MILL LINER OPTIMISATION

MILL LINER OPTIMISATION

Waldo Verster

Multotec Rubber

2021

2021 Slide: 2Mill Liner Optimisation Waldo Verster

In t roduct ion

Mill Liner Optimisation

Grind (Process

Requirement)

Installation Time

Structural Integrity

(Protecting the mill shell)

Absorbed Power

Wear Life (Abrasion,

Impact, Corrosion)

Discharge Efficiency


Types of comminut ion mechanisms

ImpactAbrasion /

ShearAttrition Compression


Zones ins ide a mi l l

Toe

(Impact

grinding)

Attrition and

compression

grinding

Kidney

shape

Shoulder

Eye

Cascading

(Abrasion)

Cateracking


Energy d is t r ibut ion ins ide a mi l l

Energy distribution is equivalent to the rate of work performed in the

different zones inside a mill (It’s a function of the collusion normal

energy and the number of collusions / particle / s)

Maximum Impact work but low rate


What dr ives mi l l ing?

Millions of impacts of grinding media and /

or larger rock on the ore particles

Need sufficient energy to break the

particles

• Excess energy is wasted

• Low energy is ineffective

Majority of grinding work is done in rising

shear region inside the charge

• Many interactions

• High pressure inside the charge

• Trapping of particles


Design parameters

Mill Design

• Diameter

• Length

• Head angle

• Trunnion diameter

• SAG, primary ball or secondary ball mill

Mill Operating parameters

• Feed PSD

• Mill Speed

• Ore Characteristics

• Total volumetric filling

• Grinding media type, size and volumetric filling

• Liner changeout plan

Liner Design

• Liner wear life

• Trajectory

• Mill effective volume

• Effective grinding length

• Discharge design

• Total throughput

• Absorbed Power

• Liner design input parameters

• In most cases the inputs are fixed


Shel l l iner des ign parameters

Cross Section through mill shell and shell liners

Shell plate

width

Shell plate

thickness

Lifter bar

release angle

Height to Angle

Lifter bar

height back

Lifter bar

height


Design parameters - Opt imisat ion

Increase mill volume and / or EGL

Increase discharge capacity

Mill liner design seeks the optimum balance between liner

life, cost, throughput and grind


Liner des ign sof tware – Single Par t ic le


Liner des ign sof tware - DEM


Case Study- Reduct ion in absorbed power

Grinding Circuit: Crusher – SAG – Ball Mill – Cyclones (Closed circuit)

Grinding media, 50 mm High Chrome balls

Fixed speed = 75 % of critical speed

Ball mill feed PSD:

PARTICLE SIZE

DISTRIBUTIONS

PSD - Sieve

Shaker x PSD - Malvern PSD - Cyclosizer

Size (µm) Mass Mass Retained Cumulative %

RetainedCumulative % Passing

+ - g %

1 1000 1400 43.60 6.3 6.3 100.0

2 850 1000 10.30 1.5 7.8 93.7

3 600 850 24.50 3.6 11.4 92.2

4 425 600 32.20 4.7 16.1 88.6

5 300 425 47.70 6.9 23.0 83.9

6 212 300 77.80 11.3 34.3 77.0

7 150 212 100.00 14.5 48.8 65.7

8 106 150 103.50 15.0 63.8 51.2

9 75 106 105.20 15.3 79.1 36.2

10 53 75 52.70 7.7 86.7 20.9

11 38 53 28.50 4.1 90.9 13.3

12 38 62.80 9.1 100.0 9.1

TOTAL 688.8


Tra jectory – New l iners

Impact

grinding on

the toe

Attrition and

compression

grinding


Tra jectory – Liner mid l i fe

No

significant

impact

grinding

Attrition and

compression

grinding

Increase in

charge cross

section


Tra jectory – Liner end of l i fe

No

significant

impact

grinding

Attrition and

compression

grinding


Absorbed Power vs . throughput

Gradual reduction in power draw over the life of the liner without

negatively influencing the grind and throughput

Attrition grinding is doing most of the work in this mill

Excess energy is wasted

Power Draw

Throughput


Conclus ion

Multotec liner design rules aim to achieve thebalance between liner life, grind efficiency, cost andthe structural integrity of the liner. The type of milldictates the liner design rules.

Every mill application is unique, and a bespoke linerdesign is required to maximize mill efficiency

Without a proper mill liner design, an increase inabsorbed power does not always result in anincrease in throughput and improved grind.

Multotec mill liner design seeks the optimum balance

between liner life, cost, throughput and grind by

considering the complete grinding circuit and process

parameters.


Thank you for your attendance at this Multotec Training Workshop

All Material & Designs in this Presentation are Proprietary Information of Multotec (Pty) Ltd.

No information may be shared or reproduced without the written consent from the author or Multotec Management.

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