Credit: Jeanette Pfeifer of BDS Bearings for original article

Bearings play a pivotal role in the functionality of various machinery and equipment, facilitating seamless movement by minimizing friction between dynamic components. The performance of bearings is significantly influenced by seals, which are essential for preventing contamination, preserving lubrication, and ensuring the structural integrity of the bearing assembly.

Seals function as protective barriers, shielding bearings from external contaminants such as dust, moisture, and debris. A comprehensive understanding of the various seal types utilized in bearings is vital for enhancing machinery efficiency and extending operational lifespan.

 Functions and Importance of Bearing Seals 

• Contamination Prevention: Seals protect bearings from ingress of dust, dirt, water, and other contaminants that can lead to premature wear, corrosion, and reduced performance. 
  
  
• Retaining Lubrication: Seals help to retain the lubricant within the bearing, ensuring proper lubrication for smooth operation and reduced friction between moving parts. 
  
  
• Environmental Protection: Bearings operating in diverse environments, including extreme temperatures or high humidity, rely on seals to maintain their functionality and reliability. 

  

Shield or Metal Seals 

Shields and metal seals are key parts of bearings, offering protection against contaminants and retaining lubrication. Made from durable metal, these seals ensure bearings operate efficiently and last longer.

Shield Design 

Non-Contact Shields (ZZ): Shields, often denoted as ZZ in bearing designations, are typically metal plates that do not make direct contact with the inner bearing ring. They act as non-contact seals and are designed to provide a physical barrier against larger particles, such as dirt, dust, and debris. The space between the shield and the inner ring allows for some ventilation but may not prevent finer contaminants from entering. 

Metal Seals (2RS) 

Contact Seals (2RS): Metal seals, indicated as 2RS in bearings, involve a more direct contact with the inner bearing ring. These seals are designed to create a tighter barrier against contaminants compared to shields. They often utilize a rubber or synthetic material coating to enhance the seal's effectiveness by reducing the gap between the seal and the inner ring, providing better protection against both larger and finer particles. 

Materials Used 

• Steel: The most common material used for shields and metal seals is steel. This material offers durability, strength, and corrosion resistance, making it suitable for withstanding varying operating conditions in different industries. 
• Aluminum: In some applications where weight is a concern or non-ferrous materials are preferred, aluminum shields can be used. Aluminum offers good corrosion resistance and is lighter than steel.
  
  

Functionality and Applications 

 Contaminant Protection 

• Shields: Non-contact shields act as a protective barrier against larger particles and contaminants, reducing the risk of external elements entering the bearing. However, they may not provide the same level of protection against finer particles as contact seals. 
• Metal Seals (2RS): Contact seals provide more comprehensive protection by making direct contact with the inner ring, offering improved resistance against various contaminants, including smaller particles, dust, and moisture. 

Lubrication Retention 

• Both shields and metal seals help retain lubricants within the bearing, ensuring proper lubrication for reduced friction and smoother operation of the bearing components. 

Applications 

• Automotive Industry: Shields and metal seals are commonly used in automotive bearings for wheels, transmissions, and engines to protect against road debris, dust, and moisture. 
• Industrial Machinery: Found in various industrial applications such as pumps, electric motors, and agricultural machinery, shields and metal seals safeguard bearings from contaminants present in manufacturing environments. 
• Household Appliances: Utilized in household appliances like washing machines, dryers, and fans to protect bearings from dust and moisture, ensuring longer service life. 

 

Metal shields and seals play a crucial role in protecting bearings from external contaminants while ensuring that lubrication remains intact. Their construction and materials are specifically designed to form effective barriers suited for various operational environments, making them essential components in numerous industries where the performance and dependability of bearings are paramount.

Rubber Seals 

Rubber seals are primarily composed of synthetic rubber materials, each offering unique properties suitable for different applications. Some of the commonly used rubber materials for seals include: 

• Nitrile Butadiene Rubber (NBR): Known for its excellent resistance to oils, fuels, and greases, NBR is a widely used material in rubber seals, making it suitable for applications where exposure to lubricants is prevalent. 
• Ethylene Propylene Diene Monomer (EPDM): EPDM rubber exhibits superior resistance to weathering, ozone, and UV radiation, making it ideal for outdoor and high-temperature applications.
   
• Fluoroelastomers (FKM/Viton): FKM seals offer exceptional chemical resistance, especially to harsh chemicals, oils, and fuels, making them suitable for demanding industrial environments.

Design and Construction 

Lip Seal Design: 

Rubber seals typically feature a lip or sealing edge that makes direct contact with the shaft, creating a barrier to prevent contaminants from entering the bearing. The lip seal is designed to retain lubricants within the bearing while keeping external elements out. 

Metal Case or Reinforcement: 

Some rubber seals may incorporate a metal case or reinforcement to provide structural support, maintain seal shape, and aid in the installation process. 

Spring or Tensioning Elements: 

To ensure proper sealing and maintain contact with the shaft, certain rubber seals utilize springs or tensioning elements within the seal structure. These elements help maintain the necessary pressure against the shaft to create an effective seal. 

Functionality 

• Contaminant Exclusion: Rubber seals excel in preventing the entry of contaminants such as dirt, dust, water, and other particles into the bearing, thereby extending the bearing life and enhancing performance. 
  
  
• Lubrication Retention: These seals effectively retain the lubricant within the bearing, ensuring proper lubrication for reduced friction and optimal functioning of moving components. 
  
  
• Versatility: Rubber seals are versatile and suitable for various industries, including automotive, aerospace, industrial machinery, and household appliances due to their adaptability to different operating conditions. 

Applications 

• Automotive Industry: Found in wheel bearings, transmissions, engines, and other vehicle components due to their ability to withstand varying temperatures and exposure to oils and contaminants. 
  
  
• Industrial Machinery: Utilized in pumps, motors, gearboxes, and other machinery where protection against contaminants and lubrication retention is critical for smooth operation.
   
• Household Appliances: Used in appliances such as washing machines, dryers, and dishwashers to protect bearings from moisture and debris. 

 

Rubber seals are known for their effectiveness in creating a strong barrier that protects bearings from contamination and helps retain lubrication. Their wide range of materials and designs allows them to adapt to various environmental conditions, making them a popular sealing choice in many industries and applications.

Felt Seals 

Felt seals are a type of sealing mechanism used in bearings and machinery to prevent contamination and retain lubrication. They are known for their simplicity, cost-effectiveness, and capability to maintain a barrier against larger particles and retain lubricants within the bearing assembly. 

Material Composition 

Felt seals are primarily made from compressed felt material, which is typically manufactured from natural or synthetic fibers. The material used in these seals often includes: 

• Natural Fibers: Felt can be composed of wool or a blend of wool and other natural fibers. Wool felt offers good resilience and can retain lubricants effectively. 
  
  
• Synthetic Fibers: Synthetic materials like polyester or polypropylene are sometimes used to create felt seals. These materials can enhance specific properties such as durability, resistance to moisture, and better sealing capabilities. 

Design and Construction 

Felt seals are usually produced by compressing layers of felt material to form a dense and compact structure. The design of the seal involves creating a shape that snugly fits the housing or the space where the seal is intended to be placed within the bearing assembly. 

Lubrication Impregnation 

To enhance their sealing ability, felt seals can be impregnated with lubricants or oils. This impregnation aids in retaining lubrication within the bearing, ensuring smooth operation by reducing friction between moving parts. 

Wicking Action 

One of the key advantages of felt seals is their ability to wick lubricants. The compact, fibrous nature of the felt material allows it to absorb and hold lubricants from the surrounding area or reservoir, ensuring a reliable supply to the bearing when required. This wicking action is vital for keeping lubrication levels adequate within the bearing. 

Functionality 

• Contaminant Exclusion: Felt seals are effective at blocking larger particles such as dust, dirt, and debris, preventing them from entering the bearing area. However, they may not offer the same level of protection against finer contaminants as more intricate seals like labyrinth or Teflon seals. 
  
  
• Lubrication Retention: Their ability to retain lubricants makes felt seals suitable for applications where consistent and reliable lubrication is necessary for smooth bearing operation. 
  
  
• Lower Speed Applications: Felt seals are commonly used in slower-speed applications or machinery where high contamination risk isn't a primary concern but maintaining adequate lubrication is essential. 

Applications 

Felt seals are widely used in industrial equipment, agricultural machinery, and automotive applications, particularly in components like pillow blocks and conveyor rollers.

Their simple design effectively retains lubrication while offering protection against larger particles, making them suitable for lower-speed machinery where fine contaminant protection is less critical.

Felt seals provide a cost-effective solution for maintaining lubrication and shielding against larger debris in less demanding environments. However, for applications requiring higher precision and protection from finer particles, more advanced sealing options may be necessary.

Labyrinth & Teflon Seals 

Labyrinth Seals 

Labyrinth seals derive their name from their intricate design resembling a maze or labyrinth. These seals are characterized by a series of non-contacting paths or channels that form a barrier to prevent contaminants from reaching the bearing. 

Composition 

Labyrinth seals can be made from various materials, including metals like stainless steel or non-metallic materials such as polymers. They are often constructed by machining grooves or channels into the housing or mating components, creating a tortuous path for particles to navigate before reaching the bearing area. 

Functionality 

• Contaminant Exclusion: Labyrinth seals are highly effective in blocking contaminants due to their intricate design, preventing particles from directly accessing the bearing surfaces. 
  
  
• Low Friction: They offer the advantage of minimal contact with the bearing, resulting in lower friction compared to contact seals like rubber or metal shields. This characteristic helps maintain higher efficiency and reduces wear on components. 
  
  
• Adaptability to Harsh Environments: Their ability to resist contamination makes labyrinth seals suitable for applications in harsh environments such as heavy machinery, mining equipment, and industrial settings where exposure to abrasive particles is common. 

 

Teflon Seals 

Teflon seals, also known as PTFE seals, utilize Polytetrafluoroethylene, a synthetic fluoropolymer with unique properties, as the primary material for sealing purposes. 

Composition 

• PTFE: Teflon seals are predominantly made of PTFE due to its exceptional properties, including low friction, chemical resistance, and thermal stability. PTFE is molded or machined to create the seal components. 
  
  
• Fillers and Additives: Depending on specific requirements, fillers or additives may be incorporated into the PTFE to enhance certain characteristics like wear resistance or thermal conductivity. 

Functionality 

• Low Friction: Teflon seals offer remarkable low-friction properties, minimizing heat generation and energy loss, which is critical in high-speed applications. 
  
  
• Chemical Resistance: PTFE exhibits excellent resistance to chemicals, making Teflon seals suitable for applications where exposure to corrosive substances is a concern. 
  
  
• Temperature Stability: They can withstand a wide range of temperatures without losing their sealing properties, making them ideal for applications involving extreme temperatures. 

Application 

Both labyrinth and Teflon seals are commonly used in high-performance bearings where maintaining low friction and preventing contaminants from entering the bearing are essential. 

• Labyrinth Seals: Find applications in high-speed machinery like turbines, pumps, and gearboxes, as well as in industries such as aerospace, where precision and reduced friction are crucial.
  
  
• Teflon Seals: Widely utilized in automotive engines, high-speed machinery, and applications requiring resistance to chemicals or extreme temperatures, ensuring efficient and reliable operation. 

Labyrinth seals excel in their ability to block contaminants with minimal contact, while Teflon seals offer low-friction performance and resilience to various environmental factors, making both types indispensable in diverse bearing applications. The choice between these seals depends on the specific requirements of the application and the operating conditions in which the bearings will function. 

 

Magnetic Seals 

Magnetic seals are specialized sealing devices used in bearings and machinery to prevent the ingress of metallic particles and contaminants. Unlike traditional physical barriers, magnetic seals utilize magnetic fields to attract or repel metallic particles, thereby preventing them from entering the bearing area. These seals are particularly beneficial in applications where metal debris poses a risk to the machinery's performance and longevity. 

