The Importance of Balancing and Weighing a Bulk Materials Handling Machine

During the commissioning process for a balanced mobile Bulk Materials Handling Machine (BMHM) such as a bucketwheel reclaimer, stacker, bucketwheel stacker reclaimer or shiploader, an important step is to balance and weigh the machine. Although it may be tempting to forego this vital step due to schedule demands and the impending commencement of operations, it is imperative that proper balancing and weighing be carried out to ensure the safe and reliable operation of the machine for many years to come.

Validates the Design Intent

Balancing and weighing of a new machine on site allows for comparisons to be made between the measured and design values. Any discrepancies regarding the luffing structure balance and total weight of the machine may require further investigation and rectification prior to commencement of operation. This practical validation step is an important hold point before handover. The Australian and international standards for mobile BMHM do not allow the as-constructed weight to be more than a 5% variation to the design value, in which case the design checks and calculations must be repeated.

Avoiding False Confidence

If only balancing or weighing is undertaken, and not both, this does not provide the machine’s owner a complete picture of their new investment. As an example, weighing alone might indicate the machine’s mass matches the design value. But this might give the project team a false sense of confidence, because without also undertaking appropriate balance and centre of gravity checks on-site the machine’s stability cannot be verified and it might be improperly balanced, which may not be obvious from weighing alone.

Achieve the Fatigue Service Life

The stability, balance and centre of gravity is critical for a machine that undertakes luffing and/or slewing motions, such as a bucketwheel reclaimer, stacker or shiploader. If the machine is not properly balanced, the fatigue stresses caused by each luffing and/or slewing motion can be amplified and the slew bearing load distributions may also be outside its design load envelope. As such, an incorrectly balanced machine will have a shortened slew bearing service life and premature onset of fatigue cracking.

Confirm Wheel Loads on Rail

The loads imposed on the wheels and rails for a bulk materials handling machine depend not only on the machine’s overall weight but also its balance and overall centre of gravity. An overweight or incorrectly balanced machine will have excessive wheel loads which can lead to wear issues for the wheels and rails. It can also mean that the long travel drive power may not be adequate for the machine to operate efficiently. These increased loads can also have significant consequences for the wharf or rail foundations, which were designed and built for a specific design wheel load spectrum.

The Best Methodology

The best method for balancing and weighing will depend on the design and configuration of the particular machine, therefore using an incorrect methodology can give erroneous or inconclusive weight and balance results. There are many factors to consider which add together to create complexity. Taking measurements with the boom horizontal is sufficient for some machines but not for others. If the conclusion is that the machine is overweight or improperly balanced, what is the path forward? Adding or removing counterweight can have significant implications elsewhere on the machine that need to be fully understood.

In recognition of the importance of weighing and balancing, the requirement of Australian Standard AS4324.1 (2017) states that:

“After a machine has been constructed, the mass and centre of gravity of the as-built machine shall be accurately determined”

— Clause 5.9 of AS4324.1 (2017)

The team at LEC are experienced in preparing suitable procedures to validate the luffing structure balance and weighing of the entire machine in accordance with the requirements of AS4324.1 as well as other international standards such as ISO 5049-1 and FEM Section II (2 131 / 2 132).

Click here to contact LEC and discuss the best methodology for weighing and balancing your particular bulk materials handling machine.

Service Life Extension for a Bucketwheel Reclaimer

A bucketwheel reclaimer had been decommissioned after 25 years due to extensive structural defects, including cracking in the luffing pivot rocker region.

For these defects to be repaired, the traditional approach would be to fully dismantle the reclaimer in the reverse order to which it had been constructed, however this would require an extensive laydown area, high capacity cranage and months of construction work with the associated high risk. Another alternative would be the complete replacement with a new reclaimer, which would require a significant cost and timeframe for the procurement and commissioning of the new machine.

Instead, an in-situ structural remediation solution was undertaken which enabled the client to resume operations in 12 months, sooner than a traditional refurbishment and at a cost saving of several million Australian dollars.

