Effect of Water & Density on Grinding Mill

Retention Time Rod Mill

The Time that the ore spends in the grinding mill is called, RETENTION TIME. This is a very important variable, the longer the retention time, the more the ore comes in contact with the rods, the better and finer the grind becomes. To understand this important control it must be remembered that any volume that … 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

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

Grind to Liberate Mineral Grains


The next piece of information that is of value to the operator is to know the hardness of the ore. The WORK INDEX, as the hardness is referred to, is calculated on the amount of electrical energy that is required to grind the ore to a predetermined size. Said in another way, it is the … Read more

Rods or Balls

Steel Rods Steel Balls

Mill operators will not get to design too many mills, but this doesn’t mean that the information that has been compiled isn’t of interest to the operator. Knowing the ore body shape, size, and content will give the operator prior knowledge of operating conditions to be expected. It is also beneficial to know how this … Read more

Simple Grinding Circuits & Flowsheets

Ball Mill Rod Mill Circuit

To start the discussion on grinding circuits I would like to begin by showing you some simple Flowsheet SCHEMATICS of some sample circuits, but before I do there is one thing that I must explain for the schematics to make sense. When the ore is put into the first piece of equipment for grinding, water … Read more


Sizing Grinding Circuits

Plants designed using The Barratt Method as published in the Book Mineral Processing Plant Design, Practice, and Control Proceedings, include: Alumbrera Batu Hijau Cadia (one consultant among others) Candelaria Clarabelle (Inco) Collahuasi (line 1 & 2) Dreifontein El Teniente SAG 1 Ernest Henry Esperanza Fimiston Freeport 95K expansion Lisheen Numerous benchmarking exercises to operating grinding … Read more

Effect Of Primary Grind Size On Mineral Liberation


The extrapolated ore fragmentation and copper sulphide liberation plots reveal that the liberation levels and hence the flotation responses of the minerals would be essentially constant across a broad range of flotation feed sizing. This observation would indicate that flotation feed sizing coarser than 200µm K80, the practical norm for copper porphyry ore processing worldwide, … Read more

Chilean Mill

chilean mill

The Quartz Mill AKA Chilean Mill is one of the more popular types of the original Chilean mill. Still used for certain grinding problems, this mill employs the convex-concave principle of crushing ores, resulting in a product surprisingly low in slime content and which has its particles, such as sulfides and gold, well polished and free of … Read more

Rubber Tire Driven Ball Mill -Grinding Mill on Rollers

Rubber Tire Driven Ball Mill on Rollers

These very nice rubber tire driven grinding mills do not come cheaply priced. A small, 1 meter X 1.5 meter Rod mill OR Ball Mill cost approximately $160,000 US (in 2014) The small(est) mill starts at 600mm x 900mm and goes up to the large(est) 2100mm x 4200mm Options in the small “tyre” or Rubber roller grinding mills … Read more