重载工况下车轮熔覆对轮轨磨损与损伤性能影响

利用CO2多模激光器在车轮试样表面获得Co基合金熔覆层,通过MMS-2A微机控制摩擦磨损试验机对比研究了不同轴重下轮轨试样的磨损性能与损伤机理。结果表明,车轮试样激光熔覆处理后熔覆层组织明显细化,表面硬度明显提高,约为基体的1.5倍。轮轨试样摩擦系数与磨损率随轴重增加而增大,车轮磨损率仅为钢轨的1/5~1/8;随时间增加,轮轨试样磨损量呈线性增长趋势;随轴重增加,轮轨试样表面损伤越严重,相同条件下,车轮试样损伤比钢轨轻微,轴重较小时,车轮熔覆层磨损主要为粘着磨损和氧化磨损,钢轨主要为疲劳磨损与氧化磨损。随轴重增加,轮轨试样主要为严重疲劳损伤,氧化磨损较为轻微。     

轴重对轮轨材料滚动磨损与损伤行为影响

利用WR-1轮轨滚动磨损实验机研究不同轴重下轮轨材料滚动磨损与损伤性能。结果表明:轮轨试样磨损率均随轴重增加呈现线性增加趋势,且钢轨试样磨损率大于车轮试样磨损率。轮轨试样硬化率均随时间呈现先增加后趋于稳定的变化趋势,轮轨试样塑变层厚度和硬化率均随轴重增加而增大,且车轮试样硬化率大于钢轨。车轮试样和钢轨试样表面损伤形貌不同,车轮试样表面表现为垂直于滚动方向的疲劳裂纹,钢轨试样表面表现为裂纹和块状剥落,轮轨试样表面损伤均随轴重增加而更加严重;车轮试样表面裂纹疲劳断裂和钢轨试样表面块状剥落形成磨屑,成分主要为Fe2O3和马氏体,随轴重增加,磨屑尺寸呈现增大趋势,但成分与含量无明显变化。     

激光淬火对重载轮轨磨损与损伤性能的影响

利用MMS-2A型微机控制摩擦磨损试验机研究了激光表面淬火对重载轮轨磨损与损伤性能的影响,分析了激光淬火对重载轮轨表面损伤的作用机理.结果表明:激光淬火处理后轮轨试样存在一定厚度的淬火处理层,其组织主要为均匀致密的马氏体层;激光淬火可明显提高车轮和钢轨试样的表面硬度,其硬度分别增加35.7%、33.5%;激光淬火基本不改变轮轨试样的滚动摩擦系数;激光淬火可增强轮轨试样的耐磨性,相比淬火前车轮和钢轨试样磨损量分别降低62.9%和66.0%;未处理轮轨试样表面损伤主要表现为明显的剥落损伤,激光淬火后轮轨表面损伤相对轻微,主要表现为小麻点式剥落损伤,重载工况下激光淬火处理使轮轨试样具有较好的抗表面损伤能力.     

不同滑滚比下轮轨材料损伤行为

在MMS-2A滚滑试验机上采用法向载荷120N(模拟轴重16t),转速500r/min,研究京沪高速铁路用钢轨U71MnK和车轮ER8配副在不同滑滚比下的材料损伤行为。利用SEM,EDX对不同滑滚比下的磨痕及剖面形貌和磨损表面元素进行分析。结果表明:不同滑滚比下摩擦因数变化趋势反映材料损伤的过程;轮轨材料的硬化程度随滑滚比增加而增加;不同滑滚比条件下的损伤机制不同:在近似滚动条件下,轮轨材料损伤较轻,主要为氧化磨损和局部剥落。随着滑滚比增加,轮轨材料损伤逐渐发展为疲劳磨损为主,并伴随氧化磨损和磨粒磨损,且磨粒磨损程度随滑滚比的增加而增加。     

Ti_3SiC_2-Ag复合材料与不同摩擦配副的摩擦磨损性能

采用放电等离子烧结技术制备了Ti3Si C2-Ag复合材料,研究了其在室温下与Si3N4、Al2O3、Si C等摩擦配副对摩时的摩擦磨损性能,并与纯Ti3Si C2材料在相同摩擦配副条件下的摩擦磨损性能进行了对比。运用扫描电子显微镜、X射线光电子能谱仪等对磨损表面的形貌组织和元素价态等进行了表征分析,并探讨了摩擦磨损机理。结果表明:摩擦配副材料的不同对Ti3Si C2-Ag复合材料的摩擦磨损行为有显著影响,Ti3Si C2-Ag复合材料与Si C和Si3N4对摩时,磨损率均较低,尽管存在晶粒拔出等机械磨损,但Ti O2和Si Ox等摩擦氧化膜的形成有效地抑制了晶粒拔出并起到了减摩作用;Ti3Si C2-Ag复合材料与Al2O3对摩时磨损率则较高,以脆性断裂、晶粒拔出为主的机械磨损是该摩擦副的主要磨损机制。Ti3Si C2材料与Si3N4和Al2O3对摩时,包含脆性断裂、晶粒拔出、脱落以及磨粒磨损在内的机械磨损是其主要的磨损机制;Ti3Si C2材料与Si C对摩时,磨损表面的塑性变形和氧化膜起到了抑制晶粒拔出的作用,使得Ti3Si C2的磨损率相对较低。     

