grinding ball charger in cement mill

ball mill for cement grinding process

ball mill for cement grinding process

MQ series ball mills are mainly used in grinding operations in mining, cement, refractory, chemical and other industries. According to the discharging method, it is divided into MQG series dry type lattice ball mill, MQS series wet type lattice ball mill, MQY series wet overflow type ball mill, MQZ series peripheral discharge type ball mill; according to the type of liner, it is divided into A series (high manganese steel lining). Plate, magnetic lining) standard type and B series (rubber lining, high aluminum lining, silica lining, ceramic lining) energy-saving type; according to the transmission mode is divided into edge drive ball mill and center drive ball mill.

When Ball Mill is working, raw material enters the mill cylinder through the hollow shaft of the feed. The inside of the cylinder is filled with grinding media of various diameters (steel balls, steel segments, etc.); when the cylinder rotates around the horizontal axis at a certain speed, Under the action of centrifugal force and friction force, the medium and the raw material in the cylinder will drop or roll off the inner wall of the cylinder when the gravity of the cylinder reaches a certain height.

When material particle gravity is greater than centrifugal force, they will be crushed due to the impact force. At the same time, during the operation of the mill, the sliding movement of the grinding media to each other also produces a grinding effect on the raw materials. The rest material is discharged through a discharge hollow shaft. Due to the constant uniform feeding, the pressure causes the material in the cylinder to move from the feed end to the discharge end. During wet grinding, the material is carried away by the water flow; during dry grinding, the material is taken away by the airflow drawn out of the cylinder.

When Ball Mill is running, the raw material enters the mill cylinder through the hollow shaft of the feed. The inside of the cylinder is filled with grinding media of various diameters (steel balls, steel segments, etc.); when the cylinder rotates around the horizontal axis at a certain speed, Under the action of centrifugal force and friction force, raw material in the cylinder will drop or roll off the inner wall of the cylinder when the gravity of the cylinder reaches a certain height. When their own gravity is greater than the centrifugal force, they will be crushed due to the impact force. ore. At the same time, during the operation of the mill, the sliding movement of the grinding media to each other also produces a grinding effect on the raw materials. The ground material is discharged through a discharge hollow shaft. Due to the constant uniform feeding, pressure will causes the material in the cylinder to move from feed end to discharge end. During wet grinding, material is carried away by water flow; during dry grinding, raw material is taken away by the airflow drawn out of cylinder.

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ball mill charge - grinding & classification circuits - metallurgist & mineral processing engineer

ball mill charge - grinding & classification circuits - metallurgist & mineral processing engineer

The crop load of ball mill. It =ore + mill medium +water. But usually, it was used in a percentage formation. So how to calculate this percentage. I know this is really a basic question, but it puzzled me, for most books and papers just use it but nor explain it.

The ball charge and ore charge volume is a variable, subject to what is the target for that operation. The type of mill also is a factor as if it is an overflow mill (subject to the diameter of the discharge port) is usually up to about 40-45%. If it is a grate discharge you will have more flexibility of the total charge. Ball size and ball grade is determined by the feed ore size and hardness, plus the PH level of the slurry. The ball charge is determined by the operator targeting the balance between grind and throughput, the higher the ball charge the more aggressive the milling becomes. With softer oxide ores lower ball charges are usual however the harder sulphides does need more media energies to meet the P80 target and an acceptable throughput. These comments are very broad and very much dependent on individual operator priorities. There are too many variables to cover every case in this forum. I will however mention that "spawling" has been now greatly reduced due to new media technologies and breakage of media in high ball charges is able to be overcome. High ball charges in ball mills does open that danger of media breakage through higher ball on ball incidents - now this is not the problem that it was previously.

DISCLAIMER: Material presented on the 911METALLURGIST.COM FORUMS is intended for information purposes only and does not constitute advice. The 911METALLURGIST.COM and 911METALLURGY CORP tries to provide content that is true and accurate as of the date of writing; however, we give no assurance or warranty regarding the accuracy, timeliness, or applicability of any of the contents. Visitors to the 911METALLURGIST.COM website should not act upon the websites content or information without first seeking appropriate professional advice. 911METALLURGY CORP accepts no responsibility for and excludes all liability in connection with browsing this website, use of information or downloading any materials from it, including but not limited to any liability for errors, inaccuracies, omissions, or misleading statements. The information at this website might include opinions or views which, unless expressly stated otherwise, are not necessarily those of the 911METALLURGIST.COM or 911METALLURGY CORP or any associated company or any person in relation to whom they would have any liability or responsibility.

ball charge and grinding efficiency - grinding & classification circuits - metallurgist & mineral processing engineer

ball charge and grinding efficiency - grinding & classification circuits - metallurgist & mineral processing engineer

What is the effect of low ball % full on grinding efficiency?One of our clients is thinking of the future and has bought a ball mill that will be the right size someday, but is very large now.I know what happens to mill power from adjustments to % critical speed and % balls charge. What I don't know is what happens to grinding efficiency as ball charge % filling is lowered. For example does a grinding between two given sizes that takes 6 kW/tonne at 40% full take 8 kW/tonne or some other number at 20% full?

