JPH0227072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for welding aluminum or aluminum alloy tubes.

In recent years, aluminum or aluminum alloys have been used as materials for pipes used in LNG, nuclear power, refrigeration plants, etc. in order to improve workability and processability, reduce weight, and reduce costs. In these plants, a large number of pipes having various diameters are arranged in a network in a narrow space. Therefore, the number of welding points has reached an enormous number. For welding aluminum pipes in such plants, manual tungsten inert gas arc welding (hereinafter referred to as TIG welding) by skilled welders is generally employed. TIG welding has the effect of cleaning all welded parts by destroying the oxide film on the surface of the aluminum tube due to the action of the cathode spot of the arc, but as shown in Figure 1, the AC waveform (I) is a sine wave. Therefore, the concentration of the arc is poor and the arc tends to wander, causing weld metal to easily drip. As a result, welding defects such as blowholes and poor fusion occur, making it almost impossible to weld pipes or the like in one layer. For this reason, multilayer welding has been adopted for welding aluminum pipes, which has the drawback of increasing welding time. for example,
As shown in Fig. 2, in the case of fillet welding of the joint between the aluminum pipe 1 and the sleeve material 2, the groove shape is 2
Welding is carried out with ~3 layers of welded parts 3.

In addition, the welding parts of plant piping require high airtightness, and as mentioned above, many pipings are installed in a narrow space, so there is a problem that the working environment is poor and the quality of welding is inconsistent.

The present invention has been made in view of these points,
The present invention has discovered a method for welding aluminum or aluminum alloy tubes that has excellent welding quality through single-layer welding and can improve workability.

That is, the present invention provides a method for welding an aluminum or aluminum alloy tube in which an inner tube is inserted into the tip of an outer tube and the outer tube and the inner tube are welded together. The wall thickness is 1.2 to 1.5 times that of the inner tube, and the diameter is smaller along the distal direction on the outer peripheral surface of the tip so that the wall thickness width of the tip surface of the outer tube is 0.5 to 1.0 times the wall thickness of the inner tube. form an inclined surface,
This is a welding method for an aluminum or aluminum alloy tube, in which the inner tube is inserted into the outer tube, and then the tip of the outer tube and the inner tube are welded together by low-frequency AC pulse welding.

The present invention will be explained below.

The inner pipe and outer pipe to which the method of the present invention is applied are those used in nuclear power plants, LNG plants, refrigeration plants, etc.

The groove shape of the outer tube into which the inner tube made of aluminum or aluminum alloy is inserted is determined by dividing the wall thickness (T) of the outer tube 10 by the wall thickness (t) of the inner tube 11, as shown in FIG. Set to 1.2 to 1.5 times. Further, the circumferential surface of the distal end of the outer tube 10 is arranged so that the wall thickness width (a) (root height) of the distal end surface is 0.5 to 1.0 times the wall thickness (t) of the inner tube 11 in the distal direction. The inclined surface 12 whose diameter decreases along the slope is chamfered.

In addition, in low-frequency AC TIG pulse welding performed on the joint 13 of the outer tube 10 and inner tube 11, the polarity is changed to positive polarity (base metal pole) when the welding power source is used as shown in the output waveform ( ) in Figure 4. With deep penetration, reverse polarity (base metal pole) has a cleaning effect on the weld zone, eliminates arc fluctuation, improves penetration at the bead toe, and prevents molten metal from dripping.
Set the pulse frequency to 1 to 8 Hz, which allows heat input control by pulse control. In addition, the welding current and welding speed always keep the welding heat input contributed by arc heat in equilibrium between the inner tube 11 and the outer tube 10 as well as the welding start and end positions, so that a good single-layer welded part 14 can be obtained. It is controlled so that it reaches a predetermined value at an arbitrary position.

Note that the wall thickness (T) of the outer tube 10 is 1.2 to 1.5 times the wall thickness (t) of the inner tube 11, and the wall thickness width (a) of the tip surface of the outer tube 10 is the wall thickness (t) of the inner tube 11. ) is set to 0.5 to 1.0 times to reduce the difference in wall thickness between the inner tube 11 and the outer tube 10 so that the welding heat generated by the arc heat to the inner tube 11 and the outer tube 10 is uniformly conducted. This is to obtain a one-layer welded portion 14 with a good penetration shape.

Next, examples of the present invention will be described.

As shown in Figure 3, the outer diameter is 20mmφ and the wall thickness is 2mm.
Insert the inner tube 11 made of A50830 material into the outer tube 10 made of A50830 material with a wall thickness of 2.8 mm and a chamfered end face with a wall thickness width of 1.3 mm, and remove it using a low frequency AC welding machine. At the joint 13 between the pipe 10 and the inner pipe 11, a frequency of 3 Hz, a welding current of 120 A, and a welding speed of 100 mm/min are applied.
Filler welding was performed by automatic welding under the following conditions.

The filler wire used was A5183 material with a diameter of 1.2 mm. In addition, welding pretreatment included wire brushing, acetone degreasing, drying, and welding to prevent blowholes.

After welding, as shown in the figure, it was confirmed that a good single-layer weld 14 was formed at the joint 13 of the outer tube 10 and the inner tube 11.

As explained above, according to the method for welding aluminum or aluminum alloy pipes according to the present invention,
It has excellent welding quality in single layer welding and has remarkable effects such as being able to improve workability.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing AC waveforms in conventional TIG welding, Fig. 2 is a sectional view showing an inner pipe and an outer pipe welded in multiple layers by the conventional method, and Fig. 3 is an explanatory diagram showing AC waveforms in conventional TIG welding.
FIG. 4, which is a cross-sectional view of the inner tube and outer tube welded in one layer by the method of the present invention, is an explanatory diagram showing the output waveform of the welding power source for low-frequency TIG pulse welding used in the method of the present invention. 10...Outer pipe, 11...Inner pipe, 12...Slope, 13...Joint part, 14...Single layer welding part.

Claims (1)

[Claims] 1. In an aluminum or aluminum alloy pipe welding method in which an inner tube is inserted into the tip of an outer tube and the outer tube and the inner tube are welded together, the wall thickness of the outer tube is set to 1.2 of the wall thickness of the inner tube. ~1.5 times, and the wall thickness width of the tip surface of the outer tube is 0.5 to 1.0 times the wall thickness of the inner tube.
An inclined surface whose diameter decreases along the distal direction is formed on the outer circumferential surface of the distal end so as to double the diameter, and after the inner tube is inserted into the outer tube, the distal end of the outer tube and the inner tube are connected. A method for welding aluminum or aluminum alloy tubes, which comprises welding them together by low-frequency alternating current pulse welding.