Ezequiel Alberto Gallardo-Hernández

Effect of oil and water mixtures on adhesion in the wheel/rail contact

Abstract This article details the findings of a series of twin disc machine adhesion tests that investigated the effects of oil and water mixtures on adhesion at the wheel/rail interface. Oil was found to have a dominant effect on adhesion in the presence of water. Surfaces coated with oil at 4.7×10−3 g/cm2 and sprayed with water had levels of adhesion similar to those coated by a replenishing supply of oil. The tests showed that drying a wet contact can initially give a reduction in adhesion, that increased roughness results in increased adhesion in the presence of oil, and that increased contact pressure improves adhesion in the presence of oil.

Laboratory investigation of some sanding parameters to improve the adhesion in leaf-contaminated wheel—rail contacts

Leaf contamination has been identified as the major cause of low adhesion incidents occurring on some railway networks in the last few decades. In the presence of leaf layers, the trains cannot have the required adhesion at the wheel—rail contact for adequate traction and braking operation. Under these circumstances, not only the punctuality but also the safety of the railway transportation can be threatened. In order to mitigate low adhesion problems, railway organizations have opted for different measures, particularly during the season of Autumn. The most employed measure consists of bringing sand to the wheel—rail interface, which can be performed by means of air-pumped sanders or in the form of sand-based friction modifiers. Although sand has widely been accepted as an effective adhesion improver, the effect of some sanding parameters on the adhesion improvement in leaf-contaminated contacts seems to be unclear. This hinders the possible optimized use of sand on the railway networks. In this paper, the influence of the number of sanding axles, particle size of sand, and wheel slip on the adhesion recovery in leaf-contaminated wheel—rail contacts is presented. Rolling—sliding tests under closely controlled conditions have been performed on a twin-disc roller rig. An electrical circuit has been connected to the rig for monitoring the effect of contamination on the electrical conductivity across the wheel—rail contact. The results show that the application of sand contributes to removing the leaf layers from the disc surfaces, which leads to a higher adhesion coefficient in comparison with the untreated (baseline) situation. Accordingly, the electrical conductivity across the wheel—rail contact is also improved. Furthermore, the adhesion recovery is shown to become larger and faster with the increase in sanding axles and wheel slip. Among the particle sizes tested in this work, medium particles are found to yield the most effective adhesion recovery.

Frictional Behavior of a Wet Clutch Using Blends of Automatic Transmission Fluid (ATF) and Biolubricant (Jatropha Oil) in a Pin-on-Disk Tester

Nowadays, biolubricants are being used to replace mineral lubricants totally or partially and it is of great importance due to interest in environmental protection. Jatropha oil is a good alternative as lubricant feedstock and combustible. Its production is cheap in comparison to other vegetable oils. In México, Jatropha curcas L. is widely distributed in more than 15 states, which makes a sustainable supply of this natural resource possible. The aim of this work was to investigate the frictional behavior of blends of automatic transmission fluid with vegetable oil tested in a pin-on-disk rig simulating the wet clutch operation. Two different friction materials were separately tested and used as pins against actual steel disks from a wet clutch. The frictional behavior results demonstrated that the mixtures presented antishudder characteristics. Thus, Jatropha oil could be potentially used as part of automatic transmission fluid (ATF) formulations to enhance their antishudder properties and increase the efficiency of the torque transferred of wet clutches with a controlled lock-up clutch system, which improves the full economy of vehicles.

