SU1514531A1 - Method of flash-butt resistance welding - Google Patents

Description

The invention relates to methods of flash butt welding by melting and can be used for welding various parts having a continuous section. The aim of the invention is to improve the quality of welding by improving the protection of the ends of the welded parts from oxidation. The method includes melting and draft. When reflowing, welding voltage of industrial frequency is supplied to the parts. In the spark gap between weld-! The details create a pulsating electromagnetic field with a vector in the radial direction. At the same time, the value of magnetic induction is periodically changed from zero to specified 2

values. During the action of the pulse ^{1 of the} electromagnetic field, the welding voltage is increased to a value that provides the excitation of the arc. The maximum duration of a pulse of an electromagnetic field is limited by the value determined from the ratio of 6 _MEX = ~ 2 ~~> where “the frequency of the industrial voltage, 1 / s

Carrying ---, C, where 5 - the perimeter of the section of the welded part, m;

V - arc moving speed, m / s.

During the action of an electromagnetic zero pulse, the welding voltage increases. The beginning of the pulse of the electromagnetic field is carried out with an increase in the current value of the welding current. It is advisable to create a pulsating electromagnetic field after it is established when the equilibrium thermal state of the parts to be welded is melted. The pulsating electromagnetic field ceases to be created at the moment of the spark gap closing at the draft. Sediment begins during the pulse of the electromagnetic field. 2 hp f-ly, 1 tabl about 3 ill.

The invention relates to flash butt welding by flashing various parts, mainly having a continuous compact section.

5 C 1514531

The purpose of the invention is to improve the quality of welding by improving the protection of the ends of the welded parts from oxide

Lenia.

Figure 1 shows a schematic diagram of the method of welding; Fig 2 shows a sequence diagram of the change in the welding voltage V, the welding current I, and the induction $ of the magnetic field B created by the coils of the electromagnet in the gap between the parts to be welded; in Figure "3 dependence of toughness Rij, weld in za- Yu visibility of the pulse duration of the electromagnetic field / \ C (depending shown in Figure ₁ and 2 are shown in one-time)

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The essence of the method is as follows.

“When parts are melted without application of a field, elementary bridges are formed at their ends, they are heated, exploded and evaporated.” Such a sequence of contact states is explained by its static nature. position at the end of the part. When acting in the joint planes of the pulsating electromagnetic field of the radial direction, it interacts with the axial current passing in the contact. Under the influence of the resulting effort jumper jumps up and collapses. Due to the presence of metal vapors and the high temperature of the ends of the parts, an arc arises between the ends, the direction of movement of which is determined by the influence of the electromagnetic field. The arc is shifted to the periphery of the end, having also an angular velocity. With a steady process, the arc rotates along the peripheral surfaces of the end face. The time of existence and rotation of the arc corresponds to the duration of the field pulse. ”When the arc is burning, 80% of the energy is released on the surfaces of the anode and cathode (on the end surfaces of the parts to be welded). As a result, the metal melts and evaporates. "The location of the active metal vapor emission zone in the peripheral zone of the butt-end of the parts allows to actively resist the penetration of atmospheric oxygen to the end of the parts." It was established experimentally that the linear velocity of the arc reaches 160 m / s. Therefore, craters from the explosion of overheated areas do not appear on the 55 ends, and a uniform film of liquid metal is created.

On the day of obtaining the effect of protecting the ends from the oxidation of the line, it is necessary that the arc is full rotation around the perimeter of the part and its movement close the point of its initial exit to the perimeter. The time of one revolution at the steady process is 5 / ν, with B being the perimeter of the section of the welded part; ·; M; V - movement speed, arcs, m / s. Taking into account the fact that the starting point of the arc movement can be in the center of the face of the part and additional time is needed for the arc to exit, the minimum allowable time of arc rotation and the action of the field pulse is set to 1.5 5 / ν. With this value b = = 1.5 · 5 / ν, high-quality protection of the ends of the parts is ensured.

The maximum time the electromagnetic field pulse is limited to the value used _poppy = 1 / (2 £), where £ - industrial frequency of the voltage 1 / s, for such reasons, Firstly, when exceeding the duration of a half of the welding voltage period is required to be the point at which welding current will change its direction. In this case, the direction of arc rotation should change, which is undesirable, since in this case the process is unstable, Secondly, during the existence of the arc, heat is not supplied to the central areas of the part butt, and the time of existence of the molten metal at the end without crystallization does not exceed 0 , 02-0.04 s. With a frequency of £ = 50 Hz, the duration of a half period of 1/2> G will be 0.01 s, and the Preservation of the liquid film is guaranteed.

one

When an equilibrium thermal state of the parts to be welded is established, the most favorable conditions for the initiation of the arc, its steady state, i.e. the high temperature of the ends is stably maintained, the reliable excitation of the arc and its stability provide conditions for high-quality protection of the ends of the parts being welded against oxidation,

The welding voltage is increased to a value that allows the arc to exist. The sum of the cathode and anode voltage drops for two steel electrodes is 18-19 V and the minimum en5

1514531

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voltage

exist arc, is 20 V,

During the action of the electromagnetic field, the welding voltage increases, and conducting the precipitation even after the spark gap closes at a high welding voltage may result in overheating of the joint metal. Therefore, the limitation of the time interval for the existence of a pulsating electromagnetic field and a high welding voltage to the moment when the spark gap closes during the draft allows improving the quality of welding,

The method also provides for the implementation of the beginning of the pulse of the electromagnetic field with an increase in the current value of the welding current. In this case, optimal conditions are provided20 for exciting the arc and starting its movement,

The beginning of the action of an electromagnetic field pulse must be coordinated with an increase in the current value of 25 welding current, since there is a phase shift between the welding voltage and the welding current, and the magnitude of the compr can reach 0.70.8. thirty

The main task of the method is to protect the ends of the parts being welded from oxidation at the final stage of flashing before settling. Providing protection at the initial stage of reflow practically does not affect the quality of the welded joint. The achievement of the thermal state of the parts being welded when reflowed indicates that heating is sufficient to form the joint. The duration of the pulsating electromagnetic field from this point to the closure of the spark gap during upsetting protects the ends from oxidation at the most important stage of fusion (the final stage) affecting the quality of the welded joint.

In connection with the pulsating action of the electromagnetic field, the magnitude of the excess pressure (above atmospheric) in the peripheral regions of the gap between the ends takes on the greatest values during the action of the electromagnetic field. Coordination of the start of precipitation with this moment provides the highest quality connection.

The scheme of the welding method includes welded parts 1 and 2, coils

3 and 4 electromagnets, welding transformer 5 with primary winding A and secondary winding 7, magnetic induction lines B <produced by electromagnet coil 3, magnetic induction lines В ₂ generated by electromagnet coil 4.

Example. Welding of class III valves from 25G2S steel with a diameter of 50 mm was made on a K-724 machine using the described technical solution. The reflow allowance was 18 mm, and the draft was 6.5 mm. Melting was carried out on the welding voltage of 7.8 V,

At the time of the pulse of the electromagnetic field with an induction of 50 mT, the welding voltage was increased to 20 V.

A pulsating electromagnetic field with a vector in the radial direction used in the method was obtained as follows. For an electromagnet, they were installed coaxially with the parts to be welded and covered them with their turns. The ends of the windings of the coils are connected in such a way that the fluxes of magnetic induction В _< and В ₂ (figure 1) created by them are directed oppositely. In the gap, the mtnite flows interact and in the plane of the junction a field is created with the vector in the radial direction.

The coils of electromagnets 3, 4 in the example of a specific implementation of the method of welding rebar with a diameter of 50 mm are made of a PEV brand wire with a diameter of 2 mm, the number of turns in each is 140, the coils were placed in a sealed enclosure and cooled with water, which allowed the maximum current to flow through the wire A. By changing the amount of current, you can change the magnitude of the induction of the electromagnetic field (during welding, the induction was set to 50 mT) * The coils of electromagnets were connected in parallel to the VDU-504 source with thyristor control, which allowed creating a pulse Irritating electromagnetic field.

The inclusion of precipitation was carried out after 18 mm reflow. The pulsating electromagnetic field was turned off after the end of the reflow.

With a value of soy ψ welding circuit, equal to 0.82, the current phase shift

in relation to the voltage is 7

1 3143 3!

eight

em <| "= .33 ¹¹ . Phase shift

current with respect to the voltage will be = </> / £ 360 = 35/50 * 360 = 1.9 * m10 '^ s. Fig. 2 shows the case of the application of a pulse of an electromagnetic field with an increase in the welding current with a duration of 1/4 of the welding voltage period, i.e. ΑΡ = ΐ / 4 · =

= 1/4 * 50 = 5-10 '%, 1, d - amplitudes -, θ

the value of the welding voltage in the absence of the field, 1! ^ - the amplitude value of the welding voltage during the action of the electromagnetic field pulse, 15

Experimentally determined the linear velocity of the arc along the ends of the rods. For this purpose, at a distance of 10 mm in the radial direction from the gap, an LD-3, ¹ 20 photocell was installed protected by quartz glass. Revolving at the ends of the parts, the arc illuminated the photocell with different intensities. The magnitude of the electrical signal taken from the photocell was directly 25 proportional to the intensity of illumination (luminous flux). The greatest magnitude of the electrical signal was at the moment of finding the arc at the minimum distance from the photocell. Time 30 between the two maximum signals from the photocell corresponded to time. not a single turn of the arc. Knowing the path ι traversed by the arc, and the time of one revolution, determined the speed of movement of the arc.