The volume of grinding media in a mill is directly related to grinding efficiency. The higher the volume of grinding media the more effective the grind. Balls must be added to maintain the media load and mill power draw. The power draw increases as balls are added and decreases as media wears down: add balls.

Higher ball loads will result in finer grind but dont overcharge. If throughput of slurry to BM decreases the mill power draw will increase because balls grinding against balls are drawing more power: finer grind.

I totally agree with you that the low charge rate directly affects the grinding efficiency, but in here there is another thing we have, that shouldn't be overlooked, it is the power consumption, at low charge rates below 20% the power consumption increase by 6-15% for the ball mills.

A difference (duty vs. maximum) of 5% to 10% is fairly typical and you would likely struggle to perceive an energy efficiency difference between the two operating points. Beyond this, the situation may change.

The 40% vs. 20% is a very large difference in ball charge. Under these conditions I would agree your slurry pool is going to be large and this is likely to cause issues from both a power draw and power efficiency perspective. This is not easy to quantify without more detailed analysis/benchmarking.

This shouldn't be a show-stopper, as you say, the mill is oversized so the duty throughput/grind size should be attainable, albeit the exact milling conditions/power efficiency may be difficult to pin-point.

If this is a concern, and if the client has already bought the mill, your options may be limited. One option could be to install a grate possibly with high capacity pulp lifters, to minimize the slurry pool at 20% ball charge. The grate could later be removed to allow for operation at higher ball charges. Obviously this creates its own set of separate issues.

Actually, you need to differentiate between capacity and grinding efficiency. At a lower load capacity will be reduced but grinding efficiency will increase. There are only a few examples of this (most sites go for throughput rather than efficiency) but it has been shown to hold true for overflow mills.

With very low ball charge (less than 20 %) and low slurry density power draw will increase because of increasing toe angle and also more lifting. Also with low ball charge slurry pool will reduce grinding efficiency. Beside lower ball charge will increase P80 of ball mill because of less number of impacts but mean residence time will increase by lower ball charge because of more volume to occupy. I think at last in this situation, power consumption will increase.

You missed the point that the feed rate is lower so the residence time is longer so the product size is not necessarily larger. By the way, circuit product size is not determined by the mill but by the classifier. The mill performance will affect the circulating load.

I don't get why you think that the toe angle will increase and there will be more lifting. I don't understand why the slurry density would be any lower. Why would it change (or in mill that controls it why would the target change)?

All overflow ball mills operate with slurry pooling. Do not confuse with a AG/SAG mill where pooling can be detrimental. In ball mills all the media is balls with a high SG so the impact of pooling is not as large. Additionally, in ball mills grinding is primarily through cascading not cataracting (compared to an AG.SAG) so the slurry pool is not a factor unless density is high, which leads to viscosity issues.

I have been told at a few sites I visited where the ball level is lower (e.g. 25%) that they operate at that level because they don't need the power. What they have observed is that the specific energy is lower and that the media and liner consumption is lower.

Of course all the ball mills operate in slurry pooling conditions but with low ball charge it will be larger than before so it will affect the P80 (Ball mill Product 80 % passing not circuit product) badly and it will increase. He had mentioned adding water to classifier underflow; this work will reduce slurry density. With low slurry density (under 60% solid percentages) because of more charge liberation to lift, the shoulder angle will increase (more lifting). High ball charge will result in developing toe position and because of high ball charge after a certain point of charge level; power draw will decrease so with lower ball charge there will be no toe developing.

The throughput of mill will decrease with the time;The P80 in the discharge of the Mill, will increase because of the high time of particle residence in the Mill, and for this reason the grinding will be lower efficient.The power specific consumption will increase, due to the lower feed rate.

I don't know where you got the low mill density of 60% but I don't see that in the postings above. I don't agree that the lower ball charge will lead to a higher P80 because the feed rate will be lower and pooling does not affect cascading action so low impacts will not be affected. Yes, the number of impacts will be lower but that affects capacity not efficiency. What is important for efficiency is the location of the energy spectra (high impacts vs. low impact). For ball mills low impact is more important because of the smaller particles.

You state that the residence time will increase so what is your evidence that P80 will increase? Yes, the feed rate is lower but so is the power. If the power drops more than the tonnage then the specific energy will be lower.

