JPS6015069A - Circumferential fillet welding method of al pipe - Google Patents

Abstract

PURPOSE:To progres smoothly welding and to obtain a joint part free from lack of fusion in the stage of fillet-welding an annular piping member to an Al pipe having a small diameter by forming a boss to the surface to be welded of the annular piping member and performing TIG welding with the positive polarity of DC without using a filler rod. CONSTITUTION:The top end of Al pipe having <=3.0mm. wall thickness and 30mm. outside diameter is pressed to a step part 7 formed in the through-hole 6 of a flange 2 and the Al pipe 1 is stably held. A boss 5 is preliminarily provided annularly along the lateral circumferential edge of the through-hole 6 of the flange 2 in this stage while the shape of the boss is selected freely. An extremely slight gap is formed between the inside circumferential surface of the boss 5 and the outside circumferential surface of the pipe 1 and the through-hole 6 of the flange 2 has a flush inside circumferential surface. It is equally well to press the top end of the pipe 1 to the flange surface without fitting the same into the hole 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for attaching a piping annular member to an Al pipe by circumferential fillet welding.

Al pipes (including pipes made of AI and A1 alloy, hereinafter the same) are widely used in the fields of heat exchangers and the like, and are expected to be applied to even more piping fields in the future.

When installing Al pipes, attach fitting members such as flanges and nuts to the ends of the Al pipes, and then connect the Al pipes to each other or
Connections are made between pipes and various types of equipment, but in some cases it may be necessary to connect Al pipes directly by fitting them together, or to connect various types of equipment directly to Al pipes. do not have. In this specification, among these connection partners, a member that forms a fillet weld line along the circumferential direction of the Al pipe by fitting into the outer periphery of the Al pipe or abutting against the end face of the Al pipe is referred to. It is called an annular member for piping, and all of these are included in the scope of the present invention. However, in the following explanation, for convenience of understanding, the case of a flange will be taken up as a representative example.

Now, when attaching the seven sinkers to the A1 pipe, the Al pipe 1 and the flange 2 are bottomed together as shown in Fig. 1 ('A), and the circumferential fillet 3 is The conventional method was to braze as shown in 4 of B). However, brazing is a well-known process ().Because the heating plate is wide, the range of material deterioration (particularly strength deterioration) is wide. To avoid this, Mori-Zn-Mg alloy 7N01 is currently used, but burning tends to occur.

(2) Since it is not possible to completely eliminate residual flux after brazing, there is a strong possibility that the corrosion of the base metal will be accelerated.

(3) When the above-mentioned flux is washed and removed, a cleaning fluid pollution problem arises.

(4) Making the working environment worse.

There are other problems. If you want to solve these problems all at once, you have no choice but to switch to welding, but since the target Al pipes are generally extremely small, usually less than 3.0 mmj and 30 mmφ, there is a problem of burn-through due to arc force. At the same time, a practical welding method for small-thickness, small-diameter Al pipes has not yet been developed, and the allowable range of welding conditions has become even narrower. For example, even if MIG welding is attempted, since the outer diameter of the Al pipe is extremely small, welding defects frequently occur at the start and crater portions and over the entire circumference. Also, when performing TIG welding, it is possible to obtain a weld by carefully manual welding while inserting the filler metal into the arc, but in this case, generally AC TIG welding is performed, so the arc is concentrated. The best results are not necessarily obtained because the heating range is poor and the heating range is wide.

If this process were to be automated, an extremely complicated welding sequence would be required due to the small outside diameter and wall thickness of the tube, making it almost impossible to put automatic AC TIG welding to practical use as far as this field is concerned. It is considered to be close.

In the end, the thermal conductivity of AI is too good, it is extremely easily oxidized in high-temperature environments, and the oxide formed by oxidation has a high melting point and forms a strong film on the surface of the base material. Good welding is achieved as a result of combining various factors such as: the wall thickness is small so there is a strong risk of burn-through, and the small diameter is greatly affected by fluctuations in welding conditions. It was virtually impossible to develop a welding method for AI piping that would provide stable parts.

The present invention was made in view of this situation, and aims to provide a welding method that can stably obtain good weld metal even under the above conditions, and that can even be designed to be automated. It is something to do.

