The sealing of bearings can be divided into two types: self-contained sealing and external sealing. Self-contained sealing is to make the bearing itself be a sealing performance device, such as bearing belt, dust cover, sealing ring and so on. This kind of sealing takes up a small space, easy to install and disassemble, and the cost is lower. External sealing is to make the sealing device with varieties of performances in mounting end cover and internal. External sealing is divided into non-contact sealing and contact sealing. Non-contact sealing is suitable for high-speed and high-temperature applications. Contact sealing applies to medium and low speed working conditions.