25mm厚滇青冈木材的间歇干燥工艺

滇青冈是典型难干材,易发生表裂、内裂、变形等干燥缺陷。在常规连续干燥试验的基础上,拟定25 mm厚滇青冈材间歇干燥工艺基准。结果表明:采用间歇干燥工艺,可在22 d内将板材含水率从39%降低至12%,干燥质量较好,无表裂,但扭曲和瓦弯缺陷比例偏高;适用于除湿干燥窑和气密性不佳的常规干燥窑,工艺仍需进一步优化。     

阔叶树材新干燥法的试验研究——荷术的热压法干燥

本文论述了荷木(Schima superba)板材(厚25mm)热压干燥的试验研究。研究结果表明,采用热压干燥法可大大缩短阔叶树材的干燥时间,若板材的锯剖方法合理,干燥缺陷(如内裂)可显著降低,热板的压力对板材的厚度收缩有很大的影响。从整体考虑,热压干燥较佳工艺为干燥温度160℃,压力0.7N/mm~2。热压干燥法尤其适合于小规模手工艺木制品厂和雕刻木制品厂。     

阔叶材热压法干燥的研究

本文通过对几种典型的难干阔叶材,从原料制备、干燥特征、2克优化和质量上进行分析,研究了难干阔叶材的热压板干燥。研究结果表明,采用热压板干燥法可大大缩短干燥时间,减少干燥缺陷(如蜂窝裂)。所有板材在干燥1—4h内终含水率为6％—10％左右。温度和压力对板材的厚度收缩和干燥速率也有很大影响,适宜的工艺参数为:温度160℃,压力0.7MPa。     

解决CLZ侧风机干燥窑柞木板干燥不均匀的生产性试验

ＣＬＺ侧风机型干燥窑在吉林省以及全国各地旧干燥窑中所占比例颇大，这种干燥窑防腐性能较好，结构简单，投资少，但生产中存在诸多问题：１）终含水率差别大。如白河林业局制材厂８＃窑３８ｍｍ厚的柞木板材干燥 ２９ｄ后有些终含水率仍在 ２８％以上，有些板材终含水率则在４％以下。２）干燥柞木和水曲柳常出现大面积内裂，白河林业局制材厂仅１９９５年就报废了１５窑以上，直接经济损失达２００万元以上。３）表裂、端裂和变形严重。 白河林业局制材厂干燥窑原有生产条件如下：不区分板材厚度堆垛，窑内未设挡风板；材堆侧面与侧墙间…     

石梓和米老排木材干燥特性及干燥工艺

对厚度2．5厘米的板材进行了气干和窑干试验。结果指出，石梓除易发生扭曲外，一般不发生其它缺陷；米老排除易发生扭曲外，还易发生表裂、内裂、皱缩等缺陷，提出了气干－窑干联合干燥工艺的建议。     

阔叶树小径材热压干燥工艺的研究

通过对荷木和米槠两种华南地区常用阔叶树小径材薄板材热压干燥工艺的研究，探讨热压干燥工艺参数对小径材板材干燥质量（包括密度，厚度压缩率，尺寸稳定性及部分力学性能）的影响，试验结果表明，热压干燥工艺可以大大改善小径材的物理力学性能。     

小径级柞木干燥工艺的试验研究

小径级柞木干燥试验结果表明:在干燥初期干球温度为35℃、干燥末期干球温度为70℃、干燥周期中进行两次中间处理和末期终了处理、干燥周期为15 d的工艺条件下,板材干燥前总平均含水率41.6%,干燥结束后总平均含水率11.7%,板材厚度上含水率偏差<3%;干燥结束后伸长应力和压缩应力甚微,板材表面的颜色轻微变暗,除髓心材和水纹材有少数裂纹和轻微变形外,其余木材并没有发生翘曲、变形、开裂等干燥缺陷,干燥质量满足了GB6491—86《国家锯材干燥质量标准》二级以上的指标要求。本次试验确定的干燥工艺满足了小径级柞木板材的干燥工艺要求。     

栓皮栎地板材的干燥工艺研究

本文对栓皮栎地板材的干燥工艺进行了研究。结果表明，按照本研究提出的栓皮栎地板材的干燥工艺，将厚23mm的栓皮栎地板材从初含水率48.1%干燥到终含水率9.3%，干燥周期为16天，干燥质量较好，基本无可见干燥缺陷出现，含水率均匀。     

