Wednesday, 5 January 2011

Is media shape important for grinding performance in stirred mills?

This is the question asked by Sinnott et al in a paper is Volume 24 Number 2 of Minerals Engineering

According to the authors, models for understanding the basic concepts of fine grinding and how they apply to the design of stirred media mills have not yet matured. While spherical media in tower mills has previously been studied, real grinding media shape in stirred mills can range from spherical (steel/ceramic balls) to highly non-spherical (sand or slag) resulting in very different media and grinding dynamics. Handling the contact mechanics of non-spherical particles is a challenge for numerical models, and very few studies dealing with non-spherical particle shape exist in the literature.

Discrete Element Method (DEM) simulations of dry media flow in a pilot-scale tower mill were performed for four cases with different shaped grinding media, in order to understand how flow and energy utilisation within a stirred mill depend on media shape. Differences in media transport, stress distribution, energy dissipation, and liner wear were observed in the tower mill for the spherical and non-spherical cases. A significant departure from sphericity of the media leads to strong dilation of the bed, reduced bulk density, and a reduction in active volume and collisional power levels leading to a reduction in power draw for the mill. In addition, highly non-spherical media tend to pack tightly near the mill walls forming a near solid layer around the inside of the mill shell which results in poorer transport and mixing, as well as increased wear rates on the screw impeller. Grinding performance in stirred mills appears to deteriorate strongly when using highly non-spherical media.

Does anyone have any practical experience in this area? It would be interesting to have your comments.

3 comments:

  1. Read the theory and mill results from our Cadia Mine 40 ft SAG mill publications at SAG 2001 and SAG 2006 on Mill Comminution by L. Nordell
    A total of 5 papers describe DEM applications to mills with measured performance gains at Cadia. DEM-Fluid also accurately simulated liner wear and change in power and comminution performance with wear over a 150 day period. We have modeled Vertical mills with success.
    Contact: nordell@conveyor-dynamics.com or website: www.conveyor-dynamics.com

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  2. Media Shape is very important for grinding performance, most of the researches conclude that balls are better than cones. One of the most important variables is the surface area or string generated by the grinding media, in this way balls and cones have different surface area for same diameter, so when performance is evaluated it must be corrected the surface area for each type of media...
    Levi Guzman, Moly-Cop, Peru

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  3. Cylindrical grinding media also known as cylpebs have long been replaced by smaller spherical grinding media , as they have been found to be more efficient.
    Arun Rao, Kumbalgodu Alloy Steel Castings, India

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