Lubrication plays an important role in the normal operation of mechanical equipment.  
     
(1) Reduce friction coefficient
Adding lubricant between two opposing friction surfaces to form a lubricating oil film as an anti friction layer can reduce the friction coefficient, feed the frictional resistance, and reduce power consumption. For example, under good liquid friction conditions, its friction coefficient can be as low as 0.001 or even lower. The frictional resistance at this time is mainly the low shear resistance caused by the mutual sliding between molecules inside the liquid lubricating film.  
     
(2) Reduce wear and tear
Lubricants can support wear caused by hard particle wear, surface corrosion, biting and tearing between metal surfaces between friction surfaces. Therefore, by supplying sufficient lubricant between the friction surfaces, good lubrication conditions can be formed, avoiding damage to the oil film, maintaining the accuracy of part fitting, and greatly feeding wear.  
     
(3) Reduce temperature
Lubricants can reduce the coefficient of friction and feed the generation of frictional heat. We know that the work done by a moving machine to overcome friction is all converted into heat, with some spreading outward from the body and others continuously raising the temperature of the machine. The centralized circulation lubrication system using liquid lubricants can remove the heat generated by friction, achieve accurate cooling, and control the mechanical operation within the required temperature range.  
     
(4) Prevent corrosion and protect metal surfaces
Mechanical surfaces inevitably come into contact with surrounding media such as air, moisture, water vapor, corrosive gases, and liquids, causing rust, corrosion, and damage to the metal surfaces of the machinery. Especially in high-temperature workshops of metallurgical factories and chemical plants, corrosion and wear are more severe.  
     
(5) Cleaning and rinsing function
The wear particles or foreign media generated by the friction pair during motion will accelerate the friction surface and wear. By utilizing the fluidity of liquid lubricants, abrasive particles between the friction surfaces can be carried away, thereby reducing abrasive wear. In the pressure circulation system, the flushing effect is more significant. Process lubricants are used in cold rolling, hot rolling, cutting, grinding, drawing and other processing techniques. In addition to cooling and cooling effects, they also have a good flushing effect to prevent surface impurities from scratching, resulting in better quality and surface roughness of the processed products (steel). For example, suspension dispersant additives are added to the lubricating oil used in the cylinder of the internal combustion engine to wash the gel and carbon deposits generated in the oil from the cylinder wall, disperse them into small particles and suspend them in the oil, filter them together with the circulating oil filter, to keep the oil clean, reduce the wear of the cylinder, and extend the oil change period.  
     
(6) Sealing function
The cylinder and piston of steam engines, compressors, internal combustion engines, etc., lubricating oil not only plays a role in lubricating and reducing wear, but also enhances the sealing effect, preventing air leakage during operation and improving work efficiency.  
Lubricating grease has a special effect on forming a seal, which can prevent water or other dust and impurities from entering the friction pair. For example, using oil immersed gaskets coated with lubricating grease not only provides good lubrication for the sealing of the water pump shaft head, but also prevents leakage and dust impurities from entering the pump body, thus achieving a good sealing effect.  
In addition, lubricating oil has the effect of reducing vibration and noise.