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Reasons For Applying Vfd For The Ball Mill


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#1 Xalebor

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Posted 02 December 2010 - 05:18 PM

Hello everybody.

Could you pls explain me, what is the principal idea using FC at ball mills excepting soft starting?
Traditionally ball mills are operated with constant speed (calculated critical speed), but last time many international metal companies start using frequency converters on ball mill. Why?

#2 jOmega

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Posted 06 December 2010 - 07:21 PM

QUOTE (Xalebor @ Dec 2 2010, 11:18 AM) <{POST_SNAPBACK}>
Hello everybody.

Could you pls explain me, what is the principal idea using FC at ball mills excepting soft starting?
Traditionally ball mills are operated with constant speed (calculated critical speed), but last time many international metal companies start using frequency converters on ball mill. Why?



If you were to graph the load versus speed you would discover that the load isn't constant as the drum rotates, and as a consequence, the asynchronous motor operated directly from the mains, is not delivering
constant speed.

Using a variable frequency drive, with field oriented control can respond almost instantaneously to load changes to maintain constant speed. Unlike vector type drives that use a PWM modulator, the FO drive can instantaneously change the configuration of the output switches so the resultant vectors can be ordered in direct response to changing load conditions.

An improvement in process is thus obtained.

#3 Xalebor

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Posted 07 December 2010 - 08:15 AM

Thank You for very professional explanation.

but we (in Ukraine) traditionally use synchronous motors, where speed is constant despite of changing load level.
May be there is technological benefits of varing speed during the process of grinding?

#4 jOmega

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Posted 09 December 2010 - 05:52 PM

QUOTE (Xalebor @ Dec 7 2010, 02:15 AM) <{POST_SNAPBACK}>
Thank You for very professional explanation.

but we (in Ukraine) traditionally use synchronous motors, where speed is constant despite of changing load level.
May be there is technological benefits of varing speed during the process of grinding?



Yes, but does not the synchronous motor operate at one, and only one speed ?

That being so, then how do you make adjustment for changes in process variables ?




#5 Xalebor

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Posted 10 December 2010 - 11:39 AM

QUOTE (jOmega @ Dec 9 2010, 06:52 PM) <{POST_SNAPBACK}>
Yes, but does not the synchronous motor operate at one, and only one speed ?

That being so, then how do you make adjustment for changes in process variables ?



You are right, at the moment we have no tools to regulate speed, so proper speed was calculated once 30years ago and have been constant. So, as ore hardness has been changes since that, it's needed to correct speed of mill drum. Also mill load is not constant.
But I'm not clearly understand the process of speed regulation. Will it procided in handle mode by operator according to changes in mill load level, ore hardness etc etc? Or it's needed to be automatization? We use 56 ball mill of 2,5 MWt each, so how to automatizate this process of speed regulation?




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