Sandvik Construction 1 A world leader in Construction Module 2a How material factors affecting...

Sandvik Construction1

Sandvik ConstructionA world leader in Construction

Module 2a How material factors affecting crusher performance


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.


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.


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.


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


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


Crushing concepts MaterialsAverage values


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


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


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



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



Sandvik Construction

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

19

Crushing concepts Raw materialsWhat happens if other properties change?


Smaller feed sizeCapacity upFiner productBetter shape

Bulk density increases Capacity increases but a higher risk of packing due to compression limit

Packing

20


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%


Crushing concepts Raw materialsCompression limit

23

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.


Crushing concepts Raw materialsCompression limit Packing


More cubical shapeRounder shape

Faster flow Higher capacity

Improved feed particle shape

24


Toughness.

Feed size.

Particle size distribution and specific gravity.

Bulk density.

Feed shape.

Volume crushed.

Moisture

Clay content


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


Crushing concepts Raw materialsTake home message

Sandvik Construction 1 A world leader in Construction Module 2a How material factors affecting...

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