As you may know, the larger particles will tend to rill to the outside of the product cone formed from filling. How far the larger particles move depends on the flow rate, material properties, filling velocity, adherence to one stationary loading point, allowing loading point to be directed and or elevated with cone configuraton, or allowing the feed spout to feed with a spreader or other distributor/fitting.

Selection of a best fit, in part, is determined by the degree of segregation and where/if segregation is localized and its details, and how much dust control plays a part.

The size suggests the feed is controlled by some nozzle feed to keep dust under control.

There are many variants that can be explored. More detail will promote a clearer response. ■

There are many mechanisms that cause segregation. Depending on the proportion of the fines content and loading circumstances, the powder state may be significantly dilated and in a weak condition, in which case it is likely to suffer 'impact penetration', where the fines are displaced to the sides and larger particles concentrate in the centre. As with all segregation situations, the system must be considered as a whole because there is no point in avoiding segregation in one location to find it appearing again elsewhere.

There is an assumption that the material being loaded has a homogenous composition but, even if true, the infeed should be examined to see if there is any bias in the cross sectional distribution as may occur from a chute or belt conveyor discharge. Likewise, initial and terminal conditions should be examined in relation to the origin. Consideration of the truck discharge process may highlight further divergence of fractions.

A review may then assess whether to attempt to prevent, mitigate or redress any segregation that occurs during loading. As Lawrence point out, there are many factors to consider and it is not easy to give a general answer without knowing considerably more about the situation. My book, 'User Guide to Segregation' may give a few tips on understanding and dealing with the problem. Otherwise, if it is a serious problem, I suggest that you consult a specialist. ■

It is not clear by what is meant by 'downstream' for the 're-mixing' of particles. Some uncertainty must arise from the limited access to take samples. However, your experience and corrolation of effects with smaller piles should indicate the nature of the segregating process. Assuming that the bulk is cohesive due to the finess of its main components of composition one would expect the dynamic fill conditions to produce a weak, if not fluid, mass and not form a repose pile of sufficient strength on which the larger particles would roll. A dispersed fill is a good start to minimise segregation, but attention to the flow route may also allow the material to enter in a more stable condition. Details of how the truck unloads may also be examined to see if the form of segregation can be compensated by way of controlled discharge. Specialist advice may be needed if the problem cannot be resolved by evaluating your findings and appreciating what action to take. ■

Aren't cohesive & segregation mutually opposed?

Half a percent difference isn't a lot.

What's the gripe; the material itself or the sampling regime? ■

John,

Doesn't particle size play a large part in segregation? Doesn’t moisture play the larger part with cohesion?

Larger particles (> 500um) tend not to have significant cohesion. However, their size distribution and method of handling can lead to unwanted segregation.

Smaller particles (<50 um), with varying degrees of moisture, tend to suffer from various degrees of cohesion and adhesion. Isn’t this highly dependent of wetting and liquid-bridge capillary attraction as well as other physical phenomenon?

Particles smaller than 1 um can also come under other influences which tend to reside within atomic attraction, electrostatic interaction classes, et al. Sometimes this also is resolved into a cohesion or agglomeration like observable response. ■

Of course, there is the time dependent fluidization behavior of superfine particles. Len Bates points our the significant difference in segregation behavior with superfine particle sets in contrast to larger particles.

Then there are packing and consolidation behavioral changes to the degree of segregation which may also be relaxation time and or viscous rate dependent.

In the fine particle domain, rheology measurements and characterization properties may assist in classify performance. ■