JPH06109184A - Joining method for thin wall pipe - Google Patents

Abstract

PURPOSE:To provide a method for surely joining a thin wall pipe by utilizing a joint made of shape memory alloy, namely the method which is simple in execution and can highly reliably join the thin wall pipe since threading and welding are difficult for joining a thin wall stainless steel pipe. CONSTITUTION:The end parts of pipes 2, 3 to be joined are taper-machined, and a tapered shape memory alloy joint 1 is inserted inside an opened bore and heated for joining them. Since any of too large or small slope of a tapered part is inconvenient, the slope of the tapered part is set up within a range about from 1/200 to 1/10, preferably from 1/150 to 1/50. Thus, even if the pipes 2, 3 to be joined have a difference in their outer diameter and a dent, they are reformed during taper-machining to form a joined state having extremely high reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a thin pipe and a fastening method for fastening a pipe.

[0002]

2. Description of the Related Art The types of pipes used, their applications,
There are many types according to the type of fluid to be handled, and correspondingly, there are also many types of piping construction methods. The most commonly used pipe construction method is a method of fastening the pipes by cutting a male thread at the end of the pipe and engaging with a joint having a female thread, or by welding. However, when the wall thickness of the pipe is extremely thin, it is difficult to thread the end portion, and thus it is impossible to use the threaded joint. On the other hand, the welding method cannot be used easily because the pipe is likely to be melted when the wall thickness is thin. Thin stainless steel pipes for indoor piping have excellent corrosion resistance, and despite the large demand for water pipes, the practical examples do not grow as much as expected because they have good performance and are easy to install. The main reason is that there is no joint that can be made.

Various pipe joints using shape memory alloys have great promise as joints for such thin pipes. There are various types of shape memory alloy pipe joints, but basically, shape memory alloy cylinders are manufactured with an inner diameter slightly smaller than the outer diameter of the pipe to be fastened. After the pipe is expanded to an inner diameter slightly larger than the outer diameter of the pipe, the cylindrical portion is heated after the pipe is inserted and then the cylindrical portion tries to recover its shape to the narrow inner diameter stored previously. It uses the force to tighten the pipe. Since the heating for recovering the shape is usually about 200 to 300 ° C. at most, there is no need to worry about melting the pipe like welding. Also, by threading the pipe like a threaded joint,
There is no reduction in strength due to the thinning of the originally thin pipe. Since the contraction force of the shape memory alloy cylinder acts uniformly on the circumference of the cylinder, it is characterized in that it can be fastened so as to wrap the thin-walled pipe without crushing or damaging it.

However, a pipe joint made of a shape memory alloy also has a big drawback. Among shape-memory alloys, low-cost shape-memory alloys that are easy to process and can be used in large quantities, such as pipe joints, have limited shape recovery characteristics, and the outer diameter of the pipe to be fastened is very uniform. The biggest problem is that it can't be used easily unless it's included. As a matter of course, the outer diameter of the pipe is allowed in the standard up to a certain variation. There is no problem if the magnitude of the strain generated in the shape recovery process of the shape memory alloy is a large value with a margin compared to the allowable outer diameter range of the pipe. However, for example, the actual amount of shape recovery of the iron-based shape memory alloy that is the cheapest and cheapest is at most 3.5% as the shrinkage ratio of the inner diameter of the cylinder when processed into a cylindrical shape that serves as a joint. The accuracy of the outer diameter on the one pipe side may exceed 4% in a small pipe diameter range. In such a case, if the inner diameter of the joint is made large enough to be inserted into a pipe having an outer diameter of the upper limit of the specification, the shrinkage allowance of the shape memory alloy will be reduced when the pipe is used near the lower limit of the specification. Then it will be impossible to conclude.

