木材干缩发生发展过程及干缩力的研究
发布时间：2018-09-07 11:37
【摘要】：在木材干燥和使用过程中,由于水分散失尺寸减小形成的干缩力使木材产生表裂和内裂,为了研究和测试木材干缩力,首先研制木材干缩力测试仪,研究了不同干燥条件下干缩力的变化规律;干缩力的研究需要能够同时监测水分的散失和尺寸的减小,利用温湿度试验箱、力学传感器、重量传感器、位移传感器同步测试木材在干燥过程中的干缩力、含水率、干缩量,优化了木材干缩力测试系统。基于温湿度试验箱的控温控湿干缩力综合测试系统,更好地研究和探索了木材在干燥过程中的干缩力、干缩量和含水率之间的关系,研究了干燥温度、相对湿度对木材干缩的影响,主要内容如下:1.研究测试了不同规格樟子松(P.sylvestris)板材在不同干燥条件下干缩力的变化规律。结果表明:(1)同一厚度条件下,温度高的试件达到应力平衡所需时间比温度低的试件达到平衡所需时间短,干缩力变化也较温度低的明显,但达到应力平衡时温度高的试件所受的干缩力相对小于温度低的试件。(2)同一温度条件下,薄试件所受干缩力要明显大于厚试件所受干缩力,且干缩力达到最大值所需的时间明显少于厚试件。试件的个体差异性产生的误差对试验也有一定的影响。2.为了同步测试木材在干燥过程中的干缩力、质量变化和干缩量,研制了木材干缩力测试系统。系统利用了木材干燥过程中水分散失导致外部干缩力变化的关系,设计了基于温湿度试验箱的一体化控温控湿力学测试系统,更好地研究和测试了木材在干燥和使用过程中的干缩力、含水率和干缩量之间的关系。测试结果表明:用此设备可实时检测干缩力、质量变化和干缩量的平衡情况,为木材干缩不均导致干燥过程中的开裂、翘曲变形的调控奠定了基础。3.通过系统地研究家榆(UlmuspumilaL.)干燥温度、相对湿度对干缩力的影响,得到以下结论:(1)当干缩量和含水率达到稳定时,干缩力的变化也基本很小,在较高温度时,内裂的形成会导致干缩力的急剧减小。(2)在干燥初期,干缩力是负值,是因为木材的热膨胀现象引起的;随着含水率的减小和干缩量的增加,干缩力逐渐增加并达到一个稳定值。(3)影响干缩力的显著因素是温度,影响干缩量的显著因素是收缩的方向和试件厚度,影响含水率的显著因素是温度和湿度。
[Abstract]:In the process of wood drying and using, the dry shrinkage force caused by the decrease of the size of water loss causes the surface crack and internal crack of the wood. In order to study and test the dry shrinkage force of the wood, a wood dry shrinkage tester is first developed. The change law of dry shrinkage force under different drying conditions is studied, the study of dry shrinkage force needs to be able to monitor the loss of moisture and the reduction of size simultaneously, using the temperature and humidity test box, mechanical sensor, weight sensor, The dry shrinkage force, moisture content and shrinkage amount of wood were measured by displacement sensor in the process of drying, and the system of measuring dry shrinkage force of wood was optimized. Based on the test box of temperature and humidity, the comprehensive measuring system of controlling temperature and humidity controlling dry shrinkage force is used to study and explore the relationship among the drying shrinkage force, shrinkage amount and moisture content of wood in the drying process, and the drying temperature is studied. The effect of relative humidity on wood shrinkage is as follows: 1. The change of drying shrinkage force of different specifications of Pinus sylvestris var. mongolica (P.sylvestris) plates under different drying conditions was studied. The results show that: (1) under the condition of the same thickness, the time required to achieve stress balance of the specimen with high temperature is shorter than that of the specimen with low temperature, and the change of dry shrinkage force is obviously lower than that of the specimen with low temperature. However, when the stress balance is reached, the dry shrinkage force of the specimen with high temperature is relatively smaller than that of the specimen with low temperature. (2) under the same temperature, the dry shrinkage force of thin specimen is obviously larger than that of thick specimen. And the time required to reach the maximum dry shrinkage force is obviously less than that of the thick specimen. The error caused by the individual difference of the specimen also has certain influence on the experiment. 2. In order to measure the dry shrinkage force, mass change and shrinkage quantity of wood in the drying process simultaneously, a system for measuring the dry shrinkage force of wood was developed. Based on the relationship between moisture loss and external shrinkage force during wood drying, an integrated temperature control and humidity control mechanical testing system was designed based on temperature and humidity test box. The relationship among shrinkage, moisture content and shrinkage of wood during drying and using was studied and tested. The test results show that the balance of dry shrinkage force, mass change and dry shrinkage can be detected in real time by using this equipment, which lays a foundation for controlling the cracking and warping of wood during drying process due to uneven shrinkage. Through systematic research on (UlmuspumilaL.) of Ulmus pumila The effects of drying temperature and relative humidity on the dry shrinkage force are as follows: (1) when the drying shrinkage and moisture content reach a stable level, the change of the dry shrinkage force is also very small, and at a higher temperature, The formation of internal cracks will lead to a sharp decrease in dry shrinkage. (2) at the beginning of drying, the dry shrinkage is negative because of the thermal expansion of wood, and with the decrease of moisture content and the increase of dry shrinkage, The dry shrinkage force increases gradually and reaches a stable value. (3) temperature is the significant factor affecting the dry shrinkage, the direction of shrinkage and the thickness of the specimen is the significant factor affecting the dry shrinkage, and the significant factors affecting the moisture content are temperature and humidity.
