JP7221486B2 - Fittings and tubes with fittings - Google Patents

Description

The present invention relates to a pipe joint and a tube with a pipe joint.

In order to prevent loosening of standardized screw members such as bolts and nuts and to increase axial force, it is well known that the surface of screw members is coated with lubricants or adhesives, or subjected to surface treatment such as plating. be. Techniques for applying a resin coating to threaded pipe joints used in automobile brake tubes and the like are also known (see Patent Documents 1 to 3, for example).

If the tightening torque for fastening the threaded member to the mating member is constant, the axial force increases as the frictional force acting between the threaded member and the mating member decreases. Therefore, the screw member is surface-treated to reduce the frictional force. This makes it possible to obtain a large axial force with the same tightening torque. This applies not only to standardized threaded members, but also to threaded pipe joints. For example, pipe fittings are used to join metal tubes.

JP 2015-230099 A JP 2009-299895 A EP-A-2706277

When a pipe joint is used to connect metal tubes, an annular portion called an ISO flare or a double flare is formed at the end of the tube when the pipe joint is attached to the outer circumference of the tube. Since the annular portion protrudes outward in the pipe radial direction and is larger than the inner diameter of the pipe joint, the pipe joint is prevented from coming off toward the terminal side by the annular portion. In addition, since the tube for automobile piping is bent according to the layout of the bottom of the vehicle, the bent portion of the tube prevents the pipe joint from coming off even in the direction away from the end. Therefore, when you loosen the fastening of the pipe joints and remove the tubes for maintenance or repair of various devices to which the tubes are connected, and then return them to the status quo, unless you replace the pipe joints together with the tubes, you will have to perform maintenance and repairs every time. The same pipe joint must be reused for

When repeatedly tightening and releasing with the same tightening torque in order to reuse the pipe joint, the axial force tended to decrease as the number of times increased. Therefore, if the same tightening torque is applied to the reused pipe joint, the larger the axial force reduction rate, the lower the axial force.

On the other hand, co-rotation may occur in which the tube rotates together with the pipe joint when the pipe joint is tightened. Co-rotation occurs when the frictional force generated between the annular portion provided on the tube and the pipe joint exceeds the frictional force generated between the annular portion and the mating member. If the tube is fixed and the pipe joint is tightened to prevent this co-rotation, co-rotation torque that twists the tube is generated as a reaction force that prevents co-rotation. If the co-rotating torque is large, it will damage the tube. In addition, since the reaction force of the co-rotating torque works in the direction of loosening the tightened pipe joint, if the co-rotating torque remains while the tube is attached to the vehicle, the vibration of the vehicle will cause the loosening of the pipe joint. provoke. Therefore, the upper limit of the co-rotating torque generated when the pipe joint is tightened is determined in consideration of the strength of the tube and the vibration of the vehicle.

The co-rotating torque tended to be the maximum when the pipe joint was first tightened, decreased during the next use, and did not change much depending on the number of subsequent uses. Therefore, if the co-rotation torque is less than the upper limit when the pipe joint is first connected, the co-rotation torque will not exceed the upper limit when the pipe joint is reused.

The present inventors have found that the thickness of the resin coating layer is the main factor that affects the rate of decrease in axial force due to reuse of the pipe joint and the co-rotating torque at the time of initial connection.

Accordingly, one object of the present invention is to provide a pipe joint that can obtain an initial axial force that makes the co-rotating torque less than the upper limit value and can keep the axial force decrease rate low when fastening and releasing are repeated. and to provide a tube with a pipe joint.

The pipe joint of the present invention is attached to the outer periphery of a metal tube having an annular portion protruding radially outwardly at the end thereof, and is fastened to a mating member while being in contact with the annular portion. A pipe joint capable of connecting the tube to the mating member, comprising: a threaded portion formed with a male thread that meshes with a female thread provided on the mating member; a contact portion for pressing the annular portion against the mating member while contacting the annular portion when fastening to the mating member; and a layer, wherein each of the threaded portion and the contact portion is pierced by a through hole extending in a direction parallel to the traveling direction, and the male thread is 9.53 to 14.0 [mm ], and the contact portion has an inner diameter of 4.98 to 8.44 [mm], the resin coating layer contains a polyethylene-based substance, a lubricant, and solid particles, and , when the value obtained by dividing the mass difference due to the presence or absence of the resin coating layer by the surface area of the coating region is defined as the unit area mass w [g/m ² ], 0.79<w<10.07 To establish.