Another drawback of shape memory alloy pipe fittings is that it is difficult to ensure that the required length of pipe is inserted into the opening of the fitting. In order for the shape memory alloy pipe joint to exhibit the perfect fastening performance, it is natural that the pipe must be inserted into the joint by an appropriate length. However, since it is not possible to directly confirm where the inserted pipe tip is inside the joint, it is necessary to mark in advance a fixed position from the end of the pipe, and the reference position will be the opening end of the joint. It is necessary to manage it by inserting it securely until it overlaps the part. However, in this way, even if the insertion of the proper length is performed once, it is not easy to avoid the omission during the heating of the joint.

The following measures have been considered for such drawbacks of the shape memory alloy pipe joint. First, for the former variation in pipe outer diameter, the inner diameter of the joint opening may be stepped or tapered so that the relationship between the actual outer diameter of the pipe and the inner diameter of the joint is always appropriate. (Kaihei 1-295092 gazette) or the middle portion of the joint is made thin so that the left and right sides of the joint can contract without interfering with each other according to the outer diameter of the inserted pipe (Actual Kaihei 2-29385). Issue). Further, in the latter case, that is, in order to properly secure the insertion length of the pipe into the joint, a method of providing a "positioning ring" for the pipe to abut on the central portion of the joint (Japanese Patent Laid-Open No. 3-48091) is proposed. Has been done. Of these, a joint (Japanese Patent Laid-Open No. 1-295092) that can be used for fastening pipes having an outer diameter difference in which the inner diameter of the opening of the joint is stepwise or tapered is the one previously filed by the present inventors. However, making the opening in a stepped shape has a tendency that the joint length becomes too long and has not been widely used in practice. Also, in the case of a joint with one opening tapered, the end of the pipe that has been cut is inserted into the tapered joint opening, so the contact between the inner surface of the joint and the outer surface of the pipe is likely to be incomplete, and it is not always perfect. However, there is a drawback that it is not always possible to perform such a fastening.

[0007]

The biggest drawback of pipe joints using shape memory alloys is that the stable fastening performance cannot be ensured if the outer diameters of the pipes to be fastened vary. On the other hand, we have found a solution that is as inexpensive as possible, and in particular provide a method for fastening pipes that can be used for fastening thin-walled pipes that have not had suitable fastening means in the past and that is easy to perform and has excellent joint performance. That is the object of the present invention.

[0008]

SUMMARY OF THE INVENTION The gist of the present invention is that a pipe end on the side to be fastened after being cut to a required length is tapered so that the pipe end having the above-mentioned taper is formed. Part is inserted into a shape memory alloy joint in which an opening for inserting a pipe is formed so as to have a taper such that the inner diameter becomes smaller from the end part toward the back, and then the shape memory alloy part is formed. The method for fastening thin-walled pipes is characterized in that the joint part of (1) is heated above the shape recovery temperature of the alloy. However, the shape memory alloy joint is plated on at least the inner surface of its opening,
A sealant may be applied to the inner surface of the opening, or the above-mentioned plating and sealant may be used in common.

It goes without saying that the ideal as a joint for fastening a pipe is that the fastening work can be performed without adding any work on the side of the pipe to be fastened. If there is a joint that can obtain sufficient performance by inserting the pipe cut to the required length into the joint as it is, there is no substitute for it. There is no way that some joints that use welding do not require work on the pipe side, but welding is not something that anyone can do, even if it can be subtracted that pipe end surface processing is unnecessary. It is hard to say that the work of fastening the pipe is easy. Generally, a male thread is processed on the end face of the pipe,
At present, the method of screwing into a joint having a female thread is more widely used because it is easier to carry out in construction work.

A joint using a shape memory alloy has the potential to greatly improve the existing pipe fastening method in terms of construction simplicity, which requires neither welding nor screws. A joint that can be fastened as it is without any preliminary processing on the pipe side can be made depending on the conditions. However, unless an expensive alloy with excellent shape recovery characteristics is used,
In the case of a joint that uses an inexpensive shape memory alloy that can be industrially used in large quantities, variations in the outer diameter of the actual pipe,
It is not easy to prevent a difference in the performance of the fastening part due to a cause such as a dent or a scratch caused during transportation. If the pipe to be fastened is thin, the pipe end is easily deformed, so special care is required. In order to realize a pipe joint made of a shape memory alloy or a pipe fastening method that is not easily affected by factors that make fastening unstable, it is necessary to use an alloy that is expensive but has excellent performance. This is one way of thinking. However, on the contrary, by allowing some preliminary work to be performed on the pipe to be fastened, it is possible to use a fitting made of an inexpensive alloy with insufficient performance Isn't it possible to realize the method?

