Ball mill grinding - Ramkrishna

Improvement of Ball MillImprovement of Ball Mill
grinding efficiencygrinding efficiency
Presented ByPresented By
Ramkrishna HalderRamkrishna Halder
Under the guidance ofUnder the guidance of
Dr. Preeti BajpaiDr. Preeti Bajpai
11

Presentation OutlinePresentation Outline
Introduction of grinding conceptIntroduction of grinding concept
Objectives of the projectObjectives of the project
Experimental Procedure and ObservationExperimental Procedure and Observation
Conclusions and RecommendationsConclusions and Recommendations
22

Introduction
 Grinding is used to reduce the size of a particularGrinding is used to reduce the size of a particular
materialmaterial
 To achieve the required result from grinding processTo achieve the required result from grinding process
the grinding efficiency is the most required andthe grinding efficiency is the most required and
important factorimportant factor
 Various factors like hardness, toughness, materialVarious factors like hardness, toughness, material
structure, size, shape and the ratio of feed size tostructure, size, shape and the ratio of feed size to
product size etc. affect the size reductionproduct size etc. affect the size reduction
33

How To Improve Efficiency?How To Improve Efficiency?
 By monitoring the fill levelBy monitoring the fill level
 By controlling operating speedBy controlling operating speed
 Feed material to grinding media ratioFeed material to grinding media ratio
 By choosing suitable grinding mediaBy choosing suitable grinding media
Size and shape of grinding mediaSize and shape of grinding media
Mixing ratio of various size of grinding mediaMixing ratio of various size of grinding media
44

Objectives of the ProjectObjectives of the Project
 To analyze the existing grinding system
 To optimize the factors affecting to efficiency of
grinding process
 To generate a standard operating procedure on the
basis of the evaluated parameters for grinding
55

Experimental ProcedureExperimental Procedure
Where nc = Critical speed (rpm)
R = Radius of the
mill (m)
r = Radius of the
ball (m)
Critical Speed
Observation Radius of the mill = 0.85 m
Radius of the ball = 0.025 m
nc = 33 rpm
So operating speed = 25 rpm
All basic parameters have been calculated while considering existing
experiments in ball mill-3
66

Power Consumption
Power Requirement
W = 10Wi*(1/√P80 - 1/√F80)
W = Power (KWh/t)
Wi = Working index
P80 = 80% passing size of product (µm)
F80 = 80% passing size of feed (µm)
Observation
Wi =13.57
P80 = 125 (µm)
F80 = 10000 (µm)
W = 10.8 KWh/t
77

Maximum Media Size
M = √[(FWi/KCs)/√(S/√D)]
Where M = Diameter of the top size media (inch)
F = Feed size (µm)
Wi = Work Index, Cs = percent critical speed
K = constant S = Sp. Gravity of feed (g/cc)
D = Inside diameter of Mill (ft)
Observation
F = 10000 µm, Wi = 13.57
K = 200 Cs = 75,
S = 2.23 g/cc D = 5.58 ft
M = (10000*13.57)/(200*75)
√(2.23/√5.58)
M = 2.9647 inch = 75.30 mm 88

Observation
Total height of ball mill = 67 inch = 5.58 ft
Height of Ball + Feed material = 54 inch = 4.5 ft
Empty space = 13 inch = 1.08 ft
Percentage of Fill level = 54/67*100 = 80.59%
Percentage of Empty space = 19.41%
Fill level
 The load of the ball is usually a little more than half of the volume of the mill.
 Generally 2/3 volume of the mill filled by material and ball.
 If the fill level is low, most of the energy of the balls is wasted in impacts
between them – leading to low comminution ratio.
 If mill is overloaded, the grinding material causes a damping effect that
decreases the comminution ratio. So optimization is essential.
99

Comparison between Calculated and
Observed parameters
Parameters Experimental Existing
Speed 25 rpm 20 rpm
Fill level 80.6% 81.9%
Media size 75 mm 50 mm
Power Required 10.80 kwh/t 12 kwh/t
1010

