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Ball Mill Audit

Why must the ball mill be audited?

Ball mill audit is survey, measurement and inspection of performance of the ball mill at the present time of the cement plants, to overcome the problems, improve the productivity and reduce the exhaust energy in the production process.

The following example is ball mill audit program for a coal mill plant.

Ball mill status:

A one-chamber mill uses hot wind from inlet of the kiln to dry coal. The survey of ball mill was carried out within 5 days. Before changing in combination of balls, the loading rate of 23% was equal to 8.6 ton. The mill does not have ball bearings, large balls and small balls mixed from the inlet to outlet of the mill. A small number of balls on air duct at the inlet and outlet of the mill show that there is much meal in the mill than normal. Feed chute discharge directly to the cone of the input and the bottom edge of the feed chute ~ 3 m.

Based on criteria after inspecting the ball mill, we have given the following combination levels of ball:

Temporary combination:

Based on the estimated particle size of the coal loaded into the fineness 10% mill, the largest ball size should be in the 60 mm. However, because ball 60 mm is not available, using ball 50 mm instead of ball 60 mm.

Due to the requirement of fine grinding to help burn well at a temperature of 2-750 oC, the selected ball has a larger surface than the ball used before (from the plant started)


Operation status of the ball mill 24 hours after temporary combination level of balls:

The coal mill is restarted after temporary combination. Yields were kept at 3.4 t / h in night shift, fineness 1-1.2%, and mill engine on average 160 A. In the following day, the productivity was raised to 3.6 t/h, fineness 0.6%, and the mill engine was maintained at 160A.


Due to the smooth coal bins filling, the mill was stopped abruptly to sample coal along the mill. The capacity of the mill before stopping is 3.6 t/h.

Checking and sampling inside the mill shows:

1. Within 1 m from inlet of the mill, there is no coal from the ball surface> 200 mm

2. From 2 m to outlet of the mill, there is no coal on the surface of the ball; there is coal at a depth of ~ 200 mm

Large balls and small balls are mixed, but still see the large balls focused on inlet of the mill and small balls on the outlet.

It is possible that the coal layer on the surface of the balls has been swept away by the large amount of wind that is maintained when the mill is stopped. However, it can be seen that the level of filling of coal is very low. This shows that the grinding process is good, it should increase productivity not only to reduce electricity consumption, but also reduce the wear of balls, bearings, reduce the risk of fire and explosion caused by heating and impacting together when material is low. The phenomenon of almost no coal in the ball in the 1 m area may be due to the location of the feeding chute. The material can be swept away as the wind and angle of discharge of the feeding chute.

The grinder works again with a productivity increasing 4 t/h and fineness ~ 0.7%. The mill is still capable of running over 4 t/h. Compared to the past; power consumption has dropped by 4 kWh / ton.


Combination level of balls 90% maximum of balls to grinding anthracite coal

In order to be able to grind anthracite coal at a rate of 3.6-4 t / h, 90% combination level is recommended as follows:


By adding 800 kg ball 60 mm, and 600 kg ball 40 mm into the ball volume available in the mill. The supplement can be divided into 2 sessions.

Session 1: Add 340 kg ball 60 mm and 300 kg ball 40 mm, follow the status of the mill running with anthracite coal within 48 hours to decide whether to add balls 60 mm and 40 mm.

Session 2: If the productivity is low, the return is high, fineness is difficult to reach, and it needs to add the remaining ball.

After the running time of about 6 months, if the ball is not added, the wear of ball will reduce the productivity and the product is difficult to reach than required, the mill will decrease compared to before. The factory needs to check the margins, recalculate the marbles to complement. The type of ball used to add is ball 60.

In addition, we carry out measurements and provide recommendations for other equipment in the production system, to optimize the productivity, increase profitability for the plant.

Above is the data of the ball mill audit at the actual coal mill. Through these figures, we can see the importance of audit of ball mill as well as the other machines in production line in order to enhance performance, make maximum profit and reduce production cost.