三种塑料与木纤维复合性能的研究

选用线性低密度聚乙烯(LLDPE)、聚丙烯(PP)、聚苯乙烯(PS)为原料,以2种比率与木纤维复合,用热压法制备了3种木塑复合材料,分析了塑料种类对复合材料的物理力学性能的影响.结果表明,LLDPE与木纤维的复合性能最好,其复合材料的抗冲击性好,但弯曲强度和弹性模量最低;PS与木纤维的复合性最差,其复合材料抗冲击性很差,但弯曲强度和弯曲弹性模量高;木纤维与PP复合材料的综合性能最佳.由此提出用LLDPE与PS共混改性制造木/塑复合材料的设想.     

R2000WF喷头与摇臂式喷头水力性能的比较研究

介绍Nelson公司R2000WF喷头的结构组成和工作原理,对R2000WF喷头和相近摇臂式喷头的水力性能进行了比较试验和分析.研究表明:在相同额定工作压力下,R2000WF喷头与摇臂式喷头相比,其流量平均要小13.2%,射程平均增大4.5%,末端水滴直径小,水量分布更均匀.由于其独特的阻尼部件,R2000WF喷头转速...     

木塑窗型材角部胶接与焊接技术研究

通过对木粉－高密度聚乙烯基木塑窗型材的胶接和焊接2种连接方式的角部连接技术研究,结果表明,使用环氧树脂胶接时,随着木粉含量的增加木塑窗角部受压弯曲应力呈增大趋势;对木塑型材进行等离子体处理可使角部受压弯曲应力提高97．3％。采用焊接方式连接时,随着木粉含量的增加,角部受压弯曲应力大幅度降低;向型材保温腔中填充高密度聚乙烯,可增大焊接面积,使最大受压弯曲应力提高为22．40 MPa。     

Evaluating decision rules for dryland rotation crop selection

No-till dryland winter wheat (Triticum aestivum L.)-fallow systems in the central Great Plains have more water available for crop production than the traditional conventionally tilled winter wheat-fallow systems because of greater precipitation storage efficiency. That additional water is used most efficiently when a crop is present to transpire the water, and crop yields respond positively to increases in available soil water. The objective of this study was to evaluate yield, water use efficiency (WUE), precipitation use efficiency (PUE), and net returns of cropping systems where crop choice was based on established crop responses to water use while incorporating a grass/broadleaf rotation. Available soil water at planting was measured at several decision points each year and combined with three levels of expected growing season precipitation (70, 100, 130% of average) to provide input data for water use/yield production functions for seven grain crops and three forage crops. The predicted yields from those production functions were compared against established yield thresholds for each crop, and crops were retained for further consideration if the threshold yield was exceeded. Crop choice was then narrowed by following a rule which rotated summer crops (crops planted in the spring with most of their growth occurring during summer months) with winter crops (crops planted in the fall with most of their growth occurring during the next spring) and also rotating grasses with broadleaf crops. Yields, WUE, PUE, value-basis precipitation use efficiency ($PUE), gross receipts, and net returns from the four opportunity cropping (OC) selection schemes were compared with the same quantities from four set rotations [wheat-fallow (conventional till), (WF (CT)); wheat-fallow (no-till), (WF (NT)); wheat–corn (Zea mays L.)-fallow (no-till), (WCF); wheat–millet (Panicum miliaceum L.) (no-till), (WM)]. Water use efficiency was greater for three of the OC selection schemes than for any of the four set rotations. Precipitation was used more efficiently using two of the OC selection schemes than using any of the four set rotations. Of the four OC cropping decision methods, net returns were greatest for the method that assumed average growing season precipitation and allowed selection from all possible crop choices. The net returns from this system were not different from net returns from WF (CT) and WF (NT). Cropping frequency can be effectively increased in dryland cropping systems by use of crop selection rules based on water use/yield production functions, measured available soil water, and expected precipitation.     

磷酸脒基脲与聚磷酸铵协同阻燃的木粉/HDPE复合材料

采用锥形量热仪(CONE)、极限氧指数(LOI)、热重分析(TGA)和力学试验等研究手段,分析聚磷酸铵(APP)、磷酸脒基脲(GUP)及二者复配(GUP/APP)对木粉/高密度聚乙烯(WF/HDPE)复合材料燃烧性能、热降解行为以及力学性能的影响.CONE研究结果表明:APP可显著降低WF/HDPE复合材料的热释放,但同时也使得复合材料的烟释放增加;将GUP与APP按适当比例复配不仅可以有效抑制复合材料的热释放,而且可以降低烟释放速率,表现出较好的协同阻燃和抑烟作用.TGA结果表明:GUP与APP复配使得WF/HDPE复合材料的初始热分解温度降低,残炭产率提高.此外,GUP和APP复配阻燃WF/HDPE复合材料具有较高的氧指数和较小的力学性能损失.     

超细粒耐磨精密玻璃刀的设计与制作

超细粒耐磨精密玻璃刀是一种高硬度、多损耗的玻璃切割工具,在电子行业中应用广泛。文章详细地分析了超细耐磨玻璃刀材料的选取,介绍了玻璃刀片型材的选购和加工工艺的设计。     

碳布位置对木粉/高密度聚乙烯复合板性能影响

引入碳纤维作为增强手段,通过设计不同的工艺结构,探究其对木塑复合材力学性能的增强效果。板材结构设计方案有CF313(3 mm表层木塑板+碳布+1 mm芯层木塑板+碳布+3 mm表层木塑板)、CF232(2 mm表层木塑板+碳布+3 mm芯层木塑板+碳布+2 mm表层木塑板)、CF151(1 mm表层木塑板+碳布+5 mm芯层木塑板+碳布+1 mm表层木塑板)、CF070(碳布贴在最外层)、CF7(不添加碳布的空白实验)。研究结果表明,CF070复合材的弯曲强度最大;CF151的弹性模量最大,即碳纤维放在近表层位置时,弯曲性能较好,但拉伸时木塑表层容易拉断;放在靠近中心位置时复合材的拉伸强度和冲击强度提高幅度较大。综合考虑各性能,表层厚度为2 mm时可最大程度发挥碳布优势、增强木塑复合材料力学性能。