From the above viewpoints, the present inventors have studied the simplest method for solving the problems of the current shape memory alloy pipe joints, and as a result, as the joints, the present inventors In addition, a joint for fastening a pipe having an outer diameter difference in which the inner diameter of the opening is tapered, which has been completed before, is used, and the pipe side to be fastened is as follows. It is concluded that it is best to add loose taper to the end of the cut pipe, insert it into the tapered opening of the joint, and fasten it by shrinking the shape memory alloy joint cylinder by heating. Has reached. Although the process of tapering the end of the pipe is an extra task, the process of giving a slight taper to a pipe with a thin wall is usually performed in piping work using a threaded joint. It is much easier than threading work on existing pipes and is well within the range acceptable for field work.

In the pipe to be fastened by the shape memory alloy pipe joint according to the present invention, it is necessary to taper the end portion of the pipe after being cut to a prescribed length. Since this taper processing has an important meaning in the present invention, this point will be described first. The taper processing is the outer diameter of the end of the pipe after processing (Fig. 2
It is necessary that d1) of (1) is approximately constant for a series of pipes of the same size to be fastened. Machining may be done with a lathe, but Fig. 3 (a)
In order to avoid such a decrease in the wall thickness of the pipe end as described above, it is more preferable to perform the cold drawing as shown in FIG. 3B. If the taper is too loose, the machining range will be too long, while if the taper is too steep, the pipe after fastening will easily come out, so the gradient with respect to the diameter is in the range of about 1/200 to 1/10, more preferably 1 It is preferably in the range of / 150 to 1/50. Further, it is appropriate that the outer diameter of the endmost portion, that is, the size of d1 in FIG. Since taper processing is performed according to such conditions, the length of the taper portion formed at the end of the pipe (L1 in FIG. 2) is equal to the original outer diameter of the pipe (see FIG. 2).
If D) is large, it becomes long, and if it is small, it becomes short.

A shape memory alloy joint for use in the pipe fastening method according to the present invention is a joint for fastening pipes having an outer diameter difference in which the inner diameter of the opening is tapered (see Japanese Patent Laid-Open No. The joint described in the second invention of Japanese Patent No. 295092) is used, but the taper of the opening of the joint is the same as the taper formed at the end of the pipe to be fastened. Fig. 4 shows some examples, but as shown in the figure, the opening of the joint has a taper that becomes smaller in diameter from the end face toward the back, and is the most tapered. The diameter (d0 in Fig. 4) of the open portion should be the same as or slightly smaller than the outer diameter (d1 in Fig. 2) of the tip of the tapered pipe to be fastened with this joint. To do.

Next, a specific method of inserting and fastening the above-described tapered pipe into the shape memory alloy joint having the above-described tapered opening will be described. Before that, it is desired to confirm the inconvenience that occurs when using a general shape memory alloy piping joint not according to the present invention by referring to FIG. In FIG. 5, 10
Is the most basic shape memory alloy pipe joint. Among existing shape memory alloy pipe joints, some have a protrusion on the inner surface of the joint, or have a liner and a sealant, but here, the joint having the simplest inner surface is exemplified. Among the pipes to be fastened with this joint, 20 is a pipe having a relatively large outer diameter. When this pipe is inserted into the joint 10, the gap (g ₁ ) between the joint inner diameter and the pipe outer diameter becomes a very small value as shown in FIG. If 10 shrinks the inner diameter only slightly by heating, the pipe will be tightly tightened. On the other hand, the pipe indicated by 30 has a relatively small outer diameter. When this pipe is inserted into the joint 10 made of the same shape memory alloy, the gap (g ₂ ) between the joint inner diameter and the pipe outer diameter becomes a large value as shown in FIG. Even if the joint shrinks due to heating, it may be difficult to sufficiently fasten the pipe.

