SU1328114A1 - Method of electron-beam working out of vacuum - Google Patents

Abstract

The invention relates to electron-beam processing, in particular to the deposition of an electron beam in an atmosphere of air or inert gas wear-resistant powder coatings. It can be used in ferrous metallurgy to strengthen and protect the surfaces of metal products. The aim of the invention is to increase the productivity and quality of the process by increasing the width and uniformity of the melt. To do this, a beam of electrons deduced into the / elevated pressure region is affected, periodically changing the pressure in time by a field with a strength of 11,000-140,000 A / m. The magnetic field imposed on the beam in a gas or air causes the beam electrons to deviate from a rectilinear motion. The greater the magnetic field intensity, the greater the deflection angle of the electron beam. As the beam is scanned, the surface area of the product surface increases to the scanning amplitude and the fusion width increases accordingly. The power density of the electron beam is chosen in the range from 10® to 10 W / m for (/ C reduction of electron scattering in the breathing environment. 7 or more, 4 tab. Ha

Description

eleven

The invention relates to electron-beam processing, in particular to electron beam loading in an atmosphere of air or inert gas of wear-resistant powder coatings, and can be used in ferrous metallurgy to harden and protect the surfaces of metal products.

The purpose of the invention is to increase the productivity and quality of the treatment process by increasing the width and uniformity of the melting.

FIG. Figure 1 shows an oscillogram of the time variation of the magnetic field; in fig. 2 - rollers of the melted surface of the machined part, executed with step t; in fig. 3 shows section A-A in FIG. 2; in fig. 4 - rollers of the melted surface of the part, made with overlap; in fig. 5 is a section bb of fig 4; in fig. 6 is a schematic diagram of an installation for vacuum-free electronic processing; in fig. 7 - electromagnet, deviation to the electron beam from the axis of the electron beam gun.

The method consists in acting on a beam of electrons implanted at an increased pressure, periodically varying in time, with a field strength of 11,000–140,000 A / m.

The magnetic field imposed on the beam in a gas or air causes the beam electrons to deviate from a rectilinear motion. The greater the intensity of the magnetic field, the greater the angle of deflection of the electron beam. With a periodic change of the magnetic field in time, the angle of deflection of the beam also changes periodically, as a result the beam scans with the frequency of change of the magnetic field. In this case, the direction of beam scanning is perpendicular to si-. therefore, the perpendicular to the direction of movement of the product. When the beam is scanned, the width of the area of processing the surface of the product increases to the amplitude of the scan and, accordingly, the width of the melting of the surface of the product moved under the beam increases. This leads to an improvement in the quality of the coating by increasing the uniformity of the thickness of the melted or melted layer and reducing the irregularities of its surface.

142

Since the electrons of the beam are strongly scattered in a gaseous medium, the power density of the beam of relativistic electrons is chosen in the range from 10 to 10 W / m, at which it becomes possible to scan the beam without significantly defocusing it.

The upper limit of the proposed amplitude range of the magnetic field is determined by the fact that, at a voltage of more than 140,000 A / m, the electron beam of this energy is deflected by a magnetic field at an too large angle for a given distance from the discharge device to the irradiated product. This leads to the fact that at large angles of deflection the beam falls on the surface of the product obliquely and the focal spot (heating zone) is strongly smeared at the edges of the irradiation band, which leads to less heating of these places compared to the middle of the plane of the product. In addition, when the field voltage exceeds 140,000 A / m, the electron beam defocuses strongly in a gas due to the fact that when turning in such a strong magnetic field, the turning radius turns out to be small and the electron path lengths in the beam having finite diameter turn out to be significantly different. the outer and inner (with respect to the turning radius) edges of the beam. This also leads to inhomogeneity of the power distribution: when the beam is scanned over the surface of the product, and as a result, the deposition is uneven.

The lower limit of the proposed amplitude range of the magnetic field is determined by the fact that, at a intensity of less than 11000 A / m, the electron beam of a given energy (0.4-1.5 MeV) is deflected by a magnetic field at an too small angle that does not provide sufficient scanning amplitude beam on the surface of the product is greater than two beam diameters. The amplitude of the beam scanned over the surface of the product depends both on the scan angle and on the distance from the outlet to the irradiated surface of the product. But with an increase in this distance, the beam diameter increases due to its scattering in the gaseous medium and, accordingly, the density, power in

beam, which is unreasonable to reduce below 10 W / m. Therefore, the distance from the outlet to the irradiated surface is limited by this condition. With such limitations and given that the scan amplitude should not be less than two

 beam diameters (otherwise lost;; sense of scanning and unevenness of surfacing across the strip width), it was experimentally found that the amplitude, the intensity of the magnetic field should not be less than 11000 A / m

