The bearing material should have the following 6 advantages and is more suitable for use in liquids
Bearing is one of the most important parts of mechanical equipment, its main function is to support the mechanical rotating body, reduce the friction coefficient of its movement, and ensure its rotation accuracy, its role is similar to the human body joint, so it is known as “mechanical joint”.
The use of bearings is very common, exposed and hidden, in many places you do not know there may be bearings playing a role in silence. However, with the rapid development of industrial technology, the downstream performance requirements for bearings are increasingly high. Bearings made of steel materials have been unable to meet the needs of some occasions, such as water environment, which is the enemy of steel bearings.
What bearings are more suitable for use in liquids?
Until the 1980s, the use of bearings under water was still a headache, “Are there any bearings that can be used under water? At that time, bearing manufacturers received one of the most problems.
Ceramic bearings were not yet available, but many fields of work needed to be performed in liquids, including offshore equipment construction, medical research and food production. To get the job done, manufacturers at the time had to choose equipment with stainless steel bearings. Although stainless steel has excellent corrosion resistance, but it is always a soft metal, still need frequent maintenance and replacement, the use of high costs. Therefore, in order to improve the service life of bearings, many manufacturers have been committed to the research of corrosion resistant bearings since then.
Among the commonly used materials, the traditional steel bearing can not be used because of poor environmental compatibility; Plastic bearings are also not considered because of poor fatigue strength and creep resistance. Ceramic material is inert material, excellent mechanical properties and almost not afraid of corrosion, adapt well in the liquid environment, is the most reliable choice.
Advantages of silicon nitride ceramics
It should be known that there is often more than ordinary water in the liquid environment. For example, in a sewage recovery and treatment system in the aerospace field, a certain amount of H2SO4 and strong oxidants need to be added to inhibit the growth of microorganisms in the solution. Therefore, higher requirements are put forward for the corrosion resistance of bearings.
Si3N4 has excellent chemical resistance to most acids, such as hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3) and phosphoric acid (H3PO4), and bases, such as caustic sodium solution (NaOH). Only the mixture of hydrofluoric acid (HF), hydrochloric acid and nitric acid (HCl/HNO3) can corrode Si3N4. Therefore, ceramic bearings made with Si3N4 can work for a long time in corrosive acid, alkali, salt and other solutions. In the chemical industry or nuclear power industry, ceramic bearings can replace steel bearings with poor chemical stability, and their average life is 4~25 times higher than that of stainless steel bearings.
However, simple corrosion resistance is not enough, the service life and performance of bearings are also very important. In these aspects, Si3N4 material with the title of “ceramic King” has the same outstanding advantages, or is not a problem at all — it is not only corrosion resistance, but also has small density, high hardness, high temperature resistance, electrical insulation, no magnetic conductivity, high compressive strength, good self-lubrication performance and many other characteristics. Therefore, as a bearing material, it has many advantages such as below:
01, high speed operation performance
For general bearings, when the speed factor DN value is above 2.5×106, the centrifugal force of the rolling body will increase sharply with the increase of the rotating speed, the sliding friction of the rolling contact surface of the bearing will be intensified, and the life of the bearing will be shortened. However, due to the low density of silicon nitride ceramic bearing, the centrifugal force generated by the ceramic rolling body is much lower than that of the steel rolling body at high speed, so that the pressure and alternating load of the outer ring raceway are reduced correspondingly. Compared with the steel bearing, the speed can be increased by 30%~60%, the temperature rise can be reduced by 30%~50%, and the phenomenon of “holding shaft” is not easy to appear. Its service life is 3~6 times higher than that of steel bearings; At the same time, the centrifugal force of the rolling body is greatly reduced, and the high-speed skid caused by the centrifugal force of the rolling body is also greatly reduced, so that the inertia force of the rolling body and cage components is significantly reduced.
02, high temperature performance
The temperature change will have a great impact on the rolling fatigue life of bearings. The rated life of M50 steel bearings, usually used as heat-resistant materials, at 250℃ is about 1/10 of that at normal temperature. As for ceramic bearings, ceramic materials have excellent high temperature performance and good rolling fatigue strength under high temperature conditions. The test results show that Si3N4 still maintains quite high bending strength under the high temperature of 1000℃, so ceramic bearings have better contact stress and longer fatigue life.
03. Fatigue damage mode similar to metal bearing materials
Si3N4 ceramics as bearing materials in addition to the above excellent performance, the more important is that the way of fatigue damage is non-disaster, similar to the bearing steel metal material is the occurrence of pitting or spalling, and the failure form of alumina, zirconia and silicon carbide ceramic ball is broken. In addition, the number of surface pores, size of pores, uniformity of pore distribution, surface roughness, residual stress and lubrication conditions of SI3N4 ceramic balls have great influence on the rolling contact fatigue strength of SI3N4 ceramic balls.
04, excellent self-lubrication performance
Si3N4 ceramic material itself has anti-friction, anti-wear, lubrication functions, in poor lubrication conditions such as boundary lubrication, no oil dry friction, showing superior anti-friction self-lubrication performance, can greatly improve the working reliability and service life of the machine, and can reduce machine noise, reduce maintenance costs.
05, non-magnetic and insulated
In the strong magnetic environment, when steel bearings are used, the micro powder worn down from the bearing itself is adsorbed between the rolling body and the raceway surface, which becomes the main reason for the premature spalling damage of the bearing and the increase of noise. However, silicon nitride bearings are completely non-magnetic, their insulation performance is also very good, and they have good bearing capacity, so they can be used for occasions where completely non-magnetic bearings are needed.
Although the topic of this article is to explore why silicon nitride ceramic bearings have such great advantages in water, it is clear that their advantages are not only there, in many other fields are also highly evaluated. For example, due to the characteristics of high strength and high speed, silicon nitride ceramic bearings have been widely used in machine tool spindles. Due to the characteristics of oil free and no waste generated, silicon nitride ceramic bearings have been adopted by many semiconductor manufacturers, which can be called a promising future.