As another example, according to the present invention, there is provided a joint for fastening pipes having an outer diameter difference in which the inner diameter of the opening used in the present invention is tapered (Japanese Patent Laid-Open No. 1-295092). Fig. 6 shows the fastening method when the pipe is fastened according to the original usage of the joint. When a thick pipe ((a) in FIG. 6) and a thin pipe ((b) in FIG. 6) are inserted into the joint opening as in the case of FIG. 5, only the end of the pipe surely becomes the joint opening. A state where there is no gap is realized partially by contacting the inner surface. However, it is self-evident that the contact between the inner surface of the joint and the pipe is line contact only at the circumferential portion of the pipe end. When the shape memory alloy joint is heated in this state to shrink the inner diameter, a tentatively fastened state is achieved, but the inner surface of the joint opening and the outer surface of the pipe are in close contact with each other. Since it cannot be obtained, the characteristics of the joint portion after being fastened by this method cannot always be stable and ends up.

On the other hand, the pipe fastening method according to the present invention
Will be described with reference to FIG. 1 in FIG. 1 has a taper at the opening.
A shape memory alloy pipe joint having 2;
Pipe with a relatively large outer diameter,
It is a pipe with a small outer diameter that is going to be fastened with the same joint.
For both the 2 and 3 pipes, cut the end face of the pipe
The outer diameter of the tip is
The tape should be of a certain size regardless of the outer diameter of the pipe.
It has a pad. Therefore, whichever has different original thickness
Even when these pipes are inserted into the joint, the pipe tip
After being inserted to approximately the same position as the joint opening, the joint opening
Determined by contact between the tapered surfaces of the inner surface of the part and the outer surface of the pipe
Stop at a tight position. Originally with a thick outer diameter
Since the taper processed area is long,
Although it extends to the outside of the hand, the original outer diameter is fine
On the other hand, the tapered part is completely
It fits inside and you can see the taper of the pipe from the outside.
There is a difference that it is gone. But in either case
Also, the same length of pipe is inserted in the joint,
Moreover, the joint according to the fastening method not according to the present invention described above.
When the pipe was inserted into the
Gap between the outer diameter of the₁) And (g ₂)) Gas
There is a line between the pipe and the fitting
The major feature is that they are not in contact but in close contact with each other.

In order to fasten a pipe with a pipe joint made of a shape memory alloy, in the case of the conventional method not according to the present invention, the state shown in FIGS. 5 and 6 is used, and in the case of the fastening method according to the present invention. In the state of FIG. 1, the joint is heated to a constant temperature. This heating causes the shape-memory alloy joint to shrink and fasten the pipe so as to wrap it from the surroundings. However, in the case of the present invention, even if the outer diameter of the pipe to be fastened varies, As shown in 1, the joint can be contracted after the joint inner diameter and the pipe outer diameter are always in close contact with each other without any clearance, so that all the joint contraction is converted into the pipe fastening force. , Very stable fastening can be realized.

The above description has been made for the case where the outer diameter of the pipe to be fastened has varied, but the pipe end to be fastened is also to be fastened even if the pipe end has a scratch or deformation. Since the taper is preliminarily corrected to a considerable extent, variations in fastening performance caused by these factors are extremely unlikely to occur in the present invention. Further, in the case of a shape memory alloy joint having no taper in the opening, if the pipe is pushed into the joint, it will be pushed in, and there is a risk of pushing out the pipe inserted from the opposite side. On the other hand, in the case of the method according to the invention of inserting a tapered pipe into the tapered joint opening, the outer diameter d1 of the pipe tip is equal to or smaller than the inner diameter d0 of the most narrowed part of the joint opening.
As long as the taper is properly tapered to a larger area, the tapered part of the fitting and the tapered part of the fitting will stick to each other before the pipe tip reaches the most narrowed part of the fitting. There is no need to worry about pushing out the pipe inserted from. Furthermore, even if there is a concern that the inserted state of the pipe will change while the joint is being heated, there will be almost no problem by heating while applying a force that gently pushes the pipe toward the joint. You can

