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Construction and function of a Slewing Ring Bearing
Slewing Bearing consist of an internal external ring (1) and (2) with an integrated raceway system and optional internal or external gear (3). A functional seal (4) protects the raceway system on the upper and lower sides. Slewing Rings are designed for grease lubrication which is carried out via grease nipples (5). In Slewing Rings, the rolling elements (6) carry the loads between the inner and outer ring. The load capacity of the raceway system is determined predominantly by the raceway design, the hardening depth, and the number and size of the rolling elements. Spacers (7) separate the rolling elements and minimize friction and wear. The rolling elements are inserted during manufacture through the filling plug hole (8), retained by the filling plug which is then secured by a pin (9). The force is transmitted to the mounting structure by bolts. Through holes or threaded holes (10) can be provided in the inner and outer rings for these bolts.
Inner and Outer Rings (1) (2)
The bearing consists of an inner and outer ring made of medium carbon steel. Such as: 42CrMo, 50Mn, C45 and so on. Each includes at least one precision raceway arranged to transfer loads and relative motion from one structure of equipment to the other, the raceways are selectively hardened to the required surface and depth necessary to transit high stresses imposed during operation of the equipment. In one location around the raceway, there is an unhardened area referred to as the hardness gap or soft spot. This area is relieved to minimize the ability of the rolling element to apply stress on it. Only one side of each ring is manufactured to be mated with the supporting structure. One or both rings may include an integral drive mechanism such as gear or sprocket teeth to enable the mechanical advantage necessary to overcome rotational resistance and provide relative motion through the bearing.
Slewing ring can be supplied with gear teeth as an integral part of either the inner or outer ring. They are typically a standard full depth or stub involute spur gear having a 20°pressure angle with provision for backlash and confirming to AGMA Q6 quality. However, where required, modifications of the basic tooth forms, pressure angels, and quality can be provided. For assembly purposes, the maximum point of gear runout is identified with paint. Alternative methods may be applied upon request.
A seal is included on each side of slewing ring for retention of lubricant and protection of the bearing from dust and small particle contamination. The seals are made of an elastomer material compatible with most general purpose lubricants having mineral oil and greases using lithium or calcium thickeners. If conditions require different sealing, NBF can provide details of additional options upon request.
Grease Nipple (5)
At least one grease nipple is supplied in one of the slewing ring for periodic lubrication of the raceway and internal components. On designs with integral gear teeth, it is located in non-geared ring. The number supplied typically increases with bearing diameter. More or less may be included upon request.
Rolling Element (6)
Precision rolling elements enable relative rotation and transmit load between the inner and outer rings. Hardened chrome alloy steel balls or rollers may serve as the rolling elements. They are sized appropriately for the anticipated stresses and closely matched to provide uniform load distribution between the rings and minimize rotational resistance.
Spacers separate the rolling elements and are designed to minimize friction, skidding, and jamming during rotation. These conditions occur as a result of load distribution and distortion of the mounting structures and bearing rings during operation of the equipment. Spacers are generally made of a plastic material compatible with typical lubricants and operating environments.
Filling Plug and Pin (8) (9)
The rolling elements in slewing rings may be inserted through a hole drilled radially through the non-geared race and then plugged. The plug is retained mechanically with a pin to assure proper orientation is maintained.
Mounting Holes (10)
The ideal hole pattern for attaching both rings of the slewing ring is a full circle of uniformly spaced through holes. It is recognized, however, that the equipment designer cannot always accommodate this type of arrangement and may require tapped holes and even special bolt patterns in one or both rings for assembly and maintenance reasons.