Metal pipe and metal-pipe joining method

Abstract

This metal-pipe joining method for inserting a tip of an inserting pipe (1) into an end part of an insertion target pipe (2) so as to join the pipes comprises: a pipe expansion step for expanding the end part of the insertion target pipe (2) in a tapered shape to form a pipe expansion part 3; an adhesive application step for applying an adhesive (4) onto the outer surface of the tip of the inserting pipe 1; and, after completion of the adhesive application step, a pipe insertion step for inserting the tip of the inserting pipe (1) into the pipe expansion part (3). In addition, the metal-pipe joining method according to the present disclosure comprises: a preheating step for heating the pipe expansion part (3) to increase the fluidity of the adhesive (4) by using a heating means disposed around the pipe expansion part (3) after completion of the pipe insertion step, and adjusting output of the heating means to maintain the state of the increased fluidity of the adhesive (4); and, after completion of the preheating step, a curing step for increasing the output of the heating means and further heating the pipe expansion part (3) to promote curing of the adhesive (4).

Description

Metal pipe and method for joining metal pipe

[0001] The present disclosure relates to metal pipes and methods for joining metal pipes.

[0002] In the manufacturing process of various types of equipment equipped with piping, such as heat exchangers, it is sometimes necessary to join metal pipes together in a liquid-tight or airtight manner. In such cases, a method using an adhesive is known.

[0003] For example, Patent Document 1 discloses a joining structure in which a joining end of one pipe includes an expanded pipe portion having a flared portion with an inner diameter at the tip that is larger than the outer diameter of the other pipe, the tip of the other pipe is inserted into the expanded pipe portion of the first pipe, and a thermosetting adhesive layer is formed between the two. Patent Document 1 also discloses a method in which a thermosetting adhesive is applied to the tip of the other pipe, the tip of the other pipe is inserted into the expanded pipe portion of the first pipe, and then a portion of the expanded pipe portion is crushed inward to tightly adhere the adhesive to the expanded pipe portion ( FIG. 2 ). Patent Document 1 also discloses that by crushing a portion of the expanded pipe portion inward, the adhesive can be filled into the first and second pipes without any gaps.

[0004] A similar joining structure is also disclosed in Patent Document 2. However, in the invention described in Patent Document 2, the tip of the other pipe is inserted into the expanded portion of one pipe, and then adhesive is injected between the two. In this respect, it differs from the invention described in Patent Document 1, but it is believed that this method also makes it possible to fill the adhesive between the one pipe and the other pipe without any gaps at the expanded portion.

[0005] Furthermore, Patent Document 3 discloses a joining method in which the tip of a connecting pipe is inserted into a coupling pipe socket having an expanded tip end and a sealing material introduction port on the side, and the two are joined together. According to this joining method, after the tip of the connecting pipe is inserted into the socket, a liquid or gel-like sealing material is introduced into the gap between the socket end and the connecting pipe through the sealing material introduction port. The sealing material introduced into the gap between the socket end and the connecting pipe is then hardened.

[0006] JP 2006-138468 A JP 2010-1903 A Japanese Patent No. 6604558 A

[0007] As described above, the invention described in Patent Document 1 is characterized by inserting the adhesive-coated tip of the other pipe into the expanded portion of the other pipe, and then crushing a portion of the expanded portion inward to adhere the adhesive to the expanded portion. However, this invention is considered to be feasible only when one pipe is a relatively soft pipe, such as an aluminum pipe, and the other pipe is a relatively hard pipe, such as a copper pipe. If one pipe is made of a harder material than the other pipe, applying an external force to the expanded portion of one pipe to crush it inward will also crush the other pipe, making the invention described in Patent Document 1 unworkable. The same phenomenon occurs when the one pipe and the other pipe are made of the same material, making the invention described in Patent Document 1 unworkable. As such, the invention described in Patent Document 1 has the problem of being limited in the combinations of pipe materials that it can be used.

[0008] The invention described in Patent Document 2 does not limit the combination of applicable pipe materials, but it is not easy to fill the gap that occurs between the expanded portion of one pipe and the other pipe by injecting adhesive later. Therefore, the invention described in Patent Document 2 has the problem of requiring a lot of time and effort to join them.

[0009] The invention described in Patent Document 3 also has the problem that it is not easy and time-consuming to introduce a sealing material, i.e., an adhesive, into a small gap through a small sealing material inlet. Also, since the adhesive filled into the gap cannot be visually confirmed, there is also the problem that it is impossible to confirm whether the filling was successful or not.

[0010] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a method for joining metal pipes that is applicable to any combination of the material of the inserting pipe and the material of the inserted pipe and is easy to implement.

[0011] To achieve the above object, a method for joining metal pipes according to the present disclosure is a method for joining metal pipes by inserting the tip of an insertion pipe into the end of an insertion pipe and joining the two, and includes an expanding step of expanding the end of the insertion pipe in a tapered shape to form an expanded portion, an adhesive application step of applying a thermosetting adhesive to the outer surface of the tip of the insertion pipe, and an inserting step of inserting the tip of the inserting pipe into the expanded portion after the adhesive application step.The method for joining metal pipes according to the present disclosure also includes a preheating step of heating the expanded portion using a heating means arranged around the expanded portion after the inserting step to increase the fluidity of the thermosetting adhesive and adjusting the output of the heating means to maintain the increased fluidity of the thermosetting adhesive, and a curing step of increasing the output of the heating means after the preheating step to further heat the expanded portion to promote curing of the thermosetting adhesive.

