Ball Mill Inspection

8/12/2019 Ball Mill Inspection

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BALL MILL INSPECTION PROCEDURE

Introduction

This document is intended to help the staff of the cement plants.

On a process point of view, a mill inspection is only representative if the grinding mill circuit is in a steady working

condition with a representative cement product.

If this condition is fulfilled, the whole installation must be stopped in crash-stop (it means all the equipments

must stop at the same moment).

It is better to enter first into the first compartment in order to follow the flowpath of the material from the

beginning of the grinding process.

Generally, people enter in a manhole. From time to time, when the mill diameter is larger, it is possible to enter

from the mill inlet.

This procedure was performed for a 2 compartments mill.

For other configurations of mills, a simple adjustment is necessary.

For outside staff, it is also necessary to check the kind of internals and the length of the chambers.

What we need:

Now, let's go inside the mill (for the turkish bath...)


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First chamber

Action Data-Measurement Reason

1 Mill inlet:

- Check if the inlet is clean and not

blocked

To allow a good ventilation of the mill.

- Check the mill material feeder To allow a good progression of the feed.

- Check if there are screws and their

condition

Height of screw

Number of screws

To avoid accumulation of material and

balls.

- If there is water injection system,

check its

Visual appreciation Water injection in chamber 1 can be

necessary in case of very hot clinker.

2 Feed end liners:

- Check the condition and the wear of

these liners

Thickness To maintain the mill shell protected.

- Check if there are broken liners Number

3 Volume load or filling degree

- The measurement must be achieved

in 3 points on the mill-axis (inlet,

middle of compartment and

compartment outlet). The best

procedure is probably to measure

the height from the ball charge to

the linings

3 points

(mesure height H)

To maintain the production (tons/hour) of

the mill because the volume load is directly

linked to the mill absorbed power and the

mill efficiency.

- Other method: count the number of

visible lining plates (less reliable

At least 3 points If it is the only way to measure the volume

load.


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method)

4 Linings


the linings (Lining practically worn-

out on the picture)

Thickness

Lifter height

To maintain the lining efficiency (don't

forget that the function of the 1st chamber

is TO CRUSH).

- Check if there are broken plates Number To maintain the mill shell protected.

- Check if there is coating Evaluate if it is hard

to remove, measure

the thickness

This phenomenon can happen, especially in

the case of raw mills.

Causes inefficient grinding, low throughput

and high energy consumption.

5 Ball charge

- Check the ball charge: the principle

is to evaluate visually the proportion

of big balls (90mm) and small balls

(60mm)

Better with

experienced

persons

To maintain the crushing efficiency of the

1stcompartment.

- Measure the biggest and the

smallest ball diameter

Minimum

Maximum

To determine the next ball make up

composition or the substitution of the ball

charge.

- Check if there are broken balls Visual estimation To avoid blockage of the intermediate

diaphragm.

To analyse the balls quality with the

supplier.

- Check if there is coating Evaluate if it is hard

to remove




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6 Material level

- Check the material level at mill inlet Not enough material may be due to high air

velocity.

Result is the loss of this part of chamber.

- Check the material level (too highyou don't see the balls, good if you

see the top of the balls, not enough

material if you don't see it)

Make a designVisual estimation

Measure if too high

Not enough material can cause breakage ofballs.

Too much material results in a drop of

efficiency.

- Check specially at the intermediate

diaphragm

Remove the balls Not enough material may cause excessive

wear of the grid plates of the diaphragm.

7 Sampling of the first chamber

- Take 3 or 4 samples (inlet, 1 or 2

intermediate samples, at the

diaphragm)

2-3kg/sample In order to know the efficiency of the first

compartment.

- Ideally for each sample, take

materiel in three points as shown on

drawing here below

Mill-axis point is the

best if only 1 point

This is more representative.

- Remove the balls at the sampling

point

Depth of 20-30 cm To allow the sampling with the collector.

This is more representative.

- Don't reject the unground particles

from the sample

Especially at the

diaphragm

It is important to know the percentage of

uncrushed particles, especially at the

diaphragm.

- Drop a ball on unground grains (put

these grains on the top of a ball)near the diaphragm

Height 30-40cm To have an idea of the hardness of these

grains.


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8 Intermediate diaphragm

- Check the general aspect of the

diaphragm

Visual


the plates and the grid plates

Visual and thickness To insure the protection of the diaphragm

frame.

