What are the performance changes of plastic coated bearings in low temperature environment

Plastic-coated bearings (PCBs), composite bearings formed by coating traditional metal bearings with high-performance plastics, are widely used in industries such as machinery manufacturing, food processing, aerospace, and cryogenic storage and transportation. Low temperatures significantly impact bearing performance, especially in PCBs. The plastic layer undergoes physical and chemical changes different from those of the metal under extreme low temperatures, directly impacting the bearing's service life and operational stability.

Changes in the Physical Properties of Plastic Materials at Low Temperatures

The core advantage of PCBs lies in the friction reduction and corrosion resistance provided by the plastic layer. However, at low temperatures, the molecular motion of the plastic material slows, resulting in increased rigidity and decreased impact toughness. This phenomenon manifests as a greater susceptibility to microcracks or cracking of the coating during start-up or when subjected to impact loads. Certain polymer materials, particularly common engineering plastics such as polyoxymethylene (POM) and polyamide (PA), can undergo a brittle transition at low temperatures. Use below their brittle temperature significantly increases the risk of cracking.

Changes in Friction Coefficient and Lubrication Performance

The friction coefficient of PCBs typically increases at low temperatures. The increased hardness of the plastic surface increases the microscopic frictional resistance between the contact surface and the metal shaft or inner ring. Lubricant viscosity increases and fluidity decreases at low temperatures, making it difficult for the lubricating film to form complete coverage, further exacerbating friction and wear. For plastic-coated bearings used in dry or lightly lubricated conditions, this increased friction can lead to increased starting torque and additional loads on the motor or drive.

Dimensional Stability and Thermal Expansion Behavior
At low temperatures, plastic materials experience significant thermal contraction, resulting in slight dimensional shrinkage. While the shrinkage of the metal bearing body is relatively small, the difference in thermal expansion coefficients between the plastic coating and the metal substrate can lead to increased interfacial stresses. Under extreme conditions, the plastic coating may experience slight delamination, deformation, or localized cracking. This dimensional change is particularly critical for bearings in precision machinery or high-precision instruments, potentially affecting rotational accuracy and bearing clearance.

Impact of Shock Loads and Fatigue Life
Plastic-coated bearings subjected to shock loads at low temperatures often experience reduced fatigue life. Increased brittleness and the accumulation of interfacial stresses accelerate the initiation and propagation of microcracks, leading to premature wear or shedding of the coating. Mechanical equipment that experiences frequent starts and stops or high-impact operation requires the selection of plastic materials with high low-temperature toughness or the inclusion of lubrication protection during design to ensure long-term, reliable bearing operation.

Changes in Noise and Vibration Characteristics

Under low temperatures, the increased surface hardness and friction coefficient of plastics can lead to a slight increase in bearing operating noise. Due to reduced lubrication effectiveness, uneven friction can cause slight vibration, especially noticeable at high speeds. For equipment requiring low noise, such as pharmaceutical packaging machinery, precision instruments, or cold chain transportation systems, this characteristic must be fully considered in bearing selection and maintenance plans.

Application Recommendations for Low-Temperature Environments

When using plastic-coated bearings in extremely low-temperature environments, it is preferable to select engineering plastics with high low-temperature toughness and a low brittle transition temperature, and to use them in conjunction with a low-temperature lubricant. Bearing installation tolerances should account for plastic shrinkage to avoid overtightening (increasing friction) or overloosening (inducing play). Regular inspection of bearing surface condition and lubrication is crucial to extending bearing service life in low-temperature conditions.