The only thing I will add to this discussion is that I have been to plants where they operate at low load (-25%) because they don't need to have the capacity. They do it to save energy and reduce media consumption. None of them have complained of low efficiency. So, based on my experience, tell your client that they will be fine.

Quite an interesting discussion here, with many different views! Why is efficiency important anyway? How would you define it? What would be the measured benefit? Would is matter if commodity prices were depressed? What would be considered "high" and what would be considered "low"?

I agree 100% with you regarding low loaded mills with good, even great, efficiency.In fact, some studies point out the importance of reaching this "optimal" load % that necessarily isnt this common heard 28-30% value.

I just want to add that more than a fixed load %, its important to keep the balance between both mill's chambers. In my experience Ive seen engineers planning and making calculations for a grinding media reload in Chamber 1, not considering at all the load % on Chamber 2. What happens next? : You have a wonderfully filled chamber 1, but your Chamber 2 isnt able to keep the pace with Chamber 1; in fact, you just unbalanced your mill.Just want to say that the mill will work as good as your worst chamber.

Low ball ratio is not the same as low mill density. If the slurry density falls below 80% then the slurry will not adhere to the balls and there will be no further abrasion grinding (only impact grinding).

Reducing the ball charge will reduce the grinding capacity, and the comment on installing a grate discharge is a good one as it will let ore out sooner, thus minimizing overgrinding, which will occur if the mill is (temporally) too big, or one chamber is too big in a multi chamber mill. But the reduction is not a direct reduction (50% fewer balls 50% less grinding) as there is a factor from the liner role in grinding.

There is no need to add low grade ore or to change to a grate discharge. There will not be any vacant space because this is (I assume) an overflow mill so by definition will be full. Adjusting the ball charge to meet the capacity demand will ensure that it is not overgrinding (if it is overgrinding then it has more capacity than needed and the ball charge can be reduced). In order to maintain good efficiency the grinding circuit should maintain a good circulating load (e.g. 250%).

I was doing some research trying to see if anything has been published in this area. These papers are more applicable to the cement industry and less applicable to the minerals industry, but they are interesting nonetheless:

Obviously there are numerous potential inaccuracies and uncertainties associated with commercial mineral processing operations and a handful of case studies with conflicting conclusions is not a convincing design basis.

If your project is sensitive to grinding efficiency (I'll let you decide the economics), it would be prudent to assume your project may initially have a lower grinding efficiency and put in controls to help mitigate this risk (if indeed it is an issue). As I said previously, to give a quantitative answer more detailed analysis/benchmarking is required.

If you maintain a high ball charge with low tonnage, you'll overgrind. So you can low the ball charge, these means less interaction mineral particle with steel balls so reduce grinding, but also it means that you bed density will be lower, since you'll reduce the steel (7,75 kg/m) and replaced with mineral slurry (let say 2,0 kg/m for copper mineral) to maintain the volume, thus reducing energy consumption.

But there some worth to point out and it is the consequences of not evaluating the degree of the lowering. As he mentioned paper of David S. Fortsch (2006), when lowering the ball charge to less than 25% volume the energy efficiency goes down for that operation in particularly. And it also make sense, just imagine that you're feeding the ball mill with a high P80, that needs more cataracting than cascading, a you just low the ball mill to a point that cataracting is heavily reduced.

So every operation needs to evaluate particularly the degree of ball charge, and sure there's and optimal minimum, and variables like L/D ratio, Mill Size, and feed particle size had a strong effect on this optimum value.

If the ball charge rate is between 8-12%, it will be SAG mill. If it is more than this, it will be ball mill. SAG Mill's effect is mainly crush the big ores and then use ball mill to grinding the small ores.

Ball size will also affect the grind P80. Efficiency is in part determined by the Axb value of the ore. A small lab mill can give guidance on the influence of ore strength and ball size. Larger balls will increase P80 in ball mill, thereby reducing overgrinding. If you believe the entry ball size sets the initial point on ball population and exit size is fixed, since the ball wear is near linear, in some camps, this raises the P80 = can only result in grinding larger rock.

SAG & Ball mill % ball contentSAG % ore contentSAG grate size and end mill design including grate geometry, location, shape, pan cavity, recycle % in pan cavity, et. al.SAG lifter and end cone geometry - can change SAG mill performance more than 20%-50% depending on P80 transfer size and Axb, some of which is published and some will be published at SAG 2015.SAG mill wear rates and performance changes with wear morphology, grate details, mill speed changes and optimization with speed controlBall feed sizeSAG mill water flow rateSAG mill power vs. wear geometry - maximizing kW-hr/ton & tons/hour in combinationSAG mill liner change-out life/cycle vs. tons/kg consumed

Ball mill liner efficiency based on liner geometry and its influence on kW-hours/ton, total tons/life cycle, and P80 transfer to cyclones. Ball mill grind is based on different principle; it has some attributes similar to SAG mill optimization. SAG mill breaks with stirring the kidney at optimized kidney specific gravity and maximum stir rate per mill revolution, whereas ball mill breaks down ore with increasing particle-to-ball interaction.

