Harvesting System Design and Performance - Engineering and Science of Biomass Feedstock Production and Provision - page 101

Fig. 5.16 ( a ) Round baler specifically designed for bales to be wrapped; ( b ) a wrapping machine
in operation. ( a ) Shows presence of a dual chopper and feeding of the chamber from the top.
Adapted from [ 21 ]

Large Square Baler

Rectangular balers offer better performance than round balers because they can con-
tinue to operate when releasing a bale compared to the round balers which stop when
releasing the bale. In addition, square bales are convenient to stack and transport.
The large square bale size and density (see Fig. 5.13 ) are optimized for transport.
Typicalbalesizeisabout0.9×1.2×2.4m,andbulkdensityis150-230kgm −3 . Like
round balers, rectangular balers are also towed by the tractor. A pickup head gathers
windrowedbiomassandfeedsittoachopperunit.Well-conditionedwindrowsare
smaller and easier to pick up [ 2 ]. Figure 5.17 shows a well-conditioned and a poorly
conditioned windrow. The poorly conditioned windrow on the left was difficult to
pick up compared to the well-conditioned windrow on the right [ 19 ]. The chopper
unit is equipped with crop processing knives to reduce the size of the material being
baled. In modern large square balers, biomass from the pickup is first gathered in a
pre-compression chamber. It accumulates to a designated pressure before being
pushed into the bale chamber by an electronically triggered stuffer fork (Fig. 5.18 ).
Optimal baler throughput is obtained when enough hay is entering the chamber to
produce around one stuffer stroke for each stroke of the main plunger. The baler's
monitor indicates the ratio of stuffer to plunger strokes so that the operator can main-
tain optimal performance. The re-expansion of hay in the bale chamber is prevented
by fixed wedges and spring-loaded dogs. Square balers maintain the structure of
each bale by wrapping it with twine which must be cut and knotted in each bale.

5.3.4.2 Stack Wagons

Stack wagons consist of a rectangular compression chamber, with vertical sheet
metal side walls, and a mobile canopy on top which acts as a compression element.
Typically, a flail-type pickup harvests the crop which is conveyed into the chamber
bypneumaticmeans.Thestacksareverylarge(1-6 t),andtheworkratesvaryup
to10-15th −1 . Figure 5.19 shows a self-loading wagon.