SU1699739A1 - Method of consumable electrode multiarc welding - Google Patents

Abstract

The invention relates to the metallurgical industry, in particular to the production of welded pipes of large diameter. The purpose of the invention is to reduce the metal consumption of pipes from low carbon and low alloy steels by improving the quality of the initial seam section. In multi-arc welding with melting electrodes, at the beginning of the welding process, the electrodes are set at different distances from the pipe surface and are fed simultaneously with the slowed-down speed. The welding speed in the initial part of the pipe is chosen equal to the slowed-down feed rate of the electrodes, and after igniting all the arcs, the welding speed is increased to operating values. At the same time, before the start of welding, the ends of the second and subsequent electrodes are set at a distance from the pipe surface equal to the sum of the distance from the end of the first electrode to the pipe surface and the distance between the first and next electrodes. Switching from the slowed-down feed rate of each of the electrodes to the working one is made in 0.1-1.0 s after ignition of the arc. The implementation of the method allows to reduce the length of the initial seam to be cut in half. 1 ip., 1 tab. sl C

Description

This invention relates to the metallurgical industry, in particular, to the production of large diameter welded pipes.

The purpose of the invention is to reduce the consumption of metal pipes by improving the quality of the initial seam section and reducing the cut of the front end of pipes.

The drawing shows a diagram of the method of welding.

The method is carried out as follows.

Before the start of welding, electrodes 1 and 2 are exposed at distances I and 2 from the surface of pipe 3, respectively. At the moment when the supply of electrodes 1 and 2 is turned on with a slower speed, the pipe 3 is also moving with a slow speed VTp Vn.3. During the time ti from the moment the feed is turned on, the end of the electrode 1 will travel a distance h and touch the surface of the pipe 3 at point A, which during this period of time will also travel a path equal to I. Thus, the ignition of the arc of electrode 1 will occur at point A.

If the distance from the end of electrode 2 to the surface of pipe 3 is 2 AND E2, where 32 is the distance between the ends of electrodes 1 and 2 when they simultaneously touch the surface of pipe 3, then it will meet with pipe 3 at point A.

After touching the surface of the pipe 3 with the electrode 1 and the arc is ignited

Ltd

VI

W

about

burning the end of the electrode and increasing the arc gap. Since the electrode feed rate is slowed down and does not correspond to the set value of the no-load voltage of the welding current source, the arc length will increase and the welding current will drop to complete arc breakage. the time interval from the moment of ignition of the arc to its interruption depends on the degree of decrease in the electrode feed rate and welding mode. It was established experimentally that with the recommended reduction in the electrode feed rate to 0.3-0.7 of its working value and in the range of modes used for multi-arc welding, the time from the moment the electrode touches the pipe surface and the arc starts to switch from the slowed electrode feed per worker should be in the range of 0.1-1.0 s. When switching to the working feed rate earlier than 0.1 s after the electrode touches the pipe surface, the reliability of a stable ignition drops even when the feed rate (Vn.s / 0, e) is significantly slowed down and the welding current is high (1cv 1300-1500 A). When switching to the working feed rate later than 1.0 s after the tube touches the pipe surface, the probability of an arc break even increases with a slower feed rate (Cp / 0,7UPe) and a high working voltage drop across the arc (U 50-55 V).

Thus, switching from the slowed-down feed rate of the electrode 1 to the worker should be made through (g-t- +

Vn.s. 2,

+0.1 ... 1.0), and from electrode 2 - through (Vn .3

after turning them on.

 and -r-tg- - spansVn e.

+ (0.1 ... 1.0) with Here E

The names required for the electrodes to reach the pipe surface from the initial position.

The method can be carried out with any number of electrodes, for example, with three-arc and four-arc welding. At the same time, before welding, the ends of the second and subsequent electrodes must be exposed at distances from the pipe surface equal to It + an. where If, the distance along the axis of the nth electrode from its end to the surface of the pipe, an is the distance from the end of the nth electrode to the end of the first electrode on the surface

0

five

0

five

0

five

0

five

0

five

pipes. In this case, switching from the slowed-down feed rate of each of the electrodes to the working one

 + () s after powering on

electrodes, where v n e - the speed of slow-motion electrodes.

In this case, the ignition of all the arcs occurs at a single point on the surface of the pipe, which allows, with any number of arcs, to obtain the specified geometric parameters of the seam at a very small distance from its beginning. In addition, the second and subsequent electrodes make electrical contact not with cold metal, sometimes covered with scale and rust, but with the molten metal of the weld pool formed when the arcs of the preceding electrodes are ignited, which increases the likelihood of the arcs to appear at the first contact by 100%.

The slowing down of the welding speed at the initial part contributes to the reliability of the arc burn and, moreover, to an even greater degree reduces the initial part of the seam where its dimensions do not meet the requirements. Switching from the slow welding speed to the working value should be done not earlier; what will switch the last electrode to the working feed rate. Otherwise, the ignition of all electrodes at one point of the pipe will not be ensured and the poor quality section of the seam to be trimmed will be increased.

Example. Welded pipes with a wall thickness of 12 mm in the external welding mill.

The mode of two-arc pipe welding and the parameters defining the beginning of the welding process are listed in the table.

The distances H and H were provided by the reverse of the electrodes at the end of the welding of the previous pipe.

The proposed method makes it possible to reduce the length of the initial portion of the seam to be cut from an average of 70-90 to 30-40 mm.

Claims (1)

The Invention Method A method of multi-arc welding with melting electrodes, in which at the beginning of the welding process the electrodes are simultaneously served at a slower speed, and after ignition of the arcs they increase the feed rate of the electrodes to operating values, characterized in that, in order to reduce the metal consumption during welding low-alloy steels by improving the quality of the initial weld section, the electrodes are set at different distances from the pipe surface, and the welding speed is chosen at the initial pipe section equal to a slower feed rate of the electrodes, the ends of the second and subsequent electrodes being set at a distance from the pipe surface equal to the sum of the distance from the end of the first electrode to the tube generator and the distance between the end of the first electrode and next, starting from the second electrode, determined on the tube generator. ; switching with a slower feed rate of each of the electrodes to the working one after ignition of the arc of the scribe is ignited, a time interval of 0.1-1.0 s, with switching off with a slowed welding speed to the working one, after switching to the working feed speed of the last electrode.