How drum design affect chipper performance

Chipping is an essential element in the energy supply chain and mobile chippers are very popular because they can work directly in the forest or at the roadside landing. Due to space constrain, drum chippers are dominating forest biomass operations. Drum chipper are less efficient then disc chipper but they are also less sensitive to feedstock quality. Drum chippers come in two main design types: closed drum with full-length knives and open drum with staggered narrow knives. The goal of this study was to analyse the specific effect of these design types on productivity, fuel consumption and product quality, using different raw material types. For this purpose, two commercial chipper models with almost identical characteristic were selected to represent the alternative drum designs. Both machines were fed with two different feedstock types: chestnut logs and chestnut branches. The study included 12 repetitions per combination of drum design, feedstock type and knife condition (new or worn out) for a total of 2 x 2 x 2 x 12 = 96 repetitions. Both chippers were attached to the same instrumented tractor, and all product obtained from each chipping bout was blown into big bags and weighed with a load cell attached to a forklift. The study showed that the closed drum design was better suited to handle branch material, compared to the open drum design, especially when knives were dull. Under these conditions, productivity was higher, fuel consumption lower and chip quality better for the closed drum design. No significant differences between the two designs were found when processing logs or when the knives were new. In general, the performance of both designs was significantly affected by feedstock type and knife wear.