How can ultrasonic tension measurement technology help improve the lifespan of bolts, as well as enhance the tensioning accuracy?
For industries that rely on a highly automated out-loading circuit, for instance, one key component is the bucket wheel reclaimer. In fact, a Port Hedland-based major mining company has seen the importance of keeping this piece of equipment well-maintained to ensure proper operations.
This machine allows for the reclaiming of bulk iron ore, which is then made available for conveying to another component, the Lump rescreening plant.
Moreover, the bucket reclaimer is an essential piece of equipment as it obtains a 14,000-ton per hour flow rate. Thus, it is highly necessary to keep it operational and at its best performance through regular servicing.
How to Reclaimer Slew Ring Bearings Work
The bucket reclaimer rotates in a vertical axis. This motion results in a horizontal boom, which then moves to any position in order to reach ore. The slewing ring is what makes this lateral movement possible.
Additionally, the slewing ring bearing is a primary piece of this ring. It accommodates loads coming from any direction. An annular arrangement of bolts make up the bearings and accurate tensioning is necessary to achieve the ring's optimal performance.
Original Method of Servicing Slew Ring Bearings
The prior method of servicing slew ring bearings required the involvement of two personnel. One was tasked to operate the pump while the other tightened bolts using a hydraulic bolt tensioner or a standard torque wrench.
These methods helped to tighten bolts and achieve their functional level. However, it did not allow for an accurate measurement of bolt tension. As a result, there are no means of determining if the desirable range of 975 to 1950 Nm Tension tolerance 320kN +/- 5% Nm was achieved.
Hence, there are limitations to these methods in that sense. Furthermore, the entire process is laborious and only about 10 percent of the bolts are checked.
Over time, the bearings sustain premature wear rates because of the inaccuracy of such technique. This, then results in an eventual need for a replacement, which can be costly. On top of the said expense, there are production losses when the bearings are being serviced.
It also contributes to hazards in the workplace. The most significant safety concerns of this method are the high risk of pinch points and line-of-fire potential.
An Improved Servicing Method for Reclaimer Slewing Ring Bearings
When Norbar Technical Services (NTS) stepped in, they discovered some faults in the prior methods implemented for servicing these bolts.
They conducted a full assessment and discovered that slewing ring bearing bolts with inaccurate tension had a shorter lifespan because of increased wear rates.
Thus, they recommended a better way of tackling this concern through a technologically-advanced method, which is designed to:
Enhance the bearing lifespan
Drastically minimise maintenance testing procedures
Prevent unscheduled downtimes and in-service failures
Improve safety in the workplace by eliminating risks such as pinch point injury and line-of-fire
Most importantly, this improved method offers an accurate and dependable means of measuring bolt tension of ALL the bolts.
In the bolting industry, torque has an accuracy of at best ± 25%. According to NTS, this is an optimistic value as they observe a variation that goes up as high ± 35%.
The primary goal of NTS was to make sure 100% of the bolts are checked and tested instead of the previous 10%. This would be beneficial for ensuring the required pre-load for each bolt, which then reduces the need for premature bolt replacements. It is also much quicker than mechanical 10% method.
A Comprehensive Solution for Bolt Performance and Longevity
Driven by this main goal, the NTS department created a comprehensive solution involving the following:
An experienced ultrasonic bolting personnel will implement a specialised skill and knowledge to achieve a thorough and efficient completion of the task.
Using the Boltstress G6 ultrasonic monitor, this measures the bolt tension accurately. This equipment also helps to minimise the service time by allowing the technician to identify accurately and quickly the bolts that require adjustment.
Implementing custom slimline Hydraulic Bolt Tensioners to access the bolts easily, especially those situated in hard-to-reach and confined areas.
Ultrasonic measurement has been proven to prolong the lifespan of statutory replacements from 6 years or so to 11 years. This was observed by the NTS team on a crane they serviced in the North Sea Oilfields.
Outstanding Outcomes and Benefits
The NTS reported evident benefits upon the successful completion of the job including:
Bearing life expectancy up to double that of current methods.
Accuracy with monitoring bolt stress by up to 2%. This helped to prolong the statutory replacement period by up to 2 times.
Safety in the workplace by eliminating pinch points, line-of-fire potential, and laborious lifting in tight spaces through utilising custom Hydraulic Bolt Tensioners.
Efficiency and speed in the servicing process. The NTS took about 15 seconds to service each bolt. This was also attributed not only to the knowledge of the personnel but also their expertise. Additionally, the re-monitoring phase took a quarter of the time all because of the Ultrasonic measurement. It allows technicians to pin-point the problematic bolts and implements the most suitable actions in a highly targeted manner.