ball mill grinding - ramkrishna
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Improvement of Ball Mill Improvement of Ball Mill grinding efficiencygrinding efficiency
Presented ByPresented ByRamkrishna Halder Ramkrishna Halder
Under the guidance ofUnder the guidance ofDr. Preeti BajpaiDr. Preeti Bajpai
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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
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Introduction
Grinding is used to reduce the size of a particular materialGrinding is used to reduce the size of a particular material
To achieve the required result from grinding process the To achieve the required result from grinding process the grinding efficiency is the most required and important factor grinding efficiency is the most required and important factor
Various factors like hardness, toughness, material structure, Various factors like hardness, toughness, material structure, size, shape and the ratio of feed size to product size etc. size, shape and the ratio of feed size to product size etc. affect the size reductionaffect the size reduction
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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 media Size and shape of grinding media
Mixing ratio of various size of grinding mediaMixing ratio of various size of grinding media
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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
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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
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Power Consumption
Power Requirement
W = 10Wi*(1/√P80 - 1/√F80) W = Power (KWh/t)Wi = Working indexP80 = 80% passing size of product (µm)F80 = 80% passing size of feed (µm)
Observation
Wi =13.57P80 = 125 (µm)F80 = 10000 (µm)W = 10.8 KWh/t
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Maximum Media SizeM = √[(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 ftM = (10000*13.57)/(200*75) √(2.23/√5.58) M = 2.9647 inch = 75.30 mm
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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.
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Comparison between Calculated and Observed parameters
Parameters Experimental Existing
Speed 25 rpm 20 rpmFill level 80.6% 81.9%
Media size 75 mm 50 mmPower Required 10.80 kwh/t 12 kwh/t
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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 9Sinoma 0.60 3.66 8-9
Cumi
Dry wt. of the ball = 52.3 g Suspended wt = 37.9 gSoaked wt = 52.4 gA.P = 0.689% B.D = 3.61 g/cc
Sinoma
Dry wt. of the ball = 66.7 gSuspended wt = 48.37 gSoaked wt = 66.75 gA.P = 0.60% B.D = 3.66 g/cc
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Apparent Porosity Vs Bulk Density
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Hardness
HARDNESS
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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 Container2.Sieve shaker
Sinoma:Amount of Grinding media taken = 531.8 gAfter shaking amount of media = 529.5 gMaterial Loss = 2.3 g
Wear Test
Cumi:Amount of Grinding media taken = 521.8 gAfter shaking amount of media = 521.5 gMaterial Loss = 0.3 g
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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
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Wear After Two Hours
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Experiments performed in Ball mill - 2 (capacity 50 kg)
Dimension
Length = 3ft Diameter = 3 ft.Critical speed = 45.5 rpmOperating speed = 34 rpm
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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
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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
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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
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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
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