Bearing Seal Types & How to Select the Best

Whether you’re working with roller bearings, stainless steel ball bearings, or spherical roller bearings, bearing seals play an essential role in machinery. They serve as protective barriers and help extend the bearing's service life, while also promoting smoother and more efficient operation. This article will dive into the diverse range of bearing seal types to guide your decision-making process.

What are Bearing Seals?

Bearing seals are components used to protect bearings by keeping out contaminants like dirt, dust, and moisture, while retaining lubricants inside. This helps extend bearing life and maintain reliable performance. The right bearing seal is chosen based on several factors, such as operating conditions, speed, and environment, similar to how bearing numbers help identify the correct bearing type.

Types of Bearing Seal Designations

There are two kinds of bearing seals: contact and non-contact. While both are essential in machinery, they serve different purposes and are designed for varying types of bearings and applications.

Contact Bearing Seals

Contact seals are a type of seal where the edge of the seal physically touches the inner raceway of the bearing. This contact creates a small barrier that helps keep lubricant inside and blocks out dirt, dust and other harmful contaminants.

Contact Bearing Seals

Advantages

• Superior sealing efficiency
• Versatility
• Resilience to harsh conditions

Limitations

• Friction and heat generation
• Potential for wear and tear
• Speed limitations

Main Types

• Lip Seals: These seals have one or more lips making contact with the surface to create a seal.
• Face Seals: These are typically composed of two flat surfaces that are pressed together to form a seal. They can handle high pressures and are often used in hydraulic systems.

Manufacturer Series Comparison for Contact Seals

Different manufacturers assign unique model series to their contact sealed bearings:

(1) NTN/TPI: LLU，LLH，LLE，LLU-X

• LLU: Exerts notable contact pressure on the bearing's inner raceway, providing excellent sealing at the cost of increased friction and heat.
• LLH: Light-contact seals offering a balance of speed and protection. They provide superior dust protection, water resistance, and surpass LLU-type bearings in high-speed performance.
• LLE: Features a unique water-resistant rubber seal with a three-lip design, making them ideal for applications prone to water or fluid exposure.
• LLU-X: Synthetic rubber contact seals ensure robust resistance to dust and water, with medium torque. Ideal for highly contaminated environments or when bearing replacement is challenging.

(2) NSK: DDG，DDU，DDW

• DDG: Features double contact seals for superior dustproofing. Ideal for dusty or muddy environments.
• DDU: Featuring double contact seals, these offer robust contamination protection and are suited for moderate speeds and temperatures.
• DDW: Combining double contact seals with a filling slot, these enable high-speed rotation and robust sealing. They are ideal for high-contamination risk scenarios.

(3) FAG: 2RS, 2RS1

• 2RS: Standard seals are commonly made of nitrile/BUNA-N rubber and bonded to a metal washer. For high-temperature applications, PTFE or Viton seals are available. At temperatures below -40°C, PTFE seals or metal shields offer better performance due to the stiffening of nitrile rubber and Viton. These seals produce much higher frictional torque than shields. 

 For differences about shields and seals, please see the blog “Shielded Vs Sealed Bearings”.

• 2RS1: Boasting reinforced synthetic rubber seals with steel reinforcements, these enhance durability, making them suitable for use in harsh, high-wear environments.

Non-Contact Bearing Seals

Non-contact seals operate without physical contact with the corresponding rotating part. They form a slight gap between the seal and the running surface.  

Non-contact bearing seals

Benefits

• Lower friction
• High-speed compatibility
• Good contaminant exclusion
• Minimal wear

Limitations

• Less effective sealing 
• Not suitable for contaminated environments

Main Types

• Gap Seals (or Clearance Seals): They maintain a small radial gap with the shaft, using fluid dynamics to resist contaminants and retain lubricant.
• Labyrinth Seals: This "maze" effect creates a complex pathway for contaminants to traverse to reach the bearing. They are normally used with rolling or sleeve bearings, and with oil or grease lubrication.

Manufacturer Series Comparison for Non-Contact Seals

Different manufacturers assign unique model series to their non-contact sealed bearings, such as: 

• LLB (NTN): The outer ring is designed with synthetic rubber that is molded onto a steel plate. The seal's edge aligns with the V-groove on the surface of the inner ring, forming a labyrinth clearance.
• VV (NSK): VV series bearings feature non-contact rubber seals on both sides and maintain a standard radial internal clearance, ensuring effective operation while minimizing friction.
• RZ (SKF): The integral sealing can significantly prolong bearing service life because it keeps lubricant in the bearings and contaminants out.
• 2RU (SMB): Excels in high-speed, low-torque situations, offers better protection than metal shields, but lacks the sealing efficacy of contact seals. 

Materials of Bearing Seals

The table below illustrates common materials of bearing seal types, their temperature tolerances, and key characteristics:

Selecting the Right Bearing Seal

To select the right bearing seal, particularly when developing custom bearings, you have to consider the following factors:

• Application: Assess speed, bearing loads, temperature, lifespan.
• Environment: Determine the conditions where the seal will function—whether clean or contaminated, dry or wet.
• Corrosion: Identify the type of contaminant (dust, water, corrosive substances) the seal must protect against.
• Lubrication: Ascertain the lubrication needs, including retention of grease or oil, and the ability to purge and replace bearing lubricants.
• Seal Type: Opt for contact seals for more protection but higher friction in low-speed settings, or non-contact seals for lesser heat at high speeds.
• Application-Seal Matching: Align seal with the bearing unit and machinery needs.

Maintenance and Replacement

Even the best ball bearing seals require upkeep to sustain maximal bearing life and high performance. Proper maintenance and timely replacement help to make sure the seals continue protecting against contaminants and retaining lubrication, which helps preserve the health of the bearing and surrounding components.

Maintenance and Inspection

• Regularly inspect seals for wear, leakage, or damage.
• Maintain cleanliness and perform required lubrication.
• Monitor bearing temperature and noise for potential issues.

Replacement Procedures

• Verify that the seal is the issue before replacement.
• Choose the correct new seal based on specifications and conditions.
• Use proper tools to remove old seals and install new ones.
• Post-installation, test for proper functioning.

Maximize Bearing Seal Performance with the Right Sealing Solutions

Understanding and selection of appropriate bearing seal types are crucial for maximizing machinery performance and lifespan. This choice should consider factors like the bearing application, operating environment, potential contaminants, and lubrication needs.

Keep in mind, consistent maintenance and timely replacement of these seals are key to sustaining their benefits. The efficiency of your machinery significantly hinges on the informed selection and handling of bearing seals.