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• Introduction • Some figures to introduce the subject • Successively for coarse and fine grinding – – – – – –

How grinding balls are wearing Parameters to take into account concerning the impacts Deformation of grinding balls Grinding balls of tomorrow Several words about metallurgy Quality criteria of grinding balls

• (Generations of grinding balls) • Maintenance of grinding ball charges

Figures Diameter (mm) (inch)

90 80 77 70 64 60 50 40 38 35 31.75 30 25 23 22.22 20 17 15

1/2"

3

3" 1/2

2 " 2" 1/2

1 " 1/4

1 " 1" 7/8" 3/4" 5/8"

Weigth (gr)

Surface (cm2)

2,916.841 2,048.590 1,826.658 1,372.396 1,048.878 864.249 500.144 256.074 219.551 171.549 128.061 108.031 62.518 48.682 43.895 32.009 19.658 13.504

254.469 201.062 186.265 153.938 128.680 113.097 78.540 50.265 45.365 38.485 31.669 28.274 19.635 16.619 15.511 12.566 9.079 7.069

Nbr balls Specific surface per mt m2/mt

342.837 488.141 547.448 728.653 953.400 1,157.074 1,999.424 3,905.121 4,554.750 5,829.238 7,808.779 9,256.602 15,995.393 20,541.473 22,781.638 31,241.213 50,869.875 74,052.133

8.724 9.815 10.197 11.217 12.268 13.086 15.703 19.629 20.662 22.434 24.730 26.172 31.407 34.138 35.336 39.259 46.186 52.344

Figures The composition of the ball charges plays a major role in the grinding energy consumption: • particle size distribution of the feed • hardness of the feed other factors like • motion of the charge • % of moisture • % of slag, pozzolana, ... • open/closed circuit

Figures Costs related to grinding media • grinding media consumption

• energy consumption

• grinding media charges removing and sorting

Figures

Characteristics and quality of the media :

• excellent wear resistance • adapted impact resistance • excellent resistance to deformation • manufacturing quality irreproachable and constant

BALL CHARGES FOR COARSE GRINDING CHAMBERS

Reduction from feed size between 0 and 5 to 100 mm down to product size 100 % < 1 to 2 mm Ball diameter 110 mm - 50 mm Working conditions Medium to high abrasivity Medium to high impact level

Wear factors NORMAL 1. Abrasion of ground material

2. Friction between balls 3. Fatigue due to repeated impacts 4. “Dry“ corrosion 5. Deformation ABNORMAL

6. Excessive work hardening 7. Internal foundry defects

Wear factors

3. Fatigue due to repeated impacts causes “MICRO-CHIPPING” slight chipping at the surface of the grinding media due to the hardness of the material

GRINDING BALLS WEAR ABRASION + CHIPPING

0.1 0.05

Clinker

Wear rate in mm/100h

1 0.9

0.03

0.01 Violence of impacts

Wear factors

6. Excessive work hardening causes “SCALING” chipping on an important depth at the surface of the balls leading to the destruction of the balls

Wear factors 1. Abrasion of material to be ground 2. Friction between balls 3. “Dry“ corrosion 4. Fatigue due to repeated impacts

High Cr cast iron grinding ball martensitic matrix

Chromium carbides

unstable phase

Grinding balls wear Abrasion

Hardness of ground material




Hardness of balls

high wear of balls

Mohs Scale

1 Talc

Other minerals Coal

2 Gypsum 3 Calcite 4 Fluorite

Knoop Hardness (+Shore) 20 35 40 124 136 216 (32) 175 235 305 (58)

5 Apatite

435 Glas

6 Orthoclase

Clinker

Silex

Hardness scales related to the Mohs’scale

7 Quartz

Fondu

8 Topaz

Grenat

9 Corundum

10 Diamond

455 ~ 550 (72) 620 (84) 500-800 820 (98) ~ 840 1025 1330 1735 1800 2020 1800 2800 7575

Vickers Hardness (HV)

36 110 140 200 190 70-200 170-230 300-460 318 423 440 300-600 544 640 740 500-1010 950 1020

Metallic structures

HB (3TÆ30)

110 200

Ferrite Austenite (12%Mn) Pearlite (alloyed)

Austenite (Cr. cast iron)

Martensite fx(C)

(11) (13) (5-18) 30-45 43 44 30-55 48 51

(FeCr)23C6 WC B4C/NbC

301 400

500 600

60 (48)
65 68

Fe3C 1430 1200-1600 (FeCr)7C3 1500 Mo2C 1800 1500-2000 2400 3700 10000

Rc Hardness

(712)

WEAR as a relation of the ratio existing between the hardness of the ABRASIVE (material to be ground) and the “WEAR RESISTING” MATERIAL

