This guide proposes a method to evaluate the performance of optimized log and cant breakdown equipment as a tool for mill personnel to improve production efficiency. Optimized systems are found in all aspects of modern sawmills, and evaluating their ability to maximize product value is not necessarily a simple task..
Analytical methods presented in this guide are primarily intended for sawmill technical staff, i.e. technicians and engineers responsible for process improvement. With this guide and a better understanding of optimizers’ operating mode, they will be in position to implement a control method based on the efficiency of the log breakdown equipment
To be successful, a performance evaluation test needs to be properly planned. Once objectives have been clearly defined, a methodology must be laid out for the results to be significant and conclusive. Forintek specialists are available at all times to help a company set up a project of this nature.
A 2-D heat and mass transfer finite element model based on the water potential concept was previously developed to simulate the evolution of moisture content and temperature in the cross section of a piece of lumber during drying. In order to be able to use the model with an industrial interest, an user interface was developed and the experimental parameters required for the model were determined for three Eastern softwood commercial species within the project no. 2674 Drytek Enhancement for Commercial Species. The user interface was developed using the MatLab development environment. It generates the mean drying and wood temperature curves, computes the maximum effective moisture content gradient and shows the evolution of the 2-D moisture content and temperature profiles during drying. The pressure membrane technique and equilibration over saturated salt solutions were used to determine the moisture content–water potential relationship at 30, 60 and 90oC for balsam fir sapwood and heartwood, black spruce heartwood and jack pine heartwood, in desorption from green to dry conditions. The instantaneous profile method was used to determine the effective water conductivity of the same species from 30 to 90oC in the three main directions: radial, tangential and longitudinal. Experimental determination of the parameters was initiated for white spruce sapwood and heartwood and will be available in a near future. Kiln drying tests of black spruce and balsam fir were performed in order to validate simulation results.
Finger jointing is complex and requires numerous efforts in order to evaluate the various parameters that influence the process and to optimize product performance. Some of the key parameters are related to the conditions of the lumber material such as moisture content (MC) and temperature. Attempts are made by the finger jointing industry to control the lumber conditions prior to finger jointing; however, the process has proved to be difficult. There is a need to evaluate the impact of MC and temperature of lumber and the interaction between the two, on the end product performance, especially with new adhesives systems.
Black spruce (Picea mariana (Mill) B.S.P.) 2x3 blocks in green and at different MCs (12, 16 and 20%) were condi-tioned at various temperatures (-5, 5, 12 and 20oC) prior to finger jointing. Two types of adhesives were used in this study: Polymer Emulsion Polyurethane (PEP) and a new fast curing formulation of Phenol Resorcinol Formaldehyde (PRF). All specimens were tested in tension after 24h of curing at room temperature to determine their ultimate tensile strength (UTS). Microscopic analysis of the adhesive bond was performed to evaluate the glue penetration into the wood following conditioning. Results have shown that the operating envelop for PEP adhesive is between 12 and 16% MC and between 5 and 20oC, while optimum MC for PRF adhesive was found to be around 16%. It was found that PRF adhesive performed better at high moisture content. High wood failure and uniform glue penetration profiles were associated with dry lumber. Failure in the glue and irregular glue penetration profiles were generally associated with green wood.
The purpose of this study on tamarack (Larix laricina) was to propose a drying technique adapted to the end use, to document the colour change after drying, and to assess the rot resistance of the various drying processes used. This study was divided into two parts. In the first part, 5/4’’ thick lumber was dried using superheated steam/vacuum (SS/V) drying in order to compare drying results with the results of a study conducted at Université Laval. The Université Laval study compared drying results obtained with three conventional drying schedules: high temperature (115 °C), elevated temperature (90 °C), and standard temperature (82 °C). The study compared drying time, final quality, colour change, and rot resistance. The second part of the study involved drying 7/4’’ thick lumber using SS/V drying.
It was clearly shown that drying process does not affect rot resistance of tamarack. However, drying process and operating temperature affect colour after drying. High temperature drying resulted in the greatest post-drying colour change. The SS/V process provided post-drying results that closely matched those before drying. The drying time obtained from the best SS/V test, with a time/quality trade-off, was longer than in the Université Laval high-temperature conventional test (0.9 factor). Compared to conventional drying schedules, the SS/V process was 1.4 times faster than the elevated temperature schedule, 2 times faster than the standard temperature schedule, and 3.4 times faster than schedules used in the industry.
