气门疲劳断头失效分析

采用宏、微观检验、化学成分分析和硬度测试等方法对断头的排气门进行了分析.结果表明,气门断裂方式属于疲劳失效.结合气门服役受力情况,指出气门失效主要由于气门间隙调整过大使气门盘部与座圈的落座力过大,气门与座圈经长时间撞击,在气门根部产生金属疲劳.气门杆端面在运行中不断与摇臂撞击磨损使该现象进一步加剧,导致气门颈部撞击疲劳断裂失效.     

发动机气门座圈工艺研究

简述几种气门座圈的锻造工艺,展望气门座圈的锻造工艺和材料未来的发展方向。     

渗铜量对铁基粉末冶金气门座圈材料微动磨损性能的影响

采用压制-烧结-熔渗工艺,制备一种高性能铁基粉末冶金气门座圈材料,在SRVⅣ摩擦磨损试验机上对比研究不同渗铜量下材料的微动磨损性能。结果表明:在一定范围内随着渗铜量的增加,试样密度、硬度及压溃强度显著提高,摩擦因数与磨损体积降低,磨损机理发生不同程度的变化。未渗铜或渗铜量低时,试样磨损机理主要表现为磨粒磨损及疲劳剥落;渗铜量为10%(质量分数,下同)的试样磨损机理为轻微磨粒磨损和疲劳剥落;渗铜量为15%的试样表现出最优抗微动性能,仅有轻微黏着磨损;当渗铜量达20%时,试样力学性能下降,磨损体积增大,磨损机理转变为以黏着磨损为主。渗铜后的试样抗微动磨损性能更优异。     

小型孔类零件同轴度误差工序间的快速检测

本文以汽油发动机缸盖中，气门座圈的锥孔、挺杆孔对气门导杆孔之间的同轴度误差检测为例，介绍一种工序间的快速检测方法。     

浅谈气缸盖机械加工工艺

结合近年来国内外内燃机行业发展的新趋势和工作实践,对结构复杂的气缸盖机械加工提出了进、排气门座圈锥面与导管孔的加工是其工艺技术关键,从定位方式、基准选择、气门座底孔与导管孔底孔的加工,气门座圈锥面加工方式和导管孔的加工方式等方面进行了探讨和分析。     

气门座圈粉末锻造工艺的数值模拟与实验

目的研究气门座圈的粉末锻造工艺,提高产品的致密度。方法通过建立气门座圈粉末锻造数值模型,分析锻造过程中相对密度的变化过程,研究预制毛坯初始相对密度、锻造加热温度和成形速度对致密化的影响。在此基础上进行粉末锻造实验,并与模拟结果比较。结果随着预制毛坯初始致密度、加热温度的增加以及成形速度的降低,粉末锻造致密度化所需的成形力降低;预制坯初始密度对锻件密度均匀性影响最为显著。经过粉末锻造后的气门座圈,密度从6.6 g/cm~3提高到7.46 g/cm~3,致密度达到96.4%。结论相比传统压制-烧结工艺,粉末锻造可以大幅度提高气门座圈的致密度。     

发动机气门失效分析

某发动机气门发生断裂失效,通过对失效气门杆端面和与其接触的摇臂进行宏观分析、扫描电镜分析、能谱分析、金相检验及硬度测试,找出了发动机气门失效的原因。结果表明:由于摇臂油孔存在制造偏差,导致气门杆端面与摇臂摩擦副之间润滑不良,从而造成该摩擦副之间发生了严重的磨粒磨损,使得气门杆端面与摇臂之间的间隙增大,过大的气门间隙又会导致气门锥面的落座力增大,造成气门颈部应力集中,并且萌生裂纹,裂纹不断扩展,最终造成气门断裂失效。     

汽车发动机用气门材料的选择及研究进展

首先概述了气门在汽车发动机中的重要作用,叙述了气门的服役工况以及对气门材料性能的要求,接着详细阐述了气门上常用的材料种类以及气门材料的国内外研究进展,然后对气门的整个制备流程进行了叙述,最后简述了气门使用过程中的失效问题。     

