Determination of corrosion resistance of film films

Protecting metal with a paint film is the most common method of preventing corrosion. Can be used as basic protective material for other substances such as wood.

The paint film is also affected by a variety of corrosive substances during use due to the anti-corrosion utensils. Therefore, after knowing the appropriate conditions for these utensils, you can choose a suitable one that is very stable under such conditions. coating film. The coating film is always subject to the adverse effects of certain corrosive substances during use (under the conditions of water, atmosphere, etc.), and the purpose of the corrosion contact test is to determine the protective performance of the paint coating film against these effects. When conducting this kind of test, sometimes try to strengthen some factors that can cause corrosion under the service conditions of the utensils, but this method of drastically changing the corrosion contact process is generally not considered correct. For example, Akimov once pointed out that the use of excessively rapid corrosion test methods "is often due to a completely incorrect phenomenon: corrosion resistance is only the performance of the material itself, and the degree to which the medium changes the corrosion resistance is the same for all substances. to the same extent". Therefore, the rapid test can only be adopted under the condition that "the characteristics of the corrosion process of the substance in the medium are not changed .

These provisions are also general for the tests of paint films, since the action of intensifying corrosive agents can give different results when using various types of films; this may also lead to the corrosion resistance of these films under the conditions of use. Corrosive incorrect judgment.

According to Akimov's opinion, the important factors affecting the corrosion rate and distribution of metals are: the concentration of hydrogen ions, the concentration of oxidant and oxygen in the solution, the nature of the electrolyte. The temperature and relative humidity (when exposed to atmospheric corrosion). (Related instrument: conductivity meter)

When testing paint coatings on metal, some factors on the ground also have a certain impact on the corrosion resistance of the coating. In order to obtain comparable results, all coating tests must be carried out under the same conditions, that is, with standard size plates or rods made of the same metal (the surface must be treated in the same way). Furthermore, when testing coatings in electrolytic solutions (electrolytes), for example in vaporized steel solutions, it is necessary to observe those conditions which are indispensable to ensure the reliability of the results obtained. (Related instrument: Coating rod)

The conditions are: 1) The edges and corners of the test panel must be carefully protected; 2) There is no exposed area on the surface to be tested; 3) A fixed coating film thickness; 4) Between the painted test panel and any other metal no contact. In addition, both sides of the test panel shall be coated with the same (not different) color paint, and only one color paint shall be applied on the board. (Related Instruments: Thickness Gauge)

The method used to display rot is very sloppy. A series of methods (visual inspection method, weighing method, microscope inspection method, etc.) can be used for metal corrosion contact test. When carrying out the corrosion resistance test of the paint coating, we will encounter more complicated situations than the corresponding test on the simple metal.

Since the corrosive solution does not come into direct contact with the metal, the paint film must be destroyed before the corrosion process begins on the metal so that the corrosive solution can penetrate into the metal. Therefore, when measuring the degree of metal corrosion contact during the test, it is necessary to remove the coating film first, and then measure the degree of metal corrosion according to the weight loss or increase. The state of corrosion is mostly judged by visual observation, and at the same time, the degree of damage to the paint film and the degree of corrosion diffusion are measured, and they are expressed as a percentage of the entire paint film area. After testing and removal of the coating, when the degree of metal corrosion is not significant, the tested surface is often examined under a microscope or by other methods used in the inspection of metal corrosion.

The storage time of the coating film before testing the corrosion resistance is of great significance. Yakubovich and Barker found that each color paint has its inherent storage time, during which its corrosion resistance is greatest a. In experiments with various oil-based paints, it was found that most color paints The protective performance of the paint can be significantly increased by storing it for 5 to 10 days before the start of the test. When the storage time of the samples increased to 45 days, the protective properties of most materials began to increase, and then the protective properties gradually decreased due to the aging of the paint film.

When the coating film is two or more layers, each subsequent layer must be finished after the previous layer is actually dried; after the last layer is applied, the coating film should be stored for 5 days. Under production conditions, the artificial drying method can greatly shorten the storage time of the coating film before the test. For example, when testing nitro varnish and nitro varnish and perchlorethylene varnish and enamel, drying the coating film at 60°C (relevant instrument: oven) can shorten the drying time to 2 hours (instead of 24 hours). hours of natural drying). (Related instrument: drying time Tester)

However, it should be remembered that for each individual case, the most suitable conditions - temperature and drying time - should be found so that the test results of the dried coating films can be compared with those obtained by testing these coating films after drying at room temperature. unanimous.