The friction state of sliding bearing is mainly friction between the bearing and the neck. According to the lubrication between the friction sub -surface, the friction state is divided into the following.
1. Dry friction state
Slip the liquid friction. The two relative movement surfaces are directly contacting, and the friction of any lubricant is not added as dry friction (Figure 16.1, A). Drymore will be accompanied by a large amount of friction loss and severe wear. In the sliding bearings, it will cause severe temperature rise and even burn the bearing tile. Therefore, dry friction is not allowed in sliding bearing.
Features: There is no lubricant on the surface of the friction, the power loss is severe, the wear is intensified, the temperature is elevated, and the axis tile is easily damaged.
Note: This friction should be avoided.
2. Border friction state (non -liquid friction sliding bearing)
The thickness of the boundary oil film is usually less than 1 micron, which is not enough to separate the two metal surfaces. When the two metal surfaces move each other, the micro -convex body on the metal surface will still rub each other. This friction is called boundary friction. The friction law when the boundary friction is basically the same as the dry friction, but the friction coefficient is significantly reduced, F≈0.1 ~ 0.3. Although border friction cannot completely avoid wear on the metal surface, it can greatly reduce wear.
Features: There are lubricating oil on the surface of the friction, and a thin layer of boundary oil film is formed on the metal surface. But the peak line is still in direct contact.
Note: Most sliding bearings use this friction state.
3. Line friction state (liquid friction sliding bearing)
When there is sufficient lubricating oil between the two friction surfaces, the thickness of the formation of the oil membrane is enough to separate the micro -convex bodies on the two surfaces, and only the friction between the molecules inside the fluid during exercise is called liquid. Friction, at this time, the formed oil film can withstand a pressure oil film with a certain size load, preventing the direct contact of the two friction surfaces, so the friction coefficient is extremely small (F≈0.001 ~ 0.01), which significantly reduces friction and wear.
Features: The two friction surfaces are completely separated by lubricating oil, forming a certain thickness of pressure oil membrane. This friction state is friction between lubricating oil molecules, and the friction coefficient is very small.
Note: Long -term high -speed rotating machines, bearings use this friction state.
4. Mixed friction
In actual use, more friction state is in the mixed state of dry friction, border friction and fluid friction, called mixed friction (or incomplete fluid friction).