JPS5948716B2 - Submerged discharge tube expansion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a submerged discharge tube expansion method applied to joining a tube sheet and a tube.

A tube expansion method using rollers as shown in FIG. 1 is generally used to join the tube sheet and the tube.

1 is a tube plate, 2 is a tube joined to this, a mandrel 3, a roller 4, and a cage 5 are inserted into the tube 2, and 6 is a stopper block.

The roller 4 maintains a certain angle with the mandrel 3, and rotates while rolling on the inner surface of the tube 2 as the mandrel 3 rotates. The mandrel 3 is tapered and is inserted into the tube 2 while rotating due to interaction with the cage 5 and the rollers 4, and the rollers 4 expand the tube 2 due to the taper. The tube sheet 1 and the tube 2 are joined by this tube expansion action. However, in the above joining method, (a)
As the tube expansion length increases, the number of steps increases due to multiple steps; (b) load is repeatedly applied to the tube due to the rotation of the rollers, resulting in work hardening of the inner surface of the tube; (--) The growth is large and it is necessary to pay attention to this when working.
: Many problems have been pointed out, such as when the inner diameter of the pipe is small, mechanically sufficient torque cannot be transmitted to the rollers, resulting in insufficient pipe expansion.

The submerged discharge tube expansion method is a promising method to solve these problems and replace the above-mentioned bonding method.

However, this method currently has problems such as (a) abnormal discharge is likely to occur between the power supply and the tube sheet, and (b) tube expansion conditions are not certain, so it cannot be put to practical use as it is. do not have.

This invention aims to solve obstacles to the practical application of the submerged discharge tube expansion method by clarifying tube expansion conditions including measures to prevent abnormal discharge when applying the submerged discharge tube expansion method to the joining of tube sheets and tubes. is removed.

That is, in the submerged discharge tube expansion method, a power supply part is attached to the end, a liquid-filling insulating cartridge with a thin metal wire stretched is inserted into the tube, the tube is expanded by submerged discharge, and the tube is joined to the tube plate. This invention method involves protruding an insulating cartridge for liquid filling with a wall thickness of type 2 or higher by 3 cm or more from the tube plate surface, and extending a power supply line coated with an insulating tube with a wall thickness of type 1 or higher by 5 cm from the tube plate surface. It is characterized in that the pipe is made to protrude above, and then a conventional pipe expansion operation is performed. Hereinafter, the present invention will be explained in detail with reference to the drawings.

In FIG. 2, 1 is a tube plate, 2 is a tube to be joined to this, and for the purpose of joining, a cartridge having the following structure is inserted into the tube 2.

That is, 7 is an inner cylinder made of polyethylene constituting the main body of the cartridge, the open end of which is closed with caps 8a and 8b, so that the inside is filled with water 14. A thin aluminum wire 9 with a diameter of about 0.5 to 1.5 mm is stretched inside the inner cylinder 7, and one end of the wire 9 is connected to the cap 8a.
The other end is grounded to the tube 2 via the cap 8b. Power supply section 11
is connected to a power supply line 11 made of aluminum or the like covered with an insulating tube 10 made of polyethylene, and this power supply line 11 is connected to a circuit connecting a large capacity capacitor 12, a switch 13, and a tube plate 1.

In such a configuration, when the capacitor 12 is charged in advance and the switch 13 is closed to supply power to the cartridge, the large energy discharged from the capacitor 12 instantly destroys the thin aluminum wire 9 and the water 14 around it. Vaporize.

The submerged discharge tube expansion method utilizes the explosive force generated at this time to expand the tube 2 and tightly join it to the tube sheet 1. By the way, the discharge energy is E, and the capacitance of the capacitor 12 is C.
If the charging voltage is V, then the relationship between these is E=CV
It is expressed as 2/2 (joule). The tube expansion energy is tube 2
Although it varies depending on the material and shape of the pipe, if the material of the pipe 2 is SUS and the shape is about 3/4BSch20, C=100μF when the pipe expansion length is about 15cm. V=10kV.

