Hydrophobic and tribological behaviors of a poly(p‐phenylene benzobisoxazole) fabric composite reinforced with nano‐TiO2

1H,1H,2H,2H‐Perfluorooctyl trichlorosilane (PFTS) was used to modify TiO₂ nanoparticles, and hydrophobic PFTS–TiO₂ nanoparticles were obtained by an ultrasonic reaction method. The PFTS–TiO₂ surface morphological and hydrophobic properties were analyzed with scanning electron microscopy (SEM), Fourier transform infrared spectrometry, and contact angle (CA) testing. Then, the poly(p‐phenylene benzobisoxazole) fabric–phenolic composite filled with PFTS–TiO₂ as a lubricant additive was fabricated by a dip‐coating process. The tribological properties of the composite were investigated, and the wear surface morphology was observed by SEM. The experimental results show that the water CA of the composite filled with PFTS–TiO₂ was 158°, and the composite containing 4 wt % PFTS–TiO₂ exhibited excellent antifriction and abrasion resistance. The hydrophobic surface of the composite showed excellent durable performance with a static water CA of 126.7° after abrasion. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45077.     

Wettability of a microgrid‐structured polymer film with microfabrication utilizing the stick–slip phenomenon

A microgrid structure was formed on the surface of a polyethylene terephthalate (PET) film with an original microfabrication method (termed SS processing) utilizing the stick–slip (SS) phenomenon, and the effect of this surface structure on wettability was evaluated. Microgrid‐structured films could be fabricated by two‐axis SS processing. Moreover, an arbitrary parallelogram microgrid structure could be formed by selecting the direction of the second SS processing with respect to that of the first SS processing. Both water contact angle and water sliding angle of the SS‐processed film were larger than that of the PET film. Hence, the SS‐processed film showed a petal‐like effect. Furthermore, the water sliding angle of the microgrid‐structured film showed anisotropy due to the pinning effect derived from the microgrid structure. As a result, it is revealed that a hydrophobic PET film with a petal‐like effect and anisotropic wettability can be fabricated by SS processing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45140.     

Tribological performance of filled PTFE‐based friction material for ultrasonic motor under different temperature and vacuum degrees

In this work, a glass fiber reinforced polytetrafluoroethylene (PTFE)‐based friction material with good properties for ultrasonic motor was fabricated. The effects of temperature and vacuum degree on the tribological behavior of the PTFE‐based friction material were investigated; the evolutions of friction‐wear modes and mechanisms were also discussed as function of temperature and vacuum degree. The results show that the delamination and fatigue wear are predominant under the effects of repeated shearing and dynamic contact under atmospheric environment. While wear mechanisms change from adhesive to abrasive and fatigue wear as it is cooled from 30 to ?60 °C at vacuum environment. Under high vacuum, adhesive wear was prone to taking place at room temperature for high frictional heat which increased the wear rate and extended the running‐in period. Experiment shows that the highest no‐load speed, output power, and holding torque of ultrasonic motor at room temperature under atmospheric environment are 220 rpm, 9.9 W, and 1.21 N m, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45358.     

An investigation on the graphitic carbon nitride reinforced polyimide composite and evaluation of its tribological properties

This article presented a novel application for the graphitic carbon nitride (g‐C₃N₄), which was used as nanofillers to improve the tribological properties of polyimide (PI). The composite based on PI and g‐C₃N₄ was prepared by mechanical mixing process and hot compression molding process. The characterizations of g‐C₃N₄ and PI/g‐C₃N₄ composites were investigated by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Friction and wear tests were carried out using UMT‐2 reciprocating tribo‐tester against stainless steel ball under dry friction. The results showed that the amount of g‐C₃N₄ was decisive to the tribological properties of PI/g‐C₃N₄ composites. The optimal tribological properties occurred when the amount of g‐C₃N₄ was 10 wt %, which showed the smallest friction coefficient and the lowest wear rate. Furthermore, this work provided an example of application for the g‐C₃N₄ as the excellent nanofiller in polymer matrix composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45403.     

