Exploring Varieties and Design Features of Rotary Shaft Seals

Nov 09, Material | LIP Seals | Mechanical Seals

The performance of most industrial processes depends on various scalar and vector quantities such as motion, speed, force, and more, which are based on direction, magnitude, or both. All of these quantities together facilitate the working of any machine or equipment in terms of mobility, movement in a particular direction, and so on. Some of them demand oscillating movements, hydraulics, and continuous rotation to get the desired outcomes. Here, the biggest challenge is that the equipment or machine that oscillates or rotates should be well connected to the fixed portions, well-lubricated, and not cause friction. Additionally, with continuous usage, these parts may get exposed to environmental parameters, such as dust and moisture, which must be prevented. Rotary shaft seals make a significant difference here. Popularly called rotary shaft oil seals, they are used to seal lubrication fluids in these parts, thus increasing their operational life and contributing to the system's overall performance. Today, different types of rotary shaft seals are available in the market. Each is differentiated based on its design characteristics. Are you intrigued to know more about them? If yes, then read this post till the end.

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Understanding Rotary Shaft Seal Types and Their Distinct Design Characteristics

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Here are some common types of rotary shaft seals with their design characteristics.

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1. Radial Lip Seals: These are the most commonly used rotary shaft seals. As the name suggests, they feature a flexible elastomer lip that contacts the shaft. This helps in creating a dynamic sealing interface. Here are some key design characteristics of these seals.
   
   

• Lip Geometry: The lip design can vary depending on the application requirements. Single lips, double lips, and even triple lips are popular options for enhanced sealing performance.
• Spring-Loaded: Many lip seals comprise a spring to ensure constant lip-to-shaft contact, even when there are variations in shaft speed.
• Materials: They are made using materials such as nitrile rubber, Viton, silicone, and polyurethane. The material selection depends on factors such as fluid compatibility, temperature, and chemical resistance.
• Lubrication Grooves: Most lip seals have lubrication grooves on the sealing lip. This maintains a thin layer of lubricant between the lip and the shaft.

2. Mechanical Seals: They find application where leakage control and high performance are paramount. The design characteristics of mechanical seals are as follows.

• Materials: They are made from materials such as ceramic, silicon carbide, carbon, and various elastomers. These materials offer great resistance to heat, wear, and chemical corrosion.
• Stationary and Rotating Components: They consist of stationary and rotating components engineered to create a seal that can withstand high pressures and temperatures.
• Leakage Control: Their robust design and precise manufacturing provide superior control over leakage.
• Applications: These seals are commonly used in compressors, pumps, and other high-performance machinery.

3. Magnetic Seals: They are designed especially for high-speed and high-temperature applications. Here are the design characteristics of magnetic seals.

• High-Speed Capability: They are ideal for high-speed applications such as centrifugal pumps, turbochargers, and more.
• Hermetic Sealing: They provide hermetic sealing, preventing any contamination or leakage.
• Magnetic Coupling: These seals use the principle of magnetic coupling to create a seal without physical contact between the seal and the shaft.
• Low on Maintenance: The maintenance cost of these seals is minimal, reducing the need for regular replacements or servicing.

4. Labyrinth Seals: As the name suggests, these seals have multiple barriers or labyrinths, thus the name. They use a series of intricate paths or channels to deter contaminants and fluids. They don’t create direct physical contact between the seal and the shaft. Here are some key design characteristics of labyrinth seals.

• Multiple Barriers: They have multiple barriers that create tortuous paths. These paths prevent the ingress of contaminants.
• Air or Gas Barrier: They can prevent the passage of air or gas, making them suitable for applications like rotating equipment in power plants.
• Minimal Friction: They introduce minimal friction in the system as there is no direct contact between the seal and the shaft.

5. V-Ring Seals: These seals have a V-shaped cross-section, thus named. This cross-section allows them to confirm the shaft's surface, providing a secure seal. They are self-centering, and auto adjust to changes in the shaft position, which makes these seals a versatile and reliable option in various applications. Here are some design characteristics.

• V-Shaped Cross-Section: The V-shaped cross-section of the seal provides effective sealing while accommodating shaft runout.
• Self-Centering: These seals are self-centering. It means they adjust automatically to the changes in shaft position.
• Low Pressure Sealing: They are ideal for low to moderate pressure sealing applications.
• Wide Range of Sizes: V-ring seals are available in different sizes, making them adaptable to shaft dimensions.

6. Hydraulic Seals: They are crucial components in hydraulic and pneumatic systems. They can prevent the escape of hydraulic fluids while simultaneously avoiding the entry of contaminants like dust and moisture. Here are some key design considerations of these seals.

• Materials: They are made using materials such as nitrile rubber, PTFE, polyurethane, and more. These materials are chosen for their ability to endure challenging operating conditions and compatibility with hydraulic fluids.
• Pressure and Temperature Resistance: They are designed to withstand high pressures and temperature variations, which is common in hydraulic systems.
• Lip and Wiper Seals: These seals include sealing lips to prevent fluid leakage and wiper seals to remove contaminants from the shaft.

7. Cartridge Seals: These specialized sealing solutions find several industrial applications. They are designed to simplify installation, maintenance, and replacement processes. These seals are known for providing high performance for industrial pumps and similar equipment, where reliability and ease of maintenance are paramount. Here are some design characteristics of these seals.