Drying times required to reach a final moisture content of approximately 12% in the four 7/4” lumber tests ranged from 132.2 hours to 175 hours. Compared to current industrial results, drying by SS/V is approximately 2.6 to 3.1 faster. Warping was better controlled during the 7/4’’ tests. Winter conditions during the tests made it difficult to maintain conditions in the SS/V kiln. Nonetheless, the use of concrete dead loads on the charges and high temperature conventional kiln drying appear to provide good possibilities for Canadian manufacturers.
NRCan Value to Wood Program which discusses Larix laricina; Seasoning - Vacuum, Steam and Kiln drying
Engineered wood flooring (EWF) is gaining in popularity since it appeared in Europe in the 70’s. 40% of the wood flooring installed in the USA is EWF and 75% are EWF in Europe. In layered wood composites such as engineered wood flooring, dimensional stability is of primary importance. The non-homogeneous adsorption or desorption of moisture by the composite may induce cupping, thus decreasing product value. These products were developed by the industry with the result that knowledge on the product and its behaviour is very limited. The objective of this study is to develop a finite element model of the hygromechanical cupping induced by moisture desorption in layered wood composites. The model is based on two sets of equations, 1) the three-dimensional equation of unsteady state moisture diffusion, and 2) the three-dimensional equations of elasticity including an orthotropic Hooke’s law, which takes into account the shrinkage, and swelling of each layer. The model was used to assess 34 different constructions. Results may be used as guideline in the design of new engineered wood flooring construction.
This report analyses softwood-drying practices in Canada and identifies the R&D efforts required in this field. These issues need to be examined in order to address environmental concerns and implement solutions that will improve energy efficiency and reduce greenhouse gas emissions.
Developing advanced softwood-drying control systems would reduce energy use and enhance product quality. According to some researchers, the potential reduction in energy use by kilns in Canada would be 5.5 PJ per year, or 335 kT per year in carbon dioxide (CO2) emissions. Furthermore, it is estimated that CO2 emissions could be reduced by an additionnal 90 kT per year through a decrease in the amount of lumber that is downgraded.
This study aims to give an overview of the main trends in developing control systems and to identify barriers to their introduction. It will also serve as a starting point for launching and directing projects on control procedures for lumber-drying in cooperation with the industry, universities, private and public laboratories, manufacturers and users.
In keeping with this objective, researchers for this study surveyed members of the Quebec Lumber Manufacturers' Association and a few mills in British Columbia. The main findings are as follows:
- Industry opinion is that its facilities are sufficiently modern to meet current market needs.
- Industry opinion is that quality (grade reduction / rejection rate) is the most significant factor when evaluationg drying systems.
- Because it is not easy to measure the quality of the drying process, drying time is the most often used to evaluate drying performance.
- Although quality was identified as the main variable in the drying process, the proportion of under-dried and over-dried lumber units was 9 and 16 percent, respectively.
- Operators play a significant role in drying operations (they manage the process before, during and after drying), and their actions affect the results of the process considerably.
- The decision to purchase a drying-control system is driven more by the acquisition of a kiln than by requirements related to the process itself.
The researchers reviewed current technical knowledge of the main dry kiln control systems by considering two types of controls : air temperature control when drying ; and setting up drying programs. The figures in this report illustrate the use of these two approaches along with various other control methods employed in the industry.
There are five softwood kiln controller manufacturers in Canada, which together account for 75 percent of the Canadian market. Although they use similar controllers, there are differences in how drying programs are set up and how changes in moisture content are measured during drying. In spite of recent technological advances, proper drying operations still depend on operator expertise.
R&D on new measurements instruments and mathematical models has not resulted in advanced kiln controllers so far. Innovation in this area has not kept pace with the advances in other leadings sectors. One technical problem that has not been resolved is that of measuring moisture content. In spite of more than 20 years of effort, mathematical models are still being developed in the scientific community, and few applications resulting from this work have benefited the industry other than those supporting operator training.
The research community and the industry acknowledge that the development of an advanced controller represents a promising avenue for improving the lumber-drying process. Unfortunately, problems in modelling the drying process and measuring moisture content remain represent major obstacles to the development of high-efficiency controllers.
Another obstacle relates to the difficulty of evaluating the financial benefits that would accrue from potential advances with the necessary speed and accuracy. These, then, are the key factors hindering the introduction of new drying technologies. They also explain why length of drying time is still the most frequently used control variable, despite the fact that the industry considers finished product quality more important. Furthermore, it appears that operators' actions significantly affect what happens not only in the kiln but at all stages in the process, from sawmill to shipping.
