Snow and black ice sometimes turn driving into a slippery experience in winter. Although spreading salt makes the roads slightly safer, it is harmful to the environment as well as to the metal parts of a car. The salt attacks the metal on the bodywork, leading to blisters in the paintwork and ultimately to peeling and corrosion. The resistance of a material to corrosion can be tested in standardised test processes, for example, in a salt spray chamber.
Salt spray tests are common in the automotive industry and the most frequently used method to test paints and other coatings. Components in automation technology, too, have to pass the test. In technology terms, corrosion is seen as an electrochemical reaction of a metal with its surroundings. This reaction may impair the material’s properties and the function of the component made from that material.
Almost every material rusts eventually. The best-known type of corrosion is red rust. This forms when iron or steel oxidises when exposed to damp surroundings. White rust is the corrosion product of zinc.
Festo tests the surfaces of components and new types of coating in the salt spray chamber. The parts are hung on thin hooks and are sprayed with a salt mist, often for days on end. This is much saltier than sea air and can thus reproduce exposure that is similar to years of use in damp, salty surroundings in a very short space of time. Material experts then evaluate the corrosion.
A wide range of components and parts are subjected to the salt spray test.
As Festo components are exposed to very harsh or mild environmental conditions depending on their application, there are different corrosion resistance classes. For example, parts used in water treatment plants must meet the standards of corrosion resistance class 3 (the second highest). That means that they withstand five days in the salt spray chamber without corrosion occurring. In order to attain corrosion resistance class 4, components even have to last ten days in the salt mist without corrosion.
There are various ways of reliably protecting components: metallic coatings – made of zinc, for example – can protect steel parts. Inorganic coatings, such as wet paint and powder paint, are another example.
The salt spray test shows the differences in the quality of the coatings: the parts were all in the salt spray chamber for the same length of time, have the same coating, but come from different suppliers.