竹木地板坯料的干燥方法及干燥设备

竹木地板坯料的干燥方法及干燥设备的选择是十分重要的 ,它直接关系到产品的质量与企业的经济效益。作者提出了地板坯料的干燥方法及干燥设备的选择。     

Movement in a board of impermeable wood during drying

 Creep and sorptive-mechano-effect are defined in terms of complementary partial derivatives. The nett strain and the distribution of mechanical strain in a board of rectangular cross-section is predicted where the board is dried by the progression of a square front. The effects of creep and sorptive-mechano-effect are considered separately and when both are effective. Received 20 September 1999     

装饰薄木窑干工艺的研究

介绍了一种简单、实用的薄木干燥方法，即用常规干燥窑干燥薄木的方法。采用这种方法，薄木含水率从54.82％干燥到17．54％需26h，干燥的薄木无变形、无破损，木材保持原有的天然色泽，设备投资低，干燥成本低，能够满足企业的生产需求。     

Moisture content gradient in a softwood board during drying: simulation from a 2-D model and measurement

Summary A 2-D mathematical model was developed to simulate moisture movement and heat transfer in width and thickness directions within a softwood board during drying. The model is based on wood physiological features and behaviour observed during drying. In sapwood, liquid water movement is assumed to be a consequence of capillary action between liquid and gas phases inside the cell lumens. However, liquid flow does not occur in wood close to the exposed surfaces because at timber surfaces the wood cells are damaged during the sawing process and consequently the liquid column is broken. In heartwood, liquid flow is negligible since the pits are normally aspirated during the formation of heartwood in the growing tree. Water vapour moves under a partial vapour pressure gradient while bound water diffuses within the wood material due to differences in chemical potential. The model was solved numerically to predict moisture-content profiles. Experiments were undertaken to measure the moisturecontent gradient. Samples were removed from a tunnel dryer at intervals throughout drying, frozen overnight and then cut into slices for moisture-content determination. The experimental results were used to verify the model.This work is supported by the New Zealand Foundation of Research, Science and Technology under contract CO4415     

Influence of heating and drying history on micropores in dry wood

To investigate the influence of heating and drying history on the microstructure of dry wood, in addition to the dynamic viscoelastic properties, CO₂ adsorption onto dry wood at ice.water temperature (273 K) was measured, and the micropore size distribution was obtained using the Horvath-Kawazoe (HK) method. Micropores smaller than 0.6 nm exist in the microstructures of dry wood, and they decreased with elevating out-gassing temperature and increased again after rewetting and drying. Dry wood subjected to higher temperatures showed larger dynamic elastic modulus (E′) and smaller loss modulus (E″). This is interpreted as the result of the modification at higher temperature of the instability caused by drying. Drying history influenced the number of micropores smaller than 0.6 nm in dry wood not subjected to high temperature, although the difference in the number of micropores resulting from the drying history decreased with increasing out-gassing temperature. A larger number of micropores smaller than 0.6 nm exist in the microstructure of dry wood in more unstable states, corresponding to smaller E′ and larger E″ than in the stable state. Consequently, unstable states are considered to result from the existence of temporary micropores in the microstructures of dry wood, probably in lignin. Part of this report was presented at the 55th Annual Meeting of the Japan Wood Research Society, Kyoto, March 2005, and at the 56th Annual Meeting of the Japan Wood Research Society, Akita, August 2006     

Thermal degradation of bending strength of plywood and oriented strand board: a kinetics approach

The construction industry has relied heavily on wood and wood-based composites, such as oriented strand board (OSB) and plywood for timber frame construction. Therefore, it is highly imperative to categorize the response of wood-based composites when exposed to elevated temperatures for a sustained period of time. The essence of fire-resistant structural design is to ensure that structural integrity be maintained during and after the fire, prevent collapse and maintain means of egress. Another aspect is to assess post-fire structural integrity and residual strength of existing structure. The objective of this project was (a) to study the effect of exposure time on bending strength (MOR) of OSB and plywood at elevated temperatures, (b) to interpret any relationships between different temperature and time of exposure using a kinetics model for thermal degradation of strength, and (c) to develop a master curve representing temporal behavior of OSB and plywood at a reference temperature. As much as 1,152 samples were tested in static bending as a function of exposure time and several temperatures. Strength (MOR) of both OSB and plywood decreased as a function of temperature and exposure time. These results were fit to a simple kinetics model, based on the assumption of degradation kinetics following an Arrhenius activation energy model. The apparent activation energies for thermal degradation of strength were 54.1 kJ/mol for OSB and 62.8 kJ/mol for plywood. Furthermore, using the kinetics analysis along with time–temperature superposition, a master curve was generated at a reference temperature of 150°C which predicts degradation of strength with time on exposure at that reference temperature. The master curves show that although plywood has a higher initial strength, OSB performs better in terms of strength degradation after exposure to elevated temperature.     

