ELECTROMAGNETIC SYSTEM FOR IMPROVING THE ADHESION OF WHEELS TO RAILS

Yuriy OSENIN, Lidiya ANTOSHKINA Berdyansk University of Management and Business 117-А Freedom, Berdyansk, 71118, Ukraine Igor SOSNOV, Evgeniy SHAPRAN National Technical University "Kharkov Polytechnic Institute" 2 Kirpicheva, Kharkov, 61002, Ukraine Aleksei CHESNOKOV* State Budget Institution of Higher Education of the Moscow Region "University of Technology" 42 Gagarina, Korolev, Moscow region, 141070, Russia *Corresponding author. E-mail: chesnokov@ut-mo.ru


INTRODUCTION
The operation of many heavily loaded rolling friction pairs is maintained under conditions, by presenting hard particles of different origin in the zone of their contact.These particles may be either products of wear of contacting surfaces or various foreign bodies, often of mineral origin, which is sometimes artificially fed into the contact area [1][2][3][4].
The pulling force strongly depends on the climatic influences, which causes loss of adhesion, and this can lead to slippage of wheels and damage to the wheels and rails [5].The presence of a third body between wheel and rail significantly affects the adhesion.Poor adhesion of the wheels to rails can cause various problems, such as high-frequency noise [6], fatigue of the contact surface [7], increased corrugation of rails [8], energy dissipation [9], unstable adhesion before acceleration [10], and poor braking performance [11].
Traditionally, sand is used to increase the coefficient of adhesion of locomotive wheels to rails.This method has widespread usage in railway transportation; however, it has significant limitations, the main ones of which are [12][13][14]: • low efficiency (the ratio of the amount of sand placed between the wheel and the rail to the total amount of sand directed under the wheel of the locomotive); • the use of large volumes of sand in the rolling stock, leading to clogging of the rail tracks, which causes environmental problems; and • increased wear of the working surfaces of wheels with rails.
One way to solve this problem is the use of alternative sand bulk materials [4].As the latter, it is proposed to use abrasive materials having magnetic properties [15][16][17][18], for example, magnetite (FeFe2O4), which is the iron oxide of natural origin, and iron scale (FeOFe2O3), which is a by-product of foundry and forging.These materials are similar to quartz sand in terms of hardness.
In this regard, the study of the use of magnetite and iron scale in order to increase the coefficient of adhesion of locomotive wheels to rails is a task of current interest.

MAGNETIC PROPERTIES OF WHEEL AND RAIL MATERIALS
Magnetic properties of abrasive materials and wheel and rail materials ensure a reliable retention of abrasive loose material on the working surfaces, as well as its uniform distribution in the friction contact zone.
It was shown in [19 -22] that the steel used for the production of rails and bands has satisfactory magnetic properties (residual induction 0.65 ... 0.87 T, coercive force 898 ... 963 A/m), which enables holding of particles of abrasive loose material on working surfaces.
With local magnetization of the working surfaces, a relatively small volume of material must be brought to saturation, since the average value of the nominal contact area between the wheels and rails is about 1×10 -4 м 2 [21].
Fig. 1 shows the amplitude variation graphs of the horizontal (Hx) and vertical (Hy) components of the magnetic field, depending on the depth of magnetization by magnets of different types [20].For the rod-type magnets, the schematic model with the designation of the main geometric dimensions (2D is the width of the magnet pole) is given.The abscissa axis lies in the same plane as the magnetized surface.
Dependencies shown in Fig. 1 correspond to the case when the gap between the magnet pole and the magnetized surface is zero.The values of the component of the magnetic field of the rod magnet Hx, constructed in dependence on the magnitude of this gap, are shown in Fig. 2. In view of the foregoing observation, to magnetize the working surfaces of the wheels with the rails, it is sufficient to use an electromagnet that creates magnetic fields with a strength of 500-650 A/m.This electromagnet is oriented by one of its poles perpendicular to the rolling surface, while the magnetic field lines create a locally magnetized unipolar zone.
Electromagnetic system for improving the adhesion of wheels to rails 61.
In the process of magnetization (or demagnetization) of the wheel and rail surfaces, the electromagnet can work both in pulsed and continuous modes, which is determined by external conditions affecting the state of the frictional contact of the wheel with the rail and the mode of operation of the rolling train.
The gap between the electromagnet pole and the rolling surface of the rail, taking into account the movement of the carriage relative to the rail, is 40-50 mm for maintaining the necessary magnetic field strength (averaged values for the rolling train of different types).In the case of magnetization of the wheel circle, the gap is smaller (15-20 mm) and determined for the safe operating reasons of the device.
For using in these purposes, a rod magnet is preferred that is simple in design and has satisfactory magnetic characteristics necessary to magnetize rolling surfaces with the required magnetic field density.

