Continental Conveyor & Equipment notes that today conveyors can think for themselves even (Continental's Smartveyor technology) and adjust instantaneously to changing conditions. "Of perhaps even more importance, is conveyor technology which offers near 100% availability."

Globalisation is currently the trend and this is something at which Continental, today's largest supplier in belt conveying, has been very active recently taking on such companies as Meco, FSW and Huwood. According to Doug Rome, managing director of its southern African operation, Continental Meco: "Today, high productivity conveying demands challenging performance requirements that necessitate a Total Systems Approach in order to prevent serious potential problems which could impact on the entire mining operation." He points out that Continental's worldwide engineering team has been able "to develop advanced proprietary information on conveyor behaviour under the full range of mining conditions and circumstances. This information provides insights into the dynamic phenomena that occur in operational extremes and in normal day to day operation." Each company in today's Continental group has proprietary technologies and is active in the ongoing development of new conveying technology.

The company notes that much of today's conveyor technologies were developed in response to the demanding requirements of longwall mining, while some were developed in response to age-old conveyor challenges, such as steep angle conveying and belt-tension management. Evolution, beyond the most basic pulley and belt configurations, began with a collection of engineering breakthroughs by Continental in the early 1980s. Paramount among these, was the precise modelling of conveyor system behaviour under a variety of special conditions ­ including system behaviour under extreme loads and during high-stress starts and stops. This was later developed into advanced computer software (such as the Continental Statix program) which is key to the reliable design of today's high-performance conveying systems. Also, during the last decade, specific conveyor components have been developed which greatly enhance overall conveyor performance capabilities. These include large, very powerful drives and small drives which are quick and easy to align, in addition to being extremely portable; constant tension winch technology which is precise and quick; belt storage units which are trouble-free; and high angle conveying which is simple and reliable, even in high-volume applications.

Among the technologies Continental has acquired recently are conveyor belts that can turn at 90° angles, systems which advance and retreat while the conveyor is in full operation and specific, noise-limiting Stealth Roller components.

Continental advises that: "The new challenge of the mining community is to imagine and incorporate conveyor applications into their planning which reach beyond today's accepted productivity levels, and use the advanced versatility of current conveyor technology to create their own strategic advantage."

As with so much mining equipment today, partnerships are becoming important in conveying. Last year, for example, Martin Engineering signed two major long-term deals. In Brazil, under a $16.5 million, five-year contract it is supplying belt cleaning and sealing equipment, replacement parts, and maintenance and cleanup services for 153 belt conveyors in Cia Siderurgica de Tubarao's Victoria steel mill. In Germany, its three-year contract with Rheinbraun, the world's largest lignite mining company, is to supply belt cleaning systems, including blades, mainframes and tensioners for Rheinbraun's four surface mines. Managing director Goran Ottosson commented: "Through this contract, Rheinbraun hopes to improve cleaner performance and system standardisation, while reducing operating costs and the overall number of suppliers. Martin Engineering will provide a full range of cleaning systems to suit even the widest, fastest belts serving Rheinbraun's high-volume bucketwheel excavators.

Safeguarding the belt

Lars Vistrand, president of Svedala's conveying division, believes that though conveyors are rather complicated, there are still many buyers that see them as simple and buy their components like commodities, especially the belt. He also points out that in the majority of cases, belt replacement is required not because of wear but as a result of mechanical damage.

Among the causes of mechanical damage Mr Vistrand identifies is belt slippage. There are three main reasons why belt to pulley slippage occurs. There may be too low a coefficient of friction between the belt and the pulley, or the angle of wrap is too small or the pre-tensioning of the belt is too low. The most cost efficient solution to a slippage problem is to increase the coefficient or friction by using pulley lagging. With the right design the pulley lagging will also prevent build up of transported material and snow and ice on the pulley.

