Tag Archives: carryback

Loadscan load volume scanner study highlights OPEX, revenue opportunities at Queensland gold mine

Loadscan says a recently released report focusing on the results from using a Loadscan load volume scanner at an underground gold mine in central Queensland, Australia, has reinforced the economic and environmental value of its solution.

The study, ‘UNDERGROUND MINING; Economic benefits of load volume scanning of underground mining trucks,’ was conducted over a seven-month period at the mine mine by Professor Peter Knights and Maximillian Reuter from the University of Queensland in Brisbane, Australia. The data gathered over that period indicated a significant incidence of carryback, excessive fuel consumption and under-utilisation of equipment, all of which contributed to unnecessary operating costs and considerable lost revenue, Loadscan says.

The Loadscan Load Volume Scanner (LVS) is designed primarily for the civil construction sector and uses eye-safe LiDAR laser scanning technology, combined with proprietary Loadscan software, to measure the exact volume of material in the bin of a truck. Loadscan’s Mine Payload Technologies division has further developed its Mine Payload Scanner (MPS) for mining applications using technology based on its LVS system.

In operation, empty haul trucks are driven below an elevated scan head to create a reference scan in the database and then, when loaded, are scanned during every pass from the mine, with those scans compared with the reference image to accurately measure the volume of the truck’s load.

Because trucks don’t need to come to a complete stop during the scanning process, the MPS system allows for a time saving over the use of traditional weigh bridges, reducing truck cycle times, while installation, operating and maintenance costs of an MPS are also considerably lower than in-situ weighing systems, according to the company.

Trucks are fitted with RFID tags for automatic recognition and tracking, which allows for detailed real-time reporting and data acquisition. The scan information returned can highlight underloading, overloading – negatively effecting revenue – or uneven loading, which can cause unnecessary stress and wear on truck components and substantially increase operating costs.

“One of the most important factors that the MPS can highlight is the incidence of carryback (or haulback), where material isn’t discharged from the bin during unloading and is carried back into the mine portal, reducing effective payload and having a considerable impact on productivity and, ultimately, revenue,” Loadscan says. “By identifying carryback, the material can be accounted for, deducted from shift tallies where necessary, and removed from the bin to ensure accuracy and improved payload capacity.”

Data for the study was gathered from four articulated haul trucks – three Epiroc MT6020 models with a rated capacity of 60 t, and a single Epiroc MT65 with a rated capacity of 65 t. More than 6,600 scanner readings were recorded over the four trucks during the seven-month period. Carryback was identified in more than 60% of the trucks’ haulage cycles and accounted for more than 980 cu.m of payload over the duration of the study, with an estimated revenue loss of A$370,000 ($243,969), according to Loadscan. In addition, figures were as high as almost 3,500 litres of additional fuel used hauling carryback over the study period, adding almost A$7,000 in estimated additional operating costs.

Loadscan Managing Director, Carey West, said: “Mining across the world is coming under a more intense focus to meet increased best practice requirements such as efficient use of equipment, reduced operating costs and a wide range of environmental issues, which is why metrics such as carryback, fuel consumption and loading efficiencies are so important.”

MPS data showed the average load volume for the 60 t-rated MT6020 trucks was just under 26.53 cu.m, which returned an average payload weight of slightly more than 48 t (based on an estimated bulk density of 1.82 t/cu.m). Isolated scans of the MT65 however, showed average volumes of less than 30 cu.m, equivalent to a payload of just under 54 t – considerably below its rated capacity of 65 t.

Conclusions from the report showed that the capacity of the MT65 could be considerably better used by increasing the average load. Estimations show an increase of just 10% in the average load would be valued at slightly under A$1 million per year, Loadscan said.

West added: “Inefficient loading cycles can have a huge impact on profitability. The MPS provides real-time data of every load with an accuracy of +/- 1% and, by identifying underloading, equipment can be better utilised and operators can be trained in more efficient loading practices.”

Overloading of trucks increases both cycle times and fuel consumption, reducing efficiencies and adding increased stress to machinery components, especially if trucks are loaded unevenly.

Potentially due to the presence of carryback in the bin, just over 9% of the trucks recorded during the survey period showed load volumes that could be categorised as overloading, with load volumes skewed to the right-hand side of the haul truck (potentially due to the location of the carryback material).

Uneven loading can create excessive tyre wear, add unnecessary load to suspension components and create stress through the driveline, Loadscan said.

The MPS allows operators to monitor off-centre loading by scanning the truck bin in four quadrants and generating visual warning indicators, according to the company.

West concluded: “Volumetric load scanning is an extremely valuable tool that can be utilised effectively to reduce mining operating costs and increase effective and efficient use of equipment.

“This report, which has been compiled on the back of collecting comprehensive amounts of data, indicates very clearly that the Loadscan system provides vital and useful information for operators, allowing them to work far more efficiently, generating better bottom-line returns and reducing operating costs.”

Martin Engineering on ‘carryback’ issues with conveyors

“Carryback” is defined as the material that fails to unload from a conveyor belt, adhering to the belt and typically falling off at some point other than the intended discharge, and it’s one of the main sources of fugitive materials, estimated to account for 85% of all conveyor maintenance issues, according to Martin Engineering.

Accumulation on moving components from dirty belts can cause premature wear and require frequent cleanup, which exposes workers to potential workplace injuries and respiratory diseases, it warns.