Materials Used 

Magnetic seals are primarily composed of materials that can generate magnetic fields or enhance magnetic properties. Some common materials utilized in magnetic seals include: 

• Permanent Magnets: These seals may incorporate permanent magnets made from materials like neodymium (NdFeB), samarium-cobalt (SmCo), or ceramic (ferrite) magnets. These magnets offer strong magnetic fields and can attract ferrous particles effectively. 
  
  
• Soft Magnetic Materials: In some designs, soft magnetic materials such as iron, steel, or certain alloys are used to enhance magnetic flux or guide the magnetic field, improving the efficiency of the magnetic seal.

Design and Construction 

Magnetic Circuit Design 

Magnetic seals are designed to create a magnetic circuit that effectively influences the path of metallic particles away from the bearing. This design comprises specific arrangements of magnets and magnetic materials to ensure a strong magnetic field within the sealing region. 

Field Intensity and Configuration 

The strength and configuration of the magnetic field are crucial factors in the effectiveness of these seals. Engineers design the seals to produce a sufficiently strong magnetic field to capture and divert metallic particles away from the bearing while considering factors like the size and speed of the particles. 

Shielding and Containment 

Some magnetic seals incorporate additional shielding or containment structures to confine and redirect captured metallic particles, preventing them from re-entering the bearing area once attracted by the magnetic field. 

Functionality and Applications 

• Metallic Particle Exclusion: Magnetic seals are highly effective in capturing and preventing metallic particles, such as iron filings or debris from machining processes, from entering the bearing. This prevents abrasion, wear, and damage to critical components. 
  
  
• Maintenance of Bearing Integrity: By reducing the presence of metal contaminants, magnetic seals contribute to the integrity and operational efficiency of bearings, thereby extending their lifespan and reducing maintenance requirements. 

Applications 

Magnetic seals are utilized across a range of industries and machinery, particularly in applications where the presence of metal debris could compromise the integrity and performance of bearings.

• Heavy Machinery and Industrial Equipment: Used in manufacturing plants, mining machinery, and metalworking equipment to protect bearings from metal particles generated during machining or industrial processes. 
  
  
• Automotive Industry: Employed in automotive applications where metal wear particles from engines or transmissions can impact bearing performance and longevity. 
  
  
• High-Precision Machinery: Utilized in precision equipment and high-tech machinery where even minute metallic contamination could compromise performance. 

Magnetic seals present an innovative solution for safeguarding bearings against metallic debris by employing magnetic fields to either deflect or capture contaminants, thus enhancing the performance and durability of machinery and equipment in areas prone to metal particle pollution.

 

Applications of Different Seals in Bearings 

• Metal and rubber seals are commonly used in various industrial applications, automotive machinery, and household appliances where protection against contaminants is critical. 
  
  
• Labyrinth and Teflon seals find applications in high-speed machinery, such as aerospace and automotive industries, where reduced friction and effective sealing are essential. 
• Magnetic seals are often employed in heavy machinery, mining equipment, and industrial settings where metal debris is prevalent.  

 

Nomenclature Designations 

The terminology and classifications employed for bearing seals differ according to industry standards and the specifications set by manufacturers. These classifications are typically standardized to provide precise information regarding the seal's type, material composition, and distinctive characteristics. Below are several prevalent nomenclature classifications for bearing seals:

