Day 1_5_ball Mill Internals_mbu.pdf

BALL MILL INTERNALS Ball Charge, Liners and Diaphragm

Melchior Buhendwa HTC Global – Operational Support Cement Production Intense Training Casablanca, 15th to 19th May 2017

THE BALL MILL INTERNALS Outlet diaphragm Intermediate diaphragm Feed Head Liners First Chamber liners

Second Chamber liners

Central Screen

Slide (5); 15/5/2017; Ball Mill Internals

BALL MILL INTERNALS – Functions in a nutshell

 Feed Head Liners – Protection; no process role  1st Chamber Liners – Protection; Impart energy to the balls for effective crushing  Intermediate Diaphragm – Process role – Fencing; Fineness controller; material flow regulator; Ventilation

 2nd Chamber Liners – Protection; Impart energy to the balls for effective fine grinding.

 Outlet Diaphragm – Process role – Fencing; Ventilation;  Grinding Media – Crushing/Grinding

Slide (5); 15/5/2017; Ball Mill Internals

IMPORTANCE OF MILL INTERNALS! Output,TPH SPC, kWh/T

Operational costs for a 4 m X 15 m Cement mill 6500X10X53250000 100 Annual running hours 6500 Prodn.in 5 years,MT 18000 30 GM wear rate, g/T 30 Power cost, €/kWh 0,06 Normal Wt.req.in 5 Total cost lifetime Hrs yrs in 5 years

Wt. 10,0 35,0 10,0 5,0 5,0 55,0 8,0 5,0 133,0

Feed Head Liners 1st Chamber shell liners Intermediate diaphragm frame Grate plates Intermediat diaphragm Back plates Intermediate diaphragm 2nd Chamber shell liners Outlet diaphragm frame Grate plates Outlet diaphragm Total

Liners GM Power Total

Cost/Ton 0,11 0,04 1,8 1,95

18000,0 30000,0 60000,0 15000,0 30000,0 60000,0 60000,0 30000,0

18,1 37,9 5,4 10,8 5,4 29,8 4,3 5,4 117,2

Liner Cost/Ton

54166,7 94791,7 27083,3 54166,7 16250,0 74479,2 21666,7 27083,3 369687,5

Grinding media Grinding Grinding tonnage for 5 media cost media years for 5 years cost/Ton

97500000

Power cost in Power cost 5 years / ton

369687,5 30X3250000 32500001000000

0,11

% 5,8% 2,0% 92,2%

Power in 5 years,Kw

97,5

126750,0

0,04

5850000,0

1,80

Cost/Ton

Liners 6%

GM 2%

Liners GM Power Power 92%

All costs in €

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Ball Main design criteria

 Design itself is a matter of experience

 Mainy parameters are used for the design of ball mills:

 Material to be ground  Mill Speed

 Filling degree  Ratio mill length to diameter  Length of chambers  Quantity of grinding media  Shape of shell liners  Ect.

Slide (5); 15/5/2017; Ball Mill Internals

Material: Grindability test acc. Zeisel** 120

Spec. energy

kWh/t

100

Slag Clinker Limestone

From Diagram: Values for spec. Energy at 3.000 cm²/g acc. Blaine:

80

Limestone/Trass: 12 kWh/t

60

Clinker:

26 kWh/t

Slag:

42 kWh/t

40

20

0 1000

** Energy consumption at mill shaft (without mechanical and electrical losses) 2000

3000

4000

Spec. surface acc. Blaine Slide (5); 15/5/2017; Ball Mill Internals

5000 cm²/g

6000

Mill speed Critical mill speed Is the speed which is reached when the centrifugal force FC of grinding media is equal to his gravity force FG. In the case the grinding ball runs on the mill lining without falling down. F C = FG m* De : m: w: g:

Deff * 2

w²crit = m. g

Effective mill diameter (inside liners) Mass of grinding ball Angular mill speed Gravity

The critical mill speed ncrit can be expressed as a function of the mill diameter De

Slide (5); 15/5/2017; Ball Mill Internals

ncrit 

42,3 Deff

Mill speed  The ratio between the mill speed n and the critical ncrit can be

expressed in percentage k. n k ncrit

 Modern ball mills in the cement industry work with a ration k of

round 75% to 76 %.  Older mills operate between 69% – 73%  Special case USA: Some ball mills are running with k in the

range of 76% - 80%

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Action of grinding balls as function of k and f The optimum action of grinding ball is achieved for f = 30% and k in the range of 70% to 80%.

Ball throwing

Cataract: smooth rolling of all the ball layers without throwing Slide (5); 15/5/2017; Ball Mill Internals

Dead Zone

BALL MILL INTERNALS: What is important?  Design – to stand upto the Process demands

Chamber configuration Lifting profile for 1st chamber liners Slot size/configuration, Ventilation, material retention Classification effect of the 2nd chamber liners Ball charge configuration

 Quality – to stand upto the Maintenance demands

– – – –

Metallurgy – different for different parts; Liners/Grates Minimum thickness Useful lifetime Grinding Media quality - Maintenance and Process impact

Slide (5); 15/5/2017; Ball Mill Internals

Upto 25% impact on efficiency

– – – – –

AGENDA

1. Ball Charge Management

2. Liner types 3. Diaphragm types

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Ball Charge Management

 Deciding the Quantity

– Calculation of ball charge quantity – Calculation of absorbed motor power  Deciding the pattern

– Feed size and composition/product size/Circuit type/internals  Deciding the Quality

– Impact/Wear/Corrosion levels  Characteristics of High Chromium Balls

– Specific weight and mass

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Calculation of ball charge quantity

G=

  Deff2  Leff  f  MK 4

Deff = effective diameter of chamber in m

Deff = D – 2 x liner thickness

Leff = effective grinding length of chamber in m

f

= Grinding media filling ratio

MK = bulk density of grinding media in t/m³

Reference values: For coarse ball charge 1st chamber (90 – 60 mm): MK = 4,5 t/m³ For ball charge 2nd chamber (60 – 20 mm):

Slide (5); 15/5/2017; Ball Mill Internals

MK = 4,6 t/m³

Calculation of absorbed power consumption Method 1: – Use Absorbed Power Formula  P = 0.2846 DAWN - Where D = effective diameter; A = 1,073 – J; W = total media weight in MT; N = RPM of mill; J = Volume load (Ball charge filling degree) in decimals: Example 30% = 0,3

 The above formula has accuracy within +/- 6%.

– When calculating power separately for the 2 chambers use  10 to 12 kWh/T for 1st chamber  Balance power for the 2nd chamber

Slide (5); 15/5/2017; Ball Mill Internals

Method 2: Mill absorbed Power - Slegten Formula 1.27

N Vcr

P = L* Where :

2.379 * Deff. *

P

: the motor absorbed power (kW)

L

: the useful length of mill (m)

N

: is mill speed (rpm)

ρ *C

Vcr

: is the critical speed inside liners = (42.3/ Deff. ^0.5)

Deff.

: internal diameter (inside liners) (m)

J

Slide (5); 15/5/2017; Ball Mill Internals

* J * Kj *

π 4

: Volume Loading (filling degree)

Kj

: = (1.36 - 1.2*J)

ρ

: is the bulk density of load (t/m3)

C

: is a constant depending on the material and the liners = 11.262

- for clinker mill closed circuit with Slegten eq

= 10.70

- for clinker + slag

= 12.16

- for raw mix

Methode 3: Mill power calculation – VDZ Formulas MT22 Formulas for practical calculations of ball mills: Critical speed Mill speed

42,3 Deff n k ncrit

ncrit 

in rpm

  Deff2  Leff  f  MK 4

Quantity of ball charge

G=

Mill absorbed power

Pabs. = c  G  Deff  nR

at mill shaft

Combination of formulas Slide (5); 15/5/2017; Ball Mill Internals

[in Tons]

[in kW]

L f k D3,5eff Pabs  33,22 * c * * * * * Deff 100 100

Methode 3: Mill power calculation – VDZ Formulas MT22 Pabs. counter = Pabs 

1

A

Total efficency A The total efficiency A = mech * el Following values can be used: For mill with girth gear drive: A = mech *  = 0.92 – 0.94 For mill with central drive:

Slide (5); 15/5/2017; Ball Mill Internals

A = mech *  = 0.94 – 0,96

Power consumption factor c The factor c depends on filling degree and ball charge.

1st grinding chamber c1 = (0,31 – (0,00275*fch1)) 2nd grinding chamber c2 = (0,3016 – (0,0028*fch2)) fch1: filling degree 1st chamber fch2: filling degree 2nd chamber

Slide (5); 15/5/2017; Ball Mill Internals

Ball Charge Management

 Deciding the Quantity

– Volume loading  Deciding the pattern

– Feed size and composition/product size/Circuit type/internals  Deciding the Quality

– Impact/Wear/Corrosion levels  Characteristics of High Chromium Balls

– Specific weight and mass

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Ball Charge Management Deciding the pattern

Size reduction by: Cataracting motion

Coarse Grinding

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Cascading motion

Medium Grinding

Fine Grinding

Ball Charge Management Deciding the pattern – 1st Chamber

Cataracting motion

Coarse Grinding Ø 90 – 60 [mm] balls

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Medium Grinding

Fine Grinding

Ball Charge Management 

Deciding the Pattern (ball charge composition) – First Chamber – For conventional cement mills an average ball weight of 1,4kg/ball to 2 kg/ball is used in the 1st chamber. There are several ways to achieve this:  If the clinker is consistently coarser than 15mm then 40% by weight of 90mm … if clinker is consistently finer then can reduce the proportion of 90mm media to as low as 15% … if clinker size variable then better to have 40% 90mm balls.  Remainder of first chamber media should be split between equal numbers of 60, 70 and

80mm media balls.  The following would be typical charge grindings for the first chamber of a cement mill with coarse, medium or fine clinker feed:

90mm (%) 80mm (%) 70mm (%) 60mm (%)

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Coarse 40 29 19 12

Clinker size Medium 25 36 24 15

Fine 15 41 27 17

Ball Charge Management 

Deciding the Pattern (ball charge composition) – First Chamber – Rules of thumb:  In case of new ball charge composition start and new mill shell liners start with round 75% of balls for each size then ball charge adjustment and optimization to

100% after mill operation/evaluation of operating data and mill axial samples.  If ball charge composition is known, start with 80 to 85% and adjust to 100% as explained before.

– These pattern provide an initial guideline; Fine-tuning always by taking samples axial sample or at least sample at the diaphragm. – For closed circuit finish mills… targets should be to attain:  Before intermediate diaphragm: - 15 – 25% R 0.5 mm - max. 5% R 2 mm

Slide (5); 15/5/2017; Ball Mill Internals

Before discharge diaphragm 15 – 25% R 0.09 mm max. 5% R 0.2 mm

Ball Charge Management 

Deciding the Pattern – Second Chamber – In the second chamber the primary function of the media is to finely grind the cement

– The cement must become progressively finer as it progresses from the intermediate to the outlet diaphragm – This means that progressively smaller media is required along the length of the second chamber – The second chamber might therefore fitted with a classifying lining.

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Ball Charge Management 

Deciding the Pattern - Second Chamber – If the first chamber of the mill is achieving 2,5% residue on 1mm then there is no requirement for large media in the second chamber of a cement mill … 1mm particles require media of max size 25mm for optimum grinding … particles of 0.5mm need media of max size 18mm for optimum grinding – If grinding efficiency were the only consideration then very small media would be used … for fine grinding the surface area of the grinding charge is the factor determining grinding efficiency … there area 9,000 x 30mm balls in a tone of media with a surface area of 26m2/t … there are 72,000 x 15mm balls in a tone of media with a surface area of 50m2/t …

meaning grinding efficiency should be more than doubled with 15mm compared with 30mm media. Slide (5); 15/5/2017; Ball Mill Internals

Ball Charge Management Deciding the pattern – 2nd chamber

Cascading motion

Coarse Grinding

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Medium Grinding

Fine Grinding

Ball Charge Management 

Deciding the Pattern - Second Chamber – As for coarse grinding chamber, in the fine grinding chamber the average ball weight determines the residue of the product. 28gm/ball for open circuit and 46gm/ball for close circuit.

– Dam/Curtain consisting of 60/50/40mm balls. This dam is near the Intermediate diaphragm and ensures that the nips and coarse particles are broken. Normally it is in range of 15% to 25% of the total ball charge. – Medium ball charge consisting of 30/25mm balls. It is in the middle of the 2nd chamber and is 25% to 50% of the total ball charge. – Fine ball charge consisting of 20/17mm balls. It is 30 to 70% of the total ball charge. – Balls are better for generation of higher Blaine. Cylpebs are sometimes used for reducing the residues but at a higher power consumption (@5%) Slide (5); 15/5/2017; Ball Mill Internals

Ball Charge Management 

Typical Ball Charge Pattern - Second Chamber Ball charge of 2nd chamber Ball Size (mm)

Coarse charge %

middle charge %

Fine Charge (%)

50

10

40

15

10

30 25 20 17

20 25 30

25 25 20 20

15 15 30 40

Total

100

100

100

Avrg. Ball Weight (g/ball)

52

37

28

Specific Surface (m2/T) 29

33

39

Remember These pattern provide an initial guideline … their appropriateness then has to be checked and fine-tuned by plotting the grinding diagram. Slide (5); 15/5/2017; Ball Mill Internals

Ball Charge Management

 Deciding the Quantity

– Volume loading  Deciding the pattern

– Feed size and composition/product size/Circuit type/internals  Deciding the Quality

– Impact/Wear/Corrosion levels  Characteristics of High Chromium Balls

– Specific weight and mass

Slide (5); 15/5/2017; Ball Mill Internals

Ball Charge Management  Deciding the Quality

– This is covered extensively in the metallurgy selection section.

Slide (5); 15/5/2017; Ball Mill Internals

Ball Charge Management

 Deciding the Quantity

– Volume loading  Deciding the pattern

– Feed size and composition/product size/Circuit type/internals  Deciding the Quality

– Impact/Wear/Corrosion levels  Characteristics of High Chromium Balls

– Specific weight and mass

Slide (5); 15/5/2017; Ball Mill Internals

Ball Charge Management  Characteristics of High Chromium Balls Number of balls per MT Specific surface (m2/MT)

Diameter (mm)

Weight (gm.)

100

4.001

250

7,854

90

2.917

343

8,728

80

2.049

488

9,812

70

1.372

729

11,222

60

864

1.157

13,805

50

500

2.000

15,708

40

256

3.905

19,628

30

108

9.257

26,173

25

63

15.996

31,408

20

32

31.242

39,259

17

20

50.870

46,185

15

14

74.052

52,347

Slide (5); 15/5/2017; Ball Mill Internals

AGENDA

1. Ball Charge Management

2. Liner types 3. Diaphragm types

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Liner Types

1. First Chamber Liners

2. Second Chamber Liners

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Liner Types - 1ST CHAMBER SHELL LINERS  Function

– Prepare the material for 2nd chamber or fine grinding chamber – Crush particles to less than 5mm size  Target values (Cement Mills) - Open Circuit » R1mm < 2.5% » R90µ 40 to 50% - Close Circuit » R1mm < 5% » R90µ 40 to 50%

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Liner Types - 1ST CHAMBER SHELL LINERS Influence of Liner shape on lifting effect

