03 ball mill edm
DESCRIPTION
This poerpoint is about the ball mills .TRANSCRIPT
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Grinding with Ball Mill Systems
EDM
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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