Cast iron and carbon steel valves are usually sprayed with different varieties and thicknesses of paint to obtain a good protective effect. These valves are generally used for water, oil, steam, etc., which are in direct contact with metal surfaces and are prone to serious corrosion under the action of oxygen in the air.
Generally, the paint on the valve surface can protect the valve metal material in the following three aspects:
1. Shielding
After the metal surface is coated with paint, the metal surface is relatively isolated from the environment. This protective effect can be called shielding effect. But a thin layer of paint cannot provide absolute shielding. Because polymers are breathable to a certain extent, they can pass freely when the coating is thin. It can be seen that for many coatings the value is greater than the uncoated steel surface. In order to improve the impermeability of the coating, the anti-corrosion coating should use a film-forming substance with low air permeability and a solid filler with a large shielding property, and at the same time, the number of coating layers should be increased so that the coating reaches a certain thickness and is dense and non-porous.
2. Corrosion inhibition
By reacting the internal components of the coating with the metal, the metal surface is passivated or a protective substance is formed to improve the protective effect of the coating. Pay attention to the composition of the paint to avoid serious adverse effects.
3. Electrochemical protection
Electrochemical corrosion under the film occurs when the dielectric permeable coating comes into contact with the metal surface. Use metals with higher activity than iron as fillers in coatings, such as zinc. It will play the protective role of the sacrificial anode, and the corrosion products of zinc are basic zinc chloride and zinc carbonate, which will fill the gaps of the membrane and make the membrane tight, which greatly reduces the corrosion and prolongs the service life of the valve.
Post time: Nov-07-2022