Estimation of sand electrification influence on locomotive wheel / rail adhesion processes

The desire for threshold of use of traction effort and power of locomotives is associated with an increased tendency of the driven wheelsets to slippage. This determines the need to use different means to increase the level of the adhesion of the locomotive wheels with rails and to ensure the stability of the traction [25, 26]. On the other hand, a high value of the adhesive coefficient is a major factor for realizing the maximum braking force of a train when using friction brakes and significantly increases the level of traffic safety [20]. This is especially true in case of emergency braking or an emergency stopping of trains before prohibitive traffic lights have turned on unexpectedly, i. e. it is essential to avoid the case of the railway station overruns or SPAD signal passing at danger [16]. The most common way to increase adhesion is to use silica sand or other mineral materials similar in hardness properties. This method, along with indisputable advantages (high efficiency, ease of use, relative cheapness) has obvious disadvantages: clogging of ballast, increased wear of wheels and rails [7, 23], increased resistance to movement in traction mode. Given the above disadvantages, the optimization of the use of sand is relevant. The spraying of sand into the wheel–rail contact is one of the most effective ways to enhance the friction between the driven wheels and rail under conditions of low adhesion, especially on intensive acceleration or emergency braking running modes. The scientific works carried out by worldwide researchers on reasons of low adhesion showed that wheel/ rail adhesion coefficient (the ratio of normal to friction force in the contact) varied between 0.04 and 0.55, averaging 0.3 in dry conditions. The impact of adding moisture to the rail reduced this average to 0.2, still the leaves can reduce the adhesion coefficient as low as 0.02 [23, 24]. Other causes of low adhesion have been identified as: general moisture/dampness combined with contaminants such as rust, ice, coal dust, leaf, spilled diesel fuel/ lubricating oils/flange lubricating grease/hydraulic fluid, airborne kerosene from nearby airports, or other chemicals from industrial sites [3]. Lewis S. R. et al. and Wang et al. [24, 35] carried out comprehensive research work using a full-scale laboratory rail–wheel test machine to find the position for the hose and sand flow rates that give optimum sand entrainment to the contact. It was found that ideGorbunov M, KrAvchenKo K, bureiKA G, Gerlici J, nozhenKo o, vAičiūnAs G, bučinsKAs v, steišūnAs s. estimation of sand electrification influence on locomotive wheel / rail adhesion processes. eksploatacja i niezawodnosc – Maintenance and reliability 2019; 21 (3): 460–467, http://dx.doi.org/10.17531/ein.2019.3.12.