Selection and Protection of Linear Bearings in High-Temperature Environments

In production lines such as injection molding, drying and heat treatment, linear bearings often operate at temperatures above 80°C. Standard linear bearings are designed for -10°C to +80°C, and can briefly withstand up to 100°C. When operated above this range for extended periods, service life drops sharply. For high-temperature applications, the principle can be summed up in three points: lubrication first, materials follow, clearance last.

1. Three Major Threats of High Temperature to Linear Bearings

Lubricant failure. Ordinary lithium grease begins to oxidize and thin above 80°C, and carbonizes above 120°C; once the film breaks, balls and raceways run dry, creating a vicious cycle of heat and wear.

Loss of hardness. Bearing steel GCr15 shows a tempering effect above 120°C, reducing hardness, load capacity and fatigue resistance.

Thermal-expansion seizure. The rings, balls, cage and mating shaft expand at different rates, consuming the internal clearance; the bearing tightens as it runs and may lock up completely.

2. Selecting by Temperature Grade

Up to 80°C: standard linear bearings are sufficient with routine lubrication.

80-120°C: standard types remain usable, but the grease must be upgraded to synthetic fluorinated or polyurea grease with shorter regreasing intervals.

120-200°C: choose high-temperature bearings with heat-treated steel, FKM (Viton) or PTFE seals, and thermal-expansion compensation design.

200-300°C: use heat-resistant stainless steel or special alloy steel, with metal or PEEK cages.

Above 300°C: grease lubrication is no longer viable; use full-ceramic bearings (silicon nitride, Si3N4) or solid lubricants such as MoS2 and graphite.

3. Five Protection Measures

Upgrade lubrication. Above 150°C, use PFPE grease, which withstands about 250°C; as a rule of thumb, grease life halves with every 15°C rise in temperature, so regreasing intervals must be shortened accordingly.

Change seal materials. NBR hardens and cracks above 100°C; switch to FKM or PTFE seals.

Increase clearance. Select C3, C4 or even C5 clearance groups to reserve room for thermal expansion.

Change cage materials. Above 150°C, use steel, brass or PEEK cages.

Allow for expansion during installation. Use floating supports or leave expansion gaps, and improve ventilation and heat dissipation to extend bearing life.

4. Three Common Pitfalls

Considering only ambient temperature: the bearing generates heat at high speed, so selection must be based on the combined temperature of ambient plus bearing temperature rise.

Mixing old and new grease: incompatible base oils accelerate failure; remove old grease completely before regreasing.

Overlooking the shaft material: the shaft also expands at high temperature; choose heat-resistant shafting and perform thermal-expansion calculations at the design stage.

Closing

For high-temperature applications, the essence of selection is simple: lubrication first, materials follow, clearance last. When in doubt, contact the HENGLI technical team for a joint evaluation to choose the solution that truly matches your temperature conditions.