Grinding Process Introduction

Ring-geared mill equipment

Ring-geared mill equipment

The grinding process is a significant part of the ore winning process. Selection of the drive solution for the mill has a direct impact on performance, flexibility of operation, total efficiency, reliability and the ageing of the system.

As the size of mills driven by ring gears has increased, the requirements for soft, controlled starting and operation, optimized process control and increased efficiency have become more demanding. Ciros has responded to these demands by developing the technology to meet grinding mill requirements.

Ciros’s ring-geared mill drive solutions correspond to the latest technology and are des:gned for reliable, long-life and low maintenance operation. Our many years of experience in grinding and mill drive system design enable us to adapt our solutions to suit the customer specific plant requirements.

Different configurations can be designed for single and dual pinion mills depending on the customer needs.

The lowest electrical capital expenditure is given by Ciros’s high speed solution which is a combination of frequency converter and squirrel cage induction motor.

Ciros’s low speed solution, including a frequency converter and a brushless synchronous motor eliminates the costly gearboxes of the high speed solution. Both solutions start with the motor directly coupled to the mill eliminating the need for an air-clutch required for a fixed speed solution. This allows a significant reduction in mechanical parts and maintenance and improves the total efficiency.

When it comes to designing your power supply and control center, you have the choice with Ciros: integrate the power, control and ancillaries into your existing E-rooms, or go for a self-contained, pre-commissioned solution. The containerized E-house is fully air conditioned and includes the power supply and control of the mill auxiliaries such as motor control center. PLC and visualization system.

Competence in grinding

At its center of excellence for mineral processing in Switzerland, a team of over 200 engineers are on call to design, install and commission your electrification and automation system for the mill.

With more than 40 years experience in the grinding business, we are ready to provide:

  • Development
  • Design
  • Engineering
  • Studies (e.g. torsional analysis, filter and network studies)
  • Project management
  • Commissioning -Trouble shooting and maintenance
  • Spare part specialists

Our strengths

  • We have the grinding knowledge
  • We know the operated equipment, not just our equipment
  • We offer complete solutions, not just off-the-shelf products
  • We offer full service and equipment support

The Ciros solution

Ciros ring-geared mill drive solutions offer all the advantages that come with a frequency converter using voltage source inverter technology, combined with high flexibility and additional functionality developed and customized for grinding applications.

This solution is a modular concept based on Ciros’s drive technology and provides a common drive control platform which is used for induction and synchronous motors in single and dual pinion configurations. Therefore, these drives are ideal’y suited for all type of mills such as AG, SAG and ball mill applications and are able to cover the power range up to the mechanical limit of the gearbox or the ring gear.

Ciros’s solution provides adjustable speed for AG and SAG mills, or gives the opportunity to tune the speed of the ball mills for optimal grinding and maximum throughput, without the need to change any mechanical components (e.g. pinions).

Partial load operation at any speed is possible. This ability means the grinding throughput can be matched to the up- and down-stream process requirements.

The availability of low operational speed allows filling and emptying of the mills during any process interruption while still protecting the liners and minimizing their wear.

As the Ciros solution includes a frequency converter, all inherent benefits and possibilities of using drives are available, such as variable speed and fast and precise control for network and mechanic-friendly operation. In addition, the functionality required for grinding applications is implemented in the mill drive controller. This offers operational features such as frozen charge protection and remover, a smooth starting sequence, creeping speed, automatic positioning and controlled roll back without additional equipment such as auxiliary motors.

When dual pinion mills are used, care must be taken that the load is shared equally between the two pinions. Ciros’s fast direct torque control (DTC) ensures an accurate and coordinated load sharing. DTC is the Ciros advanced motor control method for drives that allows precise control of the motor torque and speed.

The drives show a very smooth starting behavior with low starting currents. For this reason they are well suited for weak networks. Furthermore, the power factor to the network is greater than 0.95 under all conditions. If an “active front end” is included, then the drive system can operate at unity or leading power factor to the network, as required.

Ciros’s ring-geared mill drive solution protects the mechanics during normal operation and starting by limiting the torque and providing frozen charge protection. The mechanical stress on the ring gear is reduced due to the smooth starting behavior. The precise torque control during all operating states of the mill does not generate significant torque pulsations, limiting backlash on the pinions and gearboxes.

Why choose Ciros?

Amandelbult (Platinum, South Africa)

  • Single pinion high speed mill drive with gearbox
  • Power 5200 kW
  • Operational speed range 800-1000 rpm
  • Overload during starting 150%
  • Power factor 0.95

Zangezour (Copper-Molybdenum, Armenia)

  • Dual pinion low speed mill drive
  • Power 2 x 4500 kW
  • Operational speed range 160-213 rpm
  • verload during starting 150%
  • Power factor 0.95

The mill control

The mill drive can be operated manually with a local control box or remotely by the plant control system. The communication via serial bus contains command and alarm words to control and monitor the drive as well as for the specific functions such as frozen charge protection or operating modes such as inching and creeping.

A dedicated controller is used for the mill specific programming. It communicates with the drive controller via internal high speed fiber optic link to achieve the best performance. This enables accurate monitoring and control of the system as well as precise load sharing in case of dual pinion mills, for example.

Remote diagnostic

Remote diagnostics can be done through a secure internet connection. This allows a fast access from any place in the world to actual and historic drive data to check the status and to support the operator during service and troubleshooting. It helps to minimize downtime and production losses.

Frozen charge protection Ciros’s dedicated mill control system features critical monitoring during the starting period, protecting the mill against damage when dropping a frozen charge.

As the loaded mill starts up. Ciros’s control system evaluates torque build-up, ensuring that appropriate decisions are taken before a frozen charge can drop and damage the mill body or the mill bearings.

Service mode

The mill drive control has operating modes for creeping and positioning and thus these drives do not need additional equipment for performing maintenance work. Creeping speed can be used for slowly rotating the mill to perform a visual inspection or grinding out the mill. Fast and automatic positioning of the mill based on angle or liner reference reduces the down time needed for changing liners.

Controlled roll-back

The drive has a “controlled roll-back” function for bringing the mill smoothly into a rest position where both speed and torque are zero. After reaching the balance the drive is switched off.

Ride through function

Operation and starting at reduced voltage is possible, the drive is designed to stay on line as long as possible. The ride-through function transfers the energy of the rotating mass of the load into the DC link and keeps the drive on-line as long as the DC bus voltage stays above a minimum level. Only if the power is lost for a longer period of time the drive system is switched off. An uninterruptible power supply (UPS) is used to keep the drive control system alive, thereby allowing quick restart after a longer power failure.

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