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Mill Axial Test

You crash-stopped the mill, took samples along its length, and this page turns that lab data into a simple picture of where the grinding is happening, where it stops, and what the charge is telling you. Press SAMPLE SHEET on the board to enter your readings and let the tool build the report.

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

Map the mill metre by metre to identify where grinding is effective, where material is bypassing the duty and where mill length is being wasted.

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

Dead / slow stretches — No profile yet

Coarse work finish — Waiting for data

Charge match — Ball charge not checked yet

Biggest sample gap — Will update with the sheet

How to read the graph: the lines show how much material is still retained on each sieve at each metre along the mill. A line that falls steadily means the mill is grinding. A sudden flattening or collapse means a dead or slow stretch. The higher the line, the more coarse material is still left behind.

Where the mill is working

The mill

First chamber length Metres, inside the lining. The diaphragm sits at the end of it.

Second chamber length Metres, inside the lining. Leave 0 for a one-chamber mill.

The material and the speed

Only used to work out the ball size each metre needs. These are the same values, and the same Bond formula, as the biggest ball tool — change them here if your material is different.

Mill inside diameter Metres, inside the lining.

Mill speed Revolutions per minute.

Work index of the material kWh per tonne. Clinker is usually 13 to 15.

Specific gravity of the material Grams per cubic centimetre. Clinker is about 3.15.

Media shape

Grinding

The sample sheet

Per cent retained on each sieve, at each distance from the mill inlet. Leave a whole row blank if you did not sample there.
The last column is optional: if you measured the distance from the lining down to the balls at that manhole, type it in millimetres and the tool works out how full the mill is just there. Leave it blank everywhere you did not measure — nothing is guessed in between.

Sieve sizes used

Metres in Retained on sieve Ball level mm

THE SAMPLE SHEET

HOW THE WORK SPLITS

WHAT IS WRONG

WHAT BALL SIZE EACH PART NEEDS — BOND, FROM YOUR OWN SIEVE SHEET

Sampling points used

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Length they cover

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Coarse work in chamber 1

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Fine work in chamber 2

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Stretches doing nothing

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Gap between samples

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Half the fine work done by

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Coarse work finished by

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Fine work starts at

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Samples that cannot be right

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Feed end needs balls of

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At the wall it needs

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Outlet needs balls of

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1st chamber balls vs need

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2nd chamber balls vs need

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Stretch by stretch, and sieve by sieve

What the profile is telling you

Read this against the charge

An axial test says where the mill is not working. The ball charge in that stretch usually says why.

How full is it Check the ball charge

How the numbers are worked out

This is a real mill picture, not a model. Every value starts with your sieve sheet. The machine does a simple subtraction: residue at the start of a stretch minus residue at the end, divided by the distance between them. That gives the mill's real work rate in that section, in points of residue per metre.

Every sieve is judged on its own curve. A 5 mm sieve and a 90 micron sieve are not the same job. Their numbers are never mixed together and they are never averaged into one false number. That is why the chart stays honest and the diagnosis is based on the actual section of the mill.

How a dead or slow stretch is found. A healthy curve falls steadily. A dead stretch looks like a gap or a flat spot: one metre does far less grinding than its neighbours and then the line picks up again. A slow stretch still works, but much less than the rest of the mill.

Where the work is split. The tool reads the material around the diaphragm. Everything lost before that point is treated as first chamber work; the rest is second chamber work. The sieve with the biggest loss before the wall is the one used to describe the first chamber, and the one with the biggest loss after the wall is used for the second chamber.

Two checks keep the sheet honest. The residue must rise as the sieve gets finer, and it must fall as you move down the mill. If a result goes the wrong way, the tool flags it. In most cases that is a bad sample, a bad sieve stack, or a mix-up in the lab, not a problem in the mill.

How the ball size is calculated. The tool takes the 80% passing size from your own sieve points and then uses the same Bond equation used in the ball charge tool. This tells you the largest ball size the material at that point really needs. If the 80% point falls between two sieve sizes with a large gap, the tool marks it with a warning symbol because the number is less certain.

What the ball charge means. If you enter the actual ball size in the charge tool, the page compares what the material needs with what the mill is carrying. If the charge is too small, the material is not being broken. If it is too big, the mill is carrying weight without making enough fineness.

Why the measure is useful. This is not a textbook curve. It is a direct picture of your mill, your sample, and your real operating conditions. That is why it is used to decide where to open, what to inspect, and whether the answer is in the charge or in the grinding profile itself.