PRE-GRADING OF DOUGLAS-FIR LOGS FOR GLULAM LAMELLA PRODUCTION

摘要

The assessment of timber quality at any time in the production chain promises to be a big advantage for the forest and timber industry. This paper presents results for pre-grading analysis, which were performed on the complete processing chain — starting with standing trees through to sawn timber. The quality of wood (timber) was detected by means of the dynamic modulus of elasticity. The measurements were conducted on 108 trees of Douglas-fir growing at different forest experimental stands in Germany. Long logs of about 13 m were bucked into short logs of 4.1 m. The dataset contains 630 boards (50×160 mm2) cut from 247 short logs. Dependencies were studied by simple linear regression analysis. The investigation shows high correlation between different stages in production chain of timber. The strongest relationship exists between wet and dry boards (r~2 = 0.97, n = 630). But also the relationship between long logs and short logs cut of them is very good (r~2 = 0.94, n = 180). Finally, the effects of pre-grading long logs on the yield of sawn timber are shown. A possible threshold value of 11000 for long logs leads to an increase in board yield of up to 30 percentage points for C 24. The boards were strength graded by ViSCAN-COMPACT in C-classes according EN 338. The increase in yield depends on the raw material quality and the strength class combination.