JPS6035234B2 - Narrow gap carbon dioxide arc welding method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a narrow gap carbon dioxide gas arc welding method.

Carbon dioxide arc welding is generally applied to carbon steel or at most low alloy steel as an inexpensive welding method.
Since its mechanical properties are comparable to those of shielded arc welding and there are fewer cracks, it has become quite popular recently, and the shape of the tip used for it is as shown in Figure 1a.
As the size of the structure increases, the thickness of the plates increases, resulting in problems such as longer welding time and increased welding distortion.

As a solution to this problem, a narrow gap welding method using a narrow gap shown in FIG. 1B has been proposed, but the equipment used therein is extremely complicated. The present invention aims to solve these problems from the aspect of welding work. For this reason, the present invention provides a method for circumferential butt welding of steel pipes made of carbon steel or low-alloy steel by a narrow-gap carbon gas arc welding method while rotating the steel pipes.
Welding current 1 (unit A) and arc voltage V (unit V) are adjusted according to changes in (unit side) laSI between lower limit values la, Va and upper limit values lb, Vb that satisfy the following formulas.
Slb Va mi VSVb Here, la=7.5X+239.5 1b=9.9X+299.6 Va=0.57X+27.57 Vb=0.75X+28.25.

Embodiments of the present invention will be described below with reference to the drawings.

When the joint gap is narrow as shown in Fig. 2, the dendrites of the bead grow perpendicularly from the groove surfaces la and lb on both sides, so that at the end of solidification, the low melting point liquid phase 2 forms in the center of the bead 3 at the groove surfaces la and lb.
It will remain as a plane parallel to lb, and the shrinkage pressure of the weld metal will act on this, causing cracking.
The current cannot be made too high.

On the other hand, if the current is too low, the inside of the bead becomes narrow, resulting in poor penetration at both joint surfaces la and lb. In this sense, the relationship between the joint gap and the current is important, and the current range that allows for sound welding is determined by itself. Figure 4 shows the experimental results. The relationship between the arc voltage and the tip gap is also determined automatically, and the experimental results are shown in FIG. Here, the welding conditions are both polarity D. C. R. P. , the welding speed was 380 mm/min, the shielding gas pressure was 3k9/min, the shielding gas flow rate was 40 min, the torch angle was 100 mm, the wire was
The protrusion length was 3 mm and the pipe thickness was 5 mm. Incidentally, the torch angle is the inclination angle 8 that is obtained by shifting the torch 5 in the welding direction from the position directly above the pipe 4 to be welded, as shown in Fig. 3, so that the molten metal is moved toward the rear of welding (downward side in the direction of pipe rotation). This can eliminate poor arrival at the port due to dripping of the bead, and poor penetration of the upper layer bead into the first layer bead due to the contact angle between the female end of the first layer bead and the bottom of the groove becoming smaller and rising. Yes, and a range of 10 to 20 degrees is suitable. In FIG. 4, a range A sandwiched between curves a and b indicates a nucleation region, and welding currents la, which correspond to these curves a and b,
The relationship between lb (unit A) and joint gap x (unit rib) can be determined from the figure as shown in the following equation. la=7. Ball ten 239.5
m lb: 9.9 be.

In addition, in Fig. 5, the A range sandwiched between curves a and b indicates the appropriate area, and the welding voltages Va and Vb (unit: V) corresponding to these curves a and b correspond to the joint gap X (unit side )
The relationship with is calculated from the figure as follows.

Va = 0.57X + 27.57 Leg Vb = 0.75X + 28.25 (4' Therefore, the appropriate arc voltage V has the relationship Va3V≦Vb.

Note that B and C indicate defective areas, B is the range of poor fusion, and C
is the range where "gouge" occurs. The reason why the appropriate arc voltage increases as the groove gap becomes wider is as follows.

As the arc voltage increases, it increases during the bead, but
Since the gap is wide, penetration becomes appropriate. However, if it is too high, the "gouge" on the side surface of the groove becomes large, the molten pool becomes large, and the molten metal flows down in the welding direction, resulting in poor penetration at the bottom of the groove. On the other hand, if the voltage is too low, the arc area will be narrow and the inside of the bead will be small, resulting in poor penetration on the side surfaces of the groove. As described above, according to the present invention, according to the change in the groove gap, '1} to {4}
By determining the welding current and arc voltage as shown in the formula,
It has now become possible to easily perform narrow gap welding without the use of complicated equipment and without the drawbacks of weld metal running down from the welding surface or poor port penetration.

[Brief explanation of drawings]

Figures 1a and b are front views explaining the groove shape, Figure 2 is a sectional view explaining the welding state of narrow joint welding, Figure 3 is an illustration of the torch angle, Figures 4 and 5. 1 is a characteristic diagram showing one embodiment of the present invention. la, lb...both side groove surfaces, 3...bead. Figure 2 Figure 3 Figure 1 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. Changes in groove spacing X (unit: mm) when performing circumferential butt welding of a steel pipe made of carbon steel or low alloy steel by a narrow gap carbon dioxide gas arc welding method while rotating the steel pipe. Welding current I (unit A) and arc voltage V (unit V) are set to lower limit values Ia and V that satisfy the following formulas according to
a and upper limit values Ib and Vb, Ia≦I≦Ib Va≦V≦Vb Here, Ia=7.5X+239.5 Ib=9.9X+299.6 Va=0.57X+27.57 Vb=0.75X+28.25 A narrow gap carbon dioxide arc welding method characterized by: