Generation Mechanism of Localized Wear of Cu-impregnated Metalized Carbon Contact Strip

Abstract

Localized wear on pantograph contact strips is a serious issue that needs to be addressed urgently, as it can cause the pantograph head to fuse and the overhead contact wire to break. However, the exact causes of localized wear are still unclear, and effective solutions have not yet been developed. This study aims to identify the causes of localized wear in copper-impregnated metalized carbon contact strips. To achieve this, worn strips were analyzed using a micro-Raman spectrometer and the sliding wear behavior of contact strips with different levels of carbon graphitization was examined using a block-on-ring wear tester.

1. Introduction

The most commonly used current collection system for electric railways is the overhead contact line system. In this system electric rolling stock collects power from a contact wire via a pantograph. A sliding contact component, known as the pantograph contact strip (hereinafter referred to as the contact strip), is mounted at the top of the pantograph and makes direct contact with the contact wire (Fig. 1(a)).

Fig. 1　Schematic drawings of pantograph and contact strip

Contact strips are worn due to friction with the contact wire. Wear profiles of contract strips usually correspond to the lateral deviation of the contact wire (Fig. 1(b)), as shown in Fig. 1(c). However, in rare cases, wear can develop locally, leading to uneven wear such as stepped wear or grooved wear (Fig. 1(c)). Figure 2 shows an example of actual localized wear. Even when detected at an early stage, localized wear can cause train delays due to the need for unscheduled replacement of the contact strip. If detection is delayed, it may result in fusion of the pantograph head and, in severe cases, damage to the overhead contact wire, both of which pose serious operational risks. Therefore, resolving this issue is critically important.

Fig. 2　Example of localized wear of contact strip

Nevertheless, the mechanisms underlying the initiation and progression of localized wear, particularly in metallized carbon contact strips, are still not well understood, and no systematic countermeasures have been established. Although methods to detect localized wear using sensors installed on the contact wire have been proposed [1], a fundamental solution requires a deeper understanding of its causes and formation mechanisms.

When investigating the mechanism of the localized wear, it is important to distinguish between initial formation of localized wear and rapid progression of wear in regions where wear has already begun. This study focuses on the early-stage formation of localized wear in copper-impregnated metallized carbon contact strips.

2. Current understanding on localized wear of contact strips

2.1 Localized wear with identified causes

Localized wear with already identified causes can be broadly categorized into the following three types:

(1)　Wear caused by contact loss due to frost or ice on the overhead wire;

(2)　Wear caused by contact loss resulting from insufficient followability of the overhead contact line-pantograph system.

(3)　Wear occurring at the boundary between the principal and auxiliary contact strips.

Type (1) is commonly observed with copper-based sintered alloy contact strips. When the pantograph passes over sections of the contact wire with frost or ice, continuous arc discharges are generated, leading to the melting and wear of the contact strip. Notable characteristics of this type include its frequent occurrence during winter and arc discharge damage on the side surfaces of the pantograph head. Countermeasures have included the use of arc-resistant contact strip materials and the removal of the ice coatings using dedicated pantographs for de-icing.

Type (2) occurs when the followability of the overhead contact line-pantograph system is poor, resulting in repeated contact loss. For example, localized wear has been reported in cases where the pantograph uplift force was reduced due to a low contact wire height [2], and in areas with corrugated wear on the contact wire. In cases where ground equipment-related factors are responsible, contact loss occurs repeatedly at the same location on the contact strip, resulting in consistent localized wear at the same position across different trains.

Type (3) refers to wear that occurs on the auxiliary contact strip at the boundary with the principal contact strip, typically on the auxiliary strip made of aluminum. This type of localized wear is attributed to significant differences in electrical resistivity and wear characteristics between the principal and auxiliary contact strips. Using auxiliary contact strips made of the same material as the principal contact strip has proven to be an effective countermeasure.

2.2 Influence of arc discharge on the wear of metallized carbon contact strips

The indent at the beginning of this section should be 15 milli As discussed in the previous section, many cases of localized wear are believed to result from arc discharges during contact loss events. This wear is more common in metal-based contact strips, which can melt or soften due to such discharges. However, localized wear is also found in carbon-based strips, which do not melt under atmospheric pressure, and this remains a significant concern.

Previous studies have shown that wear on copper-impregnated carbon strips increases with arc discharge energy [3], and arc exposure causes the copper to melt out, reducing the strip’s hardness. These findings suggest that localized wear results from arc energy concentrating on specific areas of the strip surface.

