Stacker reclaimers: the machine types, stacking methods and blending, the systems on each machine and how they fail, and structural integrity
Stacker reclaimers and stockyard machines: stackers, bucket wheel reclaimers, combined machines and scraper reclaimers, cone shell, chevron, windrow and strata stacking and how they blend, the long travel, slew, luff, bucket wheel, conveyor, power and structural systems and how each fails, structural fatigue inspection under AS 4324.1, and trending the slew bearing. With a drawing of a machine and a chevron stockpile.
Key takeaways
- Stockyard machines build stockpiles from the yard conveyor and reclaim them back to it. Stackers, bucket wheel reclaimers and combined stacker reclaimers run on rails beside the piles.
- The stacking method decides how well the pile blends. Chevron and windrow stacking, reclaimed across the whole face, even out grade and size. Cone shell stacking does not.
- Each machine is a collection of systems: long travel, slew, luff, the bucket wheel, conveyors, power and control, and the structure. Each has its own wear and failure.
- Structural fatigue is the failure with the worst consequence. Fatigue critical joints are identified by the structural engineer and inspected on a set frequency.
- The slew bearing is the component most worth trending. Its tilt clearance, measured over years, says when it needs planning for, which takes months of lead time.
A port or mine stockyard often runs on two or three machines. If a reclaimer stops, the train or ship loading behind it waits. These machines are large, slow, mostly structural, and many have been running for decades. The obvious failures, a worn bucket lip or a tripped conveyor, are fixed in hours. The ones that matter are slower: a slew bearing that has been wearing for years, or a crack growing in a weld behind the counterweight.
This guide covers stacker reclaimers from the maintenance side: the machine types, stacking methods and blending, the systems on each machine and how they fail, and the structural inspection that matters most. It sits beside the guides to fixed plant maintenance in mining, conveyor pulleys and lagging and the bulk materials handling design brief. Structural design and assessment belong to the structural engineer.
How a stockyard works
Material arrives on the yard conveyor, which runs along the stockyard between the piles. A tripper lifts the belt and diverts the material up onto the machine's boom conveyor, which carries it out to the end of the boom and drops it onto the pile. To reclaim, the boom conveyor reverses on a combined machine, and the bucket wheel cuts into the pile and feeds the boom conveyor back to the yard conveyor.
The machine moves in three ways: long travel along the rails, slew to swing the boom across the pile, and luff to raise or lower it. Positioning systems on each motion let the machine stack or reclaim automatically to a plan, with anti-collision systems keeping it clear of the pile, the other machines and the end stops.
| Machine | What it is | Suits |
|---|---|---|
| Stacker | A slewing and luffing boom on rails, fed from the yard conveyor through a tripper, building the stockpile | Stacking only |
| Bucket wheel reclaimer | A rotating wheel of buckets on a slewing boom that cuts into the face of the pile and feeds the boom conveyor back to the yard conveyor | Reclaiming only, high rates, outdoor stockyards |
| Combined stacker reclaimer | One machine with a reversible boom conveyor that stacks in one direction and reclaims with the wheel in the other | Smaller yards, lower combined duty, cannot stack and reclaim at once |
| Bridge or portal scraper reclaimer | A bridge or portal spanning the pile with a scraper chain or harrow drawing material to a conveyor | Blending beds, sticky material, sheds |
| Circular stacker reclaimer | A central stacker and a reclaimer rotating around a circular pile under a dome | Enclosed storage and blending |
Stacking methods and blending
How a pile is built decides how well it blends. A cone shell pile segregates, with coarse material rolling to the toe. Chevron and windrow piles lay many thin layers, so a reclaimer cutting across the whole face takes a little of every layer, and the grade and size going out are steadier than what came in. Blending is often the reason the stockyard exists, so the stacking plan is a process decision, not just a maintenance one.
| Method | How | Notes |
|---|---|---|
| Cone shell | The stacker stays in one place and builds a cone, then moves on | Simple, little blending, segregation of coarse to the toe |
| Chevron | The stacker travels back and forth along the pile, laying layers along the crest | Good blending when reclaimed across the full face |
| Windrow | Rows laid side by side and in layers across the pile | Less segregation than chevron, needs a slewing boom |
| Strata | Layers laid along the full length at successive heights | Blending of different grades into one pile |
The machine systems and how they fail
A stacker reclaimer is many machines in one: a rail vehicle, a crane slew, a luffing boom, an excavator wheel and a conveyor, with power and control running through a cable reel. Each has its own wear and failure, and its own entries in the preventive maintenance program. The asset hierarchy should break the machine down to these systems, so work and failures can be counted by system rather than lumped against the machine.
