Maintenance & Mechanical

Ball Mill Motor Power Draw Sizing and Design Formula

The following equation is used to determine the power that wet grinding overflow ball mills should draw. For mills larger than 3.3 meters (10 feet) diameter inside liners, the top size of the balls used affects the power drawn by the mill. This is called the ball size factor S.  Rod and Ball Mills … Read more

Rod Mill Design & Power Draw

The following equation is used to determine the power that a rod mill should draw. The Bottom Table lists many of the common size rod mills giving speed, loading and power data. The rod mill motor power is in horsepower at the mill pinion-shaft.  For different length rod mills power varies directly as rod length. For difference between … Read more

Putting a Ball or SAG Mill on Care and Maintenance

mill jacking cradle

  The mine is closed and now you need to know how to put the SAG or Large Ball Mill in care and maintenance does not have to be complicated to the point where you need bridge erection equipment for lifting a Mill (AG/SAG/Rod/Ball).  You actually need to lift a car higher than a mill.  All you … Read more

LSSM = Low Speed Synchronous Motor Drive Operation


In the world of mining and milling the “electrical term” LSSM stands for “Low Speed Synchronous Motor” and usually means a mill where the motor rated speed is in the range of 10 RPM, the same speed as the mill turns.  A high speed motor can run at 900 RPM and uses a gearbox to turn down the speed. … Read more

Grinding Mill Gear Assembly

Mill Gear Assembly

We will begin with the mill’s bull gear assembly and work towards the motor, The BULL GEAR, sometimes called the RING GEAR is designed to turn the mill transforming the energy of the motor into motion for the mill. By mill we refer to Ball Mills, Rod Mills and SAG Mills.  Anything gear and pinion … Read more

Leaking Mill Shell Bolts

Dealing with leaking Mill Shell bolts is common enough an occurrence in most concentrator plants. All that an operator can really do about it is to keep the problem to a minimum.  The cause of the bolts leaking is running the mill with a density that is to light or feed that requires a high impact to … Read more

Mill Trunnion Liner

Rod Mill Trunion

The Mill Trunnion Liner fits inside the bearing to protect it from wear caused by the ore being washed over the liner and through the bearing as it is fed to or discharged from the mill. The difference in the trunnions at each end of the mill isn’t in the trunnions themselves. The trunnion liner on the … Read more

Trunnion Bearing Assembly Ball Mill & Rod Mill


The first part of the mill that we will look at is the TRUNNION BEARING. This is a HYDROSTATIC BEARING which is a slow moving bearing that carries a heavy load. Usually it is constructed from Babbitt’s metal. If you happen to remember the introduction to this course Issac Babbitt was the man who devised the … Read more

Fine Ore Storage Bin and Stock Pile

Fine Ore Storage Bin

Let’s begin with fine ore storage bin or stockpile, get it out of the way and then proceed to grinding. You would think that there isn’t that much to learn about when talking of fine ore storage, after all, all that this area is really for is to provide surge capacity for each of the … Read more

Effect of Grinding Media Charge on Mill Power Draw kW

Effect of Steel Ball Charge on Mill Power Draw kW

Maximum power is drawn by a mill when the charge occupies approximately 50% by volume. The power curve becomes very flat in the range above 45%. As a result, mills are seldom run with charge levels greater than 45%. In rod mills, the charge is swollen by particles of feed which separate the rods. If the … Read more