Introduction: The Importance of Bearing Seals
Sealings are a crucial factor for the performance and lifespan of rolling bearings, especially ball bearings. They serve two main functions: they prevent the escape of lubricants and protect the bearing from the ingress of contaminants that can lead to premature failure.
In this comprehensive guide, you will learn everything about sealed ball bearings, the different seal types such as 2RS and ZZ, their characteristics, applications, and selection criteria for your specific requirements.
Why Seals for Ball Bearings are Indispensable
Without proper seals, a ball bearing can fail quickly. Here are the main reasons why seals are indispensable:
- Lubricant retention: Prevents grease or oil from escaping
- Protection against contaminants: Keeps dust, dirt, and moisture away
- Extended service life: Reduces wear and maintenance costs
- Operational safety: Minimiert das Risiko ungeplanter Ausfälle
If contaminants enter a ball bearing, it can lead to the following problems:
- Increased running noises due to particle indentations
- Progressive wear with reduced running accuracy
- Disruption of lubrication
- Acceleration of corrosion processes
The three main categories of bearing seals
Bearing seals are divided into three main categories: non-contact and contact seals. Each has its specific advantages and disadvantages.
1. Metallic cover discs (Z, ZZ)
The ZZ seal is one of the most popular non-contact seal types for ball bearings. These metal discs protect the bearing without touching the inner ring.
Properties:
- Z: one-sided metal disc
- ZZ: double-sided metal discs
- Leaves a small gap to the inner ring
- Provides a touch-free protection
Advantages:
- Ideal for high speeds
- No temperature increase due to friction
- Simple shielding against dust
- Low motion resistance
Disadvantages:
- Limited protection against dirt
- No sealing against liquids
- Not suitable for rough environments
Typical Applications:
- Electric motors
- High-precision devices
- Clean operating environments
- Applications with high rotational speeds
2. Touching Poems
Rubber contact seals (RS, 2RS, RSR)
The 2RS seal belongs to the contact seal types and offers significantly better protection than ZZ seals.
Properties:
- RS: single-sided rubber contact seal
- 2RS: double-sided rubber contact seals
- Contact lips made of elastomer
- Physical contact with the inner ring
Advantages:
- Excellent protection against contamination
- Effective fat retention
- Sealing against splash water
- Robust solution for challenging environments
Disadvantages:
- Generates friction and heat
- Reduced speed capacity
- Higher energy consumption
- Wear of the sealing lip over time
Typical Applications:
- Agricultural equipment
- Construction machinery
- Vehicle wheel bearing
- Applications with moderate to heavy contamination
3. Non-Contact Seals
Gap Seals (Gap/Clearance Seals)
Gap seals operate through a small radial gap between the seal and the shaft. They utilize fluid dynamic effects to provide a certain level of protection.
Advantages:
- Practically no friction
- Enable maximum speeds
- No heat generation
- No wear parts
Disadvantages:
- Only minimal protection against contamination
- No sealing against liquids
- Only suitable for very clean environments
Typical Applications:
- High-precision instruments
- High-speed applications
- Cleanroom applications
Sealing materials: The right material for every application
The choice of the right sealing material is just as important as the choice of the sealing type. Here is an overview of the most common materials for ball bearing seals:
Materials at a glance:
Nitrile rubber (NBR)
- Temperature range: -40°C to 110°C
- Main properties: Good resistance to oil, certain chemicals and wear
- Typical applications: Standard applications, automotive industry, general engineering industry
Acrylonitrile butadiene rubber (NBR/Buna-N)
- Temperature range: -40°C to 100°C
- Main properties: Oil resistance, good wear resistance
- Typical applications: Hydraulic applications, oil environments, agricultural equipment
Fluororubber (FKM/Viton)
- Temperature range: -40°C to 230°C
- Main properties: Good resistance to high temperatures, oil and chemicals
- Typical applications: High temperature applications, chemically demanding environments
Polytetrafluoroethylene (PTFE)
- Temperature range: -190°C to 250°C
- Main properties: High temperature stability and excellent chemical resistance
- Typical applications: Chemical industry, food industry, extreme temperature ranges
Polyetheretherketone (PEEK)
- Temperature range: -70°C to 250°C
- Main features: High temperature stability and chemical resistance
- Typical applications: aerospace, high-temperature applications
Metal (for cover discs)
- Temperature range: Total storage temperature range
- Main features: Very durable, no aging, no wear in contactless design
- Typical applications: high-speed applications, clean environments, electric motors
Gasket selection: How to make the right choice
When selecting the right seal for your ball bearings, you should consider the following factors:
1. Speed requirements:
- Maximum RPM: Gap seals
- High speed: Z/ZZ
- Medium/low speed: RS/2RS
2. Ambient conditions:
- Very clean environment: gap seals or Z/ZZ
- Heavily soiled / damp: RS/2RS
3. Temperature:
- Very high Temperatures (>200°C): PTFE/PEEK
- High Temperatures (100-200°C): FKM/Viton
- Standard temperatures (<100°C): NBR-Seals
4. Lubricant:
- Grease lubrication: RS/2RS seals for better retention
- Oil lubrication: Special sealing solutions required
5. Maintenance intervals:
- Lifetime lubric: Fully sealed 2RS ball bearings
- Regular Maintenance: Z/ZZ for easier access
Development of seals for special applications
In certain applications, it may be necessary to remove the seals of a ball bearing:
Reasons for the expansion of seals:
- Re-lubrication: With prolonged operation, it may be necessary to re-lubricate ball bearings. In this case, seals can be carefully removed to gain access to the rolling elements.
- Conversion to open bearings: In certain applications, especially at high speeds and in controlled environments, an open bearing without seals may be the better choice.
- Cleaning: In the case of heavily soiled bearings, temporarily removing the seals can facilitate thorough cleaning.
Procedure for Expansion:
- Tool selection: Only use appropriate tools that do not damage the surfaces (e.g., plastic tools or special seal pullers)
- Cautious Levering: Carefully lift the gasket evenly at several points
- Avoiding Damage: Special care with the metal cover (ZZ), as it can easily bend
Important Notes:
- No reusability: Removed seals, especially RS/2RS, generally cannot be reliably reinstalled and lose their sealing effectiveness.
- No exchange possible: Unlike larger industrial bearings, the seals in standard ball bearings cannot be replaced with new ones.
- Consider consequences: After the removal of the seals, adequate dirt protection and regular lubrication must be ensured
Frequently Asked Questions about Sealed Ball Bearings
What does "2RS" mean in ball bearings?
The designation "2RS" stands for double-sided Rubber Seal. These ball bearings have a contact rubber seal on both sides, providing excellent protection against contamination and moisture.
Are ball bearings with 2RS seals waterproof?
2RS seals provide good protection against splashes and moisture, but they are not completely waterproof. They can withstand short-term contact with water, but they are not suitable for permanent underwater use.
Can ZZ ball bearings be used in dusty environments?
ZZ ball bearings provide only limited protection against dust and are not ideal for moderately dusty environments. For such applications, 2RS ball bearings are the better choice.
Conclusion: The right seal for optimal bearing performance
The choice of the right seal for your ball bearings is crucial for their performance and lifespan. While ZZ seals are ideal for high-speed applications in clean environments, 2RS seals provide superior protection in demanding, contaminated, or humid environments.
Always consider the specific requirements of your application: speed, environmental conditions, temperature, and required maintenance intervals. With this knowledge, you can select the optimal sealing solution for your ball bearings, thereby maximizing their lifespan and minimizing downtime.
High-quality ball bearings with the right sealing solution are not a cost center, but an investment in the reliability and efficiency of your machines and systems.