| System | What it is | Typical failures |
|---|---|---|
| Long travel | Bogies, wheels, axles and drives running on rails | Wheel and flange wear, bearing failure, rail misalignment, skewing |
| Slew | The slew bearing or slew ring, pinions and drives that rotate the boom | Slew bearing wear and bolt loosening, pinion and ring gear wear |
| Luff | Hydraulic cylinders, or ropes and a counterweight, that raise and lower the boom | Cylinder seal leaks, rope wear, counterweight imbalance |
| Bucket wheel | Buckets, lips and teeth, the wheel drive and the wheel chute | Bucket lip and tooth wear, drive overload from digging into a hard face, chute blockage |
| Boom and yard conveyors, tripper | Belts, idlers, pulleys and the tripper that lifts the yard belt onto the machine | The usual conveyor failures, plus belt damage at the tripper and wheel chute |
| Power and control | Cable reel, slip rings, drives, encoders, anti-collision and positioning systems | Cable damage, encoder drift, collision with the pile or another machine |
| Structure | The boom, mast, portal, counterweight and their welded and bolted joints | Fatigue cracking at welds and connections, the failure with the worst consequence |
Structural integrity
The structure carries the boom, wheel and counterweight through millions of load cycles as the machine slews, digs and travels. Fatigue cracks start at welds and connections where the stress range is highest, grow slowly, and are found only by looking for them. A structural collapse on a stockyard machine is rare, but its consequence is severe, which is why structural inspection sits at the top of the maintenance program.
The structural engineer identifies the fatigue critical locations from the design and the machine's history, and sets an inspection frequency for each. AS 4324.1 covers the design of these structures in Australia. Inspection results are recorded against each location so crack growth can be trended, and any modification that adds mass to the boom or wheel goes through management of change with the counterweight checked.
| Check | What it covers | When |
|---|---|---|
| Routine visual | Cracks, corrosion, damage, loose or missing bolts at known hot spots | Each shutdown, by trained inspectors |
| Detailed inspection | Non-destructive testing of welds and connections identified as fatigue critical | On a frequency set by the structural engineer |
| Slew bearing | Tilt or rocking clearance measured and trended, bolt tension checked, grease sampled | Trended over years against the manufacturer's limit |
| Counterweight and balance | Weight and position checked after any modification to the boom or wheel | After every change that adds or removes mass |
| Structural audit | A review of the whole machine by a structural engineer against its design standard | Periodically, and before any life extension |
The failures that stop a stockyard for a day are mechanical. The failures that stop it for a year are structural.
The slew bearing
The slew bearing carries the whole upper structure and lets it rotate. It wears slowly, and its tilt or rocking clearance, measured the same way at the same points over the years, shows how fast. A replacement is a major job with a long lead time, often needing the upper structure lifted, so it has to be seen coming years ahead. The trend of clearance, grease samples and bolt checks is condition based maintenance on the component that most needs it, and the bearing itself is often a critical spare shared across a fleet.
Common mistakes
- Recording all work against the machine as a whole, so system failures cannot be counted.
- Structural inspection by general rounds instead of at identified fatigue critical locations.
- Slew bearing clearance measured inconsistently, so the trend means nothing.
- Adding wear plate or equipment to the boom without checking the counterweight balance.
- Running the reclaimer into hard or frozen faces that overload the wheel drive.
- Anti-collision and positioning faults bypassed rather than repaired.
- Treating the stacking plan as an operations matter only, so blending suffers.
Common questions
What is a stacker reclaimer?
A stacker reclaimer is a large rail-mounted machine in a bulk materials stockyard that stacks material from the yard conveyor into stockpiles and reclaims it back onto the conveyor. A combined machine has a reversible boom conveyor and a bucket wheel, stacking with the boom in one direction and reclaiming with the wheel in the other. Separate stackers and reclaimers are used where stacking and reclaiming must happen at the same time.
How does a bucket wheel reclaimer work?
A bucket wheel at the end of a slewing boom rotates and cuts into the face of the stockpile. The machine slews the boom across the face, taking a slice, then travels forward a step and slews back. Each bucket fills, lifts and tips its load onto the boom conveyor through a chute, and the boom conveyor carries it to the yard conveyor. The reclaim rate is controlled by slew speed, cut depth and wheel speed.
What is chevron stacking?
Chevron stacking is a stockpile method in which the stacker travels back and forth along the pile with its discharge over the centre line, laying layers on top of each other so the cross section looks like a stack of chevrons. When the pile is reclaimed across its full face, each slice contains material from every layer, which blends grade and size. It is common in blending beds and on ore and coal stockyards.
What fails on stacker reclaimers?
Bucket lips and teeth, slew bearings and pinions, long travel wheels and bearings, luffing cylinders or ropes, the boom and yard conveyors, the cable reel and slip rings, and the position and anti-collision systems. The failure with the most serious consequence is fatigue cracking in the structure, which is why fatigue critical joints are inspected on a set frequency.
What standard applies to stacker reclaimer structures in Australia?
AS 4324.1 covers the design of steel structures for mobile equipment for continuous handling of bulk materials, which includes stackers, reclaimers and shiploaders. It sets the loads, load combinations and fatigue requirements the structure is designed to. Inspections and life extension reviews are usually carried out by a structural engineer against the machine's design standard.
Key terms
Plain-language definitions from our glossary for the concepts this article leans on.
Standards and further reading
- AS 4324.1:2025 Mobile equipment for continuous handling of bulk materials, general requirements for the design of steel structures (Standards Australia)
- CEMA publications on bulk handling equipment (Conveyor Equipment Manufacturers Association)
- ISO 14224:2016 Collection and exchange of reliability and maintenance data for equipment (ISO)
Related case studies and tools
Related reading
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