Dynamic behavior of nonuniform lumber in stress-grading machines

Summary A finite element model is developed to predict the dynamic behavior of nonuniform lumber in stress-grading machines of the constant deflection type. Simulations carried out with the model showed that speed largely effects the accuracy with which grading machines can identify low-point modulus of elasticity (E) oflumber. Tests conducted at 15 and 315 m/min on lumber members containing a low E zone confirmed model predictions. However, as demonstrated in this study, machine ability to detect low-point E at high speed can greatly be improved from filtering the load signal measured by the machine.Financial support of the National Science and Engineering Research Council of Canada and the Ministère de l'Energie et des Ressources du Québec is gratefully acknowledged     

Effect of size on the bending strength of laminated veneer lumber

Summary The effect of size on bending strength has been experimentally determined for laminated veneer lumber. Width was found to have no effect on bending strength. The effect of depth times length on bending strength obtained by the slope method was about 0.075, which is in good agreement with the results obtained by the shape parameter method. The effect of length is somewhat more severe than the effect of depth. Size was found to have no effect on modulus of elasticity or modulus of rigidity.In addition, the relationships between bending strength, modulus of elasticity and density of laminated veneer lumber were experimentally modelled.The author is pleased to acknowledge Research and Development Manager Matti Kairi, who represents the Kerto laminated veneer lumber manufacturer of Finnforest Oy, for fruitful co-operation over several years. The patience of senior research scientist Markku Kortesmaa, who calculated and several times explained the details of Appendix A for the author, is also acknowledged     

Effect of utilization standard on wood supply and lumber yield

ABSTRACT

Although sustainable forest management is accepted worldwide in concept, challenges in the methods of implementation remain. Using local data sets from Alberta, Canada, we show that a simulation approach can assist the implementation of sustainable forest management by improved understanding of product potential and other forest ecosystem goods and services that forests can provide for a given forest inventory. This will assist facilitating trade-offs among them for an optimal wood utilization strategy to achieve sustainable forest management. In this example, effects of wood utilization standard on merchantable volume, lumber volume, and number of trees that can produce at least one piece of lumber are quantified, and a conversion method for wood volumes under different wood utilization standards is presented. Wood utilization standard is the combination of stump height and diameter inside bark at merchantable height, which considerably influences available volume quantity of forest resource. However, such influences have not been quantified for sustainable forest management implementation. Our results not only confirmed that merchantable and lumber volumes increased with decreasing stump height and diameter inside bark at merchantable height, but also revealed that this trend will not hold when diameter inside bark at merchantable height is less than 7 cm.     

Differences of tensile strength distribution between mechanically high-grade and low-grade Japanese larch lumber I: Effect of length on the strength of lumber

An experimental study was conducted to evaluate the effect of length on the parallel-to-grain tensile strength of Japanese larch (Larix kaempferi, Carriere) lumber. Six hundred pieces of mechanically graded lumber were tested at gauge lengths of 60, 100, and 180 cm. The lumber was sorted into matched groups according to the dynamic Young's modulus measured by the longitudinal vibration method before the lumber was cut to the particular length. The averages of the dynamic Young's modulus of high-grade (H) and low-grade (L) specimens were 12.8 and 7.5 GPa, respectively. Using nonparametric estimates, the estimated length effect parameters of H and L were 0.268 and 0.304 for the 50th percentile and 0.121 and 0.256 for the 5th percentile, respectively. We then concluded that the different length effect factors between H and L could be used when using the lumber for practical purposes. The parameters of L were larger than those for H, and the parameters for 5th percentiles were smaller than the parameters for 50th percentiles. When two-parameter Weibull distribution functions were fitted to the strength data, the estimated shape parameters of the Weibull distribution by the parametric method were almost identifical to the inverse of nonparametric parameters except the 5th percentiles for H. The influence of defects such as knots on the lower tail of the strength distribution in H may be different from that in L.Part of this paper was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998     

热处理对慈竹重组材性能的影响

以丛生竹类的慈竹竹篾为原料,运用不同的热处理温度对其进行高温热处理并压制慈竹重组材,对热处理前后慈竹的化学组分进行分析,并对慈竹重组材的物理力学性能进行测定。研究结果表明,当热处理温度从190℃上升至210℃后,慈竹化学组分和慈竹重组材力学性质出现急剧的变化,保证力学强度的前提下,考虑户外用材的尺寸稳定性及生物耐久性的要求,可选用热处理温度190℃,热处理时间2 h的热处理工艺。     

