What effects does low temperature have on the bearings of polyurethane casters?

Low temperature (generally below -10°C) affects polyurethane caster bearings primarily in four key areas: lubrication performance, material physical properties, sealing structure, and smooth rotation. Without targeted protection, this can easily lead to bearing seizure, increased wear, and even complete caster failure. The specific impacts are as follows:

1. Bearing grease solidifies at low temperatures, causing lubrication failure.

Normal bearing rotation relies on the grease forming an oil film between the balls and raceways. Low temperatures significantly alter the grease's physical state:

Ordinary lithium-based grease (commonly used in conventional casters) gradually thickens below -10°C and may solidify below -20°C. This prevents it from forming a uniform oil film on the ball surface, resulting in a sudden increase in frictional resistance between the balls and raceways. This requires additional force when pushing, and may even cause "stuckness."

If the grease completely solidifies, the bearing's "rolling friction" transitions to "sliding friction," quickly causing raceway wear and ball scratches. In severe cases, the bearing can become "locked," rendering the caster inoperable. For example, in outdoor logistics and handling scenarios at -25°C, casters that haven't been lubricated with low-temperature grease can experience bearing seizure after just one or two days of use due to lubrication failure, requiring disassembly, cleaning, and re-greasing to restore the bearing.

2. Low-temperature embrittlement of bearing metal components reduces impact resistance.

The inner and outer rings and balls of bearings are often made of high-carbon chromium bearing steel (such as GCr15). Low temperatures alter the metal lattice structure, causing changes in material properties:

At temperatures below -30°C, the toughness of bearing steel decreases significantly, while its brittleness increases significantly. If the caster experiences even minor impact at low temperatures (such as rolling over small stones or ascending or descending minor steps), the ball bearings are prone to fracture, cracks in the inner and outer rings, or even outright breakage.

This embrittlement is irreversible; even after returning to normal temperature, the microcracks will continue to expand, shortening the bearing's service life. For example, in a deep freezer at -40°C, frequently moved polyurethane caster bearings can experience ball fracture within 1-2 weeks due to low-temperature embrittlement, leading to eccentric rotation of the caster and further wear of the polyurethane tread.

3. The sealing structure hardens at low temperatures, reducing its waterproof and dustproof capabilities.

The bearing's sealing cap (such as a rubber seal or metal dust cap) is crucial for isolating moisture and impurities. Low temperatures have a direct impact on the sealing structure:

Rubber seals (such as nitrile rubber seals) gradually harden and lose their elasticity at temperatures below -15°C, weakening their fit with the bearing's inner ring and creating gaps. Moisture and frost particles in low-temperature environments can easily penetrate the bearing through these gaps, mixing with the solidified grease to form "sludge," exacerbating bearing wear.

Metal seals, while not hardening at low temperatures, may develop a small gap at the joint between the seal and the metal cap due to thermal expansion and contraction, similarly leading to seal failure. This is especially true in humid, low-temperature environments (such as rainy or snowy winter weather). The infiltrated moisture can also freeze into ice, blocking the ball.

4. Loose fit between bearing and wheel hub, causing "play"
Caster bearings are typically secured in the wheel hub with an interference fit (the outer ring of the bearing fits tightly into the wheel hub bore). Thermal expansion and contraction in low-temperature environments can disrupt this fit:
Metal wheels (such as steel or aluminum alloy wheels) and bearing steel have different linear expansion coefficients. At low temperatures, the difference in contraction between the two can cause the previously tight interference fit to become a clearance fit, resulting in slight play within the wheel hub, known as "play."
This play can cause the caster to rotate "eccentrically," unevenly applying force to the tread, leading to localized wear. Furthermore, the contact position between the bearing balls and the raceway constantly shifts, exacerbating irregular wear and creating a "vicious cycle."
For example, in a workshop at -20°C, the fit between the aluminum alloy wheel hub and bearing may develop play due to differential contraction. This can cause a "squeaky" sound from the bearing during wheel pushing, and long-term use can lead to noticeable uneven wear on the tread.