• RS or 2RS: These designations denote a rubber contact seal. RS typically indicates a single rubber seal on one side of the bearing, while 2RS indicates rubber seals on both sides, providing better protection against contaminants. 
• Z or ZZ: These designations refer to metal shields. Z generally signifies a single metal shield on one side of the bearing, while ZZ indicates metal shields on both sides, offering protection against larger particles but not necessarily providing as much defense against finer contaminants as rubber seals. 
• DDU or 2DU: Commonly used in NSK bearings, DDU designates a contact seal similar to 2RS, providing protection against contaminants on both sides of the bearing. 
• LLU or LLB: Utilized in NTN bearings, LLU refers to a contact seal on both sides of the bearing, while LLB indicates a non-contact seal on both sides. 
• TS or TSS or TSU: These designations are employed in Timken bearings. TS stands for single seal, TSS stands for double seals, and TSU represents triple seals, each offering different levels of protection against contaminants. 
• V or VL or VV: These designations are used by some manufacturers to denote non-contact seals. 
• W or WO or WN: Designations indicating various shield types in some bearing manufacturers' catalogs. 
• C3, C4, C5, etc.: These symbols are not specifically for seals but represent the internal clearance of the bearing. They may sometimes appear alongside seal designations to indicate the bearing's clearance and sealing configuration. 
• Felt Seal: Nomenclature designations for felt seals may not be as standardized or universally recognized across bearing manufacturers compared to rubber or metal seals. Felt seals, due to their simpler construction and application in specific scenarios, might not have widely used or standardized alphanumeric codes or symbols like some other types of seals. Some manufacturers may simply label the seal as a "felt seal" in their product descriptions, specifying its material composition and functionality. 
• F or FS: While less common, a manufacturer might use an abbreviation like "F" or "FS" to indicate the use of a felt seal in their bearing designations. However, this isn't a widely recognized or standardized designation for felt seals across the industry. 
• Felt Material Indication: Instead of using a specific alphanumeric code, a manufacturer might describe the seal material directly as "felt" within the bearing specification to denote the type of seal used. 
• Non-Standard Designations: In some cases, manufacturers might employ internal or proprietary codes to specify the type of seal used, but these codes might not be publicly standardized or widely recognized. 
  

Labyrinth and Teflon seals, akin to felt seals, may lack standardized alphanumeric designations across different bearing manufacturers.  

Labyrinth Seals: 

• L or LB or LAB: Some manufacturers might use abbreviations such as "L," "LB," or "LAB" to indicate the use of labyrinth seals in their bearing designations. However, the use of these specific codes can vary between manufacturers. 
• Labyrinth Designation: Manufacturers may directly mention "labyrinth seal" or describe the seal as having a labyrinthine design in their product specifications to denote the type of seal used. 
• Non-Standard Designations: Certain manufacturers might have internal codes or proprietary identifiers specific to their labyrinth seal designs, but these codes may not be standardized across the industry. 

Teflon Seals: 

• PTFE or TF: Some manufacturers might explicitly use abbreviations like "PTFE" or "TF" to indicate the use of Teflon-based seals in their bearing designations. PTFE is the common abbreviation for Polytetrafluoroethylene, the primary material used in Teflon seals. 
• Teflon Material Indication: Manufacturers may describe the seal's material directly as "Teflon" or "PTFE" within the bearing specification to denote the type of seal used. 
• Non-Standard Designations: Similar to labyrinth seals, manufacturers might have internal codes or proprietary identifiers specific to their Teflon seal designs, but these codes might not be widely standardized across the industry.

Magnetic Seals:

Magnetic seals, owing to their unique characteristics and relatively niche application compared to other seal types, typically lack dedicated alphanumeric codes or symbols specifically assigned to them.

• Magnetic Seal Description: Manufacturers might explicitly mention "magnetic seal" or describe the seal's ability to repel/attract metallic particles due to its magnetic properties within the bearing specifications. 
• Material Composition: In some cases, manufacturers might mention the use of specific magnetic materials, such as mentioning the inclusion of permanent magnets or specific magnetic alloys in the seal design. 
• Magnetic Field Indication: Manufacturers might describe the sealing mechanism based on its ability to create or manipulate magnetic fields to prevent metallic contaminants from entering the bearing area. 
  

Bearing seals are vital for ensuring the performance and longevity of bearings by protecting them from external contaminants and facilitating proper lubrication. The choice of the right seal type is determined by the unique requirements of the application, the surrounding environment, the speed of operation, and the friction levels needed.

By understanding the different seal options, engineers and maintenance professionals can make informed selections that optimize bearing efficiency and extend their service life under various conditions.

Credit: Jeanette Pfeifer of BDS Bearings for inspiration and original article excerpts.