Although the above description has been made about the simplest case of linearly fastening a pipe, it is naturally possible to apply the fastening method of the present invention to a joint portion for a bent portion or a branch. Regarding the heating required when fastening a pipe using the shape memory alloy pipe joint according to the present invention, since various types of shape memory alloy pipe joint heating devices have been already developed, Among these, it is possible to select and use one that meets the construction conditions.

The purpose of applying the plating to at least the inner surface of the cylinder is to prevent the corrosion of the joint when the fluid passing through the inside of the piping system is highly corrosive. This plating basically needs to be on the inner surface of the joint, but it does not matter if the entire surface including the outer surface and the end surface of the joint is plated for work. As the type of plating, commonly used nickel, chromium, copper, zinc, etc. or alloy plating mainly composed of these can be used. However, if hydrogen is adsorbed during plating, the alloy may become brittle and broken, so it is desirable to apply a thin coating by electroless plating. The sealant is also used for the same purpose, but an existing sealant having both heat resistance and corrosion resistance such as stainless paint can be used.

Next, the kinds of shape memory alloys used in the present invention will be described. It is not necessary to limit the type of shape memory alloy used in the present invention because a high-performance shape memory alloy cannot be used, but it is essential to form a tapered portion in manufacturing a joint. In addition, since it is necessary to taper the pipe side to be fastened after cutting, it is not preferable to use an expensive alloy and to raise the joint cost too much. In fact, since a shape memory alloy that can secure an inner diameter shrinkage ratio of approximately 1.5% or more after being processed into a joint can be sufficiently used, an inexpensive iron-based alloy will also be described later. It is one of the most desirable choices to use it as it is without processing such as training.

Finally, the process for producing the joint of the present invention will be described. First, shape memory processing is performed in a state where the shape memory alloy is processed into a cylindrical shape. For processing into a cylindrical shape, a material such as a round bar may be hollowed out or welded after forming a plate, but in the case of a joint to which a large internal pressure is applied, it is preferable to obtain a cylinder by a method that does not depend on welding. The shape memory treatment is performed by heating to a specific temperature according to the type of alloy used. Generally, it is necessary to heat with a constraint so that the shape to be memorized does not change during heating, but when memorizing the cylindrical shape, it is only necessary to heat without constraint. In most cases it is sufficient. Then, the inner diameter of the cylinder is expanded by a certain amount (expansion). Although the degree of pipe expansion varies depending on the type of shape memory alloy, it is common that the extent of expansion is from several% to at most 10%. After this, if the inner surface of the joint opening is tapered, the shape memory alloy pipe joint used in the present invention can be obtained.

However, in the joint manufactured in the above process,
If the inner diameter shrinkage ratio when heated is insufficient, the shape-expanded alloy cylinder once expanded is heated to the shape recovery temperature once to cause contraction, and then expanded for the second time. Therefore, the inner surface of the cylinder may be tapered. It is confirmed that the treatment performed by combining the tube expansion and the heat treatment in this way is known as the training treatment for the shape memory alloy, and that the shape memory characteristics are improved not only once but repeatedly up to several times. ing. In any case, the taper processing on the inner surface of the shape memory alloy cylinder may be performed at the final stage after the final tube expansion.

Further, as a simpler method for forming a taper on the joint opening, first, a cylinder made of a simple shape memory alloy is formed and shape memory processing is performed, and then each opening is formed with a tapered mandrel. The pipe may be expanded with a constant taper. When it is necessary to further improve the shape recovery performance, the training process may be performed in such a manner that the pipe expansion with the tapered mandrel is performed twice. However, the pipe expanding means is not limited to the mandrel system, and other pipe expanding methods such as water pressure and hydraulic pressure can be used.

