What is salt spray, salt spray test classification
Salt spray is a mix of tiny, salt-containing droplets in the air. It is a type of artificial environment used in three series of defense tests. Many companies need to simulate the destructive nature of coastal climates. A salt spray test simulates the generation of this phenomenon. So, we created the salt spray test chamber for this test.
The salt spray test divides into two kinds: neutral salt spray and acidic salt spray. The difference lies in their adherence to different standards and test methods. These tests are also called the ‘NSS’ and ‘CASS’ tests. They are the most common tests in the artificial three anti-climate.
Box material: The test box must use PVC reinforced rigid plastic. It should have a smooth, flat surface. And it must resist aging and corrosion. It should be easy to clean and leak-proof. Abandon the use of glass-fibre-reinforced plastic; it should be time and produce surface.
Salt spray corrosion is the deterioration of a material by the environment. Most corrosion occurs in the atmosphere. It has oxygen, humidity, temperature changes, pollutants, and other corrosive factors. Salt spray corrosion is a common and most destructive atmospheric corrosion. “Salt spray” refers to a chloride-rich atmosphere. Its main corrosive component is the chloride salt in the ocean – sodium chloride. This salt mainly comes from the ocean and inland saline areas. Salt spray corrosion of metal surfaces is due to chloride ions. They penetrate the oxidation and protective layers of the metal. This causes an internal electrochemical reaction. Chlorine ions have a specific hydration energy. This makes them easily adsorbable in the metal’s pores. They can crowd cracks and displace the oxygen in the oxide layer. This transforms insoluble oxides into soluble chlorides. It also changes the surface from a passive to an active state. This causes extremely bad adverse reaction to the product.
Fading fibre material structure
Lid Material: Transparent imported impact-resistant plate manufacturing, easy to observe the test samples during the test condition.
Brine bucket material: imported PVC board, large brine tank design, to prevent the lack of brine and interrupt the test.
High-pressure air hose material: copper or rubber hose
The saturated air bucket plays a role in heating and humidifying the imported high-grade stainless steel (SUS304) plate, following Henry’s law, to provide the necessary humidity for the experiment. The chamber utilizes thickened fluoro-silicone rubber tubing in all pipelines to maintain durability for up to fifteen years without aging or cracking while compressing the air for heating, humidification, and oil filtration.
Test Methods
Test methods can be done:
Neutral salt spray test
Acetic acid fog test
Copper accelerated vinegar instinct test
High temperature and humidity test
Test Temperature: Neutral salt spray test: chamber: 35℃±1℃, b. Saturated air drum: 47℃±1℃, Acid corrosion test: chamber: 50℃±1℃, b. Saturated air drum: 63℃±1℃, also can be set according to JIS, CNS and other standards.
Reference standard
Salt spray test reference standards: IEC60068-2-11, ISO4628-3, ASTM B117, JIS-Z2371, JIS-G3141, GJB 150.1, MIL-STD-810F, MIL-STD-883E, etc.
Neutral Salt Spray Test
The Neutral Salt Spray Test (NSS) sprays a solution containing (5 Shi 0.5)% sodium chloride and a pH value of 6.5 ~ 7.2 onto the test piece in a specific test chamber (plating equipment) using a spray device. Researchers observe the corrosion state of the test piece’s surface after a certain period of time. The test chamber requires a temperature of (35±2)℃, humidity exceeding 95%, a mist drop volume of 1~2mL/(h-cm2), and a nozzle pressure of 78.5~137.3kPa (0.8~1.4kgf/cm2).
Chinese name: Neutral salt spray test
Temperature inside the spray box 35±2℃.
Do not reuse test conditions that mist liquid through the specimen area.
Volume of salt spray box not less than 0.2m
Introduction
Test pieces in the box placed not in direct contact with the box, but to use hanging or placed on a special shelf, if the sheet, to be l5 ° ~ 30 ° angle with the plane. Conduct the spray test in an intermittent or continuous manner. Generally 24h as an observation period, intermittent is spraying for 8h and stopping for 16h, continuous is spraying all the time without stopping. We can also agree upon different observation times as needed. The product’s use and transport determine the test time.
The test time is customised according to the use of the product and the transport location/environment.
Test solution
I. Dissolve chemically pure sodium chloride in distilled water or sub-water at a concentration of 50±5g/L.
II. Measure the PH value of the solution with an acidimeter, or use precision PH test paper calibrated by an acidimeter as a daily test. You can adjust the pH value of the solution using chemically pure hydrochloric acid or sodium hydroxide. The PH value of the salt spray collection solution in the test chamber is 6.5~7.2.
III. To prevent nozzle clogging, filter the solution before using it.
Test equipment
First, the test equipment must use materials that resist salt spray corrosion. They must not affect the test results.
Second, the salt spray box, preferably not less than 0.4 m. Accumulation of droplets on the top of the box shall not fall on the specimen. The box’s shape and size should collect salt spray in line with Article 5.2.
Third, to be able to maintain the temperature of all positions in the box to achieve the provisions of Article 5.1. Place the thermometer and temperature control at least 100mm from the box wall. They must be readable from outside the box.
