The University of Queensland unit describes the results of tests to determine information on basic properties of bagasse that are important in the design of a rolling pelletizing machine. The Sugar Research Institute section of the report describes the development of the rolling pelletizer. The pilot plant and tests have demonstrated the feasibility of the rolling principle for pellet production.
PART B: UNIVERSITY OF QUEENSLAND COMPONENT
In any pelletizing machine, the compaction energy of the material is an important design parameter. Tests were conducted over a range of temperatures, compaction rates, bagasse moisture, bagasse fineness and compaction levels to investigate their influence on compaction energy. As outlined in Part A of the report, friction plays an important role in the twin roller pelletizer as friction on the rollers provides the driving force to push the material through the machine and also contributes to the back pressure provided by the chutes delivered.
RESULTS OF TESTS AT CSIRO DIVISION OF TEXTILE INDUSTRY
The results illustrate that while increasing the pressing and holding time increased the pellet density at take-off, the density after 12 hours was not adversely affected by decreasing the pressing time in the holding time to the lower limit achievable in the test rig. . 1 minute.
TESTS WITH CRUCIFORM ROLLING MACHINE
- INTERACTIONS INVOLVING PRECOMPRESSION CM and CMW Interactions
- INTERACTIONS INVOLVING TEMPERATURE
- INTERACTIONS INVOLVING MOISTURE
- OTHER INTERACTIONS - DURABILITY
- CONCLUSIONS
FIGURE 3·1 EFFECT OF PRECOMPRESSION ON DENSITY (AT 24 H) AND LUGGAGE DURABILITY (RESULTS ON OTHER VARIABLES). FIGURE 3·5 EFFECT OF MATERIAL SIZE ON DENSITY (AT 24 H) AND LUGGAGE DURABILITY (RESULTS ON OTHER VARIABLES). The interaction of XW illustrated in Figure 3.12 illustrates the fact that the effect of precompression on increasing pellet density is more pronounced at lower moisture.
PROPERTIES OF SINGLE FIBRES
- Y I E L D STRESS AND YOUNG'S MODULUS
- DENSITY OF FIBRES
- INFLUENCE OF FIBRE PROPERTIES ON PACKING THEORIES
- CONCLUSIONS
It can also be seen from Table 4.1 that the larger fibro vascular pellets tested gave significantly lower values of yield stress and Young's m o d u l u s . The relationship between Young's modulus and density was investigated and the results are shown in Figure 4.3. The Van Wyk model was developed to investigate the packing properties of wool and preliminary tests by Loughran determined that it could provide an approximation of the compaction relationship for bagasse.
Young's Modulus and fiber density values obtained in tests o u t l i n e d in T a b l e 4.1 h a v e b e e n used to d e v e l o p the pressure-density relationship for bagasse fibers. This relationship is shown in Figure 4.4. The figure also shows the density versus pressure regression relationship for the whole bagasse with 10 percent moisture developed in the experimental work. While it can be seen that the forms of the equations are s i m i l a r , there is an o b v i o u s need for controlled temperature and humidity conditions.
The work described in this section was only preliminary in nature and established the importance of the time dependence of the stress/strain ratio for cane fibers. He also emphasized the need for more thorough investigation under controlled conditions before Van Wyk's theory could be rigorously tested for applicability to the bagasse compression model.
PRESSURE RELAXATION EFFECTS
PREPARATION
T h e I n s t r o n position controller was calibrated for both speed of compression and height of ram so that the height of a sample could be readily determined from the output voltage. It has been found essential to consider the height after any accidental overloading of a specimen beyond the full dynamic load rating.
PROCEDURE
- RATIO OF PRESSURE AT 2 MIN TO PEAK PRESSURE
- PEAK PRESSURE
- RATIO OF PRESSURE AT 2 MIN TO P max
These illustrate the effect that the type and speed of loading have on the sample. 5-4 RESULTS OF TESTS AT 10 PERCENT MOISTURE - LINEAR COMPACTION A series of tests were conducted with bagasse at 10 percent moisture to investigate the effect of the following variables on the dynamic compression properties of bagasse. It is observed that the peak pressure increases as the application rate increases and decreases as the temperature increases in the range of 20° to 140°C.
Of the two-factor interactions, the TC and FC interactions shown in Figures 5.10 and 5.11 are the most interesting. These show that the effect of temperature and material size is less as compaction decreases. The values of the P2min/Pmax ratio, which is a measure of pressure release, are shown in Table 5.6, and the results of the variance analysis are shown in Table 5.7.
Of particular interest is the fact that as the rate of compression increases, the relative value of the pressure after two minutes becomes smaller. The peak pressure results obtained from the tests are shown in Table 5.8 and the analysis of variance of the results is shown in Table 5.9. As expected from previous tests, there is a significant effect of compaction level and temperature, but it was found that compression rate was of limited significance and the effect of load type was only significant at the 0.05 level, where the sin u s o i dale type of tax yielded somewhat. lower maximum pressures as shown in Table 5.10.
The results obtained for the tests are presented in Table 5.11 and the analysis of variance results are presented in Table 5.12.
CONCLUSIONS
ENERGY OF COMPACTION
- INFLUENCE OF VARIABLES ON TESTS AT 20°C - 1ST COMPACTION The results of the analysis of variance are shown in Table
- INFLUENCE OF VARIABLES ON TESTS AT 20°C - 10TH COMPACTION The results of the analysis of variance of the energies of
- EFFECT OF TEMPERATURE ON ENERGY OF COMPACTION
- CONCLUSIONS
The areas under the curves were found by integrating using digital techniques on the recorded data and the energies were calculated in k J / k g. This table shows that all factors examined had a significant effect on the energy of compaction. These results generally show the same trends as the first cycle energy, but the effects are less significant.
A v e r a g results of the ratio between the energy for the 10th cycle and the energy for the 1st cycle are shown in Table 6.6. T h e r e s u l t s of the tests are shown in Table 6.3. The results of the analyzes of variance performed on the results of these tests are shown in Table 6.7.
This shows that the difference between the compaction energies for different material sizes is greater at 20°C than at 80° or 140 C. The tests carried out to determine the compression energy have quantified the influence of the different parameters. However, the tests described in Chapter 5 have shown that the durability of fine material is not as good as that of the whole material.
The comparison is shown in Table 6.9, where it is seen that e n e r g y for a c t u al c o m p r e s s is a small fraction of the total energy absorbed, and therefore there is considerable potential for reducing energy consumption in the operation of machines.
A THEORY OF BAGASSE COMPACTION
A BAGASSE COMPACTION MODEL
It is further assumed that each beam is loaded at mid-span, and because each of the beams will be part of a multi-beam bagasse filament, the beams will deflect as if their ends were encased. The task is solved by determining which of the macro states has the greatest probability of occurrence. Although the proportion of beams with load energy u decreases exponentially as u increases relative to the average energy per beam, there are in principle always some beams with load energy greater than a given value.
For larger values of the second exponential term in the integrand of the integral inside the brackets can be written as. It turns out that there is only a significant initial return when the average deviation approaches approximately 3.0% of the yield deviation. A further increase in mean deflection then rapidly increases the permanent set due to yield to almost half of the mean deflection, after which it forms a slowly increasing portion of the mean deflection.
The final density of a compressed bagasse pellet, after the compaction process is completed, depends on the permanent hardening induced in the fibers of the pellet. This arises from the permanent expansion due to initial yield, and that due to retention (identified here as plastic creep). The average deflection of the beams is proportional to the movement of the boundaries of a pellet as it is compressed.
T h u s, if the pellet is being formed in a cylinder, the deviation in maximum pressure will be related to the movement of the piston i.e.
FRICTION TESTS
- APPARATUS
- METHOD
- RESULTS
- RESULTS FOR COEFFICIENT OF STATIC FRICTION AT 20°C The results of the tests conducted on whole material at
- R E S U L T S O F C O E F F I C I E N T O F S T A T I C F R I C T I O N T E S T S W I T H DIFFERENT MATERIAL SIZE - 20°C
- RESULTS FOR DYNAMIC COEFFICIENT OF FRICTION - 20°C The results of the coefficient of dynamic friction for
- R E S U L T S O F C O E F F I C I E N T O F D Y N A M I C F R I C T I O N T E S T S W I T H DIFFERENT MATERIAL SIZE - 20°C
- INFLUENCE OF TEMPERATURE
- CONCLUSIONS
It can be seen that all the investigated factors had a significant influence on the static friction coefficient and that all interactions were significant. It can be seen that, averaged over all other variables, the coefficient of static pressure increases with applied pressure from 1 to 10 MPa with no increase from 10 to 35 MPa. Perhaps the most interesting of the interactions is the faster decrease in the static coefficient of friction at the highest pressure as the moisture content of the material increases.
The results obtained are shown in table 8.3 and the results of the analysis of variance are shown in table 8.4. It is seen that the influence of material size is significant and similar to that found for the static coefficient of friction. The tests were performed on whole material at 10 percent moisture at three levels of pressure on each of the three surfaces.
It is interesting to note from Table 8.10 that there is no significant difference between the values of the coefficient of static and dynamic friction. The results described in this chapter illustrated the following main factors affecting the friction coefficient of relatively dry cane. The coefficient of static and dynamic friction increase with pressure except at the 30% moisture level, where the expression of moisture at higher pressures results in a decrease in the coefficient of friction.
With the coefficient of dynamic friction being somewhat less than the coefficient of static friction when the values were on average high, there was no significant difference between the two coefficients over the series of tests.
APPENDIX A
RAPID BENDING OF BAGASSE FIBRE BUNDLES
Satisfactory pictures were obtained with delays of 12.5 and 15 ms and intervals between flashes of 10 and 20 m s. The separation of the images of the white lines on the weight and dowel was measured using a traveling microscope. Once the timing of the test was determined, this was possible using a multiple linear regression program developed by Mr.
This equation was differentiated to give velocity and a c e l e r a t i o n and h e n c e the force on the fiber b u n d l e w a s obtained. F i g u r e A.3 is a p l o t of extreme fiber stress as a function of displacement for three of the fiber bundles which did not break under the specified loads.
APPENDIX B
PROBABILITY OF A MACROSTATE
