Faulty seals cause unexpected bearing failures

When bearing lubrication fails due to a faulty seal, bearing failure is not far away.

Find a shaft seal that is as good as your bearing

With the right selection, proper installation, and good lubrication, an SKF bearing in a smoothly running rolling mill can perform reliably until the next scheduled maintenance. But that requires seals that last the entire time. How can you ensure they do that, especially in the harsh environment you work in? How do you choose the correct seal?

Keep lubrication in and contamination out

Often, a non-functioning seal is the root cause of unplanned stops. According to our bearing investigation data, approximately 20% of bearing failures are due to seals leaking lubrication or allowing contamination. Common causes for leaking seals are ageing material, the seal shrinking, or the seal not being rigid enough. Whatever the reason, a leak means that the lubricant becomes ineffective, resulting in in-service bearing failures or premature bearing maintenance needs that increase maintenance and replacement costs.

Seals in the metal industry

Temperature and speed extremes, high and constant shock loads, abrasive dust, aggressive chemicals, and high humidity make sealing in the metal industry difficult. Seals must keep lubricants firmly inside the bearings while exposed to extreme heat, dirt, other contaminants, pressure, and friction. Durable materials and innovative design are a must to meet these strict requirements.

How to choose the correct seal

Many factors influence the seal design and material choice, including media, rotating speed, DRO (Dynamic Runout), misalignment, operating temperature, and pressure. When you know the operating conditions, choose the features you need to meet the demands.

Metal reinforcing

Open seal housings require a metal-reinforced, self-retaining seal, while housings with cover plates ensure stability through axial clamping of the seals, and therefore can use rubber fabric seals.

Open housing, seal self-retaining

Housing with cover plate, seal axially clamped

Re-lubrication options

Seals with lubrication grooves at the back allow for re-greasing between the sealing lips in back-to-back or tandem installations of two seals. For metal-reinforced seals, you can add spacer lugs in customized dimensions.

Back-to-back installation

Tandem installation

Adding an auxiliary lip

In slightly contaminated environments, add an auxiliary lip to the radial shaft seals for enhanced protection against contaminants. However, in heavily contaminated environments that is not enough, so include an additional seal there instead.

Lip material

Material selection significantly impacts seal performance and reliability. Important material properties are resistance to swelling, elasticity, chemical resistance, thermal resistance, and low-temperature behaviour. Seals are available in nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), and fluoro rubber (FKM).

NBR is a general-purpose sealing material with good resistance to most mineral oils and greases, and hot water. It works in temperatures from +30°C to +100°C, or up to 120°C for short periods.
HNBR improves wear and temperature resistance and withstands chemical attacks, weather, ageing and ozone, up to +150°C. Mixtures of oil and air may have a negative effect.
FKM has very good thermal and chemical resistance with very good ageing, weather, UV light and ozone resistance. The upper operating temperature limit is +200°C

Expert help

When you need help choosing the correct seal, SKF has decades of experience in industrial seals and is committed to guiding you in selecting the perfect seal for your applications – from the right material and design to the ideal size – resulting in reduced costs and increased reliability.

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