In the pilot welds carried out, the speed of movement of the arc was at the level of 160 m / s under the action of an electromagnet in the gap plane in the gap 49

field with a radial component of induction B = 50 mT.

Welding was performed at values = 5 AR 10, AR = Sdsch _LN ⁼ 1 "May 8 / ν. = 1, 5Λ · / ν = 1.5-3.14-0.05 / 160 = 45

= 1, 47 · 10- 's, A C-C _max = 1/2-ΐ =

=! / 2 * 50 = 10 ' ² s (in calculations, the perimeter is 5 =, where ά = 0.05 m diameter of the welded part' (Fig, 1). For comparative analysis, welding was performed with the duration of the field pulse, not included in the specified interval from P _mI m TO C / max ', ^namely with AP = Ο, δΊΟ' ³ s, and also (\ P =

= 1.5.10 ' ^g with. ₅₅

From the joints of welded parts were made figurative for tests on impact strength and _h at 20 C, the test results are summarized in the table.

₍ ------------------ Duration nm - Impact viscosity, pulse, AR, s and _n , J / cm ²

ig - 25 (nineteen - 31) ten'' 58 (54 - 62) u ~ ³ 61 (56 - 66) ten'* 59 (53 - 64) Yu ' ² 22 (15 - 29)

The toughness value for the base metal was 68 J / cm

When the duration of the pulse of the electromagnetic field in the range of

⁼ 1.47 * 10 '%. to Ρ _Μαί = MO ' ² s (FIG. 3), welding with high mechanical characteristics of the weld metal is ensured (up to 90-95 ^ of the toughness of the base metal}.

A batch of parts was also welded with the same technological parameters, the duration of the electromagnetic field pulse was set to AC ⁼ 5 * 10 s, but the pulsating electromagnetic field began to be created with 16 mm reflow after the equilibrium thermal state of the parts was established and ended when the spark gap closed. The value of toughness remained in the same range, but by 3 — the power consumption was reduced, since a decrease in welding time at high voltage increases the efficiency of the process.

The next batch of parts was welded with the same constant technological parameters and the duration of the action of the electromagnetic field pulse AP = 5 - 1 " ³ s * The beginning of the precipitation was synchronized with the moment of action of the pulse of the electromagnetic field. The impact toughness was controlled, the value of which lay within 60 to 66 J / cm. The average value increased slightly to 63 J / cm, but the scatter of values decreased, which indicates an increase in the stability of obtaining high-quality compounds.

The proposed method allows

increase the stability of the process of formation of high-quality welded joints and reduce the duration of the weld

ki

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Claims (3)

Claim one . The method of flash butt welding by melting parts with a continuous cross section, including melting and slump, and when melted, welding voltage of industrial frequency is applied to the parts and an electromagnetic field is created in the butt plane, about 1 K) and the minimum pulse duration of the electron of the gnit zero is limited by the value determined from the ratio 1.5-5, ^М MIN = V ---> ^C ' where 5 is the perimeter of the section of the welded part, m; V is the speed of movement of the arc, m / s, In addition, the beginning of the electromagnetic field pulse is carried out with an increase in the current value of the welding current, 2. The method according to π, 1, and tl and h ay and so that the pulsating electromagnetic field is created after the equilibrium thermal state of the parts to be welded is established and the parts that are being welded are no longer created when the spark gap is closed during the draft. 25 3. The way pop. 1, that is, the fact that the draft begins during the action of an electromagnetic field pulse. ten In order to improve the quality of welding by improving the protection of the ends of the parts being welded against oxidation, the electromagnetic field is pulsed with the vector in the radial direction, while the electromagnetic field pulse is applied, the voltage is increased to a value that gives rise to the arc, while the maximum electromagnetic pulse the fields are limited by the value determined from the ratio mks one 2- £ ~ ' ^C ' where is £ industrial voltage frequency, 1 / s; 3 In, in, (rig / I 5 I Λ 5 31 <7ζ /, ND, W / cm ²