Vacuum impregnation is a vacuum application process in which the impregnated material is impregnated into other solid materials by negative pressure in order to improve the material properties or meet certain specific requirements. Its application principle is actually the result of the comprehensive action of wetting mechanism, capillary phenomenon and adsorption.
The first is the wetting mechanism. Its essence is the adhesion between liquid molecule and solid molecule, that is, the mutual attraction is greater than the mutual attraction between liquid molecule (also known as cohesion). The primary condition of wetting is to reduce the contact angle (the angle between the liquid surface and the solid surface), and increase the adhesion between the workpiece and the infiltrated material. Therefore, degreasing, decontamination and drying are needed before vacuum impregnation.
The second is capillary phenomenon. The capillary phenomenon refers to the phenomenon that the infiltrating liquid rises in the tubule and the non-infiltrating liquid decreases in the tubule. There will be an expansion trend and infiltration. Generally speaking, the liquid surface is similar to the tensioned rubber film. If the liquid surface is bent, it will flatten. The concave liquid surface will exert tension on the liquid below, and the convex liquid surface will exert pressure on the liquid below. The capillary phenomenon in vacuum impregnation is that the impregnated material is absorbed into the micropore of the material due to the surface tension of the liquid.
Adsorption is that when the interface between impregnated material and micro-porous material is in wetting state, once the distance between the two molecules is less than 0.525 nm, it will have a strong adsorption effect, so that the infiltrated material is filled with micro-pore of the material, and after solidification, it can bond to a solid whole.
Vacuum extraction not only makes the gas in the impregnated material escape and forms voids and channels, which is conducive to the infiltration and diffusion process of impregnated material, but also forms a high concentration of infiltrated material on the surface of impregnated medium in vacuum environment compared with atmospheric pressure impregnation. Combining with the above three application principles, vacuum impregnation can reduce the operation time, reduce the consumption of raw materials and improve the quality effectively.