Thread: Time Consolidation

Definition:

Some bulk solids increase in strength if they are stored for a period of time at rest under a compressive stress (e.g. in a silo or an IBC). This effect is called time consolidation or caking.

Question:
Is there any list of time consolidated materials? I mean which bulk materials tend to time consolidation? powders? stones? lump or fine materials?

In summary: Not that I am aware of [though look forward to understanding otherwise].

In detail:
1. Tunra state that most materials are affected, and
Ref: Tunra Bulks Solids Course - Storage, Flow & Conveying Notes
2. Schulze provides a list of mechanisms that contribute to time consolidation.
Ref: Schulze, D, 2008, Powders and Bulk Solids : Behaviour, characterization, storage and Flow, Springer

Regards,
Lyle

it is not so much the name of material that time consolidates as its condition. Most fine powders will gain strength as they settle and the particles become closer to develop molecular forces. Soft particles may fuse or develop flats at contact points to resist shear. Moisture bonds and caking develop strength so it's a question of looking at the possible mechanisms appropriate to the material, its condition and ambient influences so, like 'flowability', data banks are not the answer.

..when working in Zambia I observed a cubic mass of consolidated material, about 30 tonnes, resting in the roof trusses in the TORCO plant. It had been left there because it was in a disused building and the folk thereabouts needed the bin steel for another job. The block had been there for over 10 years, undisturbed. Moisture content played its part of course, but the location, high in the building in the tropics, did not help either. I guess there was a baking effect which took place over a relatively short time. This probably caked over the walls and the outlet and then the whole block became free to solidify. I doubt anybody went aloft to examine if the internals were solid.
As Lyle and Lyn imply there are several factors involved. If a bin is ever used the underlying implication is that material is going to become stationary regardless of the desired flow conditions. Stationary material ignores the flow conditions: it is not flowing. As Lyn says ".. it's a question of looking at the possible mechanisms appropriate to the material, its condition and ambient influences." Those questions can be very difficult to answer.

I have a second generation question. Has discrete element analysis reached the stage were it can WARN about the onset of INDISCRETION: ie. is there a limiting case available already or is there still a long way to go. Would it be worth finding out?

Modelling offers huge prospects for flow potential but has a limited contribution to predict time consolidation because thermal, chemical and other effects may be involved. Possible sensitivity to time, moisture, temperature pressure product age and particle size can effect whether consolidation effects occur, so the behaviour of a product may vary according to circumstances.

One approach to time consolidation is to minimise the time and the quantity stored. This will not eliminate the problem although it will improve the situation. It is also easier said than done.
There can never be a database to rely on. A glance at the leaders board rolling above the screen indicates just how many companies are involved in making highly admirable attempt to alleviate the situation.
The maxim should be 'What can stick will stick.' Water is usually hiding somewhere in the woodpile.

Originally Posted by johngateley

Water is usually hiding somewhere in the woodpile.

Haha, ain't that the truth! I wonder if anyone has DEM'd rogue water

Water is an indiscretion in DRY BULK HANDLING and complicates the subject into a 3 phase situation.
Adherent, otherwise/intended, discrete elements lose their very definition as they agglomerate with moisture.
Because the water/moisture is fluid, Ho Ho Ho, it can travel at will through the other two phases and this must render an accurate study virtually impossible.
Impressive animations of DEM seem to have ignored this situation and although the software does have some sales merit: in practice it is always going to be a gamble.
The development costs involved in upgrading 2 phase flow into 3 phases must be prohibitive and coupled with the prevailing use of existing DEM the improvement seems destined to be ignored.