Testing Method for Resistivity of Pure Carbon Slippers of Electric Locomotive of Ministry of Railways

The core method for detecting the resistivity of the pure carbon sliding plates of the electric locomotive pantographs of the Ministry of Railways is based on the calculation of the resistance of the sample and its dimensions. Environmental control and repeated measurements are the key to ensuring accuracy.

I. Preparation Work

1. Sample Preparation: Select representative samples of pure carbon sliding plates, typically cutting them into long strips 100mm in length and 10mm in width, with the thickness taken as the actual thickness of the sliding plate.

2. Instrumentation and Equipment: Equip with a resistivity measuring instrument (with a range covering 10⁻⁶ to 10⁻³ Ω·m), a vernier caliper (with an accuracy of ≥0.02mm), and a micrometer (with an accuracy of ≥0.01mm).

II. Measurement Process

1. Sample Dimension Measurement

 - Use a vernier caliper to measure the length and width at different positions of the sample 3-5 times, and use a micrometer to measure the thickness. Take the average value and convert it to meters (m).

2. Resistance Measurement

 - Place the sample in close contact with the electrodes of the resistivity meter to eliminate the interference of contact resistance; record the value when it stabilizes, and repeat the measurement 3 or more times to obtain the average resistance value (Ω).

III. Resistivity Calculation

According to the formula: ρ = R × (W × T) / L, where:

 - R is the measured average resistance value (Ω)

 - L/W/T is the converted values of the sample's length, width, and thickness in meters (m)

 - The calculation result is in units of Ω·m. Generally, the resistivity of pure carbon skateboard should be lower than 5 × 10⁻⁵ Ω·m.

IV. Result Determination

- Calculate the average value and standard deviation of multiple measurements. If the dispersion value exceeds 5% of the standard value, re-sample testing is required.

- Refer to the railway industry standards such as TB/T 2769 to determine whether it is within the qualified range.

V. Environmental Conditions

During the testing, the temperature should be controlled within 20 ± 2℃ and the humidity within 50 ± 5%. Avoid changes in material resistance characteristics caused by temperature and humidity fluctuations.