[0012] According to the present disclosure, a preheating step is performed to increase the fluidity of the thermosetting adhesive before the curing step to promote hardening of the thermosetting adhesive. This increases the fluidity of the thermosetting adhesive before hardening. This allows the thermosetting adhesive to flow in the gap between the expanded portion of the inserted pipe and the inserted pipe. As a result, the thermosetting adhesive is evenly filled in the gap and then hardens, resulting in a good joint structure. Furthermore, the method for joining metal pipes according to the present disclosure is easy to implement because it does not require special equipment or materials.

[0013] FIG. 1 is a cross-sectional view showing the state of the insert pipe and the inserted pipe after the method for joining metal pipes according to the embodiment of the present disclosure is performed; FIG. 2 is a flowchart showing the steps of the method for joining metal pipes according to the embodiment of the present disclosure; FIG. 3 is an explanatory diagram showing the first step in the pipe expansion step of the method for joining metal pipes; FIG. 4 is an explanatory diagram showing the second step in the pipe expansion step; FIG. 5 is an explanatory diagram showing the third step in the pipe expansion step; FIG. 6 is an explanatory diagram showing the state after the surface treatment step of the method for joining metal pipes; FIG. 7 is a state after the adhesive application step of the method for joining metal pipes; Graph showing the temperature-viscosity characteristics of the adhesive used in the above-mentioned metal pipe joining method. Illustrative diagram showing the state before the start of the preheating step in the above-mentioned metal pipe joining method. Illustrative diagram showing the state after the curing step in the above-mentioned metal pipe joining method. Illustrative diagram showing the state before the start of the adhesive application step in the above-mentioned metal pipe joining method modified. Illustrative diagram showing the state after ... sealing material formation step in yet another modified example of the metal pipe joining method. Illustrative diagram showing the state after the curing step in yet another modified example of the metal pipe joining method. Illustrative diagram showing the behavior of gas particles in a resin layer that does not contain filler particles and a resin layer that contains filler particles.

[0014] Hereinafter, the configuration and operation of a method for joining metal pipes according to an embodiment of the present disclosure will be described in detail with reference to the drawings. Note that in each drawing, the same or equivalent parts are designated by the same reference numerals.

[0015] 1A is an outline view showing the state of an insert pipe 1 and an insertable pipe 2 before performing a method for joining metal pipes according to an embodiment of the present disclosure, and FIG. 1B is a cross-sectional view showing the state of the insert pipe 1 and the insertable pipe 2 after performing a method for joining metal pipes according to an embodiment of the present disclosure.

[0016] The insertable pipe 1 and the insertable pipe 2 are metal pipes to which the method for joining metal pipes according to this embodiment is applicable. The materials constituting the insertable pipe 1 and the insertable pipe 2 are not limited, but examples include stainless steel, aluminum and aluminum alloy, or copper and copper alloy. The insertable pipe 1 and the insertable pipe 2 may be made of the same type of material, or may be made of different materials. As shown in FIG. 1A , in this embodiment, the inner and outer diameters of the insertable pipe 1 and the insertable pipe 2 are the same. However, as long as the mechanical configuration shown in FIG. 1B can be finally completed, the inner and outer diameters of the insertable pipe 1 and the insertable pipe 2 may differ slightly.

[0017] As shown in FIG. 1B , according to the method for joining metal pipes according to this embodiment, a tapered expanded portion 3 having an inner diameter larger than the outer diameter of the insertable pipe 1 is formed at the end of the insertable pipe 2 on the side where the insertable pipe 1 is inserted. The tip of the insertable pipe 1 is inserted into the expanded portion 3. The gap between the expanded portion 3 of the insertable pipe 2 and the tip of the insertable pipe 1 is filled with adhesive 4. As a result, the insertable pipe 1 and the insertable pipe 2 are fixed to each other. In this embodiment, the clearance C between the upper end of the expanded portion 3 of the insertable pipe 2 and the insertable pipe 1 is approximately 1 mm, and the opening angle θ of the expanded portion 3 is approximately 8°. Increasing the clearance C and the opening angle θ makes it easier to insert the insertable pipe 1, but makes it more difficult to position and orient the insertable pipe 1 relative to the insertable pipe 2. On the other hand, decreasing the clearance C and the opening angle θ makes it more difficult to insert the insertable pipe 1. Furthermore, the amount of adhesive 4 filled in the gap decreases, resulting in a lower adhesive strength. Therefore, it is desirable to set the clearance C to 3 mm or less. It is more desirable to set the clearance C to 0.1 mm or more and 1.0 mm or less. It is desirable to set the opening angle θ to 30° or less.

[0018] Fig. 2 is a flowchart showing the steps of the method for joining metal pipes according to this embodiment. The process from the state shown in Fig. 1A to the state shown in Fig. 1B will be described below in order with reference to Fig. 2.