Measuring moisture content profiles in a board during drying: a polychromatic X-ray system interfaced with a vacuum/pressure laboratory kiln

A standard X-ray source and an energy-sensitive detector were placed on both sides of a wood dryer which operates over a wide range of drying conditions. The spectrometric X-ray intensities transmitted through the wood sample were related to the mass concentration of wood and water using a rigorous calculation needed in the case of a polychromatic X-ray beam. The source and the detector are carried by a motion controller in order to scan the sample at different drying times and determine the moisture content (MC) profile along the board thickness. Treatment on spectrometric data and the evolution of the MC profiles in a Norway spruce board (Picea abies) are presented in this work.     

Hydrolysis kinetics of hexosanes entering into the composition of white water coming from the fiber board industry

Summary Hydrolysis kinetics of hexosanes entering into the composition of white water coming from the fiber board industry to hexoses, catalyzed by sulphuric acid and hydrochloric acid has been investigated. Constant rates of the reaction, catalyzed by 0.31 m sulphuric acid, determined at the temperatures 353 °K, 363 °K, 373 °K are respectively equal to: 1.40·10^-5s^-1, 5.75·10^-5s^-1, 30.06·10^-5s^-1.Constant rates of the reaction, catalyzed by 1 m hydrochloric acid, determined at the temperatures 343 °K, 353 °K, 363 °K are respectively equal to: 0.2008·10^-5s^-1, 0.82·10^-5s^-1, 3.63·10^-5s^-1.Constant rates of the reaction, catalyzed by 2 m hydrochloric acid, determined at the temperatures 343 °K, 353 °K, 363 °K are equal respectively to: 0.52·10^-5s^-1, 2.25·10^-5s^-1, 8.15·10^-5s^-1. Constant rates of the reaction, catalyzed by 3 m hydrochloric acid, determined at the temperatures 343 °K, 353 °K, 363 °K are respectively equal to: 3.824·10^-5s^-1, 8.596·10^-5s^-1, 13.10·10^-5s^-1.The activation enthalpy of the reaction, catalyzed by 0.31 m sulphuric acid, determined in the range of temperatures 353 °K–373 °K is equal to 168.36 kJmol^-1. The activation entropy of the reaction, catalyzed by 0.31 m sulphuric acid is equal to 136.19 JK^-1mol^-1. The activation enthalpy of the reaction, catalyzed by 1 m, 2 m, 3 m hydrochloric acid, determined in the range of temperatures 343 °K–363 °K is equal to 145.37 kJmol^-1. The activation entropy of the reaction catalyzed by 1 m, 2 m, 3 m hydrochloric acid is respectively equal to: 68.97 J K^-1mol^-1, 75.73 J K^-1mol^-1, 79.68 JK^-1mol^-1.     

Cooling and steam conditioning after high-temperature drying of Pinus radiata board: experimental investigation and mathematical modelling

 Steam conditioning of softwood boards after kiln drying is of critical importance for relief of residual drying stresses and to improve distribution of final moisture content. The conditioning practice in New Zealand includes two steps: immediately after high temperature (HT) drying the load is cooled until the core wood temperature is 75 to 90°C, and then the stack is steam conditioned for a period of 1 to 4 hours depending on the lumber thickness and moisture content after drying. In this work, experimental and theoretical studies were performed to better understand the conditioning process and to investigate factors which influence its effectiveness. In the experiment, 50 mm thick Pinus radiata sapwood boards were first dried at 120/70°C for 11, 12, 13, 16 and 18 hours, respectively, to varying moisture contents, and then cooled and steam conditioned for 1 hour. To assess the effectiveness of conditioning, moisture pick-up, moisture gradient, and transverse residual drying stress (indicated by cup and strain) were measured. It was found that drying wood to a low moisture content (below 6%) increased the conditioning effectiveness. A separate matched stack was conditioned for 4 hours after 13 hours drying which showed better results than 1 hour conditioning. A mathematical model for wood drying was extended to include both the cooling and conditioning phases. The model was numerically solved to examine the wood temperature and moisture content changes during the whole process of drying, cooling and final steam conditioning. Increase in wood temperature, moisture pickup and moisture gradient during steam conditioning were predicted and validated by the experimental data. This information is currently being used at the New Zealand Forest Research Institute in simulation of stress development and relief for drying of Pinus radiata lumber. Received 6 July 1998     

Study on drying rate in contact drying with flexible screen

IntroductionA new type contact dryer with non-metal flexibleplaten was patented in 1998 in China, which specialstructure and material solved the problem of low productivity in platen drying. The machine was similar tohot press. Direct contact betWeen wood and heatedplaten allows rapid heat transfer by conduction (Sandoe 1983). Though the flexible screen conducts heatslower than metal platen does, it transfers massmuch fast6r. So water removing rate decides veneerdrying rate in the new machin…     

