RU2532779C1 - Method and device for accelerated nitration of machined parts by electromagnetic field pulses - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machine building, particularly, to ion-nitration of machine parts with the help of electromagnetic field pulses. Reaction gas is fed into nitration chamber and heated therein with simultaneous generation of alternating electromagnetic field therein by solenoid. Said solenoid houses processed part with direction of magnetic induction vector perpendicular to part processed surface and with variation nitration amount with formation of square pulses. Duration and cycle of said pulses ensure acceleration of nitrogen ions penetration in processed surface owing to vertical front of magnetic field intensity ride. Device to this end comprises part nitration chamber, reaction gas feeder, heater and electromagnetic field generator. The latter is composed of solenoid surrounding said chamber to generate pulsed electromagnetic field with square pulses and direction of magnetic induction vector perpendicular to part processed surface.

EFFECT: simultaneous acceleration of nitration, higher mechanical properties of surface plies.

4 cl, 3 dwg

Description

Technical field

The invention relates to mechanical engineering, in particular to a method for ionotriding machine parts using pulses of an electromagnetic field, aimed at improving the mechanical properties of parts of sliding friction units from iron-based alloys.

State of the art

Known methods of chemical-thermal treatment (CTO), allowing to increase the mechanical properties of steel parts and containing the operation of nitriding and exposure to nitrogen ions using an electromagnetic field. So, it is known the technical solution contained in the patent of the Russian Federation No. 2402632 (IPC C23C 8/36, publ. 10/27/2010), - a method for local nitriding of a metal part in a glow discharge plasma (analogue). It involves the creation in the chamber for nitriding of an electromagnetic field that allows you to localize the flow of nitrogen ions in a certain area, which ensures the processing of those parts of the part that need it, excluding the processing of other parts. This technical solution improves the quality of processing complex surfaces by changing the direction of movement of nitrogen ions in accordance with the localization of the treated surface.

However, it does not imply acceleration of the main nitriding process in the region where the ion beam is directed normal to the surface being treated, since the main means for accelerating nitriding is an electric field accelerating nitrogen ions in the process of their movement to the surface to be treated. In the analogue method, the action of the electromagnetic field is used only to focus the ion beam, but does not imply actions that change the diffusion permeability of the surface of the processed material for nitrogen ions.

The considered technical solution also contains a schematic description of the device for its implementation (analogue). It includes a chamber for ion-plasma nitriding and a structure located inside it containing a source emitting electrons and an induction coil forming a stream of these electrons in the direction of the treated surface area of the nitrided part. Using these devices, the desired volume and shape of the glow discharge plasma, consisting of nitrogen ions, is formed, which allows localizing the nitriding process.

However, this device does not affect the diffusion permeability of nitrogen into the treated surface. Thus, the analog device has the same disadvantages as its analog method.

There is also known a method of processing machine parts by a pulsed electromagnetic field, as set forth in RF patent No. 2299249 (IPC C21D 1/04, publ. 05.20.2007). The main features of this method are operations on the action of an electromagnetic field on the material of the workpiece, first in a fairly wide frequency range from 10 ³ to 10 ⁵ Hz with magnetic fields from 10 ⁵ to 10 ⁷ A / m for 10 seconds, followed by aperiodic processing at the same maximum amplitudes of the intensity, but with a rate of change of intensity of 10 ⁹ ... 10 ¹⁰ (A / m) s ^-1 and the number of pulses up to 100, as well as the formation of a magnetic field gradient of at least 10 ⁵ (A / m) mm ^-1 . Such an effect, according to the authors, should provide an increase in the mechanical properties of the part due to the modifying effect of the magnetic field on the surface layers of the material of the part. At the same time, the shape of the magnetic field pulses is not specified in the patent, which suggests their arbitrary shape (more likely a sinusoidal shape, which corresponds to the standard network form of electric current).

The main disadvantage of this technical solution is that the hardening processes occurring as a result of magnetostrictive deformation of grain boundaries are limited by the redistribution of those chemical constituents of the material that are embedded in it during the manufacturing process. Therefore, such an important element of hardening as dispersion hardening due to particles formed when additional elements (in particular, nitrogen ions) are introduced into the material during chemical-thermal treatment, is not used in this solution.

There are a number of technical solutions in which electromagnetic pulse processing is combined with other types of exposure. So, for example, the solution set forth in the international PCT application W02008113238 A1 (IPC C21D 10/00, C22F 3/00, publ. 2008-09-25), contains two types of exposure - in addition to the electromagnetic field, the material is also processed by ultrasound. Technical solutions have also been published in which the processing by electromagnetic field pulses is combined with various types of heat treatment. So, RF patent No. 2339704 (IPC C21D 1/04, C21D 9/22, published November 27, 2008) proposes to supplement electromagnetic processing by heating with high-frequency currents to temperatures below the Curie point, and the following parameters are proposed for electromagnetic exposure: field strength up to 8 · 10 ³ kA / m, pulse duration - 10 ^-3 ... 10 ^-6 seconds. RF patent No. 2360011 (IPC C21D 6/04, C21D 1/04, C21D 9/22, published June 27, 2009) proposes heat treatment with cold in a liquid nitrogen environment in combination with processing by pulsed mechanical vibrations and electromagnetic field pulses with an amplitude of up to 250 kA / m

However, none of the solutions containing the processing of the material by a pulsed magnetic field contains proposals for the use of nitriding. Therefore, they are characterized by the disadvantages already noted above - the lack of hardening due to newly introduced elements, in particular, nitrogen ions diffusing through the surface into the material to be processed.

