Commercial timber sawing is always done in trade-off between yield and capacity, between cost of raw material and of production. Accurate knowledge of the dimensions for every single log is needed for successful breakdown. Traditionally, mills sawing to customers’ order, i.e. timber lots of given dimension and quality, start the breakdown process by scaling and sorting unbarked logs. However, accuracy can be greatly improved if scaled after barking. Scaling barked logs to adapt sawing pattern to each log inevitably slows down production speed, and also produces a variety of sawn boards besides the ordered one. The goal of the project described in this paper was to optimise the yield while maintaining high capacity and sawing to order. A modern, medium-sized sawmill producing ca. 60 000 m3 spruce timber annually was about to renew the sawlog intake. A two-stage log scaling/sorting and sawing twin mini-series was concluded. The first stage is the traditional sorting of unbarked logs. In the new intake, when the order is to be produced, logs are debarked before a second scaling with a 3D scanner based on laser beams reflected from the smooth and bright log surface. Logs are directed to either of two log decks, or buffers, each of ca. 25 logs, and sawn in twin mini-series alternating between the two. Sorting criteria might be purely diameter, log length, quality prediction generated from log geometry, or a combination. The sawn timber yield was increased by up to 3 000 m3 annually, corresponding to the contribution margin improved by 3 mill. NOK or more. Production speed is increased by ca. 4%, but producing two orders simultaneously increases planning complexity, requiring additional training for involved personnel. It can be concluded that the chosen set-up: Two-stage log sorting with accurate scaling in the final sorting and sawing twin orders in alternating twin mini-series, has proved successful with respect to sawn timber recovery and production capacity.
Keywords: log scaling, dual mini-series, production capacity, twin orders
Authors
Gjerdrum P.
Wood Technology Section, Norwegian Forest and Landscape Institute, Ås
Hamar B.
Moelven Numedal AS, Flesberg
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