THE EFFECT OF FIBRE AND SOIL CONTENT ON SHEAR AND FRICTION COEFFICIENTS OF SUGARCANE BAGASSE

Transcription

1 Proc. Int. Soc. Sugar Cane Technol., 24: THE EFFECT OF FIBRE AND SOIL CONTENT ON SHEAR AND FRICTION COEFFICIENTS OF SUGARCANE BAGASSE BY A.C. de 0. FERRAZ1 and M. de A. PIEROSS12 Universidade Estadual de Campinas, Campinas-SP-Brasil 2Centr~ de Tecnologia Copersucaq Piracicaba-SP-Brasil Abstract Friction and shear coefficients constitute important parameters that contribute to characterise sugarcane bagasse for juice extraction purposes. A shear box was designed to investigate the effect of soil content on the values of these parameters for pressures up to 0.6 MPa, for two widely grown sugarcane varieties in Brazil. Both varieties, RB72454 and SP , showed the same mean value of for the coefficient of shear. Soil content did not affect these values. Mean value of the coefficient of friction between the bagasse and a smooth steel surface was for variety RB72454 and 0.34 for variety SP , Increasing values of the coefficient of friction were obtained as soil content increased, reaching for both varieties at 2% soil content. Further tests are suggested for higher compression pressures. Introduction Efficiency of juice extraction in sugarcane mills is a topic of continuous interest in the sugar industry (Kuebler and Jones, 1988; Owen et al., 1994). Mill feeding is an important part of the process since it increases feeding velocities and compresses the bagasse to a higher initial pressure, important to improve extraction efficiency. The interaction between the prepared cane and the surface of the rollers is mainly determined by two parameters, the coefficients of friction and shear. The friction coefficient depends on the type of material and surface finish. It determines the interaction between the roller surface and bagasse during compression. The shear coefficient expresses how bagasse particles interact internally with each other when subjected to shearing action. Both coefficients are related since the maximum shearing force limits the maximum friction force that can be obtained during feeding (Plaza and Edwards, 1994).,. Several studies have been conducted concerning these two parameters in search of better understanding of excessive wear and the necessary grip of the roller surface, including the development of mathematical models (Plaza and Kent, 1997). Plaza and Kent (1997) also utilised the Mohr-Coulomb failure criterion used for soils. The main objective of this study was to determine surface and shear coefficients for the Brazilian sugar cane varieties RB72454 (12.2% fibre) and SP (13.3% fibre) and to investigate the effect of soil content on these parameters. A shear device was specially designed and details of the methodology are given. Materials and methods Stalks of sugarcane varieties RB72454 (12.2% fibre) and SP (13.3% fibre), were harvested and prepared on the same day as the experiments. Preparation consisted of comminuting the stalks using a chopper. Part of the prepared cane was thoroughly mixed with typical clay soil from the field at 0.5% and 2.0%, on a weight basis. Shearing device A shearing box with a total internal volume of 1.5 x lo6 mm3 was designed and constructed using mild steel (Figure 1). The rectilinear movement of the lower car is performed through the rolling of low friction bearings, used as wheels, in the guiding channels. The upper car and the base constitute the static components of the device and both are fixed on the steel structure of a 20 t hydraulic press. The same device, slightly modified, was used to measure surface friction by inserting a small table into the lower car. The table surface was leveled to the top surface of the car's walls. SECTION A-A SIDE VIEW Fig. 1-Schematic representation of the shear device. A. base; B. lower car; C. upper car; D. hydraulic press head; E. compression load cell; F. compression plate; G, low-friction bearings; H. bagasse column; I. guiding channels. KEYWORDS: Friction; Shear; Juice Extraction, Bagasse, Cane Fibre, Dirt. 21 5

