Machines operating in Australian underground hard rock mining endure some of the toughest conditions on the planet.
Once the ground is blasted, it is the underground loader’s (or bogger’s) job to load the muck pile into the truck ready to be hauled to the surface and to clean up the drives. The bogger buckets need to withstand the force and wear from being driven into muck piles and scraped against the floor and side walls of the mine.
Hence, the common practice to add sacrificial wear packages to protect the structural integrity of bogger buckets in this harsh operating environment – heel shrouds, lip shrouds, underfloor wear bars and profile bars.
The Outcast® Bucket Revolution
Operating since 1988 and beginning as a repair and maintenance specialist for heavy machinery, Kalgoorlie-based Goldmont Engineering has been heavily involved in developing better buckets for the mining industry.
Australian Mining Review spoke to Goldmont Engineering managing director Roy Gregory about why the company had designed the new and innovative Outcast® bucket for underground loaders. “Conventional bogger buckets are heavy, inefficient and expensive to maintain. They have been protected with weld on and bolt on ground engaging tools and wear bars for as long as any of us can remember,” he said.
“Consequently, the underground loaders must carry extra weight and work harder to overcome the friction created by the add-on wear materials.”
The Outcast® bucket design ticks all the boxes to address these issues. It is stronger, lighter, and smoother. It has lower maintenance costs, increased fuel efficiency and reduced CO2 emissions, requires less machine downtime for bucket maintenance and reduces safety hazards. It can be fitted to any model of underground loader including the popular CAT and Sandvik loaders.
What are the magic ingredients?
No More Wear Bars or Shrouds
One of the standout features of the Outcast® bucket is the absence of wear bars on the underside of the bucket, heel shrouds protecting the edges and lip shrouds protecting the lip.
“The wear bars, heel shrouds and lip shrouds are a significant contributor to both the extra weight and the extra digging friction when using conventional buckets,” Roy said.
The ability to operate a bucket in a harsh environment without wear bars or shrouds has been achieved through a combination of using high strength, wear and impact resistant steels (Hardox® and Strenx®) and innovative design changes.
Redesign of High Wear Areas
The Outcast® Bucket has several effective design differences in the areas that are subject to high wear in conventional buckets.
“The upper section of the side walls and cutting-edge angle inwards. This reduces impact with the mine walls and improves the structural strength across the top of the bucket by reducing the bridge span,” Roy said.
The Outcast® Bucket has also been designed with a 45o transition between the floor and side-wall of the bucket which creates a void behind the bucket corners. This reduces the wear forces on the transition area to eliminate the need for heel shrouds.
“On traditional buckets the heel shrouds protecting this area would be scraping against the wall and the ground, or the rocks in the muck pile. This forces the machine to work harder as well as increasing maintenance costs,” Roy said.
Another design change is the lift in the underside of the bucket behind the cutting edge.
“The underside of the bucket is 75mm above the ground – so there is less friction when the cutting edge penetrates muck piles.” Roy said. “This makes for less wear on the bucket and less work for the bogger”.
Ears External to the Bucket
A design difference that is immediately noticeable when comparing to conventional underground buckets is the external attachment bores (ears) which enables a uniform internal bucket profile. That means no boxed-out centre section inside the bucket.
“It’s a more efficient use of volume inside the bucket and it removes an area subject to high impact forces in conventional buckets that is prone to material fatigue and cracking,” Roy said.
“The external ear set also provides better access for line boring, fitting to the loader and regular maintenance inspections.
“The removal of the boxed-out centre section also makes it easier to fill the bucket when pushing into stockpiles because there are no protrusions inside the bucket creating a tendency for voids.”
Bucket Position Relative to the Tilt Cylinder
The external bucket ears created another design challenge. In conventional bogger buckets, the boxed-out section inside the bucket is used to make space for the tilt cylinder attached to the ears. This reduces the distance to the front of the bucket lip.
However, the distance from the tilt pin cylinder on the Outcast® Bucket to the front of the lip is within 100mm of conventional buckets despite the external ears.
“This was achieved, without reducing the bucket’s volume, by changing the overall shape of the Outcast® bucket,” Roy said.
“It has a shorter base offset by a steeper side wall cutting edge. The shape was also designed to ensure the operator retained good forward vision when the loaded bucket is crowded back.”
Lip and Corner Tooth Assembly
The bucket lip and corner teeth can be customised to suit the different operating environment across different mines.
“We acknowledge that each mine has its own mining methodologies and ore characteristics such as abrasiveness,” Roy said. “We did not want to take the ‘one size fits all’ approach.”
Less Incidental Damage
A flow-on benefit from the absence of heel shrouds is less incidental damage. During loading operations, trucks might be located near ventilation bags located on the backs. The bags can be punctured if caught on the heel shrouds protecting the top of the side cutters.
This problem is eliminated by the absence of heel shrouds on the Outcast® bucket.
Roy describes another example of incidental damage: “The heel shrouds quite often grab the top of the truck tray walls when dumping ore into trucks. This causes damage to the top of the walls and discomfort for the truck operator.”
A gold mine in the WA Goldfields reports large benefits from changing to an Outcast® bucket on its R2900 underground loader. A study at the mine estimated the bucket saved $120,000 per year in maintenance costs and $8000 per year in fuel costs compared to the conventional 8.3m3 bucket it had been using. The reduction in fuel also meant 40t less CO2 emissions per year.
The reduced time maintaining the bucket increased the bogger’s availability by an estimated 150 hours per year or an average of three hours per week – that could mean an extra development cut per week or a significant improvement on production tonnes.
Cycle times were improved by the easier penetration into muck pile – the loader did not have to bog as much to fill the bucket – and quicker dumping with the ore sliding easily out of the bucket.
Another benefit of the ore sliding easily out of the bucket is the absence of hang-up, which has never been observed in an Outcast® bucket. Hang-up is a common problem in conventional buckets.
The study also found the bucket contributed to an improvement in safety. It reduced the manual handling hazards associated with replacement of wear parts and reduce the fitter’s exposure to the line of fire when fitting the bucket to the loader or servicing the bucket pins.
Goldmont Engineering can assist mine operators perform cost analysis on their buckets.
“Comparing the Outcast® bucket to conventional buckets has revealed that mines often don’t have the information required to understand the life cycle cost of their buckets,” Roy said.
“That’s not surprising. It would be easy if we measured the required data. The challenge is that a $100 to $150,000 bucket hangs off a $2 to $3 million bogger so it is natural to focus performance measurement on the bogger as a whole,” Roy said.
“The opportunity to compare the performance of different buckets is lost in the noise.”
However, the Outcast® bucket is a good reason to better understand bucket costs.
“Selecting the best bucket can add significant value to a mining operation,” Roy said.
“Goldmont is happy to share its experience in estimating the true cost of different buckets.”
- Goldmont’s Outcast® Bucket design is protected in Australia and a range of other countries.
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