Under Control
Featured in: Global Mining Review, November/December 2024
Dellner Bubenzer describes how belt conveyor control systems can increase component life and improve performance and productivity.
At the heart of production at Mongolian copper and gold mine, Oyu Tolgoi, is Dellner Bubenzer’s Belt Conveyor Control (BCC) 3000 system.
Last year, underground production began at Oyu Tolgoi, making it a high-performing surface and underground integrated copper business – and one of the most important copper producers in the world.
The integration of the underground project, part of a long-term programme, marked the dawn of a new era at Oyu Tolgoi, located in the Umnugovi province of Mongolia.
Dellner Bubenzer – a manufacturer of high-performance disc and drum brakes, hydraulic power units, couplings, clutch, and monitoring and control systems for mining, cranes, and other severe duty applications – has installed a Belt Conveyor Control BCC3000 system at the mine, which is designed for the controlled braking of mining machines and applications. It is especially suited to installation on belt conveyors, where smooth braking is vital to prevent undue belt tensions leading to reduced component life. In addition to protecting the machine from excessive stresses during braking, the BCC3000 also offers system monitoring and diagnostics functions.
Brake status view.
Around the Clock
Oyu Tolgoi originally issued a scope of work to deliver a belt conveyor control system that offered premature fault detection; precise diagnostics; planned preventive maintenance; reduction of down times; minimised costs; and improved performance and productivity.
These non-negotiables were agreed upon, despite the fact that the machines are located outdoors, are running 24-hours-a-day, seven-days-a-week – and cover long distances.
Oyu Tolgoi is harnessing several benefits of the resulting installation, including a fully integrated closed loop control system and stopping time that is constant and independent of the load. Synchronous braking times are achieved for the flight of conveyors, while automatic compensation is reached for small variations of friction coefficient.
Dellner Bubenzer also supplied a battery back-up for all control functions, and a hydraulic accumulator back-up for full control in the event of total power fail. Profibus and Profinet connection was installed for control and monitoring functions.
Four Cornerstones
The Oyu Tolgoi BCC3000 system consists of four main elements:
- Redundant encoders, to measure and control the speed.
- An electronic unit, which fully controls and monitors the system.
- Hydraulic power pack, incorporating the proportional control valve.
- Brake caliper.
On the low speed side of the machine, one or more SF brake calipers from Dellner can be used.
Encoders
The shaft speed is measured using an encoder mounted to the shaft that is to be controlled. In the case of this conveyor, the driven pulley, with the brake disc and encoder fitted to the shaft accordingly, was selected as the control. Typically, an encoder would have 2048 pulses per revolution, but this depends on the application; in this instance, the encoders have 1024 pulses and are mounted on a not driven (bend) pulley.
It was recommended that a second encoder is used for safety critical applications such that, in the event of an encoder failure, the system will be fully functional throughout, using the second encoder signal. Both encoders are fitted to the same shaft. Any failure of the encoder is detected by the electronics and a signal sent via Profibus to warn of the condition – not just when the brakes are operated.
Electronic Control Unit
The electronic BCC3000 control unit is the heartbeat of the Oyu Tolgoi unit, as it controls all of the logic and operating functions of the braking system. Its primary function at this mine is to control the deceleration (stopping time) of the machine or conveyor.
The unit is based on a Siemens programmable logic controller (PLC) with a graphics interface to view and check programme data. During commissioning, a speed ramp was entered into the system.
The value of the stopping time and the two intermediate states (percentage speed/time) can be entered and adjusted until the desired profile is achieved. When the conveyor is commanded to stop (either by a hard-wire or Profibus external command, or both), the speed of the machine is determined from the encoder and this is then compared to the desired speed profile.
If the actual speed is high, then the pressure to the brake caliper is reduced. This increases the clamping force of the unit, thus increasing the braking torque until the desired speed ramp is reached. If the actual speed is too low, then the pressure to the caliper is increased, reducing the amount of braking torque, until the desired profile is reached.
These adjustments are carried out on a continual basis throughout the stop, using a proportional/integral control algorithm to adjust pressure via the proportional valve on the hydraulic unit. Once the conveyor is at rest, then the system removes all hydraulic pressure to set maximum braking torque for parking the machine.
The system is built into a stainless-steel cabinet, and includes all interface and control relays to be able to operate and monitor the braking system.
Temperature and wear sensor at Oyu Tolgoi.
Features
- Siemens outdoor PLC with additional internal graphics display.
- Motor starter with thermal protection.
- Profibus connection to main plant PLC.
- Battery back-up to give controlled power – available for 30 minutes in the event of external power failure. n Optional local operation with external e-stop and override.
- All control relays for each valve on the hydraulic power pack.
- Drive amplifier for the proportional valve (pressure). n Two-speed inputs with failure warning.
- Central interface between customer PLC and brake monitoring systems.
Hydraulic Power Pack: Main Features
- Motor-driven radial piston pump.
- In-line filter with clogging indicator.
- Pressure relief valve, pressure switch to control operation.
- Proportional valve for a controlled stop.
- Dual 3/2 directional valves for ‘soft’ e-stop (safety feature).
- Hand-pump for manual release (switch to indicate position).
- Analogue oil level sensor.
- Analogue oil temperature sensor.
- Pressure transducers for monitoring and control. n Can operate up to four linked calipers (depending on spacing).
- Pre-wired terminal box (stainless steel).
Hydraulic power unit for Oyu Tolgoi.
Operation
When power is first applied, the pump is started to charge the main system accumulator. This accumulator is used in the event of a stop; needed when no electricity from the grid is available. Oil discharges through the proportional valve to give full pressure control.
Normally the pump will be used to provide control; when the brake is released, all parts of the circuit are fully closed with seated low leakage valves. This means that the pump operation does not cycle frequently.
All functions of the hydraulic unit are controlled through the electronics. Functional switch positions are added to the Profibus connection. This enables detailed monitoring to assess service and maintainability requirements.
Brake Calipers
Brake calipers are connected to a single hydraulic power pack and control system if they all brake the same shaft in the machine. These can be on the high speed (gearbox input shaft) or on the low speed (gearbox output shaft). In this conveyor system, there is only a low-speed application.
The brakes used on the high-speed shaft can be based on the standard calipers from Dellner Bubenzer that have many years of reliable service in a multitude of applications.
The Belt Conveyor Control (BCC) 3000 system, which is designed for the controlled braking of mining machines and applications, is especially suited to installation on belt conveyors.
In this solution, the standard electro-hydraulic thruster is replaced by a simple low friction hydraulic cylinder. On the low-speed side of the conveyor system, one or more SF brake calipers from Dellner can be used. Such brakes can be fitted with instrumentation that connects via Profibus, Profinet, or linked through the BCC controller to the main plant PLC using the CMB monitoring systems from Dellner.
Such systems, together with the monitoring of the hydraulic power pack using the BCC3000, offer complete system feedback on the operational parameter through the service life of the brake system.