WO2010024709A1

WO2010024709A1 - Method for flash-butt welding thin-walled casings

Info

Publication number: WO2010024709A1
Application number: PCT/RU2008/000575
Authority: WO
Inventors: Сергей Владимирович ЛУКЬЯНЕЦ; Николай Григорьевич МОРОЗ
Original assignee: Lukyanets Sergei Vladimirovich; Moroz Nikolai Grigorievich
Priority date: 2008-08-27
Filing date: 2008-08-27
Publication date: 2010-03-04

Abstract

The invention is directed to removing microdefects from and increasing the quality of a welded joint. The above-mentioned technical result is achieved in that the method for flash-butt welding especially thin-walled, preferably flexible casings comprises the preparation of the abutting end faces, butt-mounting said casings on centring apparatuses and combined melting under conditions in which the gap provided between the mutually adjoining surfaces which is sufficient for producing welding is initially maintained, wherein deformation of microprojections is performed on each of the abutting casings by means of plastic deformation along the surface being welded of the end face with shortening thereof by a value of Δ h = a δ + b δ2/ R by means of rollers with an irregularity parameter of Ra ≤0.16 μm, the deformed metal is moved along the end face of the semi-finished product to the side of the inner surface and an inner annular belt extension is formed thereon which has a width within the range of 0.5 - 1.5 δ and a thickness within the range of 0.2 - 0.5 δ, the abutting casings are mounted in a centring (in relation to the outer diameter) device and the abutting casings are spot-welded in advance along the perimeter in the plane of the seam, with a stepwise movement of the electrode of 20 - 50 δ, wherein the main continuous welding is performed in such a way as to form a weld penetration zone with a width of 4-6 δ, wherein heat elimination in the parts being welded begins to be achieved at a distance which is no more than 6 - 8 δ from the plane of the seam, where δ is the thickness of the wall of the casing being welded, in mm; а and b are the constant coefficients for the range δ/R = 0.003÷0.01 which are equal to 0.1 - 0.3 and 0.075 - 0.375, respectively; R is the radius of the casing being welded, in mm.

Description

METHOD OF BUTT WELDING MELTING THIN-WALLED

SHELL

Technical field

The present invention relates to welding production, and in particular to the field of flash butt welding technology in the environment of shielding gases with the supply of halogen reagents to the welding zone, and can be used for welding especially thin-walled shells, tube blanks, etc. from stainless steels.

State of the art

To perform welding of especially thin-walled products with large cross-sections, it is necessary to ensure complete coincidence of the joined edges of the products, both in thickness and in perimeter, in compliance with the alignment and accuracy of centering of the parts to be welded.

In addition, with regard to welding of especially thin-walled products without special preparation of parts, it does not seem possible to carry out high-quality melting of the butt ends due to the commensurability of the roughness parameters and the thickness difference of the butt ends with their thickness. This is due to the fact that in flash butt welding due to the random nature of the formation of contact jumpers at the butt ends under the action of the welding current flowing through the contact jumpers, the metal of the jumpers quickly overheats and is ejected from the welding zone. In addition, due to the specific features of metal heating during continuous reflow, it is not possible to obtain a sufficiently wide heating zone necessary for high-quality welding of products with large cross sections. At present, it is generally recognized that the quality of surface layer preparation (roughness, waviness, wear resistance, microhardness, residual stresses) of parts affects their weldability.

It is also known that when welding particularly thin-walled products with large cross-sections, an unequal change in the perimeters of the welded workpieces occurs due to temperature-force deformations that occur in the material of the welded workpieces during the implementation of the welding process. These changes in the lengths of the perimeters lead, at best, to warping of the welded workpieces or to burning of the welded workpieces. For high-quality implementation of the welding method thin-walled shells, it is necessary to ensure full coincidence of the joined edges of the products, both in thickness and in perimeter, in compliance with the alignment and accuracy of centering of the parts to be welded, and to maintain such a state during the welding process itself.

A known method of preparing and assembling for welding ring joints, mainly non-rigid structures, including machining the edges to a predetermined size and assembling on a centering expansion ring, first, each of the parts to be welded is mounted on a centering ring, the rings are expanded, the edges to be welded elastically deform, and their mechanical processing, and then the assembly of the joint is carried out, for which the rings are aligned on the coaxially mating surfaces (SU 1185781 Al, 04/27/2006).

