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# power kw per ton of ball mill

## ball mill capacity and power consumption relationship to mill speed

In the following analysis capacity, T, is expressed in short tons per hour, tph, and power consumption, P, in kilowatts, kw. Accordingly power consumption per unit of capacity, Po will be expressed in kilowatt hours per short ton, or kw-hr per ton. In all equations D refers to the inside diameter of the mill in feet and v to the peripheral speed of the mill in feet per minute inside the liners.

In other words, the capacity should be proportional to the mill speed raised to power m, the numerical value of the exponent being 1 m 1.5, depending on the circumstances. Eq. 5 can also be written in the following forms:

The Sullivan rod mill with its fluid drive coupling has made this test possible, a test out of the reach of practically all other grinding installations. This may be why the relationship between mill capacity and speed has not been studied earlier in more detail and why the knowledge of this relationship has been based until now on crude observations.

## bond work index (energy equation) - grinding & classification circuits - metallurgist & mineral processing engineer

I am dealing with the calculation of Bond Work Index. The flowsheet is attached. I have calculated primary ball mill bond index but for the calculation of second ball mill bond index I got trouble. In a bond energy equation, where should I select tonnage ? and where should I pick P(80), F(80) values ? Thanks in advance.

First stage, will be broken into two parts as well, you use a Bond rod mill work index for the coarse component of the ore (+2.1 mm) and the Bond ball mill work index for the fine component (-2.1 mm). It would look like this:

E is the specific energy consumption, kWh/tonne, F80 is the feed size to the primary BM; T80 is the transfer size (prim mill product size), P80 is the final product (cyclone overflow). The following "efficiency factors" may also apply, but they must be greater than 1.0 otherwise use 1.0: EF2 is the open-circuit correction factor, EF4 is the oversize feed factor, EF5 is the fine product factor.

You will not get a circulating load prediction from a Bond calculation. The assumption is that your secondary circuit is "efficient", whatever that might mean. Typically this means circulating loads of 250%, but can go to over 400% for maximum classification efficiency.

Thank you sir, but I have calculated all of the stream tonnage and size distributions. However, my only confusion is while computing the second ball mill bond index, in which stream should I take P(80),F(80) and the tonnage for mill power estimation ? For example, for P(80), should I use hydrocyclone overflow or second mill product or whatever and also for F(80 should I select hydrocyclone underflow or whatever, and for tonnage which I use in mill energy calculation should I use fresh feed tonnage, circulation load or any other ?

Thank you sir, but I have calculated all of the stream tonnage and size distributions. However, my only confusion is while computing the second ball mill bond index, in which stream should I take P(80),F(80) and the tonnage for mill power estimation ? For example, for P(80), should I use hydrocyclone overflow or second mill product or whatever and also for F(80 should I select hydrocyclone underflow or whatever, and for tonnage which I use in mill energy calculation should I use fresh feed tonnage, circulation load or any other ?

The key: in a closed circuit ball mill circuit, you put a "black box" over the whole secondary circuit. Ignore the hydrocyclone underflow and the secondary mill product, those are internal to the black box. You only care what feed enters the secondary circuit (which is the primary mill product) and what product exits the secondary circuit (the hydrocyclone overflow).

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## effect of grinding media charge on mill power draw kw

Maximum power is drawn by a mill when the charge occupies approximately 50% by volume. The power curve becomes very flat in the range above 45%. As a result, mills are seldom run with charge levels greater than 45%.In rod mills, the charge is swollen by particles of feed which separate the rods. If the mill is shut down immediately after the feed is shut off, the charge level will be greater than if the mill had been ground out prior to shutdown. Rod mills are normally operated with a 32 to 40 percent charge by volume which during operation, becomes a 40 to 50% charge, with a bulk density considerably lower than that of stacked rods. This chart shows the impact a mills grinding ball load has on the mills motor power draw.

## ball mill design/power calculation

The basic parameters used in ball mill design (power calculations), rod mill or anytumbling millsizing are; material to be ground, characteristics, Bond Work Index, bulk density, specific density, desired mill tonnage capacity DTPH, operating % solids or pulp density, feed size as F80 and maximum chunk size, productsize as P80 and maximum and finally the type of circuit open/closed you are designing for.

In extracting fromNordberg Process Machinery Reference ManualI will also provide 2 Ball Mill Sizing (Design) example done by-hand from tables and charts. Today, much of this mill designing is done by computers, power models and others. These are a good back-to-basics exercises for those wanting to understand what is behind or inside the machines.

W = power consumption expressed in kWh/short to (HPhr/short ton = 1.34 kWh/short ton) Wi = work index, which is a factor relative to the kwh/short ton required to reduce a given material from theoretically infinite size to 80% passing 100 microns P = size in microns of the screen opening which 80% of the product will pass F = size in microns of the screen opening which 80% of the feed will pass

Open circuit grinding to a given surface area requires no more power than closed circuit grinding to the same surface area provided there is no objection to the natural top-size. If top-size must be limited in open circuit, power requirements rise drastically as allowable top-size is reduced and particle size distribution tends toward the finer sizes.

A wet grinding ball mill in closed circuit is to be fed 100 TPH of a material with a work index of 15 and a size distribution of 80% passing inch (6350 microns). The required product size distribution is to be 80% passing 100 mesh (149 microns). In order to determine the power requirement, the steps are as follows:

The ball mill motorpower requirement calculated above as 1400 HP is the power that must be applied at the mill drive in order to grind the tonnage of feed from one size distribution. The following shows how the size or select thematching mill required to draw this power is calculated from known tables the old fashion way.

The value of the angle a varies with the type of discharge, percent of critical speed, and grinding condition. In order to use the preceding equation, it is necessary to have considerable data on existing installations. Therefore, this approach has been simplified as follows:

A = factor for diameter inside shell lining B = factor which includes effect of % loading and mill type C = factor for speed of mill L = length in feet of grinding chamber measured between head liners at shell- to-head junction

Many grinding mill manufacturers specify diameter inside the liners whereas othersare specified per inside shell diameter. (Subtract 6 to obtain diameter inside liners.) Likewise, a similar confusion surrounds the length of a mill. Therefore, when comparing the size of a mill between competitive manufacturers, one should be aware that mill manufacturers do not observe a size convention.

In Example No.1 it was determined that a 1400 HP wet grinding ball mill was required to grind 100 TPH of material with a Bond Work Index of 15 (guess what mineral type it is) from 80% passing inch to 80% passing 100 mesh in closed circuit. What is the size of an overflow discharge ball mill for this application?

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