Explanation of damp and heat test of the constant temperature and humidity chamber

1. The damp and heat test of the constant temperature and humidity chamber is to place a sample or object coated with a paint film in a constant temperature and humidity chamber with controlled temperature and humidity. After a certain period of time, observe changes such as blistering, corrosion, and decrease in adhesion, and evaluate the coating film. A test of the ability to resist wet and hot water vapor (sometimes including condensation). Assess the environmental adaptability and corrosion resistance of the coating to the humid tropical climate.

2. In the damp and heat test of a constant temperature and humidity chamber, the water resistance and water vapor permeability of the coating fail faster than the general normal temperature immersion test. The corrosion caused by the damp heat test is not as severe as the salt spray test.

3. The difference between constant temperature and humidity chamber damp heat test and salt spray test:

(1) The main difference between the damp heat test and the salt spray test is that the droplets of the damp heat test have no salt but distilled water, although the salt droplets have a strong corrosive effect due to their high conductivity and rich chloride ions;

(2) But in terms of osmotic pressure, the activity of distilled water is high, the coating is a semi-permeable membrane, and the ability of distilled water to penetrate the paint film is stronger than that of salt solution. Moisture penetrates into the paint film and accumulates between the two paint films, which will reduce the adhesion between the layers and cause blisters. Then it will go further to reach the gap between the paint film and the bottom plate, reducing the adhesion, causing the paint film to bubble, and at the same time, the water contacts the metal bottom plate, causing electrochemical corrosion;

(3) Absorbing water in the paint film will cause the paint film to expand and produce internal stress, reduce adhesion and foam. The water absorption rate of the paint film is higher in distilled water than in salt water. As far as the destructive power of the paint film is concerned, the damp heat test It is very demanding.