03 Ball Mill EDM

Grinding with Ball Mill Systems

EDM

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HGRS Tikaria_Mill Workshop SEPT-07

Ball Mill

Ball Mill

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What is a End Discharge Mill (EDM)?

Intermediate diaphragm

Mill feed arrangement

1st Compartment

(Coarse Grinding)

2st Compartment

(Fine Grinding)

Mill discharge

Air outlet

Air inletGearbox with pinions

Drive

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EDM

EDM =

End Discharge Mill

Product discharge

at mill end

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Elements of Ball Mill - Overview

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Mill Drive Concepts

Single pinion concept(< 2 '500 kW )

Double-pinion concept(< 5 '000 kW )

G irth gear Drives

Single drive w ithtw o pinions(< 5 '000 kW )

Double drive w ithfour pinions

(< 10'000 kW )

G irth gear units

Tw o-w ay pow er splittingreducer

(< 6 '000 kW )

Planetary gear reducer(< 12'000 kW )

Central drives

D rive C o ncepts forB a ll m ills

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Example Planetary Gear DrivePlanetary gear reducer concept MAAG

Two gear stages with three planets

All shafts with friction bearings

Pinions, planets surface-hardened

Annulus through-hardened

Annulus

Sun pinionsDrive arrangement

Planets

Gear coupling

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Gear Box Internals

Parallel shaft gear reducer (two way power branch)

Low speed gear stage

All gears surface-hardened and ground

All shafts with roller bearings

Key point:: Face load distribution of the LS-gear stage

Bearings with excentric sleevesto optimise the face load distribution

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Potential Technical Problems Drive

Girth gear drives - Fundamental Problems

Dynamic behaviour

A lot of individual rotating masses risk of resonance vicinities

Torsional/structural vibrations

Pinion shaft bending vibrations

1. Axial/radial runout

2. Alignment of the drive trains

3. Uneven power splitting

4. Centre distances variable

5. Face load distribution

6. Sealing of the girth gear

7. Girth gear is through hardenedonly, fatigue strength is limited

5 2

1

4

5 6 7

35 2

1

4

5 6 7

3

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Gearboxes

Polysius CombiflexGear reducer

Planetary Gear

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Potential Damages Drives

Breakage damage (pinions)

Cause: Inadequate transverse load distribution, brittle material

Secondary damage:Tooth breakage

Initial damage:Pitting on the pitch line

Fatigue breakage

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Potential Problems Drive

Single pinion drive (2’300 kW)

Breakage failure of the pinion in the gear reducer

Heavy (active) pitting on the drive pinion

Possible Cause: - Inadequate load distribution (1)- Overload of the tooth flanks (2) 1

2

12 12

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Mill Bearing

Advantages slide shoe bearings:

No size and capacity limitation of the mill

Simple design of wear plates

Far higher limit of gas temperature at mill inlet (e.g. for drying with heat generator)

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Feed Arrangements for Ball Mills

Preferred design today

(Slurry mill)

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Feed Arrangement (Example Step Feeder)

Advantages Good mill ventilation Easy to maintain Simple design

Ventilation air

Material feed

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Elements of Ball Mill – Overview (Internals)

Mill feedarrangement Mill head Mill shell arrangement

Mill dischargedriveMill

bearingMill

Grindingmedia

Shell Intermediatering

Retention

Internalelements

elementsExternal

liners diaphragmDischargediaphragmliners

Head

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Overview Internal Elements

A Coarse grinding compartment

B Intermediate diaphragm

C Fine grinding compartment

D Discharge diaphragm

E Grinding media

F Retention ring

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Liners for Coarse Grinding

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7 8 9 10 11 12 13 14

66

70

75

h0

h

h > 0.5 ho

Lifting Height Requirements (1st Chamber)

This criteria has to be confirmed case by case through evaluation of the coarse grinding.

