RU2704051C1 - Method and apparatus for surface hardening of heads of active railway steel rails - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: group of inventions relates to methods and apparatus for surface hardening of heads of active railway steel rails. Method includes heating of one or two surfaces of heads of one or two rails by electron beams output into air atmosphere and moving relative to rail, and subsequent cooling of said surfaces due to heat conductivity inside rail head, characterized by using electron beams with electron energy of 100–300 keV, at that, distance L, m from outlet edge of output assembly of electron beam output device to heated surface of rail head is selected on condition that: L≤0.1×K×S, where S is the electron path length in the air atmosphere, K=6–8 is a coefficient which takes into account the change in the electron path length in the air atmosphere when the air is heated to temperatures higher than 1,500 °C.

EFFECT: reduced probability of peeling a hardened layer.

5 cl, 1 tbl, 3 dwg

Description

The group of inventions relates to methods and installations for heat treatment of critical parts of the upper track structure (railway rails, metro rails, tram rails) using concentrated energy flows. The reliability of rail transport is influenced by the quality of the parts that form the track and wheelset of the rolling stock. These parts are required for wear resistance and contact fatigue strength. One of the promising directions for improving these characteristics is the use of surface hardening using concentrated flux methods. The results of such processing are to increase the service life of products, improve their operational characteristics, reduce the cost of repair work.

A known method of surface thermal hardening of steel products (USSR Author's Certificate SU 1548218 A1, publ. 07.03.90 bull. No. 9), comprising ultra-fast heating by an electron beam with specified characteristics (electron energy 0.3-4.0 MeV, power density 0, 08-10 MW / cm ² ) of a moving product. The electron energy and power are selected from the condition of ensuring the adiabatic heating of the hardened layer without melting the surface of the product with the possibility of subsequent rapid (more than 1000 K / s) cooling of the layer due to conductive heat exchange with a cold base. The disadvantage of this method is the need to fulfill too severe conditions (adiabatic heating, lack of fusion), which leads to the use of high-energy beams and, as a result, bulky, bulky, heavy electron accelerators. Based on them, it is problematic to create mobile devices for hardening the operated rails, i.e. located directly in the upper structure of the railway tracks.

A known method of heat treatment of steel rails (patent RU 2644638 C2, publ. 13.02.2018), which consists in the directed action of a high-temperature plasma jet on a moving product (rail) and its subsequent cooling, while the plasma arc is split into two heating spots. Heat treatment conditions: current strength 90-160 A, voltage 130-160 V, product movement speed 50-200 cm / min, the distance from the plasma nozzle nozzle exit to the product surface is 20-30 mm.

The disadvantage of this method is the extremely low speed of the rail (30-120 m / h), which makes its use ineffective for hardening the rails in the existing tracks. In addition, plasma quenching methods are sensitive to the distances between the nozzle exit of the plasma torch and the rail surface, which also poses a problem when hardening in “field conditions”.

Also known are the processes of surface thermal hardening of products by concentrated laser radiation (Grigoryants A.G., Safonov A.N., Methods of surface treatment. M. "Higher School", 1987). However, their use for hardening rails as part of existing rail tracks is also ineffective, due to the fact that:

- the efficiency of converting electrical energy into concentrated laser radiation energy is only 10-15%;

- the absorption coefficient of laser radiation by the surface of the product is less than 5%;

- laser systems operating in an air atmosphere have low power (at the level of 10 kW).

In contrast to laser radiation, an electron beam has a number of significant advantages:

- high efficiency of converting electrical energy into energy of concentrated radiation of an electron beam (70-80%);

- high coefficient of absorption of radiation by the rail surface (more than 75-80%);

- It is possible to create generators of electron beams in an air atmosphere of high power - 10 ... 1000 kW.

These advantages lead to a simplification of the task of ensuring the utilization of excess heat, the lack of the need for preliminary preparation of the rail surface for processing.

The closest analogues of the proposed group of inventions are the solutions disclosed in patent RU 2208650 C2, publ. 07/20/2003. This source of information discloses a method for surface heat strengthening of rails based on the use of high-energy electron beams, and a device for its implementation. This method is based on the processes of adiabatic heating by electrons of the megavolt level, the principles of which are disclosed in the copyright certificate SU 1548218 A1, 03.03.90, discussed above. The device is located in a car moving with a locomotive; the main elements of the device are a megavolt class accelerator (0.3-4.0 MeV), a high-voltage power supply and an exhaust unit, as well as an electron beam switch for hardening the right and left rails and a scanning device.