However, in experiments conducted using a contact force of 55 N, comparable to the standard uplift force of pantographs, no clear correlation was found between arc energy distribution and the resulting wear profile [4]. Further tests investigating whether arc-damaged areas initiate localized wear revealed similar wear rates in damaged and undamaged areas. In contrast, experiments with roughly double the normal contact force showed a strong correlation between electric charge of arc discharge and contact strip wear. These findings suggest that both arc discharge and high contact force contribute to increased wear of the contact strip. Nevertheless, the precise mechanism behind this phenomenon remains unclear.

Building on the previous research, this study aims to perform detailed observation and analysis of localized wear on the metallized carbon contact strips. We also conducted experiments using contact strip specimens that simulated degradation caused by arc discharge, such as copper ejection or graphitization, to investigate the effects of contact force and the surface roughness of the contact wire on the wear of the strip.

3. Investigation of localized wear occurrence and observation/analysis of contact strips with localized wear

3.1 Contact strip material

The contact strip studied is the PC78A, a copper-impregnated metallized carbon strip manufactured by Toyo Tanso. Its microstructure is shown in Fig. 3, and its chemical composition and physical properties are listed in Table 1. Typically, the carbon substrate in such strips is non-graphitic carbon fired at 1,000-1,500°C, which also applies to PC78A. When exposed to temperatures above 2,000°C, this carbon undergoes a structural transformation into graphitic carbon, a process known as graphitization.

Fig. 3　Appearance and microstructure of Cu-impregnated carbon contact strip

Table 1　Chemical composition and physical properties of contact strip

Chemical composition (mass %)
C	52
Cu	48
Physical properties
Density (103 kg/m3)	3.0
Shore Hardness (HSD)	90
Electric resistivity (μΩm)	1.8
Flexural strength (MPa)	120
Charpy impact value (kJ/m2)	4.2

3.2 Investigation of localized wear occurrence

3.2.1 Overview of the investigation

Localized wear on PC78A was investigated in Areas A and B from December 2009 to March 2012. The investigation focused on two aspects: the date of discovery and the displacement (distance from the center of the pantograph head) of the wear location. The trains operating in these areas were either 115 or 117 series electric trains, typically in a four-car formation with two motor cars and two trailers. A single pantograph (Type PS16) equipped with two rows of 40 mm-wide contact strips. The maximum current per strip was estimated from the traction motor ratings: about 520 A for the 115 series and 450 A for the 117 series.

3.2.2 Results and discussion

Figure 4 shows the monthly distribution of localized wear occurrences. If icing or frost on the contact wire were the main cause, a higher frequency would be expected in winter. However, no such seasonality was observed in the investigated areas, as shown in Fig. 4.

Fig. 4　Monthly distribution of localized wear detection

Figures 5 and 6 show the location distribution where localized wear occurred. The data indicate that wear tends to occur near the center of the pantograph head and around ±200 mm from the center-positions that correspond to the endpoints of the contact wire’s zigzag pattern. The central area of the contact strip has lower pantograph followability, making contact loss and arc discharges more likely. Similarly, at ±200 mm from the center, the contact wire is supported by fittings and has greater inertia, which also increases the likelihood of contact loss. The high frequency of localized wear occurrence in these displacements suggests that arc discharges during contact loss, as previously considered, may be the cause of localized wear on metallized carbon contact strips.

Fig. 5　Localized wear location distribution (Area A)

Fig. 6　Localized wear location distribution (Area B)

3.3 Cross-sectional microstructural observation and Raman spectroscopic analysis of localized wear regions on contact strip

The cross-sectional microstructure of localized wear regions on the contact strip was examined using a digital microscope. Figure 7 shows a representative result. In the figure, slightly darkened areas indicate regions where copper has melted and been ejected. The depth of the copper-ejected region reached approximately 1,500 μm at the flat surface of the localized wear region, but only around 10 μm on its sloped surfaces. In contrast, in normally worn regions―areas without localized wear―the depth ranged from 10 to 100 μm. These findings suggest that the flat surface of the localized wear region experienced more intense thermal effects than other areas.

Fig. 7　Example of microstructure around localized worn part

3.3.1 Raman spectroscopic analysis

To evaluate the degree of graphitization of the carbon substrate at the bottom of the localized wear area, Raman spectroscopy was conducted. Raman spectroscopy assesses the crystallinity and structural properties of carbon materials by analyzing the spectrum of light scattered by laser irradiation.

Figure 8 shows a Raman spectrum of PC78A (black line). Carbon materials typically display two characteristic peaks: the G band (~1,580 cm⁻¹), associated with graphite structures, and the D band (~1,360 cm⁻¹), related to structural disorder and defects.

Fig. 8　Example of Raman spectrum of PC78A

By deconvoluting the spectrum (red and blue curves in Fig. 8), the intensities of the G and D bands, denoted as I_G and I_D , are obtained. As graphitization progresses, the G band becomes sharper, the intensity ratio R=I_G/ I_D (also known as the R-value [5]) increases, and the full width at half maximum (FWHM) of the G band decreases. These indicators are commonly used to evaluate the degree of graphitization.

(1) Analytical method and graphitization degree evaluation indicator

The analysis was performed using an Almega Laser Raman Spectrometer (Thermo Nicolet). Although the R-value is commonly used to evaluate graphitization, this study used the full width at half maximum (FWHM) of the G band instead, based on preliminary findings showing a strong correlation with firing temperature.

(2) Analysis of standard samples

Before analyzing the actual contact strips, Raman spectroscopy was performed on standard samples prepared by varying the firing temperature of the carbon substrate to investigate the relationship between graphitization and temperature. Rockwell hardness was also measured to assess how firing temperature affected substrate hardness.

(3) Results and discussion of standard sample analysis

Figure 9 shows the relationships between firing temperature and both the FWHM of the G band and hardness. The FWHM, denoted as HG (cm⁻¹), exhibited a strong negative correlation with the firing temperature T (°C), as shown in Eq (1).

  

$$\mathit{HG}=-0.024T+113$$(1)

Fig. 9　Relationship between firing temperature of carbon substrate and half width of G band and Rockwell hardness of contact strip

Based on Eq. (1), the equivalent firing temperature experienced by a contact strip can be estimated from the FWHM of the G-band in its Raman spectrum. In the following sections, thermal history is evaluated using this estimated temperature rather than the FWHM directly.

According to Fig. 9, the Rockwell hardness of the carbon substrate, initially about 100 HRH at manufacturing, drops to around 80 HRH when the firing temperature exceeds 2,000°C, and further declines to approximately 40 HRH at 2,800°C. In this study, 2,000°C―the point at which hardness begins to decrease―is defined as the graphitization temperature. When the estimated temperature exceeds this threshold, graphitization is considered to have progressed.

(4) Analysis of the actual contact strip

Raman spectra were measured at three locations (Fig. 10) on both locally and normally worn areas of the contact strip. In total, six points were measured on locally worn areas (two samples) and twelve on normally worn areas (four samples). After surface measurements, the strip was sectioned, and similar measurements were taken on cross-sections 0.2-0.3 mm below the surface.

Fig. 10　Points of Raman spectroscopic analysis for actual contact strip

(5) Analysis and discussion of localized wear on the contact strip

Figure 11 presents the estimated thermal history derived from the measured Raman spectra. Of the 12 points measured in normally worn areas, 10 had estimated peak temperatures at the contact surface below 2,000°C (ranging from 1,400°C to 1,750°C). The two points exceeding 2,000°C were located at the edges of the contact strip, where arc discharges are more likely to occur.

Fig. 11　Estimated maximum temperature on surface and inside of contact strip

By contrast, in locally worn areas, four out of six points showed peak temperatures above 2,000°C (ranging from 2,300°C to 3,100°C), with significant graphitization observed even in the central region of the strip.

Measurements taken at a depth of 0.2-0.3 mm from the sliding surface showed similar trends. In normally worn areas, 11 of 12 points had peak temperatures below 2,000°C. In locally worn areas, four of six points exceeded 2,000°C (ranging from 2,300°C to 2,700°C), indicating that graphitization extended to these subsurface regions.

4. Arc discharge experiment

This chapter describes an experiment conducted to investigate the influence of heat generated by arc discharge on the graphitization of the carbon substrate of the contact strip.

4.1 Experimental method

First, a current of 500 A was applied between a hard copper contact wire (anode) and a PC78A contact strip (cathode) in contact. The voltage of the power supply was 70 V DC. An arc discharge was then generated by moving the contact strip vertically downward at 10 mm/s. The arc duration was controlled by turning off the arc using a thyristor to short-circuit the electrodes after ignition. Since the arc duration in actual operation is at most on the order of 100 ms, it was set between 0.2 ms and 500 ms in this experiment. Afterward, Raman spectra were measured on the arc-damaged surface and on a cross-section 0.2-0.3 mm below the surface.

