From the time the quarry gates open first thing in the morning to the end of the working day, the handling of quarry stock is a dynamic and important process that involves many movements of plant and equipment and many interactions between quarry workers and other staff.
Every time we touch quarry products with plant and equipment it increases costs in wages, tyre wear, fuel spend, machine hours, etc.
Therefore, we need to minimise our interaction with quarry products by automating processes where possible and when manual processes are required understanding them fully to maximise production output and quarry reliability.
This paper explores the key issues for stockpile management and load out and discusses the benefits that may be realised in utilising available technologies. Some of the key issues include:
- Measuring and improving load out cycle times within a quarry site.
- Identifying the real costs of delays in loading and weighbridge hold-ups.
- Unnecessary fuel costs from inefficiencies in the load out process.
- Determining how automating and streamlining load out can benefit your business.
- Ascertaining how to get real efficiencies in your mobile plant and equipment.
REDUCING LOAD OUT CYCLE TIMES
Cycle load out times are the measure of how quickly a customer will be loaded and ticketed across the quarry weighbridge and have left the site. When our customers are kept waiting in our quarry they are losing their truck utilisation and therefore profit. This poor performance in quarry cycle times will impact the quarry owner/operator, as unhappy customers shift their business to competitors.
Anything that impacts quarry load out cycle times will be costly to your quarry operation and the correct matching of mobile equipment is essential to realise the full efficiencies in this area. Quarry operators must train their people to ensure established processes and procedures are understood, clearly communicated and repeatable to maximise quarry profits. Where there is a mismatch in load out equipment, processes and staff knowledge, problems creep in and profits fall directly as a result.
Our quarry customers operate in a highly competitive environment, where margins are tight, and they are very focused on efficiencies in truck utilisation. Hauling aggregate is most profitable when the trucks are kept full at all times. Back loads on a truck?s return journey are not always available and as a result cartage costs climb rapidly as the trucks drive empty.
Most contracts/projects are priced on a set number of loads per day to achieve slim margins to tight construction time frames. When delays occur, especially within a quarry, this is seen by a customer as an unplanned delay and across a shift or day may lead to a reduction in the number of loads completed and therefore customer revenue is lost.
In the following example we explore the real measurable costs of longer cycle times within the quarry, expressed in Australian dollars (AUD). The average cost per kilometre may be broken down approximately as follows:
Let?s say that a 15 per cent margin applies on the transport (TOC) of the quarry material supply.
Note: These costs are based on the truck achieving a given number of cycles per day. If the number of cycles are not achieved then the costs, especially for the driver will increase.
Let?s review the reduced transport margin if a cycle is dropped due to truck delays. Based on a cycle of 60 kilometres return, a truck is expected to undertake seven cycles during a shift.
Note: There will be incremental reductions in costs of road charges, fuel, tolls and tyres.
The truck operator is losing approximately 14 per cent in cartage revenue which may make the business unprofitable into the future, due to hold-ups in load out at the quarry. Therefore it is vitally important that cycle times within quarry are reduced to a minimum.
As indicated in the example above, the cost to the truck operating company will be approximately AUD$200 which they will want to recover back from the quarry operation. In cases where a company owned truck fleet is used for product delivery the increase in cycle times directly affects the profitability of the operation(s).
Load and haul cycle times are influenced by a number of factors that need to be considered.
TIME IN QUARRY
The average time in quarry is dependent on a number of factors, most of them outside of the control of our customers. Therefore it must be the quarry?s task to measure time in quarry and put relevant key performance indicators (KPIs) on the different elements of this process with a plan to reduce overall times.
Time in quarry can be broken down into:
- Truck (TARE) weighed/recorded and travel time to relevant stockpile.
- Truck waiting to be loaded.
- Truck loaded and application of tarpaulin if required.
- Truck travel to the weighbridge and if required queuing to be weighed before exiting the quarry.
Once a customer has entered a site, effective stockpile layout will minimise congestion and time spent in the stockpile area. Having fast moving products close at hand or easily accessible will allow for quicker loading; slow moving products should be given a lesser priority for position within the stockpile area. By having an intuitive layout the customer is directed to position their trucks naturally in the best location for quick load out.
The quarry?s stockpiling area should be designed to ensure that there is sufficient room for mobile plant and customers? trucks to operate effectively. Where possible all vehicles should be able to move past each other with sufficient room. Pinch points should be kept to a minimum or designed out. Where there is not sufficient space for this to happen, implementing a one-way system can be effective in reducing vehicles operating in close proximity.
The design of a one-way system should be intuitive. Once a truck has passed over the weighbridge and entered the stockpile area, the driver?s route around the stockpile should be easily identifiable. Providing adequate signage indicating direction of flow and general traffic rules assists, as does providing well planned stockpile layout maps at the weighbridge and guidance as required.
If there are crossroads where traffic merges, especially at the weighbridge, this can add to congestion during high or peak periods.
One-way systems will reduce congestion at these points. Where possible the weighbridge should be designed so that dockets can be issued via a drive-up window. This means that drivers do not have to leave their vehicle to collect their docket which offers advantages both in terms of reducing driver?s time on-site, and from a safety perspective reduces the amount of pedestrian activity in the quarry environment.
In the traditional quarry environment, information sharing throughout the site is usually done verbally by use of open channel two-way Ultra High Frequency (UHF) radio. This includes communications between the weighbridge and the stockpile load out area and haul trucks. While this system is cheap and easily expandable by simply purchasing more handheld units, it relies on clearly spoken and clearly heard communications.
