PART A: DESIGN OF THE ILLOVO SUGARCANE HARVESTER
4. DEVELOPMENT OF THE ILLOVO SUGARCANE HARVESTER
4.6 Blade Design C
4.6.3 Design C: Results and discussion
Design C proved to be an improvement. It began to meet some of the requirements within the design constraints. These included cutting the cane satisfactorily and manufacturing the blades at a reasonable cost.
CUT QUALITY
The quality of the cut was slightly lower than Design A. This was expected because of fewer cutting edges. There was a tendency to cause damage up to a class 6, but on average the damage was at 2, which was assumed acceptable. Figure 4.18 shows the variance of the damage caused.
The damage circled in red has a damage rating of 4, while the yellow circle shows a damage rating of 1. This variance could be explained by the change in speed during the movement of the cutter as it is swung through the cane. Another cause might be that the higher damage could have
been cane partially cut during the first sweep and a second sweep was required to complete the cut. Another factor contributing to the damage was the type of connectors. The bolts sat proud and caused more damage by shredding the stools unnecessarily after the cane had been cut.
However, the final connector design where the thread was cut into the plate reduced this problem.
Figure 4.18 Damage of the cane caused by Design C. The red circle shows a damage rating of 4, while the yellow circle shows a damage rating of 1
HEIGHT OF CUT
The blades were slightly more aggressive due to a larger cutting edge. This, combined with the connectors lifting dust and debris, caused the operators to not always see the base of the cane. It resulted in a slightly higher base cut at approximately 17mm, compared to Design A. This resulted in a loss of 1.4 tha"1 and a monetary loss of R238.ha_1. This was regarded as acceptable and should improve if the field was prepared for the specific harvesting operation, such as not planting in furrows.
WEAR
The rate of wear was similar to Design A, but due to the larger leading edge it could be used for longer periods. The wear can be seen in Figure 4.19. These blades were hardened to 45 Re and operated in sandy soils for 64 min after harvesting approximately 3.8 tons.
Figure 4.19 Wear of Design C. Blades hardened to 45 Re after operating for 64 min
The rate of wear was lower compared to Design A and is summarised in Table 4.5. A total mass loss of 56 g was lost before replacing the blades. This occurred after working for two hours and after harvesting approximately 6.5 tons. This was a marked improvement from Design A. The blade hardness was increased gradually for safety reasons, but it was seen that blades in the range of 45 and 50 Re wore at similar rates.
Table 4.5 Mass loss and rate of wear for Design C with replaceable blades
TOTAL MASS (g) Blade Mass Loss (g)
Blade Mass Loss per minute (g.mirf1)
New
1552 0 0
1 Edge Used 1515
36 0.72
2 Edges Used 1494
56 0.47
The two fineness angles of 24 and 45 degrees were also tested but results were inconclusive.
There were no visible differences with regard to rate of wear or cleanness of cut. It is noted that the wear took place at such a high rate that after 10 min the fineness was no longer a factor.
CONNECTORS
The connectors mentioned above were tested and the alien key heads (Figure 4.15) performed the best. The bolts with the bolt heads wore down to such an extent that it was impossible to change blades without cutting the bolts (Figure 4.19). Another disadvantage was that they caused excessive damage to the stool and the cut cane. The tapered alien key heads did not have enough thread and continually pulled out and stripped the thread. Therefore, the proud alien key heads were selected as the best connector.
SAFETY
For Design C, safety became critical because of the nature of the detachable blades. It was noted that the hardness should not be taken above 50 Re. Figure 4.20 shows shattering that took place at 52 Re after the blades hit a rock in the field. This was not only a safety risk, but the unbalancing of the blade also caused damage to the drive shaft of the brushcutter.
Figure 4.20 Shattering of blades hardened to 52 Re as a result of hitting a rock
At lower Re values (46 and 48) the blades were more likely to bend. This caused some connectors to break when hitting a large rock. A test was done with blades at 45 Re in a controlled environment. When the blade hit a rock it did not shatter but rather bent the blades (Figure 4.21) and sheared the connectors. This was more favourable because when a bolt is sheared the blade remained attached and swung away as seen in Figure 4.21. The blade was useless once it hit a rock, unlike Design A, therefore, it was advisable to be careful in rocky
conditions. Depending on the skill of the operator the majority of the rocks should be moved before cutting takes place.
Figure 4.21 Blades of 45 Re that underwent a shatter test in a controlled environment showing only the connectors breaking
The connectors generated extra debris and dust that affected the operator adversely. The operator thus required goggles and a face mask to stop the dust hampering his ability. Tests showed that blades that become detached flew away from the operators and care had to be taken to ensure that no persons were in front of the operators.