Views: 0 Author: Site Editor Publish Time: 2024-10-31 Origin: Site
Bearing is an essential accessory in industry nowadays, from large machinery such as turbine, wind turbine generator to small machinery and equipment such as precision instruments, fans, skateboard wheels and so on, bearings play an important role in them. As we all know, bearings can be divided into many different types according to their structure, material, size, precision and so on, and even a slight change will make the bearing category different. According to the sealing method, they can be divided into open bearings, shielded bearings and sealed bearings.
In this article, LNB Bearing will explore the specific information of Shielded Bearings and Sealed Bearings, analyse their similarities, differences, and their respective applications, etc., expecting to help users better choose the right bearings.
Shielded bearings are bearings that contain metal dust caps on one side (the suffix code is usually Z) or both sides (the suffix code is usually ZZ) of the outside of the bearing, such as 608ZZ. These shields are mainly used to prevent relatively large foreign objects from entering the bearing. The shields are fixed to the outer ring of the bearing. They are not in direct contact with the inner ring, with a small gap between them, so that shielded bearings operate with less friction and less energy loss, and can be used in applications where general contamination and high speeds are required. Shielded bearings help to keep grease in the bearing, but allow some lubricant to escape.
In addition to the common Z and ZZ suffixes for Shielded bearings, different manufacturers and brands have their own suffix designations, if people want to know, they can inquire with the manufacturer engineer or check their catalog.
Sealed bearings are bearings with non-metallic seals on one (suffix usually RS) or both (suffix usually 2RS) sides of the outside of the bearing, such as 6203 2RS. These seals are usually made of rubber or plastic materials that form a tight barrier that not only effectively prevents the entry of small particles of contaminants, but also keeps the lubricant in the bearing and effectively prevents grease leakage. Sealed bearings are self-sealing bearings, which do not require supplemental lubrication or regular maintenance. They prevent debris, particles, and moisture from entering the bearing to prevent rusting and ensure that the lubricant is not washed away. Of course, sealed bearings have their drawbacks, for example, contact sealed bearings may generate more heat due to friction from contacting the inner and outer rings, limiting speeds and causing more wear when in use; and because they are made of materials such as rubber, they may melt under high temperature conditions.
Sealed bearings can usually be divided into contact type and non-contact type. Similarly, regarding the suffix of sealed bearings in addition to the common RS, and 2RS, different manufacturers and brands also set up different sealing structures of their respective suffix code, the specific code needs to consult the manufacturer's engineer or product manual.
Contact seal refers to a seal method in which there is direct contact between the bearing seal ring and the shaft or housing. It has good sealing performance, can effectively prevent lubricant leakage and external dust, liquid into, suitable for high pollution in harsh environments. But it also has its limitations, such as limited speed, friction heat increase, and wear and tear.
The form of non-contact sealed bearings is similar to dust cap bearings, they have a small gap between the seal and the running surface, and will not contact with the corresponding rotating parts when working. Non-contact sealed bearings reduce friction and wear and are suitable for certain high speed applications. However, again, non-contact sealed bearings have a poor sealing effect and are not suitable for environments with high levels of fine particle contamination.
In this article, the sealed bearings discussed and compared are contact types.
(1) Shielded bearing and sealed bearing belong to closed-type bearing, more expensive in manufacturing cost than the open bearing.
(2) Shielded bearing and sealed bearing are used for preventing leakage of lubricant from within the bearing and for preventing entrance of dust and other external contaminants to the bearing.
(3) Shielded bearing and sealed bearing can improve the reliability and service lifespan of the bearing by effective sealing.
(4) In the aspect of maintenance, shielded and sealed bearings will be more convenient than open bearings, since the seals can effectively block the intrusion of dust and impurities, thus reducing the damage to the interior of the bearing.
Item | Shielded bearings | Sealed bearings |
Material | Metal materials | Elastic materials such as rubber or plastic, etc. |
Structure | Simple | Various shapes, can be O-rings, U-rings, V-rings, etc. |
Prevention of contaminants entering the bearing | Good | Very good |
Prevention of moisture entering the bearing | No | Yes |
Prevention of grease leakage | No | Yes |
Friction | Lower | Higher |
High temperature resistance | High | Lower |
Corrosion resistance | Better | Worse |
Speed | Higher rotational speed | Slightly lower operating speed |
Service lifespan | Shorter service lifespan in contaminated environments | More durable in contaminated environments |
Cost | Lower | Higher |
Application scenarios | General contamination environments, higher speed requirements | Harsh environments with higher contamination, low-speed heavy-load |
In general, shielded and sealed bearings have respective advantages and disadvantages as well as applications. Shielded bearings can be applied to the working environment with ordinary pollution and high speeds. They can effectively prevent large particle pollutants and dust, but their protection against liquid water and grease is weak. Sealed bearings have better sealing performance, applicable to higher pollution, low speed, and heavy loads of harsh environments. However, when it operating, the friction is larger, generating heat and weariness that may occur in high-speed operation; moreover, since it's made of rubber and plastic and other non-metal materials, it is not appropriate to work at high temperatures and corrosion.
Some typical applications of the two kinds of bearings are as follows:
(1) Electric motors: These require contact with some dust and dirt but do not need total protection from them.
(2) Fans and blowers: Shielded bearings keep out most all but the largest-sized particles, while still allowing partial airflow to occur.
(3) Robotics: Non-contact environments where shielded protection is sufficient.
(4) Automotive: The parts that need to deal with some dust exposure but do not need to be fully sealed.
(1) Automobiles: Found in parts that have to be completely sealed to prevent dirt and water.
(2) Heavy duty equipment: Uses that are exposed to harsh conditions, such as conveyor systems, heavy machinery, etc.
(3) Food and beverage processing: Clean environment to avoid contamination.
(4) Medical instruments: The application that demands a non-contaminated, clean environment.
The two types of bearings have the same advantages in terms of less upkeep and a longer lifespan. However, the choice of sealed or shielded bearings is primarily based on the intended use and the operating environment. Every seal chosen must also be regularly checked for its effectiveness as well as its serviceability period.
Both removable and non-removable shield covers must ensure the following requirements:
(1) They are not permitted to detach in operation;
(2) No contact with the cage is permitted;
(3) No contact with the moving ring is permitted;
(4) Do not exceed the assembly height.
(5) The non-removable dust cover is not allowed to deform the bearing ring after assembly.
(1) It must not be installed in the wrong direction or damage the lip. A scar of 50μm or more on the lip may result in significant oil leakage.
(2) Prevent forced installation. Instead of hammering it in, use a special tool to first press the seal into the seat hole and then use a simple cylinder to protect the lip through the spline part. Before installation, apply some lubricant to the lip to facilitate installation and prevent burns during initial operation, and be careful to clean it.
(3) Prevent overuse and should be replaced with a new seal in time. The rubber seal of the dynamic seal has a service life of 3000 to 5000h in general.
(4) Replacement of the seal ring size should be consistent. To be strictly in accordance with the requirements of the manual, the same size of the seal.
(5) When using new seals, carefully check the surface quality, to determine the absence of small holes, protrusions, cracks and grooves, and other defects and have sufficient elasticity before use.
(6) When installed, it should be strictly cleaned to open the hydraulic system parts, it is best to use special tools to prevent metal sharp edges of the fingers will be scratched.
(7) When replacing the seal, we should strictly check the seal groove, remove the dirt, and polish the bottom of the groove.
(8) In order to prevent damage resulting in oil leakage, must be operated in accordance with the regulations, and at the same time, can not be overloaded for a long time or the machine is placed in a relatively harsh environment.
The type of sealing used in a bearing depends greatly on the application environment and working conditions.
Shielded shafts are mounted in the outer ring and are not in contact with the inner ring, possessing low friction and generating less heat. As a result, shielded bearings allow for higher speeds, but they offer limited protection against large contaminants entering the bearing.
A contact sealed bearing, on the other hand, provides better protection against contamination and grease retention, preventing moisture from entering the bearing in addition to small contaminants. However, because the seals of sealed bearings are in contact with the inner and outer rings of the bearing, they generate greater friction during operation and therefore cannot be used in high-speed environments, and because the seals are usually made of rubber or plastic, sealed bearings are usually not suitable for high-temperature environments.
In terms of purchase cost, sealed bearings are slightly more expensive than shielded bearings. This is because rubber seals are more complex than metal shields and they are installed differently.
However, in environments where there is a lot of contamination and contact with water, shielded bearings can fail quickly and require additional costs for replacement.
Generally no lubrication is required as shielded and sealed bearings are lubricated to a level that lasts longer than the expected service life. However, in special environments, periodic inspection and maintenance may still be required.
The service life of sealed and shielded bearings is usually affected by factors such as load, speed, temperature, industrial environment and lubrication condition. Regular inspection and maintenance can help to extend their service life periodically and replace or repair them when necessary.