4.2 Experimental results and discussion

Figure 12 shows the estimated peak temperatures on the surface of the arc-damaged trace and at a depth of 0.2-0.3 mm below the surface. Even with an arc duration of just 0.2 ms, the surface temperature exceeded 2,500°C, indicating that graphitization occurred within this short duration. At the 0.2-0.3 mm depth, when the arc duration ranged from 0.2 to 10 ms, peak temperatures remained below 1,200°C and no structural changes in the carbon substrate were observed. However, when the arc duration exceeded 50 ms, peak temperatures rose above 2,000°C, and graphitization was observed.

Fig. 12　Estimated equivalent temperature of arc-damaged region

5. Wear experiments under electric current

Wear experiments under electric current were conducted to:

(1) examine the effect of copper ejection on contact strip wear;

(2) identify factors promoting graphitization of the carbon substrate; and

(3) clarify how graphitization of the carbon substrate affects wear.

5.1 Experimental method

The experiments were conducted using the wear tester developed by the Railway Technical Research Institute. This tester simulates actual operating conditions by pressing a contact strip specimen (25 mm × 60 mm × 9 mm) against a pure copper ring (material: JIS C1020P-1/2H; contact width: 5 mm) representing the contact wire and sliding it while an electric current is applied. The zigzag motion of the contact wire is simulated by laterally oscillating the contact strip.

During the experiments, electric current, voltage between the contact strip and contact wire, contact force, and frictional force were measured. Arc discharge was defined as occurring when the voltage exceeded 10 V. To quantify the effects of arc discharge, the amount of charge of arc discharge Q(C) was calculated as the cumulative sum of the product of current and arc duration during arc events.

5.2 Effects of copper ejection on wear and factors promoting graphitization

Previous research suggested that the increased wear of PC78A from arc discharge was caused by oxidation of the carbon substrate, promoted by copper ejection. However, as discussed in Section 3.3, both copper ejection and graphitization occur during arc discharge. To isolate the effect of graphitization, we conducted experiments comparing wear on specimens with copper ejected from the surface to those without. The cross-sectional microstructure near the surface of the copper-ejected specimens is shown in Fig. 13. Additionally, to determine whether graphitization occurs due to Joule heating independent of arc discharge, Raman spectroscopy was performed on the sliding surface of the contact strip after the experiments.

Fig. 13　Microstructure of Cu ejected contact strip specimen

5.2.1 Experimental conditions

The experimental conditions are summarized in Table 2. To investigate whether the carbon substrate undergoes graphitization due to Joule heating induced by electric current, the maximum current was set to 500 A, which corresponds to the maximum current collected per contact strip in actual vehicles.

Table 2　Experimental conditions (effect of Cu ejection from surface)

Items	Condition
Sliding speed	100 km/h
Current	DC100, 300, 500 A
Contact load	54 N
Sliding distance	25 km
Test piece	1,200℃ fired Normal and Cu ejected
Sliding surface of simulated contact wire	Smooth※

※Surface roughness: 0.05~0.15μm (Ra), 0.1~1.0μm (Rz_JIS)

5.2.2 Experimental results and discussion

Figure 14 shows the specific wear rate of the contact strip (i.e., wear volume per unit normal load and per unit sliding distance) as a function of the average current during the experiments. There was no observable trend indicating an increase in specific wear rate for specimens simulating copper ejection from the surface.

Fig. 14　Result of wear experiment (effect of current)

To examine the effect of arc discharges on wear, Fig. 15 plots the arc discharge charge per unit sliding distance on the horizontal axis.

Fig. 15　Result of wear experiment (effect of arc-discharge)

For all strips, the specific wear rate increased with the amount of arc discharge, while copper ejection had no significant effect.

Since copper ejection also occurred in normally worn areas, it is suggested that copper ejection alone is unlikely to cause localized wear of the contact strip.

Figure 16 shows the estimated maximum surface temperature of the contact strip specimen based on the Raman spectra. Under conditions where the arc discharge rate was 0% or 0.1%, no estimated peak temperature exceeded the graphitization threshold of 2,000°C, regardless of the applied current. As a result, no graphitization of the carbon substrate was observed.

