盐雾环境对接触器动态接触电阻的影响研究

为研究盐雾环境对接触器动态接触电阻的影响,选择一种直流接触器开展了盐雾试验。通过同一个测试电路,测试了常温、常态和经过盐雾试验后的同型号、同批次的两个接触器。比较动态接触电阻的试验数据,可以看出经过盐雾试验后的接触器接触电阻明显增大,接触电阻过大使触点发生黏连导致接触器失效,寿命大幅度减少。     

开关触点接触电阻动态测量方法研究

针对动态条件下开关触点接触电阻测量困难、工业环境下高频噪声和高斯白噪声的影响大等问题,研究了一种谐波分析测量及交流比较相结合的开关触点接触电阻测量方法,并将该方法应用于开关动态测试仪上。采用交流比较法能够有效提高信号的信噪比,消除了零点漂移及温度漂移;采用谐波分析法对接触电阻数据进行处理,能够滤除A/D产生的量化噪声,减小了工业环境下的高频噪声及高斯白噪声对测量的干扰。MATLAB仿真实验获得理想的测量效果。最后在开关动态测试仪上进行了动态实验,从而验证该方法的有效性与科学性。     

基于灰色理论的继电器电接触可靠性预测

电接触可靠性是有触点电器产品可靠性的一个重要方面,所以评估触点的电接触性能及可靠性和预测其失效时间对提高有触点电器产品的使用可靠性具有重要的应用价值。针对继电器失效原因的复杂性,提出基于灰理论的电接触可靠性预测。通过建立单变量预测模型GM(1,1),较好地预测电接触失效的问题。并且用动态接触电阻测量系统进行HH52P型电磁继电器失效检测试验,证实灰预测模型的准确性。     

继电器动态电阻在线检测系统设计

以继电器触点动态电阻作为研究对象,提出了一种动态电阻在线定性检测的方案,其创新点在于利用微分回路与比例回路将继电器触点动态电阻的峰值与稳定值检测分开。该系统经实验及应用结果表明所提出的继电器动态电阻检测方案可行。     

CJ12型交流接触器触点粘连的防止措施

当电路接通电流通过触点时,由于导体电阻和接触电阻消耗电能,动、静触点接触处温度升高。当温度达到或超过触点材料熔点时,动、静触点的接触处就出现局部熔化现象。当接触处的电流减小甚至为零,熔化的触点将凝结,使触点熔焊在一起。这种故障称为触点粘连或触点熔结(包括由于剩磁作用使铁芯吸附住衔铁的磁粘附)。为防止这类故障,本文介绍一种机械制约的简易措施。     

微加速度开关力电接触仿真分析

讨论了微加速度开关触点形貌,建立了触点吸附物理模型;根据微观连续介质理论和微观电接触理论,推导出触点间包含斥力项的吸附力和接触电阻数学模型;经仿真分析,得到质量块同基座间的吸附力可以满足质量块同基座间的稳定电接触要求的结论.     

基于单片机的电饭锅接地电阻在线测试装置

本文给出了电饭锅检测上的基于８０９８单片机的接地电阻在线测装置。该装置采用了无源谐振式交流恒流源,克服了顶针接触电阻不稳定的影响,取得小值的方法消除了碳刷移动时的动态接触电阻。     

断电切换法在巡回检测装置中的应用

顾名思义,“断电切换法”就是在触点回路无电流的情况下,使触点接通或断开。这样做的直接结果就是完全防止了电击穿(亦即不可能产生火花),其间接结果是大大增加了触点容量。待触点完全接通(或断开)时再使触点回路投入工作,这就需要对触点回路的电源加以控制。在巡回检测装置中,测温电阻信号往往是很多的(如国产CK701机中仅测温电阻信号就有2000个),这时不论从可靠性还是从经济观点考虑,采用公用电桥的方法都是可取的;而对于这种公用电桥,采用“断电切换法”是最适宜不过的。     

叉车组合开关性能不稳定的解决方法

目前组合开关已经在我公司F系列2～4t叉车上普遍使用，但存在性能不稳定问题。经多次拆检、分析，确认主要原因如下：转动手柄旋钮开关的瞬间，触点之间的接触面积很小，而电流变化很大，时间一长便引起触点发热：长期使用后，触点产生磨损、氧化和腐蚀，增大了触点间电阻，从而引起触点更加发热。     

电子成果信息

JU-2型可调温度继电器系空气感温式,它具有整定温度连续可调、负载容量大、使用方便和可靠性高的特点。主要用于控制室内或箱体内的小环境温度,是自动设备及家用电器可调温度控制和过热保护的必备元件。该产品技术水平达到飞利浦公司80年代同类产品实测水平,填补了国内空白,获得了显著的经济效益。主要技术指标:触点形式1D;触点负载10A,220V.AC,阻性;动作温度0～70℃(可调),动作温度偏差±5℃;回复温度≤20℃,环境温度-25～80℃;接触电阻≤100mΩ;绝缘电阻≥100MQ;介质耐压1500VAC;触点间介质耐压1000VAC;寿命10~4次。     