Al_2O_3/TiC-Al_2O_3/TiC/CaF_2自润滑叠层陶瓷的机械和摩擦磨损性能EI北大核心CSCD

采用真空热压烧结制备了Al_2O_3/TiC Al_2O_3/TiC/CaF_2自润滑叠层陶瓷材料,其平均维氏硬度为20.7GPa,断裂韧性为4.5 MPa·m^(1/2),在垂直于叠层方向和平行于叠层方向上的抗弯强度差别不大,分别为323 MPa和353 MPa。在环盘式摩擦磨损试验机上进行摩擦磨损实验,研究了该材料在干摩擦条件下与淬火45#钢配副时的摩擦磨损规律。用扫描电镜(SEM)及能量弥散X射线谱(EDS)观察了材料磨损前后的微观形貌并分析其成分组成及其磨损机理。结果表明:Al_2O_3/TiCAl_2O_3/TiC/CaF_2自润滑叠层陶瓷材料磨擦系数和磨损率均随着转速和载荷的升高而下降;具有自润滑特性;Al_2O_3/TiCAl_2O_3/TiC/CaF_2复合叠层陶瓷材料的磨损机理主要是磨粒磨损和黏着磨损。     

Al2O3/TiC/CaF2陶瓷的摩擦磨损及自润滑膜的形成机理研究

采用热压烧结工艺制备了Al2O3/TiC/CaF2(ATF)陶瓷材料,在环-块式摩擦磨损试验机上与硬质合金配副对其进行了摩擦磨损性能实验,并分析了自润滑膜的形成过程和机理.结果表明:ATF自润滑陶瓷材料的摩擦系数随CaF2含量的增加而降低;当CaF2含量小于10%(质量分数)时,磨损率随着CaF2含量的增加而降低;当CaF2含量继续增加时,Al2O3/TiC/CaF2磨损率随CaF2含量增加而迅速升高.SEM照片表明在摩擦表面明显地形成了自润滑膜,这层润滑膜存在于摩擦副之间,从而明显地降低摩擦系数.ATF自润滑陶瓷材料中的固体润滑剂在摩擦热和摩擦力作用下,析出摩擦表面,当大量固体润滑剂析出并在摩擦表面拖覆时,便形成了自润滑膜.由于机械应力和热应力的共同作用,自润滑膜在反复摩擦下会产生裂纹,从而导致其破坏、脱落.在脱落部位,重新进入了自润滑膜的再生阶段,这样就形成了自润滑膜的生成、破损、脱落与再生的循环过程.     

连续制动条件下泡沫陶瓷/金属双连续相复合材料的摩擦磨损性能EI北大核心CSCD

为解决履带式特种车辆机械制动器过热失效问题,采用挤压铸造法制备SiC/Cu和SiC/Fe双连续相复合材料,研究两种材料在连续紧急制动工况和连续高温制动工况下的摩擦磨损性能。结合扫描电子显微镜(SEM)、X射线能谱分析(EDS)、三维形貌仪等手段分析摩擦因数、温度和磨损率的变化规律,揭示相应的磨损机理。结果表明:在连续紧急制动实验中,接触表面经历了摩擦膜形成和层间断裂过程,摩擦因数随接合次数增加略微下降,并趋于稳定。在前40次接合中,SiC/Cu和SiC/Fe摩擦副的磨损率整体下降。在40~60次接合中,SiC/Cu摩擦副黏着磨损、氧化磨损和疲劳磨损加剧,磨损率升高。而SiC/Fe摩擦副以磨粒磨损为主,磨损率较低。在连续高温制动实验中,摩擦因数在前6次接合中逐渐升高,制动时间逐渐缩短。在第6次接合后,摩擦副边缘区域出现的黏着磨损和疲劳磨损导致力矩下降,摩擦因数和制动时间均呈先降后升趋势。连续高温制动过程中以严重的黏着磨损为主,SiC/Cu和SiC/Fe摩擦副的磨损率均随接合次数增加而升高。     

硼酸铝晶须/双马来酰亚胺树脂摩擦磨损性能

研究了不同偶联剂及硼酸铝晶须添加量对硼酸铝晶须/双马来酰亚胺复合材料的摩擦磨损性能的影响。结果发现,硼酸铝晶须能有效地提高复合材料的耐磨性,晶须的加入使材料的磨损率明显降低;偶联剂对材料摩擦磨损性能的影响不明显;体系中添加硼酸铝晶须后随摩擦时间的延长复合材料的摩擦系数呈增大趋势。当晶须含量较小时摩擦机制主要是轻微的粘着磨损和疲劳磨损,当晶须含量大于8%时,疲劳磨损占主导地位,同时伴有粘着磨损和磨粒磨损。      

利用热处理改善钒钛磁铁矿直接制备的铁基摩擦材料组织与性能

以攀枝花钒钛磁铁矿为原料,通过选择性碳热原位反应和真空烧结技术直接制备得到铁基摩擦材料.为进一步提高材料性能,本工作研究了淬火与回火处理对铁基摩擦材料组织和性能的影响.结果表明:900～1 000℃淬火使材料基体组织由珠光体向马氏体转变,硬度和摩擦性能随淬火温度的升高先提升后下降,在950℃时效果最佳,摩擦磨损行为由热处理前较严重的磨粒磨损和粘着磨损转变为磨粒磨损,且磨损程度降低.950℃淬火试样分别在250℃、500℃和650℃进行回火处理,基体组织随着温度的升高先由马氏体向低硬度屈氏体转变,而后转变为硬度更低的索氏体,但500℃回火时发生的回火二次硬化和碳化物的脱溶使得材料硬度提升,摩擦性能进一步提高,摩擦磨损行为表现为轻微的磨粒磨损.综合而言,950℃淬火+500℃回火处理后的铁基摩擦材料组织及性能最优,相比未热处理材料,硬度提高32％,磨损率降低61％,摩擦系数降低18％.     

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.     

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.     

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.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

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.