A tube with a pipe fitting according to the present invention is mounted on the outer periphery of a metal tube having an annular portion projecting radially outwardly at its end, and is fastened to a mating member while being in contact with the annular portion. is a pipe joint capable of connecting the tube to the mating member, the threaded portion having the male thread that meshes with the female thread provided on the mating member, and the end on the traveling direction side of the male thread at the time of fastening provided in a coating area including a contact portion for pressing the annular portion against the mating member while contacting the annular portion when fastening to the mating member, and surfaces of the threaded portion and the contact portion. and a resin coating layer, wherein each of the threaded portion and the contact portion is penetrated by a through hole extending in a direction parallel to the traveling direction, and the male thread has a thickness of 9.53 to 14.0. [mm], the contact portion has an inner diameter of 4.98 to 8.44 [mm], and the resin coating layer contains a polyethylene-based substance, a lubricant, and solid particles. And, when a value obtained by dividing the difference in mass due to the presence or absence of the resin coating layer by the surface area of the coating region is defined as unit area mass w [g/m ² ], 0.79<w<10. 07 is established.

In the present invention, the surface of the threaded portion means the surface of the thread formation range that actually engages with the female thread or is scheduled to engage with the female thread. Also, the surface of the contact portion means a contact surface that actually contacts the annular portion or is scheduled to contact the annular portion. Including each surface of the threaded portion and the contact portion means including all or part of the surface of the threaded portion and including all or part of the surface of the contact portion.

The figure which showed the state by which several brake tubes with which the pipe joint was attached and the bending process were assembled. The figure which showed the flare nut which is an example of a pipe joint. FIG. 4 is a view showing a brake tube having an ISO flare, which is an example of an annular portion, formed at the end thereof; The figure which showed the state in which the brake tube was couple|bonded with the master cylinder which is an example of a mating member. FIG. 3 is an enlarged cross-sectional view of a V portion in FIG. 2; The figure which showed the outline|summary of the formation method of a resin coating layer. The figure which showed the flare nut which is another example of a pipe joint. FIG. 10 is a view showing a brake tube having a double flare, which is another example of an annular portion, formed at the end; FIG. 6 is a cross-sectional view showing part of a master cylinder, which is an example of a mating member to which the brake tube of FIG. 5 is coupled; FIG. 8 is an enlarged cross-sectional view of part X in FIG. 7 ; The figure which showed the list table of the test sample. The figure which showed the list following FIG. 11A. The figure which showed the structure of the axial force measuring apparatus. The figure which showed the test result of the fastening test. FIG. 13B is a diagram following FIG. 13A. FIG. 10 is a diagram in which the evaluation results are put together to organize acceptable samples and unacceptable samples; FIG. 14B is a diagram following FIG. 14A. The figure which showed the relationship between unit area mass and corrosion resistance.

As an example, a brake tube in an automobile is used as a conduit for transmitting pressure generated in a master cylinder to a brake unit provided for each wheel. In many cases, an ABS unit and an ESC unit are provided between the master cylinder and the brake unit, and the brake tube is also used to connect these units. A plurality of brake tubes having different pipe diameters are selected according to various conditions such as pressure resistance conditions required between these units.

As shown in FIG. 1, a plurality of brake tubes BT are bundled by clamps C made of resin, for example, and supplied to an automobile assembly line as an assembly product that is bent according to the layout of the bottom of the automobile. Each brake tube BT is made of a metal plate material such as a steel plate and is made of a double-wound tube having excellent pressure resistance in order to withstand the operating pressure of the brake. In the case of the brake tube, for example, a tube having an outer diameter φ within the range of 4.76 to 8.00 [mm] is selected. Each brake tube BT is fitted with a flare nut FN... matching its outer diameter. In an automobile assembly line, an operator collectively joins the brake tubes BT by tightening the flare nuts FN attached to the brake tubes BT to the above units with a predetermined common tightening torque. to implement.

The end of each brake tube BT is processed for high pressure with the flare nut FN attached. Terminal processing for high pressure includes terminal processing for forming an annular portion Rp such as an ISO flare defined by the International Organization for Standardization (ISO) and a double flare defined by the Japan Society of Automotive Engineers (JASO). Each brake tube BT is subjected to terminal processing to form an annular portion Rp and bending processing to form a bent portion Bp with a flare nut FN attached to the outer periphery thereof. Therefore, the flare nut FN is prevented from coming off from the brake tube BT by the annular portion Rp and the bent portion Bp provided at a position away from the annular portion Rp.

(first form)
FIG. 2 shows a flare nut 1A suitable for ISO flares. Flare nut 1A corresponds to an example of the pipe joint of the present invention. The flare nut 1A is a hollow pipe joint having a through hole 10 into which a tube can be inserted. The flare nut 1A includes a threaded portion 12 having a male thread 12a, a head portion 13 provided at one end of the threaded portion 12, and a contact portion 14 provided at the other end of the threaded portion 12. As shown in FIG. These head portion 13, threaded portion 12 and contact portion 14 are penetrated by a through hole 10 extending in the direction of the center line CL1. The through hole 10 of the illustrated flare nut 1A has a shape with a constant inner diameter in the axial direction, but instead of the through hole 10, for example, the through hole is changed to a stepped hole shape in which the inner diameter changes at a predetermined point in the axial direction. can.

A male thread 12a formed on the threaded portion 12 is, for example, a metric coarse thread standardized by ISO and meshes with a female thread 12b (see FIG. 4) formed on the mating member. However, the male thread 12a may be changed to a metric fine thread of the same standard as an example. A fine thread has a smaller lead angle than a coarse thread, so by changing to a fine thread, it is possible to provide a flare nut that is more resistant to loosening with the same axial force. As for the size of the threaded portion 12 of the flare nut 1A applied to the brake tube BT, there is a tendency that the larger the outer diameter of the tube to be mounted, the larger the size of the screw used. Unless there are special circumstances, the threaded portion 12 generally has a nominal diameter of M10 to M14, that is, an outer diameter of 10.0 to 14.0 [mm]. When the flare nut 1A is provided with an inch thread, a thread with a nominal diameter within the range of 3/8 inch to 1/2 inch (approximately 9.53 to 12.7 [mm]) is adopted. Therefore, the external thread 12a that can be employed in the flare nut 1A has an outer diameter within the range of 9.53 to 14.0 [mm].

The head portion 13 is a portion to which a tightening torque is input at the time of fastening, and has a standardized hexagonal shape so that it can be fastened with a general tool such as a flare nut wrench. The size of the head 13 is selected according to the size of the threaded portion 12, but unlike the standardized bolt head, it is made common to some extent in order to reduce the number of tool replacements.

The contact portion 14 is provided at the end on the right side in FIG. 2 along the center line CL1, in other words, at the end on the traveling direction side of the male screw 12a at the time of fastening. The contact portion 14 has a function of pressing the annular portion 16 against the mating member while contacting the annular portion 16 (see FIG. 3) formed as an ISO flare when fastening to the mating member. In the case of the flare nut 1A of FIG. 2, the contact portion 14 includes a cylindrical portion extending from the threaded portion 12 toward the end portion. A boundary portion between the contact portion 14 and the through hole 10 is provided with a chamfered portion 10a that is inclined at about 45° with respect to the direction of the center line CL1. The chamfered portion 10a alleviates interference between the tube outer casing and the flare nut 1A and stress concentration at the boundary between the through hole 10 and the contact portion 14 during fastening. In addition, the chamfered portion 10a has a conical surface in which the ridge line appearing in the cross section with respect to the center line CL1 is a straight line. Instead of the chamfered portion 10a, a processed portion having a curved surface whose ridgeline is drawn with one or more arcs convex toward the center may be used.

The inner diameter of the contact portion 14 is determined by the inner diameter of the through hole 10 . The inner diameter d of the contact portion 14 is, for example, 4.98 [mm] when the outer diameter φ of the brake tube BT is 4.76 [mm], and 6.0 [mm] when the outer diameter φ is 6.0 [mm]. Set to 24 [mm], set to 6.59 [mm] when the outer diameter φ is 6.35 [mm], and set to 8.29 [mm] when the outer diameter φ is 8.0 [mm]. be done. As an example, an error of +0.15 [mm] is allowed for the inner diameter d of the contact portion 14 . Therefore, the contact portion 14 that can be employed in the flare nut 1A has an inner diameter d within the range of 4.98 to 8.44 [mm].