杉木：广西优良用材树种

杉木是一种常绿乔木，主要分布在我国亚热带地区。它与马尾松并列为广西两大速生优质用材造林树种，在广西分布范围很广。杉木是上等的建筑材、造船材、工业板材和各种家饰装修材等，历来为人们所喜爱。近10年来，已研究出杉木可用作造纸材和复合木地板材，同时杉木皮、叶、枝还可提取杉萜烯类物质用作医药使用。     

甘巴豆地板材干燥特性及干燥工艺研究

采用百度试验法对22mm厚的东南亚甘巴豆地板材干燥特性进行了研究和分析,参照百度试验缺陷等级以及干燥缺陷对应的干燥条件拟订了初步干燥基准并进行相关的工艺试验及干燥质量检验。结果表明,按照本研究提出的甘巴豆地板材的工艺,将厚22mm的甘巴豆地板材从初含水率45.4%干燥到终含水率10.3%,干燥周期为7天,干燥质量好,基本无可见干燥缺陷,达到国家标准规定的二级干燥锯材的干燥质量等级。     

辐射松与杉木在高温干燥中萜烯类释放浓度研究

以40 mm厚的辐射松(Pinus radiata)和人工林杉木(Cunninghamia lanceolat)锯材为对象,研究高温干燥过程中干燥温度和锯材含水率对萜烯类产物释放浓度的影响,并与辐射松常规干燥中的萜烯类释放浓度作比较。高温和常规干燥过程中采抽气样次数均为5次,抽气速度为1.0 L/min,采样时间为30 min,采用Tenax管收集干燥过程中萜烯类产物,用气相色谱仪分析其成分及浓度。结果表明:高温干燥辐射松萜烯类释放浓度高于常规干燥辐射松与高温干燥人工林杉木,但萜烯类挥发物的组分有所差别。常规干燥辐射松锯材萜烯类释放浓度对环境是安全的,然而在高温干燥过程中,尤其在干燥中后期,当萜烯类挥发物浓度大于1.5 mg/m3时,对辐射松和人工林杉木释放萜烯类挥发物应采取回收措施,以确保对环境的安全。     

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     

Determination of diffusion coefficients for sub-alpine fir

Estimates of the drying rate for sub-alpine fir lumber and the effect of process variables on final moisture contents are valuable information for kiln operators. The diffusion approach offers one generalized way to estimate the drying time required and the final moisture content distribution. The diffusion coefficients of normal wood and wet wood of sub-alpine fir lumber were determined by two types of approaches in this study: the traditional method and the inverse moisture diffusion algorithm. The results from both approaches indicate that the diffusion coefficient of normal wood is greater than that of wet wood for sub-alpine fir.     

Climate control in vacuum dryers for convective heat transfer

The European Drying Group (EDG) proposal on a wood drying quality standard defines demands on final moisture content variation of the dried wood. The final moisture content variation will depend on material parameters as well as the production process and the wood will always show a “natural” moisture content variation after drying. Thus the drying process has to be defined well enough to allow for the natural moisture content variation in order to fulfil the demands of the drying standards. As the average equilibrium moisture content of the wood in a vacuum drying kiln with pure steam atmosphere is determined by the pressure and the temperature, the demands on the climate control system to fulfil the demands of the drying standard can be calculated with regard to the natural moisture content variation of the wood. In the first part of this contribution the demands on climate control in vacuum dryers are calculated based on the EDG-standard and the natural moisture content variation. In the second part of the contribution the demands on climate control are compared with climate and moisture content measurements from industrial production in vacuum kilns. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed.     

Moisture flow characteristics during radio frequency vacuum drying of thick lumber

Summary Thick specimens of two softwoods were dried in a laboratory radio frequency/vacuum (RF/V) kiln in order to investigate the internal moisture flow patterns. The spatial moisture distributions in the longitudinal arid transverse directions were monitored as a function of time in a number of runs. The results indicated that both longitudinal and transverse moisture transfer modes contribute on the overall moisture flow occurring within wood, but there was no distinction as to the percentage contribution of each to the overall flux. There were no abrupt drying front changes and no moisture discontinuities observed during drying. A second group of runs was also carried out using end-matched specimens to study its length effects on drying characteristics, such as drying rate, and internal vapor pressure and temperature profiles. The results demonstrated that short specimens dried faster than long ones at moisture contents above the fiber saturation point.The financial support for this work from NSERC/Canada through a Strategic Grant (STR0167393) and the lumber contribution from MacMillan-Bloedel are greatfully acknowledged.     

