JPS5926376B2 - Bending method for hollow double pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A double tube with a hollow gap between an outer tube and an inner tube is used for piping or heat exchanger tubes.

The gap between the double tubes is used for the passage of fluid to exchange heat with the fluid inside the inner tube or outside the outer tube, and is also used for the purpose of heat insulation. This type of hollow double pipe is easy to manufacture if it is a straight pipe, but it is not easy to manufacture if it has a bent part. One method is to bend the outer tube and the inner tube separately and then fit the inner tube into the outer tube, but there are restrictions on the bending angle.

Another method is to cover the bent inner tube with appropriately divided outer tubes and join them, but this complicates the process and increases costs, and may not be possible depending on the curved shape. . Therefore, it is considered that the most industrially productive method is to arbitrarily bend a hollow double pipe from a straight pipe.
However, in this case, if the tube is simply bent using a normal tube bending machine, buckling will occur, and a bent tube with a uniform gap between the inner tube and the outer tube cannot be obtained.

Therefore, a method is generally used in which the gap between the inner and outer tubes is filled with a suitable solid to transmit the bending force applied to the outer tube to the inner tube. Low melting point metals, sand, etc. have been used for this filling, but
Even if bending is performed with these fillers in place, the flatness of the beveled portion (Note) may become large after processing, or buckling may occur.
Satisfactory results have not always been obtained because the bending angle is limited to a small range. Dl-D.

(Note: Flattening ratio = ×100, however, D.

is the outer diameter of the pipe before bending, Dl is the long diameter of the pipe after bending, and Ds is the short diameter of the pipe after bending.

) An object of the present invention is to provide a method for bending a hollow double pipe which eliminates the above-mentioned drawbacks. It is also an object of the present invention to obtain a hollow double pipe with a complicated bending shape, a small oblateness, and a good quality with a simple operation. Features of the method of the present invention &
ζThe hollow space between the outer tube and the inner tube is filled with refractory powder such as silica sand or ceramic, which is evenly mixed with thermosetting resin, and the tube is heated to harden the resin in the filled powder. Therefore, it consists in fixing the powder together and bending the tube.

According to this method, even when the filling material is taken out after bending, it can be easily taken out by heating the tube and heating and carbonizing the resin component. Advantageously, this heating also removes processing strains due to bending and can also serve as an annealing treatment. The filling powder must have the property of being able to heat and harden the resin mixed therewith, thereby properly fixing the powder, and transmitting the bending force exerted by the outer tube to the inner tube.
In addition, since the resin is heated and carbonized after bending and removed together with the powder, it must be fireproof, and silica sand or ceramic powder such as alumina, magnesia, or silica is suitable. The particle size of the powder is preferably 100 mesh or less, but depending on the bending angle and bending radius, particles with a particle size larger than 100 mesh can also be used.

Thermosetting resins include phenolic resin, furan resin,
There are xylene resins, formaldehyde resins, urea resins, melamine resins, aniline resins, sulfonamide resins, unsaturated polyester resins, epoxy resins, and others, but this method has thermosetting properties and can be made into a filled powder by curing. Any material can be used as long as it properly fixes the particles together and is compatible with bending. Resin-coated sand, also known as foundry sand whose surface is coated with resin, can also be used for the above-mentioned purpose of this method. The blending ratio of thermosetting resin to the filling powder & It is difficult to make a general restriction because the conditions vary and should be determined by experiment, but a rough idea can be inferred from the examples described later. Further, the heating temperature for thermally curing the resin after filling the powder into the hollow portion varies depending on the resin, and is determined within a range that does not cause carbonization above the curing temperature of the resin.

Similarly, after bending, the heating temperature when carbonizing the resin and taking it out together with the powder varies depending on the resin.
When the annealing process is also performed, resin should be selected depending on the annealing temperature determined by the material of the pipe, and usually 3
00°C or higher is applied. In addition to the method of filling the entire hollow part and round part with powder mixed with thermosetting resin,
Depending on the degree of bending and pipe diameter, powder mixed with thermosetting resin may be used to partially fill the open end of the hollow part, or the open end and several other places, and then fill the remaining hollow part. is filled with powder such as silica sand that does not contain thermosetting resin,
Even if this method is implemented, the effects of this method can be obtained.