[0019] As shown in FIG. 2 , in the method for joining metal pipes according to this embodiment, a pipe expansion step S1 is first performed. The pipe expansion step S1 is a step of forming an expanded portion 3 at the end of the inserted pipe 2 (not shown in FIG. 2 , the same applies below) on the side where the insertion pipe 1 is inserted. After the pipe expansion step S1 is completed and the expanded portion 3 is formed, a surface treatment step S2 is performed. The surface treatment step S2 is a step of improving the properties of the inner surface of the expanded portion 3 of the inserted pipe 2 and the outer surface of the portion of the insertion pipe 1 that will be inserted into the expanded portion 3, thereby improving the affinity for the adhesive 4. After the surface treatment step S2 is completed, an adhesive application step S3 is performed. The adhesive application step S3 is a step of applying adhesive 4 to the inner surface of the expanded portion 3 of the inserted pipe 2 or the outer surface of the portion of the insertion pipe 1 that will be inserted into the expanded portion 3. Details of each step S1 to S3 will be described later.

[0020] After the adhesive application step S3 is completed, that is, after the application of the adhesive 4 to the insertion tube 1 or the inserted tube 2 is completed, the inserting step S4 is performed. The inserting step S4 is a step of inserting the tip of the insertion tube 1 into the expanded tube portion 3 of the inserted tube 2. After the inserting step S4 is completed, that is, after the tip of the insertion tube 1 is inserted into the expanded tube portion 3 of the inserted tube 2, the preheating step S5 is performed. The preheating step S5 is a step of heating the expanded tube portion 3 from the outside to raise the temperature of the adhesive 4 to a temperature at which the viscosity of the adhesive 4 decreases and the fluidity of the adhesive 4 becomes maximum. In the preheating step S5, the fluidity of the adhesive 4 becomes maximum, so that the adhesive 4 sufficiently flows in the gap between the expanded tube portion 3 and the insertion tube 1. As a result, the adhesive 4 is evenly filled in the gap. After the preheating step S5 is completed, that is, after the adhesive 4 is evenly filled in the gap between the expanded tube portion 3 and the insertion tube 1, the curing step S6 is performed. The hardening step S6 is a step of further heating the expanded portion 3 from the outside to raise the temperature of the adhesive 4 to a temperature at which the adhesive 4 hardens irreversibly. When the hardening step S6 is completed and the adhesive 4 is completely solidified, the insertion tube 1 is completely fixed to the insertion tube 2. Through the above process, the joining of the insertion tube 1 and the insertion tube 2 is completed. Details of each step from S4 to S6 will be described later.

[0021] (Tube Expansion Process) Figures 3A to 3C are explanatory diagrams showing the detailed steps of the tube expansion process in chronological order. As shown in Figure 3A, a tube expansion burette 5 is used in the tube expansion process. The tube expansion burette 5 is a mold that is inserted into the inserted tube 2 and presses the inserted tube 2, plastically deforming the inserted tube 2 and forming a tapered expanded tube portion 3 at its tip, whose inner diameter is larger than the outer diameter of the inserted tube 1. Note that in the state shown in Figures 3A to 3C, the inserted tube 2 is fixed to a fixing jig of a tube expansion machine (not shown). The tube expansion burette 5 is fixed to the operating part of the tube expansion machine and moves forward and backward relative to the inserted tube 2. When the tube expansion burette 5 is inserted from the end of the inserted tube 2, the inserted tube 2 is expanded from the inside by the tube expansion burette 5, as shown in Figure 3B, and the inserted tube 2 is expanded into a trumpet shape, forming the expanded tube portion 3. Once the expanded tube portion 3 is formed, the tube expansion burette 5 is withdrawn from the inserted tube 2, as shown in Figure 3C. The tube 2 is then removed from the fixing jig of the tube expanding machine, thereby completing the tube expanding process.

[0022] (Surface Treatment Step) In the surface treatment step, hydrophilic surfaces are formed on the outer surface 6 of the tip of the insertion tube 1 shown in Fig. 4 and the inner surface 7 of the expanded portion 3 of the insertion tube 2, that is, the surfaces that come into contact with the adhesive 4 in the state shown in Fig. 1B. The hydrophilic surfaces are formed by forming a coating containing hydrophilic groups on the outer surface 6 and the inner surface 7 by plasma spraying or ultraviolet irradiation. By forming hydrophilic surfaces on the outer surface 6 and the inner surface 7, the wettability of the outer surface 6 and the inner surface 7 is improved, and as a result, the affinity of the outer surface 6 and the inner surface 7 for the adhesive 4 is improved, thereby improving the adhesive strength.

[0023] (Adhesive Application Process) After the surface treatment process is completed, as shown in FIG. 5A , adhesive 4 is applied to the outer surface 6 of the tip of the insertion tube 1 to form a layer of adhesive 4. The means for applying the adhesive 4 is not limited. The adhesive 4 may be sprayed onto the outer surface 6 or brushed on. Alternatively, a spatula-shaped tool may be used. However, in the adhesive application process, the thickness of the layer of adhesive 4 must be accurately controlled. This is because, as shown in FIG. 1B , the amount of adhesive 4 must be controlled so that the gap between the insertion tube 1 and the insertion tube 2 is filled with just the right amount of adhesive 4. Therefore, it is convenient to use an electronically controlled dispenser that can accurately control the amount or speed of adhesive 4 to be dispensed, since this allows for accurate control of the thickness of the layer of adhesive 4. In this embodiment, a thermosetting epoxy resin adhesive is used as the adhesive 4.

