RU2269400C2 - Method of resistance welding - Google Patents

Abstract

FIELD: mechanical engineering; welding.

SUBSTANCE: invention relates to welding and it can be used in manufacture of structural members of materials featuring high plastic properties in zones of temperatures of recrystallization, particularly, in manufacture of frame members of heat liberating assemblies of nuclear reactors manufactured of zirconium alloys. Proposed method of resistance welding with simultaneously putting two weld spots of mainly coaxially arranged parts, includes compression of parts and heating of welding zone with electric current at partial shunting. Compression is done with forming of line of contact along generatrices of parts. Heating is carried out first with forming of zone of higher plasticity along line of contact of parts generatrix in which sections of diffusion character connection are formed, and at further heating, sections of cast nugget are formed in middle part of weld spots. When forming sections of cast nugget, zone of melting is made not exceeding half of area of weld spot, and at beginning of metal melting, welding current is cut off.

EFFECT: improved quality of welds, reduced labor input in manufacture of parts.

2 cl, 3 dwg

Description

The invention relates to the field of welding technology and can be used in the manufacture of structural elements from materials having high plastic properties in the temperature zone of recrystallization, and, in particular, in the manufacture of frame elements of fuel assemblies of nuclear reactors made of zirconium alloys.

A known method of contact spot welding with the simultaneous execution of two points with the formation of a molten core, which consists in compressing the parts to be welded, heating them in the zone of welding with electric current when it is supplied to one of the parts being welded through the electrodes of the welding device (see: B.D. Orlov , Yu.V. Dmitriev and others. "Technology and equipment of contact welding." - M .: Mashinostroenie, 1975, p. at least one of the details is shown increased s requirements to maintain their geometric dimensions after welding or minimal deformation, which makes it impossible to use. In addition, the method involves obtaining a welded joint due to the formation of a cast core, which is not always possible and advisable, for example, when welding zirconium alloys having high plastic properties in the region of recrystallization temperatures and which are active getters, or due to splashes that impair welding quality .

The closest in technical essence and the achieved result to the proposed method is a method of one-side contact welding using a shunt pad (see ibid., Fig.5.21 (b)) - a prototype, the disadvantage of which is the complexity of the technological implementation for the case when, at least , one of the parts is a long shell with a small inner diameter, which makes the application of the method extremely difficult or impossible due to the need to use a shunt pad, except boiling unacceptable deformation of the bottom part. In addition, the method involves obtaining a welded joint due to the formation of a molten core, which is not always possible and advisable, for example, when welding zirconium alloys having high plastic properties in the recrystallization temperature zone and being active getters, or due to temperature spikes that impair the quality welding.

An object of the invention is to improve the quality of welds and reduce the complexity of manufacturing parts.

The problem is solved in that in the method of contact welding with the simultaneous establishment of two weld points of predominantly coaxially located parts made of alloys with increased ductility in the temperature zone of recrystallization, including compression of the parts, their heating in the welding zone by electric current with partial shunting, according to the invention compression is performed with the formation of a contact line along the generatrix of the parts, and heating is carried out first with the formation of a zone with increased ductility along the line a beat along the generatrix of the parts, in which the diffusion joints are formed, and with further heating, the cast core is formed in the middle of the weld points. The task is also fulfilled by the fact that during the formation of sections of the molten core, the melting zone is performed not exceeding half the area of the weld point, and when the metal is melted in the contact zone, the welding current is turned off.

The specified set of features is new and allows you to solve the problem.

Performing welds with the formation of diffusion joints in the formed zone of increased ductility along the contact line along the generatrix of the welded parts with the size of the mutual melting zone is less than half the area of the weld point when the zone with the changed structure extends into a thicker part by an amount not exceeding two thirds of its thickness , reduces the deformation of parts and eliminates excessive heating, prevents splashes due to the release of the molten core to the surface.

Fixation by instrumentation methods of the beginning of the formation of a section of mutual melting of the parts to be welded and disconnection of the welding current can stabilize the quality of welding and reduce the cost of removing splashes.

