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, such seals do not provide adequate protection when liquids may be present, such as during cleaning of a printing press. In this case, an effective labyrinth seal is required. Effects on service life and wear Contamination can have the following serious effects: ■ A large number of fine abrasive particles can cause bearing wear. This in turn increases bearing operating clearance and noise, resulting in shortened bearing life ■ Larger, repeatedly rolled hard particles cause dents on raceways. Thus shortened fatigue life ■ Liquid contamination such as water or detergents can destroy the lubricating oil film. resulting in wear and corrosion. Non-Contacting and Contacting Seals Non-contacting seals generate no friction other than the friction of the lubricant itself. These seals are wear-free, heat-free, and operate reliably for long periods of time, Figure 1. Contact seals maintain contact with a metal running surface under a certain contact force (usually radial force), page 27, Figure 2. Simple and compact design. In the design, especially for high-speed printing presses, the non-contact seal caused by the seal must be taken into account. Sealed Design Sealing of printing press bearings can be achieved through the peripheral structure or integrated into the bearing itself. When choosing the type of seal, attention must be paid to: ■ the method of lubrication and the type of lubricant ■ the operating environment of the bearing ■ the available installation space ■ the complexity of the design ■ the peripheral speed of the sealing surface ■ the friction of the seal ■ the temperature rise caused by friction. Oscillating Bearings Three-turn and four-turn bearings Printing press bearings work in an environment where there must be dust, ink, fountain solution, cleaning agents, or lubricants on the drive end. For this reason, the oscillating bearing must be effectively sealed. With few exceptions, a very compact sealing arrangement is usually achieved by fitting annular contact rings at both ends. To achieve the best balance between sealing performance and friction torque, use specially treated O-rings and select tighter tolerances.