Re: Impingement Inquisition
Hi John,
The work we have been doing and focusing on over the last many years on chute design is all about granular flow and how particles interact. The paper I published in the technical articles in September and supported by my colleague Peter Donecker, will be the first of a few papers that we will publish over the next 12 months that explains the work we have done. Collisions with the liners of a chute or a deflector are to be avoided. We would describe a collision as any impingement where the angle of contact exceeds 20 degrees after due allowance for the angulation of the particles (in other words if you have larger rocks you need the impingement angle to be a lot less to allow for this) as we find once you have exceeded such an angle you rapidly start losing flow control. If this is unavoidable then creating a flow ledge that captures ore is the answer as the collision point will always be an area of very rapid liner wear regardless of the quality of the liner. In all the chutes we design to day we are endeavouring to create ore on ore flow. This is not always possible so we then revert to the above however we never design transfers unless it is a rock box style where the angles of interception of the ore is above 20 degrees. We will go further in subsequent papers as we are now pretty certain that most of the basic design tenets used over many years for transfer chutes have a flawed base and this has major ramifications for all those using DEM modelling. We also suspect that these flaws extend to the design of bins and hoppers as these tenets were initially developed for bins and hoppers but we have had our hands full on transfer chutes and have not gone there yet and possibly once we fully publish won't, letting others to explore this issue.
Granular flow, which is fundamental to materials handling is an extremely complex science. I think in our eagerness to solve problems we have extended the work done on such simple granular materials as grains and sized washed coal in the 1960-80 period to create mathematical flow models that seemed to work well on these materials and then extended them to more complex materials and then continued to believe that by "fine tuning" the mathematics we would eventually get it right for more complex granular materials. Based on our work we would argue the original models were flawed and that all this "fine tuning" has over complicated and misled designers of transfer chutes for a long time. Our confidence stems from our ability to design transfers for the most complex materials and not only very accurately predict the performance of the transfer chute but to deliver an almost maintenance free design that is extremely reliable.
There are some recent and excellent books on granular flow that you might find worth reading
Cheers
Colin Benjamin
Gulf Conveyor Systems Pty Ltd
www.conveyorsystemstechnology.com ■
Diverter Gates
So I guess as long as our pantlegs only divert material at an angle of less than 20 deg wrt the material flow it is not a collision but a redirection or impingement. In the end it amounts to a lot of height and structural steel. The correct design always seems to require a little more height than we would like. No one installation is ever the same and if we wanted the material to go in a straight direction we would just make a longer conveyor. You are right, redundancy and limited storage options due to capital cost create situations where designers need to be very creative and owners ask us to send material streams in many different directions.
In my opinion if you want to redirect material you need to "bang against something" your words not mine, unless it is less than 20 degrees wrt material flow then I am not sure you can call it banging anymore.
Cheers ■
Re: Impingement Inquisition
Liam,
You do not necessarily need a lot of height. It totally depends on the belt speed. Generally even for the worst case applications 4 metres belt to belt height is sufficient for simple transfers. It can be less for lower belt speeds. More complex chutes can require more height. As far as needing longer belts this also is very modest, possibly 1-3 metres at worst and anyway you can move the tail pulley forward if it is a new installation. Most of our work is on retro-fit applications where the geometry is fixed and so far we may have had to be pretty imaginative at times but we have always been able to come up with a solution.
Cheers
Colin Benjamin
Gulf Conveyor Systems Pty Ltd
www.conveyorsystemstechnology.com ■
Impingement Inquisition
Quite recently I have been castigated for suggesting that material collides with the chute walls during material transfers. However I was quoting fundamental situations from an earlier age. Times appear to have changed and I/we must accept that material impingement is considered as belonging to those dark ages. OK, progress gets to us all.
Now can someone point me in a direction where I can develop a chute which diverts material from one outlet to another without involving material contact. I have accomplished this when disposing of tioxide wastes: but once only and for different flow rates. For most other projects I have had to rely on either traveling trouser legs or good old flap gates with the associated impingement. A solitary in line transfer was a rare luxury for me and I was invariably confronted with 2,3 or 4 outlets from the same discharge. I developed an excellent flap gate after many prototypes: but it still had to get clouted.
I imagine most participants in this particular forum have been in the same situation and I ask their methods to divert material flow without banging against something. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com