RU2249863C2 - Aggregate for contact butt welding - Google Patents

Abstract

FIELD: nuclear power engineering, possibly automatic line for producing fuel elements of fuel assemblies of power nuclear reactors.

SUBSTANCE: aggregate is provided with detachable device for measuring electric resistance of fitting. Said device is arranged between collet chucks being in open position and it is made of two dielectric members spring-loaded one relative to other. End of one of said members has shape corresponding to contour of annular turning formed coaxially on end of collet chuck for plug. End of second member has shape corresponding to contour of annular turning formed coaxially on end of fitting in collet chuck for fuel element envelope. Said device has spring-loaded contacts for measuring electric resistance between fitting inside collet chuck and collet chuck itself. Caprolactam is used as dielectric material.

EFFECT: enhanced efficiency and quality of contact butt welding at sealing fuel element.

2 cl, 3 dwg

Description

The invention relates to nuclear energy and may find application in an automatic production line of fuel elements (TVEL).

Currently, most of the fuel rods for nuclear power plants are sealed from one end by electron beam welding of the plug to the shell, and from the other end after equipping the pelletized nuclear fuel into the shell by flash butt welding of the plug to the shell under inert gas pressure under the shell. A known flash butt welding assembly called KSS-2, developed in Russia. The formation of a welded joint at KSS-2 is performed under conditions of a comprehensive compression of the welding zone with a ring mandrel, and for welding, plugs of a reduced diameter are used in comparison with the outer diameter of the sealed shell (see “Development, production and operation of fuel elements of power reactors.” Book 2. Under Edited by F.G. Reshetnikov -M .: Energoatomizdat, 1995 - p. 217-222, Fig. 20.17).

The mold-refrigerator-current lead in the known unit is a ring mandrel. When clamping a fuel rod in a ring mandrel, the thickness of the fuel rod shell can be considered as the total thickness of the fuel rod shell and the ring mandrel. In this case, due to an increase in the shunt current through the collet clamp (ring mandrel), the heating of the fuel rod shell will decrease, the heating zone above the recrystallization temperature goes to the outer surface of the shell / plug connection, capturing the transition point of the shell to the end face of the plug, which is unacceptable from the point of view of the corrosion resistance of the welded connections. The welded joint obtained in a solid collet clamp (ring mandrel) is limited to no more than 1.5S (where S is the shell thickness). The margin of safety of such a connection and the corrosion resistance are low due to the fact that the electrical resistance of the collet clamp (ring mandrel) is lower than the resistance of the sheath.

As a result, the portion of the shell is not completely heated, which limits the depth of the plug fitting to the joint length - 1.5S (where S is the shell thickness).

A known flash butt welding assembly comprising collet clamps with channels for the shell of a fuel element and plugs, installed with the possibility of autonomous reciprocating motion by means of actuators with the formation of a welding chamber in communication with means of rarefaction, supply of neutral gas and a source of welding current.

(See Patent RU 2152091, IPC 7 G 21 С 21/02 of 10/07/1998, publ. 06/27/2000. "Installation for sealing tubular elements").

A disadvantage of the known flash butt welding assembly is similar to the disadvantages of the flash butt welding assembly described above.

The closest in technical essence and the achieved effect is a flash butt welding unit with a channel for a shell equipped with nuclear fuel and with a collet clamp with a snap inside in the form of a set of plates isolated from each other with a resistance of 700-1200 μOhm, with a collet clamp for plugs installed with the possibility of reciprocating motion by means of drives with the formation of a welding chamber in communication with the means of rarefaction, supply of neutral gas and a source of welding current. (see Patent RU 2127457, IPC 6 G 21 C 3/10, 21/00, 21/02 of 04/04/1997, publ. 10.03.1999, Fig.16, Fig.17).

The mold-cooler-current lead in the prototype patent is a snap fastened inside the collet clamp (see ibid., Section 21).

In the prototype patent, a snap in the form of a set of plates (gaskets) located in a collet clamp for a shell equipped with nuclear fuel may fail.

In this case, damage to the gasket plates leads to the formation of spurious chains through which the welding current is bypassed.

The current density in the contact of the welded parts decreases, although its total value remains unchanged, which leads to underheating of the welded section and the quality of welding and the properties of the welded joint are deteriorated.

Long-term work of the collet clamp under cyclic thermomechanical loads can lead to a change in the electrical resistance of the tooling in the direction of its increase (see ibid., Section 17) due to oxidation of the tooling plates, which is undesirable, since the quality of welding decreases.

In this regard, in the description of the prototype patent, it is recommended to control the electrical resistance and the absence of shunt circuits before welding (see patent prototype, section 17), however, how to do this is not indicated.

Equipment in the form of insulated plates is fixed inside the collet clamp in the form of a three-leaf collet and has an electrical resistance of 700-1200 μOhm, which exceeds the resistance of the sheath part involved in the formation of the welded joint.

The rigging according to the number of three-petal collet is divided into three sectors, which are respectively fixed to the petals of the collet (see ibid., Section 21).

