As shown in Figure 9, NSK sealed ball bearings refer to NSK ball bearings equipped with sealing rings, which are divided into two types: non-contact sealing rings and contact sealing rings. Rubber sealing ring material, nitrile rubber is used for general use. In addition, according to different temperature requirements, polypropylene rubber, silicone rubber, fluorine rubber and other materials are used respectively. These rubbers have their own specific properties and should be selected according to the purpose when used. Table 6 lists the main characteristics and suitable temperature ranges of various rubber materials. The applicable temperature range in Table 6 is a reference index for continuous use. The thermal aging of rubber is related to temperature and time. Appropriate use time and frequency may reach a larger temperature range. The frictional heat generated by the lip of the non-contact seal ring is negligible, and the heating factor that causes rubber aging is only the physical change caused by the ambient temperature and bearing temperature. Therefore, even if it is hardened by heat aging or loses elasticity, the influence on the sealing performance can be larger than that of the contact type sealing ring. It is also very small. On the contrary, the wear caused by the friction of the lip of the contact seal ring is a big problem due to thermoplastic deformation and hardening. In the event of wear and plastic deformation, the contact pressure with the sliding surface of the lip decreases, resulting in a gap. However, even if there is a gap, the value is within the minimum limit, so the sealing performance such as dustproof and leak-proof grease will not be significantly reduced. Therefore, even a little plastic deformation or sealing performance such as grease occurs. Therefore, even if there is a little plastic deformation or increased hardness, it will often be used without hindrance. However, when there is a lot of garbage or water in the external environment, the bearing sealing ring is only used as an auxiliary sealing ring, and the main sealing ring must be designed separately. As mentioned above, although the applicable temperature range of rubber materials is a reference when selecting models, but due to the high price of heat-resistant rubber, in order to select a more economical and reasonable model, the key is to fully grasp the temperature requirements. Furthermore, not only the heat resistance, but also the characteristics of various rubbers should be sufficiently compared.