Fig. 16　Estimated maximum temperature of surface of contact strip specimen

In contrast, at an arc discharge rate of 2.5%, the estimated peak temperature exceeded 2,700°C at the specimen edge, where arc discharge was more likely. While it cannot be ruled out that graphitization may occur without arc discharge under even larger electric current conditions, the results confirmed that arc discharge is a major factor promoting graphitization.

5.3 Influence of contact force and surface roughness of the contact wire on localized wear of graphitized regions of contact strip

5.3.1 Experimental conditions

This section examines the effects of contact force and wire roughness on the wear of contact strips with different graphitization levels. The strips were made from materials fired at different temperatures. Experimental conditions are shown in Table 3.

Table 3　Experimental conditions (effect of graphitization on wear of contact strip)

Items	Condition1	Condition2	Condition3
Sliding speed, km/h	100
Current, A	0-DC500
Contact load, N	54	54	98
Sliding distance, km	25
Contact strip test piece	1,200, 1,600, 2,100(or 2,200), 2,800℃ fired
Sliding surface of simulated contact wire	Smooth*1	Rough*1	Smooth*2

^*1 Surface roughness: 0.05-0.15 μm (Ra), 0.1-1.0 μm (Rz_JIS)

^*2 Surface roughness: 1.5-2.5 μm (Ra), 5-15 μm (Rz_JIS)

To investigate the effects of contact force and the surface roughness of the contact wire on wear, wear experiments were conducted under the following three conditions: (1) a typical pantograph contact force of 54 N with a smooth contact wire surface, (2) a contact force of 54 N with a rough contact wire surface simulating surfaces severely damaged by arc discharge, and (3) an increased contact force of 98 N with a smooth contact wire surface. In service lines using PC78A contact strips, surface roughness in undamaged areas (without contact loss or arcing) is approximately Ra 0.1-0.6 μm and Rz_JIS around 2 μm, whereas in areas severely damaged by arc discharge, it reaches Ra 2-18 μm and Rz_JIS 8-30 μm.

5.3.2 Experimental results and discussion

(1) Condition 1 (contact force: 54 N, smooth contact wire surface)

Figure 17 shows the experimental results under these conditions. Since no arc discharge occurred, the specific wear rate of the contact strip was plotted against the applied current. Across all current levels, strips fired at 2,100°C or 2,800°C showed no clear tendency to wear more than those fired at 1,200°C or 1,600°C. These results suggest that, under standard contact force and with a smooth contact wire surface, even highly graphitized contact strips did not show increased wear.

Fig. 17　Result of wear experiment under condition1

(2) Condition 2 (contact force: 54 N, rough contact wire surface)

The experimental results are shown in Fig. 18. Under these conditions, arc discharges occurred, so the specific wear rate of the contact strip was plotted against the arc charge. Since the arc charge in actual service is typically around 10⁻³ C/m, the comparison in Fig. 18 focuses on the range of 0-0.01 C/m. The results show that the specific wear rate of the strip made from carbon substrate fired at 2,100°C was about five times higher, and that of the strip fired at 2,800°C was about nine times higher than the average wear rate (40 × 10⁻⁶ mm³/Nm) of the strips fired at 1,200°C and 1,600°C.

Fig. 18　Result of wear experiment under condition 2

(3) Condition 3 (contact force: 98 N, smooth contact wire surface)

The experimental results are shown in Fig. 19. As in Condition 2, the comparison focuses on the region where the arc discharge ranges from 0 to 0.01 C/m. The specific wear rate of the contact strip specimen fired at 2,200°C was about 20 times higher than the average of the 1,200°C- and 1,600°C-fired strips (54 × 10⁻⁶ mm³/Nm). The strip fired at 2,800°C showed severe wear under the 100 A current, and the experiment was discontinued. As a result, its data is not shown in the figure. However, its specific wear rate at the time of discontinuation was 4,232 × 10⁻⁶ mm³/Nm―roughly 80 times higher than the average of the 1,200°C- and 1,600°C-fired strips.

Fig. 19　Result of wear experiment under condition 3

Notably, field measurements on actual vehicles have shown that contact forces exceeding 98 N occur approximately 20% of the time. This suggests that the high contact force used in the experiment can also occur in actual environments.