载荷对重型车辆发动机活塞环-缸套摩擦学性能的影响

利用SRV实验机模拟重型车辆发动机活塞环-缸套摩擦副的工作状态,测试了静载荷和动载荷条件下摩擦副的摩擦学性能。采用扫描电镜、能谱仪分析了磨痕形貌和化学成分,研究了摩擦副的磨损机制。结果表明:随静载荷的增加,摩擦副的摩擦因数减小,总失重量增加。摩擦副的磨损机理以磨粒磨损为主,在400N条件下活塞环的磨损机理为综合的磨粒磨损和黏着磨损。在低强度和中等强度动载荷条件下,摩擦副的摩擦因数随载荷的变化而呈循环变化,磨损机理以磨粒磨损为主。在高强度动载荷条件下,摩擦副的摩擦因数保持稳定,活塞环的磨损机理是综合的磨粒磨损、黏着磨损、疲劳磨损,缸套的磨损机理是综合的磨粒磨损、黏着磨损。摩擦副的总失重量随动载荷强度的增大而增加。     

汽油发动机气门弹簧断裂失效分析

某汽油发动机气门弹簧在台架试验中发生了早期断裂失效。采用断口观察和分析、化学成分分析、金相检验、硬度测试等方法,对气门弹簧断裂的原因进行了分析。结果表明:气门弹簧断裂的性质为疲劳断裂,气门弹簧断裂的原因为表面存在磨损,导致弹簧的疲劳强度和疲劳寿命下降。     

发动机排气门锥面局部出现麻坑的原因

采用宏观和微观检验、化学成分分析和硬度测试等方法对发动机锥面局部有麻坑的发动机排气门进行了分析。结果表明：因摇臂与排气门杆部端面接触点不恰当导致气门不旋转,造成排气门杆部偏磨和排气门锥面局部漏气,最终使排气门锥面局部出现麻坑。     

Application and optimisation of materials in valve train

Abstract

Recently the requirements imposed on parts in the valve train have significantly increased and different trends are apparent for different fuels. These fuels can be defined as conventional fuels, heavy fuels, and (natural) gas. For conventional fuels, no major differences exist between truck and marine engine applications. Owing to an increase in peak pressure and process temperature, new designs and materials are required in these fields of application. For heavy fuel applications, corrosion presents a continuing problem because of further increasing temperatures. Improved materials, surface protection, and heat transfer could reduce problems such as seat burning and corrosion on valve stems, valve heads, and guides. Varying compositions of natural gas and problems with the mixture control require the optimisation of the tribological system of valve seat–valve seat insert and an improvement in the behaviour of valve materials at elevated temperatures. Both technically and economically there are many problems to solve. This paper addresses the techniques and results of improvement and optimisation, for example, finite element analysis and test facilities, improvement and optimisation of valve steels, and the surface protection, heat transfer, design, and interactions between valve stem guide and the valve seat-seat insert.

MST/3156     

Effect of load on tribofilms at the contact interface under dry sliding conditions at 500 °C

This paper presents a study of the effect of load on the retention of the tribofilms formed at the interface of a dry sliding contact between exhaust valve material, Nimonic alloy (N 80A) and valve‐seat material, ductile cast iron (GGG‐40), at a temperature of 500 °C. The role of tribofilms in influencing friction and wear behaviour at elevated temperature is highlighted. Reciprocating pin‐on‐disc experiments were conducted using a hemispherical shaped pin sliding against a flat disc at 20 Hz oscillating frequency, 2 mm stroke at loads of 20 N to 50 N. Low coefficient of friction, in the range of 0.13 to 0.15, was observed at loads up to 40 N whereas at a load of 50 N, the average coefficient of friction increased to 0.29. Optical and scanning electron micrographs with energy dispersive spectroscopy analysis indicate evidence of formation and retention of well compacted and strongly adhering tribofilms at loads up to 40 N. At 50 N, even though more abrasive wear is seen, initial deterioration and subsequent reforming of the tribofilms with increasing sliding time is observed. Overall, more wear was observed for the valve‐seat material as compared to the valve material. Raman spectroscopy primarily indicates the presence of hematite on the worn surfaces at loads of 20 N to 40 N, whereas magnetite presence is strongest at the highest load of 50 N. Increase in tribofilm hardness was observed with increase in contact load whereas the thickness of the tribofilm was not significantly affected by the contact load.     