Rule of thumb: h must be greater than 50 [mm]

1st chamber lining at end of lifetime

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Classifying Liner for Fine Grinding (2nd Chamber)

Rotation sense

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Head Liners

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Open Diaphragm (Drying Chamber Diaphragm)

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Intermediate Diaphragm

1st Compartment

Coarse Grinding

2nd Compartment

Fine GrindingIntermediate diaphragm

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Function of Intermediate Diaphragm

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Intermediate diaphragm

Slot opening in 1st chamber

Material flow control system

Centre screen

Grates in the second chamber

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Discharge diaphragm

Discharge diaphragm

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Discharge Diaphragm

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Material Quality and Application of Shell Liners

Material ChemicalComposition

Hardness(HRC)

Remarks

ManganeseSteel 12 – 14% Mn 40

Recommended for small mills.Deformation of liners for largemills (initial surface hardness20 – 25 HRC)

Low chromiumalloy castliners

2 – 3% Cr 40 - 42Less deformation thanmanganese liners. Suitablefor large and small mills

High chromiumalloy castliners

12 – 15% Cr 50 - 55Most used material. Suitablefor big and small mills (Notchimpact strength 4 – 10 J/cm2)

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Life Time of Shell Liners

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Grinding Media

Coarse grinding Ø 90 – 50 [mm]

Fine grinding Ø 50 – 12 [mm]

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Grinding in Ball Mill

Coarse grinding (1st chamber)

Cataracting of grinding media

Fine grinding (2nd chamber)

Cascading of grinding media

AA

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Ball filling degree (f)

f [%]20 40 - 4530

75

Pow

er [

%]

85

93 98

25 35

Typical range

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Steps of Grinding

Coarse Grinding

Medium Grinding

Fine Grinding

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Coarse Grinding: Parameters for Optimising

Power parameters Filling degree Chamber length Mill diameter Liner design and condition Mill speed

Efficiency parameters Ball charge (filling degree &

composition) Liner design Intermediate diaphragm settings Mill ventilation

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Grinding Media

Bulk weight of a grinding media charge in a two chamber mill with classifiying liner

4,4 [t/m3] 4,6 [t/m3] 4,7 [t/m3]

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Grinding Media (1st Compartment)

1.Compartment

Ø Ball [mm] Weight [ t ] Percent [%]

90 25.0 25.0

80 35.0 35.0

70 25.0 25.0

60 15.0 15.0

Total 100.0 100

Average ball weight [ g ] 1667

Spec. media surface [m2 / t ] 10.2

Holcim Standard for 1st Compartment

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Grinding Media (2nd Compartment)

Holcim Standard for OPC > 3’200 [cm2/g], closed circuit system

2.Compartment

Ø Ball [mm] Weight [ t ] Percent [%]

50 20.0 10.0

40 20.0 10.0

30 32.0 16.0

25 32.0 16.0

20 42.0 21.0

17 54.0 27.0

15

Total 200.0 100

Average ball weight [ g ] 41

Spec. media surface [m2 / t] 32.8

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Material Quality of Grinding Media

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Specific Wear Rates of Grinding Media

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Mill Efficiency

[%R]acc.

[cm2/g]Blaine

mill length [m]

longitudinal sieving graph

[m]

Blaine Value

Sieve Residues

Chamber 1

(coarse grinding)

Chamber 2

(fine grinding)

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Lifting Liners Effects

Liner-Lifting : low high

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Optimum Material Level 1st Chamber

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Optimum Material level 2nd chamber

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Mill Ventilation

Main Tasks Mill Ventilation: Material transport Cooling Removal of fines Fluidisation of material

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Cooling and Heating Possibilities

Cooling air

Cooling air

Moist additive

Hot clinker

Hot gasesH2O H2O

H2O

Product

ProductAirDust ladden air

H2OHot gases

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Fine Grinding and Mill Cooling

SOLUTION

Adapted mill cooling, playing with: Clinker temperature Mill ventilation Water injection

Use of grinding aid (temporary solution because expensive)

PROBLEM

Insufficient mill cooling lead to material agglomeration on balls and liners

The grinding is not any more done by balls against material but by material against material

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Water Injection Systems

80

90

100

110

120

130

Product temp. [°C]

Mill length

countercurrent

no waterinjection

co-currentAir fromblower

Air fromblower H2OH2O

H2O

H2O

1st 2nd Comp.

1st 2nd Comp.

2nd Comp.

1st Comp.

(Double)Rotary union

counter current

co-current

03 Ball Mill EDM

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