Slew Ring

Slewing ring bearing bolts have a direct effect on bearing life, put simply if the bolt tension is incorrect or relaxes the bearing wear rate increases. We first became involved with these in 1995 on North Sea Offshore cranes. Together with Leibherr and Lloyds of London we extended the statutory replacement period from 6 to 11 years.

  • Increase bearing life by 80%

  • Prevent in-service failures

  • Significantly shorten maintenance testing routines

Slewing ring bearings are present on many critical machines including Drag Lines, Cranes, Stackers, Re-claimers, Shovels, Excavators, Car dumpers, FPSO turrets...

We first became involved with these in 1995 on North Sea Offshore cranes. Together with Leibherr and Lloyds of London we extended the statutory replacement period from 6 to 11 years. Find out more

A Comprehensive Solution for Bolt Performance and Longevity by Boltstress Technical Services


A major mining company based in Port-Hedland relied heavily on the bucket wheel reclaimer for a bulk of their operations. This tool is responsible for reclaiming bulk iron ore, which is conveyed to another component - the Lump rescreening plant.

Regular servicing is a necessity to maintain the bucket reclaimer's optimal performance. It is expected to obtain a 14,000-ton per hour flow rate during each operation. Furthermore, it must be able to move to any position to reach the ore.

This is made possible by the slewing ring, and its bearing is the primary piece that accommodates the load coming from any direction. Thus, accurate tensioning is required to ensure the peak performance of the slewing ring.

The team at Boltstress Technical Services introduced a more efficient and more thorough means of servicing slewing ring bearings. The result: 100% of the bolts were tested and checked instead of the previous 10%.

This led to an enhanced bearing accuracy and lifespan, prevention of unscheduled downtimes, and elimination of safety risks in the workplace such as line-of-fire and pinch point injury. All of these resulted in an increase in the client's bottom line as business productivity improved and unnecessary expenses on machinery repairs were prevented.



The challenges that BTS worked with were three-fold:

1. Lack of an efficient and accurate means of servicing slew ring bearings;

2. Production losses when bearings were being serviced; and

3. Safety hazards in the workplace


Lack of an Efficient and Accurate Means of Servicing Slew Ring Bearings

Prior to commissioning the BTS, the mining company assigned two personnel to service slewing ring bearings. One was tasked to operate the pump while the other tightened bolts using a hydraulic bolt tensioner or a standard torque wrench.

However, it did not result in an accurate measurement of bolt tension. They had no means of determining if the desirable tension range was achieved. Moreover, it was a laborious process and only a maximum of 10 percent of the bolts were inspected.


Production Losses When Bearings Were Being Serviced

Due to the inaccuracy of the original servicing methods used, this has led to an eventual need for a replacement. Thus, it interrupted business productivity and caused production losses during this servicing period.


Safety Hazards in the Workplace

The issue with defective bearings increased the chances of pinch points. In addition, there was a high risk of line-of-fire, which impacted the overall safety of individuals in the workplace.


An Improved Servicing Method for Reclaimer Slewing Ring Bearings

When BTS was commissioned to service the slew ring bearings, they discovered faults in the previous techniques implemented for testing the bolts.

They began with a full assessment of the bolts. Upon observing the issues present, they recommended a technologically-advanced means of servicing designed to:

  • Improve the bearing accuracy and lifespan

  • Prevent unplanned downtimes and in-service failures

  • Minimise testing procedures AND test 100% of the bolts

  • Maintain workplace safety

In the bolting industry, torque requires an accuracy of at best ∓ 25%. According to BTS, this is an optimistic value as they observe a variation that goes up as high ∓ 35%. This was the goal they aimed to achieve.

The BTS used the Boltstress G6 ultrasonic monitor, which measured bolt tension accurately. The tool also helped to reduce service time as it ensured a faster and more accurate means of identifying bolts in need of an adjustment. The team observed the positive effects of ultrasonic measurement to statutory replacements from 6 or more years in the crane they serviced in the North Sea Oilfields.

Furthermore, they implemented custom slimline Hydraulic Bolt Tensioners for a quick access to bolts that are in confined and tight areas. Using hydraulic pumps and torque wrenches, they were able to apply the required tension to bolts.


Impressive Outcomes and Benefits

Upon the successful completion of the job, the BTS reported the following outcomes and benefits:

  • Monitoring accuracy on bolt stress by up to 2%. This resulted in the prolonged statutory replacement period by up to 2 times.

  • Elimination of safety hazards in the workplace such as line-of-fire potential, pinch points, and the intensive lifting in tight spaces by utilising custom Hydraulic Bolt Tensioners.

  • A reduction in servicing process time. The BTS team took only 15 seconds to accurately service each bolt.

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