Whether it is a bin truck, light vehicle, water cart, haul truck or loader, multiple communications across open two-way channels can lead to mistakes where a high volume of traffic is experienced. In some cases it may be that the wrong material is loaded out and is picked up at the weighbridge where it is returned back to the stockpile area to be tipped off with the truck reloaded with the correct product(s).
In the worst case scenario, the wrong product may be sent to site where it may be used in the wrong application, incurring potential reconstruction costs or it may simply be returned to the quarry unpaid for. In any of these scenarios, the quarry and the customer are losing profit. The importance of clear and accurate communication can never be over-emphasised.
By adopting electronic technologies these risks may be minimised and ideally with the right balance eliminated completely. If both the weighbridge and the loader operators can clearly see individual material product identification, linked to a visible job number or a customer request, and the length of time a customer has been on-site is visible, the management of time in quarry can be measured. If it can be measured it can be managed.
Clear communication between the weighbridge and the stock load out area is key to ensuring that the correct product is loaded and in a timely manner. This can both reduce the time that customers have to spend on-site, and mitigate the risk of communication errors to improve both the accuracy and efficiency of the loading process. Dedicated communication solutions may also be sought through loader bucket scales interfacing with the weighbridge to further remove errors.
MEASURING LOADER PERFORMANCE
Loader performance is a key consideration for operations management and ideally the loader should be operating at peak capacity for as much of the day as possible. However with quarry customer traffic typically varying throughout the day, loader usage will also vary. Monitoring loader performance allows operators and management to understand current performance, spot where improvements can be made and to implement a plan.
LOADER OPERATION – LOADING PATTERNS
Ideally the loader should be working in a V pattern, moving in and out of the face in loading the truck, and when viewed from above creates a V pattern. While this is the ideal, it is difficult to perform in many cases and relies on a loader operator?s understanding of how important it is to load as close as possible to the V-type optimum. This will ensure the minimum distance is travelled to get the truck loaded and on its way.
MOBILE EQUIPMENT EFFICIENCY
To ensure a high level of performance, mobile equipment needs to be carefully monitored, and for this we refer to a common manufacturing facility evaluation tool.
How effectively a manufacturing facility is utilised is evaluated through the Overall Equipment Efficiency (OEE) protocol which was first developed in the 1960s and measures three factors:
- Performance. Actual throughput versus target throughput.
- Availability. Actual plant hours versus planned plant hours.
- Quality. Aggregate produced to specification for a number of units produced.
Each of the three factors is calculated as a percentage and multiplied together to give a top line metric. A world class quarry may achieve 85 per cent or higher in this metric. While a mobile plant involved in load out is quite different, the same concept can be applied to establish existing efficiency and work towards improving it. The three measures that can be used are availability, utilisation and load accuracy and they are discussed below.
Loaders should achieve key availability targets that relate to their ability to work as and when required. A high score in this measure is dependent on the maintenance regime in place, particularly preventative maintenance. Where there is no robust plan in place or the quarry has purchased problematic mobile plant (poorly engineered, defective, cheap, and so on) this metric is expected to be low.
Availability can also be affected by a shortage of operators. Having correctly trained staff on-site and ready to operate equipment is a key day to day management issue. A lack of available operators will adversely affect the availability metric.
The availability metric is determined by dividing the number of loader hours over a determined time period by the planned number of loader hours required. The result is expressed as a percentage.
The quarry has a duty of care to ensure that customers? trucks are not loaded beyond the maximum weight they are legally allowed to carry. Releasing a truck that is overweight could have serious consequences for both the quarry and the customer alike. It is primarily the loader driver?s responsibility to ensure that customers? trucks are not overloaded, and in cases where this does happen, the load must be unloaded and reloaded. This can cause lengthy delays, especially at peak times.
The TPS would characterise this kind of rework as wasteful. On sites where there are issues with loading inaccuracy, operators should be given additional training/supervision to increase their success rate. Metrics on performance should be implemented and discussed with relevant staff to ensure that the performance review is transparent. Where it is being monitored there is usually an initial performance improvement.
EXAMPLE OF MOBILE EQUIPMENT EFFICIENCY
Assume that Quarry A has three loaders operating and has the following targets in place for load out:
- Rated hourly capacity of loader fleet of 360 tonnes per hour.
- Average daily sales of 3300 tonnes.
- 11 hours per operation.
- Total loader hours of 32 hours. Operator breaks covered.
- Total 112 trucks loaded (29.5 tonne average weight), three trucks reloaded.
Availability – 32 actual hours / total 33 hours = 97 per cent
Utilisation – 110 tonnes/hour per loader / 120 tonne per hour loader capacity = 92 per cent
Loader Accuracy – 109 trucks loaded to correct weight/ total112 trucks = 97 per cent
On this given day the mobile equipment efficiency would be 87 per cent. Typically we would be targeting greater than 85 per cent.
By implementing a number of the concepts and best practice discussed in this paper you will be able to realise benefits to your operation.
If the stockpile area of your business is not run efficiently the extra costs may not be immediately obvious to your operation but will be for your customer?s profit. Stockpile areas should be well considered and the loader operators understand their importance to the load out process. Adopting technologies that limit error in the load out process and at the weighbridge will ensure that the right quantity of the right product gets loaded. This will provide greater returns by repeat business and satisfied customers.
Michael van Koeverden is a director of Quarry Mining Systems Pty Ltd. This article was originally published as a white paper on behalf of Loadrite. For further information, visit www.quarryminingsystems.com.au