Material tends to tumble and bounce when dropping onto a conveyor belt, particularly if the transfer point is at a 90° angle to the receiving conveyor. Combined with the fact that the use of idlers leads to sagging of the belt between them, this may lead to spillage of material over the side of the conveyor belt in the transfer area. From the Svedala product line, this problem can easily be solved by installing a Trellpact loading station combined with a Trellex sealing system. The impact bars prevent sagging of the belt and the low friction top cover offers a flat surface for the sealing blocks to seal against.

Impact damage is especially prevalent where belts carry very coarse or sharp-edged materials that cause weak points, holes, or even tears in the belt. In some occurrences the full length of the belt may be slit. Steel cord belt without rip-protection is especially vulnerable to this sort of slitting. One answer is, again, the Trellpact loading station. Its composite impact bars consist of an aluminium track for fastening, special rubber for impact absorption and a low friction top surface of UHD-PE to prevent belt damage.

Misstracking belts can cause major unnecessary costs. Belt guiding or training systems can cut maintenance costs substantially through actively controlling and guiding the belt back on the right track. Moreover, revenues increase as a result of higher conveying capacity due to reduced material spillage.

The most important component of a conveyor system, whatever the materials or operational problems, is still the belt itself. Lars Vistrand comments, "customers often tend to see belts as consumable commodities and are inclined to buy the cheapest available. However, a 5% saving can be lost within half an hour of operation should a belt problem occur. Additionally, a belt that is 5 mm thick, as opposed to 3 mm, costs only 20% more, but will provide 60% more operational life." Customers may ask, 'Why buy an extremely wear-resistant belt when most belts fail because of mechanical damage?' The answer is that the correct systems and components can reduce mechanical damage, making it worth buying a highly wear-resistant belt.

Svedala has such a belt ­ made from Svedala's MM30 rubber. "This belt material recorded wear of only 30 mm² according to the DIN test standard. A belt previously regarded as having good wear-resistance would have wear of 120 mm². Although the MM30 rubber belt is about 30% more expensive than standard belts, it is ideal for short belts where impacts are more frequent, since the belt is going to pass the loading station more frequently," states Lars Vistrand.

Svedala also manufactures corrosion-resistant belts. "We don't always recommend steel cord belts, even for very long or high-tension installations: when such a belt becomes damaged, the steel cords become exposed and are then subject to corrosion. Svedala's answer to this is a reinforcement textile called Aramid ­ five times stronger than steel so only 20% as much of it needs to be used and it is not subject to corrosion."

Once a belt has been damaged, as Aram Friedrich, sales & marketing manager with Global Resins, notes, repair is undertaken in one of four ways: Hot vulcanising, cold vulcanising/finger splicing, mechanical fastening/clip jointing, or with cold-curing repair compounds. The first three all require the removal of the damaged section, followed by the insertion and splicing of a replacement piece. "The fourth technique differs radically in that the damaged piece itself is treated to render it fit for continued use. Quite often, the nature of the damage is not serious enough to warrant cutting the affected section out. It is possible to repair it reliably and permanently with the minimum downtime and cost.

"Cold-curing repair compounds are ' stand-alone ' in nature. This means that they are applied solely and directly onto the damaged area with the aim of re-building or replacing the missing/damaged rubber. The repair compound will reinforce and strengthen the belt in the area subject to abuse. If this does not happen, then whatever caused the original damage could re-occur, resulting in the same damage to a different section of belt. If unchecked, this process has a habit of self-perpetuation. Merely replacing the damaged section with another piece can only be successful in the long run if the source and cause of damage is found and rectified. Because repair compounds are far stronger and tougher than rubber, they will provide protection against this damage-causing factor for an extended period."

Mr Friedrich further points out that: "polyurethane advancements in the last eight to ten years have effectively put paid to the problems of old, and are gradually restoring faith in cold repair techniques." He contends that thermo-setting polymer and polyurethane resins have significant advantages over the other two types of cold-cure repair compounds, namely solvent-based contact adhesives and heat-activated thermo-plastic compounds

He concludes that "cold-cure repair compounds offer cost-effective solutions for belt maintenance that are durable, reliable and easy to use. As urethane technology advances, the quality and versatility of cold-cure repair compounds will improve, thereby offering added value to belt operators worldwide."

