关节轴承自润滑材料摩擦学性能及轴承寿命预测研究现状

自润滑关节轴承由于具有结构简单、承载能力强、适应温度范围广、在服役过程中无需添加润滑剂等特点,被广泛应用在航空航天、水利电力、军工机械等行业.与此同时,高端、精密、大型装备的发展对自润滑关节轴承的摩擦学性能、使用寿命和可靠性提出了更高的要求.自润滑关节轴承所使用的自润滑材料性能直接决定了轴承的寿命和性能水平,因此开展对自润滑材料性能的研究成为提高自润滑关节轴承质量和延长其寿命的关键.目前,自润滑衬垫材料大致分为三种,即金属背衬层状复合材料、聚合物及其填充复合材料和PTFE纤维织物复合材料.自润滑衬垫材料的摩擦学性能、衬垫粘结前的处理方式、粘结方式、编织纹路等因素影响着自润滑关节轴承的使用性能.因此,国内外研究者们选择合适的纤维、纳米金属颗粒和PTFE进行复合,大幅改善了自润滑材料的摩擦学性能;同时对衬垫材料的编织结构、捻制方式以及与轴承的粘结方式进行优化研究.为进一步探究衬垫材料的磨损失效机理,国内外研究者通过轴承磨损试验和有限元仿真相结合的方法研究轴承服役过程中的磨损机理、磨损失效规律和静态接触等问题.研究发现,固体润滑转移膜的持续形成能力是自润滑衬垫材料润滑性能和耐磨性能的决定因素.自润滑关节轴承在服役过程中的磨损形式主要为黏着磨损、磨粒磨损,并伴随一定程度的疲劳磨损.为进行自润滑关节轴承的寿命预测和可靠性分析,国内外研究者们通过研制轴承寿命试验平台,以磨损量为反映关节轴承磨损寿命的主要物理量,建立了大量的磨损寿命分布函数,同时,推导出一系列考虑轴承自身结构特点、润滑方式和工况条件的寿命预测公式并进行可靠性分析.本文以自润滑关节轴承常用的PTFE纤维织物衬垫材料作为主要讨论对象,综述了衬垫材料的组分、编织结构、粘结性能对其摩擦磨损行为的影响;讨论了衬垫型自润滑关节轴承服役过程中的转移膜形成机理及摩擦磨损行为,以及自润滑关节轴承寿命研究方法及试验平台的研制情况;通过对现有自润滑关节轴承寿命评估和可靠性研究现状分析,指出国内建立自润滑关节轴承寿命评估相应标准和试验规范的迫切性,以及对自润滑关节轴承可靠性研究的必要性.     

自润滑关节轴承寿命试验及损伤失效机理研究现状

自润滑关节轴承具有结构简单紧凑、免维护、无需添加润滑剂等诸多优点,现已成为航空航天装备和工业设备中广泛应用的一种重要基础运动部件.目前,包括美、法、德、英等在内的多个航空航天工业发达国家很早就对自润滑关节轴承进行了全面的研究工作,并形成了完整的关节轴承标准体系.而国内对自润滑关节轴承的研究起步晚,自润滑关节轴承在高精尖工业领域中的应用研究技术趋近于空白,尤其是在关节轴承的服役寿命预测和失效机理探究等基础性研究上十分薄弱.近年来,随着高精尖领域对自润滑关节轴承服役性能及寿命的要求不断提高,自润滑关节轴承寿命演变规律及其损伤失效机理的研究受到高度重视.研究人员发现自润滑衬垫/涂层的磨损失效是引起自润滑关节轴承失效的最主要原因,在服役过程中经常面临着重载、高频、高低温循环、强氧化、强辐射等异常恶劣的工况,其损伤失效机理是否发生了改变以及如何改进轴承寿命预测模型以提高寿命预测的精度成了当今的研究热点.目前,相关研究人员分别以摆动频率和载荷为加速应力设计了加速寿命试验,提升了自润滑关节轴承寿命试验效率,并且以Weibull分布中的参数变化作为判定关节轴承失效机理变化的依据,极大地加强了关节轴承寿命预测模型的准确性.同时,国内外学者针对衬垫型和部分涂层型自润滑关节轴承的失效机理展开了研究,揭示了衬垫型自润滑关节轴承摩擦副表面在不同工况下的成膜机理和磨损失效机理,并且发现利用超声波、化学溶液等表面改性方法能够在一定程度上改进衬垫的摩擦学性能,提高其服役寿命.本文首先总结了自润滑关节轴承寿命试验的研究现状,主要对关节轴承寿命试验的设备、标准和方法展开论述.然后,重点分析了自润滑关节轴承损伤失效机理,其中对自润滑关节轴承的失效形式及失效判定准则进行了简要介绍,着重分析比较了自润滑材料性能、摩擦表面加工质量、服役工况等影响自润滑关节轴承损伤失效的主要因素.最后,对自润滑关节轴承寿命试验及失效机理的重点研究方向进行了展望.     

聚四氟乙烯纤维织物在关节轴承上的应用

聚四氟乙烯纤维织物是PTFE与Nomex、玻璃纤维(或芳纶纤维)等材料,采用特定方法纺织,并经特殊浸渍处理后制成的复合织物,具有强度高,摩擦系数小的特点.将这种纤维织物应用于关节轴承上,使关节轴承既保持了高承载、自动调心的特性,又兼有自润滑、耐冲击、长寿命等特点.这种自润滑关节轴承可广泛应用于航空、航天等高新技术领域中的关键承载部位.     

自润滑关节轴承的轴向承载能力简化模型

在变形集中在衬垫上的假设下,基于干涉模型,提出了自润滑关节轴承轴向承载能力的简化模型对PTFE衬垫自润滑关节轴承轴向受载时的接触应力与轴向承载能力进行推导,并利用ANSYS软件进行有限元分析,通过两者结果的比较验证了新模型的准确性。     

新型碳纤维增强聚四氟乙烯复合材料在航空电机上的应用

前言 固体自润滑复合材料的应用越来越广泛,本文仅对固体自润滑复合材料CF/PTFE应用于高速伺服电机轴承的情况进行探讨。固体自润滑复合材料滑动轴承的特征是:在轴承的两相对滑动摩擦面间,没有润滑油脂的流动,其润滑靠固体材料自身来实现,这类固体润滑材料不包括涂覆料外那些在常温下是固体,在摩擦状态下室现出流体性质的材料,如石腊等。这类滑动轴承具有易起动,摩擦力小,维修方便,使用温度范围宽,耐蚀性好,能耗低,环境清洁以及不用油脂而省掉润滑系统等优点。如前西德、英国等国家已应用了固体自润滑滑动轴承的微特电机,其寿命可达到一万小时左右,而轴承的成本降低数十分之一到百分之一。在目前固体自润滑轴承材料主要分为三类:金属基自润滑复合材料,如青铜-固体润滑剂;银-固体润滑剂等;粉末冶金基自润滑复合材料-如粉末冶金青铜-浸氟塑料-固体润滑剂;非金属基自润滑受合材料,如氟塑料-增强剂-固体润滑剂等,我们多年来对多种固体润滑轴承材料在伺服电机上作了使用和寿命试验,选出了适合于作伺服电机轴承用的较为理想的材料,即碳纤维增强聚四氟乙烯固体润滑复合材料。     

功能性填料改性聚合物材料的摩擦学研究进展

聚合物材料因其质轻、价廉、耐腐蚀以及优异的自润滑特性而广泛应用于工程机械润滑领域中。加入功能性减摩和增强填料复合改性聚合物树脂可以克服本征型高分子材料的一些固有缺陷,得到低摩擦因数、高耐磨性、高承载力以及耐高温等优异特性的摩擦学复合材料。本文综述了功能性填料如碳基材料、过渡金属硫化物、微胶囊、软金属、陶瓷纳米颗粒、矿物盐以及自润滑高分子对复合材料的减摩抗磨效果及机理。同时,力学性能是保证聚合物材料服役性能和使役寿命的关键参数,也会对材料的摩擦学性能带来显著影响。本文还重点论述了纳米颗粒和纤维等填料对复合材料的增强和增韧机理。最后,展望了功能性填料对力学性能与摩擦学性能的协效作用,以及计算机模拟在复合材料摩擦学中应用的发展趋势。     

