THE IMPACT OF A STRENGTH GRADING PROCESS ON SAWMILL PROFITABILITY AND PRODUCT QUALITY

A strength grading process, starting with log grading, was studied with respect to grading yield, impact on quality, and economic efficiency when visual grades according to Nordic grading rules were used for alternate product comparison. Pine (Pinus sylvestris) and spruce (Picea abies) logs and boards were graded with several varieties of commercial grading and strength-grading equipment. The boards were destructively tested, and the European grade-determining properties strength, stiffness, and density were measured. Models for these were made by partial least squares and validated. A method for the derivation of settings for multiple indicating properties, which increased yield in some cases, was proposed and evaluated. Grading to grade combinations of C40, C30, and C18 was done. The impact of visual override based on deformations was also studied. A simplified economic and sensitivity analysis was done. The outcome was that log grading can be used for strength grading with good economic and quality results. Strength pregrading on logs improves sawmill economy, depending on the species and market situation. Drying quality greatly influences the yield through visual override grading on deformations. Market prices of high grades (>C30) must improve in order to stimulate supply, as it is more economical to produce lower grades.

[1]  Anders Grönlund,et al.  Predicting board strength by X-ray scanning of logs: The impact of different measurement concepts , 2007 .

[2]  A. Tsehaye,et al.  Sorting of logs using acoustics , 2000, Wood Science and Technology.

[3]  G. Johansson,et al.  Quality of structural timber-product specification system required by end-users , 1994, Holz als Roh- und Werkstoff.

[4]  Ton Vrouwenvelder,et al.  The JCSS probabilistic model code , 1997 .

[5]  Jochen Köhler,et al.  Reliability of Timber Structures , 2007 .

[6]  Johan Fredriksson,et al.  Automatic grading of sawlogs: A comparison between X-ray scanning, optical three-dimensional scanning and combinations of both methods , 2004 .

[7]  Anders Grönlund,et al.  Predicting the Stiffness of Sawn Products by X-ray Scanning of Norway Spruce Saw Logs , 2001 .

[8]  Robert J. Ross,et al.  Acoustic assessment of wood quality of raw forest materials - A path to increased profitability , 2007 .

[9]  Armas Jäppinen,et al.  Automatic sorting of sawlogs by grade , 2000 .

[10]  Goran Turk,et al.  Analysis of strength grading of sawn timber based on numerical simulation , 2004, Wood Science and Technology.

[11]  Anders Grönlund,et al.  Fingerprint traceability of sawn products using industrial measurement systems for x-ray log scanning and sawn timber surface scanning , 2008 .

[12]  Jochen Köhler,et al.  Reliability of timber structures , 2007 .

[13]  Jerker Westin,et al.  Classification of structural timber by decision trees : a comparison to the certified method , 2009 .

[14]  Fredrik Nilsson,et al.  Modulus of elasticity of Norway spruce saw logs vs. structural lumber grade , 2006, Holz als Roh- und Werkstoff.

[15]  Antti Hanhijärvi,et al.  Development of strength grading of timber using combined measurement techniques: Report of the Combigrade-project - phase 2 , 2008 .