General structure of sealing material

The friction and wear of sealing materials are related to the cohesive work Wc and adhesion work Wab of the material. The work done on the solid column with a cross-section of 1cm2 when it is divided into two sections without changing the cross-sectional area is called cohesive work Wc, ​​which characterizes the attraction degree of the same substance. , that is, the specific surface energy after breaking is doubled. Suppose that the interface energy of the contact part of the upper-stage substance a and the lower-stage substance b of the column is . The friction surface is often in contact with the surrounding medium, gas and lubricant. Molecules on the solid surface have the ability to attract other molecules due to the unbalanced attraction of surrounding molecules or atoms, which creates a force field on the surface that points to space. When the solid surface molecules adsorb some surrounding media, the gravitational attraction of the internal molecules to the surface molecules is partially offset, the surface energy also decreases, and part of the heat is released. The heat released is called the heat of adsorption. The adsorption equilibrium of the surrounding medium molecules on the solid surface is a dynamic equilibrium. On the one hand, the solid surface attracts the molecules of the surrounding medium; on the other hand, the molecules adsorbed on the solid surface may be separated from the solid surface due to the continuous thermal motion. This process is called desorption. The adsorption reaches equilibrium when the rates of adsorption and desorption are equal. The size of the adsorption heat reflects the firmness of the adsorption of the surrounding medium molecules on the solid surface. The greater the heat of adsorption of the lubricant on the metal surface, the stronger the adsorption. The adsorption of sealing materials may be physical or chemical, which are called physical adsorption and chemical adsorption respectively. Physical adsorption is formed by the attraction between molecules. This adsorption does not change the molecular or electron distribution of the adsorption layer, its adsorption energy is weak, and it is very sensitive to temperature, and heat can desorb the molecules. This type of adsorption is generally non-selective, with any solid physically adsorbing any liquid. The adsorption speed is large and easy to desorb, and the adsorption and desorption are reversible. Chemisorption is selective. This adsorption relies on chemical bonds to adsorb surrounding molecules on the surface to form new compounds. Since the action range of chemical bond force does not exceed (2~3)×10-10m, which is equivalent to the thickness of one molecule, so chemical adsorption is the adsorption of monomolecular layers. The chemical adsorption membrane can be desorbed when heated by external energy. 4. Solid Surface Structure The friction and wear of metals are related to their surface structure. The surface of the sealing material refers to a pure ideal surface, such as the pure surface exposed during the machining process. If it is not treated, it will soon be polluted by the surrounding medium and form various films. Within the metal surface, layers of different properties are also formed as a result of the machining process. The properties of the various physical and chemical films and layers in the outer and inner surface layers are different. Below the surface is a processing deformation layer, including a Beilbylayer with a deformation layer. The Pythagorean layer is an amorphous layer. It is formed during the polishing process, which not only deforms the metal, but also produces oxidized molecules. It is about 70~100 thick (1=10-10m; 104=1μm). 5. The general structure of the metal surface layer varies according to the processing method, and the thickness of the deformation layer is also different. The grains will be refined. The surface grain refinement layer and the change layer of the material structure are as deep as tens of micrometers. Roughing extends this layer deeper, even several hundred microns. The deformed layer has higher hardness due to the effect of hardening. The Pythagorean layer is a thin layer formed due to the melting and plastic flow of the material during surface processing. Depending on the environment, there are three thin film compositions above the surface. The thinnest is a chemical adsorption membrane. The second is the monolayer lubricating film (ordinary fouling film), which is the most basic boundary layer. The thickest oxide film, which is composed of complex oxides, is closer to air, the higher the ratio of oxygen to iron (Fe-FeO-Fe3O4-Fe2O3). The properties of the oxide film are quite different from the properties of the material of the part itself. During the friction process, the structure and properties of the surface film, as well as the law of rupture and regeneration, have a great influence on the friction performance. If friction occurs mainly in the film layer, and the presence of the sealing material makes the metal friction surface less likely to stick, the coefficient of friction will be reduced, and wear may be reduced. Company website: https://www.orksealing.com/