It is most advisable to change the intensity of the magnetic field of the fluid. a zero-length back-front law. At the same time, the magnetic field oscillogram has a sawtooth shape (Fig. 1), and the beam draws on the surface of the product a series of straight flip-flops parallel to each other, angled to the direction of movement of the product (Fig. 2). The width of the reflow track is equal to or slightly less than the beam diameter due to the fact that the power density at the edges of the beam is less than at its center. The spacing of the segments of the flashing track t is determined by the velocity V of moving the product with the beam scanning frequency f. If the pitch t is larger than the beam diameter q, then the molten metal rollers on the surface of the product do not merge. At the same time, there is no continuity of the coating strip. Such a coating may be recommended in order to increase the wear resistance of the surface of the product. It saves surfacing powder and energy compared to continuous coatings.

To ensure continuous coverage, it is necessary to take a step t less than the beam diameter h. At the same time, individual segments of the flashing tracks overlap with their edges and merge into a continuous flashing strip, whose width b is equal to the amplitude of the beam scanned over the surface of the product (Figures 4 and 5). With decreasing pitch t, the degree of overlap of the adjacent melting tracks increases and the non-uniformity of the thickness of the melted layer and the roughness of its surface decrease. However, this increases the energy consumption for reflow and reduces the productivity of the process.

due to the fact that in the overlapping zones of the tracks, the coating material has to be melted twice.

. Increasing the uniformity of the thickness of the melted or deposited layer and the elimination of irregularities (combing) of its surface is achieved when the beam scanning frequency is taken in

limits from 1 to 2 values of fp 2V / a, where fp is the frequency (Hz), and is the beam diameter, V is the speed of movement of the surface of the product (m / s), which is recommended to be in the range from 1 to

4 values of the calculated processing speed, determined by the semi-empirical formula VP P / 43-103 b, where P is the beam power (kW), b is the width of the fusion strip (m), equal to the amplitude of the beam scanned over the product surface. The 4310 coefficient has the dimension kW-s / m.

Beyond the lower boundary of the proposed frequency range fp, the surface of the weld coating is no longer smooth and comb irregularities appear on it. And when the upper limit of the proposed frequency interval is reached, the thickness of the melted

The layer becomes the same at all points of the melted surface and a further increase in the frequency does not lead to an improvement in the thickness uniformity, but leads to an increase in energy consumption and a decrease in productivity. The installation for carrying out the proposed processing method (Fig. 6) consists of an accelerator 1 electrons and a device 2 exchanging the electron beam from the vacuum system of the accelerator into air or gas. This device has a multi-stage system for pumping air or gas from the channel connecting the accelerator’s vacuum system with

the atmosphere. Multistep system / pumping is equipped with vacuum pumps 3, each of which is connected to one of the stages of the pumping system. All stages of the pumping system are separated from each other by copper diaphragms 4 with a hole in them for the passage of a sharply focused electron beam. The latter diaphragm 5 separates the final pumping stage from the atmospheric air. In the diaphragm 5 there is also a hole with a diameter of 1-1.5 mm for releasing the beam into the atmosphere. Under device 2 for output ka. device is installed in the air

513

6, made in the form of a trolley for moving the product 7 relative to the beam at an adjustable speed. The distance from the outlet in the diaphragm 5 to the surface of the product 7 is 40-150 mm (adjustable). Under the diaphragm 5 (between it and the surface of the product 7) an electromagnet 8 is placed, the winding of which is connected to a current source 9 generating an electric current, varying periodically in time according to the sawtooth law with zero duration of the falling front, the frequency of which can be regulated. Between diaphragm 5 and an electromagnet 8 accommodates a ferromagnetic shield 10 in which there is a hole for the passage of the beam, which is made coaxially with the hole in the diaphragm 5. The electromagnet 8 is installed so that the gap between its poles is located coaxially with the holes in the diaphragm 5 and the screen 10, and the vertical planes of the poles are perpendicular to the direction of movement of the product 7 across the beam. One possible embodiment of an electromagnet 8 is shown in FIG. 7

The electromagnet consists of two B-shaped ferromagnetic magnetic conductors and two coils wound on the side branches of the magnetic circuits. Coils are connected to a current source 9. The electron beam passes between the poles of the electromagnet, in the gap between the central branches of the magnetic conductor.

The installation works as follows

at once.