基于双点接触电阻法的润滑状态研究*

针对目前润滑状态测试装置的局限性,提出一种双点接触自适应摩擦试验装置。该装置结合了摩擦因数法与接触电阻法的优点,在相对静止的双下试件上测量电阻,简化了电路的设计;利用浮动支撑机构实现加载力的平衡自动调节功能,采用自下而上的加载方式,降低了导轨与滑块之间的摩擦以及装置自重对测量的影响,试验测量方便,测试精度有保证。利用该装置研究点接触下不转速和不同载荷所对应的电阻和摩擦因数,并考察两者的变化规律。试验结果表明,摩擦因数与电阻的变化存在较强的关联性。结合Dowson润滑状态的划分方法,对点接触润滑状态进行划分,并绘制了相应的润滑状态图。结果表明,该装置可对润滑状态进行精确划分,为润滑状态研究、润滑油品质鉴定等提供一种新的思路。     

Thermoelastic stability of duplex heat exchanger tubes

When duplex tubes are used for heat exchange purposes, thermal distortion affects the contact pressure and, hence, the thermal contact resistance at the interface. The resulting coupling between the thermal and thermoelastic fields for the system can lead to instability and non-uniqueness of the steady-state solution and, hence, to erratic heat transfer performance.Stability of the system is investigated by determining the conditions under which a small (axisymmetric or non-axisymmetric) perturbation on the steady state can grow exponentially in time. Substitution into the governing heat conduction and thermoelastic equations enables the unknown functions to be determined except for a set of arbitrary constants, which are then determined from the thermal and mechanical boundary conditions, including a statement of the relation between thermal contact resistance and pressure, linearized for small perturbations about the steady state.Results are presented for a range of material combinations and for both directions of steady state heat flux. It is shown that unstable axisymmetric perturbations can only occur for inward heat flow and, hence, the stability boundary for outward heat flow is always associated with a non-axisymmetric mode. In the latter case, the circumferential wavelength of the critical mode is generally about twice the tube thickness and a good approximation to the stability boundary can be obtained using previously published results for the stability of two plane layers in thermoelastic contact.For inward heat flow, the critical heat flux for axisymmetric perturbations is independent of the mean contact resistance, whereas that for non-axisymmetric modes increases with contact resistance. Thus, the stability boundary in this case is determined by non-axisymmetric modes for small values of contact resistance and by axisymmetric modes for large contact resistance.     

机械结合面法向动态接触刚度理论模型与试验研究

机械结合面经常可能在动态条件下工作,使得结合面的接触状态偏离静态工作状态,导致接触刚度发生改变。为了揭示动态接触刚度的变化规律,考虑两个粗糙结合表面上单个微凸体由弹性变形向弹塑性变形以至最终向完全塑性变形转化的接触过程,建立一个振动周期内各变形阶段微凸体的平均接触刚度模型;在此基础上,基于高斯分布假设,建立整个粗糙结合表面的动态接触刚度解析模型。该模型揭示了接触面压、振动频率和相对位移振幅对动态接触刚度的影响规律,并与试验结果和静态接触刚度计算结果进行了比较。研究表明:法向动态接触刚度和静态接触刚度与接触面压之间的关系基本一致,但有一定偏离。这种偏离程度随动态位移幅值和振动频率的增加而分别呈线性和非线性增大。     

Contact state estimation based on surface-matching in virtual assembly

Contact problems are one of the most challenging fields in virtual assembly.Information of contact states could be utilized to realize compliant motion of work pieces,to analyze the contact stress,to assist positioning parts and so on.Some methods have already been proposed to estimate contact states between objects and in most of these methods contact states between objects are simplified in order to realize real-time visual reality animation.While in virtual assembly contact states between parts are required to analyze contact stress,deformation and quality.Besides the contact state estimation method for virtual assembly should be able to handle a number of complex parts in real time.There are rarely known methods which could meet this requirement till now.In this study a contact state estimation algorithm based on surface-matching for virtual assembly is proposed.Contacts between parts are categorized into six basic types according to contact region of surfaces.Based on continuous collision detection of polyhedral models a novel contact state identification algorithm which is based on surface matching is proposed.Then contact evolution algorithm,which utilizes the extern force and contact information,is implemented to handle evolution of contact state.Finally a prototype system is developed to verify the above technologies.Experiment results reveal that contact state between parts could be estimated correctly in real time virtual assembly.The proposed contact state estimation algorithm provides a complete solution to obtain the contact state between parts in virtual assembly.Information of contact state between parts could be utilized to realize contact dynamic,contact stress analysis,assembly quality analysis,and so on.     

