The Role of Oil Seals in Machinery and Applications

Oil seals, also known as rotary shaft seals or grease seals, are vital components used in various machinery and industrial applications. These seals play a crucial role in preventing the leakage of lubricants, such as oil or grease, and protecting vital components from contaminants and debris. This article delves into the significance of oil seals, their types, materials, and their widespread usage across industries.

Understanding Oil Seals

Oil seals are specialized devices designed to retain lubricants within a system while excluding external contaminants. They are commonly used in rotating or reciprocating shafts, ensuring efficient operation and reduced friction. By maintaining the lubrication levels, these seals extend the lifespan of mechanical components and prevent premature wear and tear.

Construction and Components

Typically, an oil seal consists of three main components:

a) Metal Case: The outer metal casing provides structural support and protects the seal's internal components from external pressures and environmental conditions.

b) Elastomer (Rubber) Seal: The elastomer or rubber lip is the primary sealing element of the oil seal. It forms a tight seal around the shaft to prevent lubricant leakage and the entry of contaminants.

c) Spring: Positioned behind the rubber lip, the spring exerts constant pressure, ensuring the seal remains in contact with the shaft, maintaining an effective seal.

Types of Oil Seals

There are several types of oil seals available, each catering to specific application requirements. Some common types include:

a) Radial Oil Seals: These are the most widely used oil seals, primarily employed in rotary shaft applications. Radial seals can be further categorized into single lip, double lip, and multiple lip seals, depending on the level of sealing needed.

b) Axial Oil Seals: Unlike radial seals, axial seals are designed to seal along the axis of a rotating shaft, preventing axial leakage of lubricants.

c) V-Rings (V-Seals): V-rings are specialized oil seals with a V-shaped cross-section. They are suitable for sealing applications where conventional radial seals might not be effective.

d) Cassette Seals: Cassette seals are pre-assembled units that include multiple sealing lips and protection against contaminants, making them ideal for challenging environments.

Material Selection

The choice of material for oil seals is crucial as it directly impacts the seal's performance and longevity. Commonly used materials include:

a) Nitrile (NBR): Nitrile rubber is a versatile material known for its excellent resistance to oil, water, and many other fluids. It is a popular choice for general-purpose oil seals.

b) Fluoroelastomer (FKM/Viton): FKM offers superior resistance to high temperatures, chemicals, and various fuels, making it suitable for applications in demanding environments.

c) Polyacrylate (ACM): ACM exhibits excellent resistance to mineral oils, making it suitable for automotive and industrial applications.

d) Silicone (VMQ): Silicone rubber is ideal for extreme temperature applications, maintaining flexibility at both low and high temperatures.

Applications of Oil Seals

Oil seals find widespread applications across various industries, including:

a) Automotive: In engines, transmissions, axles, and other critical automotive components, oil seals prevent lubricant leakage and the entry of contaminants, contributing to the efficiency and longevity of the vehicle.

b) Industrial Machinery: Oil seals are used in pumps, gearboxes, motors, and other rotating equipment to ensure smooth operation and prevent costly breakdowns.

c) Aerospace: In aircraft engines and various aviation systems, oil seals play a crucial role in maintaining optimal performance and safety.

d) Marine: Oil seals are utilized in ship propulsion systems, ensuring smooth operations in harsh marine environments.

Oil seals are indispensable components in a wide array of machinery and industrial applications. By providing effective sealing, they help prevent lubricant leakage, reduce friction, and protect critical components from contaminants. Proper selection of oil seal types and materials ensures optimal performance and extends the lifespan of the equipment, making them a fundamental element in modern engineering practices. As technology continues to evolve, oil seal designs and materials will likely improve, further enhancing their role in various industries.

One of the main principles of power transmission is consistent lubrication. Shaft seals play a hugely important role in this. Imagine a situation involving a shaft-mount reducer – electric motor prime mover, driven by belts, motion controlled by a torque arm – with an improperly seated seal. A blown-out input shaft seal is a nightmare situation, necessitating an entire breakdown and reassembly, not to mention re-aligning and re-tensioning the belts.