CONSTRUCTION AND PRINCIPLE OF THE NEW SYSTEM OF WHEELS TO RAILS CLUTCHING IMPROVEMENT
In the immediate vicinity of the wheel 1 and the rail 2 are placed electromagnets 4 and 5, which serve to magnetize their working surfaces.Due to this, the magnetized particles of the abrasive material adhere and remain for some time on the working surfaces.
The permanent magnet 9 serves to prevent the spontaneous introduction of the working bulk material from the hopper 3 into the spout 8 (for example, in the case of de-energizing the electromagnet system 6).In this case, the permanent magnet 9 has several times less power than the system of electromagnets 6 and is not able to prevent the movement of the working bulk material caused by it through the duct 7.

STUDY OF WORKING CHARACTERISTICS OF THE ELECTROMAGNETIC CLUTCH IMPROVEMENT SYSTEM
Tests of the electromagnetic feed system used for improving the clutching of wheels to rails were carried out on a field stand consisting of two independent wheeled vehicles, one of which was mounted on the wheelsets of the other, using them as rollers [24].One of the wheelsets was rotated by an electric motor by means of a belt drive.
During the laboratory and bench tests, it was found that the developed electromagnetic feed system allows the assurance of stable transportation of working material (iron scales or magnetite) and its relatively uniform distribution on a magnetized surface over a wide range of flow rates (for internal diameter of the supply pipeline 10 mm, the productivity may vary smoothly from 0.08 kg/min to 0.47 kg/min).At the same time, the losses of the working bulk material are insignificant.The ratio of the mass of the working material (grain size 100-200 μm) fixed on the surface of the bandage to the material fed by the electromagnetic system is 0.93 (iron scale) and 0.97 (magnetite).
The electromagnetic feed system of the working material makes it possible to ensure its stable feeding with the required capacity.In this case, the deviation of the flow values from the set value does not exceed 2-4%.
The verification results of reproducibility of the bulk material consumption rate G values at different electromagnetic feed system performances are shown in Table 1.
Electromagnetic system for improving the adhesion of wheels to rails 63.The time parameters characterizing the work of the electromagnets transporting the working material (set by the control unit) were also identical.The duration of operation of the first, second, and third transporting electromagnets (during the movement of the working bulk material in duct 7 (see Figure 3) was 10 ms (during the operating cycle).The pause between switching on the second electromagnet and the beginning of the operating cycle was 10 ms.The pause between switching on the third electromagnet and the beginning of the operating cycle was 20 ms.The first transporting electromagnet was switched on immediately after the start of the operating cycle.
The performance of the electromagnetic supply system was controlled by changing the delay time between two subsequent operating cycles, which ranged 50-200 ms.A smaller pause value corresponds to a larger system performance.
The above electromagnetic system used for improving the adhesion of the locomotive wheel to the rail has the following main characteristics: • Number of control ducts (electromagnet system 6 in figure 3): 3; • Maximum current consumed by the electromagnet: 40 A; • The initial voltage applied to the electromagnet: 40 V; • Minimum resistance of the duct with an electromagnet: 1 Ohm; • Discreteness of regulation of time parameters of the operating cycle: 0.1 ms; • Duration of the operating cycle: 0,1-1000 ms; • Duration of a pause between operating impulses of an electromagnet: 0,1-1000 ms; and • The duration of the operating pulse of an electromagnet: 0.1-1000 ms;

