A salt spray tester is a type of equipment. This test is used to measure how well materials and products withstand salty, corrosive air. It is common in industries like automotive, electronics, and aerospace. Correct maintenance can extend the service life of the salt spray corrosion tester.
Test preparation
Open the lid. Put the sample on the rack in the chamber (10% from the wall). Keep a gap between the sample and the lid. Then, close the lid.
Connect the air source, turn on the power switch after the power is turned on. Add water to the pressure drum and the chamber. Stop when the two low water level lights go out. Add water at the sealing groove to seal it. Prepare pure water and sodium chloride salt in the ratio of 1:20. Pour the prepared solution into the brine tank. Turn on the operation and spray switch after all the lights go out. Turn on the demisting switch only after completing the test.
Water source used for the test
The water added to the test box and the pressure drum must be neutral. It must not be acidic or basic so as not to affect the test. To make sodium chloride, you must use distilled or plasma water. It is forbidden to use underground or tap water.
The exhaust pipe that connects to the equipment must be smooth. It cannot have any folds or bumps. These could cause moisture in the mist to condense and block the exhaust. Then, we could not conduct the test.
During the test
In the test, you should not open the test box lid. This prevents rapid temperature changes. These changes can trigger an over-temperature alarm. They can also cause the box to corrode nearby equipment with salt spray emissions. If you need to see the product test, open the demist switch. After 1 minute, the fog will disperse from the window. Then, you can see the product.
In the process of using the equipment must be effectively grounded to ensure that the use of normal. The standard environment will use the equipment. There must be no erosive gases, intense vibration, or strong electromagnetic fields.
After the completion of the test
After the test, for a while do not do the test if the temperature is below 0 degrees Celsius. At that time, drain the test box and pressure barrel to avoid water damage or ice.
Precautions for salt spray test
1.Sample substrate cleaning
For the test with the sample plate, it must be clean. It must be free of rust, oil, and grease. You can use sandblasting, grinding, or phosphating to treat the substrate. But, be careful not to expose it to humid air. This prevents the formation of a water film on the substrate. This film can rust the metal or reduce adhesion between the coating and the metal.
2.Concentration of electrolyte solution
The key to the salt spray test is the electrolyte solution. Many solute components must be strictly weighed to ensure the pH is right. Otherwise, it will directly affect the test results.
3.Paint edge sealing
After preparing coating samples, seal exposed parts of the substrate with paint. This will prevent rust marks and board contamination. Without sealing, rust marks will make assessing the work hard.
4.Regular checking of boards and parts
When checking boards and pieces, keep the board wet. Also, reduce the time it’s exposed to air.
5.Objective evaluation of the board
After the test, evaluate the board surface fairly. Check for: blisters, color change, rust, and peeling. We can also add the test evaluation of adhesion and scratch. We can also test how far a single side rusts, as customers require.
6.Replacement of saline every month
Every month, replace the salt water test solution. Also, replace the water in the heating tank and clean the salt spray test chamber.
7.Power connection
Before using the product, you must connect its electrical parts to the power supply. Connect the power supply to the right salt spray test chamber. For example, the 60-type or 90-type. They run on 220V. You can use the 220V power supply of household electricity. After this, connect the air pressure tube. Then, open the box’s lid and pour pure or distilled water into the tank until the low-water light turns off. Otherwise, the lack of water will prevent normal work.
8.Connecting the drain and exhaust pipes
The test box will connect to the drainpipe and the exhaust pipe. After connecting, check for slack or loose connections. After isolating the water tank, add water to the pad to avoid salt spray leaks.
9.Setting test temperature
After everything is ready, press the power switch to turn on the power supply. Then, press the operation switch. Set the temperature of the test chamber and the saturator. Use the control panel on the two numerical control instruments to dial to the setup file. Set the required temperature value. Then, dial to the measurement file. The usual test temperature should be 35 ℃. The saturator temperature should be set to 35 ℃ to 40 ℃.
10.Prohibition of redeployment of over-temperature protectors
The over-temperature protector control valve is on the right side of the chamber. It is set to 55 ℃. This setting prevents the temperature control from failing. It also prevents the box from burning due to instrument failure. The power supply is cut off when the chamber’s temperature goes above 55 ℃. This is done by the over-temperature protection. The user should not change the protector.
11.Preparation of solutions such as saline
Pour the matched brine into the brine tank. Put the wet bulb cup in water. Cover the wet bulb thermometer with gauze. Put the gauze end in the wet bulb cup.
12.Sample placements
Place the sample on the shelf. Its angle is set. Users utilize the control instrument to establish the test’s parameters. Then, press the power supply and operation keys to start the test.
Extend the service life of the salt spray corrosion tester five tips:
- Choose a high-quality salt spray tester. It has better materials and manufacturing. They ensure the durability and stability of the equipment. When buying a salt spray corrosion tester, choose a maker with high quality and a good reputation. Hangzhou Aoke Environmental Test has over ten years of experience and technology in the salt spray test chamber industry. They are the best at making salt spray corrosion testers. They have good quality, reputation, and after-sales service.