[0024] (Insertion Process) After the adhesive application process is completed, the tip of the insertion tube 1 is inserted into the expanded portion 3 of the insertion tube 2, as shown in Fig. 5B. At this point, a gap 8 remains between the insertion tube 1 and the insertion tube 2. In other words, in the cross section shown in Fig. 5B, a portion where the adhesive 4 is not filled remains between the insertion tube 1 and the insertion tube 2. The gap 8 will be eliminated in the preheating process and hardening process described below.

[0025] 5A and 5B has a straight cross section, the gap 8 does not occur. However, in this case, the adhesive 4 applied to the surface of the insertable tube 1 is scraped off during the insertion process. This causes a problem that a sufficient amount of adhesive 4 cannot be filled between the insertable tube 1 and the insertable tube 2. On the other hand, in this embodiment, the insertable tube 2 has the expanded portion 3, so a sufficient amount of adhesive 4 can be filled between the insertable tube 1 and the insertable tube 2.

[0026] (Preheating Process / Curing Process) In this embodiment, the thermosetting epoxy resin adhesive used as the adhesive 4 has the temperature-viscosity characteristics shown in FIG. 6. As shown in FIG. 6, the viscosity of the adhesive 4 at room temperature (25°C) is approximately 100 Pa·s. To use a familiar example, 100 Pa·s corresponds to the viscosity of starch syrup at room temperature. When the temperature of the adhesive 4 exceeds 35°C, the viscosity of the adhesive 4 rapidly decreases, reaching its lowest between approximately 60°C and approximately 80°C and approaching zero. In other words, the fluidity of the adhesive 4 is greatest between approximately 60°C and approximately 80°C. When the temperature of the adhesive 4 exceeds approximately 100°C, the viscosity increases, and when the temperature of the adhesive 4 exceeds 130°C, the viscosity increases rapidly. Furthermore, when the temperature of the adhesive 4 exceeds 130°C, the polymerization reaction of the epoxy resin begins, and the adhesive 4 irreversibly hardens. The above-described properties of the adhesive 4 are utilized in the preheating process and curing process.

[0027] As described above, after the completion of the intubation process, a gap 8 remains between the insertion tube 1 and the inserted tube 2. Therefore, as shown in Fig. 7A , the insertion tube 1 and the inserted tube 2 are inserted into an electric heating coil 9. The electric heating coil 9 is a device that heats an object by electric heating, and in the state shown in Fig. 7A , the electric heating coil 9 is placed in a position facing the expanded tube portion 3 to heat the expanded tube portion 3. The electric heating coil 9 is an example of a heating means according to the present disclosure. The electric heating coil 9 is controlled by control means (not shown), and the output of the electric heating coil 9 is freely adjusted by the control means.

[0028] In the preheating process, in the state shown in FIG. 7A , the electric heating coil 9 is operated to raise the temperature of the adhesive 4 to around 60°C and maintain that state for a while. That is, the output of the electric heating coil 9 is adjusted so that the temperature of the adhesive 4 is maintained at around 60°C for a while. As described above, when the temperature of the adhesive 4 is raised to around 60°C, the fluidity of the adhesive 4 is maximized, so that the adhesive 4 flows into the gap 8, thereby eliminating the gap 8. That is, the adhesive 4 fills the gap between the insertion tube 1 and the insertion tube 2 without leaving any gaps. In short, the state shown in FIG. 7B is obtained. As the fluidity of the adhesive 4 increases, the adhesive 4 flows into the minute irregularities on the surfaces of the insertion tube 1 and the insertion tube 2. As a result, the adhesive strength provided by the adhesive 4 increases.

[0029] In the preheating step, the time for which the temperature of the adhesive 4 is maintained at around 60° C. can be selected arbitrarily. By repeating trials, the minimum time required to obtain good results, that is, the time required for the adhesive 4 to fill the gap between the insertion tube 1 and the inserted tube 2 without leaving any gaps, can be determined, and the time for which the temperature of the adhesive 4 is maintained at around 60° C. can be set to that time plus a small margin.

[0030] When the inventors of the present application applied room-temperature adhesive 4 using an air pressure dispenser and a tapered resin nozzle with an inner diameter of 0.4 mm at a dispensing pressure of 450 kPa, it took about 10 seconds to heat the adhesive 4 to 60°C. Then, when the temperature of the adhesive 4 was maintained at around 60°C for about 20 seconds after that, good results were obtained. In other words, the preheating process was completed in a total of about 30 seconds.

[0031] Once the preheating step is complete, the curing step begins. That is, in the state shown in Fig. 7B, the output of the electric heating coil 9 is increased to raise the temperature of the adhesive 4 to 130°C or higher. As described above, once the temperature of the adhesive 4 exceeds 130°C, the adhesive 4 begins to irreversibly harden. After that, once the adhesive 4 has completely hardened, the curing step is complete. This completes the joining of the insertion tube 1 and the insertion tube 2.

