SAG Mill Grinding Media Bunker Slot Design

Posted in: , on 22. Dec. 2011 - 11:20

SAG Mill grinding media bunker slot design problem

Hi All,

I am currently designing a concrete bunker to feed a media addition unit. The bunker will hold approx 100T of grinding media and will be sloped towards a slot in the end wall leading to a chute feeding the media addition unit. The grinding media will be 125mm spherical media.

My concern is the design of the slot to ensure that the balls do not lock and that flow through the slot remains free.

I have been advised that a width to diameter ratio of 6:1 is advisable but have now been told by the same advisor that this ratio should apply to height of the slot as well, which would make the slot huge (and no longer a slot but a large square hole in the wall). The giver of the advice tells me that this is a very tricky problem and that my current design of 900mm wide by 200mm high is 'brave' given that this won't be tested and modelled before. The giver of the advice has a reputation for pointing out problems but not following with any solutions so I have to consider the validity of the advice.

My feeling is that the lack of any such issues or design advice during my extensive internet searches on the problem tells me that this isn't a great issue in the field but having said that, I would like to find some solid design advice/information to back up my initial design ideas.

I am struggling to find any design criteria for spherical particles. There is plenty of information on the design of transfer chutes for ore flow but I can't find anything for spherical particles of this sort of size. I would be grateful if anyone can point me in the direction of any books or online resource dealing with the subject.

Thank you,


Re: Sag Mill Grinding Media Bunker Slot Design Problem

Posted on 1. Dec. 2011 - 08:25

Old rule of thumb for chute design, opening size in both directions must be 3 times largest particle size in order to avoid stable arches from forming. This has nothing to do with getting it to start flowing.

Rocky Dem

Posted on 23. Dec. 2011 - 07:53

We offer to test the mathematical efficacy with our 3-D sphereical DEM code ROCKY. You provide the details to test and we will run the analysis. No charge.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450