一、Lubrication definition :

Lubrication is an important part of tribology. Technical measures to improve the friction state of friction pairs to reduce friction resistance and wear. The purpose of lubrication is usually achieved by lubricant. In addition, lubricant and rust prevention, vibration reduction, sealing, power transmission and other functions. Making full use of modern lubrication technology can significantly improve the performance and life of the machine and reduce energy consumption.

二、Lubrication classification :

According to the different lubrication materials between friction pairs, lubrication can be divided into fluid (liquid, gas) lubrication and solid lubrication. According to the different friction states between the friction pair, lubrication is divided into fluid lubrication and boundary lubrication. The lubrication state between fluid lubrication and boundary lubrication is called mixed lubrication, or partial elastic hydrodynamic lubrication.

三、Role of lubrication 

1. Reduce friction coefficient

Adding lubricant between two relative friction surfaces to form a lubricating oil film anti-friction layer can reduce the friction coefficient, feed friction resistance, reduce power consumption. For example, under good liquid friction conditions, the friction coefficient can be as low as 0.001 or even lower. At this time, the friction resistance is mainly the low shear resistance of mutual sliding between molecules in the liquid lubrication film.

2. Reduce wear

Between the friction surfaces, the lubricant can support the wear caused by abrasive wear, surface rust, bite welding and tear between metal surfaces. Therefore, the supply of sufficient lubricant between the friction surface, can form good lubrication conditions, avoid the destruction of the oil film, maintain the precision of parts, so as to greatly reduce wear.

3. Lower the temperature

The lubricant can reduce the friction coefficient and reduce the friction heat. We know that all the work done by the machinery in motion, in overcoming friction, is converted into heat, some of which is diffused outward by the body, and some of which is continually raising the temperature of the machinery. The centralized circulation lubrication system using liquid lubricant can take away the heat generated by friction, play a cooling precision, so that the machine is controlled in the required temperature range.

4. Prevent corrosion and protect metal surface

Mechanical surface, inevitably to contact with the surrounding medium (such as air, moisture, water vapor, corrosive gas and liquid, etc.) so that the metal surface of machinery rust, corrosion and damage. In particular, corrosion wear is more serious in high temperature workshops and chemical plants.

5. Cleaning and flushing action

Friction pair in the movement of wear particles or foreign media, will accelerate the friction surface and wear. Using the fluidity of the liquid lubricant, the abrasive particles can be removed from the friction surface, thus reducing the abrasive wear. In the pressure circulation system, the flushing effect is more significant. In cold rolling, hot rolling and cutting, grinding, drawing and other processing technology using process lubricant, in addition to cooling effect, there is a good flushing effect, prevent surface fill solid impurities scratch, so that the surface of finished products (steel) has better quality and surface roughness. For example, suspension dispersion additives are added to the lubricating oil used in the cylinder of the internal combustion engine, so that the gel and carbon generated in the oil are washed down from the cylinder wall and dispersed into small particles suspended in the oil, which are removed with the circulating oil filter to keep the oil clean, reduce the wear of the cylinder and extend the oil change cycle.

6. Sealing action

The cylinder and piston of steam engine, compressor, internal combustion engine, etc., lubricating oil can not only play the role of lubrication and wear reduction, but also enhance the effect of sealing, so that there is no air leakage in operation, improve the work efficiency.

Grease has a special role in sealing, which can prevent water or other dust and impurities from dipping into the friction pair. For example, the oil immersed dish root coated with grease has good lubrication effect on the seal of the pump shaft head, and can prevent leakage and dust impurities from immersing into the pump body and play a good sealing effect.

In addition, lubricating oil has the effect of reducing vibration and noise.

四、Tehhical specifications of lubricating oil 

1. Viscosity index: The degree of oil viscosity change with temperature, and the relative value of the degree of standard oil viscosity change is called viscosity index. The higher the value is, the less the temperature affects it.

2. Viscosity: When the liquid moves under the action of external force, the resistance between the molecules is called viscosity.

3. flash point: oil under the specified conditions, heating to its steam and the surrounding air mixture, when the contact flame flash fire when the lowest temperature.

4. pour point: refers to the cooling of solid oil, inclined to place heating to the oil begins to move the lowest temperature.