Reducing the nanoparticles generated at the wheel–rail contact by applying tap water lubricant at subway train operational velocities

The formation characteristics and the reduction of nanoparticles emitted from wheel–rail contacts at subway-train velocities of 73, 90, and 113 km/h under dry and water-lubricated conditions (using tap water) were studied using a twin-disk rig. The resulting number concentration (NC) of ultrafine and fine particles increased with train velocity under both conditions. Particle generation varied with slip rate under both conditions in both the particle categories. Furthermore, the formation characteristics at 113 km/h under dry conditions showed a notable deviation from those under water-lubricated conditions in three aspects: (i) The maximum NC of ultrafine particles was higher than that of fine particles, (ii) the predominant peak diameter was in the ultrafine particles category, and (iii) the proportion of ultrafine particles was much higher than those of the fine particles. Applying water decreased the NC of ultrafine and fine particles significantly at all tested velocities (by 54–69% and 87–91%, respectively). Adding water increased the NC of particles ≤ 35 nm in diameter, possibly owing to the increase in water vapor and mineral crystals from tap water. Overall, this study provides a reference for researchers aiming to minimize nanoparticle formation at the wheel–rail contacts by applying a lubricant.

Reduction the Nanoparticles Generated at the Wheel–rail Contact by Applying Tap Water Lubricant at Subway Train Operational Velocities1

The formation characteristics and reduction of nanoparticles emitted from wheel–rail contacts at subway train velocities of 73, 90, and 113 km/h under dry and water-lubricated conditions (using tap water) were studied using a twin-disk rig. The resulting number concentration (NC) of ultrafine and fine particles increased with train velocity under both conditions. Particle generation varied with slip rate under both conditions in both the particle categories studied. Further, the formation characteristics at 113 km/h under dry conditions showed a notable deviation from those under water-lubricated conditions in three aspects: (i) the maximum NC of ultrafine particles was higher than that of fine particles, (ii) the predominant peak diameter was in the ultrafine particles category, and (iii) the proportion of ultrafine particles was much higher than those of fine particles. Applying water decreased the NC of ultrafine and fine particles significantly at all tested velocities (by 54%–69% and 87%–91%, respectively). Adding water increased the NC of particles ≤35 nm in diameter, possibly owing to the increase in water vapor and mineral crystals from tap water. Overall, this study provides a reference for researchers aiming to minimize nanoparticle formation at the wheel–rail contacts by applying a lubricant.

The Tribological Properties of Water Lubricated Ceramics with Silica Nanoparticle Additives

Water lubricated ceramics exhibited excellent tribological properties such as super lubricity and good thermal stability. However, long running-in period and low load-carrying capacity limited the application of water lubricated ceramics. Silica nanoparticles have been shown to be highly effective additives for oil lubrication. And because of their economic efficiency, eco-friendliness and excellent tribological properties, silica nanoparticles are considered to be great potential additives for water-based lubricant, especially for ceramic lubrication. Here, we present an exploratory study on silica nanoparticles as water-based lubricant additives for ceramic lubrication. Different silica nanoparticles were synthesized, characterized and added into water as additives. The tribological properties of silica nanoparticles as water based lubricant additives were tested. The tribological mechanism of silica nanoparticles was analyzed. It was found that silica nanoparticles dispersed well and kept stable in water. Both the running-in period and the stable period were influenced by silica nanoparticles. With the optimal 5 wt. % amino modified silica nanoparticles added into the water lubricant, the running-in time dropped by 97.0% and the average friction coefficient by 86.6% compared with the pure water.

A Novel Nano-TiO2 Additive Oil-in-Water Lubricant for Hot Steel Rolling

To obtain a low cost, environmentally friendly and effective lubricant, a novel nanoTiO2 additive oil-in-water (O/W) lubricant for hot steel rolling has been developed. Based on the contact angle, tribological and hot rolling tests, the performance of the nanoTiO2 additive O/W lubricants was evaluated and discussed. The results show that the strongest adhesion force between the nanoTiO2 additive O/W lubricant and the work roll is obtained after addition of 4% nanoTiO2 additive in the 1% O/W lubricant. The nanoTiO2 nanoparticles can reduce coefficient of friction (COF) and rolling force, and enhance the surface quality of the hot-rolled product. The lubrication mechanism of nanoTiO2 additive O/W-based lubricant has been proposed.