- Regular maintenance and repair are important. They keep the salt spray corrosion tester working and lasting longer. Maintenance and repair work has cleaning equipment. It also has checking and replacing parts. And, calibrating test parameters.
Avoid using too much salt spray. It will speed up wear and aging of the equipment. So, during use, avoid overloading and long hours of continuous work. The equipment needs enough rest and recovery time.
Use the environment appropriately. Put salt spray corrosion testers in a dry, non-corrosive gas. Ventilation releases the gas. Avoid direct sunlight and rain. At the same time, make sure there is enough space around the equipment. This space helps with operation and maintenance.
Train operators. They are one of the most important factors in using salt spray corrosion tester. Train operators to know the structure, principles, and how to use and protect the gear. This can reduce the risk of misuse and damage.
The key to making the salt spray corrosion tester last longer is choosing good equipment. Do regular maintenance, avoid overuse, use the right environment, and train operators. Only by doing a good job can we ensure the stable operation and prolong the service life of the salt spray tester.
Salt spray test factors
Test temperature and humidity
The critical relative humidity for metal corrosion is about 70%. When the humidity reaches or exceeds this level, the salt will dissolve. It will form a good conductor. As humidity decreases, the salt solution’s concentration will increase. It will increase until salt crystals form. This reduces the corrosion rate. Temperature increases. This intensifies molecular movement. It speeds up the corrosion rate of high salt spray. The International Electrotechnical Commission pointed out that: for every 10 ℃ of temperature rise, the corrosion rate doubles or triples. The electrolyte’s conductivity rises by 10 to 20%. For the salt spray test, people believe the test temperature should be 35 ℃.
Concentration of the solution
The corrosion rate of steel, nickel, and brass increases with concentrations of 5% or less. For concentrations over 5%, the corrosion rate falls with the increasing concentration. This is because, at low salt concentrations, the oxygen content increases with salt. When the salt reaches 5%, the oxygen reaches saturation. If the salt keeps increasing, the oxygen then decreases. As oxygen content decreases, its ability to depolarize also decreases. This weakens the corrosion effect. Zinc, cadmium, and copper all corrode faster with more salt.
Angle of placement of the sample
Salt spray settles vertically. Because it has the largest area, we place the sample horizontally. So, its surface gets the most salt and the worst corrosion. Research results show that: the steel plate and the line are at a 45 degree angle. The corrosion loss is 250 g per square meter. The plate is parallel to the vertical line. The corrosion loss is 140 g per square meter. The GB/T 2423.17-93 standard says testers should place flat plate samples to test their surface. They should be at a 30-degree angle to the vertical.
pH value
The pH value of the salt solution is one of the main factors affecting the results of the salt spray test. Lower pH values have higher concentrations of hydrogen ions in the solution. They are more acidic and corrosive. Higher pH values are less acidic. Neutral salt spray test (NSS) pH value of 6.5 ~ 7.2. The salt spray test corrodes Fe / Zn, Fe / Cd, Fe / Cu / Ni / Cr and other electroplated parts. It shows that the pH of the salt solution is 3.0 in the acetate spray test (ASS). This is harsher than the pH of 6.5 ~ 7.2 of the neutral salt spray test (NSS) by 1.5 ~ 2.0 times. The pH of the salt solution may change due to environmental factors. The salt solution has a specified pH range. We propose a method to stabilize the pH during the test. This will improve the reproducibility of the test.
Influence of salt solution pH changes in the reasons and results:
(1)The test caused it. The salt solution pH changed was the root cause. The main soluble substances came from the air. They may be different. Some dissolve in water after becoming acidic. Others dissolve in water after becoming alkaline.
(2)During the salt spray test, the air’s soluble substances dissolve into or escape from the salt solution. This is a reversible process.
(3) There are many factors affecting the change of pH value of the salt solution. For example, the nature and content of soluble substances in the air, pressure, air and salt solution contact area and contact time.
①The nature and content of soluble substances in the air
Gases like CO2, SO2, NO2, and H2S are in the air. They dissolve in water to make acid. This lowers the water’s pH. There may also be alkaline dust in the air. When dissolved in water, it raises water’s pH.
②Atmospheric pressure
The solubility of gases in water is directly proportional to atmospheric pressure.
③Contact area and contact time between air and salt solution
Spraying turns the salt solution into a salt mist of fine particles with a diameter of 1 to 5 μm. The area where they touch increases the amount of gas that dissolves into the liquid. It also increases the amount of gas that escapes from the liquid.
5.Salt mist deposition and spraying method
The salt spray particles become finer. They form a larger surface area and adsorb more oxygen. They become more corrosive. Traditional spraying methods include the air pressure and spray tower methods. The main drawback is that the salt spray is not uniform and the particles are large. Different spraying methods also have an effect on the pH value of the salt solution.
Salt spray test summary
The salt spray test is important. It assesses the ability of products to resist salt spray corrosion. The test’s scientific and reasonable results are crucial. Many factors affect the stability and consistency of salt spray test results. The key to improving the test’s results is better test technology. Testers need good knowledge and skills. They also need much experience and a deep understanding of the product. This includes many areas, like chemical and environmental engineering, materials, and structures. They need this to understand the salt spray test. It helps them make good test plans and improve products or materials.
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