Abstract
Based on data collected from seven commercial harvesting operations in Western Australia, the study developed a productivity model for chain flail delimber–debarker–chippers (CFDDCs) used in blue gum (Eucalyptus globulus Labill.) plantations. The tests covered 45 h and 3395 cycles, and were conducted using time-study techniques. Despite the observational character of the study and the dampening effect of multi-tree processing, the study yielded a viable prediction model for estimating CFDDC productivity as a function of mean tree size, tree form, bark–wood bond strength (BWBS), and machine type. Productivity increased with mean tree size on a logarithmic scale, and was lower for poorly formed trees and high BWBS. Under equal conditions, a separate delimber–debarker and a chipper were 10% to 20% less productive than the integrated delimber–debarker–chipper. Productivity estimates were consistent with those reported in published case studies of CFDDCs used in planted Eucalyptus. Neither this study nor any of the previous ones could offer a reliable estimate of long-term machine utilization, which would be an ideal subject for future research.
Highlights
While trees planted for sawn-timber products need to grow until they have reached large dimensions, trees grown for pulpwood or biomass should only be harvested when the land expectation value (LEV) is maximized, or when sufficient mature wood has been produced as per the specification of the pulp-making process [1]
The productivity of conventional harvesting techniques is directly proportional to stem size, and is especially low in pulpwood-size plantations [2]—the development of multi-tree technology that can compensate for small tree size by handling more trees at one time [3]
Combination machines handled smaller tree sizes—in order to process the same amount of clean chips from trees that were 27% smaller, combination machines took 44% more time than integrated machines
Summary
While trees planted for sawn-timber products need to grow until they have reached large dimensions, trees grown for pulpwood or biomass should only be harvested when the land expectation value (LEV) is maximized, or when sufficient mature wood has been produced as per the specification of the pulp-making process [1]. The productivity of conventional harvesting techniques is directly proportional to stem size, and is especially low in pulpwood-size plantations [2]—the development of multi-tree technology that can compensate for small tree size by handling more trees at one time [3]. CFDDs are multi-stem processing machines that knock off branches and bark from whole trees by using hardened chain links mounted on fast-rotating drums [8]. These machines may achieve a productivity in excess of 40 t per productive machine hour, and remove all limbs and most of the bark off the stem [9,10,11,12]. While somewhat rough, flailing can be fine-tuned to minimize fiber losses, which are generally lower than 5% [13,14]
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