In other words, since both ends of the hollow part of the double tube are fixed by the cured resin, if the density of the filling material is taken into consideration, the volume of the filling powder will be maintained constant in the gap space during bending, and the desired This makes it possible to perform bending processes. In this case, it becomes easier to take out the filling after bending. Note that the material of the double pipe to which this method is applied does not matter, and the method can of course be implemented even if the outer pipe and inner pipe are made of the same material or of different materials. Next, examples of this method and effects of implementing the present invention will be described.

Example 1 The outer tube was made of carbon steel, 63.5φXl. 6tX75Ol electric resistance welded tube, inner tube made of SUS3O4, 48.6φXl. 5
Using an electric resistance welded pipe of t x 7501, the hollow part between the double-pipe straight pipes is filled with a powder made by uniformly mixing 5 wt % of phenol resin powder with 100 mesh or less of silica sand as a filler, and the pipe is closed. After heating to 200℃ to harden the phenolic resin in the filling powder and fixing the silica sand, use a roll bender to bend with a radius of 195V! It was bent to lφ and a bending angle of 1300.

The appearance of the processed product was very good, with no buckling at the bent portion.
FIGS. 1 and 2 are curve diagrams showing the distribution of the oblateness of this bent double pipe and the change in the hollow space at the circumferential position of the bending center. As seen in both charts, the distribution of flatness is very small, around 4%, and the gap between the double pipes is uniform over the entire circumference. This bent tube is also annealed at 750°C.
When the tube was heated for 30 minutes in the atmosphere at .degree. C., the filling powder was easily removed, and no springback phenomenon was observed in the tube after the filling was removed. In addition, in FIG. 1, for the purpose of comparing the effects of the method of the present invention, the numerical values when only silica sand of 100 mesh or less is used as the filling powder are also shown as a curve.

In this case, the sand moved during the process, making the actual work extremely difficult, buckling occurred during the bending process, and the flatness was too large to be commercially viable. Example 2 Using the same double tube as in Example 1, bending was performed under the same conditions as in Example 1, using resin coated sand in which the surface of silica sand was coated with 3 wt% phenolic resin as the filling powder. .

As shown in Figures 1 and 2, the oblateness distribution of the processed product and the changes in the hollow space on the circumferential position are both extremely small.
Good results have been obtained. Example 3 Using the same double pipe as in Example 1, powder containing the same resin as in Example 1 was filled into 100 u of both ends of the double pipe cavity, and the remaining hollow part of 550 mJ1 was filled with 20 meshes or less of silica sand alone. The tube was heated to 200° C. to fix the filling powder at both ends, and the tube was bent under the same conditions as in Example 1.

No buckling occurred in either the inner or outer tube, and the distribution of oblateness and changes in the hollow space are as shown in Figures 1 and 2, and this degree of bending is comparable to the previous two examples. Results are being obtained. In order to take out the filling, both ends were heated at 650° C. for 30 minutes, and the filling could be taken out more easily than in the case of the previous example. From its characteristics, it is clear that the method of the present invention can process not only a straight pipe into a simple two-dimensional curve as described in the embodiment, but also a hollow double pipe having a higher-dimensional and complicated curved shape.

[Brief explanation of drawings]

Figure 1 is a curve diagram showing the distribution of oblateness after bending by this method and the same distribution when not using this method. Figure 2 is a curve diagram showing the distribution of oblateness after bending by this method. Figure 2 is a curve diagram showing the distribution of oblateness after bending by this method. FIG. 3 is a curve diagram showing a change in the interval between hollow parts.

Claims (1)

[Scope of Claims] 1. The hollow space between the outer tube and the inner tube is filled with refractory powder such as silica sand or ceramic mixed with a thermosetting resin, and the tube is heated to fill the filled powder. 1. A method for bending a hollow double pipe, comprising: curing the resin component, bending the tube, then heating the tube to carbonize the resin component and removing powder. 2 A part of the hollow part between the outer tube and the inner tube, including both open ends, is filled with refractory powder such as silica sand or ceramic mixed with thermosetting resin, and the remaining hollow part does not contain resin. Each tube is filled with refractory powder, the tube is heated to harden the resin in the filled powder, the tube is bent, and then the tube is heated to carbonize the resin and the powder is extracted. A method for bending hollow double pipes, which is characterized by the following: