RU2293001C1 - Method of submerged multiarc welding - Google Patents

Abstract

FIELD: mechanical engineering; welding.

SUBSTANCE: invention can be used for submerged multiarc welding of large-diameter tubes. Proposed method includes striking of welding arcs, welding and sequential extinction of welding arcs at simultaneous reduction of welding rate. At beginning of welding, arcs are struck in turn at a distance from beginning of tube providing identity of initial part of weld seam as to depth of penetration, width and form, to indicated parameters of seam in zone of welding at steady-state conditions. In process of welding specific heat input of welding is maintained at constant level over entire length of seam. Welding arcs are cut off at distance from end of tube providing good quality of end part of seam without formation of end crater. Stricking and extinction of welding arcs is carried out at stepless regulation of their power and speed of electrode wire feeding. Values of power of welding arcs and speed of electrode wire feeding are set depending on speed of tube movement.

EFFECT: improved quality of seam at beginning and end of welding, reduced cropping of ends.

1 ex, 1 dwg

Description

The invention relates to the field of welding and can be used for submerged arc welding of large diameter pipes.

Known methods (A.S.No.808225, class B 23 K 9/18, 1978 and No. 1232419, class B 23 K 9/18 1984), in which the crater part is welded with an additional arc, turning off the main arcs. Their disadvantages are the need for additional equipment, applicability only on the final section of the workpiece and the discreteness of parameter changes, which leads to differences in the parameters of the weld itself along the length of the pipe and on its final section.

Closest to the proposed technical solution is the method (A.S. No. 1720826 class. In 23 K 9/18 1992, selected as a prototype), in which at a distance of not less than 200 mm from the end of the pipe reduce the voltage of the first arc to 32 -37 V, and at a distance of 30-50 mm, the first arc is turned off and the welding speed is simultaneously reduced by 40-60%, after which the second arc is turned off after 1.5-2.2 s and after 2.5-3.3 s after disconnecting the first arc, the third.

The disadvantages of this method are the reduction of trimming only at the end of the pipe, discrete changes in the parameters as a function of both the distance to the end of the pipe and time, which leads to changes in the geometry of the weld and the ambiguity of its characteristics in the final section when changing the nominal welding parameters in the steady state.

An object of the invention is to improve the quality of the seam at the beginning and end of welding and reduce trim.

The problem is achieved in that in the method of submerged arc welding of large diameter pipes, including turning on the welding arcs, welding and sequentially switching off the welding arcs while reducing the welding speed, according to the invention, at the beginning of welding, the welding arcs are alternately turned on at a distance from the beginning of the pipe, ensuring the identity of the initial parts of the weld according to the penetration depth, width and shape to the specified parameters of the weld in the welding zone at the steady state, and the welding arcs are turned off at a distance from the end of the pipe, ensuring which has good quality of the end part of the weld without the formation of a crater part, the welding arcs are turned on and off while continuously adjusting their power and electrode wire feed speed, and the values of the welding arc power and electrode wire feed speed are set based on the pipe speed and the entire length seam specific heat input of the welding is maintained at a constant level.

A comparative analysis of the proposed solution with the prototype shows that the claimed method differs from the known one in that the arcs are turned on alternately at the beginning of the welding at a distance from the beginning of the pipe, ensuring the initial part of the weld is identical in penetration depth, width and shape to the specified parameters of the weld in the welding zone at steady state and disconnecting the welding arcs is carried out at a distance from the end of the pipe, ensuring good quality of the end part of the weld without the formation of a crater part, and the values of the weld power arc lengths and electrode wire feed speeds are set as derivatives of the pipe speed, and the specific heat of the welding is kept constant along the entire length of the seam.