Coatings and hardfacing alloys for corrosion and wear resistance in diesel engines

Abstract

The potential for surface engineering solutions to increase the corrosion and wear resistance of diesel valves is examined with regard to operation in residual fuel oil combustion products. The environment in which the exhaust valve operates is discussed. The corrosion test is used to sort the 27 coating treatments and 16 hardfacing alloys examined. H ardfacing materials showing the greatest potential are also evaluated in hot wear tests. As reference materials, En 52 steel, Nimonic 80A, and Stellite 6 are included. Corrosion tests over the temperature range 500–700°C have shown that the surface treatments can be ranked in terms of their composition and expected metal surface temperature. Good corrosion resistance to residual fuel oil combustion products reflects primarily the content of the alloy, the base metal (Fe, Ni, or Co) being of secondary importance. Refractory metals (Ti, Nb, Ta, Mo, and W) and other minor alloying additions do not significantly alter the corrosion behaviour, unless they are present in large quantities. Hot wear tests (650°C, 80 MN m^?2 contact pressure) of candidate hardfacing alloys have also demonstrated the importance of the Cr content of the alloy. This probably results from the ease of formation of a protective glaze, lowering the coefficient of friction and therefore the wear rate. Additions of refractory metals were beneficial. Since optimum wear resistant alloys contained high levels of Mo and vv: they were poor in terms of corrosion resistance. It is therefore necessary to balance wear resistance against corrosion resistance in the selection of materials for residual fuel oil service. Two coating systems, vacuum plasma sprayed Ni–50Cr and a chromised diffusion treatment appeared to have potential as valve surface treatments for improved corrosion resistance; and two hardfacing alloys, Tristelle TS2 and Colmonoy 8, offered balanced behaviour as seat materials with acceptable wear resistance and improved corrosion performance. These materials have been evaluated in the engine tests of three different diesel engine manufacturers.

MST/3157     

Nimonic compound exhaust valve spindles for diesel engines via hot isostatic pressing

Abstract

Until the present time the materials used for exhaust valve spindles for diesel engines have comprised a main body of heat resistant austenite steel with a Stellite layer covering the seat area. Recently, to satisfy increasing demands for higher efficiency of engines, a forged Nimonic 80A exhaust valve spindle has been developed. This valve spindle has higher strength and hot corrosion resistance than conventional austenite steel valves. This paper introduces a compound type Nimonic 80A–austenite steel valve spindle produced via hot isostatic pressing. Nimonic 80A powder metal is consolidated and diffusion bonded to an austenite spindle body. The seat area and the total combustion chamber side of the spindle are clad using Nimonic 80A. The compound valve spindle produced via hot isostatic pressing has the same performance as a forged Nimonic 80A spindle and in addition it has improved repair weldability and hot corrosion resistance compared with the forged Nimonic 80A spindle valve. Because less of the expensive Nimonic 80A material is used, there is an added advantage in that the cost of the valve would be cheaper. Successful engine test results are also described.

MST/315B     

基于冲蚀磨损理论的新型内防喷器阀座锥角研究

针对现有内防喷器失效率高等不足，提出一种结构新颖且密封可靠的自旋合式锥形密封内防喷器。对该新型内防喷器的阀座锥角进行了力学分析，并采用MATLAB对阀座锥角进行了优化。基于理论分析得到的结论，采用CFD（computational fluid dynamics，计算流体动力学）方法（标准k-ε湍流模型及Tabakoff-Grant冲蚀模型）及ANSYS CFX软件，对该新型内防喷器在不同钻井液流量及不同阀座锥角下的流场进行数值模拟分析，仿真结果表明容易发生冲蚀磨损的部位主要集中在上下阀座流道边缘及下部管壁处。通过对比多组仿真数据，提出了该新型内防喷器上下阀座的最优锥角为25°，并采用ANSYS Workbench静力学分析软件模拟了井喷时上下阀座密封锥面的接触应力分布，验证了冲蚀仿真分析得出的最优锥角的结论。样机试制后进行了密封性实验以验证其可靠性，结果表明该新型内防喷器无泄漏，满足密封性要求。研究结论为内防喷器的设计与改进提供了重要的理论依据，对油田生产设备的安全升级有重要意义。     

Method to evaluate the effect of safety belt use by rear seat passengers on the injury severity of front seat occupants