提高制材出材质量的有效措施

1　概　述在各类木材加工生产中 ,制材生产属粗加工类型 ,其任务就是把原木加工成板材、方材、枕木或其它成材 ,制材工艺过程依主锯的不同 ,分带锯制材、框锯 (立锯 )制材和圆锯制材。我国的制材企业主要采用带锯制材生产工艺 ,其特点主要表现为 :( 1)可以任意调整锯路方向 ,有利于看材下料 ,并便于剔除原木缺陷 ,从而适应低质量原木的加工利用 ,相对地比框锯制材一、二等品率要高。( 2 )可以使用较薄的锯条 ,出材率较高。( 3)能锯割特殊技术要求的成材 ,如完全径切板、弦切板、平行木纹等板材。影响制材出材质量的因素比较复杂 ,但基本表现…     

Goodness-of-fit analysis for lumber data

Summary Four different probability distributions were studied to evaluate their relative goodness-of-fit in describing the modulus of rupture (MOR) and modulus of elasticity (MOE) of populations of dimension lumber. The distributions under consideration were the normal, lognormal, Weibull and Johnson's S_B. The populations of lumber consisted of 96 data sets of various species groups, mechanical properties, sizes, structural grades and growth regions. The goodness-of-fit criteria selected in this study were the log likelihood, Kimball and Kolmogorov-Smirnov (K-S) tests. The K-S statistic was also calculated at the value of the random variable associated with the lower five percent exclusion limit of the empirical cumulative distribution. This value indicated the degree of goodness-of-fit at the lower tail of the distribution. The results indicated that the S_B distribution generally provided the best fit to the data. The maximum likelihood test overwhelmingly recommended the S_B distribution. The Kimball and Kolmogorov-Smirnov tests gave milder endorsements of the S_B distribution. No distribution proved to be superior to the others in modeling the lower five percent exclusion limit of the populations.The author would like to thank the Engineering Data Management (EDM) Inc. of Fort Collins, Colorado, for the use of their parameter evaluation software, STAtistical Data MANager     

滇产赤桉干燥工艺初探

通过百度干燥特性试验,初步获得了滇产速生人工林材赤桉的干燥特性数据,以便于开展其干燥技术的深入研究.试验结果表明：赤桉材的初期开裂多在3～4级;内裂平均等级为2级,最严重的为3级;截面变形严重,4级居多;干燥速度慢,为4～5级.分析了滇产赤桉干燥的主要缺陷以及初步解决方案,并根据百度法干燥特性与干燥条件对应表,制定了赤桉的预报干燥基准.     

桉木单板层积材生产工艺的优化

采用响应面法(RSM)和中心组合旋转设计(CCRD),研究了桉树单板层积材(LVL)的生产工艺条件,并对优化工艺所得的预测值进行了实验验证。方差分析结果表明:面粉添加量对桉木LVL的静曲强度(MOR)和弹性模量(MOE)有着显著影响,而热压温度和热压时间的影响不显著。通过回归分析,建立了相应的回归模型。回归模型的预测值与实验值的拟合良好,说明回归方程能用来预测和优化桉木LVL的力学强度性能。最佳工艺条件为:热压温度130℃,热压时间1.5 min/mm,面粉添加量5%(质量分数)。在此工艺条件下压制的桉木LVL垂直加载条件下的静曲强度(MOR⊥)和弹性模量(MOE⊥)分别为89 MPa和16 722 MPa,平行加载条件下的静曲强度(MOR∥)和弹性模量(MOE∥)分别为88 MPa和15 067 MPa,MOR和MOE分别达到了结构用单板层积材国家标准的优等品和140E级别。     

Impact of precommercial thinning on tree growth,lumber recovery and lumber quality in Abies balsamea

Abstract

Precommercial thinning (PCT) is often used to improve stand growth and value. While PCT may accelerate tree growth and reduce mortality, it may also have a negative effect on product quality. This study examined the effect of moderate and heavy thinning on tree growth, lumber recovery and quality in a natural balsam fir [Abies balsamea (L.) Mill.] PCT trial 35 years after thinning. Compared with the control, the heavy thinning increased merchantable tree diameter, stem volume per tree and lumber volume recovery per tree by 41.1%, 100.9% and 92.7%, respectively, reduced the Select Structural grade (the best grade) recovery by 33.7%. Thinning did not affect the no. 2 and better grade yield. There was a 12.2% and 15.0% difference, respectively, in the lumber bending modulus of elasticity (MOE) and modulus of rupture (MOR) between the control and heavy thinning. Moderate thinning had little impact on the visual grade recovery, lumber bending MOE and MOR. Heavy thinning is recommended if the goal is to get sizeable sawlogs in the shortest time, whereas moderate thinning is preferable if the intention is to minimize the negative effects on lumber quality while retaining modest tree growth and lumber recovery. Overall, PCT of very dense young balsam fir stands appears to be an effective and viable silvicultural treatment.     