THE EFFICIENCY VERIFICATION OF THE PROPOSED SYSTEM IN COMPARISON WITH ANALOGUES USING QUARTZ SAND
A series of experiments was carried out to measure the adhesion factor of interacting surfaces of the wheels with rails in order to verify the effectiveness of the wheel-to-rail adhesion when using bulk materials with electromagnetic properties and high hardness.
The experiments were performed on a full-scale bench unit that allowed the reproduction of the force interaction conditions between the wheels and rails in the real scale of forces, time, geometric dimensions, heat fluxes, and the physicochemical state of the contacting surfaces [25].The basis of the stand was a railroad rail of a P-65 brand, a railway wheel of a 0.525 m radius, and a strength load system.
Quartz sand, iron scale (Fe3O4), which is a by-product of rolling and forging production and iron oxide, and magnetite (FeO×Fe2O3), which is of natural origin, were used as bulk materials.The distribution density of bulk materials on the rail surface was 0.02 g/cm 2 .The results of the experiments are shown in Fig. 4. The results obtained were verified for the absence of rough errors using Student's t-test.The values of the confidence limits ±DFa for the magnitude of the adhesion force of the wheel with rails Fa (with a confidence figure a = 0.95) and the corresponding values of the average standard deviations Fas are listed in Table 2. Electromagnetic system for improving the adhesion of wheels to rails 65.
From the obtained experimental results, it follows that iron scale and magnetite are slightly inferior to quartz sand by the criterion of the adhesion force of the wheels to rails, not more than 5% and 10%, respectively.

CONCLUSIONS
• The developed electromagnetic system used for improving the adhesion of the wheels to rails allows the supply of the magnetic abrasive material into the contact area between the wheels and rails with adjustable performance over a wide range.This allows the magnetic abrasive material to be supplied under the wheels of a locomotive in the initially defined mode.• The presence of electromagnets to magnetize the surfaces of the wheel and rail in the system used for adhesion improvement allows the minimization of the loss of abrasive loose material when it is transported under the wheels of a locomotive.• The presence of magnetic properties in iron scale and magnetite creates the prerequisites for a significant reduction in their consumption, compared with the use of silica sand.This is achieved because of the long-term magnetic retention of particles of these materials on the surface of the wheel.As a result, iron scale and magnetite can be fed to the contact area between the wheels and rails in smaller quantities compared with quartz sand.• Reducing the consumption rate of iron scale and magnetite compared with quartz sand leads to a decrease in clogging of the ballast section of the railroad tracks with waste particles of these materials.• Minimizing the consumption of abrasive loose material significantly reduces the contamination of the rail.In this case, the cleaning of the rail can be easily carried out by the magnetic extraction of the used abrasive loose material from the rail.• The results of the study obtained allow us to conclude that the use of iron scale and magnetite is promising in order to improve the adhesion of wheels to rails.The proposed system for improving the adhesion of wheels to rails ensures the delivery of iron scale and magnetite to the working area and the long-term magnetic retention of particles of these materials on the surface of the wheels.

Fig. 2 .
Fig. 2. Dependences of the component Hx of the residual magnetic field at various distances from the pole of the rod magnet to the magnetized surface

Fig. 4 .
Fig. 4. The dependence of the adhesion force Fa on the magnitude of the normal wheel load on the rail N in the presence of solid particles in the contact area: 1 -quartz sand; 2 -iron scale; and 3 -magnetite

Table 1
Reproducibility of the bulk material consumption rate values of the electromagnetic system for improving the adhesion of wheels to rails

Table 2
Measurement errors of the magnitude of the value of adhesion force of the wheel to rail Fa