The disadvantage of this solution is that when machining for the case of thin-walled parts, ends are formed with a roughness commensurate with the wall thickness of the parts, which does not allow for their high-quality welding.

A known method of preparing pipe edges for welding, including turning and cold deformation of the pipe end with the formation of a filler protrusion on its upper edge, the end of one of the pipes to be welded is cut with a cutter at an angle of 90 ° to its axis, and the end of the second pipe is machined from the inside at 90 °, leaving an annular protrusion with a thickness and a length of not more than 4 mm in the upper part of the end face, then this annular protrusion is bent outward at an angle of 45 to 90 ° with the roll roller, and the resulting bent protrusion is pumped, giving it in the butt echnom sectional shape of the protrusion of the filler in the form of an isosceles triangle or isosceles trapezium or rectangle, and then a projection end of a filler eat through a cylindrical cavity with an inner diameter equal to the outer diameter of the first pipe end (RU 2288827 Cl, 10.12.2006).

The disadvantage of this solution is that it does not allow for their high-quality welding.

The prototype of the proposed solution is the decision on the application RU -N ° 95118844 A, 11/20/1997. This solution proposes a method consisting in placing a workpiece in a matrix on a support and applying upsetting forces to the workpiece from the end tool from the rolling tool to ensure redistribution of the phase composition components of the workpiece metal during shaping, up to crystallographic level with a phenomenological combination of physical characteristics.

The disadvantages of this solution is that under the action of high contact pressures, compression and redistribution of material that does not move away from the treated area occurs in a given direction, which does not ensure the quality of preparation of welded thin-walled shell blanks.

Disclosure of invention

An object of the present invention is to provide a method for welding ring joints of thin-walled shells to produce various closed containers.

The technical result of the invention is the ability to improve the quality of the weld due to the creation of a dense, fine-grained structure and the absence of microdefects, the ability to remove the necessary material from the treated area, which ensures the quality of preparation of the welded thin-walled shell blanks, as well as simplifying assembly technology using a reliable and simple in design devices.

The technical result is achieved by the fact that the method of butt welding by fusion of thin-walled mostly non-rigid shells comprises preparation of butt ends, installation in a joint on centering devices and joint melting provided that the established gap between adjacent surfaces sufficient to form a weld is preliminarily maintained, while each of the joined shells by plastic deformation carry out the deformation of microprotrusions along the welded end surface with its upset by Δ h = a δ + b δ / R with rollers with a roughness parameter Ra <0.16 μm, the deformable metal is moved along the end face of the workpiece toward the inner surface and an inner annular process is formed on it - a girdle with a width within (0 , 5 -1.5) δ and a thickness in the range of (0.2 - 0.5) δ, install abutting shells in a centering device on the outer diameter, and preliminarily along the perimeter in the interface plane perform their spot stitching-welding with stepwise movement of the electrode (20 - 50) δ, and the main continuous welding is carried out with the image a zone of penetration, the width of which is (4-6) δ, while the heat is removed in the welded parts begin to implement at a length of no more than (6 - 8) δ from the joint plane, where δ is the wall thickness of the welded shell, mm.,

a, b are constant coefficients for the range δ / R = 0.003 ^' 0.01, respectively, equal to 0.1 - 0.3 and 0.075 - 0.375;

R is the radius of the welded shell, mm

The deformation of the microprotrusions at the end and its upset is limited by the radial deformations of the outer side surface adjacent to the end.

The deformation of the microprotrusions at the end and its upset is carried out with simultaneous run-in by the rollers adjacent to the end of the outer side surface.

The deformation of microprotrusions along the welded surface of the end face is carried out by rollers with a diameter equal to (4-6) δ and with a material hardness parameter HRc> 65.

The deformation of the microprotrusions along the welded surface of the end face is carried out with a contact force of 200 to 300 H.

Spot stitching is carried out in two turns with an offset at the second turn half a step from the first stitching.

Thin-walled annular belts on the inner surfaces of the welded shells have one inner diameter for each of the welded shell blanks.

Thin-walled annular belts on the inner surfaces of the welded shells are made at an indirect angle into each of the welded shell blanks.

