COMPARATIVE ANALYSIS OF MECHANICAL PERFORMANCE IN POLYMERIC EXTENDERS, MANUFACTURED BY DIRECT 3D PRINTING FOR MECHANICAL STRIPPERS IN COFFEE HARVESTING

Abstract

Introduction: The rate of physical degradation to the coffee beans, together with grain waste in the process due to the use of rubber hose extenders at the tip of the mechanical strippers’ rod brought up the project: manufacturing, analyzing and comparing the technicals features of polymers Acrylonitrile Butadiene Styrene (ABS) and Polylactic Acid (PLA), for later adaptation of these materials on the tips of the rods. Methods: In partnership with the laboratories of the educational institution, dumbbell-shaped test specimens of ABS and PLA polymers were designed and printed following the ASTM D638-14 standard, using Solidworks® software and a 3D printer (model BFB touch dual head-smoke case). After being printed, they were submitted to tensile testing by the EMIC DL 10000 machine for data gathering and comparison for later use in mechanical strippers inside coffee fields. Results: The PLA specimens showed elastic behavior close to the rupture, presenting partial rupture stress on average 31,75% lower than the maximum stress applied, tolerating higher tensile loads after more time-consuming tests compared to the ABS ones, that have proved their plastic behavior. The printing setups (layer thickness and fill pattern) also influenced the tests performance in both polymers. Conclusion: Despite not having the PLA's biodegradable property, the ABS polymer proved to be more apt for application in the rods, presenting ultimate tensile stress limit very similar to the yield point (σ = 25,61 MPa / σ = 25,33 MPa), in which is above the partial rupture tension in PLA specimens (σ = 24,16 MPa). Keywords: mechanical strippers, polymers, tensile test, 3D printing.