# Crushing, Screening & Conveying

Crushing, Screening & Conveying 2017-04-04T06:57:13+00:00
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## Crushing work index Calculation (4 replies)

STAHI
2 years ago
STAHI 2 years ago

I have a question about CWi calculation.

We have an existing plant and I want to calculate the CWi based on Bond formulation and compare it with lab tests results.

At the existing plant the data are:

• F80= 370mm
• P80= 10mm
• Specific energy is 1,8 Kwh/t

When we apply the Bond Equation we found that CWi (Calculated) = 21,54 Kwh/t

And the CWi (lab test) = 27,4 Kwh/t.

My question is: there is same correction factor that we must apply on Bond equation?

For your information if you need it:

• RWi = 19,3 Kwh/t
• BWi = 17 Kwh/t
• F80 Rod = 10mm
• Transfer size= 886µm
• P80 final size = 75 µm

Thank you for your help 🙂

David
2 years ago
David 2 years ago

Hi,
As Alex told you: The crushing work index you calculated appears mostly correct. The only correction factor that might affect the calculation is to correct for the efficiency of the motor -- the work index is based on motor output
(pinion) power, whereas the measurement of motor power is usually based on motor input power. I have attached a calculation of operating work index that includes the motor efficiency correction, and the result is WiO=22.4 (compared to your 21.5). This correction is minor and can probably be ignored.

The Bond crushing work index test (sometimes called the "impact work index" test) is noisy, and the difference you observed is perfectly reasonable. The paper by Angove & Dunne (1997) reports a standard deviation in crushing work index tests across laboratories as 4.5. The laboratory CWi value of 27.4 (metric) is almost within 4.5 units of the 22.4 value I calculated, so what you are observing is probably the natural variation in the crushing test.

So there is nothing wrong with your calculation, and the variation between the laboratory test and your observation of the operating crusher is within the normal range of variation for this calculation. It appears normal to me -- this is a noisy test, unfortunately.

Hope that helps. Please let me know if you have any other question.

STAHI
2 years ago
STAHI 2 years ago

Hi,

I did some research for Bond equation and I found at SME Mining Engineering other equation please see attached file.

there is a difference between the two equation and it contains some correction factors.

-----------------------------------------------------------------------------------------------------------------------------------------

Another question:

There is a relation between CWi, other Work index (if we wont calculate it) and the Abrasion Index?

Thank you for you help

STAHI
2 years ago
STAHI 2 years ago

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