As shown in FIG. 3, the annular portion 16 is formed at the end of the brake tube BT. As an example of the formation procedure, first, the resin coating layer BTa of the brake tube BT is peeled off from the end in a predetermined range in the direction of the tube axis Tx in the circumferential direction, and then the end of the peeled portion BTb where the resin coating layer is peeled off. , an ISO flare-shaped annular portion 16 protruding outward in the tube radial direction orthogonal to the tube axis Tx is formed. Note that depending on the resin material of the resin coating layer BTa, the annular portion 16 may be formed on the end portion of the brake tube BT without peeling off the resin coating layer BTa.

As an example of use of the flare nut 1A, a case of connecting the brake tube BT to the master cylinder MC1 will be described with reference to FIG. A master cylinder MC<b>1 , which is an example of a mating member, has a housing 40 . An insertion hole 41 into which the brake tube BT is inserted is formed in the housing 40 . The insertion hole 41 opens to the outside of the housing 40 , and the opposite side of the opening communicates with a liquid passage 42 formed in the housing 40 . The liquid passage 42 opens at the bottom 43 of the insertion hole 41 . The bottom portion 43 is recessed toward the inside of the device so as to match the shape of the annular portion 16 of the brake tube BT. A female thread 12b that meshes with the male thread 12a of the flare nut 1A is formed on the inner peripheral surface of the housing 40 in which the insertion hole 41 is formed.

First, the brake tube BT is inserted so that the annular portion 16 of the brake tube BT hits the bottom portion 43 of the insertion hole 41 while the flare nut 1A is moved away from the end. In this state, the flare nut 1A is brought close to the insertion hole 16 so that the male thread 12a of the threaded portion 12 and the female thread 12b of the housing 40 are engaged. When the flare nut 1</b>A is rotated in the fastening direction, the contact portion 14 contacts the annular portion 16 . When the flare nut 1</b>A is tightened while the contact portion 14 is in contact with the annular portion 16 , the annular portion 16 is pressed against the bottom portion 43 by the contact portion 14 . While the flare nut 1A is being tightened, the annular portion 16 is sandwiched between the contact portion 14 and the bottom portion 43 and gradually deforms from elastic deformation to plastic deformation. As a result, the brake tube BT is fluid-tightly coupled to the master cylinder MC1. The coupling force of the brake tube BT is determined by the maximum axial force acting during such fastening operation.

In order to firmly connect the brake tube BT, as shown in FIG. 5, the flare nut 1A is provided with a resin coating layer 18 for increasing or stabilizing the axial force at the time of fastening. The flare nut 1A has a surface 17 in which a zinc-based plating layer P1 is formed on a metal base M1, and a resin coating layer 18 is provided on the surface 17. As shown in FIG. The zinc-based plating layer P1 is provided mainly to improve corrosion resistance. In order to form the zinc-based plating layer P1, any of zinc plating, zinc-iron alloy plating, or zinc-nickel alloy plating may be performed. In this embodiment, a zinc-nickel alloy plating layer is provided as the zinc-based plating layer P1.

The resin coating layer 18 is formed in a coating region R (see FIG. 2) including at least the surfaces of the threaded portion 12 and the contact portion 14 . This coating area R is set over the entire surface of the flare nut 1A. That is, the coating region R is set on each surface of the threaded portion 12, the head portion 13 and the contact portion 14 of the flare nut 1A and the inner peripheral surface of the flare nut 1A penetrated by the through hole 10. As shown in FIG. The resin coating layer 18 is formed by adhering to the coating region R a coating agent C that contains polyethylene-based substances, lubricants, and solid particles as components and that has been adjusted to have a predetermined viscosity. As the polyethylene material, for example, polyethylene or polyethylene copolymer can be selected. As the lubricant, for example, any one of polyethylene wax, molybdenum disulfide, graphite, or boron nitride, or any combination thereof can be selected. Lubricants may be solid or liquid. Also, as the solid particles, for example, any one of silicon dioxide, silicon nitride, or titanium nitride, or any combination thereof can be selected.