Creative Engineering offers software for engineering design, cost estimation and construction. This includes structural design of conveyor trusses, bents and struts. A feasibility analysis automatically determines NPV and IRR of the most cost efficient haulage system.

A major re-organisation last year was undertaken by leading belt supplier Dunlop-Enerka, integrating the international marketing operations of its Dutch, Belgian and British facilities. Dunlop belts are supplied with rubber and PVC covers in a number of grades (abrasion-resistant, heat-resistant, oil-resistant, fire-resistant, etc.) and in standard widths from 300 to 3,000 mm. Depending on the type of carcass, the tensile strength of the belts varies from 80 to 7,500 N/mm.

Massive overland systems

Krupp Canada reports that work is proceeding well on the Los Pelambres overland conveyor system in Chile (MM, April 98, p.294). The task of conveying copper ore from the open pit mine nestled on a mountain 3,000 m above sea level, down 1,300 m to the processing plant at the valley floor below has made this one of the most challenging conveyor projects ever. The system conveys ore at 8,700 t/h, at a speed of 6 m/s over a distance of 12,750 m. The total distance is divided in three individual flights, each with 1,800 mm wide belt, the longest flight being 5,630 m. Conveyor Dynamics provided support in such key areas as PLC programming, belt selection criteria, dynamic analysis and brake design.

For protection from avalanches and rockslides, the conveyors run through a tunnel system almost 12 km in length. The lowest of the three conveyor sections is equipped with a shuttling head end. With this, the conveyor discharge point can be moved back and forth by 100 m, allowing it to build up a longitudinal stock pile at its end.

To meet the extreme design parameters, the limits of conveyor design had to be pushed to further extremes. For instance, the Phoenix ST 7800 steel cord conveyor belt is the strongest belt ever installed in a conveyor system. A total drive power of 25,000 kW, consisting of ten 2,500 kW drives, is included in the design plans. In loaded condition, the electric motors act as generators and feed electric energy back into the power grid. The motors are controlled by variable frequency inverters, allowing infinite adjustment of the motor speed. This technology allows starting and stopping the conveyors precisely along predetermined acceleration and deceleration ramps. Belt jerking and stress waves, which are harmful to the equipment, can thus be avoided.

Safety has been the highest design priority. To minimise the risk of uncontrolled belt run-away, various precautions have been installed. For instance, in the event of a power failure the electric energy generated in the motors will be automatically diverted into giant resistors, and the conveyors will be brought to a controlled stop. For additional safety there is also a mechanical brake system comprised of 13 disc brakes, each with a rotor diameter of 2,500 mm. The hydraulic control circuit of the brakes is completely redundant ­ the function of each component is fully backed by another component. In the event of complete loss of hydraulic control the brakes will be engaged by mechanical springs.

The PLC system, the central nerve system of the conveyor, constantly monitors all vital conditions of the equipment. Should an abnormal condition be detected, the computer selects and initiates the appropriate reaction. The reactions can range from a simple warning signal to the operator for minor problems to an emergency conveyor stop for more serious conditions.

The conveyor pulleys are 2,500 mm in diameter and are the largest ever installed in a conveyor system. The two-stage, right angle helical bevel gear reducers are rated at 2,500 kW each. As another first, this is the largest of its kind ever installed in a conveyor system. For reliability, the reducers are capable of dissipating the generated heat without the need for auxiliary cooling.

The power and control system of the downhill ore conveyors represents the latest and most innovative state-of-the-art technology. The power distribution system consists of 23 kV power centres located on each conveyor substation. In the final phase of the project, the downhill ore conveyor system is powered by ten 2,500 kW squirrel cage induction motors controlled by variable frequency inverters with vector control (AFD). With this drive system, the closed loop speed control with secondary closed loop torque control allows a defined initial starting and stopping torque to be applied to the conveyor belt at all operating conditions. This inverter drive system further ensures that tension forces in the conveyor belts are reduced to a minimum. In addition, this means minimised mechanical and dynamic stresses to the equipment and structures by a stepless smooth adjustment of torque and speed. The inverter drive systems are equipped with braking choppers, braking resistors and UPS to maintain their normal stopping capabilities for a short time in case of line/power failure.