- Check the width of the slots and ifthere are blocked by unground

particles or scraps

Maximum widthMinimum width

% of area blocked

To insure that the slots of the intermediatediaphragm are smaller than the slots of the

outlet diaphragm.

- Check the condition of the central

screen

Visual To prevent the passage of balls from one

compartment to the other.

- Check other specific features like

control systems

To determine if these features have the

good settings.

Second chamber

Action Data-Measurement Reason

1 Intermediate diaphragm


the back plates

Visual and thickness To insure the protection of the diaphragm

frame.


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2 Volume load or filling degree

- The measurement must be achieved

in 4 points on the mill-axis (inlet, first

third of compartment, second third

and compartment outlet). The best

procedure is probably to measure

the height from the ball charge tothe linings

4 points

(mesure height H)

To maintain the production (tons/hour) of

the mill because the volume load is directly

linked to the mill absorbed power and the

mill efficiency.

- Other method: count the number of

visible lining plates (less reliable

method)

At least 4 points If it is the only way to measure the volume

load.

3 Linings


the linings

To maintain the lining efficiency (don't

forget that the function of the 2nd

chamber is TO GRIND).

- Check if there are broken plates Number To maintain the mill shell protected

- Check if there is coating on the

linings

Evaluate the impor-

tance of the problem

Evaluate if it is hard

to remove, measure

the thickness

This phenomenon can happen, especially in

the case of open circuit.




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4 Ball charge and classification

- Check the ball charge: the principle

is to evaluate visually the proportion

of big balls (60mm) and small balls

(17-15mm)

Better with

experienced

persons

To respect the initial ball charge

recommendation.

To maintain the efficiency of the 2nd

compartment.

- Measure the biggest and the

smallest ball diameter

Minimum

Maximum

To determine the next ball make up

composition or the substitution of the ball

charge.

- Check if there are broken balls Visual estimation To avoid blockage of the outlet diaphragm

slots.

To analyse the balls quality with the

supplier.

- Check if there is coating on the balls Evaluate the impor-

tance of the problem

Evaluate if it is hard

to remove



- In case of classifying lining, check the

classification of the balls (perfect,

good, poor or disturbed, mixture of

the balls, reversed classification)

Visual estimation

Sampling of the

charge but takes

time and a lot of

hard work

Bad classification may be due to a bad

lining, excessive coating or presence of

unground particles coming from the first

compartment.



5 Material level

- Check the material level (too high

you don't see the balls, good if you

see the top of the balls, not enough

material if you don't see it)

Visual estimation

Make a design

Not enough material may be due to high air

velocity.

Result is a higher wear, a drop of efficiency

and lower throughput.

Too much material may cause overfilling, adrop of efficiency and lower throughput.


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6 Sampling of the second chamber

- Take 6-8 samples (inlet, 4-6

intermediate samples at equal

distance, diaphragm)

500gr to 1kg for each

sample

In order to know the reduction efficiency of

the second compartment.

- Ideally for each sample, take

materiel in three

Mill-axis point is the

best if 1 point

It is more representative.

- Remove the balls and the material at

the sampling point

Depth of 20-30 cm To collect the material only in surface is not

correct.

- With the shovel, put balls and

material in the sieve which is above

a paper bag. Remove the balls from

the sieve. Put the collected material

in a bag

Don't forget to put possible uncrushed

particles with the material sample!

- Check the presence of uncrushed

particles, especially an accumulation

at mill outlet

Visual estimation Accumulation causes blockage of the outlet

diaphragm and a drop of efficiency and

throughput.

7 Outlet diaphragm

- Check the general aspect of the

diaphragm

Visual


the plates and the grid plates

Visual and

thickness

To insure the protection of the diaphragm

frame.


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- Check the width of the slots and if

there are blocked by unground

particles or scraps

Maximum width

Minimum width

% of area blocked

To insure that the slots of the outlet

diaphragm are bigger than the slots of the

intermediate diaphragm.

- Check the condition of the centralscreen

Visual estimation To prevent the passage of balls.

- Check the condition of the water

injection system and if it is blocked

by material (nozzle)

Visual inspection Maybe, it is useful to make a test in order

to see the trajectory of the water jet.

Ball Mill Inspection

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