Physical and Tribological Properties Degradation of Silicone Rubber Using Jatropha Biolubricant

ABSTRACT This article aims to investigate the degradation of physical and tribological properties (friction coefficients and wear resistance) of a dynamic sealing material (silicone rubber [VMQ]) exposed to Jatropha oil (JO), engine mineral oil (EMO), and a blend (B20; 80% EMO–20% JO), separately. JO has demonstrated better lubricating properties than EMO in various mechanical applications; however, the degradation of elastomers by using this oil has not been studied yet, nor have its effect on their tribological properties. The physical degradation was evaluated by conducting static immersion tests (670 h at 25 °C) based on ASTM-D471 and ASTM-D7216 methods. Hence, the changes in mass, volume, tensile and tear strengths, and hardness of VMQ were measured. In addition, creep compliance tests were conducted to determine the changes in viscoelastic properties and the changes in morphology and topography were measured by scanning electron microscopy (SEM) and optical profilometry, respectively. In addition, the compositional changes were determined by Fourier transform infrared (FTIR) analyses to complement the degradation examination. Changes in the friction coefficients were determined by ball-on-disk tests and changes in wear resistance were obtained by accelerated wear tests (microabrasion tests). Finally, VMQ exhibited no significant physical and compositional degradation due to immersion in the three lubricants. However, considerable changes in the friction coefficients and wear resistance were observed; the change in the friction coefficients was minimal using JO. In addition, the coefficients using JO were 50% lower than those for EMO and the changes in wear resistance were lowest after immersion in JO.

Mechanical stability of boron-based coatings grown on Incoloy 909 superalloy by thermochemical diffusion

ABSTRACT Incoloy 909 superalloy was treated at 950°C to form coatings of different chemical composition by thermochemical diffusion. Packing of the samples in reactive powders lead to the formation of iron borides (Fe2B and FeB) together with nickel boride, NiB, and nickel silicide, Ni2Si, on the surface of the alloy depending on the exposure time. X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses suggest that growth of the coatings is controlled by diffusion of reactive species into the metal structure. Microabrasion wear resistance of the coated specimens was studied at 1 N load for a fixed sliding speed of 0.11 m s−1 and it was compared against uncoated samples of the alloy. It was found that coating the alloy for 12 and 20 h increased the hardness of the alloy and therefore its wear resistance.

Field and laboratory assessments of the friction coefficient at a railhead

The aim of this work was to prove that the oil applied to the wheel flange using on-board lubricators not only alters the friction coefficient between wheel and rail but also influences the braking and acceleration performance of trains on one of the lines of the metro in Mexico City. A series of tests were carried out in the presence of an oil lubricant, both in the laboratory and in the field, using a pendulum tester. It was observed that the oil migrated from the rail corner to the top of the rail. In another set of experiments, water was sprayed onto the lubricant on the top of the rail. The results indicated that under these conditions, the friction coefficient has a low value in rail sections where a high value of the friction coefficient is required. Tests with water/oil mixtures presented similar levels of friction to the oil-only tests. A set of tests were performed after the rail surface was cleaned and the oil lubricant and water were applied together. The laboratory and field tests showed similar behaviour trends for the friction coefficient. The pendulum method can be used to assess railhead friction on short-length sections of rail. Points are made regarding the conditioning of the pads and calibration of the pendulum arm.

Study of solid particle erosion on AISI D2 using angular silicon carbide and steel round grit particles

Abstract In this study, the performance of AISI D2 steel subjected to solid particle erosion tests was analysed. This material has applications for tools and dies for blanking, wood milling cutters, cold-extruding and other operations requiring high compressive strength and excellent wear resistance. The erosion tests performed by using a rig developed according to some parameters of the ASTM G76-95 standard. Two abrasive were used, angular silicon carbide (SiC) and steel round grit, both, with a particle size of 400–420 μm. This allowed comparing the erosion severity of each abrasive particle. The tests were conducted using four different incident angles 30, 45, 60 and 90° with a particle velocity of 24±2 m s−1 and a flow rate of 21±2·5 g min−1 for silicon carbide and 48·5±3·5 g min−1 for the steel round grit. The exposure testing time was 10 min. Subsequently, the surface damage was analysed with a scanning electron microscope (SEM) to identify the wear mechanisms. Additionally, atomic force microscopy (AFM) was conducted in order to obtain roughness of the surface damage at 60°. The results indicated that higher amount of mass loss was obtained by angular silicon carbide particles.