The same can be noted with respect to the devices by which these methods are implemented. They contain means of influencing the workpiece with an electromagnetic field and some other means - ultrasound, heating by high-frequency currents, heat treatment by cooling. However, they do not contain means for saturating the surface of the workpieces with nitrogen, which is their common drawback.

Closest to the proposed method, the technical solution (prototype) can be recognized as the triode method of cathode-plasma nitriding of parts with holes - according to the patent of the Russian Federation No. 2279496 (IPC C23C 8/36, C23C 14/42, C23C 14/48. Publ. 10.07.2006) . This method involves the creation of a rotating magnetic field around the cathode-plasma nitriding chamber, characterized by such a value and direction of the magnetic field induction vector that the angle of incidence of ions on the side surface of the workpiece is no more than a critical angle. Thus, in this method, the nitriding efficiency of surfaces of complex shape is increased, since the uniformity of processing of complex surfaces is increased in it, allowing you to change the direction of movement of nitrogen ions in accordance with the orientation of the surface to be treated.

Nevertheless, it does not imply acceleration of the main process of nitriding of the treated surface, where the beam of nitrogen ions is directed normal to it, since the main means is the interaction force of moving ions with the electromagnetic field, directing nitrogen ions in the process of their movement to the treated surface as desired by the consumer technology trajectory, but not changing the diffusion permeability of the processed material. Thus, the effect of magnetic field pulses on the state of grain boundaries and their diffusion permeability is not used in this solution.

The device required to implement this method is schematically described in the same patent of the Russian Federation No. 2279496 and selected as a prototype of the proposed technical solution. It contains a chamber for XTO - ionization of the surface of the part, a heating device, a device for supplying nitrogen ions and apparatus for creating a magnetic field that affects the trajectory of nitrogen ions to the complex surface of the workpiece.

However, the design of the prototype device is such that it only allows you to change the angle of incidence of nitrogen ions on the treated surface, without affecting the diffusion permeability of nitrogen into the processed surface of the material, which is the main disadvantage of the prototype device, as well as the prototype method.

Disclosure of invention

The objective of the invention is the simultaneous acceleration of the nitriding process and increase the mechanical properties of the surface layers of the material formed as a result of simultaneous nitriding and exposure to both nitrogen ions and the material of the workpiece by pulses of a relatively low-power magnetic field.

The method of nitriding a part using an electromagnetic field includes feeding a reaction gas into the chamber for nitriding, heating it while generating an alternating electromagnetic field in the chamber. In this case, the generation of the electromagnetic field is carried out by means of a solenoid, inside which the workpiece is placed with the direction of the magnetic induction vector perpendicular to the workpiece surface and its value changes during nitriding with the formation of rectangular pulses. The duration and frequency of these pulses provide acceleration of the movement and incorporation of nitrogen ions into the treated surface due to the vertical front of the increase in magnetic field strength.

For the class of processes under consideration, the following parameters close to optimal that were established during processing were experimentally determined: the amplitude of the pulsed voltage exciting the magnetic field - 4 V, the consumed current - 30 mA, respectively, the power - 120 mW, the duration of the magnetic induction pulse - ^410-3 s , the steepness of the pulse front is 20 ns, the frequency is 12-10 ^-3 s and the processing time is 2 hours.

Moreover, the device for nitriding the part using an electromagnetic field contains a chamber for nitriding the part, a device for supplying reaction gas to said chamber on the workpiece, a heating device and a device for generating an electromagnetic field. Moreover, the device for generating an electromagnetic field is made in the form of a solenoid located around the chamber, which generates a pulsed electromagnetic field with rectangular pulses with the direction of the magnetic induction vector perpendicular to the machined surface of the part inside it.

The chamber for nitriding the part can be a ceramic tube of aluminum oxide Al ₂ O _{3 with a} diameter of 25 mm, around which a heat insulator with a diameter of 60 mm made of foam material SiO ₂ is placed, on which there is a solenoid made of a three-layer, from a copper wire with a diameter of 0.26 mm, each layer of which has 60 turns.

List of drawings

In FIG. 1 shows a diagram of the proposed device,

In FIG. 2 shows the dependences of the change in microhardness along the depth of the compared surface samples (a - when nitriding without a pulsed magnetic field; b - when nitriding with a pulsed magnetic field by the proposed method);

In FIG. 3 shows photographs in one scale of the transverse sections of the samples (a - when nitriding without a pulsed magnetic field; b - when nitriding with a pulsed magnetic field by the proposed method).

The implementation of the invention

In FIG. 1 shows a diagram of the proposed device, including the following items: 1 - supply of reaction gas (ammonia); 2 - ceramic heat-saving walls of the chamber for HTO; 3 - thermal insulation of the camera; 4 - heat electric heater (TEN); 5 - solenoid outside around the chamber; 6 - workpiece; 7 - exhaust gas outlet.

