电流密度对碳纤维—铜—石墨复合材料接触电压降的影响

研究了碳纤维－铜－石墨复合材料在电磨损条件下，电流密度的变化94－16A／cm62）对复合材料接触电压降的影响。结果表明，碳纤维－铜－石墨复合材料电刷与换向器之间的接触电压降具有非线性特征，即电流密度在一定范围内变化对接触电压降影响不大；用扫描电子显微镜观察了磨面形貌，发现在电刷与换向器之间形成的润滑膜保证了接触电压降的稳定，改善了换向性能；对复合材料接触电压降的变化机理进行了初步探讨。     

电流密度对碳纤维／铜／石墨复合材料摩擦系数的影响

研究了碳纤维／铜／石墨复合材料在纯机械磨损和通以不同电流密度（４～１６Ａ／ｃｍ＾２）的电磨损条件下复合材料磨擦系数的变化情况。结果表明,在复合材料表面形成的自润滑膜使复合材料摩擦系数下降;在纯机械磨损条件下的摩擦系统大于在电磨损条件下的摩擦系数;电流密度的大小对电刷摩擦系数影响不大。     

银基复合材料电刷的导电性能

研究了在银基体中加入其它金属部分替代银和石墨、碳纤维以及金属总量对电阻率和接触电压降的影响,探讨碳纤维-石墨-银基电刷材料的成分和导电性能的关系.结果表明:随着石墨和碳纤维含量的增加,材料的导电性能有所降低;在一定工艺条件下,当金属基体总量为90%,其他替代金属的含量控制在一定量时复合材料仍具有良好的导电性能.     

电流强度对碳纤维-铜-石墨复合电刷材料电磨损性能的影响

研究了电流强度的变化(4A/cm2～16A/cm2)对碳纤维-铜-石墨复合电刷材料电磨损性能的影响,并与纯机械磨损进行了对比;用扫描电镜对复合材料磨面进行了观察分析,探讨了电磨损机理.     

碳纤维含量对铜-石墨电刷摩擦因数的影响

为进一步改善铜-石墨复合材料电刷的导电和耐磨性,提高其使用寿命,研究了在通电条件下,碳纤维含量对铜-石墨电刷摩擦因数的影响。结果表明,随碳纤维含量的增加,电刷摩擦因数降低,但碳纤维含量超过5%以后,摩擦因数呈增大趋势;即摩擦因数随碳纤维含量的增加存在极小值。     

碳纤维／石墨复合电刷材料性能的研究

将不同体积百分数的碳纤维和石墨一起以适当工世复合制得了碳纤维／石墨复合电刷材料，并对所得复合材料的理化性能和电接触性能进行了测试分析，从而探讨碳纤维用于制造复合电刷材料的可能性。     

碳纳米管－银－石墨复合材料的电磨损性能

采用粉末冶金工艺制备碳纳米管—银—石墨复合材料,初压压力200 Mpa,在H2保护气氛下烧结并保温1 h,复压压力400 Mpa制得复合材料,研究电流密度(0～25 A/cm2)对碳纳米管—银—石墨复合材料摩擦磨损性能的影响。结果表明：随着电流密度的增大,电磨损过程中的发热量增大,粘着磨损加剧,润滑膜遭到破坏,导致复合材料的摩擦因数、磨损量增大。比较正、负极电刷磨损量发现,接触表面理化反应和金属转移的存在,导致正刷磨损量大于负刷磨损量;正刷磨损量随电流密度增大而成倍增长,负刷磨损量与电流密度关系不明显,电流密度越大磨损极性的差异越明显。     

C／Cu复合材料在电刷中的应用

介绍了我国独创的由镀Ｃｕ碳纤维与改性后的石墨复合而成的一种非均质结构复合材料电刷－Ｃ／Ｃｕ复合材料电刷。经过实践应用表明这种新型复合材料电刷具有载流密度大，换向性能优良，滑动接触性能好及性能可设计等优良的综合性能，是一种新型的电刷材料。     

银－碳纤维复合材料的制造及其在电接触器中的应用研究

探讨了应用粉末冶金制造银－碳纤维复合材料的方法，并把该复合材料应用于电接触器上。实验表明，碳纤维的加入明显改善了复合材料的性能，其使用性能优于银－石墨系材料。     

碳纤维增强铜复合材料

碳纤维增强铜复合材料具有强度高、摩擦系数小、磨损率低、可通过工作电流大、接触压降小等优异性能,可用作低电压、大电流电机及特殊电机的电刷材料、耐磨材料及电子材料。本文主要介绍这种材料的现状,并对材料的摩擦、磨损性能进行了研究讨论。     

Influence of high velocities and high current densities on the friction and wear behavior of copper-graphite brushes

The friction and wear behavior of Morganite CM1S powder metallurgy copper-graphite brushes at sliding velocities up to 160 m s^?1 and current densities up to 870 A cm^?2 is presented. The brushes had a cross-sectional area of 1.2 cm² and the loads employed ranged from 9 to 45 N. The wear rates as a function of velocity and the voltage drop per brush as a function of sliding velocity, brush pressure and current were determined. The wear rates under a current of 600 A are of the same order as those obtained under no current conditions. The minimum difference was obtained at a sliding velocity of 100 m s^?1 (4.1 × 10^?4 cm km^?1 with current compared with 3.4 × 10^?4 cm km^?1 without current). The wear rate exhibited by the positive brush was lower than that of the negative brush at any sliding velocity.At constant current and sliding velocity the contact voltage drop decreases with increasing brush load. The voltage drop exhibited by the positive brush is always lower than that of the negative brush. The contact voltage drop varies little with sliding speed when the current and the brush load are kept constant. At constant brush load and constant sliding speed the voltage drop increases monotonically when the current is increased. It has been determined that local rotor waviness, even of small amplitude, can produce sufficient brush bouncing to cause excessive sparking which results in pronounced damage to the brushes and rotor surface.     

Correlation analysis of brush temperature in brush-type DC motor for predicting motor life

Some critical components of motors and generators have sliding electrical contacts. Electrical brushes are usually used in these contact points to conduct current between the stationary part and the moving part of the motor. In this paper, studies on brush wear against copper commutators are briefly reviewed. The main influential factors in brush wear are associated with both mechanical wear and electrical wear. Brush wear is affected by various factors, including temperature, material properties, sliding speed, contact force, and interfacial as well as environmental conditions. The mechanical wear of brushes is proportional to brush spring pressure and sliding speed, and the electrical wear of brushes is associated with current and contact voltage drop. For characterization, a brush wear test machine is designed, and influential factors, such as electrical contact resistance, temperature, wear mass loss, and so on, are measured. The wear tests are processed using a small brush-type automotive DC motor. The study primarily aims to investigate the effects of the wear behavior of copper-graphite brushes on small brush-typed DC motors. The variable conditions of electrical current are obtained by changing the brush spring pressure and the sliding speed. The results are electrical contact resistance, voltage drop, brush surface temperature rise, and so on. Brush wear is greatly changed by electrical current, which indicates that high current itself not only produces more Joule heating but also causes an increase in voltage drop that will result in additional Joule heating.     

Friction and wear properties of two types of copper — Graphite brushes under severe sliding conditions

High speed dry friction experiments using two copper-graphite brushes against an AISI 4340 steel rotor were conducted at sliding velocities up to 230 m s⁻¹ and at current densities up to 526 A cm⁻². One brush was a commercial powder metallurgy (PM) specimen and the other was a graphite fiber-Cu/Sn matrix composite material. The composite brush was prepared by a proprietary process of liquid-metal infiltration and was run with the graphite fibers perpendicular to the rotor surface. The coefficient of friction was determined as a function of velocity, the wear rates were determined as a function of velocity and the voltage drop was determined as a function of velocity and current. The results show that the coefficient of friction exhibited by the PM brush is lower than that of the composite material at any velocity tested. The wear rates without current are much higher for the PM than for the composite brush, but they are of the same order when a current of 600 A is passed through. The voltage drop at the brush-rotor interface shows a similar variation with velocity for the two brushes, but the variation of the voltage drop as a function of current is different for the two specimens. The voltage drop increases almost linearly with increasing current for the PM brush. For the composite brush it exhibits a sharp increase up to about 50 A and then varies very little up to the maximum current of about 600 A. The damage done to the rotor surface in the case of heavy sparking is more pronounced with the PM brush than with the composite brush. It appears that the difference between the high temperature mechanical properties of the two types of brushes is responsible for their different behavior under severe sliding conditions.     

