A salty shower

Article of 24 November 2017 

Salzsprühkammer

Snow and black ice sometimes turn driving into a slippery experience in winter. Although spreading salt makes the roads somewhat safer, it is harmful to the environment as well as to the metal parts on a car. The salt attacks the metal on the bodywork, leads to blisters in the paint and ultimately to peeling and corrosion. How resistant a material is 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 are the most frequently used way of testing paints and other coatings. But components in automation technology also have to pass the test. In the field of technology, corrosion is seen as a mostly electrochemical reaction of a metallic material with its surroundings. This reaction may impair the material’s properties and the function of the component produced from it.

Not all rust is the same

Almost every material rusts eventually. The best-known product of corrosion is red rust. This is formed from iron or steel by means of oxidation in damp surroundings. White rust is the product of corrosion from zinc.

Festo tests new coatings in the salt spray chamber

Festo tests the surfaces of components and new types of coating in the salt spray chamber among others. There, the parts are suspended from thin hooks and are often sprayed for several days with a salt mist. This is much saltier than sea air and is thus able to reproduce exposure that corresponds 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.
A wide range of components and parts are subjected to the salt spray test.

Different corrosion resistance classes

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 sewage treatment plants must meet the standards of corrosion resistance class 3 (the second highest). That means they last five days in the salt spray chamber without corrosion occurring. In order to be awarded corrosion resistance class 4, components even have to last ten days in the salt mist without corrosion.

There are various ways of reliably protecting the component: metallic coatings – made of zinc, for example – can protect steel parts. Inorganic coatings, such as wet paint and powder paint, are a further example.

The salt spray test shows the differences in the quality of 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.
The salt spray test shows the differences in the quality of 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.