Sealing 101: Everything You Need to Know to Pick the Right Seal

Are you asking yourself what is a seal, and where do I find them? Today we're hopefully going to bring more clarity than Google when you search for "seal" which brings up cute animals and a British singer. Many people have heard of O-rings but many never realize that there are so many other important seals beyond a simple O-ring.
 
Seals are one of the most critical components that most people wouldn’t even think twice about. You can find seals in almost any application where you need to prevent leakage of liquids, or gases escaping or prevent outside contaminants such as dirt getting into the equipment.
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Where do I find seals?

So when I go visit my customers do they have seals in their equipment? In most cases, it will be yes because seals are one of the most critical components in equipment to prevent leaks, contamination, and damage from exposure to the environment.

​Some common examples of where you find seals would be in a shaft of hydraulics or pneumatics, pumps, engines, rollers at a steel mill, compressors, or preventing leaks at a chemical plant. The places where you find a seal are truly almost limitless, the easiest way to think of it is anywhere a liquid, gas, or solid could escape or get into the equipment there will be a seal ensuring safe and reliable operation.
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Types of seals

Okay so I can find these seals almost everywhere but what types of seals are in that equipment? Well, seals can be broken down into two main categories, static seals and dynamic seals. Static seals are found in mating glands where there is no motion on the sealing surface. Dynamic applications are used to create a barrier between a static and a moving surface. These seals are used to retain fluids, pressure and remove contaminants most commonly used in linear, oscillating, and rotating applications.
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Static seals

• O-rings: These are one of the most common seals that you can find anywhere because of the diversity of applications where they are utilized. O-rings are the most simple seal you can find on the market because it is a simple circle designed to seal around mechanical components or fill spaces along groves to prevent leaks. Due to the huge range of applications, you may find an O-ring in a massive range of sizes, materials, and hardness.
• Clamp Seals: Clamp seals are most commonly used to maintain hygienic standards during the manufacturing process in applications such as dairies, distilleries, bakeries, breweries, or other food and beverage production facilities.
• Gaskets: Gaskets are used to fill the space between mating components and prevent leakage between the two objects while under compression. These are extremely common seals to find in applications that don’t come into contact with movement such as a pipe fitting.

Dynamic seals

• Oil seals: Also called radial shaft seals are used in dynamic applications to keep oil, grease, and other harsh chemicals leaking out of moving applications. An oil seal consists of a metal case and rubber sealing lift that fits closely around the shaft. The rubber lip creates a barrier that prevents oil and other fluids from leaking and causing damage.
  Fluid power seals: are most commonly used in hydraulic and pneumatic applications and are designed to prevent fluids or gases from leaking into or out of the system. The most common fluid power seals are piston and rod seals.
• Other dynamic seals:
  • Rotary seals
  • U-cups
  • V-rings
  • Wipers
  • Guide rings

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Common sealing materials

There are truly a massive amount of different sealing materials and compounds but below are some of the most common you will see utilized.

• NBR (Nitrile Butadiene Rubber)
• FKM (Fluoroelastomer) 
• PTFE (Polytetrafluoroethylene)
• FFKM (Perfluoroelastomer)
• HNBR (Hydrogenated Nitrile Butadiene Rubber)
• Silicone

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Selecting the right seal

Selecting the right seal is critical to ensuring the efficient operation of equipment. When selecting what material to use in your application seal there are a few key aspects to consider.
 
The first thing to consider when selecting what seal is right for you is to know what the temperature range will be for the application. Every sealing material has a unique range of temperatures it performs best, and extreme heat, cold, or fluctuations affect the materials differently. It is critical to ensure the seal can perform in the temperatures you will be subjecting it to avoid a sealing failure and ensure it operates efficiently.
 