In dry cement ball mills, there are studies done in the past which clearly shows that energy saving make sense reducing 1chamber ball mill filling degree. This thread-shore level is considered between 20 and 21%. Below that level mill production/consumption curve do not make more sense increasing the specific energy consumption instead of lower it.

Give me actual data of you grinding flowsheet: feed size, product size, power of mill motor, capacity, ball size, numbers & diameter of hydrocyclone ball charge, mill speed. I'm calculate optimum capacity you flowsheet.

DISCLAIMER: Material presented on the 911METALLURGIST.COM FORUMS is intended for information purposes only and does not constitute advice. The 911METALLURGIST.COM and 911METALLURGY CORP tries to provide content that is true and accurate as of the date of writing; however, we give no assurance or warranty regarding the accuracy, timeliness, or applicability of any of the contents. Visitors to the 911METALLURGIST.COM website should not act upon the websites content or information without first seeking appropriate professional advice. 911METALLURGY CORP accepts no responsibility for and excludes all liability in connection with browsing this website, use of information or downloading any materials from it, including but not limited to any liability for errors, inaccuracies, omissions, or misleading statements. The information at this website might include opinions or views which, unless expressly stated otherwise, are not necessarily those of the 911METALLURGIST.COM or 911METALLURGY CORP or any associated company or any person in relation to whom they would have any liability or responsibility.

peri autocharge mill grinding ball charging system

peri autocharge mill grinding ball charging system

When charging a grinding mill, the standard practice is to dump tons of balls into the mill at once and replace them somewhere between once a shift and once a week. Its an inefficient practice that wastes energy, impacts product particle size distribution and risks breakage of mill linings and grinding media. Fortunately, we can offer you a better option with our Mill Grinding Ball Charging System.

Our PERI AutoCharge Mill Grinding Ball Charging System is designed to provide a controlled continuous supply of balls to maintain consistent ball loading in the grinding mill. Continuously charging grinding balls will allow your mill to maintain a consistent power draft, charge volume, ore feed rate, or consumption average (kg/t). Our system effectively mitigates the number of variables in the control formula of your mill to optimise the performance of your operation.

Worker safety is paramount for any business and our PERI AutoCharge Mill Grinding Ball Charging System will help protect your employers by minimising or eliminating the frequent movement of ball kibbles, drums or sacks by overhead crane. Youll also be able to further improve the safety of your plant by mounting our ball feeding device over a feed conveyor or bucket elevator fed by gravity from ball storage. That way, youll be able to completely avoid the inconvenience and safety issues related to placing overhead crane access and intra-plant transport over equipment and personnel.

Bulk charging will cause your mill to be either overcharged or undercharged with grinding balls, resulting in some combination of poor product sizing, reduced throughput. Our system will ensure your mill is always correctly charged by allowing the ball feed rate to be adjusted to account for changes in operating conditions. Additionally, our system provides you with alternative ball accounting choices to allow you to properly manage your grinding media.

Unlike bulk charging practices, our PERI AutoCharge Mill Grinding Ball Charging System will ensure your mill is always properly charged. That means your mill will be processing more while conserving energy. Youll also be able to better protect your staff and extend the life of your equipment.

The AutoCharge feeder continuously charges balls from the storage bin to the mill. The feed wheel picks up balls in each flight and when they pass the top-centre of the wheel, they roll off into either the counting chutes or the weighing module before dropping directly into the mill feed stream.

The AutoCharge system is primarily suitable for SAG mill balls (100150 mm). As each ball rolls through the counting chute, an electro-mechanical limit switch is activated, signalling the counter. Each count is added to the last, allowing a continual increasing total count of balls to enter the mill over a set time period. The total ball count can be monitored on the control panel at any time. A controller is used to set the ball addition rate, assign ball weight, reset the ball counter, and reset after clearing a ball jam or empty bin alert. Each ball feeder/counter system is designed to accept a narrow range of ball diameters and should not be used to charge balls of mixed sizes.

The AutoCharge systems weight-based counter is suitable for all ball diameters but is particularly applicable to smaller ball sizes (5080 mm), including ball recharge practice involving multiple sizes. As the balls exit the feed wheel, they are collected in an articulating scoop. The loaded scoop is weighed by an array of load cells; the weight is recorded and summed to the previous total; and balls are discharged into themill feed stream.

FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.

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