When installing or removing PU deep groove ball bearings, what are the special requirements for heating temperature and force application method

Due to the unique elastic outer ring structure, PU (polyurethane) deep groove ball bearings impose stricter requirements on heating temperature and force application during installation and disassembly than traditional all-steel bearings. Improper handling can easily lead to permanent deformation, cracking, or delamination of the PU outer layer from the inner steel bearing ring, rendering the bearing scrapped. Professional operation must strictly adhere to material properties to ensure bearing integrity and ultimate operating accuracy.

Key Limitation: Strict Control of Heating Temperature

The temperature limit of PU deep groove ball bearings is the primary technical challenge in their installation and disassembly. As a high-molecular elastomer, polyurethane has a thermal stability far lower than that of high-carbon chromium bearing steel (GCr15).

1. Upper Temperature Limit of PU Materials

For most industrial applications, the maximum continuous operating temperature of PU materials is typically between 80°C and 100°C. Heating to expand the bearing inner ring during installation is a common method, but the heating temperature of PU bearings must be strictly limited.

Professional Temperature Threshold: When installing PU deep groove ball bearings, the absolute upper limit for heating is typically set at 80°C, and the recommended operating temperature should be between 60°C and 70°C.

Risk of Thermal Damage: Once temperatures exceed 80°C, the molecular chain motion of the PU outer layer intensifies, potentially leading to softening, a sharp decrease in strength, and accelerated thermal aging. When temperatures approach 100°C, the risk of permanent set in the PU material is significant. After cooling, the bearing outer diameter may not return to the design tolerance, affecting the fit accuracy with the mounting hole.

2. Heating Method Selection and Prohibitions

To avoid localized overheating or uneven heating of the PU outer layer, gentle and uniform heating methods must be used.

Induction Heater: An induction heater with precise temperature control and automatic demagnetization is recommended. During operation, the temperature probe should be placed close to the inner steel ring, not the PU outer layer, and the heating time should be kept as short as possible.

Oil Bath Heating: If using an oil bath, ensure that the heating medium (oil) does not chemically react with the PU material or cause swelling. Furthermore, the oil temperature must be strictly monitored to avoid prolonged immersion of the bearing.

No Open Flame or High-Temperature Ovens: Direct heating using a blowtorch, open flame, or an oven exceeding the upper temperature limit is strictly prohibited. These methods can cause carbonization, cracking, or instantaneous melting and deformation of the PU outer layer.

Professional Standards for Force Application and Force Points

Force application standards for PU deep groove ball bearings follow the basic principle of "acting on the mating ring," but special attention must be paid to avoiding stress on the PU outer layer.

1. Force Requirements During Installation

The goal of bearing installation is to ensure that the inner ring fits tightly against the shaft journal, or the outer ring fits tightly against the bore. Due to the low elastic modulus of the PU outer layer, it cannot withstand the high stresses caused by stamping or impact.

Inner Ring Installation: When the bearing inner ring is required to achieve an interference fit with the shaft journal, the force application point must be on the inner ring.

Standard Operation: Use a sleeve or a dedicated installation tool. The end face of the sleeve should evenly contact the entire end face of the inner ring. When applying force (whether by stamping, hydraulic pressure, or tapping), the force must be perpendicular to the bearing end face and transmitted smoothly to avoid tilting or localized force.

Outer Ring Installation: Some operating conditions require an interference fit of the outer ring (rarely seen with polyurethane bearings). In these cases, the force must be applied to the outer ring.

Key Taboo: Never apply force directly or indirectly to the steel inner ring through the polyurethane outer layer. Any force acting on the polyurethane outer layer will cause it to dent, deform, or even delaminate and fail.

2. Force Requirements for Disassembly

The goal of disassembling a polyurethane bearing is to separate it from its mating position without damaging the bearing or the shaft journal.

Inner Ring Disassembly: When removing an inner ring that is tightly fitted on the shaft journal, use a dedicated puller. The puller's claws should act on the end face of the inner ring.

Thermal Disassembly Assistance: If the fit is tight, first heat the bearing to within the aforementioned safe temperature range to reduce the expansion of the inner ring before pulling. Do not strike or use brute force.

Outer Ring Removal: If the outer ring of a PU bearing has an interference fit, use a push-out device or apply a uniform thrust through the mounting hole.

PU Outer Ring Protection: During the pulling or pushing process, ensure that the tool does not contact or damage the raceway surface of the PU outer layer to prevent nicks or grooves that could affect subsequent rolling performance.

Post-Installation Technical Verification of PU Bearings

Once a PU deep groove ball bearing is installed, it cannot be simply assumed that the installation is complete. Additional technical verification is required to rule out potential problems caused by the elastic properties of the PU.

Axial Play Check: After installation, check the bearing's axial play manually or with a tool. If the PU outer layer is slightly deformed or sticks during installation, this may affect the bearing's axial positioning.

Running Accuracy Inspection: During low-speed idling or light-load test runs, a vibration meter should be used to monitor the bearing's vibration and noise levels. If the PU outer layer is damaged or delaminated during installation, abnormal vibration will typically occur, necessitating prompt downtime for inspection.

Strict adherence to the thermodynamic limitations of the PU material and professional specifications for force application points is crucial for ensuring the full performance and service life of PU deep groove ball bearings. Any inattention to temperature and force application points can lead to premature bearing failure.