High Speed Servo Drive LRS Maintenance

This SFAK series MKS Liquid Starter has been running in a metal recycling facility for a hammer mill application since 2013. The SFAK series LRS is a high-speed servo drive system usually used for metal shredding applications due to their high dynamic control and positioning characteristics. 

Unlike conventional LRSs that are only in circuit during starting, the SFAK series LRS is continuously in circuit regulating the rotor current to provide adequate torque for pulsating torque loads (for e.g. when big chunks of metal enter the metal shredder). This is achieved by the LRSs high speed servo motors dynamically controlling the position of the electrodes to regulate the current.

The effectiveness of the dynamic control is crucial in ensuring:

  • adequate torque for the continuous introduction of sudden loads

  • the electrolyte solution does not over heat during operation

  • no excessive wear or premature failure of the LRS electrodes

Depending on the severity of application, the condition of electrodes and conductivity of electrolyte must be inspected periodically to ensure a continuous trouble-free operation of the LRS. In the case this customer, our inspection revealed that some of the critical parts of the LRS required replacement due to normal wear and tear.

A minor overhaul of the LRS on site was performed which included:

  1. Draining of the LRS Tank and a complete washdown of the tank interior

  2. Inspection, replacement and alignment of electrodes and electrode holders

  3. Inspection and replacement of bushings to ensure no leakages

  4. Functional check of PLC control

One of the most crucial things that are often overlooked during an overhaul such as this is the alignment of the electrodes. The electrodes must be alignment correctly with proper clearances as incorrect installation may result in current imbalance, excessive electrode wear and premature component failure. 

After installation and alignment of new electrodes, a new batch of electrolytes were prepared and filled in the tank. Finally, the motor was started with load for verification of correct conductivity of electrolyte and current regulation.

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