This study defined the productivity levels of a CBI 5800 grinder using a truck as a base machine for processing stumps, logging residues and whole trees at a roadside landing. For defining the solid content of the truck loads, the weight of each load was recorded. Furthermore, samples from each load were collected in order to define the moisture content, dry green density, green mass, particle size distribution and ash content of processed raw material. The solid content of the chip loads was based on the relation of the recorded dry masses, dry green densities and frame volumes of each load. The time study was conducted using a hand-held field computer by means of continuous timing, where the clock is running continuously and the different work elements are separated from each other. The effective hourly productivity (E0h) of the operation was presented per solid and loose volumes (m3), green and dry mass (kg), and the energy content (MWh) of the forest chips. Furthermore, the noise and vibration of the grinding operation were measured.
The effective hourly productivity of grinding was highest for logging residues (loose volume, 224 m3/E0h & solid volume, 81 m3/E0h). The productivity of whole tree grinding was second highest (loose volume, 198 m3/E0h & solid volume, 60 m3/E0h) and the lowest productivity (loose volume, 131 m3/E0h & solid volume, 36 m3/E0h) was in stump grinding. Based on dry masses the productivity of grinding logging residues was 29022 kg/E0h. The productivities of grinding whole trees and stumps were 24958 kg/E0h and 17315 kg/E0h. The effective hourly productivity of grinding logging residues based on energy content was 135 MWh/E0h and respectively for whole trees 119 MWh/E0h. For stumps free of mineral soil, the productivity was 85 MWh/E0h and for stumps of the time study experiments with mineral soil 72 MWh/E0h, respectively.
Based on the results of this study, it can be concluded that the CBI 5800 grinder (power 462 kW/620 hp) works well for grinding logging residues, split stumps and whole trees at a roadside landing. Moreover, the grinder was consistent in terms of interruptions caused by impurities in the raw material. The bulk density of chips based on grinding was lower than the bulk density of conventional chips. The productivity of the studied grinder was significantly better compared to conventional drum chippers at the same size category when comminuting logging residues at the roadside landing. The grinding productivity of whole trees was slightly lower or at the same level than when performed by drum chippers with a truck as a base machine. The productivity of the CBI 5800 grinder was significantly lower when compared to large grinders used in terminals and end use facilities. However, the productivity was three times higher compared to the pre-grinding of stumps with slow-running grinders at the roadside landing.
Key words: stumps, logging residues, small diameter wood, comminution, chip dimension, noise, vibration, heating value.