1

2

3

4

(FeCr)7C3

Hard Martensite

Ha/Hm

0

Fe3C

Clinker

Pearlite

Gypsum

Wear or Abrasivity (friction wear essentially)

Ha/Hm

5 Mohs’scale

6

7

8

9

10

GRINDING BALLS WEAR ABRASION

0.1 0.05

Clinker

Gypsum

Wear rate in mm/100h

1 0.9

0.03

0.01 0

1

2

3

4

5

6

7

8

Ground product hardness scale / Mohs’scale

9

10

GRINDING BALLS WEAR ABRASION

0.1 0.05

Clinker

Wear rate in mm/100h

1 0.9

0.03

0.01 6 7 Ground product hardness scale

Impacts 90 mm

~ 3000 gr

According to the volume of the ball 30 mm

~ 100 gr

Impacts IMPACT energy of a ball according to its diameter and the diameter of the mill 25.00

20.00 dia 110 mm dia 100 mm dia 90 mm 15.00

dia 80 mm

kgm

dia 77 mm dia 70 mm dia 64 mm

10.00

dia 60 mm dia 50 mm dia 40 mm 5.00

0.00 1

2

3

4 Mill diam eter

5

6

Quality WHAT IS A PROPER GRINDING BALL ?

• MARTENSISTIC MATRIX • CHROMIUM CARBIDES • AUSTENITE • a PERFECT SOUNDNESS

martensitic matrix

Chromium carbides

austenite

Metallurgy

Depth of penetration of the deformation according to the impact force

Metallurgy

Depending of the force • yield deformation • plastic deformation

Metallurgy neutral fiber

TENSILE strength

Metallurgy Importance of tensile - compression stresses induced by impacts according to the quantity of residual austenite after quenching

LESS

MORE

CHARACTERISTICS OF THE MAGOTTEAUX GRINDING BALLS FOR COARSE MILLING • High hardness throughout martensitic matrix Cr carbides

martensitic matrix

Chromium carbides

• Low potential of work-hardening controlled low quantity of unstable metallurgical phase

• Identical and homogeneous metallurgical characteristics for all the specimens • Regular shape • Perfect physical soundness

unstable phase

High hardness throughout Low potential of work-hardening martensitic matrix

Chromium carbides

unstable phase

Identical and homogeneous metallurgical characteristics for all the specimens Same hardness and same homogeneous metallurgical structure are obtained thanks to :

martensitic matrix

• precise chemical composition • oil quenching • additional heat treatment • clean manufacturing conditions

Chromium carbides

unstable phase

BALL CHARGES FOR FINISHING GRINDING CHAMBERS

Reduction from feed size 60% > 90 microns down to product size 10 - 20 % > 90 microns (C.C.) 5 % > 90 microns (O.C.) Ball diameter 60 mm - 15 mm Working conditions Generally smooth conditions No strong lifting effect Limited impacts

Wearing factors

1. Abrasion of the material to be ground 2. Friction of ball against ball 3. Deformation

CHARACTERISTICS OF THE MAGOTTEAUX GRINDING BALLS FOR FINE MILLING • High hardness throughout martensitic matrix Cr carbides

martensitic matrix

Chromium carbides

• Controlled potential of work-hardening controlled low quantity of unstable metallurgical phase

• Identical and homogeneous metallurgical characteristics for all the specimens • Perfect physical soundness • Regular shape

unstable phase

Identical and homogeneous metallurgical characteristics for all the specimens Same hardness and same homogeneous metallurgical structure are obtained thanks to :

martensitic matrix

• precise chemical composition • high carbon content • oil quenching • clean manufacturing conditions

Chromium carbides

unstable phase

• High hardness throughout • Controlled potential of work-hardening martensitic matrix

Chromium carbides

unstable phase

Metallurgy Molding in cluster

Sketch of a mould filled up with liquid metal

Metallurgy

Shrinkage after solidification

Metallurgy

Magotteaux production Magotteaux yearly produces more than 200.000 Tons of Grinding Media of which 65.000 tons for the cement industry in 10 factories Worldwide

Magotteaux production

All these grinding balls are produced according to the same manufacturing procedure quality control standards securing a same high level of constant quality

Magotteaux production

Besides the activity of producing excellent grinding balls, Magotteaux also offers the services of Process Engineers Magotteaux has a permanent program of research for new more cost effective grinding ball materials

Quality Insurance

C

Destructive and non destructive visual examination

Quality

Gas holes, sand and slag holes, cracks, appearing on surface, or after light fettling Above big shrinkage which caused breakage Hereunder little shrinkage appearing after cutting and grinding.

Quality Y

Sphericity check up

X

Y

Quality

Swelling phenomenon ∅ real

And tomorrow ...

GRINDING MEDIA cost

waste ENERGY cost