2 Ferraz, A.C. de 8. and Pierossi, M. de A., Proc, Int. so=. Sugar Cane Technol., 24: Experimental setup of these treatments, five replications were performed. An illustration of the complete setup ( ~ 2) i Analysis ~ ~ of variance ~ and ~ mean comparison using features the anchoring brackets, compression plate, Duncan's Multiple Range Test were used to analyse two load cells (5 t and 1 t, Interface Load Cells, SP, the data (SANEST, Statistical Software). Brazil), connecting cable, hydraulic press head, frictionless wheels, testing machine (Ottawa Texture Results and discussion Measurement System, Ottawa, Canada) and General comments hydraulic press structure. The bagasse was compressed though the load cell placed on top of the The designed apparatus showed itself to be appropriate to measure the coefficients of shear and fricbagasse column using an auxiliary steel plate to tion of prepared cane. During the tests, the lower car evenly distribute the pressure over the exposed area showed a smooth movement and no tendency to of the bagasse column. The compression force was applied using a manually operated hydraulic press. A deviate from the straight path provided by the guided channels. The maximum force values achieved in all second load cell was attached to the head of the tests did not exceed 5000 N, corresponding to an testing machine to measure friction forces. Both load assumed uniformly distributed pressure of 0.52 MPa cells were connected to a signal conditioner and on the bagasse column. Even though this pressure data acquisition system (Spider-8, HBM-Hottinger level is relatively low, compared to 20 MPa that Baldwin Messtechnick). Data were collected at 5 Hz. occurs during actual compression in the mill, it corresponds to the initial stage of the extraction process. Testing procedures For the coefficient of shear measurements, both cars were loaded with prepared cane. Several loadings were necessary to fill the cars and to obtain a reasonably dense column of bagasse so it could undergo some pressure without much deformation. Each partial loading was characterised by evenly spreading the bagasse in the cars followed by slight compression, not exceeding 4000 N. No juice was removed from the bagasse in this preparatory stage. As the bagasse column was ready, a compression force was gradually applied until it reached N. The test machine was then turned, on pulling the lower car with constant speed of 0.17 mmls (10 mmlmin). When a displacement of three to four millimeters was observed the test was interrupted. A similar procedure was conducted to evaluate surface friction. A small steel table was put inside the lower car, providing a sliding surface with milling finish for the bagasse. In this case, the bagasse column was half the height used in previous procedures for the coefficient of shear. Both coefficients were determined for prepared cane with 0%, 0.5% and 2% of soil content. For each of compression and frictionaforce to calculate the coefficient. However, since the inflection point was not easy to identify, two tangent lines representing the two slopes were drawn and the intersection point was taken as the measurement point for both forces (Figure 3). As a result, the mean value of the shear coefficient obtained for variety RB72454 was (SD = 0.07, CV = 0.17). The mean values obtained for 0.5% and 2% soil content were 0.44 (SD = 0.02; CV = 0.05) and 0.42 (SD = ; CV = 0.07), respectively. Variety SP showed values of (SD = 0.02; CV = 0.05), (SD = 0.02; CV = 0.05) and 0.42 (SD = 0.04; CV = 0.10) for 0%, 0.5% and 2% soil contents, respectively (Table 1). Neither variety nor soil content had an effect on the mean values of the coefficient of shear for sugarcane bagasse at the pressure tested (Duncan's Test, P<0.05). Coefficient of friction Typical compression and friction force curves obtained during the tests (Figure 4) show corresponding peaks and valleys as the lower car was pulled. As the bagasse column relaxes, traction force showed similar decay tendency. Measurements were

3 Ferraz, A.C. de 0. and Pierossi, M. de A., Proc. Int. Soc. Sugar Cane Technol., 24: time (s) Fig. 3-Typical compression and friction forces obtained during shearing tests of prepared cane. The intersection of the auxiliary tangent lines determines the compression and friction forces values. Table 1-Coefficient of shear for bagasse for two sugarcane varieties, three soil contents and five replications. Variety Soil content 0% 0.50% 2% RB AVG* SD* CV* SP AVG 0.42 SD CV 'AVG = average; SDa= standard deviation; CV = Coefficient of variation (SDIAVG). taken at corresponding peaks. The mean value of the coefficient of friction for variety RB72454 was (SD =, CV = ). For 0.5% and 2% soil contents, the mean values obtained were (SD = ; CV = ) and (SD = ; CV = ), respectively (Table 2). No difference was observed at the three soil content levels for this variety (Duncan's Test, P<0.05). Variety SP showed mean values of 0.34 (SD = 0.02; CV = 0.06), (SD = ; CV = ) and (SD = ; CV = ) for 0%, 0.5% and 2% soil contents, respectively, which are significantly different from each other (Duncan's Test, P<0.05). As soil content increased, the mean value of the coefficient of friction also increased. Even though variety RB72454 has a lower fibre content, its average value () for the coefficient of friction was higher than the average value () of variety SP (Duncan's Test, P<0.05). The coefficient of friction's lowest value (0% soil content) was 0.34 and the highest (2% soil content). The majority of the tests showed little variability. The coefficient of variation was below 0.10 with the exception of the value of 0.17 for the shear test for variety RB72454 with 0% soil content. Ratio of coefficient of friction and coefficient of shear The ratio of the average values of the coefficient of friction and the coefficient of shear for all treatments was between 0.82 and As expected, the coefficient of friction of a smooth mild steel flat surface has to be increased through the addition of roughness in order to make the ratio equal to one (Plaza and Edwards, 1994).

4 Ferraz. A.C. de 0. and Pierossi, M. de A.. Proc. Int. Soc. Suaar Cane Technol.. 24: Fig. 4-Typical time (s) compression and friction forces obtained during determination Table 2-Coefficient of friction of bagasse for smooth mild steel surface for two sugarcane varieties, three soil content and five replications. Variety Soil content 0% 0.5% RB72454 AVG* SD* CW SP~O AVG SD CV *AVG = average; SD = standard deviation; CV = Coefficient of variation (SDIAVG). 2% Conclusion The specially designed device proved appropriate for measuring shear and friction coefficients of sugarcane bagasse for pressures up to 0.52 MPa. Soil content did not affect the values of the coefficient of shear for the two sugarcane varieties tested. However, increasing soil content increased the values of the coefficient of friction of variety SP Further studies should be conducted at higher pressures. Acknowledgments The authors acknowledge Antonio S6rgio Marchi (Copersucar), Carlos Cascadan (Copersucar) for the drawings and construction of the shearing device and Luciano Menegasso (Copersucar) for his help during the tests. They also thank the Farm Machinery Department (FEAGRI, UNICAMP, Brazil) for the use of lab facilities (Mechanical Properties of Biomaterials Lab) and the assistance on instrumentation through the Instrumentation and Control Lab-LIE. A special recognition is given to Dr Steven A. Sargent (University of Florida, Gainesville) for reviewing the manuscript. REFERENCES Kuebler, P.M. and Jones, K.C. (1988). The development and testing of a computer controlled machine for high productivity automated roller arcing. Proc. Aust. Soc. Sug. Cane Technol., 10: Owen, D.R.J., Zhao, S.Y. and Loughran, J.G. (1994). An overview of crushing theory investigations at Swansea. Part 2-Modeling of a two Roll Mill. Proc. Aust. Soc. Sug. Cane Technol., 16: Plaza, F. and Edwards, B.P. (1994). Shear, friction, and required roll roughness. Proc. Aust. Soc. Sug. Cane Technol., 16: Plaza, F. and Kent, G.A. (1997). Using soil shear tests to investigate mill feeding. Proc. Aust. Soc. Sug. Cane Technol., 19:

5 Ferraz, A.C. de 0. and Pierossi, M. de A., Proc. Int. Soc. Sugar Cane Technol., 24: L'EFFET DE LA TENEUR EN FIBRE ET EN TERRE SUR LES COEFFICIENTS DE FRICTION DE LA BAGASSE A.C. de 0. FERRAZ1 et M. de A. PIEROSS12 l Universidade Estadual de Campinas, Campinas-SP-Brasil 2Centro de Tecnologia Copersuca< Piracicaba-SP-Brasil RCsumC L'extraction du jus de la canne et de la bagasse est affect6 par les coefficients de friction. On a Ctudie 1'Cffet de la terre sur la valeur de ces coefficients, pour des pr6ssions allant jusqu'a 0.6 MPa et avec deux varietcs de canne populaires au BrCsil. Les deux varietcs montrent la mcme valeur de pour les coefficients de friction. La teneur en terre n'affecte pas ce chiffre. La valeur lnoyenne pour le coefficient de friction est pour la varietc RB et 0.34 pour SP Ces chiffres augment avec la teneur en terre, atteignant, pour les deux varietds avec 2% de terre. On suggkre des Ctudes pour de prcssions plus hautes. Mots clefs: Friction, exhaustion, bagasse, canne, fibre, terre. EFECTO DEL CONTENIDO DE FIBRA Y SUELO EN LOS COEFICIENTES DE FRICCION Y CIZALLADURA DEL BAGAZO DE CA~A DE AZUCAR A.C. de 0. FERRAZ1 y M. de A. PIEROSS12 Universidade Estadual de Campinas, Campinas-SP-Brasil 2Centr~ de Tecnologia Copersucar, Piracicaba-SP-Brasil Resumen Los coeficientes de fricci6n y cizalladura constituyen importantes parfimetros que contribuyen a caracterizar el bagazo de caiia de az6car para prop6sitos de extracci6n del jugo. Una caja de cizalladura fue diseiiada para investigar el efecto del contenido de suelo en estos parfimetros bajo presiones hasta 0.60 MPa. Las pruebas se efectuaron con dos variedades cultivadas ampliamente en el Brasil. Las dos variedades, RE y SP , mostraron en promedio el mismo valor de para el coeficiente de cizalladura. El contenido de suelo no afect6 estos valores. El valor medio del coeficiente de friccidn entre el bagazo y una superficie lisa de acero fue para la variedad RB72454 y 0.34 para la variedad SP Incrementos en el valor del coeficiente de fricci6n fueron obtenidos a medida que aumenta el contenido de suelo, alcanzando para las dos variedades con un contenido de suelo de 2%. Se sugiere la realizaci6n de pruebas futuras empleando mayores presiones. Palabras claves: Friccibn, cizalladura, extracci6n de jugo, bagazo, fibra de caiia, materia extrafia. 21 9