Fibre Handling
Density is a freight decision. The question is whether the container cubes out or weighs out first.
— kg/m3
Mass over the pressed volume
Bales are not rectangular prisms. They bulge between the straps, the corners are rounded and the height relaxes measurably in the hours after the press opens, so a density computed from nominal dimensions is always a little optimistic against one computed from displaced volume - which is what the freight forwarder effectively pays for. Where the two matter, measure the bale after relaxation. The bales-per-container figure is a pure volume ratio and takes no account of stacking pattern, door clearance, dunnage or the fact that bales do not tessellate perfectly; a practical load runs a few percent below it, and the honest use of the number is to compare densities rather than to book a shipment. Read the last two lines together: where payload at full volumetric fill exceeds the container limit, the container weighs out and additional density is worthless, and where it falls short the container cubes out and density is worth money all the way up. The press force here is derived from a declared compaction pressure and describes the force at final density only; the pressure needed rises very steeply through the last part of the stroke, so a press sized on the mean pressure will stall short of target.
Bale Density, Press Duty & Container Fill — free, with the formula and a worked example, at Textile School.