杉木人工林木材的高频真空干燥工艺

对人工林杉木25mm和50mm厚板材进行了系列高频真空干燥试验.结果表明:干燥后的板材变形小,表面平整,表芯层含水率差异较小.尽管试板的初始含水率差异较大,但根据高频真空干燥靠近正极板的木材比靠近负极板的干燥速度快的特点,试板的初始含水率由低至高在负极板至正极板之间进行顺序摆放码垛,干燥后的板材含水率可达到均匀一致.     

赤桉半干材的窑干与调湿处理工艺

针对移行材和早材皱缩等主要气干缺陷,拟定出赤桉半干材的干燥工艺,窑干前进行回复皱缩和减小表面硬化的汽蒸处理,窑干至目标含水率时进行终了调湿处理.结果表明:汽蒸预处理可以有效地回复皱缩材和显著地减小表面硬化;5 d内将试材的平均含水率25.61%下降到11.72%;3 h的汽蒸处理和24 h的湿空气处理均可有效地减小含水率梯度和残余塑性变定,但后者效果更佳;板材干燥质量达到国家标准二级质量的要求.     

高温水供热干燥速生杉木方材

运用高温水供热系统干燥速生杉木方材。生产性试验表明，6天内初含水率为55．5％的杉木方材干至始含水率5．4％，干燥质量符合细木工板生产的要求（少数高含水率木材除外）。此干燥法集中供热，具有热效率高、运行安全和经济可行等特点。     

Drying of timber in progressive kilns: Simulation,quality, energy consumption and drying cost considerations

Abstract

Progressive (semi-continuous) kilns for softwood drying are very common in Finland and Sweden and are used in some other countries too. A simulation program has been developed that covers all three types of this kiln. The program calculates the climate in the length direction of the kiln and moisture content, moisture profile, wood temperature, slicing test gap and stress development. Energy consumption and drying costs may also be determined. The temperature level is the most important parameter regarding kiln efficiency. Two-zone progressive kilns are found to be more efficient than single-zone kilns. Progressive kilns have lower energy consumption and drying costs than batch kilns. Experimental full-scale tests show that the timber quality from a progressive kiln is comparable to, or in some cases even better than, timber dried in batch kilns.     

Calculation of CFP and verification of effect on CO2 emission reduction for the use of certified wood in Kyoto Prefecture

The representative carbon footprint of product (CFP) value of “certified wood in Kyoto Prefecture” was calculated as 241?kg-CO₂/m³. The CFP value was 158?kg-CO₂/m³ when wood was not kiln dried and final processing was not involved, whereas that of “kiln-dried, finished wood” was 284?kg-CO₂/m³. Comparisons of different types of wood were also conducted to examine CO₂ emission-reducing effects of “certified wood in Kyoto Prefecture”. We compared the CFP of lumber produced (in Japan) from logs supplied from Japan and other countries and that of “certified wood in Kyoto Prefecture”; the lumber products as a target for comparison are shipped to markets throughout the country. The CFP of “certified wood in Kyoto Prefecture” was approximately 50% lower compared to that of North American wood lumbered in Japan and shipped to markets throughout the country, and about 30% lower compared to the mean CFP of lumber produced (in Japan) from logs supplied from Japan and other countries and shipped to markets throughout the country. We then compared the CFP of “products imported from other countries after being cut into lumber” to that of “certified wood in Kyoto Prefecture”. The CFPs of lumber products from North America and Europe were lower than that of “certified wood in Kyoto Prefecture” (kiln-dried, finished wood). However, when only woodchips were used as a heat source in the process of kiln drying, the CFP of “certified wood in Kyoto Prefecture” was lower than any other kiln-dried lumber products. Regarding “certified wood in Kyoto Prefecture”, the use of woodchips as a heat source in the process of kiln drying or a shift to air drying decreases the CFP.