Protective gas media of various compositions are supplied to the material heating point from the outer and inner surfaces of the welded shells.

After plastic deformation before welding, the end surfaces of the workpieces are washed with solvent.

The advantage of the invention lies in the simplicity of its implementation and consumer appeal.

Brief Description of the Drawings of the Invention

In FIG. 1 and FIG. 2 shows a diagram of a plastic deformation process. In FIG. 3 shows a diagram of the surface roughness of a part. In FIG. 4 shows a simplified diagram of a stress field. In FIG. 5 shows a diagram of an formed bead.

In FIG. 6 shows a diagram of the formation of stresses during single-pass butt welding of plates.

In FIG. 7. shows the formation of transverse shrinkage during single-pass butt welding.

8 and FIG. 9. shows the deformation in the plane when welding narrow and long plates.

Embodiments of the invention

As a rule, manufactured especially thin-walled shells and tube blanks from semi-finished sheet products due to deformation during their production have deviations in the linear dimensions of diameters, thicknesses, end face finish, etc.

It is known that the microgeometry of a real treated surface depends on a large number of different factors (cutting conditions, shape errors, vibration of the technological system, etc.), therefore it is considered as the realization of a random field of microroughnesses and is determined by indicators of the type Rz, Rc and Ra.

Adsorption of various gases occurs on parts with surface irregularities, which, in addition to the effects noted above, leads to significant difficulties in welding thin parts. The amount of adsorbed gases in metals and alloys strongly depends on the degree of roughness of their surface. So, in most ultrahigh-vacuum chambers of analytical and technological installations produced by many well-known companies, their inner surface is usually machined to a roughness level of Ra 1-3 microns. Such a surface in cross section looks approximately as shown in FIG. 1.

If it is possible to polish this surface to a roughness Ra of 0.1-0.3 μm, then its real area decreases by more than an order of magnitude. The total number of defects in the structure becomes much smaller, and this surface looks approximately as shown in Figure 2.

It is possible to achieve high purity of the treatment by treating the prepared surface with plastic deformation methods, for example, by rolling rollers with the working surface cleanliness parameter Ra <0.16 μm and the material hardness parameter HRc> 65. On Fig.3 shows the deformation of the surface layer when the tool is moving perpendicular to the plane of smoothing. Pressed to the work surface with a force P _{y, the} tool is embedded into it to a depth of R _d and during its movement smooths out the initial irregularities. After the passage of the tool, a partial elastic restoration of the surface by Δ ^ occurs.

As a result of plastic deformation of the treated surface, the initial roughnesses are smoothed out and a new surface microrelief is formed with a significantly lower roughness height Rz. The size of the part is reduced by the value of permanent deformation Δ pv-

A feature of the process of plastic deformation is that in front of the smoothener a platically deformed metal roller R B _{is formed} , which is smeared as a result of repeated exposure.

A feature of the proposed solution according to the invention is that in this case, when smoothing, the deformed material roller is not smeared or removed, but undergoes additional elastoplastic deformation in the direction perpendicular to the movement of the tool. That is, this solution proposes to shift the material roller formed in front of the smoother in a direction perpendicular to the motion of the smoother.

The optimum deformation smoothing force is Py = 200 - 300 H. At Py = HOO, the depth of the hardened layer increases, the microhardness in the lower layers increases, but the microhardness in the upper thin surface layer decreases, due to a decrease in ductility.

Figure 4 shows a simplified diagram of the stress field that occurs during plastic deformation of the roller.

Point A 'defines the length L of the front wave outside the contact surface of the wave BA ¹ . A ⁷ K ⁷ D ⁷ C ⁷ is the boundary of the region of developed plastic deformations, the lower point of which determines the thickness of the hardened layer h. Deformation fields located below this point do not cause a noticeable change in the metal resistance to plastic deformation. Lines BK ⁷ and KA ⁷ approach BA ⁷ at an angle π IA. For geometric reasons:

At the most frequently used processing modes 1 "h _in . h - 0.7Z (2) Studies have found that

L - 2, W ^W (3)

Substituting (3) in (2) we obtain the amount of draft in one pass of the deforming tool. k = \, 5 <Jd (4).

As already noted, in accordance with the proposed solution, in the process of smoothing the end of the part, the formed wave of material is proposed to be displaced in the direction of the inner surface of the part to be welded, and as a result, to form an annular collar (process - girdle), locally increasing the thickness of the part wall and several times increasing local bending stiffness of the trot. (Figure 5). So, with the flange values equal to 0.5-1.5 of the wall thickness, the local bending stiffness of the end increases by 3.37 - 15.625 times.

The formation of a shoulder with such parameters greatly simplifies technological manipulations during the preparatory work for welding.

Taking into account the value of the end face settlement h obtained in one pass of the deforming tool and based on the equality of the displaced volume of material and the volume of material in the formed collar, the total value of the end face settlement Δ h can be determined by the simplest dependence

Δ h = a δ + b δ ² / R

where a, b are constant coefficients for the range δ / R = 0.003 ^' 0.01, respectively, equal to 0.1 - 0.3 and 0.075 - 0.375; δ is the thickness of the initial metal billet, mm; R is the radius of the neutral layer of the workpiece, mm

It is also well known that when welding shells or plates end-to-end, a biaxial stress state of the metal arises in the welding zone.

A typical picture of the stress distribution in a metal during movement of a hot heat source is shown in Fig.6.

The part of zone // adjacent to zone / is characterized by the presence of significant transverse compressive stresses σу. Here, plastic deformations of the metal occur. In zone IIIa, which experiences heating during the movement of the heat source, compressive stresses σx and σy increase, and near the zone / stress σy are insignificant. The increase in compressive stresses σx with the occurrence of plastic shortening strains is replaced at the boundary of zones IIIa and IIIb by a decrease in compressive stresses, and then their transition as the metal cools into tensile stresses. At the boundary of zones / and IV, the stresses are close to zero, and in zone IV σx and σy are tensile. As the source moves away in a zone of width 26 where plastic deformations occurred, residual tensile stresses σx arise. In a metal outside the zone of plastic deformation 26, with a large plate width, the stresses turn out to be close to zero.

The results of determining the displacements of the plate edge when heated by a moving heat source can be used to explain the mechanism of the formation of transverse shrinkage in the weld zone.

If two plates are welded with a gap (Fig. 7, b), then the edges of each of the plates will experience transverse displacements v. In front of the heating source, nothing prevents the edges from moving towards each other. At the moment of welding of the edges, the displacements reach the maximum value vmax, and the mutual approximation of the edges is 2 vmax. If the metal after welding, being at high temperature, had high strength, then a decrease in v behind the heating source would immediately lead to the pulling of the plates to each other and the formation of transverse shrinkage 2vmax. In fact, in the OA region, the metal has a small resistance to plastic deformation, as a result of which the metal flows in this region and elongates by 2 (vmax - vA).

At point A, the plastic elongation of the metal in the direction across the seam ceases; mutual convergence of edges is 2vA. Subsequently, after complete cooling of the metal, transverse shrinkage Apop = 2vA occurs. The magnitude of plastic deformation, i.e., the difference 2 (vmax - vA), depends mainly on the mechanical properties of the metal and on heat transfer to the air. The higher the heat transfer, the faster the v curve behind the source decreases. In this case, the decrease in v does not correspond to the decrease in the temperature of the metal. Therefore, with a smooth decrease in v (dashed curve in Fig. 7, a), the value of 2 vA increases and plastic deformation decreases.

In fusion-welded plates, the edges in front of the heat source cannot move unhindered. Up to a certain point B (Fig. 7, a), an elastic indentation of the metal occurs due to the fact that the edges abut against each other. From point B to point D, plastic deformation of the metal deposition occurs. In this area CB, which experiences elastic deformation, affects the value of Vmax at point D due to the elastic interaction of the metal sections of the BC and BD. As a result, when welding plates without a gap, and also when a whole uncut plate is penetrated, the value of 2 vmax is less, and therefore the transverse shrinkage of 2vA is less. Transverse shrinkage in this case is 15 - 20% less than when welding with a gap. With perfectly elastic course of the welding process of two plates end-to-end, the maximum possible value of 2 vmax is expressed by the formula

2υ - 2 -. -2-

The actual value of the transverse shrinkage that occurs at the time of welding and remains after the plates have completely cooled is less than theoretically possible.

