The friction pair is operated in full film lubrication, which is an ideal condition. However, how to create the conditions to take measures to form and meet the full-film lubrication state is more complex work. People in the long-term production practice continue to explore the principle of lubrication and research, and some more mature, and some are still studying. Now on the common dynamic lubrication, static pressure lubrication, dynamic and static pressure lubrication, boundary lubrication, extreme pressure lubrication, solid lubrication, self-lubricating lubrication principle, for a brief introduction.

1. Dynamic lubrication

Through the rotation of the bearing vice journal to the lubricating oil into the friction surface, due to the viscosity of the oil and oil in the bearing in the wedge gap formed by the hydrodynamic action of oil pressure, that is, the formation of bearing oil film, known as hydrodynamic lubricating. The hydrodynamic lubrication theory is assumed to be the viscosity of the lubricant, that is, the viscosity of the lubricating oil at a certain temperature does not change with the pressure; secondly, it is assumed that the surface of the relative friction movement is rigid, And under the action of oil film pressure, regardless of its elastic deformation. Under the above assumptions, this assumption is close to the actual case for a plain bearing that is generally non-heavy (contact pressure at 15 MPa). However, when the contact pressure between the rolling bearing and the gear surface is increased to 400 to 1500 MPa, the above-described assumed condition is different from the actual situation. At the same time, the deformation of the friction surface can reach several times the thickness of the oil film, and the elastic deformation of the surface of the friction surface and the viscosity of the lubricating oil change with the pressure to study and calculate the law and thickness of the film formation, Oil pressure distribution within the more realistic This kind of lubrication is called elastic fluid dynamic lubrication.

2. Static pressure lubrication

Through a set of high-pressure hydraulic oil supply system, will have a certain pressure of the oil to the throttle damper, forced to the friction surface of the friction surface (such as in the static pressure sliding bearing clearance, the plane static pressure sliding guide Gap, static pressure screw gap). Friction surface has not yet begun to move before it is separated by high-pressure oil, forced the formation of oil film, so as to ensure that the kinetic energy can withstand a certain working load conditions, completely in the liquid lubrication state, this lubrication is called liquid hydrostatic lubrication.

3. Dynamic and static pressure lubrication

With the development of science and technology, in recent years in the industrial production of a new type of dynamic, static pressure lubrication bearings. Liquid dynamic and static pressure bearing fully play the liquid dynamic pressure bearing and hydrostatic bearing both advantages, to overcome the liquid dynamic pressure bearing and hydrostatic bearing the lack of both. The main working principle: When the bearing in the process of starting or braking, the use of static pressure liquid lubrication method, the high-pressure lubricating oil into the bearing bearing area, the shaft to float, to ensure that the liquid lubrication conditions, thus avoiding the start Or friction during the braking process can not form a dynamic oil film and the metal friction surface (journal surface and bearing surface) in direct contact with the friction and wear. When the bearing into the full speed of stable operation, the static pressure oil supply system can be stopped, and with dynamic pressure lubrication oil supply dynamic pressure oil film, can still keep the journal in the bearing liquid lubrication conditions.

This method, in theory, in the bearing sub-start, run, brake, forward and reverse the whole process, completely avoid the semi-liquid lubrication and boundary lubrication, become liquid lubrication. Therefore, the friction coefficient is very low, as long as the oil viscosity to overcome the viscosity of the internal friction between the molecules on the line. In addition, the friction surface is completely separated by static pressure oil film and dynamic pressure oil film, so if the situation is normal, there is almost no wear, which greatly extended the working life of the bearing, saving the kinetic energy consumption.

4. Boundary lubrication (ie, boundary friction)

Boundary lubrication is the critical state from the friction between the lubricant molecules and the internal friction between molecules (ie, liquid lubrication) before the transition to the friction surface. At this time there is a layer of friction on the adsorption of the film, the thickness is usually about 0.1μm, with a certain degree of lubrication. We call this layer of film as the boundary film. The lubricating properties of the boundary film mainly depend on the nature of the friction surface. Depending on the oily additive in the lubricant, the extreme pressure additive is formed on the surface of the boundary film formed by the metal friction surface, but not with the viscosity of the lubricating oil port.

5. Extreme pressure lubrication

Extreme pressure lubrication is a special case of boundary lubrication, that is, friction in the heavy load (or high contact stress), high speed, high temperature conditions, the extreme pressure additives in the oil and metal friction surface reaction to generate a layer Chemical reaction film, the two friction surface separated, and play to reduce the friction coefficient, slow down the wear (or change the metal surface direct contact with the serious wear and tear), to achieve the role of lubrication, known as extreme pressure lubrication.

6. Solid lubrication

In the friction between the surface into the solid powder of the lubricant, the same can also play a good lubrication effect. Between the two friction surface with a solid lubricant, its shear resistance is very small, a little external force, the molecules will produce slip. This turns the outer friction between the two grinding surfaces into the internal friction between the solid lubricant molecules. Solid lubrication has two necessary conditions, first of all, solid lubricant molecules should have a low shear strength, it is easy to produce slip; followed by solid lubricants to have a strong affinity with the friction surface, in the friction process, Always keep a layer of solid lubricant on the rubbing surface, and this layer of solid lubricant does not corrode the friction surface. Generally on the metal surface is mechanical attachment, but also the formation of chemical combination. Many of the solid materials having the above properties are, for example, graphite, molybdenum disulfide, talc and the like.

For non-layered solid lubricants or soft metals, it is mainly because of its low shear force, play a role in lubrication, and then attached to the friction surface to form a lubricating film. For the lubricating mechanism of the solid lubricating film already formed, the lubrication action can be explained approximately by the boundary lubrication mechanism.

7. Self-lubricating

The above mentioned several kinds of lubrication, in the friction movement process, need to add friction between the friction surface. And self-lubricating is to have a lubricating performance of solid lubricant powder mixed with other solid materials and pressed, sintered into the material, or in the porous material immersed in solid lubricants; or solid lubricant directly pressed into the material, as Friction surface. So that the entire friction process, do not need to add lubricant, can still have a good lubrication. Self-lubricating mechanisms include solid lubrication, boundary lubrication, or both.

For example, PTFE presses made of PTFE rings, bearings, bushings, etc. are self-lubricating, so in the process of such parts, it does not need any additional lubricant can also maintain good lubrication.