DD141798A1 - METHOD OF MBL WELDING OF DICKWANDER CROSS SECTIONS - Google Patents

Abstract

The invention relates in particular to welding two tubular parts with wall thicknesses> 5 mra under use a magnetically moved arc. The goal is among these special conditions, the start-up time of the moving arc stabilize. It is necessary to provide for measures which have an impact on the start-up time of the arc taking into account the at this time building up rotating magnetic field in the welding gap. According to the invention is in the startup time of the moving Arc used a start-up flow, which in <0.05 s after the Ignition reaches a value that depends on the weld cross section and the wall thickness 1.4 to 1., 8 times the subsequently set ' Vorwärmstromes, wherein the starting flow in dependence of Stabilization state of the arc is limited in time and as Measure for the stabilization state and for the time limit of the starting current the frequency of rotation of the arc is taken and preferably, the switchover from the start-up stream to the Preheating at a circulation frequency of> 15 s "1 takes place.

Description

21.0 523

Method for liBL welding thick-walled cross-sections

Field of application of the invention

The invention relates to a method for MBL welding thick-walled cross-sections with closed seam, preferably for welding two tubular parts with wall thicknesses = 5 n "& t in particular to stabilize the arc while avoiding short circuits of the arc movement and achieving welds with a high weld quality.

Characteristic of the known technical, solutions

It is known that when welding with magnetically moved arc (MBL welding) pipe joints with wall thicknesses up to 5 πμ are welded. Under the effect of a radial magnetic field in the welding gap, the arc rotates along the closed mica surface and heats it. The molten joining surfaces are connected to each other by an upsetting impact.

After the DD-PS 129 179, the heating of the abutting edges Suren a current program controlled From the ignition of the arc out the current with a small increase to a constant value, the preheating. is then brought _ί to then briefly in the last arc burning phase, a high current with very high slew rate -check effect. Unsolved case remains a stabilization of the arc start-up phase _t the thick-walled for welding sections imperative is "The very small current rise after ignition of the arc and then adjusting to low power cause interference by jumpers *

According to DE-OS 155 5041, the starting current is kept small and the radial magnetic field is set high. When the arc has been set in the desired rotational motion, the current is increased and the magnetic field is reduced. This method is applicable to tubes up to 5 mm Wall thickness ₆ For thick-walled pipes, this does not prevent faults in the start-up phase due to short-circuit bridges. ",

Uach DE-OS 25 O? 448, the arc current is so programmed that it has a very small value after the ignition, and from the latter rises slowly _β ILrst towards the end of Erwäroiungsvorganges is the current strength very quickly erhöhte.Für uniform heating of thick-walled pipes an auxiliary magnetic field is proposed. The device for generating this field is arranged inside the tube and thus very problematic for the practical implementation. The stabilization of the start-up phase remains unresolved, too.

It is known that the rotating magnetic field built up in the welding gap is composed of

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the field of induction coils from the outside and the field of the welding arc.

Measurements in the welding gap showed that over the wall thickness, starting from the outer edge in the direction of the inner edge, a strong drop in field density is present. The field at the inner edge becomes so small for tubes with wall thicknesses> 5 mm that the arc stops at this point, forms a short-circuit bridge and goes out. An increase in the magnetic induction from the outside has a higher field density only at the outer edge but has no decisive influence on the field density at the inner edge. Only an increase of the welding current also increases at the inner edge of the arc moving field.

Object of the invention

The invention provides a method for MBL welding thick-walled cross-sections to provide that stabilizes the starting time of the moving arc under these special conditions.

The essence of the invention

The invention has for its object to develop a method for MBL welding thick-walled cross sections with closed seam, preferably for welding two tubular parts with wall thickness = 5 mm and propose measures, "take the influence on the startup time of the moving arc, taking into account at this time building up rotating magnetic Feldesim welding gap, so »that the heating process disturbing short circuits are eliminated and a tearing of the arc does not take place.

According to the invention, the object is achieved »that in the startup time of the moving arc, a start-up current .verwendet that in ~ 0 _$ 05 s- after ignition reaches a value» depending on the weld cross-section, and the wall thickness of 1.2 to 1.8 times the subsequently set preheating is, wherein the starting current is limited in time as a function of the stabilization state of the arc and as a measure of the stabilization state · and for the time limit of the starting current, the rotational frequency of the arc is taken and that preferably the switching from the starting current to the preheating current at a TJmuffre-

-1

a = 15 s is carried out »If the wall thicknesses of 7 mm are to be welded, the stabilization process is to be assisted by a variable welding gap so that this immediately after ignition at the maximum distance of the welding gap, preferably 2.2 to 2 _? 5 tarn »and then synchronously with the switching on of the Yorwärmstromes or just before it is reduced to the normal distance of the welding gap of 2 mm ... Thus, it is possible ^ thick-walled pipe parts to weld together, the arc is stabilized, the arc movement free from Short-circuiting, crater formation does not occur at the weld seam edges and weld seams with a high seam quality are achieved «

embodiment

The invention will be explained in more detail below with reference to an exemplary embodiment with the aid of the diagram shown in the drawing, which shows the welding current I ", the welding gap b and the rotational frequency η as a function of time *

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There are two welded parts to be joined together, which are pipes rait a diameter of 71 mm and a wall thickness of 5 mni, material St 35 b-2, is. The arc is ignited in a known manner by contact and moving apart of the two welding parts on welding gap b. It is welded with a constant welding gap b = 1.8 mm. For larger wall thicknesses must be worked with a variable welding gap. With the help of the ignition current "! _>, A starting current of 550 A is set, which is 1.6 times the

- '· - · -. Preheating current I _g o · It is started with a starting time t>, =

3 s worked, after which the starting current Ip reached after ignition and an effective process is ensured. On the preheating current I - is switched when the arc is stable burning, its movement is not affected by short circuits

-1 and a rotational frequency η of the arc over I5 s

is reached. The start-up time t * with increased current lasts for a maximum of 6s.

If you work with a variable welding gap b, this is set with the ignition of the arc for the duration of the starting time t _s ^ to a maximum distance Λ b ^ between 2.2 to 2.5 mm. With the Um

switching to the preheating current I- the reduction of the welding gap b to the normal distance b ₂ = 2 mm takes place. The welding process then proceeds in a known manner.

Further parameters: welding current I = 85O A, preheating time t _g2 = 19 &, welding time t _s -, = 0.1 s.

Claims (2)

E rf i η d η g s a η s ρ r u c h 1 * Method for MBL welding thick-walled cross-sections with closed seam course, in particular for welding two tubular parts with wall thicknesses = 5 HIm ₅ preferably for stabilizing the magnetically moved arc while avoiding Eursschlüssen the arc movement f characterized by _f that in the startup time (t_ ^) of the "moving arc, a starting current (I _o p) is used" in which = 0.05 s after ignition reaches a value which, depending on the welding cross-section and the wall thickness of 1, '2 to 1.8 times the subsequently set Preheating current (I-O, wherein the starting current (Ι _ο ρ) is limited in time as a function of the stabilization state of the arc _s ., That as a measure of the stabilization state and for, temporal limitation of the starting current (I _o p), the rotational frequency (n) the arc is taken, and preferably, the switchover from the start-up current (I _g p) ^{to s} ^ ^ preheating current ( "Ο at a he circulation frequency (η) = 15 s ", 2 »Method for MBL welding of thick-walled cross sections with closed seam course as per point 1 | characterized in that, in particular in the case of wall thicknesses of 7 mm to be welded, the stabilization process is assisted by a variable welding gap (b), which immediately after ignition to the maximum distance (b 1) of the welding gap (b), preferably to 2 , 2 to 2 ₅ 5 dm? and then synchronously with the switching on of the preheating current (I " _o ) or shortly before it is reduced to the normal distance (" boO of the welding gap (b) of <2 mm "). - For this a sheet of drawings "-