高温固体自润滑涂层的制备及可靠性的研究进展

高温固体自润滑涂层能够在高温环境为摩擦副界面提供高性能的固体润滑膜,解决了高温环境下传统润滑油脂失效的问题,确保摩擦副在高温环境中可靠工作,并降低了能量损耗,近年来成为摩擦学领域研究的热点问题之一,并得到了快速发展。但是,在30～400℃时,诸多高温固体自润滑剂的减摩性能弱,摩擦系数较高。因此,国内外该领域科学家期望获得在30～1 000℃范围内摩擦学系数低、性能良好的高性能复合型固体自润滑涂层,其主要由基础相、润滑相和增强相组成,且它们的共同作用提供涂层在高温环境下的润滑能力。最近的研究显示,金属三元氧化物基高温自润滑涂层——主要以过渡族金属三元氧化物为基础相,由含有Magnéli同源相的二元和三元氧化物润滑材料发展而来的新型高温固体自润滑材料,逐渐成为解决高温域自润滑问题的首选材料。对此,围绕高温固体自润滑涂层的工程应用,发现其面临三个方面的挑战:(1)高性能复合固体自润滑涂层的体系设计;(2)适应复杂结构的可靠制备工艺;(3)服役期间的寿命可靠性评估。针对以上三个方面的问题,本文从高温自润滑涂层的设计体系、制备工艺发展、可靠性评估三个层面进行了综述,期望为高可靠性高温自润滑涂层的制备提供技术支持。首先是在设计体系方面,发现高温固体自润滑涂层不但要满足传统固体自润滑涂层包含基础相、润滑相和增强相及其共同作用提供自润滑的要求,还要满足高温环境的特殊要求。其次,科学家们期望获得制备高性能高温固体自润滑涂层的可靠工艺,但是均受到了工艺简便性与适应能力以及高温零部件结构表面复杂度等问题的限制,从而难以实现工程化。根据高温自润滑涂层的设计要求,在梳理介绍高温固体自润滑涂层的工艺中,发现高压高超音速喷涂技术在此领域具有一定的技术便捷性,可实现高温固体自润滑涂层的工程化。再次,分析梳理了高温自润滑涂层在服役周期内的寿命可靠性评估进展。研究发现,高温固体自润滑涂层的服役寿命逐渐从实验统计分析、应力与涂层结构之间的关联影响,向结合涂层微观界面与宏观性能的跨尺度结合的数值分析发展,这将为高可靠性高温固体自润滑涂层的制备和服役寿命评估信息化提供技术支持。     

PTFE复合涂层的摩擦学性能及疏水性能研究现状

聚四氟乙烯(PTFE)具有优良的自润滑性能、耐化学腐蚀性能和介电性能,以及优异的高低温稳定性和化学稳定性。此外,PTFE还具有优异的超疏水性能,人工制备的超疏水表面在诸多领域有着广阔的应用前景,但单一的PTFE硬度较低、耐磨性差。本文综述了国内外近些年使用碳材料或聚合物对PTFE进行填充改性,并利用表面工程技术制备复合涂层以改善摩擦学性能及疏水性能方面的研究进展,并对未来PTFE复合涂层的研究方向进行了展望。     

陶瓷基高温自润滑复合涂层的制备及摩擦学性能研究进展EI北大核心CSCD

摩擦磨损大多数情况下不利于机械设备,我国作为机械制造大国,降低摩擦磨损对工业进步及可持续发展有重大意义。陶瓷基高温自润滑复合涂层作为工业应用中常见体系之一,主要以硬质陶瓷为基体,并掺杂润滑材料作为第二相组成,使其一方面继承陶瓷相优异的高温稳定性及强度,另一方面提高在常见摩擦环境下的润滑性能,因此被广泛应用于船舶、航空航天、生物科技、高速列车等领域,受到研究人员的广泛关注与探索。本文以陶瓷基高温自润滑复合涂层为中心,首先阐述复合涂层及固体润滑材料的基本分类;其次综述不同制备方法的最新研究进展,重点关注工艺参数对制备陶瓷基高温自润滑涂层性能的影响及改善方法;然后归纳改善陶瓷基高温自润滑复合涂层表面摩擦学性能的关键因素,探讨了提升减摩耐磨性能的可行性和研究潜力;最后总结目前陶瓷基高温自润滑复合涂层存在的问题,主要有以下2点:(1)对复合涂层的物相分析仍以解释现象为主,没有完整的理论基础;(2)对不同制备工艺下复合涂层结构和摩擦学性能的改善手段较单一。因此提出相应的解决办法以及未来可能的发展方向:(1)研究陶瓷基体和不同润滑相、附加组元、高温环境的协同作用机理,建立系统的理论基础;(2)针对不同制备工艺的成型机理,重点研究工艺参数的协同作用对复合涂层微观结构形成的影响,扩展制备工艺的改善方法。     

艉轴机械密封新型自润滑材料

为解决舰船艉轴机械密封漏泄量大、寿命短、维修工作繁重的难题，研制了新型自润滑密封材料。新型材料以聚对羟基苯甲酸酯为基材，润滑组元为聚四氟乙烯，辅助组元为石墨、铜粉等。试验结果表明，新型共混材料保持了各个组元的原有优点，而且在性能上互相补充，克服了PTFE的易蠕变性和聚对羟基苯甲酸酯的脆性。经台架试验证明，用新型材料制成的静环具有优异的性能。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.