Increase uptime and reduce maintenance on your bearings

The typical operating environment for conveyor pulleys and idler shafts often leads to premature bearing failure, with the ingress of abrasive contaminants into the bearing virtually impossible to stop unless the correct measures are taken.

In fact, research has shown that conveyor reliability in these industries is below 87%. Meeting these challenges head on will achieve uptime that you can rely on, while reducing maintenance costs and safety risks.

SKF has a strong focus on bulk handling machinery and has developed a new range of sealed spherical roller bearings for harsh environments. The development, in close co-operation with SKF industry teams, has resulted in the SKF conveyor unit three barrier solution.

In a nutshell

The effectiveness of the SKF three barrier solution is in its simplicity, protecting the bearing enclosure during assembly and operation, through the introduction of SKF L or S type housing seals, a housing grease fill and bearing with integral seals.

The result is an environmentally friendly, cost-effective solution that can extend bearing service life without complex and expensive sealing arrangements. So, let’s consider the individual components and explore the unrivalled benefits.

The majority of SKF sealed spherical roller bearings have the same internal geometry as corresponding open bearings, as well as the same basic load ratings. A small number of these bearing do have a width greater than ISO standard to accommodate the seals. The width of all remaining bearings, as well as all other principal dimensions are as standard.

Lubrication

SKF sealed spherical roller bearings have W33 feature as standard, with bearings in the lower size range coming with the lubrication groove and holes covered by a unique polymer band. Depending on your choice of lubrication mode, there are two alternatives available in handling the band.

• Greased-for-life bearings: no action needed, retain or remove the band
• Bearing to be relubricated: Band must be removed before mounting in the housing.
• For general applications bearings are 25-45% filled with a high quality EP grease SKF LGEP 2. This lubricant is designed to operate up to 110˚C (230˚F).

Misalignment

The design of sealed SKF spherical roller bearings is such that they are inherently self-aligning, meaning that the bearings can accommodate angular misalignment of the shaft relative to the housing without negative effect.

For most misalignment types, sealed SKF spherical roller bearings can accommodate angular misalignment of the shaft relative to the housing of up to 0.5˚, but where misalignment is not constant with respect to the bearing outer ring, the bearing friction increases and the misalignment of the inner ring relative to the outer should not exceed a few tenths of a degree.

SNL Housings

It’s not only the sealing arrangement in the SKF three-barrier solution that needs to be of high quality. To utilise all potential with this innovative solution, the housing itself is vitally important.

High quality SKF SNL housing are designed with smooth stiffness to avoid locally overloading the bearing, have excellent thermal conductivity, and secure axial movement of the non-locating bearing. These features contribute to unrivalled bearing reliability.

Sealing efficiency

The efficiency of integral seals has been confirmed by field test and long-running, demanding laboratory tests. Whilst sealing efficiency in wet environments is higher than single-lip seals used in other bearings, sealed spherical roller bearings should not be exposed to direct water as the seal surface can corrode reducing function.

SKF’s recommendation is that integral seals should be employed as secondary seals, ensuring that the properties of these bearings are used most efficiently.

Labyrinth seals

For high speed and/or high temperature applications, SKF recommends using a labyrinth type seal. The standard labyrinth seal is named a labyrinth ring, which consists of a metal ring with two steps arranged radially, a silicone rubber cord supplied with the seal holds the ring in place on the shaft.

Standard labyrinth seals can accommodate approximately 0.3˚ of angular misalignment and operating temperatures up to +200˚C (+390˚F).

Taconite heavy-duty seals

For bearing arrangements which operate under arduous conditions, labyrinth seals with a re-lubrication function are recommended as the grease enhances its sealing properties. With Taconite heavy-duty seals, angular misalignments of the shaft up to 0.5˚ are possible.

Four-lip seals

With shaft speeds continuously increasing, SKF have developed a robust, easy-to-mount four-lip seal allowing peripheral speeds up to 13m/s. The permissible angular misalignment for shaft diameters ≤ 100mm is 1 ˚ and 0.5 ˚ for larger shafts.

Savings all around

By introducing the upgraded SKF three-barrier solution, you can receive an average lifetime three times longer than traditional open bearings.

The overall result is fewer conveyor pulley bearing breakdowns and longer maintenance intervals – delivering up to 92% availability. This allows for scheduled maintenance of your conveyor pullies to be timed with lagging replacement.

The SKF three-barrier solution also means that regreasing is only required twice a year, instead of once a week, saving you up to 90% of the time of greasing, while increasing safety for your maintenance workers. Win Win Win.