提高科技木锯材出材率的实用技术

随着技术的不断创新,利用普通木材甚至低质速生材生产各种仿天然珍贵木材颜色和纹理的科技木得到越来越广泛的应用。但是,科技木锯材出材率低是目前国内科技木生产厂家所面临的突出问题,严重制约行业发展。采用3种研究方案,即两端头锯截表面刨切后再胶合模压(A)、两端头中间夹多层单板后再胶合模压(B)和两端头直接胶合模压(C),对科技木一次锯材得到的三角形截锯端头进行再利用,以提高科技木锯材出材率。结果表明,依照3种方案制备的试样其MOR、MOE、浸渍剥离性能均高于LYT 1655—2006重组装饰材要求,同时将科技木锯材出材率提高17%左右。综合考虑试样的力学性能、出材率及经济性,A方案和C方案优于B方案。通过表面粗糙度和接触角实验,对上述结果进行了验证。     

落叶松刨切薄木用材的改性与蒸煮工艺的研究

通过研究,筛选出一种高效、无毒、无污染的落叶松木材处理剂,并采用正交试验法得出落叶松刨切薄木用材的最佳蒸煮工艺。据此,可以达到溶出树脂、缓解应力、软化木材并制得合格的落叶松刨切薄木的目的。     

Bending strength adjustments for moisture content for structural lumber

Summary Effects of moisture content on bending strength and section capacity have been studied assuming that strength properties are linearly related to moisture content below the fiber saturation point. The models developed using the linear strength vs. moisture content relationships are compared with quadratic models developed earlier. The linear representation of strength variation with moisture content leads to predicted member bending capacity relationships which show that increases in member bending strength with moisture content will compensate for section property decreases at all bending strength property levels. Comparisons of bending strength and bending capacity models show that the two modelling approaches lead to similar predicted member performance. Simplified procedures are provided for adjusting member bending strength for moisture content which are suitable for materials properties codes or standards.     

单板层积材的研究现状

论述了国内外在单板层积材工艺及机理方面研究的主要进展，其中工艺研究包括加压工艺、材种及单板等级等，而机理研究则主要集中在力学性能和耐久性能的研究上。在此基础上对研究竹材增强单板层积材的可行性和必要性进行了探讨，并简要介绍了竹材增强单板层积材研究的进展情况。     

Mechanical stress-grading of structural timber in Europe,North America and Australia with a research programme on this field for South Africa

Summary Preparatory to undertaking research on mechanical stress-grading in South Africa and the introduction of the stress-grading of lumber by the South African timber industry, a tour of those countries already engaged in research on or practicing mechanical stress-grading, viz. Great Britain, the U.S.A., Canada and Australia, was undertaken by the author.The following aspects are discussed in detail: the principles on which mechanical stress-grading is based; the research methods used to establish these principles; the derivation of working stresses for the stress-grades; and the efficiency and reliability of the new grading method as practiced in North America and Australia.The various types of stress-grading machines in use and still being developed are critically described. It is shown that each machine has its own peculiarities and that these affect the stress-grading process to a greater or lesser degree. For this reasons it is concluded that the efficiency of mechanical stress-grading must be studied in relation to the machine used. The calibration of the machines and the methods used for controlling the grading process are discussed.The degree to which mechanical stress-grading has been put into practice by the producer and accepted by the consumer of structural timber and by grading and government authorities is discussed. The manner in which mechanical stress-grading is being incorporated in the overall grading and handling process in sawmills in the United States is described with emphasis on the tendency to mechanization and automation.Among the conclusions drawn from the survey, the need for further work on the application of mechanical stress-grading in industry is stressed.The research and development work required to establish mechanical stress-grading in South Africa is summarized in the form of a schedule which serves as the broad framework of a research programme.