For single-pass electric arc welding of plates, when they are assembled without a gap, α q

Δ _rtαfl <(0.5 ÷ 0 _f 7) 2v _mzh = (1.0-I.4) -— - ^

The formula is valid for low carbon, low alloy and austenitic steels, as well as for titanium and aluminum alloys up to a thickness of about 16 mm.

The transverse shrinkage of the butt-welded plates is not detected immediately after welding, but only after the plates have completely cooled, although the edges converge directly during their welding.

During the passage of the heating source, a relatively narrow metal zone, namely, heated to a high temperature, takes part in the movements. Therefore, the fixing of the plates has practically no effect on the lateral movement of the edges during welding. Only at the cooling stage, when the fastenings are strong enough, plastic deformation of the metal is possible, leading to a decrease in transverse shrinkage. In the initial sections of the seam, quasi-stationary movement of the edges is not achieved, the transverse shrinkage is somewhat smaller in magnitude than in the rest of the seam.

When re-heating in the same place, the transverse shrinkage from the second seam is equal to the shrinkage from the first seam, if the heating conditions have not changed. If the plates are welded with a gap, it may turn out that even before the heat source approaches due to temporary deformations, the edges can approach or move away from each other. In this case, the complete transverse shrinkage will consist of displacements resulting from temporary deformations of the plates as a whole and displacements directly in the weld zone. When welding plates assembled without a gap or assembled on tacks, transverse shrinkage, as a rule, does not depend on temporary deformations. The exception is cases when, for example, parts assembled without a gap, but not fastened together, during the welding process depart from each other. Departure of the plates from each other and the opening of the gap during welding can occur due to two reasons: the so-called temporary structural deformations and uneven heating of narrow plates in width. The deformations of narrow plates from uneven heating in width are essentially longitudinal bending deformations in the plane (Fig. 8). The bending of the plates occurs due to the fact that the heated side of the plate expands, while the cold side resists this expansion. As the plate width decreases with constant power of the heating source, the deformations caused by the rotation of the sections increase. However, very narrow plates can warm up completely to high temperatures and not have significant angular deformations.

The width of the plates, at which deformations from the rotation of the sections can be neglected, depends on the welding mode and the thermophysical properties of the metal. For

an objective assessment of the width of the plates should use the ratio b _a , where B is the width of one plate, 60 is the width of the zone heated to a temperature at which the yield strength of the metal is close to zero.

If we use the theory of powerful fast-moving heat sources, then the bO value can be found by the formula h - °> ²⁴² I 0 ^~ cγГ _β ^' M ^#

At ⁰ O ratios, the plates can be considered wide, and the angular deformations from uneven heating are insignificant.

Longitudinal residual shortening strains during butt welding, if there were no bending strains during welding, is determined by the formula

Δ - b £ p _ ι j I where * "° c ^' - shrink power,

/ and F is the length and cross-sectional area of the welded plate.

When welding two plates of different widths (Fig. 7, b), the shrinkage force Rus, located at a distance yO from the central axis, creates a bending moment M. The welded plates after cooling, in addition to longitudinal shortening

Δ 1 „ ^{? U} < ¹ will also bend.

The above considerations and dependencies make it possible to choose the optimal dimensions of the fused zone, the minimum length with which it is necessary to remove heat from the fused zone, as well as to establish the optimal dimensions of the length of the stuck parts in order to eliminate warpage during welding and reduce residual stresses in the welded structure.

In accordance with the proposed solution, the task of choosing the optimal parameters of the welding process is achieved by the fact that the concentrated abutting shells around the perimeter in the joint plane are pre-stitched by spot welding with a given step electrode movement (20 -50) δ, and the main continuous welding is carried out with the formation of a penetration zone, whose width is (4-6) δ.

The task is also achieved by the fact that during the implementation of the welding process, heat is removed in the parts to be welded at a length of no more than (5 - 8) δ from the junction plane of thin-walled shell parts.

The technical result of the invention is achieved in the ranges of these ratios obtained experimentally.

The inventive method is as follows.

Preliminarily, on special devices on the shells of the workpieces, microprotrusions are deformed along the welded surface of the ends with their draft by Δ h and the end roughness parameter Ra <0.16 μm is reached. On these special devices, the deformable metal is moved along the ends of the workpieces towards the inner surface and inner ring belts are formed on them with a width in the range of (0.5-1.5) δ and a thickness in the range of (0.2 - 0.5) δ.

