Sometimes the logistics processes demand bulk packaging for some hard-to-flow products.
Each case can be unique but we have to pay attention to some specific things that will allow us to plan ahead and make the shipping of hard-to-flow products less troublesome.
There is one important thing to define at the beginning, that is:

How to define a hard-to-flow product

The first and unquestionable way is through practice.

If you know the product because you have already dealt with it, then you can say whether you have previously had difficulties accommodating the product on the way in or discharging the product on the way out.

But this is not that simple because, sometimes, in more complex supply chains, parts of the chain deal with products that they have never had contact with previously.

Being the one who loads the hard-to-flow commodity or unload it, will not make things easier.
So, we have some simple rules of thumbs to follow and approximately define if the product is hard-to-flow or not.

The first one is the relationship between the angle of repose and bulk density.

For the lower bulk density products, if the angle of repose is too high, this means that the product is most likely a hard-to-flow bulk solid.

In order to have a high angle of repose with a low density, either the particle form makes it stand higher or there are cohesion forces between the particles that keep them from falling. Both options result in a hard-to-flow bulk solid material.

Most of the hard-to-flow bulk solid materials have angles of repose higher than 45 degrees but this is not a rule. There are materials that repose in angles as low as 30 to 35 degrees.

We have a simple table below with some data that we developed during research and development activities. We share it with you here so that you can see how those parameters are related.

All materials presented in the following table are considered hard-to-flow:

MaterialDensity (lb/ft3)Density (lb/ft3)Density (kg/m3)Density (kg/m3)Repose Angle
alfalfa, meal1422224,26352,4145+
asbestos, shredded2025320,37400,4645
ashes, coal, -1, dry3540560,65640,7445
ashes, coal, -3, wet4550720,83800,9345
barium carbonate721.153,3345
bark, wood, refuse1020160,19320,3745
beets, whole48768,8950
benzene, hexachloride56897,0445+
brewers grain, spent, dry2530400,46480,5645
bronze chips, dry3050480,56800,9344-57
cast iron chips902001.441,673.203,7045
cement, Portland, packed72991.153,331.585,83varies
chalk, 100 mesh65751.041,201.201,3945
coal, bituminous, -50 mesh5054800,93865,0045
cocoa, powdered3035480,56560,6545
coconut, shredded2025320,37400,4645 .+
cottonseed hulls12192,2245
earth, clay and mud, wet1001101.601,851.762.0445
flour, wheat3540560,65640,7445
garbage, average3050480,53800,9335
grain, distillery, spent, wet4060640,74961,1145
grain, wheat flour3540560,65640,7445
hops, spent, wet5055800,93881,0245
iron oxide pigment25400,46up to 40
lead sulfate1842.947,4045
magnesium sulfate4050640,74800,9330-44
milk, dried, powder36576,6745
oil cake4850768,89800,9345
phosphate, ground, triple super, fertilizer5055368,43800,9345
rubber, scrap2350368,43800,9335+
silica, flour65801.041,201.281,4845
sodium sulfite961.537,7845
sugar cane, knifed1518240,28288,3345
tobacco, scraps1525240,28400,4645
tobacco, stems15240,2845
wood chips, heavy fir25400,4645
wood chips, hogged fuel1525240,28400,4645
zinc oxide, light1015160,19240,2845

There aren’t any graphs, theories or equations available yet to relate those two parameters since the study of hard-to-flow bulk solids is somewhat new.
All that we can say is to, first, be alert with products that have high angles of repose.
Secondly, look out for high angles of repose plus low density.

The table above makes it is easy to pick out some high density products.

What is the simplest solution, though?

All we are discussing in this article is how to transport hard-to-flow products using bulk container liners. The traditional solutions are to increase the angles (loading and unloading) or use fluidizing liners.

Increasing the unloading angle can be very dangerous for the container because once the hard-to-flow product is packed inside the container, it forms a vacuum on the way out to a point that permanently damages the container.

container hard-to-flow

On the other hand, from our experience, the easiest way to load or unload a hard-to-flow bulk solid material is by using fluidizing liners.

Fluidizing liners can reduce the angle of repose up to two thirds of the original angle, making the whole operation a lot smoother, so, a lot safer and faster.

Our fluidizing system also helps during the loading process, making it faster and better distributed, reducing the loading costs and increasing the container’s capacity.

Need help with hard-to-flow commodities?

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Posted by Team BULK FLOW

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