Crushing blows

New machines are good news if you are quarry operator, bad news if you are a piece of limestone. This is the kit that is beginning to crawl in to the region.

GRIND TO A CRAWL: Tracked crushing plants can improve efficiency, while gravity powered conveyers are a safe and effective way of moving the stone fro
GRIND TO A CRAWL: Tracked crushing plants can improve efficiency, while gravity powered conveyers are a safe and effective way of moving the stone fro

New machines are good news if you are quarry operator, bad news if you are a piece of limestone. This is the kit that is beginning to crawl in to the region.

Gaining stone from a quarry is a hard way of making a living - even with the high level of demand for construction materials across the UAE. Production outputs have to be maintained at a constant level, while priority must be given to the quarry product with the highest value. Obviously, the amount of saleable product must be kept to a maximum while time and money wasted through handling materials twice must be avoided at all costs.

This is where the modern machines step in. Three months ago we looked at the drive for efficiency in Ras Al Kaimah's limestone and gabbro mountains Now, we look how new technology could help the site operators produce the gravel for less money.

Modern drills

For decades, drill and blast has been the preferred way of getting rocks out from the face. David Matyus, general manager of equipment company Quarry and Mining explained "Drilling and blasting is still the high production method." While the technology has remained the same, the size of the drills used has increased dramatically.

German plant maker Leibherr's latest product, the R 996 Litronic is modular in design. Markus Mogel, export sales, Mogel explained, "All the drill's modules can be transported by flatbed truck or ship and easily assembled in the mine. The modular design also minimises downtime for maintenance work or the replacement of components.

Moving rocks

Ask most people what the most dangerous aspect of quarrying is the reply invariably is drilling and blasting. In fact, the overwhelming majority of accidents happen on the rocky road between the cliff face and the crusher. Dozens of huge dumpers thundering down a steep incline, laden with hundreds of tons of rock have the potential for devastating accidents with whatever is coming the other way, no matter how well run the quarry is.

Although things are changing, some quarries still pay scant attention to the safety of the workers.

Matyus said "Most of the accidents over here, and there have been some horrendous ones - have involved vehicles." He added "There are two extremes, some are very European in outlook and some pay absolutely no regard to safety so you have small cars driving around in areas where there are enormous trucks.

Obviously, safety begins by removing the small cars from the boulder trails and by better training the truck drivers. However, new innovations can further improve the run down the hill. While weighing trucks has been the norm for some time, one electronics manufacturer can now supply the region with a device designed especially for articulated dump trucks.

The dash-mounted device looks similar to electronic weighing machines that have been around for a while, but the new Weightloader ADT has been especially designed for quarry applications.

Mike Shaw, UAE Manager of Prolec said "The Weightloader ADT can help site managers with features such as the ability to accurately weigh even when the machine is on an incline." He added that site efficiency could be monitored as the real-time data could be uploaded to a computer.

While having trucks carrying the right load is a good start, both safety and efficiency can be made even better, by simply removing the dumpers altogether.

Taking a belting

Many modern plants around the globe have invested in conveyer belt systems instead of relying on trucks. Although belts are expensive to install, David Matyus explained "A conveyor system is very efficient, For a start, it doesn't need any power as the weight of the stone pulls it down the hill, so the whole thing is self generating. In fact, it needs brakes to stop the conveyor going too fast".

Large installations can see conveyors hundreds of meters long being constructed, with stone going directly to the pthey get no rimary crusher.

The job of the primary crusher is to turn the rock into rubble. These machines need to be manufactured to a high quality, as rest. "A well managed plant will be running at 85 per cent efficiency, 20 hours a day" Matyus said. In fact, were it not for the mandatory downtime in the early afternoon as demanded by law in the northern Emirates, it is highly likely that the machines would simply never stop.

In the past these plants would handle a few hundred tonnes per hour, but now modern equipment is pushing this figure much higher, with plant such as the Kleeman SSTR 1600 unit handling up to 1200tph.

There are several basic types of crusher, but generally only two are used for primary crushing, being jaw and gyratory. Jaw crushers consist of a pair of jaws, one being fixed and the other moving by a cam or pitman mechanism to grind the stone.

A gyratory crusher, meanwhile, uses a concave surface and a conical head; both surfaces are typically lined with manganese steel surfaces. The inner cone has a slight circular movement, but does not rotate; the movement is generated by an eccentric arrangement.

As with the jaw crusher, material travels downward between the two surfaces being progressively crushed until it is small enough to fall out through the gap between the two surfaces. The site operator needs to be sure that he is buying the right crusher for the job, as the wrong one can litterally halve productivity.

Process control

These modern static plants with new technology including process control which is a way of increasing efficiency in the secondary plant. This involves fitting computer equipment to manage the output to a steady level, and so ensuring constant production.

Most machines are governed simply by what goes in at the front, and a whole variety of manual controls are needed to govern what comes out at the other end. The whole process is similar to a carburettor governing a petrol engine, while process control is like fitting the same motor with engine management.

A computer controls the input variables, ensuring both a steady flow rate and even quality of production so there will be no need to handle the materials twice. However, plants with process control are not common in the Middle East, even among the larger quarries because of the increased complexity that it brings into the operation. Also, it is sometimes difficult to find the right service people.

In spite of the high-tech computer systems involved Matyus would recommend investing in such equipment. "If you have a PC control plant, you have the benefits of making the most of productivity by monitoring the process." He added that operating with tight margins it was important to eliminate needless and time-intensive tasks such as double handling of materials.

Making Tracks

However, there is no reason why the plant can't be brought to the mountain. The last few years have seen the rise of tracked crushers, with a few beginning to crawl their way in to the UAE. With machines such as the German-made Kleeman Mobicat range now available over here can now be easily maneuvered anywhere on site.

This can be very useful when plants are required to change location frequently, for example, move with a quarry face or dig.

When processing material in a quarry, or when recycling, it is clear that substantial savings are achievable by moving the plant to the material rather than moving the material to the plant. Matyus explained "The machines can also be adapted to special applications due to their modular design which is independent from the drive system.

"All of these plants have the use of an onboard generator which is used to drive the conveyor belts, vibrating chutes and screens.

"The excess capacity of this generator can be used for the operation of additional plant such as stockpile conveyors or screens, therefore saving the costs of additional engines and running costs."

So next time you order some aggregates for a concrete mix, spare a thought for where the rock has come from, and the machines that made it possible.

Building the world

As well as limestone being ground up for aggregates, the northern Emirates are currently supplying the huge lumps of gabbro used as the base for the many man-made islands on the Dubai coast.

These rocks are usually moved by truck to the deepwater port in Ras Al Khaimah, where they are shipped out, directly to their destination in the sea.

Huge cranes are used in laying the stones, which are individually signed off by a diver. It is unclear exactly how much material is needed for each project, but official estimates suggest that the first two Ã'palms' alone required 100m tons of rock and sand.

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