It can be shown practically and theoretically that a conveyor belt cannot be cleaned 100% because the surface of the belt and the blades are not without imperfections. However, this does not do away with the need for operators to take a proactive approach to keeping the belt clean. Most industries have gravitated to basic mechanical scraping with a metal or elastomeric blade for flat rubber or PVC belting as the best combination of effectiveness, ease of maintenance and low belt wear to yield the lowest cost of ownership.

Belt cleaning effectiveness varies day to day with changing conditions and the number and type of cleaners applied, as well as the maintenance they receive. Keeping the material in the process is always better than letting it accumulate on components and build up under the conveyor. Without effective belt cleaning, experience has shown that as much as 3% of the total cargo can be lost due to spillage, dust and carryback.

The exposure to hazards and injuries is also reduced when less cleanup is required, saving significant – but seldom considered – indirect costs. The key to consistent cleaning effectiveness is to control the process through proper selection, installation, inspection and maintenance of the belt cleaning system and establish a safe cleanup routine and schedule.

The use of multiple mechanical scrapers on a belt has been accepted for quite some time as an effective cleaning approach. In most operations, multiple cleaners are required to reduce the carryback to a safe, acceptable level while limiting manual cleanup to weekly or even monthly tasks.

Effectiveness vs efficiency

The undulating action of the loaded belt passing over idlers tends to cause fines and moisture to migrate and compact on the surface of the belt. The amount of carryback that clings to the belt can range from a few grams to a few kilograms per square meter. The level of belt cleaning required is a function of the operational schedule and method of collecting/disposing of the carryback that is cleaned from the belt or dislodged by return idlers and collects outside of the conveyor discharge chute.

When discussing the efficiency of a belt cleaner, it’s meaningless to talk about efficiency without stating the initial level of carryback. When considering the beginning and ending levels of carryback as a measure of improvement, effectiveness is a better term. Some guidelines do exist. The US Bureau of Mines states that an average of 100 g/sq.m of carryback is a reasonable level of performance for belt cleaning. At this level, a 1,200-mm wide belt traveling 2 m/s and operating 24/7 would create a cleanup workload of about 7 t/d, a significant labour investment that also increases worker exposure to a moving conveyor and the associated risks.

Carryback level determines the cleanup schedule, but, in reality, a typical belt cleaner loses effectiveness over time due to wear, lack of inspection and maintenance. On systems with average or poor maintenance, effectiveness values are generally in the range of 40-60%, thus the need for multiple cleaners.

Cleaning location

Unfortunately, designers often focus on the lowest installed cost of the structure around the head and snub pulleys, without allowing enough space for optimum cleaner installation. The figure below shows the clear areas needed on a discharge chute for installation of belt cleaners in the optimum positions. The installations should be at an ergonomic height above the work platform to encourage proper inspection and service. Consideration in the design stage for locating cleaners in the optimum locations will lead to more effective inspections, maintenance and belt cleaner performance.

Belt cleaning positions (© 2022 Martin Engineering)

Belt cleaners can be placed anywhere along the return run of the belt, as long as the belt is supported in some fashion. Since it’s desirable for the carryback cleaned from the belt to be returned to the main material flow, most belt cleaners are installed inside the discharge chute. Cleaning on the head pulley – labeled the ‘primary cleaning position’ – is preferred. Cleaning the dirty side of the belt before it reaches a snub, bend pulley or return idlers is considered less desirable, requiring a dribble chute for cleaners in the secondary position.

Typical installation of primary, secondary and tertiary cleaners (© 2022 Martin Engineering)

The secondary position is complicated by another fact: the nature of carryback is such that it can adhere to vertical surfaces and not flow down a sloped dribble chute. A tertiary position is sometimes required for difficult materials or critical applications such as conveying over wetlands. In such cases, the tertiary cleaners are often enclosed in a spray box and the effluent directed to a settling basin.

Belt cleaning pressure & blade wear

Without enough cleaning pressure, the blade cannot stay in contact with the belt, resulting in poor carryback removal effectiveness and increased blade and belt wear. With too much cleaning pressure, the cleaning performance declines due to deflection of the elastomeric blade or metal blade indentation into the rubber belt. Power consumption also increases dramatically with excessive cleaning pressure.

Elastomeric primary blade pressure at a positive rake angle (left) and metal secondary blade pressure at zero rake angle (right)

Keeping a belt cleaner properly tensioned is critical for maximum effectiveness and lowest cost of ownership. The cleaning pressure usually varies over time, based on the maintenance department’s attention or lack thereof. Some manufacturers have begun to offer automatic tensioners and wear indicators which maintain the optimum cleaning pressure and alert operators when blades are worn.

Automatic tensioner maintains optimum cleaning pressure without operator intervention (© 2022 Martin Engineering)


Many belt cleaner systems are installed and forgotten. A survey of technicians indicated that about 25% of all belts have cleaners installed, and of that percentage only about 25% are properly maintained. Lack of inspection and maintenance results in a gradually lower level of effectiveness, higher operating cost and an increased exposure to the hazards associated with cleaning up carryback.

Effective belt cleaning starts in the design stage, with adequate space for cleaners and well-positioned work platforms for ergonomic inspection and maintenance access. Service-friendly designs improve production, minimising carryback and prolonging the life of equipment. If the cleaners are located in the optimum positions and easy to access, it is more likely that regular inspection, cleaning and maintenance will be performed, delivering optimum results.