The electron beam generated by accelerator 1 exits the accelerator’s vacuum system to device 2 for the output of the electron beam and moves along its axis shown in FIG. 4 by a dot-dash line. Passing through the openings in diaphragms 4, the Kits section of the pumping stage, the beam gets into the region of increasing gas pressure (all the worst vacuum), and after passing through the hole in the copper diaphragm 5 it gets into atmospheric air or shielding gas. Air or gas continuously flows in the pumping stage of the device 2 through these openings in the diaphragms. It is then pumped out continuously with the help of pumps 3. Falling into atmospheric

-50

0 5

0

five

0

five

146

air or gas, due to scattering, the electron beam begins to gradually increase in diameter. But since the total path length of relativistic electrons in the air is 1 m or more, at a distance of 100–150 mm from the outlet in the diaphragm 5, the beam is still sufficiently concentrated to melt the powder coatings. The passage through the gap between the poles of the electromagnet 8, the electron beam is exposed to a magnetic field and is deflected by it in the direction perpendicular to the direction of the magnetic field lines and the direction of movement of the electron electrons. In this case, the deviation angle of the beam axis from the original direction is the greater, the greater the magnetic field strength. And when the magnetic field strength varies according to a periodic law, the angle of deflection of the beam also changes according to a periodic law. As a result, the beam scans in the direction perpendicular to the direction of movement of the carriage 6 with a frequency f equal to the frequency of the current supplying the electromagnet 8. When electromagnet 8 is in operation, the stray field created by it can reach a diaphragm 5 if there is no magnetic shield 10. In this case - one

The choke is exposed to a magnetic field already within the hole in the copper diaphragm 5 and starts scanning before it exits this hole. In doing so, the scanning electron beam melts the edge of the hole and increases its size in the scanning direction, turning the round hole into an elliptical one. Through a larger hole in the diaphragm 5, the air or gas leaks into the vacuum system of the installation, necessitating the installation of more powerful pumps 3 for pumping out air. To avoid this, a thin ferromagnetic screen 10 is installed between the electromagnet 8 and the diaphragm 5, which prevents the magnetic field from entering the diaphragm 5. As the ferromagnetic screen 10, a steel plate with a hole in it can be used to pass the beam. Screen 10 is especially necessary when working with a beam of electrons of relatively low (up to 1 MeV) energy.

7

which are strongly deflected even in weak magnetic fields.

Example 1. At the facility (Fig. 6, the surface of the plates 10 mm thick are made of metals listed in Table 1 by melting them in atmospheric air with an electron beam generated by the ElB-3 accelerator. The accelerator allows you to regulate the electron energy in limits 0.4-0.7 MeV. Pastin of each metal is placed on a trolley moving under the accelerator across the beam at a speed V. The distance from the outlet hole in the diaphragm to the surface of the plate is set equal to 1. The electron beam in the air between the diaphragm and the surface of the plate impose a magnetic field that varies periodically in time according to a linear law with a frequency f. To do this, an electromagnet is placed between the diaphragm and the surface of the product, and a sawtooth current is set in the gap between the electromagnet poles the amplitude of the magnetic field H. The cross section of the pole tips is 20–20 mm. A ferromagnetic shield of a steel plate 1 mm thick is installed between the electromagnet and the diaphragm. As a result of processing the plate in a single pass of the carriage, reflow rollers with a width b equal to the amplitude of the beam scanning are formed.

The results of measuring the geometrical dimensions of the deposited rollers are given in Table. 1, which also shows the results of experiments on wear resistance.

The wear resistance of the surface of the product before and after reflowing is determined on a Skoda-Savin car. After testing on the surface of the samples control the depth of the wells.

The wear resistance of the surface is defined as the ratio z / h, where z is the path of friction, h is the depth of the wiped hole, mm. In this case, the condition h S is satisfied, where S is the thickness of the melted layer. The test results are shown in Table. one.

And p. M. 2. The surface treatment of plates with a thickness of 6 mm of steel St 3 is carried out by surfacing a continuous powder coating. For

g o 5 o

about

g

five

1148

This powder is evenly poured on the cleaned surface of the plate, the characteristics and composition of which are given in Table. 2 and 3. The layer of powder is leveled with a scraper to obtain a layer of uniform thickness with a smooth and equal surface. The plate is placed on the trolley being moved under the accelerator. The electron energy is regulated in the range of 0.8-1.5 MeV. Irradiation is carried out in atmospheric air. The distance from the outlet in the diaphragm to the plate surface is chosen equal to 1. The beam in the air between the diaphragm and the plate surface is superimposed with a magnetic field of intensity H, periodically varying in time according to a linear law with a frequency f. A ferromagnetic screen of 1.5 mm steel plate is installed between the electromagnet and the diaphragm. As a result of processing, a weld bead is formed on the surface of the plate, having a width equal to the amplitude of the beam scanning.

