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Considering the weight of mill lining and grinding media, work out the motor power required, in consultation with the mill manufacturer.
To calculate media charge for cylindrical mill
| Formulae are given below: |
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| 1. For batch type ball mill : |
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| M = 0.000691 x D2 x L |
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| where : |
M = Weight of grinding media charge in kgs |
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D = Mill Internal Dia in cms. after lining |
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L = Internal length of the mill in cms. after lining. |
| 2. For continuous type ball mill : |
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| M = 0.000503 x D2 x L |
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| Example - To calculate grinding media charge for a steatite ceramic lined batch type mill size : Dia 6' x 6' Long (Dia 180 cm x 180 cm L) (mill openings are not considered). |
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| Thickness of tapered bricks = 6.5 cms |
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| Thickness of straight bricks = 4.2 cms |
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| Therefore |
D = 180 - 13 = 167 cms |
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L = 180 - 8.4 = 171.6 cms |
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M = 0.000691 x 167 x 167 x 171.6 |
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| Grinding media quantity = 3307 kgs |
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| To calculate the motor power required for a cylindrical type ball mill, the following formula can be applied : |
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W = 0.04116 x D3 x L x n x (0.6d + 0.4d1) |
| where : |
W = Required motor power in HP |
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D = Internal dia of the mill in mtr |
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L = Internal length of the mill in mtr |
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d = Specific gravity of grinding media |
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d1 = Specific gravity of substance |
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n = Speed of ball mill in rpm. |
Example - 1: Let the internal dia of the mill be 1.8 mtr and internal length be 1.8 mtr. If Alumina grinding media is used density d = 3.6. If milling substance is alumina in slurrry form with around 70% solids then d1 = 2.0 |
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| Therefore |
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W = 0.04116 x (1.8)4 x 19 (3.6 x 0.6 + 2 x 0.4) = 24.3 HP |
| Example - 2: If Steatite grinding media are used to mill the glass frit |
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d = 2.65 and d1 = 1.6 then, |
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W = 0.04116 x (1.8)4 x 19 x (2.65 x 0.6 + 1.6 x 0.4) = 18.3 HP |
| To calculate the speed of the mill, use the following formula: |
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| Nc = |
76.6 |
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D1/2 |
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|
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| Where : |
Nc = Critical speed |
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D = Internal dia in ft. |
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