Split bearings

Split bearing solution cuts conveyor maintenance costs and risks

For companies and employees in the mining, mineral processing and cement industries, maintenance and replacement of conveyor bearings may come at a very high price. Clive Jennings, SKF Cooper Split Bearings Product Manager at SKF, presents a way of reducing safety risks as well as material and downtime costs.

Anatomy of an SKF Cooper split spherical roller bearing – including optional seals

According to some studies, 43 percent of accidents and 24 percent of fatalities in these sectors happen while maintaining conveyors. A key danger often lies in the need to hoist heavy couplings and gearboxes to access bearings. If the process of replacing a bearing could be made quicker and simpler, and if bearings were made to last longer, everyone would benefit. Workers would be safer, maintenance would be less expensive and loss of production would be minimised.

Harsh challenges

The challenges SKF has overcome to make this possible are considerable. First, there are the extreme temperature, heavy loading and contamination conditions faced by rotating machinery and their bearings in plants which handle minerals and cement. The conveyors typically use standard open (unsealed) pulley bearings, which are vulnerable to contamination. These have a relatively short service life (usually less than that of the pulley lagging) and require large amounts of grease to purge contaminants.

Rapid wear and damage necessitate frequent bearing repair and replacement, typically in hard-to-reach locations. Replacing a standard bearing in the machine’s trapped position is especially difficult and hazardous, requiring a long sequence of procedures. It can take up to 24 hours in total.

Increased bearing life, performance and operational economy

SKF Cooper split spherical roller bearings answer all these problems with a durable design that brings improved reliability and longevity. The range includes sealed versions which give better protection against contaminants, for even longer life and lower grease consumption. Best of all, the bearings are designed for in-situ replacement in much fewer steps, with no need to remove or hoist the gearbox and drive coupling.

Their anatomy includes inner and outer rings, a cage and rollers, an outer shroud and two inner clamp rings. The shrouds and clamp rings are bolted together with screws. Two seals are added if that option is chosen.

Rings are split using a precision wire-cutting technique, rather than by fracturing. This minimises discontinuities in the inner and outer rings and means that the two halves align more accurately, and superior clamping is achieved. Outer race and

shroud joints interlock to ensure close alignment between the halves and to lower the chances of damage at the splits while operating. The angular inner race joints are also wire-cut, contributing further to the smoothness of the roller path. This wire-cutting approach not only improves clamping and reduces looseness but lowers the chances of fretting corrosion at the shaft interface.

In combination, these design elements extend the bearing’s life and improve its performance. Tested against comparable competitors’ split spherical bearing products, its steel clamp rings increase permissible axial loads by around 50 to 100 per-

cent. An additional bonus is a reduction in running noise levels.

By adding seals, the bearing’s service life can be more than doubled and, in some cases, multiplied by 2.9, compared with an unsealed bearing. At the same time, this can reduce grease consumption by 90 to 95 percent, saving on lubricant expense, labour, exposure to safety risks and impact on the environment.

Quicker bearing replacement

SKF Cooper split spherical roller bearings are especially useful when it comes to bearing replacement in the trapped position. To replace a standard, non-split bearing, the gearbox and drive coupling must be disconnected, hoisted out of the way and then replaced afterwards in the correct alignment. These are time-consuming tasks which require rental of equipment such as cranes and alignment tools. Workers are exposed to safety hazards throughout this long operation, in which hoisting of heavy components poses particular concerns.

By contrast, replacement with an SKF Cooper split bearing takes substantially less time and consequently, reduces workers’ exposure to risks. Table 1 highlights the much smaller number of procedural steps involved in using a split bearing.

Crucially, gaining access to replace a split bearing does not require movement of the conveyor belt, and it involves little or no disturbance to the drive coupling or gearbox. There is certainly no need to disconnect and lift them from the machine. Only a slight raising of the shaft is necessary. As well as removing a significant hazard, this solution saves maintenance staff from having to spend time repositioning and aligning the assembly after bearing replacement.

A long-awaited breakthrough

Over a hundred years since the heavy-duty belt conveyor’s introduction, many operators still see maintenance as its Achilles’ heel. Heavy grease consumption and premature bearing failure – together with the difficulty and time demands of repair and replacement – generate high costs, limit productivity and endanger maintenance teams. These are major concerns for all industries, and nowhere more so than in the world of mines, minerals and cement.

Designed for faster and safer pulley bearing replacement in the trapped position, SKF Cooper split spherical roller bearings slash mean time to repair (MTTR) and improve worker safety. Their design and manufacturing techniques also enhance performance and extend service life, especially when sealed variants are chosen to counteract contamination, so fewer replacements and less grease are needed. In short, they offer a safer alternative that cuts maintenance costs, increases machine availability and minimises lost production.

SKF Cooper split spherical roller bearing

Easy applicability

The split outer ring dimensions match those of standard spherical roller bearings, enabling an easy fit into split block housings with standard locating rings where necessary. Shaft requirements for the split bearing (ISO h9 shaft diameter tolerance and IT5 form) also match those of a standard spherical bearing mounted on an adapter sleeve.

The SKF Cooper products are interchangeable with competitors’ split spherical roller bearings. They are also compatible with any SKF metric (SNL, SNLD) or inch (SAF, SAFD, SDAF) split plummer block housing. First to be launched was the 231 series, with shaft diameters ranging from 240 to 450mm and from 9.5 to 18 inches. These can replace standard 23152 K to 23192 Anatomy of an SKF Cooper split spherical roller bearing – including optional seals K spherical roller bearings mounted on adapter sleeves. www.skf.co.uk

Standard, non-split bearing SKF Cooper split spherical roller bearing

Safety lockout/tagout Safety lockout/tagout Block machine (pulley) from rotation Block machine (pulley) from rotation Block and move belt to access pulley Disconnect gearbox coupling from motor Disconnect gearbox coupling from machine Remove coupling from machine Lift and remove gearbox Remove split block housing cap Remove split block housing cap Lift and support machine shaft Lift and support machine shaft Remove and replace bearing Remove and replace bearing Replace housing cap Replace housing cap Reposition gearbox Connect gearbox to machine Connect gearbox to motor Check alignment of motor to gearbox Remove machine blocking Remove machine blocking Remove safety lockout/tagout Remove safety lockout/tagout

Table 1: Comparison of general in-situ sequence of bearing replacement procedures between standard and split bearings in the trapped position About the author:

Clive Jennings is the SKF Cooper Split Bearings Product Manager at SKF.