In view of this, we believe that a system for monitoring the entire drying process is worth investigating. Such a system would :
- serve to collect all data generated by measuring instruments at all stages in the process, from the sawmill to the planing mill
- help to establish productivity and quality indicators for measuring the monetary value of process enhancements introduced by operators
- make it possible to provide a rationale for other promising research approaches such as multivariate analysis and experimental design
This approach would make it possible to enhance control of the drying process and process quality while also revealing potential energy savings.
Le présent rapport porte sur l’analyse des pratiques de séchage actuelles du bois résineux au Canada et sur l’identification des besoins en R-D associés à ce domaine. Les préoccupations au sujet de l’environnement justifient une réflexion dans ce secteur pour mettre en œuvre des moyens afin de diminuer la consommation énergétique et les émissions de gaz à effet de serre.
Il est reconnu que l’implantation de systèmes de contrôle-commande avancés constitue un bon moyen de diminuer la consommation énergétique tout en améliorant la qualité du produit. Selon certaines hypothèses, la réduction potentielle de la consommation énergétique serait de l’ordre de 5,5 PJ/année soit 335 kt/année d’émission de CO2 au Canada pour les séchoirs à bois. De plus, on peut évaluer une réduction potentielle additionnelle d’émission de CO2 de 90 kt/année découlant de la diminution du déclassement du bois.
L’objectif général de l’étude est donc de présenter une synthèse des principales tendances en matière de développement des systèmes de contrôle-commande et d’identifier les facteurs limitant leur implantation.
Pour atteindre cet objectif, une enquête a été menée auprès des membres de l’Association des manufacturiers de bois de sciage du Québec et quelques usines en Colombie-Britannique. Les principaux résultats de l’enquête se résument comme suit :
L’industrie perçoit ses installations actuelles suffisamment modernes pour répondre aux besoins actuels des marchés.
L’industrie mentionne que la qualité (le déclassement) est l’élément le plus significatif pour évaluer le séchage.
Toutefois, la qualité n’étant pas facilement mesurable, le temps demeure l’outil le plus utilisé pour évaluer les performances de séchage.
Bien que la qualité ait été identifiée comme la principale variable du procédé de séchage, la proportion de pièces surséchées et sous-séchées est de 16 p. 100 et 9 p. 100, respectivement.
L’opérateur joue un rôle significatif dans l’ensemble des opérations de séchage (gestion avant pendant et après séchage). Ces actions ont une incidence sur les résultats du procédé.
L’achat d’un contrôleur est davantage motivé par l’achat d’un séchoir que par les exigences relatives au procédé lui-même.
Les connaissances techniques sur les principaux systèmes de contrôle-commande des séchoirs à bois en faisant référence à deux types de commande, soit la régulation des températures de l’air de séchage et l’implantation des programmes de séchage, ont été passées en revue. Ces deux types de commande sont schématisés et facilitent la présentation des différentes méthodes de commande utilisées dans l’industrie.
On constate que cinq manufacturiers de contrôleurs de séchoirs à bois résineux satisfont à eux seuls 75 p. 100 du marché canadien. On observe aussi que leurs contrôleurs se ressemblent passablement. La caractéristique qui les distingue est la façon d’implanter les programmes de séchage et la façon de mesurer l’évolution de la teneur en humidité lors du séchage. Malgré les récents développements technologiques, les programmes de séchage demeurent la responsabilité des opérateurs et le bon fonctionnement du séchage dépend de l’habilité de ceux-ci.
On observe que la R-D entourant les nouveaux instruments de mesure et les modèles mathématiques ne permettent pas d’appuyer l’élaboration de contrôleurs de séchoirs. On constate que l’innovation dans le domaine des contrôleurs ne suit pas le rythme observé dans d’autres secteurs de pointe. En fait, la mesure de la teneur en humidité demeure un problème technique non résolu. Les modèles mathématiques, demeurent pour leur part l’apanage du milieu scientifique avec quelques percées industrielles pour la formation des opérateurs, et cela, malgré plus de vingt ans d’efforts.