A resin coating layer 18 may be provided on the surface 17 on which the zinc-based plating layer P1 has been chemically treated. In other words, a chemical conversion treatment layer may exist between the zinc-based plating layer P1 and the resin coating layer 18 . This increases the adhesion between the surface 17 and the resin coating layer 18 . The conversion layer may contain metal atoms selected from titanium, zirconium, molybdenum, tungsten, vanadium, manganese, nickel, cobalt, chromium, and lead. Also, some of these metal atoms may be contained in the chemical conversion treatment layer as compounds such as oxides. The conversion layer may be a chromium-free conversion layer. The chemical conversion treatment step for forming the chemical conversion treatment layer may be a reaction type or a coating type, and may be a trivalent chromium chemical conversion treatment or a chromium-free chemical conversion treatment. The coefficient of friction of the resin coating layer 18 is smaller than the coefficient of friction of the surface 17 on which the zinc-based plating layer P1 or the chemical conversion treatment layer is formed.

As an example, a method for forming the resin coating layer 18 will be described with reference to FIG. First, in the preparation step A, an untreated nut 1' that has undergone the plating treatment described above and has not been formed with the resin coating layer 18 is prepared. A plurality of untreated nuts 1' may be prepared. The prepared unprocessed nuts 1' are put into a processing basket 30 having meshes of a predetermined size. The next coating step B is carried out with the untreated nuts 1' housed in the basket 30 for treatment.

In the coating step B, a dip coating method is performed as an example. The coating process B includes an immersion process b1 for immersing the untreated nut 1' in the coating agent C, and a drying process b2 for drying the coating agent C adhering to the untreated nut 1'.

In the immersion step b1, the treatment basket 30 containing the untreated nuts 1' is submerged from above in the immersion tank 31 containing the coating agent C up to a predetermined level. The immersion bath 31 has the function of adjusting the temperature of the liquid contained in the bath. The temperature of the coating agent C is adjusted within the range of 30 to 40 [° C.], for example. The immersion bath 31 contains a sufficient amount of the coating agent C so that the temperature change of the coating agent C due to the immersion of the untreated nut 1', which is the object to be treated, can be ignored.

After that, the processing basket 30 submerged in the immersion tank 31 is lifted out of the immersion tank 31 to perform the drying step b2. In the drying step b2, the processing basket 30 containing the unprocessed nuts 1' is put into the dryer 32. As shown in FIG. The dryer 32 has a processing space 33 that can be adjusted to a predetermined temperature range, and a rotating mechanism 34 that rotates around the axis Ax while holding the processing basket 30 . In the drying step b2, the temperature in the processing space 33 is maintained at a predetermined temperature, and then the processing basket 30 held by the rotating mechanism 34 is rotated at a predetermined speed. The rotation mechanism 34 can change the rotation speed. For example, the rotation speed can be adjusted within the range of 100 to 900 [rpm]. The processing time by the dryer 32 is appropriately set. As a result, the excess coating agent C is shaken off by the centrifugal force of the rotating mechanism 34, and the coating agent C adhering to the coating area R is dried and fixed. The flare nut 1A provided with the resin coating layer 18 is manufactured by performing the drying step b2.

The thickness of the resin coating layer 18 provided on the flare nut 1A is controlled. As will be described later, it is known that the thickness of the resin coating layer 18 is a factor that affects mechanical properties such as the axial force of the flare nut 1A. It is also known that the thickness of the resin coating layer 18 affects the corrosion resistance of the flare nut 1A. For example, the thickness of the resin coating layer 18 can be controlled by preparing a coating agent C whose viscosity is adjusted and adjusting the temperature of the coating agent C when the object to be treated is immersed. Furthermore, the thickness of the resin coating layer 18 can be controlled by adjusting the temperature in the processing space 33 and the rotational speed of the rotating mechanism 32 in the drying step b2 described above. In other words, the parameters for controlling the thickness of the resin coating layer 18 are the viscosity of the coating agent C, the temperature during immersion, and the temperature and rotation speed during drying. Since the thickness of the resin coating layer 18 is not uniform regardless of the portion of the flare nut 1A, the unit area mass, which will be described later, is used as a physical quantity that correlates with the thickness of the resin coating layer 18. quantitatively control or manage