The oil seal is our first line of defense in regards to keeping lubrication inside the reducer. It might also be described as the last line of defense – keeping contaminants outside the reducer where they belong. The average seal is incredibly simple in design – made up of a case, a lip or lips, and frequently a garter spring. Of course, some are exponentially more intricate and are manufactured with unusual materials, but the majority are straightforward.

The care taken during the installation process will pay off by allowing the seal to work quietly and operate efficiently behind the scenes of your application.

Prepping for Oil Seal Installation

Before you begin the installation process for any power transmission component, the first goal is making sure everything is clean and free of any material flaws such as nicks, burrs, scratches, dents, et cetera. Most of these components have very tight tolerances, so maintaining this accuracy is important in their performance. This is especially critical for oil seals because of their function.

Begin with a thorough inspection of all involved surfaces: shaft sealing surface and housing bore, seal lip(s), and outside diameter. Maintaining the integrity of the sealing lips is “Priority 1″. The slightest tear or nick can develop into a more significant issue during operation.

Over time, the seal lip(s) will wear a shallow groove into the shafting due to the pressure the seal imposes upon it. Visible scoring on the shaft indicates a genuine possibility that the seal will not perform as well as intended. The potential for lubricants leaking out and particulates working their way through the seal drastically increases when placed over a worn location.

There are a few options to remedy this situation:

• Using a spacer to move the seal forward is a possibility, assuming there is enough room in the housing bore to allow a shift. Ideally, the seal outside diameter (OD) should be in full contact with the housing.
• There are also shaft repair sleeves that can add a “new surface” to the shaft. Measuring a few thousandths of an inch in thickness, they cover shaft flaws so the seal can make proper contact with the surface.
• Probably the least appealing solution is to either replace or refinish the shafting. In some cases, this is not possible; in others, it could benefit the application in the long term.

Which option is best? This decision is left entirely to you. Whatever solution you choose, the seal needs a proper fit to function.

With the application cleaned and the components ready, you’ll begin your installation.

Oil Seal Installation

Many seals come with a garter spring, found within the backside of the seal. It provides contracting pressure against the sealing surface. Making sure the spring seats correctly within the seal is an excellent first step.

Next, apply a small amount of grease to the seal lip(s) and the area of the shaft in contact with the seal.  When using a double-lip seal, fill the small cavity between the two lips with grease as well. This both protects the lips during initial installation and break-in, and also acts as another barrier keeping contaminants out. When installing rubber-coated seals, apply lubricant to the outside diameter as well. This will help prevent the seal from rebounding or backing out from its mounting place.

Orient your seal the same way as the initial install. The sealing lip should face the lubricant that requires sealing. The second lip on a double lip oil seal is intended as a dust lip. The seal must be installed at a 90°, or perpendicularly, to both the shaft and housing bore. This is an issue in cases where the housing does not have a counterbore or shoulder the seal can seat up against.

When a seal is angularly misaligned – or cocked on the shaft – an irreversible process begins. Excessive pressure on one section of the seal, when not installed properly, can cause the spring to become dislodged or the seal to heat up and become brittle through excessive wear, both leading to a premature failure.

Some Tools Required During Installation

In situations where the shaft has splines or an integral gear on the end, you’ll want to take precautions. These gears and splines often have very sharp edges that are quite detrimental to the seal’s integrity. You may use an installation sleeve that will allow the seal to slide past these hazards undamaged.

The last step involves the actual pressing-in of the seal. There are tools and tool kits available that can help with seal installation. Their biggest benefit is that they apply a very uniform force to the seal case, eliminating the possibility of the seal seating in any way other than flush.

If these specific tools aren’t available, it’s entirely possible to correctly seat an oil seal in its housing using a hammer. Ideally, this hammer will be plastic or rubber due to it’s more forgiving nature. Using this and a strike plate that covers the entire seal will lend you accuracy while driving it in. The downside to this method is the inability to drive the seal any further than the strike plate will allow.

The small little oil seal has an outsized role in power transmission.

Proper techniques and diligence during oil seal installation will result in what seems like an unremarkable situation – a component holding its lubrication. When something you’ve installed works effectively and quietly, you know you’ve done it right.

Want to find an oil seal or shaft repair sleeve for your application? Visit the Durus website.