The control system is linked to the overall DCS system and is executed by three programmable logic controllers (PLC) and several remote I/O stations. The PLC's are interconnected by an industrial open network (H1 network) used for interlocking, diagnostic and operator control as well as for video and telephone communication. The H1 network information is carried between the substations and the operator control rooms, over a redundant fiber optic network (OTN network). Two local profibus networks are used in each substation. The first network is used to interconnect the AFD drives and the PLC. The second network is used to connect the PLC to its remote I/O modules, the maintenance workstation and local operator interface terminals.

The entire downhill ore conveyor system is operated from four supervisory computer stations (HMI) located in various control rooms. All four HMIs communicate to all the PLCs via the H1/OTN network. All HMIs have monitoring and control capabilities. Furthermore, advanced help and diagnostic information is available through the use of a separate interactive help file system working in conjunction with the supervisory system (advanced help function).

The P8 conveyor at Red Dog is currently housed in a fabric enclosure to protect it against winds of up to 175 km/h and temperatures as low as minus 50° F.

Each substation is equipped with a maintenance workstation for local and manual control and status information of all equipment. A small operator interface is also provided at each substation for basic status information.The conveyor system is scheduled to be commissioned during the middle of 1999.

Phoenix, supplying the conveyor belt for Los Pelambres, reports that in the development and production of a steel cord conveyor belt it will be a new world record. The 25 km long, 1,800 mm wide ST 7800 Phoenocord steel cord belt has the integrated Phoenotec active protection system and Phoenocare electronic protection systems.

The longest single belt curved overland conveyor in the world is believed to be the 15.6 km system supplied to Zimbabwe Iron and Steel Co. by Bateman Materials Handling (MM, July 1998, p.5). Designing, constructing and commissioning this 500 t/h system won Bateman the project category of the South African Conveyor Manufacturers Association 1998 Award of Excellence Programme.

......and in the Arctic

During a three-month shipping window at Cominco Alaska's Red Dog mine, in northwest Alaska 200 km north of the Arctic Circle, when the Bering Strait is free of ice, zinc concentrate is loaded into ocean-going vessels at the DeLong Mountain Regional Transportation System's port facility, also operated by Cominco Alaska, 84 km from the mine. The backbone of the conveyor system at the port facility is the 1,070 m long, 1,067 mm wide, 'P8' overland conveyor, which carries reclaimed concentrates from storage buildings to the shiploading conveyors.

In 1998, Simons completed the EPCM contract for a US$200 million expansion of mine and port facilities, including upgrading P8 to raise its nominal capacity from 1,500 to 2,000 t/h and its peak capacity to 2,400 t/h, in addition to other improvements. Simons and subcontractors have recently started engineering and procurement, and construction assistance for the replacement of the overland structure for improved long-term structural stability and environmental performance.

In order to achieve the increased capacity, the belt speed was increased from 137 m/min to 174 m/min and the drive unit replaced with twin 186 kW units installed on a single drive pulley. The design goal was to achieve this upgrade without having to replace the conveyor belt, pulleys, take-up system and structural components. Normally, a 67% increase in installed power would result in a substantial increase in belt tension, requiring the costly replacement of such equipment. Several design features were employed to accommodate this increase in capacity and installed power while maintaining acceptable belt tensions and startup conditions.

The 186 kW drive units were equipped with fluid couplings. During startup, these limit the amount of torque applied to the conveyor, thereby allowing a prolonged start and reducing belt tension by 'slipping' at a controlled rate while the conveyor accelerates

With two drives installed, the motor starting sequence is staggered such that the second motor starts about 1.5 seconds after the first reaches full speed. This allows an even longer acceleration time, reducing belt tension as well as power demand requirements

A new drive pulley was installed with ceramic-tiled lagging, which offers up to 50% more traction than conventional grooved rubber lagging. With higher pulley traction, the take-up tension required to prevent belt slippage was reduced by almost 20%.