The major remediation works included:

• Repair of structural cracking in the rocker arm assembly.

• Hydraulic luffing cylinders were removed, refurbished and re-installed.

• Slew bearing replacement.

• Bucketwheel replacement, including shaft and drive assembly.

• Replacement of heavily corroded structural members on bucketwheel boom.

The superstructure of the reclaimer was lifted in-situ with the boom and counterweight still assembled, which allowed the change out of the slew bearing and the repair of the rocker assembly.

This implementation required purpose-built temporary luffing cylinders, temporary support frames, and the installation of safety features such as strain gauges to monitor the loads and stability throughout the construction process.

Why do I need an independent design review?

Every machine is unique

When procuring a new Mobile Bulk Materials Handling Machine (BMHM), such as a bucketwheel reclaimer, stacker reclaimer, stacker, bridge/portal-type reclaimer or ship loader, the machines configuration will depend on many factors:

• Required throughput;

• Stockpile layout and footprints;

• Yard conveyor arrangements;

• Bund or wharf rail gauge;

• Properties of the material to be handled.

It would therefore be very unlikely to find an “off-the-shelf design” that would suit all the required design parameters for a particular mine or port site.

Higher rates of structural failure

A new BMHM is a major capital expenditure asset with an expected design service life of 25+ years, however, they experience a higher rate of structural failure when compared to other heavy industrial structures.

Historical evidence shows that catastrophic structural failures can occur at any time during a machine’s service life, including during the commissioning stage.

Safety and cost benefits

Engaging an independent or third-party design reviewer during the early stages of procurement can provide many benefits:

• Implement “Safety in Design” early in the design phase;

• Satisfies legislative requirements (duty of care / due diligence);

• Anomalies in the machine configuration and potential constructability issues can be identified and notified to the supplier (OEM) early in the design phase;

• Design code compliance issues can be identified in the design phase and promptly rectified;

• Costly production delays due to design issues and associated on-site remedial work can be minimised;

• Identifying design issues early in the design phase minimises cost overrun and schedule delay;

• Structural modifications can be incorporated during fabrication without undue cost or schedule penalty;

• Minimise the risk of commercial and/or legal disputes which potentially lead to expensive litigation.

Prevention is better than Remediation

LEC personnel have undertaken independent detailed design reviews, structural condition assessments and failure investigations for more than 50 bulk materials handling machines since 1993. Often this involved detailed Finite Element Analysis (FEA) using 2D and 3D elements.

Based on our experience, the detailed design review often identifies structural design issues related to:

• Safety in Design;

• Omissions and ambiguities in the Technical Specification documents;

• Materials and constructability issues;

• Serviceability issues;

• Member strength issues;

• Member and local plate buckling issues;

• Fatigue service life compliance.

These design issues can generally be resolved with the Original Equipment Manufacturer (OEM) during the design phase, thus eliminating potential schedule drift and cost overruns.

An independent detailed design review can be carried out in accordance with the following standards, generally nominated in the client’s technical specification for the new Bulk Materials Handling Machine:

• Australian Standard AS 4324.1

• FEM Section II (2 131 / 2 132)

• ISO 5049-1

Click here to contact LEC and discuss your requirements for an evaluation of a machine’s technical specification and an independent design review.

Weighing of a Stacker Reclaimer

A rail-mounted bucket wheel stacker reclaimer had recently been refurbished following a partial structural failure, but before it could be returned to service it was necessary to weigh the machine to confirm its as-built condition matched the design intent for balance, stability, slew bearing loads and wheel loads.

LEC prepared a weighing method statement and undertook on-site supervision of the weighing, which was undertaken by jacking the eight-wheel bogie structures.

LEC then processed the site measurements to calculate the total weight and weight distribution (centre of mass) of the stacker reclaimer, and compared these to the design values to determine whether re-ballasting might be necessary to ensure the slew bearing service life would not be compromised due to an out-of-balance condition.