Sealed and delivered : How SKF Explorer sealed spherical roller bearings deliver performance in conveyor applications

Increasing performance and the service life of equipment to save money is a major preoccupation for most industries these days. This is the thinking behind SKF’s promotion of the sealed bearing solution for the mining and process industries. Targeted at users and designers of belt conveyors, SKF has an extended range of sealed spherical roller bearings designed to beat conventional bearings in the performance department.

The SKF Explorer sealed spherical roller bearing has been developed to deliver a reliable bearing solution that offers significantly reduced need for maintenance coupled with extended service life and fewer unplanned breakdowns and production stops. That can add up to increasing maintenance intervals by up to 100% or, in practical terms, extending maintenance times from one or two years to up to five years with significant savings in operating costs and staff time.

At a time when concern for the general environment has increased, the fact that the sealed spherical roller bearing is greased-for-life also has the positive environmental effect of reducing the use of potentially polluting grease, plus cutting the cost of waste grease disposal. In many applications, the bearing housing can be filled with biodegradable grease which, as part of  SKF’s three barrier protection (housing seal, grease and bearing seal), results in a clean solution even for bearings working in such tough environments as conveyors. In this respect, the three barrier solution offers an easier heavy-duty solution than taconite seals frequently used in conveyor systems exposed to harsh conditions. The sealed spherical roller bearing design has already proven its worth with a number of customers. At RWE’s open-cast coal mine operation in Germany, replacement of open cylindrical roller bearings on impact idlers with sealed spherical roller bearings resulted in a 100% increase in service life.  Mounting the complete sealed spherical roller bearing unit took half the time of conventional bearings and the greased for life solution eliminated relubrication costs and disposal of used grease.

Maintenance staff were also able to focus on more critical mining operations.  For another major operator, Askania, which has a large sand processing facility in Sweden, sealed spherical roller bearings were tested on its extensive conveyor system. The plant handles more than 35,000 tonnes of sand a year and uses 11 vertical and 11 horizontal conveyors with 88 bearing positions. Over a two-year test period, the sealed bearings were compared against conventional open bearings and open bearings with taconite seals. While the original arrangement with open bearings failed every nine months, the sealed spherical roller bearing solution kept going. So, in challenging applications where the bearings are subjected to sand, dust and grit, the sealed spherical roller bearings proved superior. The sealed bearings offered the advantages of lower maintenance costs, and trouble-free operation while eliminating the need for the environmentally unfriendly grease required by the taconite seals and the added disposal costs.

Sealed bearings reduce grease consumption
The issue of grease use and disposal is increasingly important in conveyor and other industrial applications. The sealed spherical roller bearing design, as its name implies, is a sealed for life solution. This means that for operators who are heavy grease users, consumption can be reduced by 90% or more over the lifetime of the bearing. For LKAB, a large iron ore mine in Sweden, grease use was cut by 100kg per year for each bearing position by replacing open spherical roller bearings with sealed bearings. The investment paid for itself in one year while the operational costs associated with each bearing position were halved. This can add up to considerable savings when you consider that, while the cost of grease may be in the region of EUR 1/kg, its safe disposal adds another EUR 3/kg.

Design developments result in improved performance
Even without the new sealing solution, SKF Explorer spherical roller bearing design has undergone significant performance enhancement. This has been achieved through improved steel qualities which enable longer life at heavier loads and new heat treatment processes to improve wear resistance. In addition, refinements have been made to manufacturing processes to create smoother running bearings with improved lubrication. Changes to the internal geometries of bearings that result in better stress distribution have also been accomplished.

The inherent design features of the sealed spherical roller bearing mean that this bearing has the following attributes:

• Self-aligning – can accommodate misalignment of 0.5 degrees without increasing friction or shortening bearing life.
• High load carrying capacity and robust – excellent for conveyor applications.
• Easy mounting can cut installation time, thereby reducing maintenance time and costs.

The sealed spherical roller bearing design includes seals that are reinforced by a steel sheet plate resulting in a robust design. The bearings are filled with grease suitable for the operating conditions. The sealed spherical roller bearing is generally designed for operating temperatures up to 110oC.

Areas of use
The sealed bearing is an excellent solution for belt conveyors where extreme temperature can be expected, where the environment can be dusty or wet and abrasive and where the conveyor is moving slowly while carrying heavy loads. The sealed spherical roller bearing is suitable for application at several key points within conveyors - in the drive pulley, tail pulley and other positions where bearings are subjected to heavy loads and low speeds and need to be able to withstand contamination and accommodate misalignment.

Attraction of integral seals
The seals, which have been specially developed for spherical roller bearings, effectively prevent contamination from entering the critical rolling elements area not only during operation, but also during bearing installation. This protection contributes to a long service life. Leaking bearing housings are a common problem for many conveyors. This leaking is often caused by the external housing seals being mounted incorrectly or damaged. The sealed bearing provides extra protection as the grease is kept within the bearing received from the factory.

Deliverable benefits for operators and OEMs
Because of the importance and potential benefits of the sealed bearing solution, SKF has developed a full range of bearing sizes that adds up to 100 basic variants and up to a 340 mm bore size. They can be delivered as complete units ready for plug and play with a selected grease to give the longest possible service life. Overall, the sealed spherical roller bearing adds up to a design that can offer real benefits to conveyor designers and operators. For the OEM, incorporating these bearings into new conveyor systems offers the opportunity to downsize the complete bearing unit without compromising operating life. For the user, the benefits are clear. Sealed spherical roller bearings offer reliability, dramatically long operational life, reduced need for maintenance and lower operating costs coupled with environmental savings.

For more infornation about conveyor solutions
SKF
Mr.Tennyson Anthony- Marketing Manager, Industrial Division-India
E-mail: ibu.marketing@skf.com, Website.: www.skf.com