Paddle Shaft Bearing Assembly

Function

The bearings maintain precise shaft centricity, keeping paddle tip clearances within design limits across all load conditions. Bearing failure — typically through grease contamination, aggregate ingress, or misalignment — leads rapidly to shaft deflection, tip-to-liner contact, and catastrophic mixer shutdown. Correctly specified and maintained bearings are the single most important mechanical reliability item in the mixing unit; a contamination-induced bearing failure typically causes collateral damage to the liner plates and paddle arms in the same event.

Construction & quality

Bearing insert: spherical roller bearing (SRB) to ISO 281 dynamic rating, Grade C3 internal clearance to accommodate thermal expansion during continuous mixing. Housing: GG25 grey-iron pillow block, precision-bored and surface-ground on the mounting foot. Seals: triple-lip contact seals on both inboard and outboard faces, with a cast-iron labyrinth slinger preventing aggregate dust migration to the seal lips. Pre-packed with NLGI Grade 2 lithium-complex grease rated to 160 °C. Inner bore: machined to H7/k6 interference fit specification on the bearing inner ring.

When to replace

• Outer race surface temperature exceeding 80 °C under normal operating load
• Audible roughness, rumbling, or intermittent noise at shaft speed
• Grease purge discoloured grey or black with abrasive fines contamination
• Shaft radial play greater than 0.5 mm measured at the paddle arm hub
• Visible aggregate dust accumulation at the inner face of the seal, inboard of the labyrinth