mine liners - magotteaux · 2018. 6. 7. · ball mill, regrind, …) • ore feed size (f80 ,f100)...
TRANSCRIPT
The two main functions of a mill liner consist in protecting the mill shell against wear and in transmitting the energy of the mill motor to the grinding charge to carry out the required size reduction in the most efficient way.
For a mill liner, the design as well as the liner material are
to be considered.
The required movement of the mill charge to carry out effi-
ciently a certain type of size reduction (for instance coarse
grinding, fine grinding,...) must be promoted by the right
mill liner design. A wrong liner design choice leads to poor
grinding (excess energy usage), higher grinding media con-
sumption and even higher liner maintenance costs.
The liner choice should therefore always be seen as one
element influencing the total grinding cost of liner, grinding
media and energy, and not as a stand-alone cost. With re-
gards to liner life/cost for a specific design it is important
to choose the correct material/alloy for that application.
Grinding mechanisms:
The rules that guide the design of a liner depend on the
required grinding mechanism. Three main categories of
grinding mechanisms can be highlighted:
1. IMPACTThe mechanism of reducing the big rocks is "crushing"
which requires impacts. Either by impacting of grinding
balls on the rocks (SAG mill) or by interaction between
rocks on the one side and mill shell and toe of the grinding
charge on the other side (FAG mills). The trajectories of
grinding media and rocks promote size reduction by im-
pacts. This grinding mechanism is required in SAG and FAG
mill applications.
2. PERMEABILITYThe main size reduction in this mechanism is carried
out in the ball charge. The liner design needs to be such
that the charge is "opened-up " (permeability) to al-
low bigger grains to be drawn into the ball charge where
they will be reduced. Limited ball trajectories allow this
opening up of the charge. This mechanism is typically
needed in coarse grinding for instance primary ball mills).
3. ATTRITIONThis mechanism involves size reduction between moving
grinding balls. Adequate size reduction will require high
relative movement between the grinding balls while main-
taining the pressure within the ball load. Liner design is
such that trajectories should not occur. A compact charge
is required.
MINE LINERS ...
THE CHOICE DESIGN
1 2 3
• Mill type: SAG, FAG, Rod mill, primary ball mill, secondary
ball mill, regrind, …)
• Ore feed size (F80 ,F100) and required product size (P80)
determining the grinding mechanism to be favoured
• Mill size (diameter, length)
• Maximum ball top-up size
• Mill rotational speed (rpm, variable or fixed speed, single
or dual rotation)
• Ore type (abrasivity of the ore)
• Mill discharge type (grate discharge mill, overflow mill)
• Available drilling pattern
• Total filling degree (ore and balls)
FAG & SAG
Main design parameters:
• H (effective lift)
• S (spacing between lifters) and
• alpha (attack angle)
Iteration process to reach best-suited H,S and alpha.
FINE GRINDING
Reducing small particles by attrition requires a combina-
tion of force (F) and relative speed (v).
The selection of the liner material is linked to the applica-
tion (the main parameter also considered when choosing
the liner design) and the resulting working conditions.
The table below gives general resistance characteristics of
the most common liner alloys
ex overflow mill
ex SAG liner
ex BM3 - RGD
... THE RIGHT CHOICE
PARAMETERS EXAMPLES MATERIAL
ALLOYSAUST. MN STEELS
PEARLITIC STEELS
MART.HICR ALLOYS
Composition Mn Cr-Moly 12-27 Cr
Structure Matrix MatrixMatrix + Cr carb.
(30-35%)
Hardness200-450HB after work hardening
325-400HB 600-650HB
Resistance abrasion
- to + - ++
Resistance corrosion
- - ± to ++
Resistance repeated impacts
+++ ++ +