JPH0318422A - Manufacture of welded tube small in diameter - Google Patents

Abstract

PURPOSE:To smoothly manufacture a welded tube small in diameter by stretching and reducing the welded tube through plural rolling stands arranged in the poststage of squeeze rolls. CONSTITUTION:A metallic band plate is formed in the shape of a tube, a butt part is heated by high frequency induction and pressurized and welded by squeeze rolls to manufacture the welded tube 4. Then, plural roll stands are arranged in the poststage of the squeeze rolls. Horizontal rolls 5 and vertical rolls 6 are set on the roll stand and the welded tube 4 is stretched and reduced by these rolls 5, 6. In this way, the tube manufacturing speed can be elevated and the product yield can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for efficiently manufacturing welded tubes useful as heat transfer tubes for evaporators, condensers, etc., particularly small diameter welded tubes with an outer diameter of less than 9 mm. ．． [Prior Art] Conventionally, the process of forming metal tubes made of copper, aluminum, or their alloys by high-frequency induction welding involves forming a metal strip into a tube shape using forming rolls, and then forming the tube as shown in Figure 2. A process is adopted in which the mating surfaces of the tubular body 1 are heated by an induced current from an induction heating coil 2, and then the welded surfaces are pressed and joined using a squeeze roll 3. A similar process is used when high-frequency current is supplied by direct energization. [Problem to be Solved by the Invention] However, in the case of the above process, as the diameter of the welded pipe becomes smaller, the high frequency current spreads to the circumference (outer and inner circumference) of the pipe.
This causes a phenomenon in which the flow becomes concentrated in the circuit and the amount of shunt to the butt portion decreases, resulting in local heating being inhibited and cases in which welding becomes impossible. The limit of the pipe diameter that does not cause such welding failure is about 9 mm.
It was impossible to weld tubes with an outer diameter smaller than this using high-frequency current heating. The present invention makes it possible to efficiently manufacture thin pk welded pipes with an outer diameter of less than 9 mm by adding a stretch reducing process to the conventional process. [Means for Solving the Problems] That is, the method for manufacturing a small diameter welded pipe provided by the present invention involves forming a metal strip into a tubular shape, heating the abutting portions by high-frequency induction, and joining them under pressure using a squeeze roll. In the method for manufacturing a welded pipe, the welded pipe is stretch-reduced through a plurality of roll stands disposed downstream of the squeeze roll. For the purpose of the present invention, it is preferable to use a metal band plate with grooves on one side and to form it into a tube with the grooved surface facing inside. Figure 1 shows 1 of the stretch reducing process of the present invention.
The figure shows an example in which a welded pipe 4 with an outer diameter of 9 mm or more that has been pressure-joined with squeeze rolls gradually becomes thinner as it passes between multiple rolls including horizontal rolls 5 and upper and lower rolls 6 facing each other. The material is reduced in diameter and finally processed into the desired fine diameter size. Stretch reducing roll stands can set the horizontal roll and the upper and lower rolls in the same position, and the rolls can be either driven or non-driving, and a combination of both can be installed. In addition, in the case of a trick type, each stand may be an independently driven type, or a trick type with multiple stands connected together. The degree of stretch reducing in each roll stand is desirably set to at least 0.2 m, and the maximum narrow diameter size is preferably up to 2lI. Each diameter reduction amount of the stretch reducing is 0.
If you try to make the final diameter smaller than 21111 by going below 2, the number of rolls will increase and the tube material will harden during the processing process, making it difficult to make the diameter smaller smoothly.

(Function) According to the present invention, metal tubes with an outer diameter of 9 mm or more can be reliably joined by a normal high-frequency induction welding process, and then the diameter can be continuously reduced by the subsequent stretch reducing process. Therefore, welded pipes with a diameter of less than 9 mm can be smoothly manufactured without causing welding defects. [Example] A copper metal strip plate with grooves on one side is placed with the grooved surface on the inside. It is formed into a tubular shape using a forming roll, and the output is 120.
Using a high-frequency induction welding machine with a Kw and a frequency of 40QKflz, welded the pipes under pressure through a squeeze roll at a tube-forming speed of 80 m/s+in to form a welded pipe with an outer diameter of 9 mm. Next, the welded pipe was continuously passed through a stretch reducing process in which it was connected to the rear stage of a squeeze roll. The stretch reducing device consists of four stages of horizontal roll stands and four stages of upper and lower roll stands as shown in Figure 1. Only the upper and lower rolls are moved at once, and the bottom diameter of each roll is reduced to increase the distance between the stands. It was designed to create a comfortable force. In the stretch reducing device described above, the diameter reduction amount of each roll stand is 0.3 mm for the first horizontal roll and upper and lower rolls, 0.27 ms for the second horizontal roll and upper and lower rolls, and 0.27 ms for the third horizontal roll. The outer diameter was set to 0.23 mm for the upper and lower roll parts, and 0.2 av for the fourth stage horizontal roll and upper and lower roll parts, and the outer diameter was finally reduced to 8 mm. The thus obtained small-diameter welded pipe had no welding defects and had good pipe accuracy.

〔Effect of the invention〕

As described above, according to the present invention, a small diameter welded pipe with an outer diameter of less than 9 mm can be smoothly manufactured by high frequency induction welding. Furthermore, because the tube manufacturing speed is high and the product yield is good, it can be supplied efficiently and inexpensively as heat transfer tubes for evaporators, condensers, etc.

[Brief explanation of the drawing]

Figure 1 is a side view illustrating the stretch reducing process used in the present invention, and Figure 2 is a perspective view illustrating the conventional high frequency induction welding process. 1... Molded tubular body 3... Squeeze roll 2... Induction heating coil 4... Welded tube 5... Horizontal roll 6... Upper and lower rolls

Claims (1)

[Scope of Claims] 1. In a method for manufacturing a welded pipe by forming a metal strip into a tubular shape, heating the abutted portions with high frequency induction, and joining them under pressure with a squeeze roll, the method comprises: A method for manufacturing a small-diameter welded pipe, comprising stretch-reducing the welded pipe through a plurality of roll stands. 2. The method for manufacturing a small diameter welded pipe according to claim 1, wherein a metal strip plate with grooves on one side is used and formed into a tubular shape with the grooved surface facing inside.