The function of the seal: the seal is used to keep the lubricant in the bearing and prevent external contaminants and moisture from entering the bearing. In printing machinery, the risk of contamination by solid particles is quite low, so a simple gap seal is sufficient to protect the bearing. However, this kind of seal cannot provide adequate protection when there may be liquid, such as during the cleaning process of a printing press. In this case, an effective labyrinth seal contact seal is required. Effects on working life and wear. Pollutants may cause the following serious effects: ■ A large number of small abrasive particles can cause bearing wear. This will increase the working clearance and noise of the bearing and shorten the service life of the bearing. ■ Larger, repeated rolling hard particles cause dents on the raceway. As a result, the fatigue life is shortened. ■ Liquid contamination such as water or detergent can destroy the lubricating oil film. This leads to wear and corrosion. In addition to the friction of the lubricant itself, non-contact and contact seals do not produce friction. These seals have no wear, no heat, and can work reliably for a long time, Figure 1. The contact seal maintains contact with the metal running surface under a certain contact force (usually a radial force), page 27, Figure 2. The design is simple and compact. When designing, especially for high-speed printing presses, the non-contact seal caused by the seal must be considered. Figure 1 Non-contact seal in the bearing. Sealing design The sealing of the printing machine bearing can be achieved through the peripheral structure or integrated into the bearing itself. When selecting the seal type, you must pay attention to: ■ the lubrication method and the type of lubricant ■ the working environment of the bearing ■ the available installation space ■ the complexity of the design ■ the peripheral speed of the sealing surface ■ the sealing friction ■ the temperature rise caused by friction. Swing Bearings In the working environment of three-ring and four-ring bearing printing presses, there must be dust, ink, fountain solution, cleaning agent or lubricating oil on the drive end. For this reason, the swing bearing must be effectively sealed. With a few exceptions, ring contact rings are usually fitted at both ends to achieve a very compact sealing arrangement. In order to achieve the best balance between sealing performance and friction torque, special O-rings should be used and smaller tolerances should be selected.