[0032] As described above, according to this embodiment, the adhesive 4 is evenly filled in the space between the expanded portion 3 of the insertion tube 2 and the insertion tube 1. Moreover, the adhesive 4 is evenly filled into the minute irregularities on the surfaces of the insertion tube 1 and the insertion tube 2. Even if there is a defect in the shape of the expanded portion 3, causing an unexpected gap between the expansion portion 3 of the insertion tube 2 and the insertion tube 1, the adhesive 4 flows into the gap, filling the gap. As a result, the insertion tube 1 is firmly bonded to the insertion tube 2. In other words, the adhesive strength provided by the adhesive 4 is increased. Furthermore, the pressure resistance and airtightness of the joint between the insertion tube 1 and the insertion tube 2 are improved.

[0033] Furthermore, according to this embodiment, the adhesive 4 is applied to the insertion tube 1 before the insertion tube 1 is inserted into the expanded tube portion 3 of the insertion tube 2, making it easy to apply the adhesive 4. Furthermore, since the adhesive 4 applied to the insertion tube 1 can be visually confirmed, it is easy to check the state of application of the adhesive 4. If there is a defect in the state of application of the adhesive 4, it is easy to make corrections.

[0034] (Modification of Adhesive Application Step) In the above, an example has been shown in which the adhesive 4 is applied to the outer surface 6 of the tip of the insertion tube 1, but in the adhesive application step, the target to which the adhesive 4 is applied is not limited to the insertion tube 1. In the adhesive application step, the adhesive 4 may be applied to the inserted tube 2. In this case, too, the means for applying the adhesive 4 is not limited, and the means shown below may be selected.

[0035] That is, as shown in Fig. 8A, a liquid tank 10 filled with adhesive 4 may be prepared, and the expanded portion 3 of the insertion tube 2 may be immersed in the adhesive 4. Thereafter, when the insertion tube 2 is pulled up, a layer of adhesive 4 is formed on the inner surface 7 of the expanded portion 3, as shown in Fig. 8B. At this time, by properly controlling the temperature or viscosity of the adhesive 4, and the depth and time for which the insertion tube 2 is immersed in the adhesive 4, a layer of adhesive 4 of the desired thickness can be formed. Furthermore, in the state shown in Fig. 8B, a step may be added in which unnecessary adhesive 4, i.e., adhesive 4 adhering to the outside of the expanded portion 3, is scraped off and removed.

[0036] (Bonding Method Including Sealing Material Forming Step) The above-described joining method may be supplemented with the sealing material forming step described below. That is, prior to the surface treatment step or adhesive application step, a resin material may be piled up on the outer periphery of the insertion tube 1 to form a sealing material 11, as shown in FIG. 9A . The sealing material 11 is formed to a height that abuts the open end of the expanded tube portion 3, i.e., the upper end of the expanded tube portion 3, in the state shown in FIG. 9B , that is, when the tip of the insertion tube 1 is inserted into the expanded tube portion 3 of the insertion tube 2. Furthermore, the horizontal dimension of the sealing material 11 in FIGS. 9A and 9B is set to be larger than the diameter of the upper end of the expanded tube portion 3. Therefore, as shown in FIG. 9B , the sealing material 11 functions as a "lid" that closes the open end of the expanded tube portion 3.

[0037] 9B shows the state after the completion of the sealing material forming process, the surface treatment process, adhesive application process, tube insertion process, preheating process, and curing process. As described above, the sealing material 11 functions as a "lid" that closes the open end of the expanded tube portion 3, preventing the adhesive 4, whose fluidity has increased in the preheating process, from overflowing from the upper end of the expanded tube portion 3. Therefore, the adhesive 4 is retained inside the expanded tube portion 3.

[0038] Furthermore, there are no limitations on the resin material that constitutes the sealing material 11. The resin material that constitutes the sealing material 11 can be selected arbitrarily from among, for example, silicone resin, acrylic resin, epoxy resin, urethane resin, etc., as long as it has the required performance. The resin material that constitutes the sealing material 11 may be a thermosetting epoxy resin, i.e., the same material as the adhesive 4.

[0039] Furthermore, the specific means for molding the sealing material 11 is not particularly limited. Any of various known means can be selected. For example, an electronically controlled dispenser capable of freely controlling the amount or speed of dispensing may be used to dispense the resin material constituting the sealing material 11 onto the surface of the insertion tube 1, and then the resin material may be cured. In this case, it is desirable to adjust the viscosity of the resin material dispensed from the dispenser to 100 Pa·s or more and 10,000 Pa·s or less. Adjusting the viscosity of the resin material within the above range is advantageous because the shape of the resin material dispensed onto the surface of the insertion tube 1 is maintained for a while. In other words, this is advantageous because a mold for maintaining the shape of the resin material is not required.

[0040] When molding the sealing material 11, a mold may be used to mold a resin material into a desired shape. Alternatively, the sealing material 11 may be previously formed into a ring shape and then adhered to the insertion tube 1.

