The findings of recent studies from both eastern and western Canada have shown that the drying behaviour of subalpine fir (A. lasiocarpa) and balsam fir (A. balsamea) is similar, which allows common solutions to be applied based on research conducted on one species of fir or the other. This article summarizes previous research findings and good practices that can be adopted in the short term to improve the drying of fir.
Le mandat du projet consiste en la réalisation d’essais avec un équipement d’acquisition générique NIR (Near Infrared) dans le but de développer des modèles mathématiques pouvant être utilisés pour déterminer le taux d’humidité des planches de bois franc pour quatre essences : le chêne rouge, l’érable à sucre, le merisier et l’érable argenté.
Une fois les modèles développés les objectifs plus spécifiques sont d’évaluer le niveau de précision de mesure de la teneur en humidité sur du bois parfaitement équilibré ainsi que déterminer les impacts sur les lectures provenant des facteurs suivants : l’essence, la densité, la qualité de surface, la température du bois, le gradient de teneur en humidité ainsi que la vitesse de passage des planches. Finalement, des essais doivent être réalisés sur du bois provenant directement de l’industrie et n’ayant subi aucun traitement d’équilibrage en laboratoire pour connaître le niveau de précision de lecture dans ces conditions.
The process of fingerjointing is complex and requires numerous efforts in order to evaluate the various workable and optimum conditions of jointed wood members. Many factors are known to affect the strength of fingerjoints. Some are related to wood, such as species, density, natural defects, moisture content (MC), temperature, and gluability of the species. Others are related to wood machining, including type of adhesive and gluing processes, such as condition of the cutting tools, curing time and applied assembling pressure.
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3.1 MoistureContent Distribution
In British Columbia, due to the decline of lodgepole pine, mills should expect higher volumes of sub-alpine fir in their species mix. The impact on drying is significant. For example, drying times for green SPF (spruce, pine, sub-alpine fir) vary from 24 to 36 hours whereas drying times for sub-alpine fir can easily exceed 70 hours. In addition to longer drying times, the drying of species such as sub-alpine fir using current procedures often results in wet lumber and value loss can be higher than $100 per Mfbm. The potential annual impact for a typical BC mill is estimated to be in the range $1,000,000 to $1,500,000.
Along the years, sawmills have invested millions of dollars in drying technology (conventional drying and green sorting systems) which, for the most part are efficient and relatively low cost. Thus, under the circumstances outlined above, sawmills urgently need to find ways to minimize the problems associated with the drying of sub-alpine fir that is, new procedures or combination of methods, to ensure maximum grade recovery at the end of drying and reduce drying times (increase productivity and lower processing costs). In addition, the pressure exerted by typical longer drying times for sub-alpine fir will impact the drying of spruce and pine. Thus, strategies to speed the drying for those two species are needed to maintain annual production targets.
The main objective of this project is to evaluate several strategies using existing technology so that sawmills can readily implement them throughout their drying operations dealing with larger volumes of sub-alpine fir and for mills with kiln capacity constraints which could compromise their production targets.
Ce manuel assemble les renseignements existants sur la technologie du séchage des placages. Il est destiné aux opérateurs de séchoirs, aux contremaîtres et aux gérants. Il est conçu spécialement pour les usines de l'Est du Canada mais contient des références aux essences et aux méthodes de séchage couramment utilisées dans l'Ouest canadien. Les sujets suivants sont abordés dans ce manuel: humidité du placage, hydromètres, processus de séchage, types de séchoirs, opération et entretien des séchoirs, incendies, pollution et défauts des placages causés par le séchage.
Correction factors are provided for the Delmhorst resistance-type moisture meters equipped with 2-pin insulated electrodes. These factors allow the operator to adjust the meter reading for a wood temperature range of -40 degree centigrade to 50 degree centigrade. Factors are provided for 12 softwood species and 14 hardwood species.
A total of 48 peeler blocks and 256 mini-billets were sampled from mills to investigate the effects of yard storage time, and artificial yard drying and sprinkling on residual moisture contents (MCs) and veneer quality. MC in fresh and stored log inventories varied greatly across mills according to geographic location of their wood supply zones, bark damage and loss, and storage time and conditions. The main findings were as follows:
1. DF logs supplied by three BC mills from the Cariboo, Thompson Okanagan, or Kootenay regions were highly variable in wood MC.
2. Winter-cut DF logs with high sapwood MC stored had good bark retention and high moisture retention over 6 and 9 winter-spring months. No effects on veneer peeling roughness from longer-term winter storage up to 9 months.
3. Summer-cut logs had little or no residual bark, or the bark slipped off very easily during debarking. Exposed, bark-free summer-cut logs can dry and crack on edges and ends very quickly, within a few weeks.
4. A marked decline in veneer quality with piling time in Summer for spruce and DF, suggesting an optimum window of processing of such exposed logs of about two weeks. Veneer quality and recovery suffered markedly once the logs had fully air dried mainly because of edge splits creating natural fragmentation of the ribbon.
5. Mills receiving dry-zone logs with much lower MC have a very limited storage window, especially over winter. As little as 2-3 weeks if bark is damaged or missing.
6. Veneer quality could not be definitively tied to log residual MC. Under the controlled laboratory conditions used here it was observed that peeling quality could still be good at low sapwood MC (35-40%) and or very high (MC>100%). Whether this is still the case in mill production is unknown.
7. Logs must never be allowed to fall below FSP and develop edge-checks or deep end checks.
8. Wax emulsion end sealants were effective at hampering drying and end checking on high MC logs, but not effective on low MC logs.
9. Sprinkling retained log freshness and peel quality in high MC DF for several months and prevented log drying and end splitting as well as inner log staining. Ends absorbed considerable extra moisture. Some variability in peel quality was noted.
10. The prototype EM1000 Ground Penetrating Radar could only be reliably used in log edge mode in DF. The unit would also require re-calibration for the very high sapwood MC in spruce and wet-zone DF logs.
