JPS6316874A - Butt welding method for steel pipe - Google Patents

Abstract

PURPOSE:To prevent a butt of the inside peripheral surface, and to increase the strength of a weld zone by allowing the other steel pipe end face to butt against a steel pipe end face whose peripheral surface has been covered with copper, etc., and subsequently, bringing both the steel pipes to pressure and electric conduction, and executing the welding for a prescribed time. CONSTITUTION:Each end face of a covered steel pipe 2 and a steel pipe 1, which have formed a copper clad layer 2b on the inside and outside peripheral surfaces is allowed to butt each other, and electrodes 6, 7 are provided, respectively. Subsequently, the steel pipes 1, 2 are brought to electric conduction and heating under pressure of about 10-50kg, and by setting an electric conduction and heating time of >= 0.2 second, welding of a weld zone 8 is executed. In this case, the copper clad layer 2b of the outside peripheral surface of the pipe 2 is extruded to the outside peripheral surface side as a butt 8a is growing, and generation of a butt on the inside peripheral surface side is prevented. Also, mixing of copper into an interface of the weld zone is prevented completely, therefore, the strength of the weld zone 8 can be increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for butt welding steel pipes, and in particular to a butt welding method that can prevent the occurrence of flashing on the inner peripheral surface of a steel pipe when connecting pipes such as a heat exchanger. Regarding welding methods.

[Conventional technology]

Traditionally, steel pipes have been used as piping for heat exchangers.
The pipes are connected to each other using phosphor copper solders that do not require flux. However, recently, there has been an active movement to use steel pipes instead of steel pipes due to cost considerations, and steel pipes are now joined together using silver solder or brass solder. There is.

However, when using silver solder, the advantages of replacing steel pipes with cheaper steel pipes are diminished because silver solder is expensive. There are problems such as insufficient soldering to the joints, resulting in poor solder penetration and unstable quality.

In addition, in the case of both silver soldering and brass soldering, flux must be used when brazing, which is popular, so it is necessary to remove the flux after brazing is completed. It is not easy to do it perfectly. However, if the flux is not completely removed, the flux itself is corrosive and will corrode the pipe, causing perforation.

By the way, phosphorous copper solder has long been known as an inexpensive brazing material that does not require the use of flux, and is widely used for brazing steel pipes and brass pipes. It is not suitable for brazing steel pipes.

This is due to the difficulty of brazing numbers and analogy 4.
-J G.J.: This is the reason why the phosphorus component contained in the brazing filler metal diffuses into the steel pipe and makes it brittle.

Therefore, a pipe connection device has been proposed in which a steel pipe and a copper pipe are joined via an intervening pipe whose inner and outer peripheries are coated with a layer of copper or copper alloy in advance.

FIG. 5 shows this type of pipe connection device, in which a copper-clad steel pipe 2, in which both the inner and outer circumferential surfaces of a steel base 2a are coated with a copper clad layer 2b, is attached to one end of the steel pipe 1 via a butt weld 3. The ends of the copper-clad steel pipes 2 are fitted into the copper pipes 4 to be connected and joined by phosphor copper brazing 5.

By adopting such a pipe connection structure, it becomes possible to join the steel pipe 1 and the copper pipe 4 using phosphorous copper solder.

By the way, when joining a steel pipe 1 and a copper-clad steel pipe 2 via a welding part 3, conventionally, the end face of the steel pipe 1 and the end face of the copper-clad steel pipe 2 are butted, and both steel pipes 1.2 are joined. A butt welding method is used in which the parts are joined by instantaneous electrical heating for 0.1 seconds or less while applying a predetermined pressure.

[Problem that the invention seeks to solve]

However, in the conventional butt welding method, as mentioned above, the energization heating time is extremely short, 0.1 seconds or less, so the inner and outer surfaces of the contact surfaces of both steel pipes 1 and 2 reach the same degree of welding at the same time. The molten metal at the joint protrudes to the inner and outer circumferential sides of the welded part 3, and after welding is completed, acute-angled outer surface cracks 3a and inner surface cracks 3b are generated in the welded part 3, as shown in Fig. 5. There's a problem. Therefore, when these burrs 3a and 3b occur, especially the inner burr 3b, it is necessary to grind it later using a drill or the like, and furthermore, the chips remain inside the steel pipe 1.2 after grinding. , (2) It is necessary to remove the chips by blow blowing, etc., which causes the problem that the work requires a lot of time.

The present invention was developed in view of the current situation, and it is possible to unevenly distribute the flashes generated in the welded portion only on the outer peripheral surface of the steel pipe, and prevent flashes from occurring on the inner peripheral surface, and furthermore, it is possible to prevent the flash from occurring on the inner peripheral surface of the steel pipe. It is an object of the present invention to provide a method for butt welding steel pipes by which the cracks occurring on the surface side can be welded into a rounded shape.

[Failure to solve the problem]

The present invention abuts the end face of a coated steel pipe whose peripheral surface, at least one of the inner and outer sides, is coated with a layer of copper or a copper alloy, and the end face of the steel pipe. The welding process is characterized in that welding takes a time of 0.2 seconds or more.

[For production]

In the bulk welding method for steel pipes according to the present invention, butt welding time is as long as 0.2 seconds or more, and heating is performed slowly. Therefore, the humidity of the welded part increases first on the outer circumferential surface side and softens, and the particles are pushed out toward the outer circumferential surface side. If the current heating is continued, the humidity will gradually increase toward the inner circumferential surface, but when the inner circumferential surface has softened, welding has been completed, and therefore no cracks will occur on the inner circumferential surface. rare. In addition, as mentioned above, the welded part is heated slowly, so no electric sparks are generated, and the welded part gently rises toward the outer circumferential surface due to the pressurization of the joint, so that the welded section is heated slowly. The resulting Paris will be rounded.

〔Example〕

Hereinafter, one aspect of an embodiment of the present invention will be described with reference to the drawings.

In Figs. 1 to 3, reference numeral 1 indicates a steel pipe, and reference numeral 2 indicates a copper-clad steel pipe in which copper clad layers are arranged on both the inner and outer peripheries. Electric 1k 6 divided into upper and lower halves.

7 are respectively attached to the outer peripheral surface. Then, with the end surfaces of the steel pipes 1 and 2 butted together and pressurized at 10 to 50 Kgf, for example, I
A current of V1200A is applied for 0.2 seconds or more, and both steel pipes 1.2 are joined via the welded portion 8 as shown in FIG.

In this way, in the butt welding according to the present invention, C is set to be open for a long time, 0.2 seconds or more during energization heating during welding, so that the welded portion 8 is heated slowly. In the welded part 8, since the current flows through the skin part which is the shortest path between the electrodes 6 and 7, the temperature rises first on the outer peripheral surface side and softens it. It is pushed out toward the outer circumferential surface. When the current heating is continued, the welded portion 8 gradually moves toward the inner peripheral surface. However, when the inner circumferential surface softens, welding is complete and C
There is. Therefore, as shown in FIG. 3, almost no burrs are formed on the inner circumferential surface 8b of the welded portion 8. Furthermore, even if a breakout were to occur, it would be so small that it could be ignored in practical terms.

In addition, by gently heating the welding part 8,
Unlike the case of conventional instantaneous heating, no electric spark is generated, and therefore, the burr 8a maintains the shape in which the welded part 8 gently swells toward the outer peripheral surface due to the pressurization of the joint part. Therefore, the burr 8a has a rounded shape.

Further, the copper clad layer 2b on the outer circumferential surface of the copper-clad steel pipe 2 is once drawn into the interface slightly due to capillary phenomenon in the early stage of welding, but is pushed out toward the outer circumferential surface as the burr 8a grows. On the other hand, the copper clad layer 2b on the inner peripheral surface of the copper clad steel pipe 2
Since the iron base melts first and there is no gap at the interface, it is not drawn into the interface by capillary action. As a result, copper is almost completely prevented from entering the weld interface, making it possible to increase the strength of the weld 8 and improve reliability.

172 (Experimental Example) The present inventor conducted welding of pieces 1 to 1 under the following conditions, and obtained the results described later.

(1) Steel pipe used: outer diameter 4.76mm, wall thickness 0.7m, length 5m,
Copper plating is applied to both the inner and outer circumferences! (ERW steel pipe copper clad steel pipe: A clad steel pipe with an outer diameter of 4.76M, a wall thickness of 0.7mm, a length of 26m+, and a 20μm thick copper cladding layer arranged on both the inner and outer circumferences (2) Equipment used for welding: Butt welding machine conditions: Two ends were butted together, pressurized with 30 Kgf, and heated with electricity for 0.8 seconds at I Vl 200AT (3) As a result, there was no burr on the inner circumference side, and the burr on the outer circumference side was rounded. A welded part was obtained which had a tinged shape. Also, the airtightness of the welded part was extremely good.

FIG. 4 shows another embodiment of the present invention, in which, for example, the end surface of the copper-clad steel pipe 2 that meets the steel pipe 1 is made into an inclined surface 9 that gradually moves away from the steel pipe 1 toward the axis. .

By doing so, it is possible to more reliably obtain the effect of contacting the steel pipe 1 from the outer peripheral surface side first and heating and melting it sequentially from the outer peripheral surface side toward the inner peripheral surface side.

Note that in both of the above embodiments, no particular mention was made of the current flowing between the electrodes 6 and 7, but if a high frequency current is used for this current, the skin current will increase and the The same effect as the inclined surface 9 shown in FIG. 4 can be obtained.

Further, the copper clad layer disposed on the copper clad steel pipe 2 may be provided only on one of the inner and outer sides of the steel base.

〔Effect of the invention〕

As explained above, the present invention performs τ welding on a pair of steel pipes whose end surfaces are abutted against each other and pressurized at a predetermined pressure by one current heating over a period of 0.2 seconds or more. This makes it possible to prevent the occurrence of flash on the inner surface of the steel pipe by unevenly distributing the flash that occurs in the weld on the outer surface of the steel pipe. You can say J-.

It also prevents the copper or copper alloy layer provided on the outer or inner circumferential surface of the coated steel pipe from getting caught up in the welding area, improving the strength and reliability of the welded area. can.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of butt welding showing one embodiment of the present invention, Fig. 2 is a sectional view taken along the line ■ to ■ in Fig. 1, and Fig. 3 is an explanatory diagram showing the state of steel pipes joined by butt welding. , FIG. 4 is an explanatory diagram showing another embodiment of the present invention, and FIG. 5 shows the state of a steel pipe welded by the conventional butt welding method.
! ! This is a clear diagram. DESCRIPTION OF SYMBOLS 1... Steel pipe, 2... Copper clad steel pipe, 2a... Iron base, 2b... Copper clad layer, 6, 7... Electrode, 8...
...Welded part, 8a... Paris, 8b... Inner peripheral surface, 9.
...Slope surface. Figure 1 L■ *28 3rd eye

Claims (1)

[Claims] 1. The end face of a coated steel pipe whose peripheral surface at least on either the inside or outside is coated with a layer of copper or a copper alloy is butted against the end face of the steel pipe, and both steel pipes are pressurized with a predetermined pressure. A method of butt welding steel pipes, which is characterized in that the welding is carried out by applying electrical current and heating for a time of 0.2 seconds or more. 2. The method of butt welding steel pipes according to claim 1, wherein both steel pipes are pressurized at 10 to 50 Kgf. 3. Butt welding of steel pipes according to claim 1 or 2, characterized in that the end face of one steel pipe forms an inclined face that gradually separates from the end face of the other steel pipe toward the axis. Method.