JPH02286992A - Attaching flange to metallic pipe - Google Patents

Abstract

PURPOSE:To increase joint strength and improve the ease of fitting work by fitting a flange having a heated hub section over the end of a metallic pipe, making them in a body by the thermal contraction, and fillet welding them together. CONSTITUTION:A metallic pipe 1 is made of for example ductile cast iron with its end outer circumferential surface machined by about 1 mm to form a stepped portion 2 for fitting. A fitting flange 3 of the same material with the cast iron pipe 1 consists of a flange portion 4 and a hub portion 5 with its flange inner diameter machined to a specified dimension. After expanding the flange 3 by heating with a burner to 200 - 400 deg.C, it is quickly fit over the fitting step portion 2 of the pipe 1. The fitting is easily performed as clear ance fit because of thermal expansion of the flange 3. After the fitting, the flange 3 comes in tight contact with the cast iron pipe 1 with the thermal con traction of the heated flange 3. The cast iron pipe 1 and the end of the hub portion 5 are fillet welded 7 to form a ductile cast iron pipe with welded flange. The end surface of the cast iron pipe 1 and the flange 3 are machined to obtain a product.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of attaching a flange to a metal pipe such as a ductile cast iron pipe.

[Prior art] As one of the conventional methods, it has been proposed to attach a flange to a metal pipe by press-fitting (for example, Japanese Patent Laid-Open No. 5
5-131433).

In this press-fitting method, as shown in FIG. 4(A), a metal tube 1 having a dimensional relationship of interference fit is inserted, and a mechanical external force is applied by a hydraulic jack 8 to the flange 3 along the tube axis of the metal tube 1. Push-in assembly, the metal pipe 1 and insertion flange 3
are welded 7 as shown in Fig. 4 (b).

[Problems to be Solved by the Invention] However, if the outer diameter of the metal tube and the inner diameter of the insertion flange are distorted or the center axes of the two are misaligned, it is difficult to obtain uniform fitting force (bonding force) over the entire fitting surface. In some cases, local gaps may occur. For this reason, there was a limit to obtaining higher bending strength.

Therefore, flanges having a hub portion are often used. As a result, the distance from the tube end to the welded portion becomes longer, so it can be said that the bending strength increases.

On the other hand, by having this hub part, it is necessary to increase the pressing force during press-fitting, which not only increases the size of the press-fitting equipment, but also increases the bonding force after fitting in proportion to the increase in this pressing force. The problem is that it does not.

In addition, in this press-fitting method, if there is no dedicated equipment, it takes time to assemble the jig and center the fittings, and the fitting operation cannot necessarily be said to be good.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a method for attaching a flange to a metal tube that has high bonding strength and good fitting workability.

[Means for Solving the Problems] The method of attaching a flange to a metal tube of the present invention involves fitting a flange having a heated hub portion to the end of a metal tube, integrating the flange by heat shrinking, and attaching the flange to a metal tube. This involves fillet welding the tube and hub.

[Operation] A flange having a hub portion whose inner diameter is thermally expanded by heating to a required temperature is fitted into a metal tube. Since this fitting is performed by a clearance fit, it is easily performed without using a pushing device.

After fitting, strong integration is achieved due to heat contraction accompanying cooling (air cooling) of the flange.

Moreover, even if there is some distortion in the roundness of the two, the thermal contraction of the flange will gradually and evenly tighten the two, resulting in a fit with better adhesion. It is difficult for the center axis to shift or tilt.

[Example] Embodiments of the present invention will be described based on the drawings.

In FIG. 1, reference numeral 1 denotes a metal pipe, for example, a ductile cast iron pipe, and the outer circumferential surface of the end thereof is cut to a depth of approximately 1 mm to form a fitting stepped portion 2. As shown in FIG.

Reference numeral 3 designates an insertion flange made of the same material as the cast iron pipe 1, and consists of a flange portion 4 and a hub portion 5, and the inner diameter of the flange 3 is also cut to a predetermined size. Note that 6 is required for the bolt hole.

The relative dimensions of the cast iron pipe 1 and the flange 3 are processed so as to provide a clearance fit.

The insertion flange 3 manufactured as described above is attached to a burner (
or heating furnace) to 200'C to 400'C
After heating and expanding it, it was immediately fitted into the fitting stepped portion 2 of the cast iron pipe 1. The iN fitting is easily inserted due to clearance fit and thermal expansion of the flange 3.