The essence of the method is illustrated by drawings.

Figure 1 shows a variant of the flowchart for welding a long pipe with a thin-walled sleeve.

Figure 2 illustrates the application of the welding method for welding to a long pipe simultaneously two thin-walled bushings.

Figure 3 schematically shows a welded joint.

The method is implemented as follows.

The parts to be welded 1, 2, 3 are pre-installed on the part 4. Electrodes 5 are fed alternately to the weld points. The parts to be welded are compressed by the welding force P to form a contact line along the forming parts. The magnitude of the welding force P is insufficient for unacceptable deformation of the parts to be welded. A pulse of the welding current from a power source (not shown) is passed through the formed contact. The magnitude of the welding force, the pulse parameters of the welding current are selected depending on the material of the parts to be welded and the thickness of their walls. Due to the fact that the material of the parts has increased plastic properties in the recrystallization temperature zone, the welding zone is heated with a short pulse. As a result, the metal of part 4 located under the welded joint warms up to the state of increased ductility only by the value Z, which is no more than two-thirds of its wall thickness (Fig. 3). This prevents unacceptable deformation of part 4 from the inside and avoids unwanted contact of the superheated metal with the atmosphere. As the process proceeds between the sections in the welding zone heated to a plastic state, the diffusion-type connection sections 6 are first formed (Fig. 3). Their further heating leads to the beginning of the melting of parts in the contact zone and the formation of sections of the cast core 7. The appearance of these sections can occur simultaneously from two ends of the welded joint or from one, depending on the initial distribution of resistance in the contact of the parts being welded. In the middle part of the weld point, where maximum compression of the parts is achieved through the use of spherical or elliptical electrodes, the resistance of the weld zone is minimal, and the cast structure is formed last. If the area occupied by the molten metal at the weld point exceeds half its size, a splash through the part 1 or 3, 4 is usually noted (Fig. 1 and Fig. 2, respectively).

The proposed method is implemented when welding guide channels and a central pipe with spacer grids of a fuel assembly of a VVER-1000 nuclear reactor. The guide channels and the central tube are long tubes with an outer diameter of 12.6 mm or 13 mm and a wall thickness of about 0.9 mm, made of zirconium alloy E-110 or E-635. On the guide channels and the central pipe, spacing grids are installed with a certain step, consisting of separate cells welded to each other by contact-spot welding with a wall thickness of 0.3-0.25 mm. The cells form a honeycomb structure and are intended for installation of fuel elements in them. In places of passage through the spacer grids of the guide channels and the central pipe, the corresponding cells are absent. The contact between the guide channels, the central tube and the cells having a complex geometric shape, inscribed in a regular hexagon with a key size of about 12.8 mm, is carried out along the line. The inner diameter of the circle inscribed in the cell is about 9 mm. Welding is carried out in an assembly building using welding pliers, providing compression of the parts by electrodes and the supply of welding current to them. Welding is performed at a force of 35-50 kg with a current pulse of 6-8 kA and a slew rate of 1-15 ms, a pulse duration of 8-15 ms from an inverter type power source with control of the parameters of the mode. The cycle of compression of the electrodes, the inclusion of welding current and the expansion of the electrodes is carried out automatically after an operator's command. The installation and fixation of the electrodes in the cells is performed manually by the operator.

Claims (2)

1. The method of contact welding with the simultaneous establishment of two weld points, mainly coaxially located parts made of alloys with high ductility in the temperature zone of recrystallization, including compression of the parts and heating in the welding zone by electric current with partial shunting, characterized in that the compression is performed with the formation of a contact line along the forming parts, and heating is carried out first with the formation of a zone with increased ductility along the contact line along the forming parts, in which th form sections of the compound of a diffusion nature, and with further heating they form sections of a cast core in the middle of the weld points. 2. The method according to claim 1, characterized in that when the molten core sections are formed, the melting zone is performed not exceeding half the area of the weld point, while the welding current is turned off when the metal is melted.

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