钼酸盐离子液体的合成及其摩擦性能

以甲基三辛基氯化铵、钼酸钠、硝酸银为初始原料,合成了甲基三辛基钼酸铵室温离子液体,并通过红外光谱、核磁氢谱、质谱、元素分析对其结构进行了表征。利用热重分析仪、四球摩擦磨损试验机、扫描电镜（SEM）和能谱仪（EDS）考察了其热稳定性能和润滑性能,并初步探讨了甲基三辛基钼酸铵在400SN基础油中的润滑机理。研究结果表明：添加0.5％（质量浓度）钼离子液体能提高基础油抗烧结性能一个等级,提高PB值23.8%,降低磨斑直径34.6%。润滑性能的提升可能是由于钼离子液体在钢球表面发生了化学反应,形成了以钼的氧化物和铁的氧化物为主的化学沉积膜。     

基于气泡群相间作用力模型的加压鼓泡塔流体力学模拟

目前,多数文献报道了冷态加压湍动鼓泡塔内流动特征,并且通过实验数据回归相关经验关联式。然而,此类关联式适用范围有限,难以直接外推到工业鼓泡塔反应器条件。因此,在FLUENT平台上建立了基于气泡群相间作用力的、动态二维加压鼓泡塔计算流体力学模型。通过数值模拟考察了操作压力为0.5~2.0 MPa,表观气速为0.20~0.31 m·s^-1,内径0.3 m鼓泡塔内流场特性参数分布,并且与冷态实验数据进行比较。结果表明,采用修正后的气泡群曳力模型、径向力平衡模型以及壁面润滑力模型描述气泡群相间作用力,能够较为准确地反映平均气含率和气含率径向分布随操作压力和表观气速变化的规律。     

Influence of Relative Position of Gears and Casing Wall Shape of Gear Box on Churning Loss under Splash Lubrication Condition—Some New Ideas

A new rotatable test rig is developed to perform oil churning loss experiments to clarify the influence of the relative position of gears and casing wall shape of gear box under splash lubrication condition. Torque losses are measured and photos are taken using a stroboscope to observe the oil behavior. Based on the test results, it has been confirmed that in addition to the well-known factors, relative position and casing wall shape have significant effects on the churning loss and should be considered in the modeling process, which has been neglected in most previous studies. In this article, the importance of the steady-state oil surface profile (SOSP) is emphasized. New ideas are proposed on how other working conditions such as immersion depth and rotation speed influence the churning loss.     

润滑条件下WC-CoCr涂层的磨损行为

研究了在润滑条件下,WC-CoCr涂层与SiC摩擦副对磨时的摩擦和磨损性能,分析了加载载荷和润滑条件(干摩擦、润滑脂、金刚石研磨膏)对WC-CoCr涂层摩擦系数和磨损量的影响规律,对涂层的磨损机理进行了探讨。实验结果表明:脂润滑时,WC-CoCr涂层与SiC摩擦副对磨时的摩擦系数和磨损率降为最小,其中摩擦系数基本在0.1左右波动;金刚石研磨膏润滑时,磨损率高达1.521 24×10-6 g/m,为干摩擦条件下的2.68倍,抗磨减摩效果不理想;干摩擦时,涂层表面存在硬挤压痕,主要磨损机制为微切削并伴随着塑性变形,而在金刚石研磨膏润滑条件下,三体磨粒磨损起主导作用。     

Causes of chatter in a hot strip mill: Observations, qualitative analyses and mathematical modelling

Severe vibrations, known as chatter, occur often in both hot and cold rolling of steel. A recent chatter outbreak at the second stand of hot strip mill in Hastings, Australia, prompted an investigation into the causes of chatter by a literature review, the development and deployment of mathematical models, and a rigorous analysis of plant observations. The investigation suggests that the frictional conditions in the roll gap are the principal cause of chatter in this mill, though residual chatter marks on work rolls can occasionally cause it. The frictional conditions appear to be associated with the thickness and properties of oxide formed on rolls.     

铝板带冷轧水基乳化液润滑膜形成特点研究

探讨了不同浓度的水基乳化液形成润滑膜的特点。低速轧制时,随着轧制速度的提高,润滑膜厚度增大。当轧制速度超过临界值时,随着轧制速度的提高,润滑膜厚度降低。考虑速度对乳化液黏度的影响,用4阶多项解函数拟合乳化液黏度随轧制速度变化曲线,对Reynold方程进行修正,使非牛顿流体水基乳化液润滑膜厚度的计算更准确。