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Max Ball Size

The biggest ball your feed actually needs, worked out from Bond. A ball that is too small never breaks the coarse lumps and they pass through unground; a ball that is too big wastes grinding surface and gives you fewer impacts for the same tonnes of steel. Press MEASUREMENTS on the board to type your mill in.

Why this matters now

Clinker reduction, high electricity prices and tighter cement specifications put the grinding circuit under pressure. The fastest gains usually come from finding the real constraint before changing equipment or operation.

What this tool helps decide

Choose the largest ball your feed and mill can justify, reducing the risk of buying media that is too coarse for the grinding duty.

What subscription adds

Build a connected grinding audit: save every mill separately, reload previous measurements, compare changes over time and issue an editable report for the plant team.

Connected to the industry conversation around clinker-factor reduction, grinding energy, blended cement and quality control reported in World Cement, CemNet and Global Cement.See process-tool plans

Your mill and your feed

The mill

Mill inside diameter Inside the lining, in metres.

Mill speed Revolutions per minute of the shell.

The feed

Feed size — 80% of it is finer than this Millimetres. This is the coarse end of your feed, not the average. If your lab reports 20% retained on a sieve, that sieve size is this number.

How hard the material is (Bond work index) kWh per tonne. Clinker is usually 13 to 15. Harder material needs a bigger ball.

How heavy the material is Specific gravity, grams per cc. Clinker about 3.15.

Grinding conditions

Wet or dry grinding Cement is dry. This only changes one constant in the formula.

Grinding media shape Cylpebs need a slightly smaller equivalent size than balls.

STANDARD BALL SIZES, DRAWN TO SCALE

WHAT BOND SAYS

IF THINGS CHANGE, AND WHAT WAS USED

Ball size to charge

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Bond says exactly

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Critical speed

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Mill speed, % of critical

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Ball against the lump

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If feed gets 50% coarser

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K used

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A used

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What this means for your charge

Now work out how many tonnes

This tells you which size. It does not tell you how many tonnes to put in. Measure the free height and the volume loading tool gives you the quantity.

How many tonnes?

How the numbers are worked out

Bond's ball size. B = A × √(F/K) × ((S·Wi)/(C·√D))^(1/3) with the feed size in micrometres and the mill diameter in metres. A is 20.17 for balls and 18.15 for cylpebs. K is 355 for dry grinding, 350 for wet.

Critical speed is 42.3 / √D, your workbook formula #12. The ball size depends on how fast you run relative to that, so a slow mill needs a bigger ball to do the same job.

Small-ball rule. If the answer comes out at 25 mm or less, it is multiplied by 1.3 before rounding, on the source's own instruction.

One formula only, deliberately. Your ball-mill-volume-loading.js also carries a second "empirical coarse adjusted" method. At this mill it returns 316 mm against Bond's 100 mm, and 28 mm if the feed is read as millimetres instead. No cement mill runs a 316 mm ball, and neither reading lands near Bond, so that formula is not calibrated for anything we can verify. It is left out rather than shown as a false second opinion. If a source for it turns up, it goes back in.