Introduction of the Salt Spray Test
Salt spray test is commonly used for assessing the corrosion resistance properties of the metal. Usually, the endurance of coating on the surface is under test. As this testing process is standardised by ASTM, it is preferred by all the industries manufacturing metal products. Any material which is prone to corrosion is put under test with this process. This test is now becoming an integral part of the metal industry.
This test is performed in a salt spray chamber where a salt laden fog is injected into the highly insulated chamber. The chamber is designed in such a way so that there is no loss of fog or heat. NaCl solution is used to create the salty fog. This environment is highly corrosive and thus allows the operator to assess the behaviour of test sample under such conditions. The duration depends on the intended working conditions and properties of the surface coating. If a manufacturer is claiming to produce a highly resistant product, the duration will be long.
Standard Operating Procedure
In a zip manufacturing unit, this machine plays a crucial role in assessing the life of the coating on the zip. Some zips are available in metallic coatings, very similar to the colour of metal. On the other hand, some zips are simply painted. Corrosion prevents the smooth zipping operation.
According to the testing methods, the test specimen is kept an angle of 20°. In chambers offered by Presto, there are slits at this particular angle to hold the sample in perfect conditions. An atomiser is used to create the salty fog in combination with water. There are water reservoir and NaCl solution tank. Once the sample is placed inside the chamber and test is started, the operator cannot open the chamber until test run is complete. Usually, the corrosion resistance test of zips is carried out for 24 hours. However, the duration can be extended if the applications are harsh.
Precautions to Be Taken
The test sample should not be placed very close to the walls, as the temperature is quite high near the walls due to the presence of heaters. The sample is supposed to be kept in the centre. If multiple samples are being tested, even then there has to the minimum distance.
A close check on water level is to be kept. If the water level goes down beyond the defined limit, it could damage the salt spray chamber due to overheating.
The chamber is to be opened only after air purging.