Method of sealing tubular products

 

(57) Abstract:

Use: in the manufacture of fuel elements for nuclear reactors. The tubular product is fixed in the fixture and tighten it with a stub. Heat the Assembly with a pulse of welding current distribution along the length of the weld zone. Put the welding force. The rate of precipitation stub has two peak values. The rate of change of the equivalent energy of a pulse of welding current is not less than 25 kA2. The slew rate of the pulse welding current is not less than 1 kA/MS. The method improves the weld quality and the reliability of the sealing of fuel elements. 1 C.p. f-crystals, 4 Il.

The invention relates to the field of engineering and in particular to sealing tubular products, including fuel elements (cartridges) of nuclear reactors.

The rods usually are thin-walled metal tube filled with nuclear fuel. Their working conditions are characterized by the presence of high pressures, temperatures, factors of radiation exposure. The service life of the fuel Rods is a few years. The main requirement in determining their safe operation is the tightness of the membranes, the ka.

Known method of sealing Rods contact welding, which consists in fixing the shell to the mounting bracket with the specified departure and subsequent compression of its end with a plug having a diameter equal to the diameter of the shell, and passing a current pulse through the formed contact (cm. "The construction and operation of fuel cell power reactors", volume 2, pages 217-219, M. : Energoatomizdat, 1995) the disadvantages of the method are the need for subsequent machining and a small length of weld that does not fully guarantee the integrity of the fuel Rods.

Closest to the claimed its technical essence is a way of contact-butt resistance welding pipe cap, used in the manufacture of fuel Rods (see RF patent N 2082574, 27.06.97).

The method consists in fixing the depth side of the membrane in the device, compressing it with a plug, having a maximum diameter less than the outer diameter of the tube, but most of its internal diameter, and their mutual electric heating with the current distribution along the length of the weld zone. The method allows to obtain welds length of 2.5-3 wall thickness of the shell. Increase protyazhennosti. As a result, during welding, there is a significant reduction of the pressure in the junction as by increasing the area of the junction, and by reducing the component of the welding force, as the welding seam at least partially located at an angle to the axis of the fuel element. Violated the terms of the volumetric compression of the metal required to obtain a good connection. Large displacement of the stub lead to lower air pressure in the actuator welding force at the moment of precipitation stub, and accordingly to additional reduction of the pressure in the junction in the formation of a welded joint. The known method does not account for the high ductility of zirconium alloys when heated to temperatures close to the temperature of recrystallization. Because of the excessive heat deformation of the metal in the weld zone becomes cutoff and comes with a minimum specific pressure. Shown in the prototype, the ratio of distribution of welding current between the shell and the shunt does not provide the necessary heating of the shell and plug. This makes it difficult to obtain welds with the desired characteristics.

An object of the invention is to improve the quality of welds and reliability Hermetica method, consisting in fixing the depth side of the membrane in the device, then the compression cap having an outer diameter less than the outer diameter of the shell, but most of its internal diameter, and their mutual electric heating with the current distribution along the length of the zone of welding, the welding is performed with a variable that has two peaks, the rate of precipitation of the stub, when the rate of change of energy of a pulse of welding current is not less than 25 kA2and rate of rise of the welding current at the beginning of welding at least 1 kA/MS, and before the beginning of the second maximum welding force relative to the initial increase in 15-40%.

Presents a collection of characteristics is new and provides the desired effect.

The formation of a welded joint with a maximum length of weld is achieved by welding with two peaks in the velocity of the stub. Two peak velocities characterize the predominant initial heating of the welded joint parts and inner layers section of the shell at a distance equal to 3-4 wall thickness of the shell from its end. The first peak in the rate associated with the initial heating of the metal at the junction of the ends of the shell and plug. In reyaysa out, forming the outer Burr. High slew rate current at the beginning of the process (at least 1 kA/MS), defined as I/t, where:

I - peak value of the current, kA,

t is the rise time of the current from zero to the maximum value, MS

does not allow to warm up the shell to a temperature loss of strength throughout the welding area. Stub after some movement rests in the relatively cold inner layers of the metal shell, which are located approximately in the middle part of the weld and almost stops. The upper limit of the increase speed of the welding current is limited by the absence of outbursts. Further heating of this part of the welded joint is determined by several processes: heat transfer by conduction from the heated extreme areas of the membrane that are involved in the formation of the weld, the direct effect of welding current, the contact resistance between the shell and the plug, which is increased by moving the stub and reducing pressure in the joint. Uniform and excessive heating of the welded section of the shell leads to a preferential deformation of the inner layers of the shell are more massive and hard saguchi shell and the direction of action of the welding force, which leads to a sharp decrease in surface pressure in the joint and, as a consequence, the formation of the seam loose structure. To optimize the process of heating the Central part of the welded joint allows the introduction of a speed limit change of the equivalent energy of a pulse of welding current to a value not less than 25 kA2and increasing the welding force after the end of the first maximum speed for 15-40% of the original.