Next, you need to consider the environment that the seal will be in because this could greatly affect the lifespan or even cause a seal failure if the wrong material is utilized. You need to consider the pressures, chemicals, and outside environment such as exposure to sun, dirt, or water. Just like temperature certain materials perform excellently in certain chemicals but can begin to break down when subjected to the wrong contaminants.
 
You also want to consider what unique needs your industry requires. For example, if you are manufacturing pharmaceuticals or food and beverages you can’t just use any seal off the shelf. You need to take extra care in ensuring you are utilizing hygienic FDA seals to ensure you comply with the regulation.
 
We know that selecting the right seal is an incredibly important decision that isn't always easy without specialized knowledge. As a company that specializes in seals and sealing technology our experts at Freudenberg-NOK are here to support our partners at Fastenal, and your customers find the ideal seal for their unique needs.
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​Content originally from Freudenberg-NOK Industrial Services. Reused here with permission.

Skeleton oil seals, also known as radial shaft seals or lip seals, are crucial components used to prevent leakage of lubricants and protect mechanical systems from contaminants like dust, dirt, and moisture. These seals are widely used in industries like automotive, machinery, and manufacturing, and choosing the right oil seal is essential for optimal performance and longevity. Here's a detailed guide to help you choose the correct skeleton oil seal for your specific application.

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1. Understand the Application Requirements

The first step in choosing a skeleton oil seal is to fully understand the specific application for which it will be used. Factors like operational speed, temperature, pressure, and the type of fluid being sealed are important considerations.

- Operating Conditions: Determine the environment in which the oil seal will operate. Consider exposure to extreme temperatures, the presence of chemicals, and whether it will be used indoors or outdoors.

- Fluid Type: Identify the type of fluid the seal will be in contact with. This could include oils, grease, or other types of lubricants. Ensure the seal material is compatible with the fluid.

- Pressure and Speed: Know the maximum operating pressure and rotational speed of the shaft. Some seals are designed to handle high-pressure environments, while others are suitable for low-pressure applications.

Rubber Skeleton Oil Seal

2. Select the Right Seal Material

Skeleton oil seals are available in various materials, each with specific properties that make them suitable for different applications. The choice of material is critical as it affects the seal's resistance to heat, chemicals, and wear.

- Nitrile Rubber (NBR): The most common material for oil seals, NBR offers excellent resistance to oil and abrasion. It is suitable for temperatures ranging from -40°C to +120°C and is ideal for general-purpose sealing in industrial and automotive applications.

- Fluorocarbon (Viton): Viton seals offer higher resistance to heat and chemicals, making them suitable for high-temperature applications (up to 200°C). They are also resistant to a broader range of chemicals and are ideal for use in environments with aggressive fluids.

- Silicone Rubber: Silicone seals offer good flexibility at both high and low temperatures, but they are not as resistant to oil as NBR or Viton. Silicone is often used in applications where temperature resistance is more important than oil resistance.

- Polyurethane (PU): Known for its exceptional wear and abrasion resistance, polyurethane is often used in applications where the seal is exposed to high levels of friction and stress.

- PTFE (Teflon): PTFE oil seals offer excellent chemical resistance and operate well in a wide temperature range. They are commonly used in applications involving aggressive fluids or extremely high temperatures.

Rubber Skeleton Oil Seal

3. Choose the Right Lip Design

The lip design of the oil seal plays a crucial role in how well it prevents leakage and withstands pressure. Skeleton oil seals are available in different lip designs to suit varying applications.

- Single Lip (SL): Single-lip oil seals are designed to prevent leakage from the inside of the system. These are commonly used in general sealing applications where there is low pressure and no external contaminants.

- Double Lip (DL): Double-lip oil seals have an additional lip that provides extra protection against external contaminants like dust and dirt. These seals are ideal for outdoor applications or where the system is exposed to debris.

- Triple Lip (TL): These seals are used in heavy-duty applications where both high pressure and exposure to contaminants are concerns. The additional lips provide a more secure seal and extended durability.

4. Consider Seal Dimensions

Getting the correct size is essential to ensure a proper fit and effective sealing. Skeleton oil seals are typically specified by their inner diameter (ID), outer diameter (OD), and thickness or width.

- Inner Diameter (ID): This is the diameter of the shaft on which the seal will be installed. Measure the shaft accurately to avoid leakage or seal damage.

- Outer Diameter (OD): This is the diameter of the bore or housing where the seal will be installed. The outer diameter should be slightly larger than the bore to create a tight fit.

- Width: The width of the oil seal should match the depth of the groove or housing where it will be seated. An incorrect width can lead to misalignment and inadequate sealing.

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It's important to follow the manufacturer’s specifications for the proper size. Using calipers or other precise measuring tools can help ensure an accurate fit.

Rubber Skeleton Oil Seal

5. Check for Operating Temperature Range

The temperature range that the oil seal will be exposed to is another key factor. If the temperature exceeds the seal's capacity, it can lead to degradation, hardening, or softening of the seal material, leading to premature failure.

- Low Temperatures: For cold environments, choose materials like silicone that remain flexible even at low temperatures. NBR seals can handle cold temperatures but are not as effective in extreme cold.

- High Temperatures: For high-temperature applications, consider materials like Viton or PTFE that can withstand heat without losing their sealing properties.

Always ensure the material and design you select are capable of operating at the upper and lower limits of your application’s temperature range.

6. Verify Pressure Handling Capability

While most skeleton oil seals are designed for low-pressure applications, some seals are specifically designed to handle moderate to high pressure. If your application involves significant pressure levels, be sure to choose an oil seal that can withstand the force without failing.

- Low-Pressure Seals: For most general-purpose applications, standard skeleton oil seals can handle low pressures effectively.

- High-Pressure Seals: For higher-pressure environments, choose seals with reinforced lips or specialized designs that can handle the extra force.

7. Review Shaft Surface and Speed

The condition and speed of the shaft on which the oil seal will be mounted directly impact the seal’s performance. A worn or rough shaft surface can quickly damage the seal, leading to leakage.

- Shaft Surface: Ensure the shaft surface is smooth and free from grooves, scratches, or other imperfections that can compromise the seal. A polished shaft is ideal for maximizing the lifespan of the oil seal.

- Rotational Speed: Oil seals are designed to handle certain speeds. High-speed shafts require seals that can withstand the friction generated by rapid rotations without overheating or wearing out quickly.

8. Evaluate Dust and Contaminant Exposure

If your application is exposed to harsh environmental conditions, dust, or debris, consider using double-lip or triple-lip skeleton oil seals. The extra lips provide additional protection, preventing contaminants from entering the system and compromising the lubrication.

For heavy-duty applications, seals with dust flingers or wipers may also be an option to keep contaminants at bay.

9. Look for Additional Features

Some skeleton oil seals come with extra features designed to enhance performance and durability, especially in demanding applications. These include:

- Spring-Loaded Seals: Some seals feature a spring that helps maintain a tight fit around the shaft, ensuring consistent pressure and preventing leaks, even as the seal wears down over time.

- Labyrinth Seals: These seals have a unique design that provides extra resistance to contaminants, making them ideal for applications involving extreme dirt or dust exposure.

10. Consider the Cost and Availability

Finally, when choosing a skeleton oil seal, consider both the cost and the availability of spare parts. While it’s important not to compromise on quality, balance your budget with the specific needs of your application. Additionally, ensure that replacement seals are readily available for maintenance purposes.

Conclusion

Choosing the right skeleton oil seal involves understanding your application’s specific requirements, including the environment, shaft speed, pressure, and type of fluid being sealed. Consider the material, lip design, and seal size carefully, and ensure that the seal you select is suitable for the operating conditions. A high-quality, well-chosen skeleton oil seal will ensure efficient operation, extend the lifespan of your machinery, and reduce downtime due to leaks or failures.

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