导电滑环大电流电刷成型技术研究

针对电子设备高功率密度发展需求,文中研发了一种基于表带触指式多触点电刷的导电滑环,实现了旋转机构内大电流高可靠传输能力。介绍了表带电刷组件轴向插槽式导电滑环装配新型结构、多触点自润滑电刷成型技术路线及大电流导电滑环性能测试。将银石墨触点集成至表带电刷尖端,实现电刷自润滑、大电流、高寿命性能需求,制备的导电滑环通流能力达到1 kA。该多触点自润滑电刷构件制造技术为大电流导电滑环的工程化应用奠定了基础。     

The effect of brush spring pressure on the wear behaviour of copper–graphite brushes with electrical current

Electrical brushes are used to conduct current between stationary part and moving part of a motor or a generator. To ensure proper current transfer and continuous contact, brushes must be loaded against the sliding contact surface with a sufficient force. High loads increase frictional losses and wear of the brushes and/or sliding surface. While relatively low contact pressure causes arcing and higher voltage drop.In this study, a novel pin-on-slip ring-type friction and wear test machine was designed and manufactured for the purpose of brush testing. Copper–graphite-based electrical brush containing 90 wt% copper and 10 wt% graphite was manufactured by powder metallurgy and the tribological behaviour and voltage drop were investigated at different brush spring pressures at 10–200 kPa with current.It was found that the specific wear curve showed three distinct wear rate regimes, such as low, mild, and severe. Severe wear was observed below 30 kPa and above 120 kPa brush spring pressures (BSP) (3 and 12 N loads, respectively). Arc erosion was the main wear mechanism below 30 kPa brush spring pressure while abrasion was dominant above 120 kPa BSP. Low and mild regimes were observed between 30–50 and 50–120 kPa BSP, respectively. SEM observations showed that a continuous surface layer was formed at the sliding surfaces of the wear samples in low and mild wear regimes. The wear debris was examined by SEM and X-ray diffractometer.     

An analysis of the main factors on the wear of brushes for automotive small brush-type DC motor

Some critical components in motors and generators have sliding electrical contacts. Electrical brushes are commonly used in those contact points to conduct current between the stationary and moving parts of a motor. Brushes are exposed both to mechanical and electrical loading. In this paper, studies on the wear of brushes against copper commutator were briefly reviewed. The main influential factors of brush wear are associated with both mechanical and electrical wear. Brush wear is affected by various factors including temperature, material properties, sliding speed, contact force, and interfacial and environmental conditions. The mechanical wear of brushes is proportional to the brush spring pressure and sliding speed, while the electrical wear of brushes is associated with current and contact voltage drop. To characterize the wear, a brush wear test machine was designed, and influential factors were measured such as electrical contact resistance, temperature, wear mass loss, and so on. The wear tests were processed using a small brush type automotive DC motor.     

In situ graphite lubrication of metallic sliding electrical contacts

Decoupled graphite lubrication of monolithic silver brushes on a copper rotor was studied in an ambient air environment under current varying from 0 A/cm² to 200 A/cm² using a custom designed electrical contact tribometer. Bifurcation of the positive and negative brush wear rates was observed at a current density of 200 A/cm². Energy dispersive spectroscopy showed transfer of copper from the rotor to the lower wear negative brush. Scanning electron microscopy of worn brush surface cross-sections created by focused ion beam milling revealed a fine-grained metallic layer below the graphite transfer layer on the negative brush surface; no such layer was found on the positive brush surface. At 40 A/cm², steady-state brush wear rates were very low (<10⁻¹¹ m/m). Friction coefficient at steady state was measured to be 0.15 ± 0.02 and was independent of current direction. Using a scanning white light interferometer, the thickness of the graphite transfer layer on the rotor surface was estimated to be 5 μm. Ultimately, the goal is to model lubricant buildup and removal as a competitive rates problem.     

Low wear metal sliding electrical contacts at high current density

Operation of a low wear (2 × 10^?5 mm³/(N-m)), low contact resistance copper sliding electrical contact was demonstrated. The wear rate of a lightly loaded copper–beryllium metal fiber sliding on a polished copper counterface was insensitive to (DC) current density values as great as 440 A/cm² (in a brush positive or anodic configuration). Low wear and relatively low friction (μ ～ 0.2 to 0.3) was achieved by operating the contact immersed in a liquid medium consisting of a hydrofluoroether with helium cover gas, inhibitingoxidationand providing cooling of the contact. Similar experiments performed in liquid mediums of ultrapure water and dilute (3%) hydrogen peroxide show an order of magnitude increase in wear rate and provide further insight on the role of electrochemically enhanced oxidation and the degraded contact resistance and tribological behavior of non-noble sliding electrical contacts in general. In contrast to high current density slidingin hydrofluoroether, an order of magnitude greater wear rate was observed for similar sliding conditionsin hydrogen peroxide or water without the aid of externally supplied electric potential. A conceptual model is proposed correlatingthe rate of brush wear to fatigue strength and electrochemically enhanced oxidation as a result of high current density transport through the contact. A mathematical expression was derived to calculate the approximate wear volume of a single fiber laterally contacting a slip-ring, based on direct measurement of the wear scar geometry.