Plastic Cages in Rolling Bearings: A Comprehensive Overview

History

The use of cages in rolling bearings dates back to the early 19th century, with the first modern-looking cages appearing in the late 1800s1. Initially, cages were made from materials like brass and steel. The introduction of plastic cages came much later, driven by the need for lighter, quieter, and more cost-effective solutions2.

Manufacturing Methods

Plastic cages are typically manufactured using injection molding. This process involves melting plastic and injecting it into a mold where it cools and hardens into the desired shape3. The most commonly used material for these cages is Polyamide 66 (PA66), often reinforced with glass fibers to enhance strength and durability4.

Different Options

Plastic cages come in various designs to suit different applications. Common types include:

• Snap-type cages: Assembled after the rings and rolling elements.
• Roller-guided cages: Self-containing and used in specific bearing types.
• Ring-guided cages: Used to limit contact stress between rolling elements and the cage4.

Limitations

While plastic cages offer several benefits, they also have limitations:

• Temperature Sensitivity: Plastic cages generally cannot withstand extremely high temperatures compared to metal cages5.
• Chemical Resistance: They may be affected by certain organic solvents, coolants, and lubricants4.
• Elastic Deformation: Under high-frequency movements, plastic cages can experience significant elastic deformation, potentially limiting bearing performance6.

Advantages and Disadvantages Compared to Metal Cages

Advantages:

• Lightweight: Plastic cages are significantly lighter than metal cages, which can improve the overall efficiency of the bearing7.
• Low Noise: They produce less noise during operation, making them ideal for applications requiring quiet performance7.
• Corrosion Resistance: Plastic cages are resistant to corrosion, unlike metal cages which can rust8.
• Cost-Effective: Generally, plastic cages are cheaper to produce, especially in high volumes9.

Disadvantages:

• Lower Temperature Tolerance: Metal cages can withstand higher temperatures, making them suitable for high-heat applications4.
• Precision: Metal cages can achieve higher precision levels, which is crucial for certain applications10.
• Durability: Metal cages are generally more durable and can handle higher loads without deforming10.

Pricing

The cost of plastic cages is typically lower than that of metal cages due to the cheaper raw materials and manufacturing processes involved9. However, the exact pricing can vary based on the type of plastic used, the complexity of the design, and the production volume11.

Let’s break down the differences between these bearings and determine which might be suitable for your pump and motor.

Angular Contact Ball Bearings (7312 Series)

• 7312 BECBM: This bearing has a machined brass cage, which is more durable and can handle higher speeds and loads1.
• 7312 BECBP: This variant has a polyamide (plastic) cage, which is lighter and quieter but may not be as durable under high-stress conditions2.
• 7312 BECBJ: This bearing features a steel cage, offering a balance between durability and cost3.

For your pump, if it operates under high speeds and loads, the 7312 BECBM with the brass cage would be more suitable. However, if cost is a significant factor and the operating conditions are not extremely demanding, the 7312 BECBP with the plastic cage could be a viable option.

Cylindrical Roller Bearings (NU 220 Series)

• NU 220 ECM: This bearing has a machined brass cage, providing high durability and performance under heavy loads4.
• NU 220 ECP: This variant has a polyamide (plastic) cage, which is cost-effective and suitable for moderate loads5.
• NU 220 ECJ: This bearing features a steel cage, offering a good balance between performance and cost6.

For your motor, if it requires handling heavy loads and high speeds, the NU 220 ECM with the brass cage would be the best choice. If the motor operates under less demanding conditions, the NU 220 ECP with the plastic cage could be sufficient and more cost-effective.

I hope this detailed overview helps! If you have any more questions or need further information, feel free to ask.