Segment / Riding Ring

Function

The riding ring is the primary structural interface between the rotating drum and the fixed support frame, converting the distributed weight and dynamic loads of the rotating drum into predictable, controlled contact lines at the trunnion rollers at typical drum speeds of 5–12 RPM. Surface hardness must be closely matched to the trunnion roller hardness to produce a controlled wear ratio that protects the more expensive roller assembly. A cracked, spalled, or heavily worn riding ring causes knocking vibration, accelerated roller wear, and ultimately drum alignment loss leading to secondary damage across the drivetrain.

Construction & quality

Cast from high-grade alloy steel conforming to ASTM A148 Gr 90-60 or equivalent, or forged from EN 30B alloy steel billet, then rough-machined and heat-treated to achieve a through-hardness of 260–320 BHN at the contact face. The outer running surface is finish-turned on a CNC vertical lathe to a surface finish of Ra 3.2 µm and a cylindricity tolerance of ±0.3 mm. The internal bore is machined to provide 4–8 mm design clearance over the shell pad at ambient temperature. The segment version — manufactured for large drum diameters — is produced in two or three arc segments bolted together at the shell, allowing replacement without drum removal; each segment joint is precision-machined and dowelled for concentricity.

When to replace

• Visible cracks, spalling, or heat-checking on the outer running surface
• Taper wear across the ring face producing uneven contact with the trunnion roller
• Migration (creep) of the ring along the shell pad exceeding 20 mm, indicating pad or drive-lug failure
• Abnormal knocking or vibration at drum rotation frequency
• Accelerating trunnion roller wear indicating ring surface deterioration beyond serviceable limit