Il est reconnu, aussi bien dans le milieu de la recherche que par les industriels, qu’un contrôleur avancé est une solution avantageuse à explorer pour améliorer le procédé de séchage. Malheureusement et cela, malgré plusieurs années d’efforts, ces contrôleurs n’existent toujours pas. Dans ce cas, on peut conclure que la difficulté de modéliser le procédé de séchage et la difficulté de mesurer la teneur en humidité demeurent deux barrières importantes au développement et à l’implantation de systèmes de contrôle-commande avancés.
Une autre barrière tout aussi importante aux développements de nouvelles pratiques de séchage provient du fait qu’il est difficile d’évaluer rapidement et précisément les avantages monétaires d’une nouvelle pratique. Cette constatation explique en grande partie la difficulté d’adopter de nouvelles technologies de séchage et surtout pourquoi le temps demeure la principale variable de contrôle même si la qualité des produits finis est identifiée comme la variable de contrôle la plus importante. De plus, on s’aperçoit que l’importance des actions des opérateurs ne se limite pas seulement à ce qui se passe dans le séchoir, mais bien à tout ce qui se passe depuis l’usine de sciage jusqu’à l’expédition du produit.
Ainsi, le développement d’un système de surveillance de la pratique complète du séchage serait, d’après nous, une des principales applications établies comme valeurs cibles à explorer. On entendrait ici recueillir toutes les données générées par les instruments de mesure de l’usine de sciage jusqu’à l’usine de rabotage. Ce système de surveillance faciliterait la définition des indices de productivité et de qualité qui permettraient de mesurer la valeur monétaire des améliorations apportées au procédé par les opérateurs. Il serait aussi possible d’identifier et de justifier d’autres pistes de recherche prometteuses telles que l’analyse multivariée et le design d’expériences.
Finalement, dans un tel contexte, nous aurons une meilleure maîtrise du procédé et de sa qualité et nous pourrons aussi mettre en évidence la possibilité de réaliser une économie d’énergie en appliquant le procédé de séchage.
Laminated Veneer Lumber (LVL) and plywood are the two major veneer-based wood composite products. During LVL/plywood manufacturing, the hot pressing process is crucial not only to the quality and productivity, but also to the performance of panel products. Up to now, the numerical simulation of the hot-pressing process of LVL/plywood products is not available.
To help understand the hot-pressing process of veneer-based wood composites, the main objective of this study was to develop a computer simulation model to predict heat and mass transfer and panel densification of veneer-based composites during hot-pressing. On the basis of defining wood-glue mix layers through the panel thickness, a prototype finite-element based LVL/plywood hot-pressing model, VPress®, was developed to simulate, for the first time, the changes of temperature, moisture and vertical density profile (VDP) of each veneer ply and glueline throughout the pressing cycle. This model is capable of showing several important characteristics of the hot-pressing process of veneer-based composites such as effect of glue spread level, veneer moisture, density, platen pressure and temperature as well as pressing cycles on heat and mass transfer and panel compression. Experiments were conducted using several different variables to validate the model. The predicted temperature profiles of the veneer plies and gluelines (especially at the innermost glueline) by the model agree well with the experimental measurements. Hence, the model can be used to evaluate the sensitivity of the main variables that affect hot-pressing time (productivity), panel compression (material recovery) and vertical density profile (panel stiffness). Once customized in industry, the new model will allow operators to optimize the production balance between productivity, panel densification and panel quality or stiffness. This hot-pressing model is the first step in facilitating the optimization of the pressing process and enhanced product quality.
The objective of this project was to help Forintek members to improve MDF manufacturing processes and maintain cost competitiveness by evaluating the existing MDF blending technologies and developing improved or new methods for MDF blending.
MDF blending is a process of transforming a state of having fibre and resin as two separate physical identities into a state of having a “homogeneous” mixture of fibre and resin. Therefore, the author believes that an ideal blending technology should produce resin distribution uniformity very close to being “homogeneous” and retain all the resin mass within the fibres in a reactive state. Best resin droplet size and surface area coverage should be obtained as a result of very uniform resin distribution. On the other hand, it is impossible to obtain optimal resin droplet size and surface area coverage when the mixing of fibre and resin is not uniform. Two subjects are key to the efficiency of MDF blending – resin distribution uniformity and loss of resin. The former is about how well the blending process breaks up the resin into small droplets and distributes them on the fibres. The latter is about the effects of blending conditions on the loss of resin mass such as evaporation of resin light components in the tube dryer or the loss of resin reactivity such as resin pre-cure at elevated temperatures. Based on these considerations and his best interpretations of experimental data and observations, different blending methods were evaluated by the author.
The objective of this project was to help Forintek members improve MDF manufacturing processes and maintain cost competitiveness by developing improved or new methods for mat preheating and/or humidification.
MDF mat heating and humidification with steam (the H & H system) has demonstrated its great ability to increase press speed and hence production capacity in Ranger Board and WestPine MDF. Higher mat temperature allows shorter press time but it tends to drive some moisture out of the mat. Moisture content can vary significantly across the thickness of the mat depending on the conditions of the H & H system and the configurations of the formers, which have a strong influence on panel properties. It was observed that board formaldehyde emissions can be significantly increased as a result of using H & H, although emission levels can be effectively controlled by increasing the use of formaldehyde scavenger, or via resin modification, or both. Achieving the balance of mat temperature and moisture content and hence obtaining the optimal H & H conditions is challenging. Trial and error has been the only approach available to the mills so far. The approach of computer modeling, however, should be an excellent enhancement to the empirical approach. Based on mill data from WestPine MDF and Ranger Board, a preliminary computer model for mat heating and humidification with steam has been developed. It can be used to develop a deeper understanding of the individual process parameters and their interactions within the H & H system, improving process efficiency and product quality as well as training mill operators.
In co-operation with Hydro Quebec, an experiment on microwave preheating of MDF mat was conducted. It was observed that moisture movement within the mat upon microwave heating was from the centre of the mat to both surfaces and towards the edges and corners. The moisture variation was much higher across the thickness of the mat than among different locations of a layer of the mat. The variations are thought to be related to the mat density profiles, electric field distribution and penetration depth. During hot pressing, PressMan profiles showed higher core temperatures for the microwave-preheated mat than the control for most of the press cycle.
Based on the work carried out for this project, the following conclusions and recommendations are made:
1. A preliminary computer model has been completed for the MDF mat heating and humidification system at Ranger Board. It is now ready to customize to mill conditions.
2. A preliminary computer model has been completed for the MDF mat heating and humidification system at WestPine MDF. It is now ready to customize to mill conditions.
3. Microwave preheating of MDF fibre mat increases the initial mat temperature and re-distributes and moves moisture towards the mat surfaces.
4. As a result of moisture re-distribution, the moisture gradient and temperature gradient are in the same direction at the early stage of the hot pressing. Due to this effect of positive coupling between moisture gradient and temperature gradient, heat can be transferred significantly faster from the surfaces to the core and heat flux is also increased.
5. With microwave preheating, the increase of core temperature in MDF fibre mat starts earlier and the rate of the temperature increase is greater.
6. As a result of microwave preheating, hot press cycle time may be substantially reduced, leading to increase of production efficiency.
It is a normal practice in oriented strandboard (OSB) production to store logs outdoors for a period of time prior to the flaking process. The duration of yard storage depends on harvest season and sources of log supply. Outdoor log storage without protection could change the mechanical and chemical properties of wood due to attack by various fungi. To understand how outdoor log storage affects the wood and subsequently the strandboard quality, two piles of aspen logs were set up outside and stored for a period of four months (July 9 to November 14, 2001). One of the piles was treated with a biological solution to prevent fungal growth. The other one was stored without such treatment. Both piles contained non-debarked and partially debarked logs. Evaluation of sap stain development indicated that all logs had been colonized by staining fungi with an average stain coverage of 9.37 to 57.18% and maximum stain penetration of 3.58 to 7.27 cm over the log cross-section. The variation of fungal colonization depended on log treatment and bark condition. The most effective way to prevent stain growth was with the combination of biological treatment and partial debarking. This was followed in effectiveness by biological treatment and no debarking, no treatment and partial debarking, and, finally, no treatment and no debarking. A series of strandboard was prepared from fresh and aged aspen logs. It was observed that all boards made from stored logs were statistically comparable to or superior to the control boards made from fresh aspen logs. The boards made from treated/partially debarked and untreated/non-debarked logs were statistically comparable to each other except for the higher wet MOR for the former. In addition, both board types were stronger than other boards in terms of IB and water resistance. Compared to control boards, the stronger boards in terms of water resistance were also made from biologically treated/non-debarked and untreated/partially debarked logs. Some individual stained strands were observed on the finished board surface, which could affect board appearance if the wood had been highly attacked by fungi. Less staining was found in the boards prepared from biologically treated and partially debarked logs, as compared to other stored logs.