Investigation into bevel plate optimal angle required to improve nut cracking in a centrifugal nut cracker

Abstract

In order to ensure that most of the nuts discharged vertically from the rotor do not escape uncracked through the cracked nut mixture outlet; an investigation into optimal angle for palm nut cracker bevel plate assembly required to increase efficiency of the cracking process was carried out at three different feed gates. In this study, the cracked nut mixture outlet at the cracking drum of an existing centrifugal palm nut cracker was modified to include bevel plate having adjustable angle of inclination. Dried and ready to crack mixed varieties (Pisifera, Tenera and Dura) of palm nuts were sourced and moisture content determined using oven dry method. The nuts (18.6% moisture content wet basis) were subjected to impact at different angles ( = 90, 55, 50, 45, 40, 35, 30, 25 and 200) of bevel plate per feed gate aperture area, A (18, 27 and 36 cm2) of the modified palm nut cracker. The = 90o was full opening of the cracked nut mixture outlet of the existing nut cracker. For each experimental run, ninety (90) nuts were subjected to impact at 3712 rpm rotor speed. The total time taken for each set of the products to be discharged was also noted as t. Data were collected in duplicate and analyzed using Statistical Package for Social Scientists [SPSS] version 20 and Microsoft Excel TM. The performance indices [percentage of nuts cracked with release of whole and split kernels (% NCKR), percentage of uncracked nuts (%UC), percentage of partially cracked nut (%PC) and percentage of uncracked and partially cracked nuts (%UP)], bevel plate efficiency (%CEBP) and nut cracking rate (NCR) were plotted against per feed gate aperture area. The optimum performance indices (%NCKR = 96.67%, %UC = 3.33% and %UP = 3.33% and %PC = 0.00%), %CEBP (93.88%) and NCR = 5 nuts / sec were obtained at = 250 and A =18 cm2. This implies that the modified nut cracker when run at feed rate of 5 nuts/sec and = 250 would improve cracking operation by 93.88% of nuts that should have escaped uncracked at the cracked nut mixture outlet. Hence, it is necessary to incorporate bevel plate.