The sprocket ring is the internal teeth (or external teeth) of the slewing ring through which the slewing motor rotates the upper structure of an excavator or crane. A pinion on the slewing motor engages the sprocket ring and transmits the torque for 360° continuous rotation of the upper structure. Typical diameters: 600 mm (mini excavator) to 5,000 mm (large excavator).
The sprocket ring is an integral component of the slewing ring (ball or roller slewing connection) which simultaneously accommodates axial forces, radial forces, and tipping moments between upper and lower structures. The teeth are induction hardened (HRC 50–55) for maximum wear resistance. Damage to the sprocket ring (broken teeth, pitting) requires replacement of the entire slewing ring — one of the most expensive repairs on an excavator.
Regular lubrication of the teeth (daily or after operating hours) is mandatory: Open-type sprocket ring grease (e.g. Klüber Grafloscon) is applied via automatic lubrication system or manually. Contaminated or unlubricated teeth wear 3–5 times faster than properly maintained teeth.