In order to measure the electrical resistance of three sectors of the snap-in, it is necessary to disassemble the snap-in and remove it from the collet clamp, or remove the collet clamp from the unit together with the snap-in. Both are undesirable, since debugged tolerances are violated, it is very difficult to restore them, which affects the quality of welding. In addition, all these operations require labor that reduces productivity.

An object of the invention is to increase the productivity and quality of flash butt welding when sealing a fuel element.

This technical problem is solved in that a flash butt welding unit with a channel for a shell equipped with nuclear fuel has a collet clamp with a snap inside in the form of a set of plates isolated from each other with an electrical resistance of 700-1200 μOhm, with a collet clamp for plugs that can be installed back - progressive movement by means of drives with the formation in a closed state of the welding chamber in communication with the means of vacuum, supply of neutral gas and a source of welding current.

According to the invention, the butt butt welding unit is equipped with a removable snap-in device for measuring the electrical resistance of a snap made between two collet clamps in a diluted position, made of two spring-loaded parts, of dielectric material, of which the end of one part is placed and repeats the shape of an annular groove made coaxially at the end of the collet clamp for the plug, and the other end of the second part is placed and repeats the shape of the annular groove, made coaxially at the end of the snap in the collet bench for the shell of the fuel element, the electrical resistance measuring device is provided with spring-loaded contacts measuring the electrical resistance between the snap-in collet and collet clamp directly.

Another difference is the use of caprolactam as the dielectric material.

Providing a flash butt welding unit with a removable tool for measuring the electrical resistance of the tool will allow monitoring the absence of shunt circuits before welding, identifying failed insulating plates of the gasket by collet sectors without disassembling and timely removing and replacing them in case of damage to the tooling and thereby achieve the solution delivered technical task to increase the productivity and quality of flash butt welding when sealing a fuel about the item.

The drawings show the assembly of flash butt welding, where in Fig.1 is a removable device for measuring the electrical resistance of the snap in the assembly of flash butt welding; figure 2 - removable device for measuring electrical resistance; figure 3 - removable measuring device (top view).

Resistance butt welding assembly with channel 1 for nuclear-powered 2 shell 3 with collet clamp 4 with snap 5 inside in the form of a set of plates isolated from each other with a resistance of 700-1200 μOhm, with collet 6 for plugs (not shown) installed with the possibility of reciprocating motion (shown by an arrow) by means of actuators (not shown) with the formation in a closed state of the welding chamber in communication with the means of vacuum, supply of neutral gas (not shown) and a welding current source 7.

The flash butt welding unit is equipped with a removable snap-in device 5 for measuring the electrical resistance of a snap 5 located between the collet clamps 4, 6 and made of two spring-loaded parts of dielectric material, of which the end of one part 8 repeats the shape of the annular groove 9 made coaxially at the end of the collet clamp 6 for the plug, and the other end of the second part 10 repeats the shape of the annular groove 11 made at the end of the snap 5 in the collet clip 4 for the shell 3 of the fuel element. At the same time, the device for measuring electrical resistance is equipped with spring-loaded contacts 12 for measuring electrical resistance between the snap-in 5 inside the collet clamp 4 and directly with the collet clamp 4. Caprolactam is used as the dielectric material for the device for measuring electric resistance.

Measurement of electrical resistance is as follows.

Before measuring the electrical resistance of the flash butt welding unit, the scaling clamps 4, 6 are spread coaxially to the sides, between them, one part 8 of the electrical resistance measuring device is installed in the groove 9 of the collet clamp 6, and another spring-loaded part 10 is installed in the groove 11 in the snap-in 5. spring-loaded contacts 12 are directly connected to the collet clamp 4 and snap 5 inside the collet clamp 4. By rotating around its axis parts 10, 8 in the grooves 11, 9 measure the electrical resistance of all t ex display sectors 5 fastened to the collet chuck trilobal petals 4, and the measurement results are transmitted to the measuring device 13.

Based on the measurement results, a decision is made to continue butt welding with an electrical resistance of 700-1200 μOhm, and when deviated to a greater or lesser extent, replace the collet clamp 4 with snap 5 inside. Due to the fact that the parts 8, 10 are spring-loaded with each other in the device for measuring electrical resistance, it is not difficult to remove the device from collet clips and install the device in them.

Claims (2)

1. Resistance butt welding assembly with a channel for a shell equipped with nuclear fuel with a collet clamp with a snap inside in the form of a set of plates isolated from each other with an electrical resistance of 700-1200 μOhm, with a collet clamp for the plugs installed with the possibility of reciprocating motion by means of drives with the formation in a closed state of the welding chamber in communication with the means of vacuum, neutral gas and a source of welding current, characterized in that the assembly of the contact butt weld The rkki is equipped with a removable device for measuring the electrical resistance of the snap, placed between the collet clamps in a diluted position, made of two spring-loaded parts of dielectric material, of which the end of one part is placed and repeats the shape of an annular groove made coaxially at the end of the collet clamp for the plug and the other the end of the second part is placed and repeats the shape of the annular groove made on the end of the snap in the collet clamp for the shell of the fuel element, while The measurement of electrical resistance is equipped with spring-loaded contacts for measuring electrical resistance between the equipment inside the collet clamp and the collet clamp itself. 2. The assembly according to claim 1, characterized in that caprolactam is used as the dielectric material.

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