However, from the description presented in the patent, the following points remain unclear:

1. How is the vacuum provided in the exhaust device, communicating with the air through the aperture (3-5) × 25 mm ² ? With this aperture, to ensure a forevacuum, a vacuum pump capacity of more than 10 m ³ / s is required, which seems problematic at the current level of technological development.

2. The issue of cooling (or heat removal) also remained outside the consideration. With characteristic beam powers of 50-60 kW, the required cooling level can reach 15-20 kW, which requires an independent heat removal system.

In the absence of these systems (vacuum pumping of the required level and cooling system), the device will not function reliably.

The disadvantages of the most famous analogue include the fact that the use of high-energy electron beams leads to an increase in the thickness of the hardened layer. The question of the optimal thickness of the hardened layer in the case of rails experiencing contact loads is ambiguous. With increasing depth of hardening, the rail resource increases, but stresses at the “hardened layer – base” interface increase due to differences in their crystal structures (plate perlite and martensite). Experimental facts are known when, when a significant thickness of the hardened layer is reached, it peels off.

The purpose of the invention is the creation of a new method and installation for hardening the existing rail tracks, providing a multiple increase in the resource of the rails.

The technical result of the group of inventions is to reduce the likelihood of peeling of the hardened layer.

To solve the problem and achieve a technical result, a method for surface hardening of the heads of steel rails of the active track is proposed, comprising heating at least one surface of the head of the rail of the track with electron beams brought into the air and moving relative to the rail, and subsequent cooling of this surface. Moreover, electron beams with electron energies of 100-300 keV are used. The distance L, m from the output cut of the output node of the electron beam output device to the heated surface of the rail head is selected from the condition:

L≤0,1⋅K⋅S, where

S is the mean free path of electrons in the air;

K = 6 ÷ 8 is a coefficient that takes into account the change in the mean free path of electrons in the air atmosphere when air is heated to temperatures above 1500 ° C.

An apparatus for surface hardening of steel rail heads of an existing rail track is also proposed, comprising a rail vehicle on which at least one electron beam output device is installed, comprising a high voltage power supply, an electronic accelerator, an output assembly. Moreover, the device for outputting the electron beam is installed on a rail vehicle with the possibility of directing the electron beam of the output node to the upper or side surface of the rail head, and the distance L, m from the output section of the output node to the heated surface of the rail head is selected from the condition:

L≤0,1⋅K⋅S, where

S is the mean free path of electrons in the air;

K = 6 ÷ 8 is a coefficient that takes into account the change in the mean free path of electrons in the air atmosphere when air is heated to temperatures above 1500 ° C.

As an output node, a differential pumping system equipped with power supply, cooling and vacuum pumping systems can be used.

The installation can be equipped with a scanning system located at the output of the output node.

The installation may contain from one to four devices for outputting the electron beam.

The hardening method is based on processing the surfaces of the rail head with an electron beam, which provides high-speed and short-term heating of these surfaces, followed by high-speed cooling of the heated layer due to natural conductive heat exchange with the base, i.e. thermal conductivity inside the rail head. A feature of this invention is to use for the implementation of low-energy electrons (100-300 keV), released into the air. This method can significantly reduce the weight and size characteristics of equipment for generating and outputting an electron beam. In particular, the transition from an electron accelerator with an electron energy of 1–4 MeV to an accelerator with an energy of 100–300 keV reduces the characteristic dimensions of the equipment by several times and the mass by more than 15 times. These quantitative changes are already of a qualitative nature - it becomes possible to install such equipment on any rail vehicles (cars, highways and other vehicles that can move along existing railway, tram tracks, monorails and underground tracks) and implement effective hardening of the rails directly as part of existing ways.

Another advantage of using beams of low-energy electrons is a significant simplification of the operation of the installation - the ability to carry out repair and maintenance procedures without the use of special equipment and in shorter times. These advantages are important when using mobile equipment to strengthen existing rails. In addition, such equipment has a lower cost, and also makes significantly lower requirements for radiation protection.

The proposed group of inventions quickly and effectively hardens the heads of one or two rails to a relatively shallow depth (0.4-0.8 mm), while reducing the likelihood of peeling of the hardened layer. Moreover, the hardening of the rails using the proposed group of inventions can be carried out regularly as the hardened layer is worn. When critical wear is achieved, the rails can be restored by surfacing (which is also possible using extra-vacuum electron beam technology), which will significantly increase the life of the tracks currently in operation.

