A common challenge in conveyor maintenance is recurring bearing damage. Maintenance teams replace failed bearings with identical spare parts, only to see the new units fail again within weeks. Even after upgrading bearings, adjusting lubrication schedules and correcting shaft alignment, failures persist. Many attribute this issue to insufficient bearing load capacity or manufacturing defects. However, abundant field cases reveal the root cause is often a mismatch between the load type the bearing is designed for and the actual forces generated under operating conditions.
Forces acting on rotating shafts fall into two categories by direction: radial load and axial load. Radial load acts perpendicular to the shaft axis, while axial load, also called thrust load, pulls or pushes along the shaft centerline. Most industrial equipment operates under combined loading conditions. Distinguishing between these two load types lays the foundation for bearing selection, failure diagnosis and equipment reliability improvement, applicable to conveyors, crushers, bucket elevators, screw conveyors and other rotating machinery.
Axial load acts along the shaft centerline. It arises from material conveyance in screw conveyors, gear meshing, pump and fan operation, as well as shaft thermal expansion caused by temperature variation. When axial forces are significant, the selected bearing must be capable of withstanding thrust load; otherwise, rolling elements and raceways will suffer excessive stress and progressive damage.
Radial load points perpendicularly toward the shaft radius, representing the most prevalent load condition for rotating equipment. Belt tension, dead weight of shafts and pulleys, and forces from chain drives all qualify as radial loads. Most general-purpose bearings are primarily engineered to carry radial loads, with limited capacity for light to moderate axial loads.
Pure single-load conditions are rare in real-world applications. A screw conveyor bears radial loads from the weight of its screw and conveyed material, alongside axial thrust generated by material movement. Conveyor pulleys mainly endure radial loads from belt tension, yet misalignment, thermal expansion and frame deformation can introduce additional axial forces. Bearing selection therefore cannot rely solely on rated load values. Engineers and maintenance personnel must comprehensively evaluate load direction, magnitude and combined load effects to ensure reliable equipment operation.
Not all axial loads damage bearings, as most bearings are designed with a certain margin for axial force. Failures typically occur when axial load exceeds design limits, compounded by misalignment, contamination, shock loading or poor lubrication. These conditions accelerate bearing wear, raise vibration and operating temperature, and drastically shorten service life. Different bearing types exhibit distinct failure modes: ball bearings tend to suffer edge overload and raceway spalling; spherical roller bearings may experience unloaded roller slippage on one side, leading to premature cage damage; excessive thrust on cylindrical roller bearings causes severe wear on roller ends and ribs, accompanied by rib discoloration from overheating and increased axial movement.
Spalling, brinelling and false brinelling are usually triggered by multiple adverse operating conditions. Troubleshooting should not focus merely on the damaged bearing itself but review the full operating scenario. Common triggers for premature bearing failure include excessive axial thrust, improper bearing selection, assembly errors, misalignment, inadequate or contaminated lubrication, ingress of dust and moisture, and cyclic shock loads. The superposition of these factors can rapidly degrade operating conditions and reduce bearing service life.
Load direction governs bearing structure selection. Mounted ball bearings suit applications dominated by radial loads with light to moderate axial thrust. Mounted spherical roller bearings handle heavy combined loads and tolerate shock, contamination and minor shaft misalignment. Mounted tapered roller bearings are used for high axial thrust scenarios requiring precise axial shaft positioning.
In summary, bearing failure is not always caused by heavy loading. More often, it stems from misjudgment of load types and a bearing structure incompatible with real forces. Understanding radial and axial loads and identifying combined loading conditions helps maintenance staff optimize fault investigation, spare parts replacement and equipment modification. Matching load conditions, operating environment and bearing design not only extends bearing service life but also reduces unplanned downtime and cuts spare parts and labor maintenance costs. Recognizing load direction is just the starting point of bearing reliability management. Complete bearing selection also requires assessment of alignment, contamination level, lubrication, rotating speed and maintenance requirements, so the bearing can truly fit the field operating environment.