Harvesting System Design and Performance - Engineering and Science of Biomass Feedstock Production and Provision - page 98

handling and shipping. Bale dimensions and bale density are the two important
parameters, and Fig. 5.13 shows different types of bales and their properties.
Duringthe1950sand1960s,smallrectangularbalesweighing20-30 kgwere
popular.However,bythelate1960s,balehandlingbecamethemajorbottleneckand
could not be solved by the simple bale accumulators and sophisticated bale wagons.
The first solution suggested was the densification of the forage into bite-size pack-
ages with characteristics approaching those of a fluid, so that they could be con-
veyed using augers or conveyor belts. The second solution suggested was to make
the bales large enough to justify their individual manipulation with dedicated lifting
equipment. The first concept led to the development of hay cubers, which was aban-
doned due to high energy costs and limited applications. The second concept led to
the development of big balers generating both round and rectangular bales and mak-
ing use of stack wagons.
Small Square Balers
A trailed and PTO-powered baler lifts forage from the windrow through a pickup
unit and conveys it to an auger or feed fork mechanism. The forage is then forced
into a compression chamber (Fig. 5.14 ) where a plunger, driven by a crank arm and
pitman,movesatabout80-100strokesperminute.Thesectionofthecompression
chamberisgenerally36×46cmwithadjustablebalelengthfrom0.60to1.2m.The
smallbalesweighabout20-30 kgwithacorrespondingbulkdensityof120-
170kgm −3 . These balers achieve high-quality levels and work rates that can exceed
10th −1 of hay.
Round Baler
Round balers are of two types, namely, core compacted balers and loose core balers.
The compression chamber has a variable section for the core compacted balers and
a fixed section for the loose core balers. The variable compression chamber guaran-
tees uniform compression of the whole biomass, from core to periphery. The fixed
compression chamber produces bales that are less dense in the center but increas-
ingly dense towards the periphery. The loose core balers facilitate greater air circu-
lation in the central area of the bale facilitating drying and forage fermentation. The
compression chamber in round balers can be constructed in different ways (Fig. 5.15 )
with a variable chamber using belt, bar, and chain components or fixed chamber
relying on belt, roll, bar, and chain components.
Since1980,largeroundbalingsystemsofferthemainadvantageofproducing
weather-resistant bales because the bales can be wrapped with a plastic film
(Fig. 5.16 ). The main components of these large round balers are a fixed-section
compression chamber, presence of a chopper (based on rotor and knives or flails),
and feeding of the chamber from the top (see Fig. 5.16 ). Typical dimensions of the
large round bales are 1.2 × 1.5 m.