What are the advantages and disadvantages of commonly used rubber materials for supermarket trolley casters?

Analysis of the Advantages and Disadvantages of Commonly Used Rubber Materials for Supermarket Trolley Casters
The rubber material used in supermarket trolley casters directly affects their wear resistance, load-bearing capacity, quietness, and applicable applications. Currently, the mainstream materials on the market include natural rubber (NR), nitrile rubber (NBR), polyurethane rubber (PU; although a synthetic elastomer, it is often classified as a rubber-based application), and ethylene propylene diene monomer (EPDM). The advantages and disadvantages of each material, as well as their applicable applications, vary significantly, as follows:

1. Natural Rubber (NR)

Natural rubber is made from the sap of rubber trees and possesses excellent elasticity and toughness. It was a common material for early casters.
Advantages:
Excellent elasticity: Rebounds quickly from impact, minimizing vibration during pushing and reducing cargo turbulence.
Excellent low-temperature performance: Maintains excellent flexibility in temperatures between -50°C and 80°C, making it suitable for use in supermarket cold chain areas (such as fresh produce refrigerated areas).
High initial friction coefficient: Provides strong grip on the ground, preventing slippage during pushing, making it especially safe on smooth tiled floors. Disadvantages:
Poor wear resistance: The material itself has a low hardness (Shore A 60-70). Prolonged contact with rough surfaces (such as concrete) can easily cause wheel tread wear and smoothing of the wheel grooves. With an average service life of only 2-3 months, these wheels are not suitable for frequent use.
Poor oil and aging resistance: They are prone to swelling and deformation when exposed to common supermarket cooking oils and detergents. They are prone to cracking and hardening when exposed to sunlight and high temperatures for a long time.
Limited load capacity: The rated load of a single wheel is typically ≤50kg, which is insufficient for a fully loaded trolley (200-300kg). Overloading can easily cause wheel dents.

2. Nitrile Rubber (NBR)
Nitrile rubber is a copolymer of butadiene and acrylonitrile. Its core advantage lies in its oil resistance, making it commonly used in applications exposed to oil contamination. Advantages:
Excellent Oil Resistance: Highly resistant to mineral oils, vegetable oils, and lubricants. Even contact with oil spills from supermarket food areas is not susceptible to swelling or cracking, making it suitable for carts in fresh produce and snack areas.
Superior Abrasion Resistance: Higher hardness (Shore A 75-85), wheel tread wear resistance is increased by approximately 30%, extending service life to 4-5 months.
Good Compression Set Resistance: The wheel tread is less likely to develop permanent dents after prolonged heavy loads, maintaining stable rolling performance.
Disadvantages:
Poor Low-Temperature Performance: Hardens and becomes brittle in temperatures below -15°C, increasing vibration and even cracking during pushing. Unsuitable for cold chain areas.
Fair Aging Resistance: Long-term exposure to sunlight or high temperatures can cause yellowing and loss of elasticity. Avoid prolonged storage in the sun near supermarket entrances.
Poor Quieting: The material's high hardness results in a high noise level (≥65dB when pushing), which can negatively impact the shopping environment.

3. Polyurethane Rubber (PU)
Polyurethane rubber (often called "PU wheels") is currently the mainstream material for supermarket cart casters. It combines the elasticity of rubber with the wear resistance of plastic, offering optimal overall performance. Advantages:
Extremely wear-resistant: Through formula adjustments, high hardness (Shore A 85-95) is achieved, with a wear resistance coefficient 3-5 times that of natural rubber. It can roll for 100,000 kilometers without noticeable wear, and has a service life of 6-12 months, making it suitable for frequent supermarket use.
Quiet: The material has a certain degree of elasticity, resulting in low noise levels when rubbing against the floor (≤50dB when pushing), meeting the requirements of a quiet supermarket shopping environment.
Balanced load-bearing and weather resistance: Each wheel has a rated load capacity of 80-100kg, meeting the requirements of a fully loaded trolley. It is also oil-resistant, aging-resistant, and low-temperature resistant (-30°C to 100°C), making it suitable for all supermarket areas (normal temperature, cold chain, and oil-contaminated areas).
Balanced grip and rolling performance: The flexible wheel tread pattern ensures slip resistance on smooth surfaces while reducing pushing resistance, ensuring effortless and stable operation. Disadvantages:
High Cost: The unit price is 2-3 times that of natural rubber wheels, resulting in a high initial purchase cost.
Easily softens at high temperatures: The wheel surface can soften and deform if exposed to temperatures above 100°C (such as near heating equipment in supermarkets) for extended periods. Avoid high-temperature exposure.
Weak resistance to sharp objects: The wheel surface can be easily scratched by sharp objects such as metal scraps and shelf edges, requiring frequent floor cleaning.

4. EPDM (Ethylene Propylene Diene Monomer)
EPDM is a copolymer of ethylene, propylene, and a small amount of non-conjugated dienes. Its core strengths lie in its weather and chemical resistance, making it suitable for specialized environments. Advantages:
Extremely weather-resistant: Resistant to UV rays, ozone, and high and low temperatures (-40°C to 150°C). Even with long-term exposure to the open air at supermarket entrances or in cold chain areas, it resists aging and cracking, with a service life of up to 8-10 months.
Good chemical resistance: Highly resistant to common supermarket cleaning agents (such as dishwashing liquid and disinfectant) and weak acids and bases (such as fruit juices), preventing corrosion.
Excellent water resistance: The dense material is impervious to water molecules, making it suitable for use in humid environments such as supermarket aquatic areas and cleaning areas. The axle is also less susceptible to rust due to moisture.
Disadvantages:
Moderate wear resistance: While better than natural rubber, it is weaker than polyurethane. Long-term use on rough concrete surfaces will cause the wheel surface to wear rapidly.
Fair grip: The smooth surface of the material can be prone to slipping on wet surfaces (such as those in aquatic areas), requiring optimization of the wheel surface texture.
Difficult to process: The material is highly elastic and has a large shrinkage rate, which can lead to dimensional deviations during molding. High-precision molds are required, further increasing costs.