Grinding & Classification Circuits

Grinding & Classification Circuits 2017-04-04T06:57:16+00:00
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What make a Quality Grinding Media (1 reply)

Carl Jenkins
2 years ago
Carl Jenkins 2 years ago

How to define Quality of Grinding Media?

Grinding media used in SAG Mills are subjected to strong abrasion and impact. They lose mass both in a continuous microscopic abrasive process and through discrete fracture of pieces that may range from a thin cell to the ball divided in two halves. From a user point of view, the most common measurements to check quality are mass, hardness and surface defects. Metallographical examination or classical mechanical tests do not add useful additional information. Fracture is still a highly unexplored topic. The Repeated Impact Ball Tower first developed at the Bureau of Mines for small sizes and later applied by us to large 5" and 5.5" balls is now used by many producers as a quality control tool, but there is no standard.

I would like to see opinions about how to check that a given batch of balls will have an appropriate in-mill performance. Which factors do control in-mill performance? What to measure? How to measure?

Marshal Dienes
2 years ago
Marshal Dienes 2 years ago

Many of our customers write their own specification for ball chemistry and physical characteristics. Some also test every batch to ensure compliance with what specification is ordered. Getting what you want and what you pay for is of course very important.

What is equally important, is knowing what is now available in media - especially SAG media.

Recent technologies have enabled some ball makers to design with new alloys and adjusted heat treatments to, in most circumstances, overcome the major enemy - IMPACT BREAKAGE.

After all, what is wear rate worries, if you have high breakage?

I wont use the forum as a sales platform, but I will outline some characteristics that are very important in what the general industry considers "essential" for evaluation.

I will keep the language simple for fear of the message being even slightly, misunderstood:

1. Hardness and wear rates are not in a full lineal relationship. "Toughness" has a greater effect on wear rates = fine grain structure.

2. Structural integrity (stability) through a consistent fine grain structure of uniform size.

3. Heat treatment controls to ensure that the alloy ingredient benefits are fully utilized.

4. That there is little or no residual stress remaining after the forging/forming process.

5. Through hardness, shell to center, for even wear and maintaining sphericity.

6. Drop testing (2,000-3,000 cycles) to ensure breakage is not going to be an issue.

All of these tests can be done in a laboratory BEFORE deciding that this product is good enough to load into your expensive equipment. Any of the good manufacturers will agree and possibly add a couple more lab tests before moving to a production trial.

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