Case Study: Conveyor Alignment at Iron Ore Mine

TL;DR

This conveyor alignment iron ore case study follows a 2.4 km overland conveyor at a Pilbara iron ore operation that had been mistracking, spilling fines and tearing edge cover off a near-new belt. Working across two short maintenance windows, ISS surveyed the stringer line, idler frames and head/tail pulleys with a Leica Nova MS60 MultiStation and a FARO Focus Premium scanner against the conveyor designer's straightness and pulley-squareness tolerances, found a 31 mm horizontal stringer wander and two head-end pulleys out of square by up to 7 mm, and issued idler-by-idler shim and shift values that stopped the belt drift before the next belt change was due.

Key takeaways

• A 31 mm horizontal drift in the stringer line over one 180 m zone, plus a head pulley 7 mm out of square to the belt centreline, were driving the belt hard against the structure and shedding edge cover and fines onto the walkway.
• The conveyor had never had a survey-grade alignment check since commissioning in 2019; fitters had been chasing the symptom by tilting idlers, which masked the geometric cause and accelerated belt wear.
• ISS measured the conveyor as a relative-geometry problem in a local along-conveyor coordinate frame, not GDA2020/MGA2020 zone 50, because belt tracking depends on whether idlers and pulleys are square and straight to the centreline — not on national grid position.
• Field acquisition fitted inside two existing maintenance windows totalling about 11 hours; idler-by-idler correction values were issued progressively so fitters could start shimming the worst zone before the second window.
• Post-correction verification brought stringer straightness inside ±2 mm over 10 m and both head pulleys square to within 1.5 mm, ending the chronic drift. Total fee was AUD 16,800 including mobilisation from the ISS Karratha base.

The challenge: a near-new belt being destroyed by drift

The client runs a large iron ore mine in the eastern Pilbara, feeding crushed ore from the primary crusher to a train load-out via a network of overland and transfer conveyors. The 2.4 km overland conveyor at the centre of this conveyor alignment iron ore case study carries roughly 6,500 t/h of minus-300 mm ore on a 1,800 mm belt — a single critical link with no parallel path, so when it misbehaves the whole load-out feels it.

The symptom was belt drift. For months the belt had been wandering off centre, riding hard against the stringer and skirt structure through several zones, shedding edge cover and spilling fines onto the maintenance walkway below. The belt had been installed new in late 2023 and should have had years of service left, but the maintenance superintendent was already forecasting an early belt change — a six-figure consumable — because the edge damage was advancing. Clean-up labour under the spillage zones had become a standing weekly cost, and the spillage itself was a slip and housekeeping concern raised in successive site audits.

Site fitters had been managing the drift the way most crews do: knocking idlers askew to "steer" the belt back to centre. It worked locally and briefly, but it treated the symptom. Every tilted idler added rolling resistance and uneven edge loading, and the underlying geometric fault — wherever it was — kept reasserting itself. Nobody had a measured picture of the conveyor's actual straightness, and the structure had never been surveyed since it was commissioned in 2019.

The constraint, as always at a producing mine, was access. The conveyor could only be walked safely and measured at frame level when it was isolated and the belt stopped. There was no appetite for a dedicated shutdown on a critical-path asset, so the work had to fit inside maintenance windows already booked for idler changes and chute repairs.

The approach: find the geometry, not chase the symptom

ISS scoped this as a troubleshooting alignment survey against the conveyor manufacturer's installation tolerances — the practical reference for belt tracking, since there is no single Australian Standard that fixes overland-conveyor straightness the way AS 1418.18 fixes crane runways. The governing numbers came from the original equipment supplier's drawings: stringer horizontal and vertical straightness, idler-frame squareness to the belt centreline, and head/tail pulley squareness and level. CEMA and ISO 5048 conveyor-design principles framed the diagnosis, but the tolerances measured against were the designer's own.

The key decision, made before mobilisation, was to work in a local along-conveyor coordinate frame rather than tie the survey to the site GDA2020 / MGA2020 zone 50 grid or AHD heights. Belt tracking is a relative-geometry problem: a belt steers toward the end of an idler or pulley that it reaches first, so what matters is whether each idler and pulley is square and straight relative to the running centreline — not where the conveyor sits on the national datum. Establishing the centreline as the survey axis and measuring everything against it gave directly usable correction values and avoided burning window time on control transfer that would not improve a single tracking measurement.

ISS established a braced control traverse along the conveyor walkway, defined the design centreline from the head and tail pulley shaft centres, and measured the structure against that axis. The team mobilised from the ISS Karratha base so that the moment each isolation was confirmed, surveying started without a separate mobilisation eating into the window.

Equipment and method

With the belt stopped and locked out, the MS60 was leapfrogged station to station down the 2.4 km walkway, holding tight sight lines along each span. At every idler frame the team measured both stringer rails relative to the established centreline, recording horizontal offset, vertical level and the frame's squareness to the belt line. At the head end — where most tracking faults originate, because pulleys there have the greatest steering authority — the FARO scanner captured the head, drive and bend pulley faces and shaft ends, so squareness and crown alignment could be derived from a dense surface rather than a handful of points. The take-up and tail pulleys were measured the same way. Total field time across the two maintenance windows was about 11 hours, with on-site processing between them so the worst zone could be corrected first.

What the survey found

The data located the fault that idler-tilting had been masking. Over a 180 m zone roughly a third of the way along the conveyor, the stringer line had wandered 31 mm horizontally off the design centreline — a smooth, structural drift consistent with differential footing movement on the made ground beneath that section, not a single damaged frame. The belt was steering steadily into that bend every cycle, which explained the spillage and edge wear concentrated there.