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Zusammenfassung Vorbereitend zu Untersuchungen über die mechanische Festigkeitsklassifizierung von Bauholz in Südafrika und zur Einführung der Festigkeitsklassifizierung in der Südafrikanischen Holzwirtschaft, unternahm der Verfasser eine Studienreise durch Länder, die bereits Forschungen auf diesem Gebiet durchgeführt haben und dieses Klassifizierungsverfahren anwenden, und zwar England, Kanada, die Vereinigten Staaten und Australien.Im einzelnen wurden die Grundlagen, auf denen die mechanische Festigkeitsklassifizierung beruht, die angewandten Forschungsmethoden zur Bestimmung dieser Grundlagen, die Bestimmung der zulässigen Spannungen für mechanische Güteklassen, sowie die Eignung und die Zuverlässigkeit des neuen Sortierungsverfahrens wie es bereits in Nordamerika und Australien angewandt wird, geprüft.Die verschiedenen Maschinen für die Klassfizierung, die zur Zeit benutzt oder entwickelt werden, wurden eingehend untersucht. Es wird gezeigt, daß jeder Maschinentyp besondere Eigenschaften hat, die das Klassifizierungsverfahren mehr oder minder beeinflussen können. Die Zweckmäßigkeit der mechanischen Festigkeitsklassifizierung steht deshalb mit der Geeignetheit der Maschinen für die Praxis in enger Beziehung. Die Eichung der Geräte und die angewendeten Kontrollmethoden des Klassifizierungsverfahrens werden besprochen. Es wird eine Übersicht über die Anwendung des neuen Klassifizierungsverfahrens in der Praxis aus den Ländern gegeben, wo es bereits in Erzeuger- und Verbraucherkreisen sowie durch Behörden und Normenausschüsse anerkannt wird. Die Art und Weise, wie die mechanische Festigkeitsklassifizierung in den Gesamtsortierungs- und Transportbetrieb in einigen Sägewerken der Vereinigten Staaten unter besonderer Berücksichtigung der herrschenden Mechanisierungs-und Automatisierungsbestrebungen eingeführt wurde, wird erörtert.Die Notwendigkeit weiterer Entwicklungsarbeiten im Hinblick auf die spätere Einführung der mechanischen Festigkeitsklassifizierung in der Industrie wird in der Untersuchung hervorgehoben.Die Forschungs- und Entwicklungsarbeiten, die zu einer erfolgreichen Einführung der mechanischen Festigkeitsklassifizierung in Südafrika erforderlich sind, werden in Form einer Aufstellung zusammengefaßt, die als Rahmen für ein zukünftiges Forschungsprogramm dienen kann.

     

An estimation of thawing time for hemlock dimension lumber

Since the heat-treatment of lumber may start at a temperature below freezing, two distinct stages, thawing and heating, are encountered during this treatment. This paper discusses the estimation of both thawing and heating times for hemlock (T. heterophylla) dimension lumber. An approximate analytic solution is used for the thawing process while a numeric simulation is utilized for the heating process. Heat-up experiments were carried out in a laboratory kiln. Core temperature in lumber was accurately determined when heating under various combinations of dry and wet bulb temperature. The results indicate that the calculated heating rates agree well with the experimental outcome.     

Effect of species and log diameter on the volumetric yield of lumber in northern Brazilian Amazonia: preliminary results

ABSTRACT

Volumetric yield analysis is critical to optimizing performance in the timber industry. In the Amazon and in the Amapá state, this information is still little known and scarce, and therefore this study was developed to obtain and analyze the volumetric yield coefficient of ten commercial tree species and to test the variation by diameter class. We collect data of volumetric yield from for ten commercial species. For each species, the yields in different diameter classes were analyzed, as well as the yield difference between the species. The overall yield obtained for the sawmills (43.95%) and the yield of each species are within the established standards for operations in the industry according to the legal requirements. There were no differences (p ≥ 0.05) in diameter classes for species with the exception of Dinizia excelsa and Handroanthus albus. However, there was no linear increase (p ≥ 0.05) between the diameter and yield of lumber for all species. The species Dinizia excelsa, Hymenolobium petraeum, Ocotea rubra and Vochysia guianensis show a significant difference in yield for the other species due to the higher obtained values, however, they are statistically similar when compared to each other.     

Effect of Cutting Speed on Surface Quality by Bandsawing

Introducti0nSincetI1ebandsa\`canbequickl}'andaccLIratel}'setal1dtllereisvirtuaII};noupper-sizeIilnitinIogdiameter,tI1emachinecanberegardedasthemosleffectiveaII-r0undmachine.Lumbermillsshowgro\"inginterestintI1ebal1dsawingconceptduetotl1el1ighthroLIghputan…     

小径山杨板材干燥工艺

本文对小径山杨30mm厚锯材进行了干燥试验,结果表明：锯材厚度含水率偏差为1．6％;干燥平均度为7．4％-1．4％-7．4％＋1．6％;应力为0．75;一级材为87．5％,二级材7．5％,三级材5．0％;未发现内裂及裂纹扩大现象。     

Factors affecting the fungal colonization of pine lumber

This study investigated whether the physiological condition of wood influenced patterns of colonization by mould and sapstain fungi. The extent of fungal defacement on sawn pine lumber Pinus nigra var. maritima that had been killed by gamma‐irradiation was compared with the defacement on untreated, still living timber that had been aged for up to 16 weeks prior to being sawn. All the sawn lumber was exposed to the natural inoculum of sapstain and mould fungi in a working sawmill environment over a 4‐week period. The results indicated that the pattern of fungal defacement differed markedly in dead or aged wood compared with untreated wood. Mould fungi were most prevalent on the dead irradiated wood, whereas sapstain fungi dominated the freshly sawn lumber which was still living. The differences appear to be independent of wood moisture content and may be related to the production of inhibitory compounds by living cells in wood as it becomes senescent and dies.