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Marked Ball Wear Test (10 replies)
Good question, but there needs to be clear determination firstly, of what you currently use: (two random samples).
- Physical properties.
- Chemical check.
Then have the same done with, again two randomly selected samples of a proposed me
Unfortunately most operations are limited in selection of grinding media to one or two suppliers due to freight charges. Work with them to develop a media that fits your need that can be supplied at a reasonable cost. Conversely you are sometimes faced with a supplier who will say this is what we have, take it or leave it. That is when you have to go through the time and effort to develop a new source, cost be damned. You have a better chance to get a good fit media if you are a larger operation. This is particularly true in North America and Australia. Not so much in Africa. Look at the mill rejects for split balls and odd shapes. This will go a long way to determine a solution if needed.
Totally agree with the problem of transport costs adding up on the landed price. However today I do believe that balls are known to be of greatly varying qualities. Performance gaps are very considerable impacting on the media cost per ton of ore milled. I have seen small operations get less than good media (even perhaps, possible factory rejects) - but a good reputation for quality (in all consumable mine site products) is hard to earn and so easily destroyed. We have supplied as little as 40,000lbs per month to small operations; I personally like medium size customers as you have the best chance to sit across the table with a Mill Manager to form a partnership. To get the best adjustments to media design a partnership is perfect - data and design information going two ways...
Our favourite scenario is to have an enquiry from a mine site with a problem - breakage, throughput, grind, strategic supply, technical development - makes our people very excited!
The problem with marked ball tests is that if the metallurgy of the marked balls is significantly different from the main charge of media, there are galvanic reactions going on that can make the balls look better or worse than a mill full of those balls exclusively would look. We did marked ball tests on high chrome balls in mills with a forged high carbon ball charge. The galvanic reaction tended to protect the chrome balls at the expense of the forged balls. There weren't enough chrome balls in the charge to significantly affect the forged ball wear rate.
Once we converted a mill to chrome balls we found that the consumption rate was significantly higher than the marked ball tests predicted. The reason was that now there were no forged balls to act as sacrificial anodes. We had to re-evaluate the decision to use chrome balls and wound up going back to forged balls on a cost per ton ground basis.
In short, marked ball tests may point towards a benefit, but the real test is when the mill is converted to the new media.
Understand this well - we still see Chrome media and forged carbon steel balls together in the same mill for that very reason. Production testing is the really most accurate way.
There has to be a better way to screen unsuitable media. I am not questioning value of the full scale trials here. Full scale trials can be costly if, particularly, they are failure. And what are the chances of success? We cannot assume success before full scale trial. We need to be able to screen unsuitable grinding media from going to full scale trial. How long do you think a full scale trial should last? Ideally all of the host media should be replaced with the trial media and that will take time. In the meantime ore type fed into the mill can also change. There has to be some homework done before committing to a full scale trial.
It does take as long as 10 months to fully purge some mills of the resident media. We actually do that calculation before a test to ensure that enough media is supplied to that end. Plus enough additional media to get the final trending of the data. However small mills, small ball charges and SAG mills can take a little as 3 weeks. Ore variations are also accounted for in the pre test collection of information so that grind, throughput and ore variations are fully accounted. Ideally the test mill will have at least one "sister" mill which can be run as a benchmark based on historical data information. Some sites have mills that in almost all cases mirror image other mills on that sane circuit which is ideal.
The discussion so far just shows, no grinding media trial should be taken lightly and some serious homework needs to be done before, during and after the trial.
Yes, so much effort and expense to do this work - the cheap and easy part is the final data analysis.
See page 101 of https://books.google.ca/books?id=sFhUPTaREnsC&lpg=PA103&ots=XC4BoEG8K2&dq=Marked%20Ball%20Wear%20Test&pg=PA92#v=onepage&q=Marked%20Ball%20Wear%20Test&f=false is has a section on marked-ball wear tests in ball mill.
As a grinding media designer/supplier SGI considers that an MBT is not the best method for media selection.Do marked ball tests help determine if you have selected the best media for you mill?