Abstract

Multi-stem delimbing devices may rationalise processing of small-sized trees. Different types of delimbing device are reviewed. Some basic features of cradle delimbing were studied experimentally for Scots pine (Pinus sylvesiris L.) and Norway spruce (Picea abies (L.) Karst.) separately. As standard for delimbing quality, the proportion of branches cut shorter than a specified value is proposed. Acceptable delimbing quality was defined in the study as 75 per cent of the branches cut shorter than 25 mm. Efficiency was measured as the time required to achieve the defined delimbing quality. Loss of stemwood mas measured simultaneousy with delimbing efficiency. The delimbing process followed an S-shaped function. When a bunch of trees first enters the cradle, little delimbing takes place. A period of fairly rapid delimbing follows, succeeded by a period of decreasing efficiency in the final stages. Active delimbing devices, with a momentum of their own. are more efficient than passive devices. The delimbing devices must have sharp edges for efficient delimbing of Norway spruce. Rotors were the most efficient of several delimbing devices tested. The design of the cradle itself, especially the inclination of the longsides, was shown to be important in improving dclimbing efficency. The optimum speed of the conveyor rotating the bunch within the cradle was found to be ca l.5 m s -1