In the process of hardening occurs:

- high-speed surface heating to temperatures above the austenitization point (900-1500 ° C),

- the propagation of the temperature front deep into the material and the occurrence of phase transformations of the α - phase of iron in the γ - phase, i.e. the conversion of body-centered crystals to face-centered,

- dissolution of carbon and other alloying inclusions in face-centered crystals of γ-phase iron, the formation of new phases,

- high-speed cooling due to thermal conductivity inside the rail head,

- the formation in the hardened layer of a martensitic structure with high hardness.

The group of inventions is illustrated by drawings.

In FIG. 1 shows the initial structure of lamellar perlite (below the line) of P65 steel and the martensitic structure of the hardened layer (above the line) formed after hardening by the proposed method.

In FIG. 2 shows a diagram of the proposed installation (option with one beam output device).

In FIG. 3 schematically shows the hardening process of the upper and lateral surfaces of one rail.

As an example, the result of surface hardening of rails made of steel grade P65 (Fig. 1). Hardness can be judged by the prints from the diamond pyramids, as you can see, the hardened layer has 3 times greater hardness. The initial hardness is 2300 MPa, the hardness of the hardened layer is 9000 MPa, the thickness of the hardened layer is -850 microns.

Processing Mode:

Electron energy - 100 keV,

Beam current - 300 mA,

Power - 30 kW

Beam diameter - 5 mm,

The exposure time is 20 ms

Processing medium - air atmosphere,

The distance (L) between the slice of the output node and

heated surface of the rail head - 0.08 m

This example shows that surface hardening can be carried out by an electron beam released into the atmosphere and having an energy of 100 keV, by the mechanism of heating the layer with a temperature front (and not just by the adiabatic heating mechanism) in the high-speed heating-cooling mode. In this case, the specific energy input is (1 ÷ 3) ⋅10 ⁶ J / m ² , and the speed of movement of the car on rails is 1 ÷ 3 km / h with a beam power of 15-50 kW.

In this case, the distance L between the output slice of the output unit and the machined (heated) surface of the rail head is important. It was found that the mean free path S of electrons in the air atmosphere depends on the energy U of the electron beam, the data are given in the table:

Studies have shown that when a concentrated beam is removed, the air in the path of the beam is heated to high temperatures (1500-2000 ° C), the concentration of air particles decreases by a factor of K, which leads to an increase in the path length, which becomes equal to:

S ^* = К⋅S, where

S is the mean free path of electrons in the air;

K is a coefficient taking into account the change in the mean free path of electrons in the air atmosphere when air is heated to temperatures above 1500 ° C, and K is 6 ÷ 8.

Calculations of electron beam transportation in a gaseous medium show that in the initial section, which is 10-12% of the total path length, the proportion of energy losses does not exceed 5-8%. In view of the foregoing, the processing of the hardened surface of the rail head by an electron beam must be carried out in the initial section of the beam propagation in the atmosphere when it has maximum parameters. Thus, it is most effective to conduct hardening of the rails at a distance (L, m) between the output section of the output node and the heated surface of the rail head, determined by the formula:

L≤0,1⋅K⋅S, where

S is the mean free path of electrons in the air;

K is a coefficient taking into account the change in the mean free path of electrons in the air atmosphere when air is heated to temperatures above 1500 ° C. Conducting the hardening process at such a distance L will lead to the rapid production of a high-quality uniform shallow hardened layer in the machined surface of the rail, the probability of peeling of which is negligible from the base.

A schematic diagram of an installation for implementing the above method of hardening rails, including one device for outputting the beam, is shown in FIG. 2. Depending on the tasks to be solved, the installation may include several devices for outputting the electron beam mounted on a rail vehicle (wagon). For example, for the simultaneous hardening of the upper (horizontal) and inner side surfaces of the heads of two rails of the same track, an installation with four electron beam output devices mounted on a rail vehicle is used.

To harden the upper surface of the rail head, the beam output device is mounted on the rail vehicle so that the electron beam exiting the output node is directed perpendicular to the surface being machined, i.e. the angle between the axis of the output unit and the work surface is direct, and for hardening the side surface of the rail head, the beam output device is mounted on the rail vehicle so that the angle between the axis of the output unit and the work surface is sharp (45 ± 10 degrees). To do this, in the right place on the bottom of the car provide a power inclined metal platform with holes for fixing at the required angle of the output node and the accelerator coaxially connected to it. The use of low-energy electron beams allows the creation of small-sized electron beam output devices that can operate in any spatial orientation.

The main elements of the beam output device are (Fig. 2) a high-voltage voltage source 1, an electronic accelerator 2, and an output unit 3.

