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Abstract Chipping weighs heavily on the total delivered cost of wood fuel, which calls for accurate chipping cost estimates. Chipper repair and maintenance cost is perhaps the most obscure among the figures required for a reliable estimate of chipping cost. To clarify this issue, the authors examined the long-term repair and maintenance records for 51 wood chippers operated by 48 chipping service contractors. Repair and maintenance represented between 1.5% and 29% of total chipping cost, inclusive of fuel and labour (mean = 14%). The ratio between total accumulated repair (TAR) cost and machine price averaged 32% and varied with total use. The relationship between total use and TAR to price ratio was explored through regression analysis, which produced a very strong model (R2 = 0.8). This model predicts a TAR to price ratio of 0.64 at 10000 h, with no significant differences between tractor-driven and independent-engine machines. While the coefficients are different, the structure of this model offers a good match with the repair and maintenance cost models developed for farm tractors and other agricultural machinery. A second model was developed for estimating repair and maintenance cost as a function of fuel consumption. The study also provides reference figures for the contribution of labour cost to total maintenance cost. Farm tractors incur more repairs than preventive maintenance, contrary to the other dedicated components of the chipping operation, where preventive maintenance represents most of maintenance cost. Forestry users should make allowance for the lower structural strength of tractors and select large models. Highlights • Long-term maintenance records were obtained for 51 wood chippers. • Maintenance is 14% of chipping cost on average, and ranges between 1.5 and 29%. • At 10000 h, total accumulated repair (TAR) cost amounted to 60% of machine price. • A model was developed for predicting TAR as a function of total use. • Maintenance was also estimated as a function of fuel consumption. [ABSTRACT FROM AUTHOR]

Abstract Currently different trade units are used throughout the forest energy supply chain in Sweden: chipping contractors are paid per m3 chipped volume, dry metric tonnes or MWh, hauliers per raw tonnes or m3 chipped volume and the company supplying the chips to the heating plant most often per delivered MWh. This introduces business risks for all market players, and affects studies of chipping equipment. Lately, Skogforsk has used oven dry tonnes, but stakeholders that measure chips in other units want results to be presented in these units as well. To raise awareness about output unit selection and its effect on productivity and fuel consumption studies, Bruks 806 chippers were studied when chipping spruce and beech residues. Results show that the selection of output unit affects the capacity of detecting treatment differences and the direction of such differences. Chipping productivity based on effective chipping time was higher for spruce residues when calculated using chipped volume, and for beech when calculated using raw weight. Similar trends were found for fuel consumption per product unit. As both feedstock characteristics and output measurement unit selection affects study results, a proper experimental design to control these effects is important. In many cases it is a matter of keeping feedstock constant during comparisons of machines/treatments. Care is needed when using chipped volume, as chipper settings may influence chip bulk density and thus chip volume. The use of different units throughout the supply chain reduces transparency and increases the risk for sub-optimal decisions. Highlights • Output unit affects the possibility to detect differences in chipper efficiency. • The direction of treatment differences may depend on the choice of output unit. • Output unit choice is an issue when comparing feedstocks or published results. • Effects of output unit choice can be controlled by a proper experimental design. [ABSTRACT FROM AUTHOR]

Experiments made with a model helical chipper have shown that the infeed angle has a huge impact on chip quality parameters. Furthermore, it could be pointed out that the self feeding mechanism of the helical chipper was impeded with larger infeed angles and finally failed. This situation led to the hypothesis that the infeed angle must have an impact on power requirement during chipping. In the present investigation this conclusion was tested. Standardized preformed test rods were chipped with a helical chipper at seven different infeed angles while torque, rotational speed and chipping time were recorded. The experimentation was done using poplar wood with different moisture content. Based on the measurements power requirement and energy consumed was calculated for each test series. The results of the experiments show that power requirement and energy consumed are decreasing with increasing infeed angle. The results seem to be extraordinary since increasing infeed angles lead to decreasing chip sizes being produced. Based on theoretical deliberations and experimental data it can be assumed that besides the anisotropic character of wood geometrical settings of helical chipping could be a reason for the experimental findings. But, because the chipping time is also dependent on the infeed angle there still must be other reasons concerning the occurring forces during helical chipping, too. For this reason there is a need to have a closer look onto the different forces occurring during helical chipping. Against this background the Discrete Element Method (DEM) could be a simulation method for future research. [ABSTRACT FROM AUTHOR]

Abstract: The Authors surveyed 6 industrial chipping operations for a whole work year, collecting data about machine usage, product output, fuel consumption and chipper knife wear. Despite the challenging work conditions offered by mountain operations, industrial chipping contractors manage to achieve a high machine use, ranging from 500 to over 2,500 h year−1. Product output varies between 18,000 and over 120,000 m3 loose chips per year. In order to acquire enough jobs, operators may travel between 1,500 to over 20,000 km in a year. Industrial chipping contractors adopt different operational strategies to achieve their production targets, and they equip accordingly. Some operators prefer to tap smaller local areas and opt for smaller tractor-powered chippers, which are less powerful and productive than larger independent-engine units, but cheaper and capable of negotiating low-standard forest roads. Others prefer to explore larger areas and achieve higher product outputs, and they opt for larger independent-engine chippers, often mounted on trucks. Long term productivity varies with machine type: tractor-powered units produce between 40 and 50 m3 loose chips per hour, whereas larger independent-engine chippers produce between 60 and 90 m3 loose chips per hour. Specific fuel consumption is about 0.5 L diesel per m3 loose chips, regardless of chipper type. A sharp knife set can process between 200 and 1,500 m3 loose chips before getting dull. Disposable knives last longer and are cheaper to manage than standard re-usable knives. [Copyright &y& Elsevier]