Experimental determination of highly dynamic forces during wood trunk comminution with a drum chipper

Using large wood chips for heating systems in industrial applications is becoming popular. As a result, the requirements of the machinery that produces these large wood chips have increased, especially on the chipping tools and on the surrounding supportive components. This paper evaluates the acting main forces on a chipping drum that produces large wood chips via field and laboratory-based experimental measurements. In this study, a variety of strain gauges are applied to selected areas of the rotating chipping drum to measure localised strain conditions during wood-stem cutting. Four different wood species were investigated for comparison. Furthermore, the influence of sharp and dull knives is analysed. With the aid of experimental measurements and analysis on a laboratory scale, linear models are developed to determine the chipping force, which is cutting depth-dependent, for a variety of wood species. Testing parameters for such models are proposed via load spectra. The variability of the acting force value is evident. The maximum load on the drum affects at 10% of the time of a single cut. The largest applied forces are between 1.6 and 1.8 higher than the calculated average force. The commuting hornbeam sample exhibits the highest resistance against chipping compared to the three-other species. Additionally, a change in the load is easily recognised in the field test when utilising dull chipping blades. A reconstruction of the alternate load direction is based on laboratory testing.