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Why CGB cause production drop of cement ball mill ?

[Nov 26,2019]

Speaking of CGB (Ceramic grinding ball) technology,many cement plants take it for granted.They think it of nothing special than just replacing the HC ( high chrome) steel balls with CGB.However,once they did so they found themselves trapped in production decline issue.If the production capacity remain the same, the quality of cement has to be sacrificed (the fineness,blaine,etc). Some veterans are not aware of this, they treat the CGB completely based on their experience in HC steel grinding media. When 20-30% production capacity drop,they were confused extremely.

As a matter of fact, the hardness and grinding characteristic of CGB is not inferior than HC steel balls.many test results verify this through mini-mill in laboratory.It suggests that under equal conditions (dimension, same loading volume and same grinding duration) the grinding result between CGB and HC steel balls are nearly the same too for output and quality.Why does it vary too much after being loaded in practical ball mills?

Analysis :

1, The bulk density of CGB is 2.2t/m3 whereas 4.5t/m3 for HC steel ball.In the same chamber of ball mill, given same loading weight,the filling level of CGB shall be around 2 times of HC steel balls ( if HC steel balls is 100MT@ 30%, 100MT of CGB might approach 55-60% of filling level ).However,our current design of ball mill do not allow us to load grinding media with filling level upto 50% or higher.Therefore we have to keep it at around 30% higher than HC steel balls ( HC steel balls: 30% Vs CGB: 40%).Consequently,the loading weight of the ball mill decline,but the grinding efficiency more or less are affected too.

2, In cement ball mill operation,the clinker stay around 18-20 minutes from the inlet to the outlet.If it’s big ball mill with 2nd chamber length upto 8-9 meters or even longer,the grinding duration is boiled down to 10-15 minutes. As the filling level is limited when CGB work, the loading weight can not be managed as high as steel balls ( thanks to this reason,the loading weight drop,and the main motor drive operation capacity drop too,and power saving is achieved! ).Hence to grind the clinker to designed quality is a challenge if the production rate is to be maintained.The solution lies in 1st chamber,or pre-grinding system.This is why sometimes the 1st chamber length need to be extended,which aims at loading more HC steel balls.Only by doing that,could the grinding efficiency caused by CGB in 2nd chamber be compensated.In that case,the production capacity and cement quality will be remain unchanged, along with other technical modification, if not.

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