In our industry, there are several terms which include the word "density" which can make a considerable difference in the values.

Bulk Density is typically accepted as being a 1 cubic meter container, having the material lossely poured in until full, screeting the top level and weighing the contents. (remember to subtract the weight of the empty container). This value is used for most commercial transactions and USUALLY for sizing of aulilary equipment to handle the material on a volumetric basis.

Aerated Density is the density of the product when subjected to various forms of aeration or fluidization which make it easier to discharge from hoppers, bins and silos. Often, if the product falls by gravity in long vertical chutes it also develops charactreristics of being fluidized. In some cases, product which has gone through bag filling machines or gaylord box filling operations has a lower density when the container is filled and a few moments later, the volume settles and there is space left in the bags. The Aerated Density will be LESS than the Bulk Density. The methodology of handling the product can have an infuence on the degree of Aerated Density variance to the Bulk Density.

Compacted Density will typically be MORE than the Bulk Density and results from material being stored and compressed under its own weight. This is the value typically used for structiral calculations of silos and bins but NOT used for volumetric calculations.

Finally, True Density or Particle Density is the measure of the products density in absence of any voids of air in the interstices between the particles. Assume a container full of water which has a True Density of 1000 Kg/m3 (at standard conditions). This also is referred to as Specific Gravity of 1. If a product has a Specific Gravity of say 0.5, it's True Density, relative to water, is 500 kg/M3. etc.

Depending on how you supplier fills the containers, either a short time delay can be built in to allow the material to settle before the finally "topping off" the containers or the use of low amplitude vibration acan accelerate the drivign off of the excess air enytrained in the material to acheive closer to it's normal bulk density without crossing the line to Compacted Density.

Hope this helps. ■

Jack Hilbert covers most points, the settled state from a loose poured condition being a basic measured value. The value may be expected to vary slightly with the particle size distribution as fines will tend to infill the voids of larger fractions unless separated by segregation. The scale of discrepancy mentioned would suggest that a degree of compaction is applied to attain the higher density figures. This would not seem to be a suitable basis for contract unless the conditions were pre-defined. ■

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