Both lifting effects might be insufficient for very hard feed…. Lifting effect also depends on the speed of the mill…… Slide (5); 15/5/2017; Ball Mill Internals

Liner Types - 1ST CHAMBER SHELL LINERS 

Most Popular Designs – Step Liners (Plain/Wave) – Heidelberger (HTC) Profile – Double Wave / Block type – Lorraine type – Modular type – xlift, UVL

Slide (5); 15/5/2017; Ball Mill Internals

Liner Types - 1ST CHAMBER SHELL LINERS  Step Liners

Step & Wave (boltless)

Step & Wave (bolted)

- Good mechanical life (Very Safe) - Process life can be an issue - Useful life for OPC around 30000 Hours (4Yrs)

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Plain Step (bolted)

1ST CHAMBER SHELL LINERS  The step size (lifting power)

depends on

Direction of rotation

– Size of the mill – Mill rotation speed (% Critical Speed) – Volume load – Grindability of feed material

 Boltless step chamber 1 liner

– Less material spillage – Avoids bolt breakage – More homogeneous construction.

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1st chamber lining plates: Type of shapes Shapes:

- Step liners, Duolift, Xlift all created by Maggotteaux / Belgium

- Heidelberger profile created by Mr. Rock - HeidelbergCement R1 = 200 – 600 mm

Step liners -Easy shape, create more fines -Earlier lost of lifting effect due to high slippage -Adjustment of the ball charge required -Earlier replacement of the liners Slide (5); 15/5/2017; Ball Mill Internals

R3 < R2 < R1

Heidelberger (HTC) profile -High lifting effect, limited slippage -Profile stable during wearing -Carefully manufacturing (casting) needed -Sensitive to low filling degree

1ST CHAMBER SHELL LINERS Heidelberger (HTC) Profile

• Heidelberg Cement developed special “in-house” profile • Lifting step increases with wear • Supports the decreasing media size (when media wear smaller they need higher lift for same impact)

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Design of a liner plate with Heidelberger (HTC) profile

B, H, R, D depends on mill diameter, material to be ground (Particle size, art of material), critical speed of the mill, ect... B = 60 – 100 mm H = 90 – 140 mm R = 200 – 600 mm D = 45 – 75 mm

Slide (5); 15/5/2017; Ball Mill Internals

1st chamber lining plates

Step liners

Norcem Kjopsvik, CM 4 Slide (5); 15/5/2017; Ball Mill Internals

Heidelberger profile

Anneliese Ennigerloh

1ST CHAMBER SHELL LINERS  Heidelberger (HTC) Profile

HTC Profile (bolted) - Good process benefit as slippage low and profile can be maintained longer - Sharp lifting angle means high risk of breakage; choice of alloy important; filling degree, speed of mill and process parameters very important - Useful life for OPC around 30000 Hours (4Yrs) - Semi boltless solution can be adopted to take advantage of the system Slide (5); 15/5/2017; Ball Mill Internals

1ST CHAMBER SHELL LINERS  Double Wave Liners

Double Wave (Semi boltless)

- Good process benefit as slippage low and profile can be maintained much longer - High productivity throughout useful life; good profile for hard feed material - Sharp lifting angle means high risk of breakage; choice of alloy important; filling degree, speed of mill and process parameters very important - Useful life for OPC around 30000 Hours (4Yrs) Slide (5); 15/5/2017; Ball Mill Internals

1ST CHAMBER SHELL LINERS  Some designs that are getting obsolete…

Lorraine

Grooved

Volst Alpine

Block



And beware of some new ones…. Modular

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1ST CHAMBER SHELL LINERS

How to avoid excessive wear (within the whole Mill)? • • • • • •

Never run the mill without material for extended time Interlocking to stop mill when feed less than X t/h for more than 10 min. Diaphragm adjustments for material level in first compartment Internal Material Transport to be observed (Crash Stop) Media Charge too coarse = Material Transport too fast (gaps) Media Charge too fine = Material Transport too slow (gaps)

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Liner Types

1. First Chamber Liners 2. Second Chamber Liners

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2ND CHAMBER SHELL LINERS  Grinding by attrition required – so many design possibilities like

Classifying, Dragpebs, Plain, Grooved etc.  Most Optimum Design – Classifying or Self Sorting – Why?

