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
2
© Metso
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
© Metso
11/21/2008
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
4
© Metso
11/21/2008
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
6
© Metso
11/21/2008
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
© Metso
11/21/2008
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
9
© Metso
11/21/2008
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.
10
© Metso
11/21/2008
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
11
© Metso
11/21/2008
• 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
© Metso
11/21/2008
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
13
© Metso
11/21/2008
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
© Metso
11/21/2008
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
© Metso
11/21/2008
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.
17
© Metso
11/21/2008
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
© Metso
11/21/2008
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
© Metso
11/21/2008
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
© Metso
11/21/2008