The modified conveyor can now start fully loaded, and actually operates with lower tension despite the increase in capacity and power. This has eliminated the need to replace the belt and pulleys, and also stops the belt from lifting off the curve.

The conveyor was originally built on a compacted gravel pad and housed in a fabric enclosure to protect it against winds of up to 177 km/h and temperatures as low as minus-50° F. The seasonal thawing and freezing of the underlying permafrost has damaged the pad, causing many sections of the conveyor to become misaligned, jeopardising performance. Also, some of the seams in the fabric enclosure have come apart during periods of high winds.

By June 2000, the overland structure will be replaced with a new conveyor housed in a 3 m diameter, enclosed steel gallery. The new gallery will provide maintenance access, and will accommodate power and communication cables. This approach offers the most cost-effective design for this particular application. Six of the nine new conveyors designed by Simons for the recent port expansion were of this type.

......and underground

On a recent project in South Africa, Melco supplied a versatile conveyor structure that can either be suspended or foot-mounted. The benefits of suspended underground conveyors in coal mines range from ease of access and under-conveyor cleaning to improved safety levels. The design of the cleats for the suspension chain on the conveyor enables easy adjustment and this solves the greatest difficulty encountered with underground conveyor systems, that of achieving straight, true structures over uneven surfaces. Achieving this will in turn ensure good belt tracking characteristics. Its idlers can be mounted at various pitches in order to cater for convex curves and high tension areas.

More recently, the lightweight, heavy duty roof slung Melco-Loc structure has been used in various US coal mines. Melco-Loc is available for belt widths up to 1,524 mm and is designed to handle up to 4,000 t/h. The idler bearings provide a B10 life of up to 100,000 hours.

Multolag is a ceramic composite lining from Multotec Wear Linings for conveyor pulleys. It was displayed at last year's Electra exhibition as a prototype while testing continues. Product features include a high coefficient of friction which eliminates conveyor slip and a self-cleaning capability for reduced maintenance.

Better control

Siemens new Simovert three-phase drive systems, both in the low and medium voltage ranges, can adapt the conveying speed of a belt installation to a plant's specific logistics system and save energy in doing so. The controlled belt installation reduces operating, maintenance and service costs, in turn reducing belt transport costs.

Although previous successful use has been made of slipring rotor drives with rheostatic starters in belt installation applications, operators wanted to be able to adapt belt conveying speeds to their plants' logistics system. Thus, the transvector control implemented in Simovert three-phase drives makes it possible to enter a specific motor torque and speed. The belt control system returns the speed setpoint depending on the load on the belt, attenuates any occurring speed swing if two motors are operating on the drive drum and ensures load compensation if the drive drums have unequal diameters.

In comparison with a drive using a slipring rotor, this system can save energy because the belt speed is dependent on the conveyed volume. Also the continuous slip stage and the dc braking systems have been dispensed with. Thanks to load-independent startup and return times, belt sections can also start up and decelerate simultaneously. For belt inspections, a belt speed that is adapted to operation is possible. Closed-loop speed control ensures that the belt installation is able to start up and decelerate without slip. Abrupt torque changes can be avoided thanks to controlled torque build-up or dissipation. The Simovert can also avoid belt vibrations arising from jolt-free startup and deceleration. Maintenance is reduced because brushes have been eliminated, and mechanical components such as belts, drum linings, brakes and bearings have longer useful lives.

Hansen Transmissions is supplying three P4 gear units, each of 800 kW motor power rating, to form the triple-drive for a high-duty drift conveyor at Jining No.3 mine in China. The order was placed by Continental Conveyor after the success of similar installations at Raspadskaya mine in Siberia and the Mimosa mine in Mexico.

Total transmitted power will be 2,070 kW and the reduction ratio 27:1. Controlled-release backstops are included, together with input couplings in the form of cardan shaft assemblies.

In addition, Hansen is supplying a low-speed drive package to provide for inspection of the conveyor. This comprises a 65 kW motor, V belt, SK3 right-angle gear unit and a disengaging claw clutch coupling.