• Self-Contained Unit: Cartridge seals come as a self-contained unit with all the necessary components for sealing.
• Easy Installation: They are easy to install, making them a preferred choice for applications where rapid maintenance is crucial.
• Reduced Downtime: They reduce downtime during seal replacement or servicing.

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Hi, everyone

I am a long time reader but this might be my first post. I am currently in a Senior Design Project and doing research for my project.

I am doing a rotating shaft with flow through the middle of the shaft to a exiting hole on the other side radially out the shaft. ( I can explain more later if needed ) One end of the shaft is enclosed, so it needs to be sealed so no leakage is allowed. It will then exit a meter on the enclosed section.

The requirement that I am looking for is seals for 30k+ RPM. 50-100 psi. This is for the shaft.

I have looked into labyrinth seals and carbon seals. Would this be a right assumption?
Is there any other seals that would do?

Does anyone have knowledge of motors that spin 30k+ RPM?

I was think a gearing up a electric motor or use a air driven motor. The torque that is needed should not be that much since it is not driving anything but the shaft and bearing friction.

Any hints or toward a direction is greatly appreciated.

Thank you for your time.

Al I have pretty good experience with high speed rotating seals. However, I am not quite understanding your layout. I understand that one end of your shaft will have radially spaced holes which the fluid will flow from. However the rest is a bit fuzzy. You say that one end is enclosed, yet you also say this is the end that needs to be sealed?

First off, can you post a picture? Secondly, do you need a face seal or a radial seal? Labby seals will have a characteristic leakage rate associated with them. They are not perfect seals. However, the leakage can be minimized by proper buffering and they can take any speed that you throw at them assuming proper design and material selection. Depending on the diameter of your shaft, I'll bet you that you will not find a radial lip seal that will handle the surface speeds you'll be seeing. Carbon seals are another good option, but your machining and design need to be precise.

Let's get a better picture of what you are doing and go from there.

here is a picture of the item. It is the red part of the picture. The shaft size will be 2.5 inches. Air would be entering the shaft in the middle and exiting out of the green cylinder (thru a venturi, not in pictured). The shaft would be rotating at 30K + rpm. There will be bearings on both sides so the red part is only needed for sealing. I was told that labyrinth seal would work and they are zero contact.

Can I use a grease/crank type seal if possible?

Where can I get more info on labyrinth seals?

Info on 30k+ electric motor with to turn almost a 1-2 pounds at the most?

Info on couplers that can can be connected to the end of this?

It is needed so air can be directed in. So far I just found 2/3k rpm couplers.

The motors that I have found was mostly rc car engines.

Sorry for the newbie questions but my school has limited resources since it has been cutting back and engineering department is on first on the list.

skizm240 said: The shaft would be rotating at 30K + rpm. There will be bearings on both sides so the red part is only needed for sealing. I was told that labyrinth seal would work and they are zero contact.

They are zero contact. However, like I mentioned, they do have an inherent leakage rate associate with them because they are zero contact. If you can run a buffer air source to the labby cavity, that can help tremendously.

skizm240 said: Can I use a grease/crank type seal if possible?

You will never find a lip seal that will handle that surface speed, especially with a Ø2.5" shaft.

skizm240 said: Where can I get more info on labyrinth seals?

Unfortunately, labby seals are in that black area that companies like to keep to themselves. There are a lot of technical papers out there on their analyses and influences on other components.
http://www.gmnbt.com/labyrinth.htm

skizm240 said: Info on 30k+ electric motor with to turn almost a 1-2 pounds at the most?

Oy. You're in trouble. You're going to have to use something like a gear box or air turbine to get those speeds. You can't just slap an electric motor that turns 30 krpm, especially one that is cheap. In this speed range, nothing is cheap.

skizm240 said: Info on couplers that can can be connected to the end of this?

See the response above. At these speeds, you're looking at custom designs. I would suggest starting to do some research with companies like Rexnord and Lovejoy for couplers. Honestly, I would be surprised if you found a large enough coupler to handle those speeds. I know Rexnord makes some nice flexible disc couplers that can do it (their instrumentation coupler line), but not at Ø2.5 ID. I'd sugest you figure out how you're going to turn it at that speed first and then move on the coupler. I am thinking you'll have to go with a splined shaft connecting the two. At least that way you could have a hollow shaft to inject the air through.

I hope you have an adviser that has experience in this area. You're dealing with some serious rotational energy. Have you given any thought to what bearings you'll be using? How about the shaft dynamics of the rotating hardware? How are you going to lubricate this? There are a bunch of other things to look at. I hope your bases are covered. Here a quick update, We came to the conclusion that it is not within our budget to go 30k+.

We were given a electric motor the is rated at 22k ( not sure of the voltage) and electric fan bearings that are sealed and almost matches the speed. The bearings so ceramic type bearings the ID is .47 inch.

Do manufactures give leakage rates through the bearings assuming perfectly sealed on the ID and OD? (leakage rate at a certain pressure though the inside of it)

And for the sealed bearing gurus, Does anyone know of a sealed ball bearing 2.5ID that can go 30k at room temp, for a 1 to 2 min, the loading is minimal? ( I am just asking again because there might be a item that could work under these conditions)

Thank you
Engineering in Training
Al