[0025]

According to the method of fastening a joint according to the present invention, which uses a shape-memory alloy joint having a tapered opening, the end of the pipe to be fastened is preliminarily tapered and then the joint opening is formed. It is carried out by heating the joint and shrinking the joint. The tapered pipe is simply inserted into the opening of the joint, and the tapered surfaces of both the joint and the pipe are brought into close contact with each other. This guarantees the conditions for converting the inner diameter shrinkage force of the shape memory alloy pipe joint into the pipe fastening force most effectively. Then, the pipe and the joint are completely fastened by heating the joint portion to the shape recovery temperature of the shape memory alloy being used to shrink the joint opening. Even if the outer diameter of the pipe to be used is uneven or dented, it is corrected during the preliminary tapering process, so stable joint performance is always ensured.

[0026]

EXAMPLE A 20-Su size thin wall stainless steel pipe for indoor piping was fastened by the method of the present invention. The joint used was an iron-based shape memory alloy containing 28% Mn-6% Si-5% Cr as a main component, and a rolled plate having a thickness of 2 mm was formed and then welded to form a cylinder having a length of 65 mm. After the shape memory treatment was performed, the taper mandrel was used to have a gradient of 1/100 in diameter, and the both sides were expanded one by one while leaving the middle portion of the cylinder 5 mm. The appearance of the joint is the one shown in FIG. 4 (d).
The term "expansion ratio" used in the description of the joint manufacturing process below means the expansion ratio of the inner diameter of the end of the opening.

First, 6% tube expansion-600 ° C heating-6% inner diameter
In the process of pipe expansion (process 1), the maximum inner diameter (end) of the final joint opening is 21.85 mm and the minimum inner diameter is 21.55 m.
The joint was made to be m. Moreover, after performing the shape memory treatment at 900 ° C, it is only necessary to expand the tube by 6% once.
We also made a joint whose inner diameter is 0.2 mm smaller in each part than the joint of step 1, and performed electroless nickel plating so that the target plating thickness was 10 μm.
Stainless steel paint was applied to the inner surface of the joint and dried (step 2). The former step 1 includes a training process for improving the shape memory effect, and the latter step 2 corresponds to the case where no training is performed. In addition, since the stainless steel paint was applied to the inner surface of the opening so as to have a thickness of about 0.1 mm, the joint of step 1 and the joint of step 2 had almost the same final opening size. It was

The pipe side to be fastened is JIS standard 20-
Among the Su-sized thin-walled stainless steel pipes for indoor piping, pipes having different pipe outer diameters were selected and used. The average outer diameter of the pipe used is in the range of 21.88 to 22.19 mm, and it should cover a range close to the entire outer diameter range of 21.85 to 22.22 mm that is allowed by the JIS standard. I was able to.

The taper processing for the end portion of the pipe was performed using a rotary drawing machine. The outer diameter of the tip of the squeezed pipe was set to 21.55 mm. Since the slope of the taper part is 1/100, which is the same as the joint side, the length of the taper part is 33 mm when the pipe with the smallest outer diameter is 21.88 mm, and the pipe with the largest outer diameter is 22.19 mm. The length of the taper portion was 37 mm. Since the length of the tapered opening on the side of the shape memory alloy joint used is 30 mm on one side and the diameter of the recessed innermost part of the opening is 21.55 mm, these pipes Is the tip 3 of the tapered part when inserted into the joint opening.
The 0 mm length will fit into the joint opening.
Since the outer diameter allowable range of a stainless steel thin-walled pipe is specified by a standard in a considerably small range, it is possible to use a shape memory alloy joint having an extremely slight taper as in this embodiment. The taper processing applied to the ends is almost unnoticeable to the eye.

