# Creating/modifying a mill

## Contents

## Entering/changing a mill

*Mills* are added to *projects,* and then *circuits* are created out of combinations of mills. See the section on Creating a project to create a project to add a new mill to.

For the purposes of the model, a crusher is considered a special type of mill. Adding a crusher is the same as adding a mill. Primary gyratory (or jaw) crushers are not part of the modelling because all Power Models start with a feed F_{80} size that is assumed to be primary crusher discharge.

### Entering a new mill

From the *circuit flowsheet* page, click the [Add new mill to circuit] link at the bottom of the flowsheet. This will bring up a dialogue containing a series of pre-configured mills or a "blank" template. Click the mill you want to add.

The editing page for that mill will appear. Continue with the instructions to change a mill.

### Changing an existing mill

The list of attributes that can be modified on the mill editing page is different for each mill power draw model.

If you change the model type, some of the data needed will be different and certain data fields will disappear from the dialogue, and other data fields may appear. Some items may be blank if a particular attribute of the new model did not exist in the old model.

## Mill fields

Each mill power draw model requires different parameters; not all of these fields will be available depending upon which class of mill model you choose.

**Name**(text) A name to refer to this mill**Class**the model to use to estimate the power draw of this mill. See details here.**Comment**(text) optional comment to include with this mill. Not displayed on the model output.**Quantity**(integer) Number of mills with these conditions to simulate in this circuit. Entering zero will display the mill with a strike-out and will not include any power draw (used to indicate a stand-by or out of service mill).**Motor power**(integer) What is the rated output power of*each motor*. In the case of a twin-pinion arrangement, the power available is two times this value.**Motor mechanical efficiency**(decimal, 0 → 1) Efficiency of transmitting power from the motor output to the mill shell. Read this for details.- gearless drive: 1.000
- pinion & gear drives with intermediate speed (synchronous) motors: 0.985
- gearbox, pinion & gear drive with high speed (wound-rotor induction) motors: 0.970

**Motor efficiency to DCS**(decimal, 0 → 1) Electrical efficiency between the power measurement position in the electrical network and the motor output. Includes the motor efficiency. Used in the model to calculate the DCS power draw based on the power draw evolved at the mill shell. Read this for details.- Gearless drive (modern): 1.00
- Gearless drive (older, pre-2010): 0.951
- synchronous medium-speed, fixed speed: 0.950
- synchronous medium-speed, variable speed: 0.941
- wound rotor induction high-speed, fixed speed (& slip-energy recovery): 0.950
- wound rotor induction high-speed, variable speed (CCV or similar): 0.941

**Diameter**(number) Diameter of the mill inside the shell (ignoring liners)**EGL**(number) Effective grinding length of the mill, also referred to as the "belly length". Distance along the shell from the feed head liner to the discharge head liner or grate.**Ball load**(number) Volumetric ball loading inside the mill. Typically 10 to 15 for SAG mills and 32 for ball mills.**Ball density**(number) ball density as a multiple of density of water (typically 7.8 for forged steel balls)**Mill load**(number) Volumetric total mill charge load inside the mill. Typically 25 for SAG mills and 32 for ball mills.**Percent solids**(number) Weight percent solids in the feed slurry. Typically 70 to 80.**Pinions**Quantity and type of mill motors (gearless, single or twin pinion)**Speed**(number) Rate of rotation of the mill. Typically 72 to 78 percent or can be specified in revolutions per minute.**Rated speed**(number) The*mill*revolutions per minute at which the motor is capable of operating at both maximum torque and maximum power. This is the speed of the*peak*of the tent diagram.**Liner thickness**(number) The*average thickness*of a liner if the lifters were to be smoothed and combined with the plates. See here for detailed description and example calculations**Cone angle**(number) Cone angle of the mill heads measured from vertical. Typically 15 to 20 for SAG mills and 30 for ball mills.**Trunnion diameter**(number) The diameter of the mill trunnion inside the liners.**k-net:gross factor**(number) Empirical calibration factor for Morrel C-models. Typically 1.26.

## Adding a mill to the default list

The list of default mills (those that appear in the "Add new mill to circuit" menu) is determined by your Administrator.