– Feed is fine enough – need for adapting the right size of balls to the material size. Compatible ball charge 15% efficient against mixed. – Possibility to go wider range of balls and also lower size of balls – Possible to use big balls (60mm) to handle nibs – Classifying liners have almost 20% higher material speed – Ball charge management is easier – sorting/scrap/nibs removal – Possibility to use extremely hard and wear resistant alloy for very long useful life

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2ND CHAMBER SHELL LINERS  Classifying liners - principle

– Liners cascade bigger balls more vigorously than smaller balls – Works better if L/D > 2 – The segregation of the media occurs when the larger balls fall onto the sloped surface of the plates they pick up enough energy to ‘bounce’ backward. – The lighter, smaller balls, work their way to the outlet end of the mill, thus classification takes place Flow Direction

Large Ball More Mass More Impulse More Deflection

Large Ball

Small Ball

Small Ball Less Mass Less Impulse Less Deflection Liner Mill Shell

PRINCIPLE OF CLASSIFYING LINERS Slide (5); 15/5/2017; Ball Mill Internals

2ND CHAMBER SHELL LINERS  Classifying Liners

Classifying liner Mill Dia. > 4.4m

Classifying liner Mill Dia. < 4.4m

- Best process and maintenance solution for second chamber - Easy for ball charge management - Useful life for OPC more than 60000 Hours (10Yrs)

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2ND CHAMBER SHELL LINERS – Classification in action

Outlet end

Krivyi Righ, CM1: 2nd Chamber

Inlet end Slide (5); 15/5/2017; Ball Mill Internals

2ND CHAMBER SHELL LINERS  Variations of the Classifying design

Lifting Classifying Conveying Classifying

Thin Classifying

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2ND CHAMBER SHELL LINERS - Ripple type (Dragpebs) 

Used in 2nd chamber for Grinding media < 30mm in FLS mills

- For maximum loading - Combidan diaphragm - Danula rings in open circuit

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2ND CHAMBER SHELL LINERS – trapezium type (Russian) 

Used in 2nd chamber for Grinding media < 30mm

- Poor power use - Protection of shell not full proof Slide (5); 15/5/2017; Ball Mill Internals

- For maximum loading

AGENDA

1. Ball Charge Management

2. Liner types 3. Diaphragm types

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Diaphragm types Diaphragms chamber 1 chamber 2

•

separation of the mill body into two chambers with different process conditions

•

transfer of ground material with a certain particle size from …  

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from chamber 1 to chamber 2 from chamber 2 to the mill discharge

DIAPHRAGM TYPES

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Diaphragm types

1. Intermediate Diaphragms 2. Discharge Diaphragms 3. Drying Chamber Diaphragms

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Intermediate Diaphragm types 1. Conventional Diaphragms 1. 2. 3. 4.

FLS Polysious KHD Other OEMs

2. Material Flow Control 1. 2. 3. 4.

Estanda Christian Pfeiffer Slegten – Magotteaux/Vega Some OEMs

3. Other – Combidan (FLS)

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Main Components of a classic Intermediate diaphragm

1 diaphragm segment 6

3 5

2

supports

3

clamping ring

4

wearing plates, slotted

5

central opening & grid

6

adjustable lifter

2

4 1

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INTERMEDIATE DIAPHRAGM – How it works

Feed End View of Diaphragm without Grate Segments

Side View of Diaphragm

3. Material gravity drops through the center hub and into the next compartment. 2. Material is lifted by mill rotation.

.