The rate of change of the equivalent energy of a pulse of welding current is defined as

< / BR>
where I is the instantaneous peak value of the welding current, kA;

- infinitesimal time;

T - time flow of welding current, with.

Increasing the welding force is less than 15% inefficient, more than 40% leads to the bursting of the door, and the formation of welded joints with the length of the weld is less than desired, while the second peak speed during the welding process is missing. The upper limit on the increase in the minimum rate of change of energy of a pulse of welding current limited also by the requirements on the length of the weld. The use of welding conditions with the rate of change of the equivalent energy of less than 25 kA2leads to excessive heating of the welded parts, the ear is mswb.

The proposed method is illustrated by drawings.

In Fig. 1 presents the scheme of welding;

in Fig. 2 - change the speed of movement of the caps in the welding process (V) and welding force (P);

in Fig. 3 - option of pulse form of the welding current;

in Fig. 4 shows the resulting welded joint.

The method is implemented as follows.

The end of shell 1 (Fig.1) is installed and fixed in the fixture 2. To the end of the shell is pressed welding force P cap 3, sandwiched in the clip 4. From welding source 5 through parts 1 and 3 is skipped impulse of welding current I with a slew rate of at least 1 kA/s and the rate of change of the equivalent energy of not less than 25 kA2(Fig. 3), which device 6 is distributed over the section 7 of the shell, causing increased heating due to the contact resistance in zones 8 and 9 of the shell.

As a current source the most appropriate use of specialized devices like inverter, providing a rapid increase in welding current of a given amplitude adjustment of the leading edge of the pulse due to the current feedback. Cover 3 under the action of the welding force P1 is moved vnutrivodnoe force P2. Under the action of high welding force and continuing the heating of the inner layers of the shell cap receives a second pulse speed V2 and enters the zone 9 of the shell. As a result of mutual deformation of the compressed surfaces of the shell and a stub formed welded joint (Fig. 4), the weld bead 10 which is located at an angle to the axis of the shell 11, is equal to approximately 15oand has a dense structure without rihlat and poor penetration.

1. Method of sealing tubular products contact welding, including fixing with a deep end of shell products in the fixture, followed by compression it with a plug having an outer diameter of more internal and less external diameter of the shell, mutual heating pulse of welding current with a current distribution along the length of the weld zone and the application of welding force for welding, wherein the welding is performed with a variable that has two peak values, the rate of precipitation of the stub, when the rate of change of the equivalent energy of a pulse of welding current is not less than 25 kA2and rate of rise of the pulse of welding current at the beginning of welding at least 1 kA/MS.

2. The method according to p. 1, characterized in that before the beginning of the second peak welding

 

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FIELD: mechanical engineering.

SUBSTANCE: proposed method is intended for manufacturing fuel elements using resistance-butt welding primarily for their joining to zirconium alloy cans. Welding is effected at equipment electrical resistance not over 30-fold resistance of can section forming welded joint having or not point discontinuities in the form of separate spots or chain of such spots forming no continuous line and measuring maximum ten thicknesses of weld in cross-sectional area of welded joint under check disposed at distance equal to two or three thicknesses of can wall from butt-end of plug located inside fuel element, welded joint being checked by uniformity of external fin. Length of poor fin formation section does not exceed 10% of joint perimeter.

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EFFECT: reduced labor consumption; enhanced operational stability; extended functional capabilities.

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FIELD: machine engineering, namely methods for contact-butt welding of tube with plug for making fuel elements of nuclear power stations.

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EFFECT: improved characteristics of articles, enhanced versatility of method.

4 cl, 3 dwg, 1 ex

FIELD: nuclear engineering; fuel elements of nuclear reactors.

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EFFECT: reduced hydraulic resistance to coolant flow in reactor, facilitated manufacture, universal mechanical design.

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EFFECT: provision of multipurposeness of method, improved quality of welding and service and technological characteristics of article.

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FIELD: mechanical engineering; welding; nuclear engineering.

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EFFECT: improved operating qualities of welded joints and their manufacturability.

1 ex, 2 dwg

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