Desenvolvimento de um revolvedor mecânico de café e seu desempenho operacional e ergonômico

• Autor(a) principal: Moreira, Raphael Magalhães Gomes
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/3586
• topic: Projeto de máquinas; Mecanização; Cafeicultura; Ensaio de máquinas; Machine design; Mechanization; Coffee; Test machines; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA::MECANIZACAO AGRICOLA

The drying process is considered the stage of the coffee post-harvest that involves more costs and it demands more time and greater care, because it may interfere directly in the final product quality. This process in stationary layer dryers is a low cost alternative that allows it to speed up the process and minimize the used area. On the other hand, it needs the revolving of coffee grain mass, at regular intervals of time. The revolving process prevents the formation of high gradients of water content in different layers of the product during the drying process and facilitates the air flow through the mass, making the drying faster and homogeneous. The shortage of workmanship associated to the constant revolving makes necessary to mechanize somehow this step. This study aimed to design, build and evaluate the operational and ergonomics characteristics of a prototype to perform the revolving of the coffee grain mass in the drying process in stationary layer dryer, making the process ergonomically and less arduous, raising homogenization efficiency of the coffee water content. The mechanical homogenizer was built having a helical screw as the grain transportation element, mounted inside a tubular duct. Parchment coffee grains of Coffea arabica L. Catuaí Red-pulped from Araúna farm in Viçosa, Minas Gerais. Aiming to check the transport capacity (TC), the volumetric efficiency of transport (EV), the revolving efficiency (ER), power demand and increasing of the percentage of mechanical damage to grain (GD), tests were performed using spinning speeds of 41.8, 52.4 and 62.8 rad s-1 equivalent to 400, 500 and 600 rpm, respectively. The CT showed a quadratic behavior. At spinning speed of 52.36 rad s-1 it occurred slightly downfall from the point where the water content of the mass reached 28.50% wb. The maximum values for EV were found 30.37, 28.87 and 23.65% for rotations of 41.88, 52.36 and 62.83 rad s-1, respectively. The operations of the revolving speed of 52.36 and 62.83 rad s-1 showed the best results of grains of ER at the end of the drying process, indicating that mixing occurred between superior, middle and bottom layers of coffee. The results of maximum power demand were on a rotation of 52.36 rad s-1 reaching 8.7 Wh kg-1, other rotations demanded 2.6 and 2.4 Wh kg-¹ to the rotations of 41, 88 and 62.83 rad s-1 respectively. GD was found only in the rotations of 52.36 and 62.83 rad s-1 with 0.59 and 2.47% respectively. In order to characterize the ergonomic use of the mechanical homogenizer and to compare it with conventional methods of revolving, trials were conducted regarding the physical charge of work, need to adapt the work, vibration and possible damage to joints, anthropometric adequacy, postural biomechanics and climatic factors. The evaluation of physical load was determined by collecting the cardiovascular frequency. It was considered "moderately hard" to the revolving using the mechanical homogenizer and "very heavy" for the revolving performed manually. The cardiovascular charges for mechanized revolving slightly surpassed the 40% limit. On the other hand, the revolving performed manually showed cardiovascular loads greater than 73%. When performing the appropriateness of work for 8 hours a day, it was recommended the practice of repose or rest. Using the mechanical homogenizer, the maximun repouse indicated was 30 minutes. Still, the manual process requires revolving needs up to 3 hour a day. The vibration and noise levels to which the operators of the mechanical homogenizer were subjected during the tests remained below the limit for an 8 hour workday. It was performed an anthropometric suitability to improve the equipment regarding the opening and height of the handlebars, placement of the switch and installation of vertical lever. Biomechanical analysis was performed by simulating the operation body posture using the mechanical homogenizer and manual revolving through the University of Michigan software 3DSSPP and the Gimp 2.6. For none of the body postures using the protoytpe the limits of compression of the discs L4/L5 and L5/S1 were surpassed. The segments knees, hips and ankles were slightly flexed leading to unsatisfactory results during the tests with the mechanical homogenizer. To evaluate biomechanically the body postures during manual revolving, values for compression of the discs L4/L5 and L5/S1 surpassed the recommended limit, indicating a high probability of serious injury. The thermal comfort conditions during the revolving operation were below than what is recommended by the Brazilian labor standards.