1. Material fills the chamber, in between the slotted plates and blind plates

Material is lifted by mill rotation and is then gravity dropped into the next compartment. 1

Gas Flow

BM Load Level

Material passes through the slots and fills the lifter chamber. Slide (5); 15/5/2017; Ball Mill Internals

2

INTERMEDIATE DIAPHRAGM – How it works

-

Material passes through slots into hollow sections Mono-Directional Scoops lift material Material slides down and passes through opening into center hole Mill sweep gas flow carries Material into 2nd Comp. Centre hole needs to provide enough area to allow sufficient, not too fast gas flow

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INTERMEDIATE DIAPHRAGM – How it should work….  In 1st Chamber the ball charge is very coarse and the permeability is high. Hence there is no material at the end of the 1st Chamber.

 Flow Control Diaphragm helps in good retention of the material and thereby increasing the crushing efficiency in the 1st Chamber.

 Maximum efficiency corresponds to the maximum power.  The difference in efficiency of Flow Control and Conventional diaphragm is 15 %. Since L1 is 30% of the total length, efficiency of the mill with Flow Control Diaphragm is 5 % higher.

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INTERMEDIATE DIAPHRAGM – Controlling material level

Conventional Material Transport

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Effect of Material Flow Control

Intermediate Diaphragm – Christian Pfeiffer

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Intermediate Diaphragm - SLEGTEN

 Magotteaux/Vega

– Scoop Assembly – Number of open scoops regulates the material flow

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Intermediate Diaphragm - SLEGTEN

Q = S X h = constant Slide (5); 15/5/2017; Ball Mill Internals

Intermediate Diaphragm : FLS Combidan • • • • • •

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5 to 8mm screen behind the blind plates Principle of recirculation of coarse Since Blind plates – higher hardness/carbides/life Maintenance of screen is very difficult. Breakage in screen disturbs the performance. Ventilation generally poor

Intermediate Diaphragm – Central Screen Good permeability (Estanda)

No permeability

Good permeability (Slegten)

Low permeability

Good Permeability (Pfieffer)

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Intermediate Diaphragm – Slot configuration

Vertical slots: Plugging but also material transfer low; no self cleaning

Circumferential slots: Good material transfer; difficult to cast.

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Tangential slots: Good material transfer; self cleaning possible.

Perforated slots: Poor permeability of slots.

Intermediate Diaphragm – Slot Design of Grate Plates

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Diaphragm types

1. Intermediate Diaphragms 2. Discharge Diaphragms 3. Drying Chamber Diaphragms

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Discharge Diaphragm What is the function of the outlet Diaphragm?

-

-

-

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Keep media in 2nd Compartment Allow ground material to leave 2nd Comp. Control the material flow out of the 2nd Comp. Provide enough open area for the mill aeration without over-speeding the gas / over-”sucking” the slots Typically not adjustable Slots need to be larger than in Intermediate Diaphragm to allow large Particles from 1st Comp. to leave 2nd Comp. Provide support for water injection

Discharge Diaphragm  Double wall, full liftered design is the most common

Feed End View of Partition with Grate Segments Outer Grate Segment Inner Grate Segment Center Hub or Cone Center Screen (Mill Sweep)

Typical Chamber Filling Level

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Discharge Diaphragm – Central Discharge Mills (Dopple Rotator)

Drying comp.

1st comp.

2nd comp.

Drying Chamber Diaphragm Double outlet diaphragm

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Discharge Diaphragm Slot profile for Grate Plates

Slide (5); 15/5/2017; Ball Mill Internals

Diaphragm types

1. Intermediate Diaphragms 2. Discharge Diaphragms 3. Drying Chamber Diaphragms

Slide (5); 15/5/2017; Ball Mill Internals

Drying Chamber Diaphragm  Grate plates only on the grinding Chamber side

– Careful about the slot size and orientation – Careful about the axial load on the frame  Central Screen to have proper openings to allow bigger

feed sizes to enter the grinding chamber

Slide (5); 15/5/2017; Ball Mill Internals

for better building…..

Thank You!

Slide (5); 15/5/2017; Ball Mill Internals