Re: Finding Material Properties Without Jenike Shear Tests
A potential source may be AS3774, Table 3.1, "concrete agregate" (against steel, anyhow).
Regards,
Lyle ■
Re: Finding Material Properties Without Jenike Shear Tests
Thanks Lyle,
Coincidentally I have actually been using Table 3.1 in AS3774 already, but it says at the bottom the values are for a polyethylene wall liner. I will use this if I'm unable to find another source (I'll probably need to line my chutes with something anyway for wear resistance, might as well use polyethylene...).
If there is a source out there somewhere for steel chutes that would be teriffic! (and for a rubber belt). Admittedly beggars can't be choosers... ■
Angle Of Wall Friction
A conservative value of wall friction can easily be obtained by a sliding plate test. Just place a sample of the product in a light plastic ring whilst resting on the surface of interest, and slowly tilt the surface until the sample sides down the slope.. A few simple tests with different masses of the product will show any effect of wall cohesion, but slip at a consistent inclination can be taken as a reasonable guide for wall friction with the particualr material/contact surface combination.
These results are usually of the order of 4 -5 degrees greater than values measured with a force guage and a controlled strain mechanism, but the procedure will suffice for chute design, where a margin is needed to allow for possible variations in ambient, product and operating conditions and certainly much more reliable that taking data from a remote, unconnected source. The process will also give you more of a feel for the slip behaviour of the material that any figures. Get practical and not be afraid of getting dirty hands if you want to progress in solids handling. It compements theory. ■
Re: Finding Material Properties Without Jenike Shear Tests
Originally Posted by armstrongg89
Coincidentally I have actually been using Table 3.1 in AS3774 already, but it says at the bottom the values are for a polyethylene wall liner. I will use this if I'm unable to find another source (I'll probably need to line my chutes with something anyway for wear resistance, might as well use polyethylene...).
If there is a source out there somewhere for steel chutes that would be teriffic! (and for a rubber belt). Admittedly beggars can't be choosers...
I believe this is just for coal - brown, lower bound wall friction?
Regards,
Lyle ■
Colin Benjamin
Hi Dan,
We have published papers and will publish further papers based on the work we have done on transfer chute design over the last many years but in summary;
> The flow within transfers is very different to the flow within bins and hoppers and we will argue that inputting such factors such as wall friction into DEM software has no relevance to reality. If you are using DEM software then the only way to accurately calibrate it is have an existing chute operating with similar material and through videos etc. manipulate the software to create a DEM simulation that replicates the existing transfer and then apply this to the new transfer. We have found this for even the most sophisticated of DEM software.
> If you do not have access to an existing operation using similar materials then you need to work through the design process based on first principles. The key material characteristics that you need are ore size distribution, maximum percentage of micro fines, moisture content and moisture content variability and the degree of angulation of the particles (smooth more rounded particles have less surface area and therefore have lower effective friction and therefore flow better, conversely very angulated material will not flow anywhere near as well)
Cheers
Colin Benjamin
Gulf Conveyor Systems Pty Ltd
www.conveyorsystemstechnology.com ■
Re: Finding Material Properties Without Jenike Shear Tests
Thankyou all for your advice,
I don't have access to DEM software, and I am using first principles based on Roberts, Korzen, etc.
I have also been referring to the design manual you helped write Colin, and have found it very useful. I remember reading an article about finding more accurate methods of calculating the wall friction for chutes, based on continuous kinetic flow rather than flow from static conditions to improve this sort of analysis... perhaps it was yours!
As I am unable to do any sort of practical study, my report will be more of an investigation of design techniques including various recommendations as a base for someone needing to design a chute, as opposed to producing a specific, useable solution.
I completely agree that physically measuring things like discharge angles and trajectories, and conducting basic shear tests with the material is the only way to achieve a realisitic design.
Nonetheless, through reading various articles and books I have found the study of bulk materials and flowability quite interesting. This might be a field I could get into when I graduate next semester....
Thanks again for everyone's input,
Dan.
Dan. ■
Colin Benjamin
Hi Dan,
If you are working from first principles the best guide that you can use to assess how the material will flow is doing simple tests that give you an idea how the angle of repose of the material varies as moisture is added/deleted and as the fines ratio varies. This will give you a pretty good idea of the flow angles you need to preserve within the transfer to stop build-up. You can also use these angles to better understand how to slow the material flow down if abrasion is an issue
Cheers
Colin Benjamin
Gulf Conveyor Systems Pty Ltd
www.conveyorsystemstechnology.com ■
Simple Powder Testing
Whereas there is no substitute for thorough testing by an expert, some usful guide information can be provided by simple apparatus and hands-on experience. A collectionof notes on 'The characterisation of bulk materials' is available from lyn@ajax.co.uk. These includes details of relevant features pertaining to flow, together with details of simple and other test methods. I am also putting together 'A paupers powder testing kit' that would be useful for anyone with limited means and is prepared to get their hands dirty. Contact lyn@ajax for details. ■
Finding Material Properties Without Jenike Shear Tests
Hi everyone,
I'm working on my final year Mechanical Engineering major design project. I'm wondering if anyone has a good source for typical wall friction angles and/or internal friction angles for a range of materials??
I'm designing transfer chutes for a concrete treated road base with ≈20% moisture and particle size range of 0.075 - 35mm, bulk density 2000kg/m3.
From trawling through various sources, I've found the (kinematic) effective angle of internal friction to be 30 - 40 degrees for moist concrete aggregates. But I am now looking for an angle of wall friction for:
- between the aggregate and conveyer belt, and
- between the aggregate and mild steel
I know it is unreliable to use external data because flowability is so variable with moisture content and specific properties, etc. However the client is unable to supply a sample (they are based overseas) not to mention testing apparatus are hard to get access to. I need some approximate numbers that I can design from, it is more about the method but I'd rather come up with a realistic design.
Any approximate data or sources to find data would be greatly appreciated...
Dan. ■