[0041] (Regarding the Adhesive) In the above-described embodiment and modified examples, the type or chemical composition of the adhesive 4 is not particularly limited. The type or chemical composition of the adhesive 4 can be selected as desired depending on the intended use of the device including the metal pipe or the environment in which the device is installed. However, the resin material constituting the base material of the adhesive 4 allows gas to pass through, albeit to a small extent. As a result, gas leaks, albeit to a small extent, from the joints of the metal pipes. In particular, in air conditioners or refrigeration systems, if refrigerant gas leaks from the joints of the metal pipes, the performance of the device deteriorates. Furthermore, if refrigerant gas is released into the environment, it has a negative impact on the environment. Therefore, in air conditioners or refrigeration systems, high levels of airtightness are required at the joints of the metal pipes.

[0042] In order to solve the above problems, the inventors of the present application attempted to improve the adhesive 4. As a result, they came to the conclusion that if the adhesive 4 is made into a filler-containing adhesive in which a filler is added to a base material, it would be possible to effectively suppress the leakage of refrigerant gas from the joints of the metal pipes.

[0043] The filler material is not limited. The filler may be composed of either an organic material or an inorganic material. However, good results can be obtained by selecting the following materials and compositions.

[0044] That is, an ethylene vinyl alcohol copolymer resin having an average particle size ranging from several μm to several tens of μm may be selected as the organic material filler added to the adhesive 4. When using an ethylene vinyl alcohol copolymer resin as the filler, good results can be obtained by adding it at a ratio of 5 to 10 wt % to the base material.

[0045] Silica having an average particle size ranging from several μm to several tens of μm may be selected as the inorganic filler added to the adhesive 4. When using silica as the filler, good results can be obtained by adding it at a ratio of 10 to 20 wt % to the base material.

[0046] In the above, spherical particle shapes are selected for the filler particles, but other particle shapes may also be selected. The particle size distribution of the filler contained in the adhesive 4 can be measured using laser diffraction or dynamic light scattering. Alternatively, it can be measured using a transmission electron microscope or a scanning electron microscope. Using these methods or devices, the particle size distribution of the filler contained in the adhesive 4 can be controlled. In other words, the particle size distribution of the filler contained in the adhesive 4 can be always maintained within an appropriate range, thereby maintaining good airtightness at the joint of the metal pipe.

[0047] Finally, the function of the adhesive 4 to which a filler has been added will be described with reference to Fig. 10. Fig. 10 is an explanatory diagram showing the behavior of gas particles 14 in a resin layer 13a that does not contain filler particles 12 and a resin layer 13b that does contain filler particles 12. The resin layer 13a corresponds to a resin layer formed by curing the adhesive 4 to which no filler has been added, and the resin layer 13b corresponds to a resin layer formed by curing the adhesive 4 to which a filler has been added.

[0048] As shown in Figure 10, since there are no filler particles 12 in the resin layer 13a, gas particles 14 move the shortest distance within the resin layer 13a. Therefore, gas particles 14 pass through the resin layer 13a relatively easily. On the other hand, filler particles 12 are present in the resin layer 13b. The filler particles 12 have gas barrier properties, that is, properties that hinder the movement of gas particles 14. Therefore, gas particles 14 move while bending within the resin layer 13b, and therefore the movement distance becomes longer. As a result, the passage of gas particles 14 is suppressed.

[0049] It is known that the gas barrier performance of ethylene-vinyl alcohol copolymer resin deteriorates in a high humidity environment, but because adhesive 4 has low moisture permeability, the ethylene-vinyl alcohol copolymer resin encapsulated as filler particles 12 in resin layer 13b is not affected by the humidity of the surrounding environment. In other words, even if the humidity of the surrounding environment increases, the gas barrier performance of the ethylene-vinyl alcohol copolymer resin does not deteriorate.

[0050] Furthermore, a filler may be added to the sealing material 11. By adding a filler to the sealing material 11, the airtightness of the sealing material 11 is improved.

[0051] As described above, the method for joining metal pipes according to this embodiment can be applied to any combination of the material of the inserting pipe and the material of the inserted pipe, and can be implemented simply and easily.

[0052] However, the technical scope of the present disclosure is not limited to the above-described embodiments, and the present disclosure can be freely applied, modified, or improved within the scope of the technical ideas described in the claims.

[0053] The mechanical configurations and dimensions of the insertable pipe 1, the insertable pipe 2, and the expanded pipe portion 3 described in the above embodiments are merely examples. Therefore, the technical scope of the present disclosure is not limited by the mechanical configurations or dimensions of the insertable pipe 1, the insertable pipe 2, and the expanded pipe portion 3 described in the above embodiments.

[0054] In the above embodiment, a thermosetting epoxy resin adhesive was used as a specific example of a thermosetting adhesive, but the technical scope of the present disclosure is not limited to the use of an epoxy resin adhesive. In the present disclosure, it is sufficient for the thermosetting adhesive to have the temperature-viscosity characteristics shown in FIG. 6 , and the type of base material of the thermosetting adhesive is not limited. In other words, a thermosetting adhesive has a considerable viscosity at room temperature, and when the temperature exceeds room temperature, the viscosity decreases and becomes fluid. Furthermore, as the temperature rises, the viscosity increases, and the adhesive eventually hardens irreversibly. In the present disclosure, any adhesive having such characteristics can be selected and used as the thermosetting adhesive.