Install mating shells in a centering device on the outer diameter. Moreover, the design of the centering device provides special cooling elements. After installing the shells of the workpieces in the centering device and checking the alignment of their ends along the perimeter in the joint plane, they perform spot stitching-welding with stepwise electrode movement (step) (20 -50) δ. After local stitching of the blanks shells, the main continuous welding is carried out with the formation of a penetration zone, the width of which is (4-6) δ. In this case, heat is removed in the parts to be welded in the direction perpendicular to the seam at a length of no more than (6-8) δ from the joint plane. The cycle of spot stitching and main welding can be carried out automatically, that is, by the software of the welding machine.

To verify the claimed technical solution, samples of welded shells with a thickness of 0.5 mm and a diameter of 147 and 213 mm were made of stainless steel 08X18Hl OT. Samples of welded pipe joints were obtained by pulsed-arc welding with a non-consumable electrode in an atmosphere of argon, nitrogen and hydrogen. Welding was performed with a TIG welding head. The results obtained confirmed the technical and economic efficiency of the proposed solution.

Using the proposed method, it became possible to obtain welded structures such as closed vessels in the form of thin-walled liner shells. The manufacture and testing of thin-walled shells - liners made using the proposed method have confirmed their high reliability and efficiency.

Industrial applicability

The invention can be used in the aviation, space, chemical fields of technology in the manufacture of containers from corrosion-resistant steels, aluminum alloys and other materials. In addition, the invention can be used in the manufacture of pressure cylinders and the construction of pipelines, for storage and transportation of liquid and gaseous media.

Claims

Claim

1. The method of butt welding by fusion of thin-walled shells, characterized in that it contains the preparation of abutting ends, installation in a joint on centering devices and joint melting, provided that the established gap between adjacent surfaces is sufficient to form a weld, while on each of the joined shells by plastic deformation carry out the deformation of the microprotrusion along the welded surface of the end with its draft by the value Δ h = a δ + b δ ² / R roll with a roughness parameter Ra <0.16 μm, the wrought metal is moved along the end face of the workpiece toward the inner surface and an inner annular process is formed on it - a girdle with a width in the range of (0.5-1.5) δ and a thickness in the range of (0, 2 - 0.5) δ, install the mating shells in a centering device on the outer diameter and pre-perimeter in the plane of the joint perform spot stitching-welding with stepwise electrode movement (20 -50) δ, the main continuous welding being carried out with the formation of a penetration zone, width which d is (4-6) δ, wherein the heat dissipation in the welded parts begin to carry a length of not more than (6 - 8) δ from the joint plane where δ - the wall thickness of the welded shell mm .;

a, b are constant coefficients for the range δ / R = 0.003 ^" 0.01, respectively, equal to 0.1 - 0.3 and 0.075 - 0.375; R is the radius of the welded shell, mm.

2. The method according to claim 1, wherein the deformation of the microprotrusions at the end and its upset is limited by the radial deformations of the outer side surface adjacent to the end.

3. The method according to claim 1, wherein the deformation of the microprotrusions at the end and its upset is carried out while rolling the rollers adjacent to the end of the outer side surface.

4. The method according to claim 1, wherein the deformation of the microprotrusions along the surface to be welded is carried out by rollers with a diameter equal to (4-6) δ and with a material hardness parameter HRc> 65.

5. The method according to claim 4, in which the deformation of the microprotrusions along the welded surface of the end face is carried out with a contact force of 200 to 300 H.

6. The method according to claim 1, in which the dot stitching is carried out in two turns with an offset at the second revolution by half a step from the first stitching.

7. The method according to p. 1, in which thin-walled annular belts on the inner surfaces of the welded shells perform one inner diameter for each of the welded shell blanks.

8. The method according to p. 1, in which thin-walled annular bands on the inner surfaces of the welded shells are performed at an indirect angle into each of the welded shell blanks.

9. The method according to claim 1, wherein various compositional protective gas media are supplied to the heating point of the material from the outer and inner surfaces of the welded shells.

10. The method according to claim 1, wherein after plastic deformation before welding, the end surfaces of the workpieces are washed with solvent.