Method of Salt Spray Fog Test for Surface Finishing

The method of salt spray fog test is a commonly used technique for evaluating the corrosion resistance of surface finishes on metallic materials. This test involves exposing the surface finish to a highly corrosive salt spray fog for a period of time and then evaluating the degree of corrosion that has occurred. The salt spray fog creates a corrosive environment that accelerates the natural corrosion process in metallic materials.

This salt spray fog test is widely used in industries such as automotive, aerospace, and electronics to assess the durability and quality of surface finishes. The salt spray fog test is an important tool for ensuring that surface finishes can withstand harsh environmental conditions and continue to perform well over time.

1. Scope : This method of salt spray fog test for surface finishing standard provides for various metal substrates in the electroplating, the organic or inorganic coating of the surface treatment after the other with the touch of salt spray resistance test method.

2. Test Method: This method is to use the salt spray test machine will be sodium chloride solution to be sprayed mist of the plating is coated on a corrosion test method. The main test conditions as shown in below table. Hope these Excel files will make you easier understand the salt spray fog test.

3. Preparation of test solution: dissolving reagent grade sodium chloride in distilled water (or total dissolved solids is less than 200 ppm below the water), to deploy into a concentration of 5 ± 1% of the test solution. This test liquid spray at 35 ℃, its collection of liquid PH value should be 6.5 ~ 7.3. And spray ago, this experiment does not contain liquid state of floating objects.

●	Sodium chloride can not contain copper-nickel impurities, solid within the sodium iodide content of less than 0.1%. Because the impurity may contain corrosion inhibitors, so the total content of impurities to be less than 0.3%.
●	In 33 ~ 35 ℃ measured ratio, test liquid of proportion of should be 1.0258 ~ 1.0402, at 25 ℃ measured the proportion compared with was 1.0292 ~ 1.0443. This experiment the concentration of liquid can also be starting a silver nitrate titration or other methods calibration.
●	Test solution required to test drug class dilute solution of hydrochloric acid or sodium hydroxide to adjust pH value, and to pH measuring instrument, or other reliable method, The preparation of test solution water containing carbon dioxide, carbon dioxide solubility in water with Temperature changes affect the solution pH, will have to be carefully controlled pH value, pH value according to the following below any method adjustments:
●	① Room temperature preparation of test fluid, at 35 ℃ spray, because temperature raising part of the carbon dioxide would be escaped to higher solution pH. Therefore, the preparation of test solution at room temperature while pH value should be adjusted to within 6.5, we can make the collection of solution pH value between 6.5 ~ 7.2.
●	② pH value is adjusted before the test fluid prior to boiling and then cooling to 35 ℃, or maintained at 35 ℃ temperature for 48 hours. The adjusted pH, spray at 35 ℃, it will not produce much change.
●	③ first water heated to above 35 ℃ to remove dissolved carbon dioxide, while the later modulation test and adjust the pH value of liquid, so when you spray at 35 ℃, the adjustment of pH, does not produce much change.
●	In order to avoid the spray nozzle blocking, filtering or the test fluid to be injected carefully tilting a bucket of salt, or in the front spray suction tubes fitted with glass screen filter to filter.

4. Equipment: The test equipment required for spray nozzle, a bucket of salt, test piece bracket, spray liquid collection containers, laboratory, saline supply pail, pressure pail, the supply of compressed air equipment needs of the pipeline should be inert materials, can not spray corrosion and impact on the test or their own corrosion.

4.1 Spray nozzle can’t directly spray the test sample, spray room at the top to gather the test solution should not drip on sample chip.

4.2 Test-piece drops of test solution should not flow back into a bucket of salt, and used for testing.

4.3 Compressed air can not contain grease and dust, so must have clean air devices. Air pressure should be kept at 1.00 ± 0.01kgf/cm2, because the compressed air in the expansion, there are endothermic phenomenon.

4.4 The horizontal area of spray collected device is an area of 80cm2, a diameter of about 10 cm, placed near the test piece (close the nozzle of the recently and the furthest two places).

4.5 The spray volumes for the whole test time to count, taking containers should be collected on average from 1.0 to 2.0ml of the aqueous salt solutions per hour. Spray liquid should be collected at least 16 hours, with its average amount of table does spray volume.

4.6 In testing bucket of salt, the sodium chloride concentration should be maintained 40 ~ 60g /L

4.7 The temperature of the pressure barrel should be kept at 47 ± 1 ℃, the temperature of salt bucket should be kept at 35 ± 1 ℃.
 
4.8 Test room relative humidity should be kept at more than 85%, higher relative humidity requirement is met by the sale and purchase.

5.Specimen:	To Take Place: The specimen can be taken from the products of the major surface or the products themselves as a specimen. However, if the product can not be tested or the determination may be mutually agreed between the parties concerned to test pieces instead. The test piece must be able to represent the products are.
Samples Size:	Test piece standard size of 150 × 70mm, or 100 × 65mm.
Number :	The number of samples from the sale and purchase agreement of the parties.
Test Pre-treatment :	Cleaning the sample according to the nature and extent of coating to be done properly cleaned, can not be so abrasive and corrosive or inhibited with a solvent cleaning, and cleaning methods shall not damage the surface. As for the stainless steel samples follows the sale and purchase agreement between by the use of nitric acid cleaning and passivation. After the sample after clean (by removing water-based test), with a clean cloth or absorb water to dry, or use the oil-free air drying. a last resort, you can use magnesium oxide paste. This paste material is 10 g reagent grade magnesium oxide by adding 100mL of distilled water.
Test Pre-treatment :	Unless other prescribe, in the specimen notch and peg color caused by exposing part of the substrate, or for identifying marks caused by defects at plating in the test should be covered with the right of the protective layer. Such as a hard wax (ceresin wax), vinyl tape and other insulation.
Test Pre-treatment :	Hand pattern will cause serious pollution to bad test results, the specimen was clean without any hand pattern of pollution.

6. Specimen of the placement: in testing, the location of the indoor samples to comply with the following conditions:

6.1 The main surface of the specimen with the plumb line into the 15 degrees to 30 degrees of tilt, but also from the top overlooking the test chamber and the spray should be parallel to the main flow direction. The direction of the special parts with many major surface, will need to test, it is desirable pieces of the specimen placed, be sure to make each of the major surface can also accept salt spray.

6.2 The arrangement of the specimen should be made free to spray down of all the specimens, the spray should not impede the free fall.

6.3 The contact between the specimen is not, nor can come into contact with metallic conductor or a capillarity effect of the substances, and beside other support objects.

6.4 Do not salt water solution from a trickle to other sample.

6.5 Sample identification mark or hole assembly should be under sample below.

7. Action: Temperature of the test chamber and buckets of salt adjusted to 35 degrees Celsius, temperature of pressure pail was 47 degrees Celsius, spray pressure maintained at 1.00 ± 0.01kgf/cm2, they can start spraying.

7.1 Test time: for from the beginning to the end of the continuous spray time. Test time for the plating layer of a key quality data, the time required by the buyer and seller agreements.

7.2 After the test treatment: spray test is completed, open the lab cover without solution drip and carefully take out the specimen shall not damage the major surface, rapidly use the below 38 ℃ of water wash away the adhesion of the particles of salt, with hair brush or sponge to remove corrosion products, and immediately with a clean compressed air to dry.

●	8. Records: Buyers and sellers unless other agreed, the record of this test should have the following:
●	8.1 When preparing salt water, using salt and water quality.
●	8.2 Test temperature records.
●	8.3 The device of spray collector, a day shall be as the following records:
●	8.3.1 Spray volume
●	8.3.2 Collect solution at room temperature for the proportion or concentration.
●	8.3.3 Collection solution PH value
●	8.4 Sample types, shapes, size and number.
●	8.5 Sample pre-treatment cleaning and processing cleaning methods.
●	8.6 Sample in the test room placement method.
●	8.7 In accordance with section 5.4.2 of the coating method used.
●	8.8 Spray time.
●	8.9 Test time, if interrupted, shall record the reasons for their break and time.
●	8.10 All the results of other tests.

9. Judge Method for Salt Spray Fog Test: To judge the surface corrosion, such as blistering, cracking, etc. using a standard chart is difficult to determine who can be used to determine the magnifying glass with a ruler or by the method of sale and purchase convention to judge.

The salt spray fog test is a widely used method for evaluating the corrosion resistance of surface finishing on metals and other materials. In this test, a salt solution is atomized into a sealed testing chamber, creating a continuous fog of saltwater mist. The test samples are then placed in the chamber and exposed to this saltwater mist for a specified period, which can range from a few hours to several hundred hours depending on the desired level of corrosion resistance.

After the exposure period, the samples are inspected for signs of corrosion, such as rust or discoloration, which are then compared to a standard chart to determine the level of corrosion resistance. The salt spray fog test is an important quality control measure for surface finishing manufacturers, as it allows them to evaluate the durability and lifespan of their products under harsh environmental conditions and make necessary improvements to the manufacturing process｜Salt Spray Test