Gearbox Sealing Solutions: How a Little Component Does a Big Job

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lip seal
sealing systems

Drive Sealing Systems

One of the most critical pieces of any gearbox system is the shaft seal. These under-appreciated gearbox components are essential for long term, leak-free operation, and have a surprising impact on thermal performance as well.

Longer lip seal life results in longer life of the drive system, less unplanned downtime, and a lower incidence of drive failure. Here’s why the lip seal is a key component of your gearbox.

Why the Lip Seal is Critical

A lip seal is simply a little bit of rubber holding lubrication in place to lubricate rotating components. Still, this small piece of rubber serves a critical role in your gearbox operation.

Almost every gearbox on the market today uses a contact lip seal.  For some applications, users prefer a single lip seal, while other applications require a more robust solution. The lip seals on gearboxes serve two primary functions: retain the gearbox lubrication, and prevent contaminants from entering (and leading to long-term damage).

Single Lip Seal

A simple single lip seal is the standard seal option in many applications and gear drives. This seal configuration features a single-sealing lip that faces inboard to keep the lubrication inside the gearbox.

The single lip serves double duty by also keeping contaminants out--a job it’s not well suited for. Dirt and debris will accumulate under the lip seal over time, and the seal will eventually fail. Users often select a single lip seal solution for the sake of simplicity in light-duty applications.

Single Lip Seal with Dust Lip

Lip seal with dust lipA single lip seal with a dust lip consists of two lips used together in a single seal. The outside lip is designed to keep dirt, contaminants, and debris out, while the inner lip keeps oil in.

The single lip seal with a dust lip is an improvement over the simple single lip design. The drawback of this configuration is that it blocks lubricant from reaching the outer lip. Over time, contaminants and temperature will breakdown the outer lip causing it to fail. With that failure, comes the accumulation of dirt and debris against the primary (inner) sealing lip. This very fine debris eventually builds up beneath the seal, creating an abrasive slurry, like wet sandpaper. Slowly, the friction grinds into the shaft, creating a leak and ultimately causing seal failure.

Labyrinth Sealing System

A labyrinth seal is a step up in design from the standard single seal or single seal with a dust lip.They feature a series of small, narrow channels to provide very high levels of resistance to flow. Labyrinth seals come in many variations, but they all feature a series of small, narrow channels to reduce the amount of dirt and debris in contact with the sealing surface. There are also non-contact labyrinth seals, used in high-speed applications to avoid the heat generation that accompanies contact seals, but they aren’t a true seal and provide no sealing ability statically.

Some labyrinth seal design variations include an integrated lip seal to seal statically and improve dynamic oil retention. Most gearbox labyrinth seals feature a drain back to prevent oil from building up behind the seal since their dynamic sealing performance is generally inferior to standard lip seals.

The Falk V-Class Magnum Seal System

The Falk V-Class Magnum Seal is a heavy-duty sealing system that offers the best of all sealing worlds—a true solution.

To keep contaminants out, the Falk V-Class Magnum Seal features the grease-filled cavity outboard of a lip seal. A small gap between the grease cavity cover plate and the shaft retains the grease and blocks larger contaminants. The grease inside the cavity traps smaller contaminants and prevents them from reaching the lip seal. The grease cavity is fitted with a zerk to allow purging of the cavity with fresh grease should it becomes contaminated. An added benefit of the grease cavity is that it ensures lubrication reaches the outer dust lip to reduce heat generation that can lead to premature failure.

On the inboard side, the Falk Magnum Seal System features an integrated labyrinth-style oil exclusion design. This design minimizes the amount of oil that reaches the sealing lip and is further augmented with an oil drain back. This combination ensures sufficient lubrication of the primary lip seal to minimize heat generation, without creating hydrostatic pressure on the seal. Combined with the already eco-friendly features of the Falk V-Class Drive, such as less oil consumption, cooler operation, and along with a quieter drive train, the Falk V-Class is a superior drive solution.

MCF Rigid Mount Coupling

Seal Material: Where the Rubber Meets the Drive

Lip seals are typically made of polymer rubber, like HBR (High-cis Polybutadiene Rubber), Butadiene, or FKM (Viton®). In most gearboxes, a garter spring sits behind the rubber lip. The spring holds the rubber against the shaft, increasing sealing pressure.

The materials have various strengths and weaknesses suited to their applications. FKM materials are known for their high-temperature performance but can be more prone to damaging the shaft due to their increased stiffness. Butadiene is less prone to causing shaft damage but degrades rapidly at temperatures over 200F.

For the Falk Magnum Seal System, the output shaft seals use Butadiene, and the input shaft seals use FKM, offering the best of both options. The higher temperature performance of FKM is the logical choice for input shafts, where speeds and temperatures are higher. Using Butadiene on the output shafts is equally ideal because the temperatures and speeds are lower. Specific chemical applications may also require FKM lip seals or another type of material to prevent chemical reactions with the seal material.

The design of the shaft-sealing surface is just as important as the lip seal material. The shaft-sealing surface plays a significant role in how long a seal holds in oil. The right hardness and surface finish are critical. Falk V-Class shafts were designed with input from the engineering experts at the seal manufacturers to ensure the right material, hardness, and surface finishes are in place to maximize seal life.


The Importance of a Grease-Purgeable Cavity

Grease Purgable CavityMany seal configurations use grease to exclude contaminants. The designs vary from configurations where grease is added between the inner and outer lip seals to more intricate options. While these design variations extend seal life for some time, eventually, heat and debris will win.

Think about stirring a very thick liquid. If you added color to it, stirring it in, the color gets incorporated very slowly. It takes a long time until it’s mixed throughout. The same idea applies here—the dirt and debris take a long time to get to the inner seal, where it starts doing damage. Polymer rubber is durable, with long life under extreme conditions.

Even with the contaminant-resistant cavity featured in many labyrinth seals, it's impossible to drive all the contaminated grease out and refresh the lubricant. Eventually, dirt and debris will back into the contact seal, causing it to fail. The best way to maintain a seal for the longest possible life is with the grease-purgeable cavity of the Falk Magnum Seal System.

Of course, even with perfect maintenance and care, all seals will eventually fail. Your Rexnord product support representative will work with your maintenance team to schedule your gear maintenance and replacement.

Fortunately, when the time for replacement comes, the Falk Magnum Seal System is designed so you can switch out the gearbox lip seals easily and quickly. Remove the cover, switch out the lip seal, put the cover back on and you’re good to go.

Many gear drives feature lip seals that are difficult to access and tricky to replace or install. Adding to the challenge, most labyrinth seals have very tight tolerances, with a small margin for installation error. With Falk Magnum Seals and genuine Rexnord components, you can rest assured you’ll face a stress-free installation.

The Falk V-Class Drive is made to deliver power, durability, and reliability under the harshest conditions. Because the Falk Magnum Seal System was engineered for these extreme environments, built-in standard with every Falk V-Class Gear Drive. When you purchase a Falk drive, you get the best sealing solution on the market.

Nathan Zastrow

Nathan is a Senior Engineer and Design Supervisor in New Product Development Engineering at Rexnord Industries, Gear Group. In 2006, Nathan joined Rexnord and has previously worked in a variety of engineering functions in product development.  He is also an active member of the MATC Mechanical Drafting and Design Advisory Board.

Nathan holds a Bachelor of Science in Mechanical Engineering from the University of Wisconsin – Platteville.