While ball bearings seem like a simple mechanical part, they comprise multiple components that ensure proper functioning. Besides the rolling elements or balls in a ball bearing, inner and outer rings are commonly known elements. But did you know that the bearing cage or retainer plays a critical role in the smooth running of the ball bearings?
The bearing cage keeps the rolling elements in place, ensuring they do not collide with each other to minimize friction and improve smooth functioning.
This article covers everything you need to know about bearing cages or retainers, including factors to consider when choosing a ball bearing cage.
What is a Bearing Cage?
The bearing cage is a structure within the ball bearing that helps keep the rolling elements separate. Its unique design enables it to maintain uniform radial spacing between the balls or rollers (in roller bearings) and prevents friction. The surface between the outer and inner rings in the ball bearing guides the cage.
Besides avoiding friction, bearing cages are often used for lubrication by acting as an oil reservoir or supplying a solid film via a coating on the cage.
However, all bearing cages produce friction that increases torque (starting and running), making the right choice of bearing cages crucial to better performance in specific conditions.
Bearing Cage Types
Apart from the difference in size, different ball bearings use specific materials for the best functionality. Typically, they are categorized into metal and non-metal cages, but further classification gives numerous material options with particular characteristics. The common types of bearing cage types based on the material are:
Steel Bearing Cage
Steel bearing cages are widely used in roller bearings because of their high strength and toughness. High-quality carbon steel sheets are used to prepare steel bearing cages through cold stamping and other mechanical processes as needed. Heat treatments like high-temperature tempering and annealing the steel cages help restore plasticity and remove stress. Adequate treatments make streel perfect for applications with vacuum and high temperature.
Commonly used steel cage materials include 20, 30, 45, ML15, ML20, 40CrNiMo, 0Cr18Ni9, 1Cr18Ni9Ti, etc. Steel cages are among the most economical options for ball bearings, but they may rust over time.
While carbon steel is another possible choice, it is not best suited for electrical or non-magnetic applications because of its conduction.
Nonferrous Metal Bearing Cage
Nonferrous metal bearing cages refer to those made with non-magnetic metals that contain less iron. Nonferrous metal cages include aluminum, brass, zinc, copper, etc.
Aluminum alloy: These cages offer good corrosion resistance, thermal conductivity, and low density.
Bronze: Bronze bearing cages are best for high-speed applications because of their strength capacity and thin cross section with high ball groove shoulders.
Copper alloy: Good formability, thermal conductivity, and high operating temperatures make copper alloy cages a preferred choice for high-temperature applications.
Brass: They offer a heavy-duty solution for applications in high temperatures of up to 250 °C. However, brass cages are not best for high–speed usage.
Zinc-aluminum alloy: Zinc-aluminum alloys have a low density, perform well, and cost less.
Non-Metal Bearing Cages
Non-metal bearing cages are widely used for high-speed applications, especially where metal bearings may be susceptible to corrosion. They are lightweight and elastic, making them the top choice in numerous situations. However, non-metal cages are not suitable for high-temperature usage.
Polyamide: Polyamide nylon is among the top non-metal materials for bearing cages because of its lightweight, self-lubrication, and sliding properties. However, they cannot be operated beyond 120°C and are unsuitable for vacuum applications.
PTFE: Polytetrafluoroethylene, or PTFE, is one of the best non-metal materials for ball bearing cages. It is insulating, non-magnetic, chemical resistant, and hydrophobic. While they are corrosion-resistant, these bearing cages are unsuitable for high-temperature applications.
PEEK: When looking for ball bearings for vacuum applications, PEEK or polyether ether ketone is a preferred material with low particle generation. It is used in hybrid as well as ceramic bearings and resists temperatures between -70°C and +250°C.
Reinforced Nylon: These bearing cages offer better sliding than their steel counterparts and make less noise. However, the temperature limit is similar to polyamide.
Polyethylene: Widely used in 316 stainless steel bearings, polyethylene bearing cages are corrosion resistant with a temperature range of -40°C to +80°C. But, they are preferable for low-speed applications only.