Also indicated: IP - power sources separately for powering the heater and for powering the solenoid; B is the vector of magnetic induction.

The main difference of the proposed processing method is that the accelerated formation of an enhanced diffusion zone occurs simultaneously under the influence of two complementary factors: supply of a reaction gas (ammonia) to the chamber for nitriding - position 1 in FIG. 1, which under the influence of temperature (at least 500 ° C) created by the heater 4 dissociates with the formation of nitrogen ions and acquires increased reactivity, and the supply of magnetic field pulses inside the chamber, which accelerate the movement and penetration of nitrogen ions and magnetostrictive deformation into the surface grain boundaries of the surface of the processed material (parts 6 in Fig. 1), and the magnetic induction vector B should be directed perpendicular to the processed surface (in Fig. 1 this is the upper horizontal end Details 6). In more complex cases, it is recommended to carry out processing as close as possible to the specified configuration.

The pulses of the magnetic field must have a rectangular shape and a sufficient duration for the manifestation of the desired effect on the workpiece surface. The rectangular shape of the magnetic field pulse is an essential feature of this method, since it is in this case that the maximum (impulse) acceleration of particles interacting with the magnetic field is created due to the vertical front of the increase in field strength.

The following close to optimal mode was established experimentally: the amplitude of the pulsed voltage exciting the magnetic field is about 4 V, while the current consumption is about 30 mA, respectively, the relatively low power consumption is about 120 mW, the magnetic induction pulse is 4 · 10 ^-3 s, the steepness of the pulse front is about 20 ns, the frequency is 12 · 10 ^-3 s, the time of complex processing is 2 hours.

For experimental testing of the proposed method, a chamber for machining a part was manufactured; it could be a ceramic tube of aluminum oxide Al ₂ O _{3 with a} diameter of 25 mm, around which a heat insulator with a diameter of 60 mm made of foamed SiO ₂ material was placed, on which a three-layer solenoid made of copper wire with a diameter of 0 , 26 mm, in each layer of 60 turns.

The technical result is illustrated by comparative graphs of figure 2 and photographs of figure 3. Figure 2 shows the dependence of the change in the microhardness of the material (VKS-7 steel) along the depth of the samples, constructed in the coordinates: vertical - microhardness (HV), horizontal - distance from the surface of the sample in mkm (microns). Graphs: a) microhardness during nitriding without switching on the pulsed magnetic field of the solenoid; b) - microhardness during nitriding with the action of a pulsed magnetic field. The processing time in both cases is 2 hours. The technical result is due to the acceleration and intensification of the nitriding process under the influence of magnetic field pulses and is expressed in a significant increase in microhardness (on average about 1.5 times, which is clearly seen in the photographs of figure 3 - when comparing black surface layers of the two compared samples) as a result of inclusion in the process of nitriding pulses of a relatively low-power magnetic field.

Therefore, the combination of a number of well-known features, namely, the diffusion saturation of the surface layers of the material with nitrogen and the simultaneous exposure to the same material with pulses of a relatively low-power magnetic field gives a synergistic effect - a significant additional increase in the mechanical properties (for example, microhardness parameter) of the material, which is not achieved at Using these features individually.

The method can be used as part of a set of technological operations in the manufacture of machine parts, for example, involved in sliding friction and subject to intense wear.

Claims (4)

1. The method of nitriding a part using an electromagnetic field, comprising supplying a reaction gas to the chamber for nitriding, heating it while generating an alternating electromagnetic field in the chamber, characterized in that the electromagnetic field is generated by a solenoid, inside which the workpiece is placed with the direction of the magnetic vector induction perpendicular to the surface of the workpiece and a change in the process of nitriding of its value with the formation of a straight nyh pulse duration and the frequency of which provide acceleration movement and introduction of nitrogen ions into the surface to be treated due to the rising edge of the vertical magnetic field intensity. 2. The method according to p. 1, characterized in that during the processing, the amplitude of the magnetic field exciting magnetic field is set to 4 V, current consumption is 30 mA, respectively, power is 120 mW, the duration of the magnetic induction pulse is 410 ^-3 s, the slope of the front pulse - 20 ns, frequency - 12-10 ^-3 s and processing time - 2 hours. 3. A device for nitriding a part using an electromagnetic field, comprising a chamber for nitriding the part, a device for supplying reaction gas to said chamber on a workpiece, a heating device and a device for generating an electromagnetic field, characterized in that the device for generating an electromagnetic field is made in the form a solenoid located around said chamber, which provides the generation of a pulsed electromagnetic field with rectangular pulses from the direction the vector of magnetic induction perpendicular to the machined surface of the part inside it. 4. The device according to p. 3, characterized in that the chamber for nitriding the part is a ceramic tube of aluminum oxide Al ₂ O _{3 with a} diameter of 25 mm, around which is placed a heat insulator with a diameter of 60 mm of foam material SiO ₂ , on which a solenoid made three-layer, from a copper wire with a diameter of 0.26 mm, in each layer of which 60 turns.

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