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SAG Mill Liner Peening (11 replies)

Ace Levy
8 months ago
Ace Levy 8 months ago

What are the chances to get peening in liners after a grind-out? Is it common to see the whole mill liners under these conditions when a grind-out occurs or is it correct to deduce these ball-hitting marks come from operational conditions?

8 months ago
OberstGruppen 8 months ago

It mainly caused by operational conditions but the peening getting worse when you have the mill running at empty condition (underload). Nowadays most of the liners installed with anti-peening effect that can minimize the issues.

John Koenig
8 months ago
John Koenig 8 months ago

You should be careful every time you make a grind out. Reduce your mill speed as much as you can in order to prevent liners damages.

8 months ago
Obergruppenfuhrer 8 months ago

I agree with you, in a gear less mill reduce the speed as much you can. In the case of fixed speed mill the best option is use a model or just inspections.

Helena Russell
8 months ago
Helena Russell 8 months ago

Ball hitting the liners is an event that can happen both in normal operation and during grind outs (run the mill without feed).

Probability of this event happening is as follows:

< 5% for a mill run "Perfectly" between 10 and 20 % for normal operation
> 20% for a mill run poorly
> 90% during grind-outs.

Observing the density of impact marks per given area, you could figure out how it happens. You may also observe variation of intensity along the mill shell, usually less at F/E and more at D/E, this is a different story.

To reduce the chance of this event at grind-out stage, you would like to reduce mill sped and run time, to minimum, as advised above.

Carl Jenkins
8 months ago
Carl Jenkins 8 months ago

Peening is also related to the metallurgy of the liner material - a more ductile liner will peen more easily, a more brittle liner will be more likely to shatter or break.

Work hardening of the liners at the end of their service life can make a ductile liner more brittle. Unless the liners are very ductile to start with, most peening would be the result of operations and their normal wear life.

I agree with all the above that when grinding out, reduce mill speed (if possible) and grind out time. You may also consider increasing water addition to compensate for no fresh ore in the mill.

8 months ago
Gruppen 8 months ago

You can reduce peening by better liner designs, without loss of wear life. By example, we designed a set of liners that lasted for many years without peening. Then client changed filling volume and increased ball ratio that now shows high peening action. We have simulated the events and see the new kidney action, throws steel balls farther onto bare liners. In theory, this can be improved back to no-peening condition. The change in kidney volume has also exacerbated end cone lifter wear, which will be studied together will new mill geometry.

A short grind-out period will do some damage, but, I doubt this will cause substantial peening. We can quantify the degree of impact energy transfer from normal operation and from grind-out by totalizing impact kinetic energy by ball intensity and frequency using our DEM code ROCKY.

Dizzy Flores
8 months ago
Dizzy Flores 8 months ago

Grind outs should be short, slow (if you have variable speed) but extremely dangerous to the money you have invested in grinding media. As for the peening, sure there is a higher possibility if there is less ore in the mill but liners and lifters are not greatly affected as they are somewhat impact injury designed. Grind outs should be only considered if very necessary not just a scheduled happening.

8 months ago
Amar 8 months ago

Thank you all for your insightful comments and contributions. It has been helpful to me as a non-metallurgical person involved in mill maintenance.

Dizzy Flores
8 months ago
Dizzy Flores 8 months ago

I do keep in contact with mill maintenance guys regularly. After all you are the first line of information when it comes to visual inspections of the ball charge.

It is a totally useful experience to take high resolution digital images of the ball charge, then inch the mill and take a few more.

The data in these images is shape, size seasoning of the charge. Breakage can also be a worthy observation. Take these images and pass them to the metallurgist - they will be grateful to have this in hand for assessments. Frankly we do encourage all sites to do this and create a date folder of images, as all media designers will be very interested in ball charge appearance history. This is one of the best tools that can be used in new media tasting - the before and after images.

8 months ago
Amar 8 months ago

Can you help me with a procedure on how to do this media testing? Is there a website that I can look up for this procedure?

Dizzy Flores
8 months ago
Dizzy Flores 8 months ago

As with everything, we continually learn how to improve such procedures such as these - listed below are our current and well considered steps with explanations of why each step is made.

[In priority of steps in sequence]

•Request a blank data sheet for the metallurgists to complete. (This is a two page document that pin points a single spot in time that covers the important variables making it site specific. Data such as mill dimensions, mill speed, feed material size/hardness, throughput, discharge sizes at both SAG and ball mills, current ball sizes and their hardness ratings in both shell and center if available).

•Discuss internally where your operations people want to go. (is it a case of media cost reduction, higher throughput, finer grind at average discharge, if it is grind - where is the point of particle size that is clearly over grinding).

•Sit across the table with the ball designers/suppliers to clearly determine what is possible from your wish list. (Ball suppliers need to be accountable regarding what improvements are realistically possible and what protection they can offer to take out any downside risk out of a trial).

•A mutual plan is proposed and discussed, targeting the priorities of the operations management. This plan must cover the calculation of the purging period required to fully replace the ball charge with the new selected media, this then assigns the length of the test for final comparative analysis. (There is no point running a test that does not have a clear upside in processing costs or is not targeting what the customer wants to happen). A test start date is mutually agreed and a high definition image is taken of the ball charge.

•Run the test, adding the new media to the charge. (Suppliers at this time should advise if they predict media reduction, the quantity and regularity of media additions to avoid ball charge creep).

•The assessment. Revisit the original data to compare performances over every data point. Take the second high definition image of the ball charge and compare this with the first image taken before test start-up.

Point 6 is the whole point of the exercise. Look and evaluate data differences. Study the two images of the ball charge - is the media still maintaining shape, is there any sign of breakage, is there a well-seasoned ball charge being formed.

Sometimes I have asked the stupid question about what a Processing Manager wants; "is it throughput? Is it grind improvement? is it steel media savings?" The question is stupid as all Processing Manager always reply with, "all of the above". This is why the understanding of operational priorities must be known - frankly, this is really where the test begins. Knowing what you have and where you want to go is the reasoning for what is possible.

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