The results of the experiments are summarized in table. 2

PRI me R 3. Surface treatment of plates with a thickness of 4 mm of steel St3 and copper is carried out by overlaying individual tracks of powder coating forming a wear-resistant grooved on the surface of the plate. All processing operations are carried out analogously to example 2, with the difference that the scanning step is chosen larger than the beam diameter and the installation does not have a ferromagnetic screen. This leads to an increase in air leakage into the vacuum system of the installation through an opening in the diaphragm and to the need to increase the capacity and power of the pumps by 1.5 times compared with the performance of example 2,

PRI me R 4. Surface treatment of duralumin plates of grade D16T 20 mm by overlaying on them separate tracks of powder coating forming a wear-resistant grooved on the surface of the plate. All operations are carried out analogously to example 3, with the difference that in the installation between the diaphragm and the electromagnet a ferromagnetic screen of steel with a thickness of 1 mm is placed, and the treatment area on the plate is continuously flushed with a protective shield 91

for - argon, with a consumption of 3. As a result of processing, rollers are formed on the surface of the product, shown in FIG. 2. In table. 4 shows the results of processing plates according to examples 3 and 4,

From tab. Figures 1 and 2 show that, when the amplitude of the magnetic field H is exceeded beyond the boundary values of the magnetic field H, the heterogeneity of the type of the melting or cladding layer sharply increases. Here, the non-uniformity of the layer thickness is understood as the ratio of the width of the edge sections of the flashing strip, which have a reduced thickness compared to the middle section, to the width of the entire flashing strip, expressed in%, - When the output of the trolley speed limit (4Vp) sharply increased, the nonuniformity melted layer When the trolley speed (LlVp) exceeds the lower limit value, the surface quality does not improve further, but the amount of penetration in the substrate metal increases excessively and the specific energy consumption of the treatment increases. When the lower frequency limit of the scan frequency (If) is exceeded, irregularities in the surface of the deposited layer appear and its thickness heterogeneity increases, and when the upper limit value of the proposed scan frequency interval (2fp) is observed, the fused powder does not melt well with the substrate .

When using the proposed method, as compared with the known method, the productivity of fusing or melting the surfaces of products is increased due to the fact that the width of the fusion strip increases;

14

ten

received in one pass of the product under the accelerator, and there is no need for multiple reciprocating movements of the product under the accelerator, of which one movement is working and the second (in the opposite direction) is idle.

The technological capabilities of the method are expanded due to the occurrence of the possibility to obtain a surfacing strip of a given width, having a smooth surface or, on the contrary, having a corrugated surface with a predetermined (adjustable) corrugation pitch.

In addition, when using the proposed method, the uniformity of the thickness of the melted or deposited layer is increased and the irregularities of its surface are reduced by increasing the width of the melting strip and eliminating the formation of tight meniscuses on its surface.

Claims (1)

Invention Formula The method of non-vacuum electron-beam surface treatment of products with an electron beam with an energy of 0.4-1.5 MeV, which is different in that in order to increase the productivity and quality of the process by increasing the width and uniformity of the melting, the electron beam is affected by a magnetic field with intensity , periodically changing, in time, according to a sawtooth law with zero trailing edge duration, and the magnetic field lines are directed perpendicular to the beam axis and along the direction of movement being solved surface, the amplitude of the magnetic field strength. nitral floor is chosen from 11,000 to 140,000 A / m. Thickness slr reflow $, mm Heterogeneity of the layer thickness of the melt along the melting strip & S, mm Surface roughness iq, m Heterogeneity of the thickness of the reflow layer along the width of the oplavleic strip, Z. Wear resistance of the CI surface Before melting after melting 0.2 0.25 0.35 0, 3 0.4 0.4 0.35 0.2 45 40 16 0.15 O, t 0.05 0.5 0.02 0.05 0.05 0.05 0.1 0.12 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0, 0 0.0 16 16 16 25 55 50 0.005 0.005 0, OOS 0.005 0.002 0.004 0.004 0.005 0.004 0.00t 0.0t 0.012 0.00a 0.005 0.01 0.008 0.004 0.4 0.35 0.2 0.15 16 16 16 25 55 50 15 13281U sixteen Table E 1 / 7-X7 ag.2 fpuz.S Jl. M FagL FIG. five Ryg. 6 Formation of the scanner Compiled by G. Kvartalnova Editor S. Pekar Tehred L. Serdyukova Corrector A. Zimokosov Order 3433/16 Circulation 974 Subscription VNIISCH State Committee of the USSR for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, 15 str., 4  Rig, 7