Media Quality
Calculation
%AP = (W2 – W1) *100 Where W1 = Dry wt (gm)
(W2 – W3) …. (a) W2 = Soaked wt (gm)
W3 = Suspended wt (gm)
B.D = W1
(W2 – W3) …. (b)
Observation
Types of
Media
Apparent
Porosity (%)
Bulk Density
(g/cc)
Hardness
Moh’s scale
Cumi 0.689 3.61 9
Sinoma 0.60 3.66 8-9
Cumi
Dry wt. of the ball = 52.3 g
Suspended wt = 37.9 g
Soaked wt = 52.4 g
A.P = 0.689% B.D = 3.61 g/cc
Cumi
Soaked wt = 52.4 g
A.P = 0.689% B.D = 3.61 g/cc
Sinoma
Soaked wt = 66.75 g
A.P = 0.60% B.D = 3.66 g/cc
Sinoma
Soaked wt = 66.75 g
A.P = 0.60% B.D = 3.66 g/cc
1111

Apparent Porosity Vs Bulk Density
1212

Types of
media
Before
shaking wt.
of the balls
(g)
After
shaking
wt. of the
balls (g)
Shaking
Time
(hrs)
Material
loss
(g)
Cumi 521.8 521.5 2 0.3
Sinoma 531.8 529.5 2 2.3
Apparatus :
1.Hard Plastic Container
2.Sieve shaker
Sinoma:
Amount of Grinding
media taken = 531.8 g
After shaking amount
of media = 529.5 g
Material Loss = 2.3 g
Wear Test
Cumi:
Amount of Grinding
media taken = 521.8 g
After shaking amount
of media = 521.5 g
Material Loss = 0.3 g
1414
Fresh grinding
media
Jar used
for shaking
Sieve
Shaker
Grinding
Media after
shaking

Wear test for Cumi & Sinoma
Cumi
Sinoma
Before Shaking After Shaking
Before Shaking After Shaking
1515

Experiments performed in Ball
mill - 2 (capacity 50 kg)
Dimension
Length = 3ft Diameter = 3 ft.
Critical speed = 45.5 rpm
Operating speed = 34 rpm
1717

Observation of packing ratio of grinding media
Experiment
Number
50 mm
balls
taken
(%)
40 mm
balls
taken
(%)
30 mm
balls
taken
(%)
Before
shaking
height
of the
balls
(cm)
After
shaking
height
of the
balls
(cm)
Difference
in height
(cm)
1 50 24 26 12 11.6 0.4
2 50 15 35 10.8 10.0 0.8
3 75 12 13 10.5 10.2 0.3
The experiments were started using the combination of various media
size mentioned in Exp-2 because of having the best packing ratio
1818

Observation of Grinding Time
Grinding time can be reduced by crushing the feed material before ball milling
 Further , the grinding time can be reduced by use of grinding aid
 Frit (GF-204, 30 kg)
 0.05 % grinding aid (tri-ethanol amine)
 0.05 % water
1919

Contd..
Parameters Amount
of feed
material
(kg)
Amount of
grinding
media (kg)
Grinding
time
(h)
Sieving (240 mesh)
Passing Residue
Without
crushing
30 60 10-11 98.5% 1.5%
Using
grinding
aid
30 60 8 97.5% 2.5%
With
crushing
30 60 5 95.8% 4.2%
2020
Frit powder after
grinding
Sieve from 60 to 240
mesh
Frit powder after
sieving

Types of
crusher
Amount of
feed material
Before
crushing max
size of feed
After
crushing max
size of
product
Crushing
Time
Jaw Crusher 20 kg 50 mm +15 mm 5.50 min
Smooth Roll
Crusher
20 kg 50 mm +5 mm 3.45 min
Further Reduction of Grinding Time
Jaw Crusher Smooth Roll CrusherFrit material
before crushing
2121

Conclusions and Recommendations
 The optimized operating speed was 25 rpm while in the existing
system it was observed as 20 rpm
 The recommended media size is 75 mm but existing is 50 mm
 The existing fill level is almost in optimized range
 On the basis of the physical and mechanical properties it is
recommended to use cumi grinding media
 It is recommended to use a suitable grinding aid to reduce
further the grinding time
 It is recommended to crush (if suitable) the material before
grinding 2222

Ball mill grinding - Ramkrishna

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