sandvik construction 1 a world leader in construction module 2a how material factors affecting...
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Sandvik ConstructionA world leader in Construction
Module 2a How material factors affecting crusher performance
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What are the major influences?
From material factors?
From equipment/mechanical factors?
Crushing concepts Raw materialsWhat do we really know about crushing?
The major influences on crusher performance.
material factors such as
1. toughness,
2. bulk density/particle size distribution
3. reduction ratio
4. not discussed here –but abrasivity has a long term effect.
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Crushing concepts Raw materials What are we about to examine?
Rock is crushed when the strength of the rock particle cannot absorb the strain energy applied by the crusher and the rock deforms beyond it’s plastic limit to ultimate failure.
Rock needs to be breakable!!!!!
Plastic fines in the chamber will become compacted and absorb energy without deformation and failure.
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Crushing concepts Raw materialsWhy do we need to know about the material properties?
The toughness of the rock is one factor affecting the performance of the crusher.
it will determine the power drawn by the crusher from the motor or engine and therefore will determine the minimum setting at which the crusher will operate and give satisfactory mechanical reliability.
all crushers have a maximum mechanical design limit related to the maximum power they are permitted to absorb.
it will determine the capacity.
The abrasivity of the rock will affect the liner life and the performance of the crusher over a period of time.
The grain structure will influence the way in which the rock fractures and therefore the cubicity of the end product.
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Crushing concepts Raw materialsWhy do we need to know about the material properties?
Impact Work Index (WI)
Description of the Crushability
< 10 Very soft
10 – 14 Soft
14 – 18 Medium
18 – 22 Tough
22 – 26 Very tough
> 26 Extremely tough
Abrasion Index (AI) Description of the Wear
< 0.1 Very low wear
0.1 – 0.2 Low wear
0.2 – 0.4 Intermediate wear
0.4 – 0.6 Normal medium wear
0.6 – 0.8 High wear
> 0.8 Extremely high wear
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Crushing concepts Raw materials Work Indices Abrasion Indices
Material WI AI Compressive strength (Mpa)
Amphibolites 16 0.4 200 - 300
Andesite 16 0.5 170 - 300
Basalt 20 0.25 300 - 400
Diabase 18 0.28 250 - 350
Dolomite 12 < 0.02 50 - 150
Diorite 19 0.4 170 - 300
Gabbro 21 0.4 200 - 350
Greywacke 18 0.3 150 - 300
Material WI AI Compressive strength (Mpa)
Gneiss 16 0.48 200 - 300
Granite 16 0.46 200 - 300
Limestone 11 < 0.01 80 – 180
Marble 12 < 0.02 100 - 200
Quartzite 16 0.75 150 - 300
Sandstone 10 0.75 30 - 150
Iron ore (Hematite)
11 0.5 100 - 200
Iron ore (Magnetite)
8 0.2 50 - 150
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Crushing concepts MaterialsAverage values
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Crushing concepts Raw materialsParticle size distribution
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000Size (mm)
% p
assin
g
Max sieve size = 90mm/100mm for practical laboratory screening
Above 90mm by estimation/photo analysis
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Crushing concepts Raw materialsParticle size distribution
70mm
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
1 10 100 1000
Product
Feed
350mm
Reduction Ratio: F80/P80
350/70=5.0
70mm
Reduction ratio
A ratio recognising the reduction in size of a material when passed through a crusher.
F80: the size at which 80% of the feed will pass
P80: the size at which 80% of the product will pass
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Crushing concepts Raw materialsReduction
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
HSIH-ConeS-ConeJawFeed
Normal reduction:
Jaw crusher 2-3
Gyratory crusher 3-4
Cone crusher 3-5
Impact crusher (VSI) (F50/ P50) 4-6
Impact crusher (HSI)
7-10
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Crushing concepts Raw materialsReduction
F80 Feed: 400 mm
P80 Products: 16 mm
Min. required plant reduction ratio:
Using reduction ratio to predict
required no. of crushing stages
2516
400
2-stage Impact Plant:10x7=70 OK, Only for Ai <0.3
2-stage Jaw/cone Plant:3x4=12NOT OK
3- stage Jaw/cone Plant3x3x4=36OK
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Crushing concepts Raw materialsReduction
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Increased crushing force and power draw
Coarser product size
Lower capacity
Tougher rock
Increased moisture content0
0,2
0,4
0,6
0,8
1
1,2
0 1 2 3 4 5
Moisture content (%)
Ca
pa
cit
y
Jaw crusher,CSS 100 mm
Jaw crusher,CSS 50 mm
Cone crusher,CSS 20 mm
Cone crusher,CSS 10 mm Lower capacity
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Crushing concepts Raw materialsWhat happens if other properties change?
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Smaller feed sizeCapacity upFiner productBetter shape
Bulk density increases Capacity increases but a higher risk of packing due to compression limit
Packing
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Crushing concepts Raw materialsWhat happens if other properties change?
1,9
1,8
1,7
1,6
1,5
1,4
0-32 mm
4-32 mm8-32 mm
12-32 mm16-32 mm
0-11,2 mm
4-11,2 mm
8-11,2 mm
Bulk density (t/m3)
2,65 t/m3specific gravity
Bulk density increases - higher risk of packing as feed becomes finer.
Bulk density- a combination ofSpecific gravity & particle size distribution
Specific gravity increases from 2.65 to 3.2 - capacity increases by 20.75%
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Crushing concepts Raw materialsCompression limit
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Packing in the chamber is caused when there are no voids for the newly crushed fines to move into. This results in the crusher trying to compress the material back together again.
The result of packing is extreme crushing pressure surges which will require the setting to open and allow the pack material to leave the chamber. Cone crusher’s are measured on both power and
pressure. Any major spike in either will result in the opening of the chamber to relieve the overload.
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Crushing concepts Raw materialsCompression limit Packing
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More cubical shapeRounder shape
Faster flow Higher capacity
Improved feed particle shape
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Crushing concepts Raw materialsWhat happens if other properties change?
Toughness.
Feed size.
Particle size distribution and specific gravity.
Bulk density.
Feed shape.
Volume crushed.
Moisture
Clay content
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Crushing concepts Raw materialsSummary
All crushers have a volumetric and a mechanical limit
Toughness of material, feed material particle size analysis, volume and reduction ratio all play their part in the ability of the crusher to perform the duty over an acceptable lifecycle.
If any combination of these factors overstress the mechanical capability of the crusher (demands too much energy from the motor) it will be necessary to reduce the influence of another.
Eg. The demand for greater throughput at the expense of reduction.
Work done(energy)=volume x toughness x reduction ratio
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Crushing concepts Raw materialsTake home message