At the head end, the survey found a second, compounding fault: the head pulley sat 7 mm out of square to the belt centreline and the bend pulley 4 mm out, both steering the belt the same way as the stringer drift downstream. The "corrective" idler tilts the fitters had applied were partly cancelling and partly reinforcing these errors, leaving the belt hunting.

The picture was now coherent. The structural drift in the made-ground zone was the primary steering input; the out-of-square head and bend pulleys added a second steer at the most sensitive point on the conveyor; and the field-applied idler tilts had scattered the belt's behaviour enough that no fitter could read the underlying cause by eye. Only a measured straightness profile of the whole 2.4 km run — over 400 idler frames referenced to one centreline — separated the structural fault from the pulley fault and from the noise the manual fixes had introduced.

The result: drift stopped across two windows

Because ISS processed on site and issued correction values progressively, the fitting crew did not wait for a final report. They received an idler-by-idler schedule: which tilted idlers to return to square, the shim and lateral shift values to bring the stringer back toward centreline through the 180 m fault zone, and the adjustment values to square the head and bend pulleys.

In the first window the crew re-squared the idlers the fitters had previously knocked askew and corrected the worst stringer span. Between windows ISS finalised the head-end values; in the second window the crew shimmed the head and bend pulley bearing blocks back to square and completed the stringer correction. ISS then re-measured the corrected zones before the conveyor was re-energised.

The as-corrected stringer line came back inside ±2 mm over 10 m through the previously failing zone, and both head and bend pulleys squared to within 1.5 mm of the centreline. On the first loaded run after re-start the belt tracked centrally through the zone that had been spilling for months, with no contact against the skirt structure. Residual stringer level error in the made-ground zone was held just outside tolerance by the existing footing, which the client accepted pending a longer-term structural fix, with the belt now tracking acceptably regardless.

The outcome: belt life recovered, monitoring established

The survey cost AUD 16,800, including mobilisation from Karratha, field and processing time across the two windows, the FARO pulley scanning, and the final report. Against that sat the avoided cost of an early belt change — well into six figures for a 2.4 km, 1,800 mm belt — plus the standing weekly spillage clean-up labour and the audit pressure from the walkway housekeeping problem. By stopping the edge-cover damage, the survey returned the belt to something near its design life, and the one avoided premature belt change paid for the work many times over.

ISS flagged the made-ground settlement under the 180 m fault zone for structural monitoring before it could drift further, and recommended a baseline straightness dataset and a periodic alignment check timed to the conveyor's belt-change and major-shutdown cycle, so future structural movement is caught as a measured trend rather than through belt damage. The client adopted both and added the overland conveyor to a routine survey schedule alongside its other critical conveying assets.

Frequently asked questions

Why not just keep tilting idlers to steer the belt?

Tilting idlers steers the belt locally but treats the symptom, not the cause. Every tilted idler adds rolling resistance and uneven edge loading, and it masks the underlying geometric fault — here, a 31 mm structural stringer drift and two out-of-square head pulleys. Manual steering also scrambles the belt's behaviour enough that no fitter can read the real cause by eye. A survey-grade straightness profile finds and fixes the geometry, after which the idlers can sit square as designed.

Why use a local datum instead of GDA2020 / MGA2020?

Belt tracking is a relative-geometry problem: a belt steers toward whichever end of an idler or pulley it reaches first, so what matters is squareness and straightness relative to the running centreline, not position on the national grid. Tying a 2.4 km conveyor survey to MGA2020 zone 50 or AHD would have consumed control-transfer time inside tight maintenance windows without improving one tracking measurement. ISS establishes the design centreline as the survey axis and measures everything against it.

How did the problem go unnoticed since 2019?

The conveyor had never had a survey-grade alignment check since commissioning, and the drift developed slowly as the made ground beneath one zone settled. Crews managed the growing symptom by tilting idlers, which kept the belt running and hid the trend. Without a measured baseline there was nothing to compare against, so a gradual 31 mm structural wander only became visible once it was destroying a near-new belt.

What does a conveyor alignment survey like this cost?

This job was AUD 16,800 for a 2.4 km overland conveyor, including Karratha mobilisation, total station and laser scanning across two windows, processing and reporting. Conveyor alignment surveys range widely — from a few thousand dollars for a single short transfer conveyor to well over twenty thousand for long overland systems in remote locations. Conveyor length, number of pulleys and transfers, access, mobilisation distance and turnaround drive the figure; fitting the work inside existing maintenance windows keeps it down.

How quickly can correction values be provided?

For troubleshooting surveys inside maintenance windows, ISS processes on site and issues idler-by-idler shim, shift and pulley-squaring values progressively, so the crew can start correcting the worst zone immediately and ISS can verify the result before re-energising. A formal report with full straightness profiles follows within five business days.

Request a quote

If a conveyor on your site is mistracking, spilling fines, chewing edge cover or forcing your fitters to chase it with tilted idlers, the cause is almost always measurable structure or pulley misalignment — and finding it is far cheaper than an early belt change. ISS surveys overland and plant conveyors across the Pilbara and nationally with Leica total stations and FARO 3D laser scanning, works inside your maintenance windows, and delivers idler-by-idler correction values against your conveyor designer's tolerances. Call us on 0407 057 015 to scope a conveyor alignment survey or to build a baseline straightness dataset for your next planned shutdown.