[0055] The thermosetting adhesive may be a filler-containing adhesive, which is formed by adding a filler to a base material. By using a filler-containing adhesive as the thermosetting adhesive, the airtightness of the joint between the metal pipes can be improved. The material of the filler is not particularly limited, and the filler may be, for example, an ethylene-vinyl alcohol copolymer resin or silica.

[0056] In the above embodiment, the electric heating coil 9 is exemplified as the heating means used in the preheating step and the heating step, but the heating means used in the preheating step and the heating step is not limited to the electric heating coil 9. A laser heating device, a high-frequency induction heating device, or various other heating means can be selected as desired.

[0057] The metal pipes to which the present disclosure is applicable are not limited to those constituting air conditioners or heat exchangers constituting air conditioners, but are broadly applicable to the joining of metal pipes used for various purposes or the joining of metal pipes constituting various devices.

[0058] Aspects of the present disclosure are described below as appendices. (Appendix 1) A method for joining metal pipes, in which the tip of an insertion pipe is inserted into the end of an insertion pipe to join them, comprising: an expanding step of expanding the end of the insertion pipe in a tapered shape to form an expanded portion, an adhesive application step of applying a thermosetting adhesive to the outer surface of the tip of the insertion pipe, an inserting step of inserting the tip of the insert pipe into the expanded portion after the adhesive application step, a preheating step of heating the expanded portion using heating means arranged around the expanded portion after the inserting step to increase the fluidity of the thermosetting adhesive and adjusting the output of the heating means to maintain the increased fluidity of the thermosetting adhesive, and a hardening step of increasing the output of the heating means after the preheating step to further heat the expanded portion to promote hardening of the thermosetting adhesive.

[0059] (Supplementary Note 2) A method for joining metal pipes, in which the tip of an insertion pipe is inserted into the end of an insertion pipe to join them, comprising: a pipe expansion step in which the end of the insertion pipe is expanded in a tapered shape to form an expanded pipe portion; an adhesive application step in which a thermosetting adhesive is applied to the inner surface of the expanded pipe portion; an insertion step in which the tip of the insertion pipe is inserted into the expanded pipe portion after the adhesive application step is completed; a preheating step in which, after the insertion step is completed, the expanded pipe portion is heated using heating means arranged around the expanded pipe portion to increase the fluidity of the thermosetting adhesive, and the output of the heating means is adjusted to maintain the increased fluidity of the thermosetting adhesive; and a hardening step in which, after the preheating step is completed, the output of the heating means is increased to further heat the expanded pipe portion to promote hardening of the thermosetting adhesive.

[0060] (Supplementary Note 3) The method for joining metal pipes according to Supplementary Note 2, wherein the adhesive application step is performed by immersing the expanded pipe portion in the thermosetting adhesive held in a liquid bath.

[0061] (Supplementary Note 4) The method for joining metal pipes according to Supplementary Note 2, wherein the adhesive application step is performed by spraying the thermosetting adhesive onto the expanded pipe portion.

[0062] (Supplementary Note 5) A method for joining metal pipes according to any one of Supplementary Note 1 to Supplementary Note 4, comprising a sealing material forming step of forming a sealing material on the outer periphery of the insertion pipe before inserting the insertion pipe into the insertion pipe, the sealing material contacting the tip of the insertion pipe and closing the open end of the expanded portion when the insertion pipe is inserted into the insertion pipe.

[0063] (Appendix 6) The method for joining metal pipes according to any one of Appendices 1 to 4, further comprising a surface treatment step of applying a surface treatment to the outer surface of the tip of the insertion pipe and the inner surface of the expanded portion of the inserted pipe to improve hydrophilicity prior to the adhesive application step.

[0064] (Supplementary Note 7) The method for joining metal pipes according to Supplementary Note 1 or Supplementary Note 2, wherein in the adhesive application step, the thermosetting adhesive applied to the inner surface of the expanded pipe portion is a filler-containing adhesive obtained by adding a filler to a base material.

[0065] (Appendix 8) The method for joining metal pipes according to Appendix 7, wherein the filler-containing adhesive contains an ethylene-vinyl alcohol copolymer resin as a filler.

[0066] (Appendix 9) The method for joining metal pipes according to Appendix 7, wherein the filler-containing adhesive contains silica as a filler.

[0067] (Supplementary Note 10) A metal pipe constructed by inserting the tip of an insertion pipe into the end of an insertable pipe, and by interposing a thermosetting adhesive between the outer surface of the tip of the insertion pipe and the inner surface of the end of the insertable pipe to join them, wherein the end of the insertable pipe has a tapered expanded portion, and the thermosetting adhesive is a filler-containing adhesive constructed by adding a filler to a base material.

[0068] (Appendix 11) The metal pipe according to Appendix 10, wherein the filler-containing adhesive contains an ethylene-vinyl alcohol copolymer resin as the filler.

[0069] (Appendix 12) The metal pipe according to appendix 10, wherein the filler-containing adhesive contains silica as the filler.

[0070] (Supplementary Note 13) The metal pipe according to any one of Supplementary Note 10 to Supplementary Note 12, further comprising a sealing material formed in a ring shape on the outer periphery of the insertion pipe, the sealing material abutting against the tip of the inserted pipe to close the open end of the expanded pipe portion.

[0071] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to illustrate the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of equivalent disclosures are considered to be within the scope of the present disclosure.

[0072] This disclosure is based on Japanese Patent Application No. 2024-073245, filed on April 26, 2024. The entire specification, claims, and drawings of Japanese Patent Application No. 2024-073245 are incorporated herein by reference.

[0073] The present disclosure is useful for metal pipes and methods for joining metal pipes.

[0074] REFERENCE SIGNS LIST 1 Insertion tube, 2 Inserted tube, 3 Expanded tube portion, 4 Adhesive, 5 Expanding burette, 6 Outer surface, 7 Inner surface, 8 Gap, 9 Electric heating coil, 10 Liquid tank, 11 Sealing material, 12 Filler particles, 13a, 13b Resin layer, 14 Gas particles

Claims

1. A method for joining metal pipes in which the tip of an insertable pipe is inserted into the end of an insertable pipe to join them, comprising: a pipe expansion process in which the end of the insertable pipe is expanded in a tapered shape to form an expanded pipe portion; an adhesive application process in which a thermosetting adhesive is applied to the outer surface of the tip of the insertable pipe; an inserting process in which the tip of the insertable pipe is inserted into the expanded pipe portion after the adhesive application process is completed; a preheating process in which, after the inserting process is completed, the expanded pipe portion is heated using heating means arranged around the expanded pipe portion to increase the fluidity of the thermosetting adhesive and the output of the heating means is adjusted to maintain the increased fluidity of the thermosetting adhesive; and a hardening process in which, after the preheating process is completed, the output of the heating means is increased to further heat the expanded pipe portion to promote hardening of the thermosetting adhesive.

2. A method for joining metal pipes in which the tip of an insertable pipe is inserted into the end of an insertable pipe to join them, comprising: a pipe expansion step in which the end of the insertable pipe is expanded in a tapered shape to form an expanded pipe section; an adhesive application step in which a thermosetting adhesive is applied to the inner surface of the expanded pipe section; an inserting step in which the tip of the insertable pipe is inserted into the expanded pipe section after the adhesive application step is completed; a preheating step in which, after the inserting step is completed, the expanded pipe section is heated using heating means arranged around the expanded pipe section to increase the fluidity of the thermosetting adhesive and the output of the heating means is adjusted to maintain the increased fluidity of the thermosetting adhesive; and a hardening step in which, after the preheating step is completed, the output of the heating means is increased to further heat the expanded pipe section and promote hardening of the thermosetting adhesive.

3. The method for joining metal pipes according to claim 2, wherein the adhesive application step is performed by immersing the expanded pipe portion in the thermosetting adhesive held in a liquid tank.

4. The method for joining metal pipes according to claim 2, wherein the adhesive application step is carried out by spraying the thermosetting adhesive onto the expanded pipe portion.

5. A method for joining metal pipes as set forth in any one of claims 1 to 4, further comprising a sealing material forming step of forming a sealing material on the outer periphery of the insertion pipe before inserting the insertion pipe into the insertion pipe, the sealing material contacting the tip of the insertion pipe and closing the open end of the expanded portion when the insertion pipe is inserted into the insertion pipe.

6. A method for joining metal pipes as set forth in any one of claims 1 to 4, further comprising a surface treatment step, prior to the adhesive application step, of applying a surface treatment to the outer surface of the tip of the insertion pipe and the inner surface of the expanded portion of the inserted pipe to improve hydrophilicity.

7. A method for joining metal pipes according to claim 1 or claim 2, wherein in the adhesive application step, the thermosetting adhesive applied to the inner surface of the expanded pipe section is a filler-containing adhesive formed by adding a filler to a base material.

8. The method for joining metal pipes according to claim 7, wherein the filler-containing adhesive contains an ethylene-vinyl alcohol copolymer resin as a filler.

9. The method for joining metal pipes according to claim 7, wherein the filler-containing adhesive contains silica as a filler.

10. A metal pipe in which the tip of an insertable pipe is inserted into the end of an insertable pipe, and a thermosetting adhesive is interposed between the outer surface of the tip of the insertable pipe and the inner surface of the end of the insertable pipe to join them, wherein the end of the insertable pipe has a tapered expanded portion, and the thermosetting adhesive is a filler-containing adhesive formed by adding a filler to a base material.

11. The metal pipe according to claim 10, wherein the filler-containing adhesive contains an ethylene-vinyl alcohol copolymer resin as the filler.

12. The metal pipe according to claim 10, wherein the filler-containing adhesive contains silica as the filler.

13. A metal pipe as claimed in any one of claims 10 to 12, comprising a sealing material formed in a ring shape on the outer periphery of the insertion pipe, which abuts against the tip of the inserted pipe to close the open end of the expanded pipe section.

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