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Crusher Type and Product Shape (12 replies)
Try Chapter VI "Attributes of Comminution" in A M Gaudin "Principles of Mineral Dressing" First Edition (1939) page 124. "The shape of crushed or ground particles varies but little with size and the finest particles that can be examined under the microscope are as angular as any". Note though, that the separation device after the crusher or grinder may affect the shape of the product (screen or cyclone, for example).
One obvious exception I must mention is that of malleable materials such as gold (in an old-fashioned stamp mill, for example). In this case the shape of the particle will be distorted by the 'crushing' process. But, in general, (and I think that this is the point of the question), we see little change in particle shape parameters by comminution processes (such as micronization in the pharmaceutical industry). Materials split along cleavage planes and the basic crystal shape is preserved in size reduction. Gaudin knew this well in 1939.
What I am trying to figure out is which crusher would give a definite type of particle (cubical, flaky, etc), because this might help me to take a decision about which crusher to pick in a determined process (metallurgical processes preferably).
Unfortunately it doesn't work like that; the only way to get (approximately) cubic particles out is to start with a material with cubic structure - for example NaCl or perhaps iron pyrites. Mica or talc would produce flaky particles on comminution.
You would be able to make a lot of money if you could arrange a top-down process to produce particles of a defined shape.
Depending on the comminution mechanism, would it be different if I start with a cubical particle and I want a better shaped flaky particle, so it is more suitable to the downstream process?
All you could do is put the processed material through, say, a screen and this would select somewhat on the basis shape (also a cyclone where there's also a separation based on size, shape, and density). The shape of the starting material governs the shape of the crushed material- back to Gaudin again.
To some extent, one can effect on the particle shape with crushing. I take an example. Flaky chippings (do I use the right word?) for roofing felt is produced from shale type of rock material. If you crush this type of rock with a cone crusher, the shape of the particles is more “cubical” compared if you do the crushing with a hammer (impact) crusher. Impact crusher obviously produces better chips for the said purpose. For more amorphic or non–oriented rocks type of crushing obviously is of lesser importance.
HPGR crushers are said to produce fragmentation along grain borders. To produce cubical particles is very difficult unless impossible. (Of course, you can find one almost cubical piece from 10 000 pieces of crushed rock.)
To summarize; if you want a certain type of crushed product, do tests with different crusher types / crushing - screening flow sheets in lab scale and examine / compare the differences.
Speak to Magnus Evertsson from Chalmers University. They have conducted lab-scale as well as industrial tests to improve the yield of crusher product shape. They have developed control methods to produce particular shaped product based on the CSS, throw and compression ratio. There are opportunities in the down-stream process if you can bias the crushing to produce particular product shape. Read "The Effect of Blends of Rock Shapes in AG / SAG Mills and Comminution Circuits" - SAG 2011
Yes, I agree there can be some selectivity for shape especially if a shape specific separation technique is utilized after the comminution stage. However, I would think that such selectivity would be small - although I'd love to be proved incorrect! The example of shale is similar to that of mica and talc and shows the validity of Gaudin's comment in 1939 - again we're starting with a material that cleaves along a preferred axis or grain boundary - exactly as states. The other roofing example is roof tiles (shingles in the US) made of slate - these are made by a size reduction process in the broadest sense.
So basically the shape is ore orientated not crusher orientated. The final product is dependent on what type of ore it is not the crusher type.
A high speed high throw crusher, like the Weir Enduron cone is used in the aggregate industry for cubic shape. If you requirea finer product size than the Enduron VSI could be what you’re looking for.How many tons per hour do you need to process?
My experience with crushers!
A. Primary crushing form 60'' boulder to 300mm. There are different types of primary crushers.
Gyratory
Jaw
Hammer mills.
Flaky ore: Example Lime stone
Gy Cr and Jaw will not work. You need hammer mill. Product will be flky lime stone.Normal dry ore: Both Gy Cr and jaw are good.
B. Secondary crushing:
Flaky ore: same as above
Normal ore:
Dry: Cone and impactor is good.
Wet ore: Flush and impactor are good.
C. Tertiary crusher:
Dry ore: Cone
Wet ore: Flush, or impactor.
NEW GREEN TECHNOLOGIES:
HPGR -- Replaces teritiary crushing, but product is much better than cone. It enhances cleavage, fractures which help in down line operation.
I'd like to know what effect the type of crusher used has on the particle shapes it produces. I would appreciate your answers based in knowledge and experience you have.