Fourth, the spray device includes the following parts:
1. Spray air source: compressed, de-oiled, and purified air. It goes into a saturated tower with distilled water. The water is a few degrees warmer than the box, and it will wet the air. The clean wetting of the air source is through the pressure control valve. It must be in the range of 70 to 170 kPa (0.7 to 1.7 kgf/cm).
2. Spray chamber: It consists of sprayer, brine tank and baffle plate. Users can decide to use one or more sprayers based on the size of the test area. The baffle can prevent the salt spray from shooting directly on the specimen. The placement of the nozzles and baffles affects the salt spray and its distribution.
3. The salt water storage tank must have a specific device to regulate the level of salt water in the spray room. Note: Adjust the spray pressure, water temperature, and baffle position. This will ensure the box salt spray settlement and the sodium chloride in the liquid reach 5.2.
Fifth, salt spray collector.
The diameter of a 250px funnel inserted it into a container with a 2000px collection area. box at least 2 collectors, one near the nozzle, one away from the nozzle. Only collect salt spray, not from the specimen or other parts of the liquid drops.
Sixth. If you have made the salt spray box different from the test solution, you must fully clean it before using.
Specimen
First, base the type, number, shape, and size of the specimens on the requirements of the test coverings or product standards. If there is no standard, the parties concerned may decide by consulting with each other.
Second, the test specimen must be fully cleaned before the test, cleaning methods depending on the specimen surface conditions and the nature of the dirt, can not use abrasives and solvents that will erode the surface of the specimen. After cleaning the specimen, avoid staining.
Third, cutting the specimen from the workpiece should not damage the covering layer near the cutting area. Unless otherwise specified, you must protect the cutting area with a suitable covering such as paint, paraffin, or bonding tape.
Specimen Placement
First, place the specimen in the salt spray box with the test surface facing up to allow the salt spray to settle freely on it, ensuring that the test surface does not directly receive the spray of salt.
Second, placing the specimen at the right angle is important. Flat plate specimen test surface and vertical direction into 15 ° ~ 30 °, and as far as possible into 20 °. Specimens with irregular surfaces (such as the entire workpiece) should also be as close as possible to the above provisions.
Third, the specimens shall not touch the box and cannot touch each other. The distance between the specimens should not affect the free fall of salt spray on the test surface, the droplets on the specimen shall not fall on other specimens.
Fourth, the specimen holder with glass, plastic and other materials. Suspension of the specimen material, can not use metal, shall use man-made fibres, cotton fibres or other insulating materials.
Test conditions
Salt spray settling speed, after 24h spray, each collector collected by the solution, in terms of 2000px should be 1 ~ 2mL / h, containing sodium chloride concentration of 50 ± 10g / L, PH value of 6.5 ~ 7.2.
Test cycle
The parties concerned shall determine the duration of the test according to the requirements of the test cover or product standard; if there is no standard, they can decide through consultation. The recommended test cycle is: 2, 4, 6, 8,, 24, 48, 72, 96, 144, 168, 240, 480, 720h, 1000h.
ii. Do not interrupt the spraying during the specified test cycle, and only open the salt spray chamber when observing the specimen for a short period of time.
III. If the time when corrosion starts to appear determines the end point of the test, researchers must check the specimens frequently. Therefore, we cannot test these specimens with specimens that have a predetermined test cycle.
IV. During the scheduled test cycle, you can check according to cycle (a), but you should open the box and check the specimen quickly without damaging the test surface.
Cleaning of specimens after the test
At the end of the test, remove the specimen to reduce the shedding of corrosion products. Place the specimen in the room to dry naturally for 0.5 ~ 1h before cleaning. Then, clean it gently with clean flowing water not higher than 40 ℃ to remove the residual salt spray solution on the surface. Finally, dry it immediately with a hair dryer.
Evaluation of test results
To meet different test purposes, researchers can use a variety of evaluation criteria for test results, such as weight change, microscopic observation, and mechanical properties. The covered layer or the product standard should typically propose the evaluation criteria for the test results. For routine documentation in general tests, you only need to consider the following aspects.
a. Appearance after the test;
b. Appearance after removal of corrosion products;
c. Distribution and number of corrosion defects such as pitting, cracks, bubbles, etc.
Please assess the above three aspects using the method specified in ‘Rating of metal coverings on plated specimens after corrosion test of the substrate as cathodic coverings’.
d. The time when corrosion begins to appear.
Test report
i. The test report shall state the evaluation criteria used and the test results obtained. If necessary, there shall be results for each specimen, average results for each group of parallel specimens, or photographs of the specimens.
II.The test report must include information on the test method, which may vary according to the purpose of the test and its requirements. It generally includes the following:
a. A description of the cover or product under test;
b. Shape and size of the specimen, specimen area and surface condition;
c. The preparation of the specimen, including the discipline of cleaning and methods of protection of the edges or other special parts of the specimen prior to the test;
d. Known characteristics of the covering and a description of the surface treatment;
e. Number of specimens;
f. The procedure describes how to remove corrosion products from the specimen after the test and shows the resulting weight loss when weight change is a criterion for evaluation.
g. The way to place the specimen
h. Test temperature;
i. Test period;
The purpose of checking the accuracy of the test conditions, the nature of the reference specimens specially placed in the salt spray chamber and the results obtained.
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