Although the effectiveness of seat belts for reducing injury to rear seat passengers in traffic accidents has been well documented, the ratio of rear-seat passengers restrained by seatbelts remains lower than that of drivers or passengers in front seats. If passengers in rear seats do not wear seat belts, they may sustain unexpected injury to themselves when involved in accidents, and also endanger front occupants (drivers or front seat passengers). This paper focuses on the tendency of front seat occupants to sustain severer injuries due to forward movement of passengers in rear seats at the moment of frontal collisions, and evaluates the effectiveness of rear passengers' wearing seat belts in reducing injuries of front seat occupants. Since the occurrence of occupant injuries depends considerably on the crash severity, we proposed to use pseudo-delta V in regression analysis to represent velocity change during a collision when analyzing statistical accident data. As the crash severity can be estimated from pseudo-delta V, it becomes possible to make appropriate estimations even when the crash severity differs in data. The binary model derived from the ordered response model was used to evaluate the influence on the injury level based on pseudo-delta V, belted or unbelted status, gender and age. Occupants in cars with a hood in the case of car-to-car frontal collisions were extracted from the statistical data on accidents in Japan. Among 81,817 cars, where at least one passenger was present, a total of 6847 cars in which all passengers sustained injuries and which had at least one rear seat passenger aboard were analyzed. The number of killed or seriously injured drivers is estimated to decrease by around 25% if rear seat occupants come to wear seat belts. Also, the number of killed or seriously injured passengers in front seats is estimated to decrease by 28% if unbelted rear seat occupants come to wear seat belts. Thus, wearing of seat belts by previously unbelted rear seat passengers is considered effective in reducing not only injuries to the rear seat passengers themselves but also injuries to front seat occupants.     

四通换向阀中采用新型材料的节能效果

为了降低四通换向阀传热损失导致的热泵空调系统的性能损失,提出采用低导热系数的阀座材料替代原阀座材料的方案,并结合实验和系统仿真分析了该方案的实际节能效果。研究结果表明:现有典型四通换向阀的传热损失不可忽略;考虑到结构设计和加工工艺等影响因素,采用低导热系数阀座材料是降低四通阀传热损失较为可行的方案;阀座材料导热系数由常见的110 W/(m.K)降为60 W/(m.K)后,四通阀传热损失减小21%,热泵系统COP提高0.4%。     

Ventilwerkstoffe für Verbrennungsmotoren

Valve Materials for Combustion Engines An overview is being given on production numbers, requirements and properties of valve materials. Their development from the beginning till today's state of the art is reviewed with a focus on Chromium-Manganese-Nitrogen-alloys. Valve materials are grouped by the criteria of density – heavy, lightweight – and alloying elements. The multiple stresses of the material in the valve are being met with a few standardised grades and specific ways of manufacture. The path of the material from bar stock to the finished valve is being followed. Engine development in the past decades increased the load on the valves which could be met by continuously developing their structural strength. Also the strength of all valve materials could be raised to nominal strength above 1100 Mpa by applying specific methods. Higher strength at the surface is being effectuated by work hardening effects. The technology to increase reliability of hollow valves and new aspects of valve seat facing including residual stress is explicitly discussed. General aspects of alloy utilisation is followed by a discussion of lightweight valve materials as Titanium alloys, intermetallic Titaniumaluminide alloys and ceramic materials, spec. Silicon Nitride, which all have a potential as forthcoming valve materials capable of reducing fuel consumption of the engines.     

Evaluation of materials for artificial heart valves

The heart of a normal human being beats about 38 million cycles every year. An artificial heart valve, to perform at this rate in the adverse conditions inside the heart for 20 years or more, should be highly wear-resistant with excellent fatigue strength. Thus, the study of mechanical and physical properties of the materials intended for use in artificial valves becomes an inseparable part of the valve development process itself. The physical and mechanical requirements of the materials used in the Chitra heart valve have been evaluated by studying their water absorption, adhesive wear and abrasive properties. The mechanical durability of the device has been assessed by accelerated life cycle testing. The test systems developed for the above are described here. The results show UHMW-PE to be a highly wear-resistant material suitable for the occluder. The accelerated wear tests show that the valve with Haynes-25 alloy cage and UHMW-PE disc has durability in excess of 50 years.