【学位授予单位】：内蒙古农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S782.31
[Abstract]:In the process of wood drying and using, the dry shrinkage force caused by the decrease of the size of water loss causes the surface crack and internal crack of the wood. In order to study and test the dry shrinkage force of the wood, a wood dry shrinkage tester is first developed. The change law of dry shrinkage force under different drying conditions is studied, the study of dry shrinkage force needs to be able to monitor the loss of moisture and the reduction of size simultaneously, using the temperature and humidity test box, mechanical sensor, weight sensor, The dry shrinkage force, moisture content and shrinkage amount of wood were measured by displacement sensor in the process of drying, and the system of measuring dry shrinkage force of wood was optimized. Based on the test box of temperature and humidity, the comprehensive measuring system of controlling temperature and humidity controlling dry shrinkage force is used to study and explore the relationship among the drying shrinkage force, shrinkage amount and moisture content of wood in the drying process, and the drying temperature is studied. The effect of relative humidity on wood shrinkage is as follows: 1. The change of drying shrinkage force of different specifications of Pinus sylvestris var. mongolica (P.sylvestris) plates under different drying conditions was studied. The results show that: (1) under the condition of the same thickness, the time required to achieve stress balance of the specimen with high temperature is shorter than that of the specimen with low temperature, and the change of dry shrinkage force is obviously lower than that of the specimen with low temperature. However, when the stress balance is reached, the dry shrinkage force of the specimen with high temperature is relatively smaller than that of the specimen with low temperature. (2) under the same temperature, the dry shrinkage force of thin specimen is obviously larger than that of thick specimen. And the time required to reach the maximum dry shrinkage force is obviously less than that of the thick specimen. The error caused by the individual difference of the specimen also has certain influence on the experiment. 2. In order to measure the dry shrinkage force, mass change and shrinkage quantity of wood in the drying process simultaneously, a system for measuring the dry shrinkage force of wood was developed. Based on the relationship between moisture loss and external shrinkage force during wood drying, an integrated temperature control and humidity control mechanical testing system was designed based on temperature and humidity test box. The relationship among shrinkage, moisture content and shrinkage of wood during drying and using was studied and tested. The test results show that the balance of dry shrinkage force, mass change and dry shrinkage can be detected in real time by using this equipment, which lays a foundation for controlling the cracking and warping of wood during drying process due to uneven shrinkage. Through systematic research on (UlmuspumilaL.) of Ulmus pumila The effects of drying temperature and relative humidity on the dry shrinkage force are as follows: (1) when the drying shrinkage and moisture content reach a stable level, the change of the dry shrinkage force is also very small, and at a higher temperature, The formation of internal cracks will lead to a sharp decrease in dry shrinkage. (2) at the beginning of drying, the dry shrinkage is negative because of the thermal expansion of wood, and with the decrease of moisture content and the increase of dry shrinkage, The dry shrinkage force increases gradually and reaches a stable value. (3) temperature is the significant factor affecting the dry shrinkage, the direction of shrinkage and the thickness of the specimen is the significant factor affecting the dry shrinkage, and the significant factors affecting the moisture content are temperature and humidity.
【学位授予单位】：内蒙古农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S782.31
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