Graphite bearing

Graphite bearings refer to sliding bearings made of carbon-graphite materials. Sliding bearings are divided into radial bearings and thrust bearings. Carbon-graphite sliding bearings are used in high-temperature and low-temperature, high-speed and low-speed sliding situations, and have corrosion resistance to gas and liquid media with strong corrosive effects.
Due to the many unique advantages of carbon-graphite bearings, its application range is rapidly expanding, and there are more and more varieties. In particular, various composite carbon-graphite bearings have appeared, which have improved the strength and toughness of carbon-graphite bearings. The scope of use is wider. Bearings include sliding bearings and rolling bearings. Carbon materials are specially used to make sliding bearings. Various carbon bearings mainly include the following types: bearings for plywood dryers, bearings for waterproof pumps, bearing sleeves for plywood manufacturing machines, bearings for submersible pumps, Bearings for gasoline flowmeter parts, bearings for chemical pumps.

Properties of graphite bearings
1. Good self-lubricating performance
Carbon-graphite bearings have good self-lubricating performance, mainly for two reasons. One of the reasons is that the carbon atoms in the graphite lattice are arranged in regular hexagons on each plane, the distance between the atoms is relatively close, which is 0.142nm, and the distance between the planes is 0.335nm, and they are staggered along the same direction. The third plane repeats the position of the first plane, the fourth plane repeats the position of the second plane, and so on. On each plane, the binding force between carbon atoms is very strong, but the distance between the planes is large, and the Van der Waals force between them is very weak, so the layers are easy to separate and slide relative to each other. This is why graphite materials have The root cause of self-lubricating properties.
The second reason is that graphite materials have strong adhesion with most metal materials, so the graphite that flakes off when rubbing against metals is easy to adhere to the metal surface, forming a graphite film, which becomes graphite and graphite. The friction between them greatly reduces the wear and friction coefficient, which is one of the reasons why carbon-graphite bearings have excellent self-lubricating properties and anti-friction properties.
Just because carbon-graphite bearings have good self-lubricating properties, they can run dry without lubricating oil during use. Therefore, carbon-graphite bearings are widely used in industrial sectors that do not allow lubricating oil during work.
2. Has good chemical stability
Graphite material is a chemically stable material, and its chemical stability is not inferior to that of noble metals. Its solubility in molten silver is only 0.001%-0.002%. Graphite is insoluble in both organic and inorganic solvents. It is non-corrosive and insoluble in most acids, alkalis and salts.
3. High temperature resistance of carbon-graphite bearings
After experiments, the service temperature of general carbon-grade bearings can reach 350°C; metal graphite-grade bearings are also 350°C; and electrochemical graphite-grade bearings can reach 450-500°C (under light load conditions), and their physical and mechanical properties remain unchanged. , if it is under vacuum or protective atmosphere, its service temperature can reach 1000°C.
4. Other properties of carbon-graphite bearings
Compared with other bearings, carbon-graphite bearings also have high thermal conductivity, small linear expansion coefficient, and resistance to rapid cooling and rapid heating. However, carbon-graphite products are brittle, low-hardness materials. Its mechanical strength depends on its structure and process conditions. High density and high mechanical strength. The bulk density of general carbon-graphite materials is between 1.55-1.98g/cm3, its compressive strength is 20-68MPa, and its specific strength is medium, but its mechanical strength increases with the increase of temperature, at 2000 Its mechanical strength approximately doubles that at room temperature between -2500°C, and at such a temperature its specific strength is higher than that of many existing materials. However, because the carbon-graphite material is a brittle material and its inherent strength (at room temperature) is not high, its application range is limited.
This problem has been solved, the main methods are: first, improve the particle size of raw materials; second, impregnate metal, resin or polytetrafluoroethylene, etc.; third, add materials such as carbon fiber in the carbon-graphite matrix, and use Solid lubricants, etc., therefore, not only improves its running performance, but also greatly improves the strength and toughness of the bearing. According to reports, impregnating carbon-graphite bearings with resin can increase their strength by 2-3 times, and impregnating them with metal can increase their strength even more.
5. Performance of carbon-graphite impregnated bearings
Which material to choose for carbon-graphite bearings as the impregnating agent is more suitable, it should be determined according to the working conditions of the bearing. Used to impregnate carbon-graphite bearings with phenolic resin, furan resin, epoxy resin and so on.
6. Carbon-graphite composite bearing
There are many types of carbon-graphite composite bearings. In addition to a single carbon or graphite material, in order to improve lubricity and wear resistance, increase strength and hardness, etc., change the type of raw materials, proportioning and manufacturing conditions to manufacture These materials have a short history of industrial development, but they have developed rapidly and have great potential for development.
This kind of bearing has good corrosion resistance and is relatively stable to acids, alkalis and organic solvents. Good heat resistance, because of its small thermal expansion coefficient, it has good thermal stability, and can be applied to a wide temperature range of -250°C-250°C.
7. Add solid lubricant
The solid lubricants that people are familiar with include graphite, molybdenum disulfide, mica and talc, etc. Later, graphite fluoride was newly developed. In addition to being used alone in the form of powder, solid lubricants are often dispersed in water or oil, or added to grease [3].

The scope of application of graphite bearings
1. Applied in the place where the use of grease lubricant is not allowed when the bearing is running
For example, bearings used in conveyors used in food, beverage, textile, chemical and other industrial sectors, dryers in paper industry, cloth dryers in textile industry, artificial fiber looms, cigarette manufacturing equipment and submersible pumps. Grease lubricants are prohibited in these places, and carbon-graphite bearings have strong self-lubricating properties, and can run dry without using lubricating oil. Therefore, they can be widely used in these departments.
2. Applied in places where ordinary bearings cannot be used due to high temperature
Carbon-graphite bearings can be used in the bearings of ingot conveyors, boiler preheaters, flame tube ventilation doors and blowers in boiler rooms, high-temperature furnace feeders, feeders in the iron and steel industry, and flue valve regulators. to ensure its normal operation.
3. Applied in chemical and textile industries
Some bearings operate in corrosive gases or liquids. In this case, not only the use of grease lubricants is prohibited, but also the metal bearings will be corroded quickly. For example, centrifugal pumps with impeller bearings immersed in various liquids; fuel metering pumps with bearings operating in gasoline, paraffin, kerosene, etc.; central heat circulation pumps with main impeller bearings immersed in hot water; bearings operating in Mixers in various corrosive media; automatic washing machines with main impeller bearings immersed in hot water; liquid measuring meters with bearings immersed in various liquids, and artificial fiber wet processes with bearings operating in acid splashes Textile machines, etc., all use carbon-graphite bearings. In addition, modern technology also requires carbon-graphite bearings to be used safely in complex environments with radioactive media, etc.