The welding method of the present invention that has succeeded in achieving the above object is that an annular member for piping is placed opposite to an Al pipe with a wall thickness of 3.0 mm or less and an outer diameter of 30 mm or less, and a corner is formed in the circumferential direction of the Al pipe. To carry out flesh welding, a boss part is formed along the circumferential direction on the fillet welding surface of the annular piping member, and DC positive polarity TIG welding is performed along the boss part without using a filler rod. The main idea is to apply a method to fuse the boss portion to the Al pipe.

The configuration and effects of the present invention will be explained below with reference to the drawings. Figures 2 (5) to (F) are cross-sectional views of fillet welds suitable for TIG welding (or more accurately, fusion welding) according to the present invention, particularly Figures 2 (2) to (E). )teeth,
The tip of the Al tube 1 is stably held by abutting the stepped portion (sometimes tapered portion) 7 formed in the through hole 6 of the flange 2, and the boss portion 5 is held along the periphery of the through hole 6 side of the flange 20. This is an example in which the boss portion 5 is arranged in a ring, and shows that the shape of the boss portion 5 can be freely designed. In Figure 2), an extremely small gap G is formed between the inner circumferential surface of the boss portion 5 and the outer circumferential surface of the A1 pipe 1, and the inner circumferential surface of the flange 20 through hole 6 is flush. The tip of the 9AI pipe 1 is not fitted into the through hole 6 and is in contact with the flange surface.

By applying TIG arc to the boss part 5 designed and manufactured in this way, the boss part 5 and the Al pipe 1 in contact with it are
These are integrated by fusion welding by melting the outer peripheral surfaces of the two, but if a TIG arc is generated using an AC power source at this time, the arc tends to be poorly concentrated, resulting in insufficient penetration, and this can be prevented. If the arc continues to work until the amount of molten metal increases, over-melting will occur and the wall thickness of the Al tube 1 will tend to become thinner, resulting in a concave shape as shown in Figure 3 (B). In many cases, the result is fused metal 8'. If this happens, various mechanical problems will appear, so it will be necessary to change the welding conditions, and we came up with the idea of using a DC power source, but with the opposite polarity, the penetration will be shallow and the melt width will widen. In the end, it seems that there is no big difference from using an AC power source, and the actual experimental results show that the disadvantage that the Al tube 1 tends to become thinner cannot be avoided. Therefore, when a TIG arc was generated under the condition of positive DC polarity and acted on the boss part 5, it was found that
), it was found that a fused metal with a good shape as shown in 8 was obtained and the desired purpose was achieved. However, since there is no cleaning effect when the direct current is of positive polarity, it was necessary to sufficiently remove the oxide film and oils and fats from the surface of the base material in advance. Furthermore, if the gap G shown in Fig. 2 (E) is too large, it will be difficult to obtain a complete fusion state, so it is desirable to make it as small as possible, and according to various experiments. I have learned that keeping it below 0.3 degrees will guarantee the best results. There are no particular restrictions on the thickness or height of the boss portion 5, but as the extra thickness increases, the amount of heat input must increase, so it is recommended that the thickness be kept below 5+ nm.On the other hand, the thinner the extra thickness, the less the fusion effect. cannot be obtained, so the maximum thickness part [Figure 2 (B).

(C), (D), and (E) bottom portions] is desirably 1 mm or more. Further, the height of the boss portion 5 is desirably 1 mm or more from the viewpoint of ensuring fusion strength, but it is unnecessary to exceed 5 mm.

By adopting the above configuration, the boss part can be melted and
Although the fusion to the L tube proceeds smoothly, more preferred implementation conditions will be described below.

In the present invention, TIG welding is performed using DC positive polarity, but when pulsed current is used, the fusion integrity with the Al pipe is improved due to the stirring effect of the molten metal, and a strong welded joint can be obtained even when the gap G mentioned above is somewhat large. be able to. Also, with pulsed current, high current and low current are repeated, but by ensuring sufficient penetration depth during high current and adding low current periods, excessive heat input is prevented and a cooling effect is achieved. There is an advantage. However, if the frequency is less than 0.5 Hz, each pitch of the weld bead becomes large, and defective welding tends to occur due to insufficient heat input, especially in a low heat input region. On the other hand, if it exceeds 50 Hz, both the molten metal stirring effect and the molten metal cooling effect will become insufficient due to the high frequency, so it is recommended to set it within the range of 0.5 to 50 Hz.