7. However, when such a high voltage is applied, abnormal discharge is likely to occur between the power supply section and the tube plate 1.

As a result of repeated research on measures to prevent abnormal discharge, the inventors found that
The inner cylinder 7 has a wall thickness of 2 mm or more, and is arranged so as to protrude so that the distance 1 from the surface of the tube plate 1 is 3 cm or more, and the thickness of the insulating tube 10 is 1 mm or more,
By arranging the power supply line 11 so that it protrudes so that the distance L from the surface of the tube plate 1 is 5 cm or more, and by taking these considerations, it is possible to prevent sparks between the power supply line 11 and the tube plate 1, and to prevent internal damage. The tube expansion operation could be carried out smoothly without damaging the tube 7. The inner tube 7 and the insulating tube 10 may be made of any material as long as it has insulation properties, workability, elongation, and appropriate rigidity, and in addition to polyethylene, vinyl chloride resin, rubber, etc. can be used.

Further, the thin wire 9 inserted into the inner tube 7 may be made of any metal or alloy that has a low melting point and good electrical conductivity, so that copper, tungsten, etc. can be used in addition to aluminum.

It is preferable that the insulation tube 10 and the inner cylinder 7 be thinner.

This is because if the thickness is too large, the member itself will act as a cushioning material. On the other hand, as a result of experiments, the inventors were also able to discover that energy per tube expansion length can be used as a tube expansion parameter.

First, the inner diameter of the expanded tube was actually measured, and the relationship shown in FIG. 3 was obtained when the length in the tube axis direction was plotted on the horizontal axis and the tube expansion rate was plotted on the vertical axis.

The pipe expansion rate was calculated using the following formula. As is clear from FIG. 3, in general, in discharge tube expansion, the tube expansion at both ends of the region filled with liquid is insufficient, and uniform tube expansion cannot be achieved.

According to research, it has been found that the tube expansion rate of the stationary portion is determined by the above-mentioned discharge energy as the energy per unit length of the thin wire in the liquid. That is, if the energy per unit length of the thin wire is e, then this is expressed as.

FIG. 4 is a graph showing the correlation between the tube expansion rate and e.

Although this correlation was not derived from strict mathematical considerations, the above graph is easy to handle and has a reasonable degree of accuracy, and has industrially useful value.

As described in detail above, the present invention has been developed by clarifying the tube expansion conditions, including measures to prevent abnormal discharge, when applying the submerged discharge tube expansion method to join a tube sheet and tube. This method has been put to practical use and will make an industrially important contribution to the field of joining.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view showing the process of joining a tube sheet and a pipe using a conventional pipe expansion method, and FIG. 2 is a partial cross-sectional view showing a process of joining a tube sheet and a pipe using a pipe expansion method according to an embodiment of the present invention. Figures 3 and 4 show the tube expansion conditions obtained in one embodiment of the present invention. Figure 3 shows the correlation between the tube expansion rate and the tube axis direction, and Figure 4 shows the correlation between the tube expansion rate and the discharge energy e. shows. 1...Tube plate, 2...Tube, 3...
・Mandrel, 4...Roller, 5...
Cage, 7...Insulating inner cylinder, 8a, 8b...
... Cap, 9 ... Aluminum thin wire, 1
0... Insulating tube, 11... Power supply line, 12... Capacitor, 13... Switch, 14... Water.

Claims (1)

[Claims] 1. In the submerged discharge tube expansion method, a liquid-filling insulating cartridge with a power supply line connected to the end and a thin metal wire stretched is inserted into the tube, the tube is expanded by submerged discharge, and the tube is joined to the tube plate. An insulating cartridge for liquid filling with a wall thickness of 2 mm or more protrudes from the tube plate surface by 3 cm or more, and a wall thickness of 1 mm.
A submerged discharge tube expansion method characterized in that a power supply line covered with the above-mentioned insulating tube is made to protrude 5 cm or more from the tube plate surface, and a conventional tube expansion operation is performed in this state.