Timmersorteringens inverkan på sågverksekonomin

Abstract: Modern sawmills are using the raw-material and the production-capacity more efficiently today, due to rising raw-material prices and higher production costs. Log sweepness has a negative effect on the sawn yield, for sawmills with straight-sawing. It is desirable that these logs could be sorted based on more criteria, if it increases value-yield and consequently the utilization of raw-material. Bow-heights over 1 cm have a negative effect on sawn yield, since the surface of the mantle cuts down in the sawn pattern. Some of these small bow-heights reduce the logs yield of value which affects the production planning negatively. Nearly half of all the Swedish logs have a bow-height over 1 cm. Small bow-heights are almost impossible to detect without a 3d-optical log-scanner. Magnus Widerström, manager of the sawmill Södra Timber Lenhovda, has initiated a closer examination of the timber-sorting problem for this sawmill, and if more criteria in the timber-sorting could increase the economical profit. The results are based on a sample of 110 logs from one timber-class, with a diameter interval of 23-23,9 cm, arriving at the sawmill in Lenhovda. These logs were randomly selected at the measuring station by VMF (the wood-measuring association), and were then manually measured. The logs were sawn in a straight-sawing sawline with a fixed sawingpattern, which was chosen according to the logs topdiameter at 23 cm. A model for an alternative timber-sorting was established, where the log was sorted not only based on topdiameter, but also on taper and sweep, for the determination of timber-class. These criteria ensured that the surface of the log not entered the sawn yield. A possible sawn value-yield was estimated based on the alternative timber-sorting and sawing pattern. This estimated value-yield was compared with the actual value-yield, of the sawn logs. The difference in value-yield showed if it is profitable to apply the alternative timber-sorting. The results show that the value-yield decreases with increased bow-height, if the timbersorting only depends on the topdiameter of the log. The value-yield difference shows that the profit from sweeped logs increases if the sorting-diameter is reduced with up to 2 cm. Bigger reductions of the sorting-diameter involves a loss. If the alternative timber-sorting model had been applied, the sawmill would have increased its profit by 300 sek or 9 % for the 110 logs. If one is willing to generalize the results of the study to a larger sawn volume, the sawmill would have had a potential for an increased profit of 70 000 sek for the whole timber-class sawn volume of 4 500 m3 (by top measurement) in 2002. For the sawn volume of a whole year, 200 000 m3 (by top measurement) in the year 2002, the potential profit increase is about 3 000 000 sek. If a more efficient log-scanner is installed, more criteria could be used in the timber-sorting. Then the raw-material could potentially be used more effectively and the production-planning could be further improved.