Phenolic Resin: Phenolic resin crown cages made from paper or linen-based phenolic materials provide additional lubrication to the ball bearings. Thus, they offer high wear resistance and strength.
Benefits of Bearing Retainers
- Higher load capacity: The particular shape of ball bearing cages or retainers enables the bearing to handle higher loads.
- Reduced friction: If the bearing cage is absent, the rolling elements will collide with each other, resulting in higher friction. Thus, the ball bearing retainers reduce friction, eventually improving speed and efficiency while minimizing wear and tear.
- Longer life: Ball bearing cages increase the lifetime of bearings by reducing wear and tear and distributing the load uniformly.
- Less noise: Bearing cages reduce vibration by restricting the movement of balls within the structure. Eventually, the noise is also less, especially in non-metal bearings.
- Easy maintenance: Bearing cages are quite easy to remove and replace, allowing you to fix the bearing when needed instead of replacing the whole assembly.
How to Choose a Bearing Cage?
The choice of a bearing cage for a particular application depends majorly on your requirements and the properties of the cage material. Some ball bearing cage materials are suitable for high temperatures, whereas others are preferred for high-speed applications. At the same time, some materials, like non-metal cages, can also help avoid corrosion because of their nature.
Here are the factors to consider when choosing a bearing cage for your needs:
Temperature
When choosing a ball bearing cage, check the material’s temperature resistance to ensure it is best-suited to your particular need. Some perform well at high temperatures, while others are better at low temperatures.
Speed
Other than the temperature, the required speed and the material’s properties must align. Choosing a low-strength material for high-speed applications is not the best pick.
Corrosion resistance
When looking for a bearing cage material for applications with chances of corrosion, it’s better to opt for non-metal ball bearing cages and ensure corrosion resistance.
Load Capacity
The load capacity of the ball bearing cage influences the durability and strength, improving the load capacity.
What Could Cause Damage to a Bearing Cage? (with Solutions)
While ball bearing cages are not fragile, continuous usage can lead to wear and tear. Moreover, the cages may also experience damage and stress if not used properly. Some of the most common reasons for damage to ball bearing cages are:
High friction: High friction in the ball bearing cage due to insufficient lubrication can cause overheating and damage due to wear and tear.
High speed: It’s important to avoid high-speed usage when using a material unsuitable for high-speed applications. High rotational speed or vibration may cause stress and distortion to the cage, leading to failure.
Extra load: An excessive amount of radial or axial loads on the bearing cage can damage it, reducing its efficiency and life.
Misalignment: Misalignment is a common cause of early wear and damage to the ball bearing cage, as it may lead to uneven loading.
Contaminants: Sometimes, contaminants like dust and moisture may enter the ball bearing, leading to corrosion and abrasion within the assembly.
Solutions to Preventing Bearing Cage Damage
- In case of damage due to insufficient lubrication and high speed, provide better lubrication and use adequate material for high-speed applications.
- For damage due to misalignment, check and ensure proper alignment of the housing and shaft.
- Damage resulting from overloading or high vibration must be managed by using adequate ball bearing cage material suitable for high-load applications.
- If your ball bearing cage is eroding because of contaminants or exposure to moisture, use an effective sealing method to seal the assembly properly and avoid further damage. Moreover, corrosion-resistant materials are suggested for such uses.
The Bottom Line
The ball bearing cage is an important part of the ball bearing assembly that ensures the balls roll smoothly within the bearing for maximum functionality. They also help improve the load capacity, improving efficiency and longer life. At the same time, the particular structure keeps the balls restricted, reducing friction between them and ensuring minimal noise production. However, choosing the right ball bearing cage material is critical to high efficiency.
Choose from steel, nonferrous metals, and non-metal ball bearing materials depending on your needs. While metal options are best for high-speed applications, non-metal materials are better suited to applications that involve moisture. Furthermore, you must closely monitor the damage to the ball bearing cage, such as misalignment, overloading, insufficient lubrication, etc. Failure to attend to these issues timely might lead to further damage and replacement of the cage or ball bearing assembly.
We hope this article has helped you understand the different types of ball bearing cages and potential damage. For any further queries, get in touch with our experts!