镍铬接触对接触电阻失效原因分析

描述了用于K型热电偶回路中的镍铬接触对在电连接器的振动过程中发现接触电阻变大的失效现象,从接触电阻的理论构成和失效接触对的实物状态进行原因分析,通过更换绝缘体材料、固定接触对及更换接触对等方式进行试验验证,确定主要原因。针对分析结果,通过降低表面粗糙度、提高接触压力、涂覆固体膜润滑剂和调整接触对固定机构等方式,解决了镍铬接触对在振动过程中的接触电阻失效问题。通过一系列的试验,总结了避免镍铬接触对失效的关键措施。     

烧蚀作用下石墨焊接池与电极接触行为研究

通过测试分析不同石墨焊接池表面形貌、烧蚀率等性能，提出石墨焊接池均匀退化烧蚀特征，建立以线烧蚀系数为表征的烧蚀状态下动态接触电阻模型。且通过实验验证分析了15 N夹持力作用下，石墨表面烧蚀作用对接触电阻的影响。结果表明：石墨焊接池在直径方向的烧蚀速率较大，石墨表面烧蚀作用使得界面接触电阻呈缓慢增加趋势，普通石墨的烧蚀对界面接触电阻的影响相较于精细石墨的作用更加明显，并且模型的计算值与实测值基本一致，误差在合理范围内，保证了模型建立的合理性和准确性。     

船用柴油机凸轮动态摩擦学分析及型线优化设计*

柴油机配气凸轮工作环境较为恶劣,工作过程中配合界面间载荷、速度及曲率半径等工况周期性变化,导致润滑接触条件苛刻,磨损情况恶劣。以某船用柴油机配气凸轮机构典型工况为算例,针对凸轮-挺柱常见的磨损问题,研究凸轮-挺柱动态接触特性;采用余弦-等速段和高次五项式对凸轮型线进行优化设计,并对凸轮-挺柱副动态接触及弹流润滑状态进行数值分析。结果表明:原凸轮磨损的原因是凸轮-挺柱副在运动周期内动态接触应力出现明显波动,最大值超过许用应力值;经型线优化设计后,凸轮-挺柱动态接触应力降到许用值以下,改善了动态接触特性,凸轮型线具有较好的润滑特性,运行过程中可保持较稳定的油膜润滑状态;凸轮转速和接触载荷的改变会直接影响凸轮-挺柱的润滑状态,尤其是随凸轮转速增大,润滑膜厚增大,压力减小,润滑接触状态明显改善。     

A Contact Force Model Considering Meshing and Collision States for Dynamic Analysisin Helical Gear System

The current research on gear system dynamics mainly utilizes linear spring damping model to calculate the contact force between gears. However, this linear model cannot correctly describe the energy transfer process of collision that often occurs in gear system. Focus on the contact-impact events, this paper proposes an improved gear contact force model for dynamic analysis in helical gear transmission system. In this model, a new factor associated with hysteresis damping is developed for contact-impact state, whereas the traditional linear damping factor is utilized for normal meshing state. For determining the selection strategy of these two damping factors, the fundamental contact mechanics of contact-impact event a ected by supporting forces are analyzed. During this analysis, an e ect factor is proposed for evaluating the influence of supporting forces on collision. Meanwhile, a new restitution of coe cient is deduced for calculating hysteresis damping factor, which suitable for both separation and non-separation states at the end of collision. In addition, the time-varying meshing sti ness(TVMS) is obtained based on the potential energy approach and the slice theory. Finally, a dynamic analysis of a helical gear system is carried out to better understand the contact force model proposed in this paper. The analysis results show that the contribution of supporting forces to the dynamic response of contact-impact event within gear pair is important. The supporting forces and dissipative energy are the main reasons for gear system to enter a steady contact state from repeated contact-impact state. This research proposes an improved contact force model which distinguishes meshing and collision states in gear system.     

Rolling contact fatigue endurance of powder-extruded bearing steel

The mechanical and toughness properties and rolling contact fatigue endurance of powder-extruded bearing steel made from nitrogen atomized remelted turning powder in as-extruded and as-heat treated state are presented. The mechanical and toughness properties are comparable with those of wrought bearing steel. Rolling contact fatigue endurance was tested by the AXMAT method in as-extruded and as-spheroidizing annealed states depending on the austenitizing temperature, which ranged from 790 °C to 870 °C. Powder-extruded bearing steel in both states showed slightly higher hardness (63 HRC), higher contact fatigue resistance (L₁₀ = 80.7 and 55.2 million load cycles, respectively) in comparison with wrought steel (L₁₀ = 31.8 million load cycles). The results demonstrate the advantageous properties of powder-extruded bearing steel for high dynamic loading.     

粗糙度对接触界面动态特性的影响研究

接触界面的刚度和阻尼对机械结构的动态特性有重要影响,为了描述接触界面粗糙度对机械结构动态特性的影响,建立了振动应力波在粗糙接触界面传播的数学模型,并进行了数值仿真和模型试验。试验结果表明：较小的表面粗糙度有利于振动应力波通过接触界面传播;随着粗糙度值的增加,通过接触界面的振动应力波减少,说明较大的粗糙度界面消耗振动能量,但是产生了高次谐波,使振动状态变得复杂。