Next, as for the shielding gas constituting the TIG welding atmosphere, He is used in order to improve the concentration of the arc, but other gases such as Ar may be mixed. In this case, as the Ar mixing ratio increases, the penetration becomes shallower and the AC TIG
Since the same drawbacks as in the case of the method appear, it is desirable that He exists in at least 25 coefficients or more. From the viewpoint of increasing the concentration of the arc, it is further recommended that the tip of the W electrode be made as sharp as possible.

Next, a more detailed explanation will be given by presenting specific examples of the present invention.

A3003-H24 AI tube C1,5n+mj x
20 pusφ (outer diameter) x 450mm') and A6063-T5
An AI flange (20 mm t x 60 mm φ) manufactured by A.I. was assembled as shown in Fig. 4 (4) I (B). In Fig. 4 (4), brazing is performed, and in Fig. 4 (B), DC without filler metal is used.
-8P-TIG welding was performed. In the latter welding, the torch is fixed, the workpiece is rotated at a constant speed, and the current (8
0A), number of pulses (4Hz), peripheral speed (500mm/min)
, shield gas (He: 151/min), and use of a sharp W electrode. The Vickers hardness of the pipe side and flange side was measured and the results shown in Figure 5 were obtained. The lower part of Fig. 5 shows the position of the measurement point (x mark). In the case of brazing, the softened area is widely spread on both the flange side and the pipe side. It can be seen that the softened area is localized to an extremely narrow position in the welded specimen.

Next, AC-
When 74'G welding (current +135A, no pulse, other conditions were the same as the previous time) was performed, an extremely thin part was generated in the welded part of the AI tube, as shown in FIG. 3(B).

Furthermore, while feeding the filler rod to the joint shown in Figure 4,
3P-TIG welding was performed (current and other welding conditions were the same), but since the welding object itself was small and the current was small (80A), the arc length was short and practical welding workability could not be ensured.

Next, as shown in Figure 6 (B), when DC-3P-TIG welding was carried out while placing the filler metal 9 in the placing method, only the ring-shaped filler metal 9 was removed. Initially, it became spherical due to the upper surface tension when it melted alone, escaped on the flange surface, and did not fit into the weld metal of the AI pipe, resulting in a joint failure. If the size of the ring-shaped filler metal was increased to a certain extent, the fusion with the AI pipe would proceed, but the shape of the bead would be extremely irregular.

Since the present invention is configured as described above, welding between the AI pipe and the annular member for piping progresses smoothly, and it is possible to secure a reliable joint without fusion defects.

[Brief explanation of the drawing]

Figure 1: (B) is a conceptual diagram of the law of brazing, Figure 2 (5)
~(F) is an explanatory diagram of the joint of the present invention, FIG. 3(5) is an explanatory diagram showing a good fusion state, FIG. 3(B) is an explanatory diagram showing a poor fusion state, and FIG. B) , Figure 6 Prisoner, (B
) is an explanatory diagram of the joint used in the experiment, and FIG. 5 is a graph showing the distribution of the softened region. 1...AI pipe 2...Flange...Boss department applicant Kobe Co., Ltd. l+1! steelworks

Claims (1)

[Claims] (+) A having a wall thickness of 3.0 mm or less and an outer diameter of 30+ nm or less
In this method, fillet welding is performed in the circumferential direction of the Al pipe by placing an annular member for piping opposite to the pipe, the boss portion being welded along the circumferential direction on the fillet welding surface of the annular member for piping. in the circumferential direction of the Al pipe, and the boss part is fused to the Al pipe by applying a direct current positive polarity TIG welding method that does not use a filler rod along the boss part. Fillet welding method. (2. In claim 1, 0.5 to 50H
A method for circumferential fillet welding of an Al pipe using a pulsed current of z. (3) A method for circumferential fillet welding of an Al pipe according to claim 1 or 2, in which the shielding gas composition is set to He: 25% or more. (4) A circumferential fillet welding method for an At pipe according to claim 1, 2, or 3, in which a W electrode having an acute-angled tip is used for welding.