Re: Grinding In A Ball Mill
Your reduction ratio is 13.3 : 1. This is a significant reduction and should take longer than normal retention time to achieve. Since you do not provide the tonnage and rock strength, the point seems mote.
There is a way to increase the rate, with an improved liner configuration, if this is of interest. Certainly you can alter the mill speed using a VFD control which would also maximize your output and whatever P80 you selected. ■
Re: Grinding In A Ball Mill
thank you very much for your reaction.
the total amount we want to achieve is a mininum of 2 metric tons per hour. I have consulted different advisors but they give me different kind of information. one advisor tells me the througput will be between 8-10 ton/hour for the 75micron (90%<75micron), with about 16-20 tons/hour circulation, other advisor tells me about 2-3 tons/hour with 15 tons/hour circulation and he was afraid that the ready product will be to fine. grinding to fine costs me throughput.
for us it is a totally new product, the hardeness is about 6 mohs but it is very brittle. (glassfibers)
I am not very experienced in adapting a ball mill and since I get different opinions of experts, it is nice to know what parameters there are available to get a good installation. the lining and balls will be aluminiumoxide.
So, you can vary:
air velocity in mill increases fines increases
ball mill rpm decreases fines decreases
filling of bals increases fines decreases?
are there any references for me to find?
and what are the most logical parameters to vary to be most efficient. ■
Re: Grinding In A Ball Mill
If capital investment funding is available as an option for your new product/project you may want to consider an air swept classifier milling system. This type of high speed impact mill typically produces a very narrow particle size distribution with one-pass processing, the energy input is relatively low vs capacity and the particle size is easily controlled to target. I encourage you to visit our website to learn more...www.cms-can.com.
Kind regards,
Kevin Layton
Independent Sales Representative
Email: klayton@insight.rr.com
Tele: 419.450.4404
Fax: 614.987.5781
Skype: kevinlayton
Columbus, Ohio, USA
CMS - Classifier Milling Systems
35 Van Kirk Drive, Unit 17
Brampton, Ontario, Canada L7A 1A5
Sales: sales@cms-can.com
Tele: 905.456.6700 Fax: 905.456.0076
Toll Free: 1.877.353.mill (6455) www.cms-can.com ■
Re: Grinding In A Ball Mill
thank you very much for your reply,
but the ball mill is existing. the whole new lay out is planned around this mill. ■
Re: Grinding In A Ball Mill
The ball mills I am familiar with running on a similar product application (flaked glass frit) were of the type with one end inlet and the other end outlet. I see yours has inlets on both ends and the discharge in the middle. For the former type, the mass material flow (Kg/hr) was an important control parameter as well as the pitch, or elevation difference between inlet and outlet of the ball mill as installed on the base. In this case the discharge end was at some degree of elevation (~10 to 20 degrees) higher than the inlet. This pitch, along with the other control factors such as rpms, liner type, ball load, ball type and ball size distribution regulated the materials fineness. The cutpoint of the Secondary Classifier also is a control point. The pitch, or elevation difference, from end to end also regulated material residence time corresponding to the material bed height inside the mill. Material mass flow balance is very likely an important factor for you to consider when you sample for your type ball mill too. If you can sample at the various key points throughout your system this will greatly aid you in optimizing particle size and throughput. These key location points would be the Classifier discharge, Ball Mill discharge, final product discharge, and dust collector fines streams. At some point after commissioning, and once you have obtained the desired particle size, you may wish to perform a series of designed experiments on these factors with the objective of optimizing rate and throughput. Your Ball Mill supplier may be able to provide guidance.
Kevin ■
Re: Grinding In A Ball Mill
One clarification... the sample point I was referring to as "Classifier discharge" was the closed loop, or return-to-ball mill material stream. I assume your final product stream is the Classifier discharge.
Kevin ■
Re: Grinding In A Ball Mill
One more thing for completeness...For the Classifier discharge stream-to-product collector... speeding up your Classifier Wheel (with suction airflow constant and the additional factors in steady state control) = finer distribution to product collector PLUS coarser median PSD (particle size distribution) returned to Ball Mill. The inverse is true (more coarse to product collector and finer to return loop) if you increase suction airflow at constant Classifier Wheel rpms. I prefer using a graphical flow sheet like you have to record process data and sample results. Plan your overall approach, step through each process adjustment with patience, record the data, take good representative samples and you will forever learn your way to running the most efficient Ball Mill in the land. This experience will help you later with other new products.
Kevin ■
Re: Grinding In A Ball Mill
thanks for the answer,
I have mixed up some things,
the mill has for the moment two chambers, but I want to make it an air swept mill with one chamber. according attachment.
then the total length of the mill will be 6.5 meters and the diameter is 2meters.
after a sieve analyses of the product on a 225 micron sieve, 75% went through and 25% not. the diameter of the glass is 11 microns, and its length varies.
if we want to go to 90%<71microns, we have the fear that the mill is too long, but as I understand, we should start with a low ball filling percentage of about 25% estimated, because filling balls is easier then decreasing this percentage.
we dont have a pitch (slope?) on the mill, it is only possible to vary the outlet diameter,
The most mills I know, the coarse of the classifier returns directly into the mill. Is it wise to put the coarse of the classifier into the hopper of raw material?
I think the advantage to put it into the hopper with raw material, you can control better the charge (feeding) of the mill?
Or is it a disadvantage, because the materials (coarse of classifier and raw material) get mixed and the difference in fines gives an instable proccess?
Attachments
flow sheet airswept mill (PDF)
■
Fine Mill Grinding & Classifying
Dear Coe,
I am not an expert on air swept and fine particle mill production. I do have a working knowledge of their principles. I seems to me the size classification has many variables. In order to select for a size some points are:
a) air velocity must meet a minimum (optimized) standard to liberate and entrane the appropriate size group - higher speed means coarse cut size
b) mill speed must circulate the mineral at a sufficient rate to create the surface area to liberate by air motion - mill internal configuration can have a profound impact on product size, shape and through-put. Product circulation is very important and that is determined by mill motion and product motion in mill charge.
c) secondary classifier (cyclone) may be necessary to select the product size from oversize - where else would you put oversize other than raw feed stream - however, I don't think it needs to go through hopper other than to maintain a known feed rate and size distribution - so, it depends on recirculating stream percentage and mix?
d) ball percentage and size most likely is a trial process to optimize mill throughput and product size passing
You might try reading the volumes of the SAG 2006 conference. Although not dedicated to you mill and product size, the principles of mills is thoroughly explored on larger machines. Mostly wet mills are discussed. ■
Re: Grinding In A Ball Mill
hello,
you seem to be very experienced in milling. do you know perhaps the bond work index of glass fiber or glass?
I found that this would be the figure to compare differtent product to each other. this might be the way to estimate the throuhg put of the mill
I would like to compare the grindability with other materials, like bauxite, feldspat, wollastonite, etc,
are there any tables to find where this index is mentioned?
these kind of product are we milling, (also aluminium oxide) ■
Re: Grinding In A Ball Mill
Obtaining Bond energy/grinding coefficients would need to be obtained from those that either do similar modeling or a lab that does such testing.
A word of caution - the Bond Work Index is valid only in a narrow range of lab or site testing. The actual number tagging the energy coefficient to the F80 (feed size passing) and P80( product size passing 80%) are phenominological values, not tied to classical breakage mechanics of rocks/glass/ceramis et al. This error is more so in the finer particle range less than 1mm. Bond says is proportional to the sqrt without regard to size range. It is not.
Metso, Sandvik, Outokumpu, Lakefield Research, JK Tech, CSIRO, and others may have such knowledge. We do not. ■
Re: Grinding In A Ball Mill
This ball mill is horizontal type and tubular running device, has two warehouses. This machine is grid type and its outside runs along gear. The material enters spirally and evenly the first warehouse of the milling machine along the input material hollow axis by input material device. In this warehouse , there is a ladder scaleboard or ripple scaleboard, and different specification steel balls are installed on the scaleboard, when the barrel body rotates and then produces centrifugal force ,at this time , the steel ball is carried tosome height and falls to make the material grinding and striking. After grinded coarsely in the first warehouse, the material then enters into the second warehousefor regrinding with the steel ball and scaleboard. In the end, the powder is discharged by output material board andthe end products are completed.
From: crusher and mill ■
Re: Grinding In A Ball Mill
hello,
the mill has two chambers for the moment, but we want to remove the two grids in the middle, so the mill will have just one chamber. the dimensions of the mill will be diameters 2meters and length will be 6.3meters. Also a change is that the mill will be an air swept mill. 20.000m^3/hour goes through the mill for transporting the fines out of the mill.
do you have experience in grinding glass fibers? or perhaps you know what the grindabilty is of glass fibers?
it is supposed, that an airswept mill is much easier to adjust in the proces. you can vary the air speed,
filling percentage of balls about 28%, so a grid is not needed any more at all.
liners and balls of aluminium oxide. ■
Grinding in a ball mill
hello,
we are planning to grind an other product in an existing ball mill.
it is a traditional system: air swept ball mill, air classifier, product filter, see attachment
the feed product is maximimum about 1mm
the supposed ready product must be about 75 micronmeters.
the ball mill diameter is 2 meters and length is 6,5meters.
is there a possibility that the mill is to long, so the ready product is to fine?
if the product becomes too fine, what is the solution?
what are the parameters to vary in an traditional system to achieve the right finenesses?
Attachments
flow sheet (PDF)
■