The joint was fastened by inserting a pipe pre-processed with the taper into the joint and heating the joint using a shape memory alloy pipe joint heating device utilizing the induction heating method. The heating temperature was 240 ° C., and the actual heating time was 30 seconds or less in each case. Heating to 300 ° C. is desirable to sufficiently restore the shape memory alloy used for this joint, but when it is used for fastening the pipe according to the present invention, the shrinkage of the joint does not need to be so large. To make it easier, the temperature was set to a low temperature of 240 ° C and the fastening was performed.

In both the joints of Steps 1 and 2, after the fastening, the fastening portion was subjected to a tensile test, and as a result, a high pull-out preventing force of 400 kgf or more was obtained. Since the standard for pipe joints of this size set by the Stainless Steel Association is 190 kgf or more, it can be seen that a sufficiently high fastening force is obtained. It was also confirmed that when the joints in Step 2 were used for fastening, no leak occurred when an internal pressure of 5 kgf / cm ² was applied.

When one of the fastening tests using the joint in step 2 was heated to 300 ° C. and fastened, the value of the tensile test was 1500 kgf, which was extremely high. In the case of fastening requiring high fastening force, it was effective to raise the heating temperature of the joint.

[0033]

The fastening method of the thin-walled pipe according to the present invention is as follows.
Even if there is a variation in the outer diameter of the pipe or a dent or the like on the outer surface, it is possible to perform fastening that stably secures excellent joint performance. It is necessary to taper the end of the pipe, but after that, the pipe fastening operation is completed simply by inserting the pipe into the joint and heating. Deformation and scratches are easy to occur,
Moreover, particularly excellent performance can be exhibited as a joint for fastening a thin pipe which is difficult to weld and screw. Also, since the opening of the shape memory alloy joint is contracted from the state where the outer surface of the pipe to be fastened is in close contact with the inner surface of the joint opening, the shape recovery performance of the shape memory alloy is maximized to the pipe effectively. Since it can be converted into the fastening force of No. 1, there is also a feature that sufficient joint performance can be secured even if the heating of the joint is suppressed to a lower temperature.

[Brief description of drawings]

FIG. 1 is a view showing a fastened state of a pipe according to the present invention.

FIG. 2 is a diagram showing a state in which the end portion of the pipe to be fastened is preliminarily tapered when fastening the pipe according to the present invention.

FIG. 3 is a diagram showing a difference in pipe wall thickness change between a case where a preliminary taper process is performed on a pipe by cutting (a) and a case where the pipe is drawn by a drawing process (a).

FIG. 4 is a view showing an example of a shape memory alloy pipe joint used in the pipe fastening method according to the present invention.

FIG. 5 is a diagram showing a typical example in which a pipe is fastened using a conventional shape memory alloy pipe joint not according to the present invention.

FIG. 6 is a view showing an example of a case where a shape memory alloy pipe joint used in the present invention is used for fastening a pipe according to a conventional method not according to the present invention.

[Description of Reference Signs] 1 pipe joint for shape memory alloy according to the present invention 2, 3 pipe to be fastened 10 example of pipe joint for shape memory alloy not according to the present invention 20, 30 made of shape memory alloy not according to the present invention Gap between pipe g ₁ and g ₂ joints to be fastened by piping joint and pipe

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Hiroyuki Tanahashi Inventor Hiroyuki Tanahashi 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Nippon Steel Co., Ltd. 6 Tokyo Branch of Awaji Sangyo Co., Ltd. (72) Inventor Ryoji Shibata 1117 16 Minami-Nakamaru, Omiya City, Saitama Prefecture

Claims (1)

[Claims] 1. A pipe end on the side to be fastened after being cut to a required length is tapered and an opening for inserting a pipe into the pipe end having the taper is formed at the end. Insert into a shape memory alloy joint that is formed to have a taper whose inner diameter decreases from the inside to the inside, and heat the shape memory alloy joint part to a temperature above the shape recovery temperature of the alloy. A method for fastening a thin-walled pipe, characterized by: