New Product Info
Gearless Drives Offer Alternative for High Capacity Belt Conveyors(Apr 15,2014)
Individual belt conveyors in hard rock mining operations can extend over distances of up to 16.8 km and overcome height differences of up to 500 m, while normally achieving outputs of approx. 12,000 tons/hr. Such belt conveyors have had a significant impact on the development of individual components. Conveyor belts with strength of up to 7,800 N/mm are still in use today. Electromechanical drives, consisting of electrical motors (wound rotor or squirrel cage motor) and helical bevel gears with a capacity of up to 3,150 kW, are currently in use in South American copper mines.
The performance limits of belt conveyors are redefined by lower ore contents and deeper deposits. Nowadays conveyors are routed through the tunnel systems such that the maximum length available is required in order to reduce the number of underground transfer stations. This leads to new requirements on the quality of the conveyor belts. The St 10.000 with strength of 10,000 N/mm of belt width is now available.
An alternative for continuously improving belt quality with ever-increasing drives located at both ends of the conveyor is to optimize the application of drive forces on the belt. Possible alternatives include:
•Belt on belt drives (TT drives)
•Intermediate drives in the top strand and/or bottom strand
•Driven carrying rollers1
Unfortunately it is not always possible to implement such drive concepts. For driven carrying rollers there is still no cost-effective and reliable solution. That's why the current development projects focus on adapting conveyors with the traditional head and/or tail pulley drive systems to new challenges and demands.
Takraf GmbH is currently involved in studies that focus on a belt conveyor system that utilizes belts having a strength class of St 10,000. The limits of conventional drives with helical bevel gears are exceeded with the required drive capacity of 21,000 kW per individual conveyor. Low-speed synchronous motors, like those frequently implemented as drive solution for mine hoists in underground mining operations, do permit larger drive capacities. As part of the above-mentioned study, a conveyor is equipped with three gearless drives, each delivering an output of 7,000 kW.
The advantages of gearless drives compared to electromechanical drives cannot only be reduced to the possibility of installing larger drive units. The curve of the motor's efficiency in relation to the motor's torque shows over the entire spectrum values that are above the characteristics of traditional conveyor drives with wound rotor or squirrel cage motors completed with gears.
Belt conveyors do not always work at full load over the entire period of operation. Partial load conditions and even (short-term) idle periods are all part of a belt conveyor's operating regime. While asynchronous motors perform at lower efficiency levels with lower utilization ratios, the efficiency of synchronous motors increases in this range.
The higher efficiency of synchronous motors in general and especially in the partial load range and the fact that mechanical loads are eliminated during transfer of torque lead to lower operating costs for the conveyor. The maintenance of the gear unit including oil change intervals can be omitted just like the maintenance of the high-speed coupling. This is of particular interest wherever maintenance processes involve considerable effort. Prime examples of this would be operating conveyors in Canada at ambient temperatures of -45°C or conveyor systems that set up at an altitude of 4,500 m and more above sea level.
Takraf GmbH
URL: www.takraf.com
Individual belt conveyors in hard rock mining operations can extend over distances of up to 16.8 km and overcome height differences of up to 500 m, while normally achieving outputs of approx. 12,000 tons/hr. Such belt conveyors have had a significant impact on the development of individual components. Conveyor belts with strength of up to 7,800 N/mm are still in use today. Electromechanical drives, consisting of electrical motors (wound rotor or squirrel cage motor) and helical bevel gears with a capacity of up to 3,150 kW, are currently in use in South American copper mines.
The performance limits of belt conveyors are redefined by lower ore contents and deeper deposits. Nowadays conveyors are routed through the tunnel systems such that the maximum length available is required in order to reduce the number of underground transfer stations. This leads to new requirements on the quality of the conveyor belts. The St 10.000 with strength of 10,000 N/mm of belt width is now available.
An alternative for continuously improving belt quality with ever-increasing drives located at both ends of the conveyor is to optimize the application of drive forces on the belt. Possible alternatives include:
•Belt on belt drives (TT drives)
•Intermediate drives in the top strand and/or bottom strand
•Driven carrying rollers1
Unfortunately it is not always possible to implement such drive concepts. For driven carrying rollers there is still no cost-effective and reliable solution. That's why the current development projects focus on adapting conveyors with the traditional head and/or tail pulley drive systems to new challenges and demands.
Takraf GmbH is currently involved in studies that focus on a belt conveyor system that utilizes belts having a strength class of St 10,000. The limits of conventional drives with helical bevel gears are exceeded with the required drive capacity of 21,000 kW per individual conveyor. Low-speed synchronous motors, like those frequently implemented as drive solution for mine hoists in underground mining operations, do permit larger drive capacities. As part of the above-mentioned study, a conveyor is equipped with three gearless drives, each delivering an output of 7,000 kW.
The advantages of gearless drives compared to electromechanical drives cannot only be reduced to the possibility of installing larger drive units. The curve of the motor's efficiency in relation to the motor's torque shows over the entire spectrum values that are above the characteristics of traditional conveyor drives with wound rotor or squirrel cage motors completed with gears.
Belt conveyors do not always work at full load over the entire period of operation. Partial load conditions and even (short-term) idle periods are all part of a belt conveyor's operating regime. While asynchronous motors perform at lower efficiency levels with lower utilization ratios, the efficiency of synchronous motors increases in this range.
The higher efficiency of synchronous motors in general and especially in the partial load range and the fact that mechanical loads are eliminated during transfer of torque lead to lower operating costs for the conveyor. The maintenance of the gear unit including oil change intervals can be omitted just like the maintenance of the high-speed coupling. This is of particular interest wherever maintenance processes involve considerable effort. Prime examples of this would be operating conveyors in Canada at ambient temperatures of -45°C or conveyor systems that set up at an altitude of 4,500 m and more above sea level.
Takraf GmbH
URL: www.takraf.com
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