Influencing to aggregate quality - Metso.com

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Nov 21, 2008 ... Quality and how to impact. Quality of aggregate is judged by: • Product distribution. - Amounts of desired fractions. • Shape, flakiness index.
Influencing to aggregate quality

Jarmo Eloranta March 1, 2006 Poland

Why high quality (shape& distribution) is needed (1/2) ? Roads:

• Better compacity ( less voids ) • Improved mechanical properties • Better stability • Improved wear resistance Cement:

• Better ability to flow • Better compacity • Higher strength • Less cement

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11/21/2008

Why high quality (shape& distribution) is needed (2/2) ? Cost and Volume Proportions of Ingredients in "average" Concrete

100 Proportion [%]

It is needed due to cost & volume proportions

Mass [kg/m3] Cost [cost/m3]

80 60 40 20 0 Aggregate

Cost and Volume Proportions of Ingredients in Asphalt

100 Proportion [%]

Volume (kg/asphalt ton)

80

Cost (cost/ton)

60 40 20 0 Aggregate

Bitumen

Filler

Concrete with poor workability 3

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Cement

Water

Admixtures

Quality and how to impact Quality of aggregate is judged by:

• Product distribution - Amounts of desired fractions • Shape, flakiness index Influencing factors:

• Rock • Equipment - crushers - screens • Process

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Impact of Rock

Los A versus Flakiness index

Flakiness index vs. LosA in different fractions Flakiness index

40 30

4-5 10-12.7 16-20

20 10 0 7,2

10,5

15,1 20 LosA

21,8

43,3

Some correlation between Los A and flakiness index -> this influences to the process planning

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Fraction size

Impact of crusher and process parameters

Some basic rules to make shape (cones)

Full crushing chamber Stable and continuous feed Correct and even feed distribution Machine Setting closed to required product Maximum feed size (reduction ratio) Crushing cavity Impact of feed gradation Closed circuit Flow-sheet Some examples in next pages 8

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Crusher setting vs. flakiness index

GP300 M. Cubicity acc. to DIN , Feed 25-55 100

90

%

80 css=20

70

css=14

60

50 40 4-8

8-12

12-16

16-20

Fractions

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20-25

25-32

Crusher reduction ratio vs. flakiness index Limestone / EN flakiness

If the crusher setting is same with two different feed size, the reduction ratio is bigger with the coarse feed.

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Reduction Ratio 2.54 3.98 4.88 7.42

% Flakiness * 8.6 15.2 19.0 22.3

Impact of crushing cavity • Single layer crushing - poor shape

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• Multilayer crushing - good shape

Impact of feed gradation vs. flakiness index (1)

Cubisity DIN. GP500 F, css=16mm, 214kW, 17bar, 235t/h. Feed 25-55mm

100 90 80 70 60 50 40 30 20 10 0 1

10

100

Screen hole size (mm) feed

12

100 Cubsity acc.to DIN

% passing

GP500 F, css=16mm, 214kW, 17bar, 235t/h

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product

90

80 70 60

50 4-8

8-12 12-16 16-20 20-25 Fractions

Impact of feed gradation vs. flakiness index (2) Cubisity DIN. GP500 F, css=16mm, 244kW, 20bar, 271t/h. Feed 1255mm

GP500 F, css=16mm, 244kW, 20bar, 271t/h 100 % passing

Cubsity acc.to DIN

100 90 80 70 60 50 40 30 20 10 0

1

10

100

Screen hole size (mm)

feed

product

90 80 70 60 50

4-8

8-12 12-16 16-20 20-25 Fractions

Lesson: importance of feed gradation can not be overestimated -> feed should contain 15-25% fractions < css, excluding 0-5mm

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Closed circuit vs. flakiness index In the closed circuit feed change from narrow to wide fraction improves the shape of aggregates. Also the closed circuit increases crushing stages, same grains are crushed more times giving better shape. Smaller is the screen mesh size, better quality for the final product.

Cubicity in % (3:1, DIN 52114

GP100, feed granite rock 25-55 mm c.s.s. 12 mm, screen mesh size 12 mm 100 90 80

70 60 50 40 30 20

4-8 mm

8-12 mm

Open circuit 14

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What impacts to shape in vertical shaft impactors? Excellent Shape

Excellent Shape

Good Shape

Good Shape Speed of rotor

Strength of feed

material Excellent Shape

Excellent Shape

Good Shape

Good Shape Amount of fines in feed

Excellent Shape

Good Shape Feed rate 15

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M/M R/M

R/R

Impact of process and screens By using jaw and cone crushers

Two examples

SELECTIVE and NON SELECTIVE CIRCUITS

Machines used for a typical 3 stages crushing plant, producing sand , 5/10 mm and 10/20 mm.

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NON SELECTIVE CIRCUIT 262 tph when the tertiary crusher is 100% loaded

Small flake particles present in the feed will be present in the product too.

The machines are connected in order to maximize the capacity. But a flake particle coming from the feed won’t be crushed by any crusher, giving a poor final product quality. 18

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5/10 10/20 Shape out of the secondary 50% 30% Shape out of the tertiary

20% 15%

Shape of finish product

34% 22%

Selective circuit 171 tph when the tertiary crusher is 100% loaded

The machines are connected in order to maximize the cubicity. All the finish products come out of the tertiary, which is fed by a secondary in closed circuit.

5/10 10/20 Shape out of the secondary NA 19

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NA

Shape out of the tertiary

15% 10%

Shape of finish product

15% 10%

Screens also contribute to quality Screen functions in crushing process n

n

n

20

SCALPING è normally before primary crusher in order to get by pass for material smaller than setting è no requirements for screening efficiency SCREENING IN CLOSED CIRCUIT WITH A CRUSHER è no hard requirements for efficiency, except 2-stage plants, where same screen is used for product screening è process balancing and to adjust correct feed distribution to crusher PRODUCT SCREENING è hard requirements for efficiency, which is measured in share of undersized/oversized material in product

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11/21/2008