Grinding & Classification Circuits

Grinding & Classification Circuits2018-06-17T09:51:34-04:00
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Ball Mill: Low output and gradation issues (2 replies and 2 comments)

9 months ago
amyerscalcean 9 months ago

We have a 4x16 ceramic lined ball mill and we are milling precipitated calcium carbonate. We are trying to to get to a gradation of D50: 3 micron and D90: 8 micron, however we are having trouble getting the gradation down. Currently we are at a D50 of 5.5 micron and D90 of ~15 micron. We are using grinding aid and running the mill at 28 rpm. Our air classifier's rotor is running at 2200 rpm. We are also only getting approximately 100 lbs an hour, when our mill manufacturer said our mill has the capability of 3,000 lbs per hour. 

The two main issues we are struggling with are getting the gradation down in size AND the amount of output we are getting. Does anyone have any suggestions for us on these issues? 

We also believe we have an issue with static causing our air classifier to miss the smaller particles since they are clumping. We are going to try pumping ionized air into our mill to help with this issue, does anyone have any experience with this?

9 months ago
SmartDog 9 months ago

In reading your question one thing stands out, your next to last sentence, "since they are clumping".  That can be a major contributor to both your through put and size issues.  This would indicate a high circulating load which immediately reduces your through put.  The question is why the clumping.  And while static could be the issue, another cause could be moisture.  Particularly is your feed completely dry.  If there is any moisture at all, upon grinding this will release it and led to clumping as your describe.  

9 months ago

Hi SmartDog,

Thank you for your response! We do moisture analyses at different points in our process line. It is important for us to keep moisture below 0.20%. Our last moisture analysis of the feed into our mill was 0.09%. I'm not sure if that's enough to cause clumping, which is why we were thinking it was static causing the particles to cling together. Is below 0.20% still too much moisture? Another thought is condensation. We do not run our mill 24/7. The mill warms up during the day and then sits through the evening or weekend in a cooler climate. Would this cause condensation to build up in a ceramic mill leading to a moisture issue? Additionally, the grinding aid we add is a liquid, would this affect the moisture and thus lead to clumping? We really appreciate your feedback!

9 months ago
SmartDog 9 months ago

0.2% should not cause issue, but the liquid grinding air, and the condensation during down periods might.  For the condensation, try warming the mill up with dry air before using.

9 months ago

Hi SmartDog, Thanks again! We've added the ionized air and that seems to be helping with our static. However, we are experiencing moisture issues. The feed into the ball mill is the lowest moisture content. The material then seems to gain moisture in the ball mill as the MC is higher on the ball mill output. Strangely, however, the MC increases dramatically in our fines out of the air classifier. It seems our material is now gaining some moisture in the ball mill and then gaining a lot of moisture between the ball mill and the output of the air classifier. We haven't had this problem before. The only variable that is different is the amount of grinding aid, however, this would explain the MC difference between the input and output of the ball mill but not the increase between the ball mill output and the fines from the classifier. Do you have any suggestions? We asked our air classifier manufacturer about the possibility of condensation and he said there may be some at first start up but it should dissipate quickly once running. It's just baffling at this point, do you have any suggestions?

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