Compressive mechanical cracking of pili (Canarium ovatum Engl.) nuts: Concept and mechanism design

Abstract

A mechanical pili nut cracker that used gradual compression for cracking was proposed and developed. This was a deviation from the traditional practice of applying impact for cracking pili nuts. The cracking unit of the machine accomplishes gradual compression by a rotating assembly of discs and compression bars travelling along an arrangement of cam rails. The cracker’s performance was established using pili nuts at different moisture levels.  The tests followed a single-factor three-level experiment where the response variables included cracking capacity, cracking efficiency, cracking recovery, whole kernel recovery, kernel damage, kernel losses and purity of output. The machine performed satisfactorily using nuts dried for three days after depulping (moisture content wet basis = 11.6%). At this moisture level, the machine showed consistent and satisfactory performance in terms of cracking capacity (25 kernels min^-1), cracking efficiency (74.0%), cracking recovery (62.6%) and whole kernel recovery (84.3%). Modifications were recommended to further reduce kernel damage (30.6%) and kernel losses (37.4%) and to improve the purity of output (46.8%). It was successfully demonstrated that gradual compression can be used for cracking pili nuts. It is recommended that the operating characteristics of the machine should be optimized to improve its performance.  Furthermore, a dedicated feeding assembly and a more suitable separation method should be explored to further enhance the performance of the cracker.