The source of high voltage voltage 1 is designed to provide a high rectified voltage output with the parameters required for the electron beam (energy 100-300 keV, power of one output device of the electron beam - 15-50 kW).

The electron accelerator 2 forms an electron beam in a deep vacuum. The output node 3 allows you to bring the beam 4 into the air atmosphere for processing the surfaces of the rail head 5. Since a concentrated beam is needed for hardening, it is necessary to use a gas-dynamic window as the output node, for example, based on a differential pumping system. For its operation, it is necessary to involve a number of auxiliary systems, hatched in FIG. 2. The output node based on the differential pumping system consists of several autonomously pumped lock chambers through which the beam 4 passes from the electronic accelerator 2. The chambers communicate through small holes in the partitions. The required level of pressure (vacuum) in the accelerator volume is created by vacuum pumps 7 by pumping gas through the corresponding windows. To limit the transverse dimensions of the beam using solenoids (not shown), a magnetic field is created. The solenoids are fed from source 6 and cooled from cooling system 8.

To control the hardening zone, a scanning system 9 can be used located at the output of the output unit and aligned with it (Fig. 2). With the right choice of the diameter of the beam and the speed of the car, scanning along the movement becomes unnecessary. The scanning system is designed to provide the power density of the concentrated energy flow at the level of 10 ⁷ -10 ⁸ W / m ² .

The total mass of all elements of the beam output device does not exceed 3 tons, which allows you to place it on any rail vehicle.

Using the example of Russian Railways, the following estimates can be given. With a processing speed of 2 km / h and the organization of three-shift round-the-clock operation by the shift method per year, one mobile unit strengthens 15 thousand kilometers of tracks. The total length of railways in Russia is almost 90 thousand kilometers. This means that 6 mobile units will strengthen all rails of the country in one year.

Currently, rail maintenance costs amount to 20 billion rubles. A triple increase in the resource of roads (expected with a three-fold increase in the hardness of the surface layer of the working sections of the rails) corresponds to an annual savings of 13 billion rubles, which will ensure a quick payback on the cost of manufacturing mobile devices for hardening.

The operation algorithm of the proposed installation, according to a variant with one device for outputting an electron beam, is as follows (Fig. 2, 3):

1. Include primary power sources (not shown in the figures).

2. Turn on the vacuum pumps for pumping the lock chambers of the output node 3.

3. When the pressure reaches 10 ^-3 Pa in the volume of the electronic accelerator 2, acceleration is applied to the installation until the required speed is acquired (for example, 2 km / h). Further the movement is uniform.

4. Turn on the cooling system of the focusing solenoids.

5. Turn on the power supply system of the focusing solenoids and scan the beam 9 according to the hardening program.

6. Turn on the high-voltage power supply 1 and generate an electron beam 4. Hardening of one upper surface of the head of one rail 5 is carried out.

Shutdown is carried out in the reverse order.

The implementation of this algorithm is carried out using a control panel located, for example, in an adjacent carriage and not indicated in the drawings.

Claims (11)

1. The method of surface hardening of the heads of steel rails of the existing rail track, comprising heating at least one side or top surface of the rail head of the track with electron beams moving relative to the rail, and subsequent cooling of this surface, characterized in that the use of electron beams with an electron energy of 100- 300 keV, the distance L, m, from the output cut of the output node of the device for outputting the electron beam to the heated surface of the rail head is selected from the condition: L≤0,1⋅ К⋅S, where S is the mean free path of electrons in the air; K = 6 ÷ 8 is a coefficient that takes into account the change in the mean free path of electrons in the air atmosphere when air is heated to temperatures above 1500 ° C. 2. Installation for surface hardening of the heads of the steel rails of the existing rail track, comprising a rail vehicle, on which at least one device for outputting an electron beam containing a high voltage power supply, an electronic accelerator, an output assembly, characterized in that the device for outputting electronic the beam is mounted on a rail vehicle with the ability to direct the electron beam of the output node to the upper or side surface of the rail head, and The distance L, m, from the output node to the output cutoff heated rail head surface is selected from the condition: L≤0,1⋅K⋅S, where S is the mean free path of electrons in the air; K = 6 ÷ 8 is a coefficient that takes into account the change in the mean free path of electrons in the air atmosphere when air is heated to temperatures above 1500 ° C. 3. Installation according to claim 2, characterized in that the differential pumping system equipped with power supply, cooling and vacuum pumping systems is used as the output unit. 4. Installation according to claim 2, characterized in that it is equipped with a scanning system located at the output of the output node. 5. Installation according to claim 2, characterized in that it contains up to four devices for outputting the electron beam.

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