Highly compressed bales have a number of advantages:—they provide compact storage and thus save space; they have better cohesion and are less prone to damage in handling. In the case of bales of silage and similar fodder, because the dense bale structure is less permeable to air than a conventional bale structure, the contents of the bale are less prone to oxidisation and to drying out than in a conventional bale.
In the case of baled silage, the reduced air permeability provided by a highly compressed bale structure is especially valuable because it is important that silage should be stored under anaerobic conditions, because silage is preserved by the action of anaerobic bacteria.
Highly compressed silage bales have the further advantage that, for a given weight of silage, a highly compressed bale gives a much smaller surface area to be sealed. It will be appreciated that silage must be well sealed from the air (ideally, completely sealed from the air) for optimum anaerobic digestion and good storage characteristics. The density of the bale depends upon the compaction pressure and the compaction time. Obviously, it is advantageous in a majority of situations to produce the bales as rapidly as possible, and the time taken to achieve a given bulk density can be reduced by using an increased compaction pressure. However, many materials have some elasticity, and therefore have hysteresis losses when compacted; to reduce such losses, it is necessary to use a lower compaction pressure for a longer time.
It follows that, to optimise the efficiency of the compaction process, it is necessary to be able to adjust compaction pressures and compaction times to obtain rapid compaction but minimize hysteresis losses; these factors will vary according to the materials being compressed.
A further factor which must be taken into account is the size of the compaction equipment:—while size seldom is critical for stationary equipment, it is important that mobile equipment is not too large, since overlong equipment is very difficult to move safely.