Design, Fabrication, and Experimental Evaluation of a Power-Operated Kenaf Decorticating Machine
DOI:
https://doi.org/10.63746/njtd.v23i2.4387Keywords:
Decorticating force, Design analysis, Fibre, Machine construction, PrototypeAbstract
Kenaf (Hibiscus cannabinus L.) is a renewable bast?fibre crop with broad industrial potential, but its commercial uptake in Nigeria is constrained by labour?intensive, time?consuming retting and by mechanical decorticators that are often unsafe, immobile, costly, and prone to clogging. Objective: to design, fabricate, and experimentally validate a low?cost, locally manufactured power?operated kenaf decorticating machine that improves throughput, fibre yield, and operator safety. Mechanical design and structural checks (ASME) established decorticating force (2,779.5 N), torque (166.8 Nm), shaft sizing (calculated 27 mm; 35 mm provided), and a peak theoretical power requirement of 7.9 kW; belt?drive and gear analyses informed transmission selection and belt tensioning. Performance testing used a Box–Behnken response surface design with four factors (maturity stage, operating speed, stem diameter, moisture content) across 27 randomized runs with replication. Measured responses included throughput, decorticating efficiency, trapped/waste fibre, and fibre?quality indices (length distribution, retention ratio, cleanliness, tenacity, fineness, damage index). Fibre length was measured by calliper; tenacity followed single?fibre tensile testing; cleanliness was determined gravimetrically. ANOVA and RSM were used for model fitting, diagnostics, and multi?response optimisation. The prototype delivered throughput of 72.9–84.3 kg·h?¹ and decorticating efficiencies of 86.3–90.2%. The quadratic model showed strong predictive power (R² = 0.94; adj. R² = 0.91; pred. R² = 0.89) with validated residual diagnostics. Fibre quality was robust (mean lengths 1,200–1,470 mm; retention ratio 67.0–72.3%; mean tenacity ? 18.7 cN/tex; fineness 3.5 dtex; cleanliness 7.8%; damage index 6.3%). Operating speed and moisture content were the dominant factors affecting performance and quality. The locally fabricated decorticator attains internationally comparable performance while lowering extraction costs and improving safety, making it suitable for pilot deployment by farmer cooperatives and SMEs and supporting sustainable bast?fibre value chains.
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