5.3.3 Summary

The results suggest that the wear rate of the contact strip increases significantly when the carbon substrate is graphitized and contacts a rough wire surface, or when the contact force is higher than usual. This increase is likely caused by abrasive wear from a cutting action. Abrasive wear occurs when two solid surfaces slide against each other and the harder, rougher surface cuts into the softer one. As shown in Fig. 20, after graphitization, the carbon substrate becomes softer than the simulated contact wire, reversing their original hardness relationship. This reversal likely led to abrasive wear.

Fig. 20　Comparison of hardness

6. Localized wear mechanism and countermeasures

6.1 Mechanism

Based on the above results, the localized wear mechanism in copper-impregnated metallized carbon contact strips can be described as follows:

(1) Arc discharge due to contact loss promotes graphitization of the carbon substrate, leading to arc-damaged regions with reduced hardness.

(2) When these softened regions interact with a rough contact wire surface or experience high contact force, a cutting action occurs, significantly increasing the wear rate and resulting in localized wear.

6.2 Countermeasures

Since localized wear in the copper-impregnated metallized carbon contact strips is presumed to be caused by arc discharge, a fundamental countermeasure is to reduce arc discharge caused by contact loss. Arc discharge can also occur when an oxide film on the contact wire surface hinders electrical contact, not just during contact loss. In such cases, removing the oxide film effectively suppresses localized wear.

As noted in Section 6.1, localized wear tends to occur in graphitized regions of the carbon substrate, which appear glossy and are visually identifiable. Field maintenance has confirmed that early replacement of contact strips with such glossy areas reduces the incidence of localized wear.

7. Conclusion

To clarify the mechanism of localized wear in copper-impregnated metallized carbon contact strips, we conducted a field survey, observations of worn strips, and wear experiments. The following findings were obtained:

1) Localized wear tends to occur at the center of the contact strip or at the edges of the contact wire deviation.

2) At locations with localized wear, the carbon substrate of the contact strip is graphitized.

3) Graphitization of the carbon substrate in the contact strip progresses even with very short duration of arc discharges, and the graphitized area expands internally with longer duration of arc discharge.

4) The hardness of the graphitized contact strip is lower than that of the contact wire. When the contact wire surface is rough or the contact force is high, the wear rate increases by approximately 5 to 20 times compared to non-graphitized strips.

It should be noted that this paper is a partially revised version of the article published in IEEJ Transactions on Industry Applications, Vol. 141 [6]. The copyright of the original paper is held by the Institute of Electrical Engineers of Japan.

References

• [1]  Koyama, T., Usuda, T., Kawasaki, K., Nakamura, K., Kawamura, T., “Methods for Detecting Pantograph Defects Using Sensors Installed on Contact Lines,” QR of RTRI, Vol. 57, No. 3, 2016.
• [2]  LIU Guo-liang, “Analysis of pantograph carbon contact strip abnormal wear on Guangzhou Metro Line 2 train,” Electric Locomotives & Mass Transit Vehicles, No. 2, 2008.
• [3]  Kubo, S., Kato, K., “Effect of arc discharge on wear rate of Cu-impregnated carbon strip in unlubricated sliding against Cu trolley under electric current,” Wear, Vol. 216, Issue 2, pp. 172-178, 1998.
• [4]  Kubota, Y., Hayasaka, T., Miyauchi, T., “Effect of Arc Discharge on the Wear Profile of Cu Impregnated Carbon Based Pantograph Contact Strip,” presented at ICEC 2014 (The 27th International Conference on Electrical Contacts), Dresden, Germany, June 22-26, 2014.
• [5]  Tuinstra, F., Koenig, J. L., ”Raman spectrum of graphite,” J. Chem. Phys., 53, 1126-1130, 1970.
• [6]  Kubota, Y, Hayasaka, T., Koga, S, Nozaki, H, “Generation Mechanism of Localized Wear of Cu-impregnated Metalized Carbon Contact Strip,” IEEJ Transactions on Industry Applications, Vol. 141.

Authors

	Yoshitaka KUBOTA Senior Researcher, Frictional Materials Laboratory, Materials Technology Division Research Areas: Tribology, Sliding Contact, Current Collecting Materials
	Takamasa HAYASAKA, Ph.D. General Manager, Head of R&D Planning, Research and Development Promotion Division Research Areas: Arc Discharge Plasma, Contact Line Structures, Current Collection
	Shinichiro KOGA Senior Engineer, West Japan Railway Company Research Areas: Vehicle Maintenance
	Hidehiko NOZAKI Technical Manager, Toyo Tanso Co,Ltd Research Areas: Carbon Materials