OK™ raw mill

The OK™ raw mill is the latest VRM offering from FLSmidth. It is designed with the same proven technology and modular design as the OK cement mill, which has proven to be the most reliable and efficient vertical roller mill (VRM) available.

OK raw mill
  • The basics
  • Maintenance

Key benefits

  • Energy-efficient
    The OK cement mill uses five to ten percent less energy than other vertical roller mills and 30-50% less energy  than ball mill systems. The OK raw mill is based on the same proven technology
  • High run factor
    Operating time availability is typically 90 to 95 percent for the OK cement mill. The OK raw mill is based on the same proven technology
  • High capacity
    The mill is offered in a full size range including the largest VRM sizes available
  • Operating flexibility
    The OK mill achieves 60 to 70 percent of nominal output with half the number of rollers in operation
  • Easy maintenance
    Wear liners can be replaced or rewelded inside the mill or the roller swing-out feature can be used for maintenance work externally from the mill
  • Concrete mill stand
    Concrete mill stands have faster installation time and reduced cost of installation

Design advantages

  • The modular design allows for parts commonality with OK cement mill, resulting in reduced spare parts inventory and consistent maintenance practices
  • The patented grinding profile and integral separator ensure the mill’s energy-efficiency, stability and reliability 
  • Concrete mill stands have faster installation time and reduced cost of installation
  • Operation with half of the rollers out of service, allows for continued operation at 60-70 percent of nominal output
  • Simple layout and fewer machines in the mill circuit ensure high run-factor and low maintenance costs
  • Optimal wear protection on all internal surfaces extends lifetime 
  • Segmented roller wear parts made of the hardest possible material without the risk of cracking; very suitable for hard-facing


How it works

The OK™ raw mill combines the drying, grinding, material conveying and separation processes into just one unit, which simplifies the plant layout. Its low noise level makes outdoor installation feasible – substantially reducing civil construction costs and improving the working environment.

An ounce of prevention

Even though the OK™ mill is very sturdy, it is important to:

  • Stop wear from air blasting in good time
  • Keep seals in good condition to avoid false air that can lead to increased wear
  • Change filters and keep lubrication systems in good condition
  • Adjust roller stoppers frequently as wear progresses to avoid roller table contact
  • Change nitrogen pressure in hydraulic accumulators according to grinding pressure
  • Fix oil spills/leakages and change hoses as needed

Reduce maintenance turn-around time

FLSmidth has incorporated the following features:

  • The rollers and the wear liners of the grinding table are segmented and easy to replace when worn out
  • Roller wear segments can easily be reversed or replaced while inside the mill – without taking rollers out of the mill
  • The wear segments of the rollers can be reversed to use both sides of the segments, enhancing higher utilization
  • Swinging one roller out and changing the seals takes 24 hours, while changing a hydraulic cylinder takes 10-16 hours
  • The mills have two access doors for ease of maintenance, and entry is possible as soon as the mill is stopped. Any jobs done inside the mill have to wait until it is cooled down – typically three-four hours.

Rollers and wear liners

The separator reject cone is provided with rail and trolley for that purpose.


Normal maintenance

We recommend visually inspecting the mill every two weeks, both while in operation and stopped.

Major maintenance

Major jobs include reversal/change of segments and/or hardfacing. A full hardfacing usually takes three-four days. For a cement clinker grinder, hardfacing is usually required annually; for slag grinding, expect to hardface every three-four months.

The grinding mill’s swing-in/out roller support system makes it easy to maintain the rollers and suspension system.


Take a tour inside and around the OK mill
OK mill