挤出机载荷特性分析

从摩擦载荷、惯性载荷和环境载荷三方面 ,分析了挤出机负载峰值力矩和均方根力矩的特性 ,载荷分析为挤出机的设计和执行机构的合理选取提供依据。相对传统的类比、实测设计方法 ,载荷分析可为机械设计提供更准确的数据 ,提高机械的性能 /成本比     

双锥型螺杆挤出机固体输送离散元分析

利用EDEM软件对一种普通锥形和两种双锥型螺杆挤出机固体输送段进行模拟.分析了高密度聚乙烯(PE-HD)颗粒在锥形双螺杆挤出机内的运动状态和分布规律.对比分析了3种锥形螺杆挤出的质量流速率、填充率、平均速度、平均压力、平均剪切应力和力矩等参数,给出了普通型和双锥型螺杆挤出机固体输送机理以及主要影响因素.结果表明,相比于...     

非满载充液罐车转弯过程瞬时液体冲击影响分析

采用流体计算软件模拟非满载充液罐车的转弯过程,监测不同充装率下瞬时液体质心坐标、冲击载荷和侧翻力矩,并与准静态法(QS)估计值进行对比,分析瞬时液体冲击对罐体载荷参数的影响。在此基础上依据准静态罐车侧翻模型建立力矩平衡方程,分析瞬时液体冲击对罐车侧翻阈值的影响。计算结果表明:非满载充液罐车在转弯过程中,瞬时液体冲击会产生附加力和附加力矩,罐内液体质心坐标、冲击载荷和侧翻力矩的QS法估计值小于最大瞬时值而近似等于瞬时平均值;瞬时液体冲击所产生的附加力矩减小了充液罐车的侧翻阈值,因而降低整车侧倾稳定性。     

膜片联轴器扭转特性实验研究

为了研究螺栓法兰连接、波动载荷和不同预紧力矩对膜片联轴器扭转刚度的影响,搭建了联轴器扭转刚度测试实验台。通过扭转实验机施加扭矩,并采用角位移编码器测量了主动、从动法兰盘的相对扭角;采用扭力扳手实现螺栓预紧力矩的调节。实验结果表明:随着负载的增大,法兰螺栓连接出现了严重的松弛;负载波动情况下,载荷变化越大,刚度变化越大;预紧力矩的减小使滑移力矩减小,但第3阶段的刚度变化不大。预紧力矩减小至6N·m时,第1阶段和第4阶段的刚度明显减小。     

车门限位器用改性PA66的制备与性能

采用双螺杆挤出机熔融共混和注射成型方法制备了PA66/玻璃纤维/PTFE/石墨复合材料。研究了减摩剂添加量对复合材料的力学性能和摩擦磨损性能的影响。通过持久性台架试验表明,100000次开关门循环试验后力矩降低≤50%,满足限位器的要求。     

对BS 5500附录G中圆筒形壳体由局部载荷引起的应力计算方法的几点意见

BS 5500附录 G 中的计算圆筒形壳体矩形区域上径向力和力矩引起应力的方法十分复杂,试用简化计算的参数测量图后,表明:(i)附录 G 方法的可靠性要求几何参数所作的限制,致使该方法的使用范围受到许多限制。(ii)在周向力矩作用引起应力的计算方法中,因忽略第二承载区上载荷引起的应力,而得出不正常的结果。(iii)在纵向力矩载荷条件下,当矩形区域偏离容器长度中点时,附录 G 要求计算两个承载区     

泵的配管和布置

为了避免管道、阀门的重量及管道热应力所产生的力和力矩超过泵进出口所允许的最大外载荷,故在泵的吸入和排出管道上须设置管架,如图7所示。泵管口允许最大载荷应由泵制造厂提供。     

新型螺杆挤出机螺杆强度的有限元分析

介绍了一种新型螺杆挤出机的原理及结构特点。对该新型挤出机的外螺杆建立了符合实际尺寸与形状的有限元模型，利用ansys有限元软件对其进行了应力分析。研究结果表明，安全系数达到3时。承受内外压力的特殊结构外螺杆危险截面的内外表面处。各主要应力值均小于许用应力，强度符合要求。从理论上证明了该螺杆在新的工作载荷条件下具备正常运转的能力。为该新型挤出机进一步的开发提供了保证，同时证明了有限元方法在强度分析中是可靠且高效的。     

新型螺杆挤出机螺杆强度的有限元分析

介绍了一种新型螺杆挤出机的原理及其结构特点，对该新型挤出机的外螺杆建立了符合实际尺寸与形状的有限元模型，利用Ansys有限元软件对其进行了应力分析。结果表明：安全系数达到3时，承受内外压力的特殊结构外螺杆危险截面的内外表面处，各主要应力值均小于许用应力，强度符合要求。从理论上证明了该螺杆在新的工作载荷条件下具备正常运转的能力，为该新型挤出机进一步的开发提供了保证，同时证明了有限元方法在强度分析中是可靠且高效的。     

有拧紧力矩复合材料单钉接头疲劳寿命预测

通过对有拧紧力矩复合材料单钉接头疲劳加载过程应力分析及材料三维疲劳失效准则损伤判定,并结合建立的疲劳加载材料退化模型、材料性能退化方法及复合材料接头最终失效判据,建立了基于三维累积损伤分析的层合板接头疲劳载荷作用下寿命预测方法。最后,对拉-拉疲劳载荷作用下有拧紧力矩层合板接头的疲劳寿命及破坏模式进行了模拟分析,并与试验结果进行了对比,结果表明,建立的寿命预测方法能够很好地预测有拧紧力矩复合材料单钉接头的寿命以及破坏模式。     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Highly moisture-proof polysilsesquioxane coating prepared via facile sol-gel process

A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by ¹H MAS NMR. For direct comparison purposes, an SiO₂ coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N₂ absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.