device malfunction: If the mist funnel and graduated cylinder inside the test chamber are tilted, the hose is blocked, or the graduated cylinder is placed incorrectly, the collected sedimentation data may not accurately reflect the actual spraying situation, misleading users into convincing that the spray is normal.

• Inconsistent temperature settings in the test chamber: If there are temperature differences at different locations inside the chamber (usually caused by uneven power distribution of heating tubes or poor fan circulation), it can directly affect the corrosion rate. When the temperature setting deviates, test results will inevitably differ.

2. Detailed Inspection and Operational Methods

Step 1: Conduct a comprehensive inspection to ensure the salt spray sedimentation is uniform

According to GB/T 10125, the sedimentation should be 1~2mL/80cm²·h. Use at least five standard collection funnels (fog collectors), placed simultaneously in various corners inside the box (front left, front right, rear left, rear right, and center), and after continuous operation for 24 hours, the sedimentation amount is read separately. The difference between settlement amounts at each point should not exceed 20% of the average. If the settlement at a certain point is significantly low, it indicates insufficient spraying in that area; If a point has significantly higher settlement (more than 40% different from other points), it indicates that the area may be directly impacted by spray airflow.

Step 2: Inspect and clean/replace the nozzle

If uneven settlement distribution is found, first check the nozzle condition. Turn off the device power, open the lid, and carefully remove the glass nozzle. Use a magnifying glass to check for cracks or notches at the tip of the nozzle. If the nozzle is intact, soak it in 5% dilute hydrochloric acid for 30 minutes to dissolve the crystalline salts, then rinse thoroughly with distilled water, and dry it from the nozzle tail toward the nozzle with compressed air (pressure not exceeding 0.2MPa). If the nozzle has cracks, it must be replaced with the original glass nozzle of the same model (if the glass nozzle breaks, the spray distribution will seriously deviate from the standard).

Step 3: Check whether the mist collection system has a "false underperformance" issue

If the brine consumption is normal (the water level in the brine tank drops significantly), but the sedimentation is small or the distribution varies greatly, the fog collection device should be a key concern. Check whether each collection funnel remains level (can be measured with a spirit level), and whether the top edge of the funnel is deformed; Check whether the plastic hose between the mist funnel and the graduated cylinder is blocked—the inner wall of the hose tends to accumulate saltwater crystallization, reducing the inner diameter. Use fine wire to unclog it, then rinse with distilled water; Check whether the graduated cylinder is placed vertically; tilted cylinders can cause reading errors.

Step 4: Calibration temperature uniformity

Precision thermometers (accuracy ± 0.1°C) are placed at different locations inside the chamber (corresponding to the sedimentation collection points). After stable operation for 30 minutes, the temperature at each point is read. The standard requires 35°C ± 1°C. If the temperature difference at a certain point exceeds ±1°C, check whether the heating tubes in that area are aged or damaged. If the temperature differences at each point are within the allowable range, it indicates that temperature uniformity is not an issue.

Step 5: Daily preventive recommendations

• Inspect the glass nozzle once a month; if crystals are found, clean them promptly with dilute hydrochloric acid. Never use metal needles to poke micro-holes.

• Before each test, be sure to place the collection funnel horizontally and the graduated cylinder vertically.

• After preparing the brine, the pH must be measured with a pH meter and adjusted to between 6.5~7.2. Once non-neutral brine is used for experiments, the corrosion level on the sample increases exponentially—when pH ≈ 3.5, the corrosion level is 7~8 times higher than when pH = 7.0.

• A "five-point settlement uniformity test" is conducted quarterly, recording data and comparing it with standard values to establish equipment health records.