Writer: Eric Bearing Limited
The lubricant can be firmly adsorbed on the friction surface of the machine parts to form a lubricating film of a certain thickness. It has a strong bonding force with the friction surface, but the friction coefficient between its own molecules is very small. When the friction pairs are separated by the lubricating film, they will not be in direct contact during relative motion, so that the friction between the two friction pairs is transformed into the friction between the lubricant itself, the friction coefficient is greatly reduced, and the friction and wear are reduced. the goal of.
1. Common types of lubricants
(1) Mineral oil: It is refined from petroleum. The main component is hydrocarbons and contains various additives. According to the molecular structure of hydrocarbons, it can be divided into alkanes, cycloalkanes, aromatic hydrocarbons and unsaturated hydrocarbons.
Mineral lubricants are divided into three categories: distillate lubricants, residual lubricants, and blended lubricants.
a. Distillate lubricating oil, with low viscosity and light weight, usually contains less asphalt and gum. Such as high-speed machine oil, steam turbine oil, transformer oil, instrument oil, refrigeration oil, etc.
b. Residual lubricating oil, with high viscosity and heavier quality. Such as aviation oil, steel rolling oil, cylinder oil, gear oil, etc.
c. Blended lubricating oil is a mixture of distillate lubricating oil and residual lubricating oil. Such as gasoline engine oil, diesel engine oil, compressor oil, industrial gear oil, etc.
(2) Synthetic oil (synthetic grease): a lubricating oil with certain characteristic structure and performance made by organic synthesis. Synthetic oils have better performance than natural lubricating oils. When natural lubricating oils cannot meet the existing working conditions, synthetic oils, such as silicone oils, fluorinated esters, silicates, polyphenylene ethers, fluorine, can be used instead. Chlorocarbon compounds, diacetate, phosphate ester, etc.
(3) Water-based lubricating oil: Two immiscible liquids are processed so that one side of the liquid is dispersed and suspended with fine particles (about 0.2-50 microns in diameter) in the other liquid, called emulsified oil or emulsion . Such as water-in-oil or oil-in-water emulsified oil, water-glycol hydraulic oil, etc. Their main functions are flame resistance, cooling, fuel saving, etc.
(4) Grease: Disperse the thickener evenly in the lubricating oil to obtain a viscous semi-fluid bulk material, which is called grease. It is composed of three parts: thickener, lubricating oil and additives. Usually thickener accounts for 10%-20%, lubricating oil accounts for 75%-90%, and the rest are additives.
(5) Solid lubricant: A powder or film-like solid substance used to reduce friction and wear between relatively moving bearing surfaces. It is mainly used for friction parts that cannot or are inconvenient to use grease. Commonly used solid lubricating materials are: graphite, molybdenum disulfide, talc, polytetrafluoroethylene, nylon, tungsten disulfide, graphite fluoride, lead oxide, etc.
(6) Gas lubricant: some inert gases such as air, nitrogen, helium, etc. are used as lubricants. Its main advantage is that the friction coefficient is lower than 0.001, which is almost equal to zero. It is suitable for the lubrication of precision equipment and high-speed NSK bearings. ERIC BEARING have rich stock for NSK 22213CDE4C3S11 , if you interested , pls click here :
2. The main performance indicators of lubricants
Viscosity indicates the viscosity of lubricating oil. It refers to the internal frictional resistance generated when relative displacement occurs between oil molecules, and the size of this resistance is expressed by viscosity.
There are two types of viscosity: absolute viscosity and relative viscosity. The absolute viscosity is divided into dynamic viscosity and kinematic viscosity.
What we commonly use is kinematic viscosity. Since the viscosity of lubricating oil varies with temperature, it must be indicated at what temperature the viscosity was measured. The commonly used test temperature is 40°C, at which the viscosity is measured and used as the grade of lubricating oil.
(2) Flash point and ignition point
When the lubricating oil is heated under certain conditions, the evaporated oil vapor is mixed with air to reach a certain concentration when it comes into contact with the flame, and the lowest temperature at which short-term flicker occurs is called the flash point.
If the flash point time is extended for more than 5 seconds, the temperature at this time is called the ignition point. The flash point is a safety index for the storage, transportation and use of lubricating oil. Generally, the maximum working temperature should be 20-30℃ lower than the flash point. There are two methods for flash point determination: open and closed methods. The results of the open method are generally 20-30°C higher than the closed method.
Indicates the degree of softness and hardness of the grease, which is an important basis for classifying grease grades.
Test method: A standard cone with a weight of 150 grams is sunk into the grease within 5 seconds at a temperature of 25C (unit: 1 I 10 mm), which is called the penetration of the grease. The deeper the plunge, the softer the grease and the smaller the consistency; conversely, the smaller the penetration, the harder the grease and the greater the consistency. The penetration of lubricating grease increases with the increase of temperature, and the selection should be based on temperature, speed, load and working conditions.
(4) Dropping point
Indicates the heat resistance of grease.
Put a sample of grease into a dropping point meter and heat it under specified conditions. The temperature when the first drop of oil drops after the grease melts is used as the dropping point of the grease.
The dripping point of grease determines its working temperature. Grease with a dripping point 20-30℃ higher than the working temperature should be selected for application.
3. Selection basis for NSK bearing lubricant
There are many types of lubricants and greases, and many factors must be considered in a reasonable selection, such as the type, specification, working conditions, environment, and lubrication methods and conditions of the friction pair. There are different selection methods for different situations. The following can only take the main factors as the basis for selection under the condition of generality.
(1) Movement speed:
The higher the relative movement speed of the two friction surfaces, the lower the viscosity of the lubricating oil and the larger the penetration of the grease. If oils and greases with high viscosity and small penetration are used, the resistance of movement will be increased, a lot of heat will be generated, and the friction pair will heat up.
(2) Work load
The greater the work load, the higher the viscosity of the lubricating oil, and the lower the degree of the lubricating grease. All kinds of oils and greases have a certain bearing capacity. Generally speaking, the oil film of the friction pair is not easy to damage the oil with high viscosity. In boundary lubrication conditions, the dry viscosity does not play a major role, but the oiliness. In this case, the extreme pressure of oil and grease should be considered.
(3) Working temperature
Working environment temperature, friction load, speed, material, lubricating material, structure and other factors all affect the working temperature. When the working temperature is high, lubricating oil with greater viscosity and lubricating grease with less penetration should be used. Because the viscosity of the oil decreases with increasing temperature, the penetration of the grease also increases. There is no strict standard for the division of working temperature, it is divided by experience:
Less than -35℃ is lower temperature,
-34-16℃ is low temperature,
-15-69℃ is the normal temperature,
70-99℃ is a medium temperature,
100-120℃ is high temperature,
Above 120°C is a higher temperature.
Working conditions, surrounding environment, and lubrication methods must also be considered. If the lubrication conditions are in contact with water, lubricating oil and grease that are not easily emulsified by water, or water-based lubricating fluid should be selected.
The lubrication method is centralized lubrication, that is, grease with good pumpability should be selected. The precision friction pair should choose grease with low viscosity and high penetration, etc., which should be determined according to the actual situation.
The several basis considered above should be comprehensively analyzed according to the actual situation during application and cannot be used mechanically. In the event of a conflict, the main needs should be met first, and the speed, load, temperature and other factors should be considered, and then the viscosity and penetration should be determined.