The proposed technical solution allows the switching on of the arcs at the start of welding at a certain point at a certain insignificant distance from the beginning of the pipe at a reduced speed of the pipe and the corresponding minimum arc powers and wire feed speeds, followed by smooth - after ignition of the last arc - increasing these parameters to the specific heat input values set for this mode, which ensures the identity of the initial part of the weld in terms of penetration depth, width and shape of its parameters in steady state zone. And at the end of the pipe, a gradual decrease in the speed of movement of the pipe with a corresponding decrease in the power of the arcs and wire feed speeds with their subsequent switching off at the same point near the pipe end ensures good quality of the end part of the weld without the formation of a crater part. All this together contributes to the reduction of the cut part of the pipe.

Thus, the proposed method allows in transient and in steady state conditions to maintain a constant linear energy of welding and the amount of deposited metal along the entire length of the weld, ensuring the invariance of the characteristics of the weld and reducing the amount of trim at the ends of the pipes.

An example implementation of the method for three-arc welding is presented in the form of graphs of changes in the welding speed, wire feed speed and specific power of the arcs in the drawing, where the following notation is adopted:

- Vtr., Vе1, Vе2, Vе3 - pipe and electrode feed speeds

welding arcs respectively;

- Pe1, Pe2, Pe3 - power of the corresponding arcs;

- t0, t1, t2, t3, t4 - times of the beginning of the movement of the pipe, ignition of the corresponding arcs

and

time to reach steady-state welding parameters;

- t5, t6, t7 - start times of decreasing arc powers and wire feed speeds;

- t8, t9, t10 - arc turn-off times;

The method is implemented as follows

way:

- at time t0, the pipe begins to move and in t1 they ignite the 1st arc in the given

point at the minimum possible power for burning the arc, the feed speed of the welding wire, and the speed of the pipe in this interval is set corresponding to these three minimum powers (for three-arc welding) and these parameters do not change until the last arc is ignited;

- when this point approaches the second electrode at time t2, the feed

welding wire and excite the 2nd arc with the same parameters as the first and do not change them until the last arc is ignited;

- when this point approaches the last electrode at time t3 include

it feeds the welding wire, the 3rd arc is excited, and then the power and feed speed of the welding wire of all arcs are raised to the values specified for the given welding mode smoothly with a pace corresponding to an increase in the speed of the welded pipe;

- in steady state with t4 no t5 welding parameters

are supported

unchanged at a given level;

- at the end of welding at a certain distance from the end of the pipe at time t5 start

smoothly reduce the speed of the pipe and alternately (t5 - 1st, t6 - 2nd, t7 - 3rd), starting from the 1st arc, at a corresponding pace, they begin to reduce the power on the arcs, the wire feed speed and when approaching them to the end of the weld disconnect them in

the same sequence (t8 - 1-a, t9 - 2nd, t10 - 3rd).

The proposed method has been tested and implemented using a microprocessor control system for welding modes, capable of adjusting the above-mentioned parameters of the welding process with a given speed and having sensors for the beginning, end of the pipe and its path traveled during welding. Testing was carried out on the internal welding mill when welding pipes 813> <8.0 from steel X60. 326 pipes were welded. The trimming of the ends of the pipes was not more than 100-130 mm from each end of the pipe. Without the application of the method, the total trimming of the ends is at least 320-360 mm. The quality indicators of this batch of pipes welded in the internal welding mill amounted to 99.31%.

Claims (1)

A multi-arc method for submerged arc welding of large-diameter pipes, including turning on the welding arcs, welding and sequentially switching off the welding arcs while reducing the welding speed, characterized in that at the beginning of welding, the welding arcs are switched on alternately at a distance from the beginning of the pipe, ensuring that the initial part of the weld is identical in depth penetration, width and shape of the specified parameters of the weld in the weld zone in the steady state, and disconnect the welding arcs at a distance from the end of the pipe, ensuring good quality the main part of the weld without the formation of a crater part, the welding arcs are turned on and off while continuously adjusting their power and electrode wire feed speed, and the values of the welding arc power and electrode wire feed speed are set based on the pipe speed, and the specific linear along the entire length of the weld welding energy is maintained at a constant level.