低温等离子处理对重竹板材浸渍剥离性能的影响

采用低温等离子处理已经疏解的竹片,研究低温等离子处理对重组竹上胶量及浸渍剥离性能的影响。结果表明：随着低温等离子处理时间的增加,竹片上胶量先上升后趋于平稳,且浸渍剥离性能的变化与上胶量变化一致,其最佳处理工艺为低温等离子处理时间5 s,胶液固体含量25%,浸渍时间10 min。     

热压温度及板材密度对竹木复合层积材顺纹抗压强度的影响

通过单因变量两因素重复试验,以毛竹竹篾和桦木单板为原料,使用酚醛树脂胶黏剂压制竹木复合层积材,分析热压温度及板材密度对竹木复合层积材顺纹抗压强度的影响。结果表明,在试验选定因素水平范围内,热压温度和板材密度对竹木复合层积材顺纹抗压强度影响显著,板材顺纹抗压强度随热压温度的升高而增强,但145℃与160℃两水平之间差异并不显著;不同密度对板材顺纹抗压强度的影响差异显著,板材的顺纹抗压强度随板材密度的增大而增大;在其他工艺参数相对不变的情况下,热压温度与板材密度的交互作用对板材顺纹抗压强度的影响并无显著的影响。     

A numerical study of the shape stability of sawn timber subjected to moisture variation Part 2: Simulation of drying board

A theory for analysing the shape stability of sawn timber was implemented in a finite element program. To illustrate the types of results that can be obtained, the behaviour of a board during drying was simulated. The simulation yields information about unfavourable deformations and stresses during the drying process. To investigate factors that influence drying deformations, a parameter study was performed in which the influence of different constitutive models and different material parameters was studied. In addition, the influence of the spiral grain angle was examined. Received 22 April 1997     

在没有强度要求的前提下如何确定土场掺灰比例

在公路建设过程中，经常遇到如何向土中搀加石灰以降低土中含水量的问题。本以试验为基础，从质量和经济两方面，其中主要是质量方面论述了在土壤中应掺加多大比例的石灰才是最佳的比例的问题。     

臭椿干燥工艺的研究

臭椿板材在干燥过程中易开裂，采用低温干燥方法，使初期干燥温度和末期干燥温度较低，解决了干燥过程中的开裂问题，且满足了《国家锯材干燥质量标准》二级以上的指标要求。     

木荚豆木材干燥工艺的初步研究

通过百度干燥试验法的试验，获得了木荚豆的木材的干燥特性数据，便于开展其干燥技术的研究。同时，干燥试验方法补充了观测干燥速度和扭曲的内容，较为完整和便于应用。结果表明，木荚豆木材的干燥特性是：内部开裂与截面变形的干燥等级为1级，初期开裂的干燥等级为3-4级。根据这些特性因子编制了木荚豆板材的干燥基准。     

Influence of forbs and shrubs on ruminal fermentation and digesta kinetics in sheep fed a grass hay/straw diet

Four ruminally cannulated, Debouillet wethers were used in a 4×4 latin square experiment to evaluate the influence of a forb mix, a shrub mix and alfalfa (ALF) hay on ruminal fermentation characteristics and digesta kinetics of a basal grass hay/straw (GH/S; 1.04% N) diet. The grass hay was mostly blue grama (Bouteloua gracilis) mixed with barley (Hordeum vulgare) straw. Wethers were fed either the GH/S mix (7030), GH/SALF (295813), GH/Sforbs (265420), or GH/Sshrubs (265420). The forb component consisted of equal parts of scarlet globemallow (Sphaeralcea coccinea) and leatherleaf croton (Croton corymbulosus) while shrubs were composed of equal parts of fourwing saltbush (Atriplex canescens) and mountain mahogany (Cercocarpus montanus). Ruminal pH, ammonia-N, as well as total VFA concentrations and molar proportions of individual VFA did not differ among diets. Particulate passage rates tended (P>0.10) to be greater for diets containing ALF, forbs or shrubs (2.8, 2.9 and 2.8% h^–1) than the GH/S diet (2.5% h^–1). In situ DM and NDF disappearance of a GH/straw (5050) mix did not differ among treatments at most incubation times, except at 96 h when extent of both DM and NDF disappearance were greater (P<0.05) in sheep fed either forbs or shrubs than in those fed other diets.     

木材干燥专家系统的建立

当前我国木材干燥生产面临的主要问题是：①干燥设备不足，主要采用的都是常规(传统)干燥器，能耗高，质量差；②环保对节能与减少污染的要求更加迫切；③从业人员素质较低；④人工速生材、难干阔叶材及进口材将成为主要原料。针对上述情况，开发木材干燥自动控制系统，     

木材微波干燥缺陷产生原因及其预防措施分析

从木材介电特性、微波穿透深度、微波设备、干燥工艺等方面分析了木材微波干燥缺陷产生的主要原因,并从优化干燥器设计,改善微波场分布均匀性,控制微波辐射功率和辐射时间,改变微波辐射方式等方面探讨了预防干燥缺陷产生的主要措施,以期为木材微波干燥技术的研究和应用提供参考。