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The basecutters sever the cane stalk at or below ground level and assist in feeding the stalk, butt-first,
into the feed train. The basecutting process interacts with the soil, the stool and the harvested stalk.
The level of damage to the stool associated with the cutting process is an important performance
criteria as this impacts on yield of the ratoon crop.
Much research has been undertaken on the relationships between various basecutter parameters and
the severity of damage and failure modes of stalks during the basecutting process. Henkel et al.
(1979), Ridge and Dick (1988), Garson (1992), Ridge and Linedale (1997), Kroes and Harris (1994),
Kroes (1997), DaCuhna Mello and Harris (2000), Crook et al. (1999) and Davis and Norris (2001)
have identified cultural, operational and design features as affecting soil levels in the cane supply and
basecutter interaction with the crop in an attempt to quantify the level of damage and juice loss
occurring in the base cutting process.
On the majority of industry-standard harvesters, the basecutters rotate at a fixed rotational speed.
The forward speed at which modern harvesters are able to harvest current crop sizes have increased
concurrently with the increase in available engine power. A typical 100 tonne/ha standing crop
would be harvested at about 9 km/hr.
For a given ground speed, an overly high basecutter rpm will result in stool being cut by the blades
multiple times. When the basecutter rotational speed is too slow for the forward speed, then a tearing
cut results and stalks are torn off by the disc before a blade reaches the stalk. This causes severe
damage to the stool.
Kroes and Harris (1994) found that a major cause of damage to the cane is contact between the
basecutter disk and the stalk prior to the completion of the cut. Cane damage due to disk contact is
attributed to excessive harvester ground speeds or feed rates.
The billeting system (chopper box) is required to chop a cane stalk and trash mat, up to 250 mm thick
into lengths generally between 150 mm and 250 mm.
The rotary pinch-chop concept for the billeting of cane is the system in use in all production chopper
harvesters. Rotary-pinch chopping systems consist of two machined contra-rotating drums with
hardened steel replaceable blades (three or four blades per drum equi-spaced around the
circumference) mounted parallel to the axis of the drums so as to pinch and sever material passing
between the drums.
Even though a considerable amount of time have been undertaken on redesigning the chopper system,
the primary focus of the designs has been on maintenance and reliability, with little emphasis on
increasing the quality of the cut.
Norris et al. (1999) quantified that losses up to 9% can occur in the billeting process and that machine
design and operation can significantly impact on the magnitude of these losses.
The most appropriate way to quantify billeting losses is in percentage loss per cut per metre (%
loss/cut/metre). That is, a 330 mm billet has 3 cuts per metre, whereas a 100 mm billet has 10 cuts per
metre.
The percentage loss per cut per metre (%/cut/m) will range from:
• a minimum of 0.6% for new blades, pour rate < 120 tonne/hr and billet length > 2 nodes, to;
• greater than 1.5 % for high pour rates, worn blades and shorter billet lengths.
Mallee system
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