After the fitting, the heating flange 3 is tightly attached to the cast iron pipe 1 by thermal contraction.

Thereafter, the cast iron pipe 1 and the end of the hub part 5 are fillet welded 7 to produce a welded flange-equipped guktile cast iron pipe, and the flange 3 and the end face of the cast iron pipe 1 are machined to produce the product shown in Fig. 2. I got it.

In addition, especially when the cast iron pipe 1 is made of pearlitic cast iron or bainitic cast iron with low toughness, the elongation is relatively small.
The shrink-fit method is more advantageous than the press-fit method in terms of crack resistance. Moreover, the flange 3 may be made of SS material.

(Example) Ductile cast iron pipe with nominal diameter 200φ (inner diameter 208φ,
Using a tube with an outer diameter of 220φ, a tube length of 5000mm, and a wall thickness of 6゜0mm, the outer periphery of the tube end was cut to make the outer diameter dimensional accuracy of the fitting step part 218φ (10, -0, 1).Similarly, Machining the inner diameter of a homogeneous flange (width 47m>) with inner diameter accuracy of 2
It was set to 17.75 mmφ (10, -0,05).

The flange thus formed is heated to 250°C using a burner.
After heating, the flange was immediately fitted into a cast iron pipe and the flange was waited for to cool. Thereafter, the end of the hub portion and the cast iron pipe were fillet welded to obtain a test pipe.

(Example 2) Ductile cast iron pipe with a nominal diameter of 200φ (inner diameter 205φ,
1q of test tubes were used as in Example 1, using an outer diameter of 220φ, a tube length of 5000 mm, and a wall thickness of 7°5 mm. The flange was the same as in Example 1 above.

(Example 3) The same cast iron pipe as in Example 1 was used.

The width of the flange was 94 mm, and the processing accuracy was the same as in Example 1.

(Comparative Example) Using a ductile cast iron pipe having the same nominal diameter as in the above example, the outer periphery of its end was machined, and the inner diameter of the flange was also machined. Then, the machining dimensional accuracy (tightening margin) of both parts was set to 0.4.
It was set to 3 mm.

Next, the flange was tightened to 0°95T using a hydraulic jack.
After fitting into a metal tube with a pressing force of ON, fillet welding was performed in the same manner as above to obtain a comparison tube.

As shown in Fig. 3, each of the test tubes and comparison pipes prepared in the above manner was brought together at their flanges and fastened with bolts. The table below shows the results of a bending test with a load applied from the center.

In the bending test, a load was applied until the welded part broke, and the bending moment at this time was measured.

Further, the ratio is the bending moment of each example expressed in % when the bending moment of the comparative example is taken as 100%.

As is clear from the table above, the bending moment of Example 1 was significantly improved by 30% compared to the comparative example due to the strong integration.

Furthermore, as for Example 2, as a result of the increased rigidity due to the increase in the tube thickness, the bending moment was improved by 74% compared to the comparative example.

Roughly speaking, in Example 3, the integration was greatly improved by increasing the length of the 7-lunge, and as a result, the bending moment was improved by 64% compared to the comparative example.

As described above, the shrink-fitting method of the present invention exhibits superior bending moment characteristics compared to the press-fitting method.

[Effects of the Invention] Since the present invention is configured as described above, it has the following effects.

Since the flange is fitted to the metal tube using a shrink fitting method, fitting can be performed with a gap without using a pushing device such as a hydraulic jack, making the work extremely easy.

In addition, the flanged metal tube obtained in this way has a good compatibility between the metal and the 7-lunge, and is strongly integrated, and this integration strengthens the bonding force and prevents fracture bending (cracking of the welded part). This resulted in a significant improvement in terms of performance (performance).

[Brief explanation of drawings]

FIG. 1 is a partially cutaway vertical cross-sectional view before fitting according to an embodiment of the present invention, FIG. 2 is a partially cutaway longitudinal cross-sectional view after fitting according to an embodiment of the present invention, and FIG. A schematic diagram showing the test method, FIG. 4 shows a conventional example, FIG. 4(a) is a schematic diagram of a press-fitting method, and FIG. 1... Ductile cast iron pipe 3... Insertion flange 5... Hub part

Claims (1)

[Claims] (1) A flange having a heated hub part is fitted into the end of the metal pipe, and the flange is integrated by heat contraction, and the metal pipe and the hub are fillet welded. Flange mounting method.