(Second form)
FIG. 7 shows a flare nut 1B suitable for double flares. The flare nut 1B corresponds to an example of the pipe joint of the present invention. The flare nut 1B is a hollow pipe joint having a through hole 20 into which a tube can be inserted. The flare nut 1B includes a threaded portion 22 having a male thread 22a, a head portion 23 provided at one end of the threaded portion 22, and a contact portion 24 provided at the other end of the threaded portion 22. As shown in FIG. These head 23, threaded portion 22 and contact portion 24 are penetrated by a through hole 20 extending in the direction of the center line CL2. In the case of the flare nut 1B, the through hole 20 has a shape having a constant inner diameter in the axial direction. .

The male thread 22a formed on the threaded portion 22 has the same specifications as the male thread 12a provided on the threaded portion 12 of the flare nut 1A of the first embodiment. It is within the range of 9.53 to 14.0 [mm]. The specifications of the head 23 are also the same as those of the head 13 of the flare nut 1A. The specifications of the contact portion 24 are the same as those of the contact portion 14 of the flare nut 1A. be.

The contact portion 24 is provided at the end on the right side in FIG. 7 along the center line CL2, in other words, at the end on the traveling direction side of the male screw 22a during fastening. The contact portion 24 has a function of pressing the annular portion 26 against the mating member while contacting the annular portion 26 (see FIG. 8) formed as a double flare when the mating member is fastened. In the case of the flare nut 1B, the contact portion 24 is provided near the terminal end of the threaded portion 22 and does not have a distinct cylindrical portion unlike the contact portion 14 of the flare nut 1A. However, there are also flare nuts suitable for double flares that clearly include a cylindrical portion such as the contact portion 14 of the flare nut 1A. The contact portion 24 has a conical contact surface 24a with an inclination angle of about 42° with respect to the axial direction.

As shown in FIG. 8, the annular portion 26 is formed at the end of the brake tube BT. As an example of the forming procedure, first, the resin coating layer BTa of the brake tube BT is peeled off from the end of the brake tube BT over a predetermined range in the direction of the tube axis Tx in the circumferential direction. A double-flare-shaped annular portion 26 projecting outward in the pipe radial direction orthogonal to the pipe axis Tx is formed with respect to the portion. Depending on the resin material of the resin coating layer BTa, the annular portion 26 may be formed on the end portion of the brake tube BT without peeling off the resin coating layer BTa.

An insertion hole 51 having the structure shown in FIG. 9 is formed in the mating member to which the brake tube BT having the annular portion 26 is coupled. For example, the insertion hole 51 is formed in the master cylinder MC2, which is an example of the mating member. The insertion hole 51 opens to the outside of the housing 50 , and the opposite side of the opening communicates with a liquid passage 52 formed in the housing 50 . The liquid passage 52 opens to the bottom 53 of the insertion hole 51 . The bottom portion 53 is formed in a shape protruding to the outside of the device so as to match the shape of the annular portion 26 of the brake tube BT. A female thread 22b that meshes with the male thread 22a of the flare nut 1B is formed on the inner peripheral surface of the housing 50 in which the insertion hole 51 is formed. Since the connection of the brake tube BT using the flare nut 1B is the same as the case of the flare nut 1A, the explanation is omitted.

As shown in FIG. 10, a resin coating layer 28 is provided on the flare nut 1B. The flare nut 1B has a surface 27 in which a zinc-based plating layer P2 is formed on a metal base M2, and a resin coating layer 28 is provided on the surface 27. As shown in FIG. The zinc-based plating layer P2 is provided mainly to improve corrosion resistance. In order to form the zinc-based plating layer P2, any of zinc plating, zinc-iron alloy plating, or zinc-nickel alloy plating may be performed. In this embodiment, a zinc-nickel alloy plating layer is provided as the zinc-based plating layer P2. A chemical conversion treatment layer may exist between the zinc-based plating layer P2 and the resin coating layer 28, as in the first embodiment. Also, as in the first embodiment, the coefficient of friction of the resin coating layer 28 is smaller than the coefficient of friction of the surface 27 on which the zinc-based plating layer P2 or the chemical conversion treatment layer is formed. The formation method of the resin coating layer 28 is the same as the formation method shown in FIG.

A: Fastening test

By repeatedly tightening and releasing the flare nuts 1A and 1B with the same tightening torque, the axial force at the time of tightening tends to decrease as the number of repetitions increases. It was found from the fastening test described below that the thickness of the resin coating layer is the main factor affecting the rate of decrease in axial force. Since no significant difference was found between the flare nut 1A and the flare nut 1B in the fastening test results, the test results of the flare nut 1A will be disclosed below.

1. Test sample (1) Preparation of test sample As shown in FIGS. 11A and 11B, four types of coating agents C1 to C4 are used to form a resin coating layer on each of three types of flare nuts with different shapes and sizes. Then, they were classified into a total of 12 groups G1 to G12. As a method for forming the resin coating layer, the dip coating method described above was adopted. Each group G1 to G12 includes a plurality of samples having different resin coating layer thicknesses. As described above, the parameters that control the thickness of the resin coating layer are the viscosity of the coating agent, the temperature during immersion, and the temperature and rotation speed during drying. By changing these conditions, a plurality of samples with different coating layer thicknesses were prepared for each of the groups G1 to G12. The thickness of the coating layer was quantified by the mass per unit area w [g/m ² ], which will be described later and correlates with the thickness.

(2) Measurement of Viscosity of Coating Agent In preparing the coating agent, the viscosity of each coating agent was measured by the following method.

・Equipment used: Rotational viscometer conforming to ISO 2555:1990 standards
(Equipment name: TVB-10M, Manufacturer: Toki Sangyo Co., Ltd.)
・Spindle rotation speed: 60 [rpm]
・Measure the viscosity at 25 [°C] under the above conditions

(3) Viscosity of Coating Agents The viscosities of the coating agents C1 to C4 at 25° C. are as follows.
- Coating agent C1: 4.51 [mPa s]
- Coating agent C2: 5.27 [mPa s]
- Coating agent C3: 4.25 [mPa s]
- Coating agent C4: 4.24 [mPa s]
(4) Components of Coating Agent Each of the coating agents C1 to C4 contains the above-described polyethylene-based substance, lubricant, and solid particles as common components.
(5) Calculation of unit area mass The thickness of the resin coating layer correlates with the mass of the substance adhering to the coating area. Therefore, as a physical quantity correlated with the thickness of the resin coating layer, a value obtained by dividing the difference in mass due to the presence or absence of the resin coating layer by the surface area of the coating region was defined as unit area mass w [g/m ² ]. This unit area mass w was used to quantify the thickness of the resin coating layer.

The unit area mass w was calculated by dividing the mass difference between the mass of the flare nut before the resin coating treatment and the mass of the flare nut after the formation of the resin coating layer by the total surface area of the flare nut. Contrary to this method, the mass per unit area w is the mass difference between the mass of the flare nut with the resin coating layer formed and the mass of the flare nut after removing the resin coating layer, which is the total surface area of the flare nut. It may be calculated by dividing by . As a method for removing the resin coating layer, for example, after immersing the flare nut on which the resin coating layer is formed in a high-temperature organic solvent, the immersed flare nut is washed with an organic solvent separately prepared for washing and dried. There is a way. As the organic solvent in which the flare nut is immersed, for example, an organic solvent capable of dissolving polyethylene such as benzene or decalin can be used. The immersion time and drying time are set to such an extent that the flare nut can be identified with the flare nut before the resin coating treatment. For example, the immersion time in the organic solvent may be set to 5 hours, and the drying time may be set to 1 hour after washing with the organic solvent for washing. The flare nut from which the resin coating layer has been removed by this treatment can be regarded as the same as the flare nut before the resin coating treatment.

The total surface area of the flare nut was calculated using the surface area calculation function attached to the CAD software based on the design drawing data of the flare nut. By using this function, the surface area can be calculated for any range of the flare nut.

Although the calculated surface area may vary slightly depending on the CAD software, the difference can be ignored in calculating the unit area mass w, which is calculated to two digits below the decimal point. Further, the error between the calculated value by CAD software and the calculated value calculated based on the measurement data obtained by three-dimensionally measuring the external dimensions of the actual product is also negligible.

(6) Sample Numbers As shown in FIGS. 11A and 11B, each sample was given a sample number #101 to #421 to distinguish them from each other. The first digit of the sample number is assigned to correspond to the type of coating agents C1 to C4.

2. Fastening Test Method (1) Axial Force Measuring Device An axial force measuring device shown in FIG. 12 was used to measure the axial force of each sample. FIG. 12 schematically shows the configuration of the axial force measuring device 100. As shown in FIG. A test tube T corresponding to the brake tube BT is set in the axial force measuring device 100 . The test tube T is set in the axial force measuring device 100 so that the tube axis Tx and the reference axis SAx are aligned. A flare nut sample S is attached to the test tube T, and the end of the test tube T is formed with a test annular portion TR. The axial force measuring device 100 tightens the sample S to a predetermined tightening torque to couple the test tube T to the test member TM corresponding to the mating member. The axial force measuring device 100 measures the axial force of the sample S and other physical quantities during the tightening operation.

The axial force measuring device 100 includes a frame 101, and the frame 101 is installed, for example, on the floor of a test room. The frame 101 of the axial force measuring device 100 includes a tightening operation section 102 that performs a tightening operation on the sample S, a mating member holding section 103 that holds the test member TM, and a tube holding section that holds the test tube T. 104 are provided respectively. The tightening operation portion 102, the mating member holding portion 103, and the tube holding portion 104 are provided on the frame 101 so as to be aligned in the direction of the reference axis SAx.

The tightening operation unit 102 includes a tool 110 fitted to the head of the sample S, a motor 111 that rotates the tool 110 around the reference axis SAx, and a tightening torque that outputs a signal corresponding to the drive resistance of the tool 110. and sensor 112 .

The mating member holding portion 103 holds the test member TM with a first jig 103a and a second jig 103b divided in the direction of the reference axis SAx. The test member TM is divided in the direction of the reference axis SAx, one first part TMa is held by the first jig 103a, and the other second part TMb is held by the second jig 103b. The first part TMa has a threaded hole 115 formed with a female thread 115b that meshes with the male thread of the sample S. As shown in FIG. The second part TMb has a bottom 116 against which the test ring TR of the test tube T is pressed. When the threaded hole 115 and the bottom portion 116 are concentrically butted together, a hole shape corresponding to the insertion holes 41 and 51 described above is formed. The first jig 103a and the second jig 103b can hold the screw hole 115 of the first part TMa and the bottom portion 116 of the second part TMb concentrically butted against each other. The first jig 103 a is fixed to the frame 101 . On the other hand, the second jig 103b is constrained in the direction of the reference axis SAx with the first part TMa and the second part TMb abutting against each other and with the load cell 117 interposed therebetween.

The tube holding unit 104 includes a fixing mechanism 118 that clamps a fixing position set at a predetermined distance (for example, 0.3 [m]) from the end of the test tube T, and a torque generated in the fixing mechanism 118 around the reference axis SAx. and a co-rotating torque sensor 119 that outputs a signal corresponding to.

When the sample S is tightened by the tightening operation portion 101, the sample S advances while meshing with the internal thread 115b formed in the first part TMa of the test member TM, and the test annular portion TR moves toward the second part TMb. is pressed against a bottom 116 formed on the . As a result, a force acts on the first part TMa and the second part TMb to separate them from each other in the direction of the reference axis SAx. The first part TMa is held by the first jig 103a fixed to the frame 101 and thus cannot move in the direction of the reference axis SAx. 117 is interposed and restrained in the direction of the reference axis SAx. Therefore, since the load acting on the second part TMb corresponds to the reaction force of the axial force of the sample S, the detected value of the load cell 117 can be treated as the measured value of the axial force. That is, the axial force of the sample S can be directly measured based on the output signal of the load cell 117 without calculation based on the tightening torque. Signals from the tightening torque sensor 112 , the load cell 117 , and the co-rotating torque sensor 119 are input to the controller 120 . The control device 120 may be a personal computer as an example. The control device 120 performs predetermined processing on the input signal from each sensor, and stores data in which the tightening torque input to the sample S is associated with the axial force and the co-rotating torque as the measurement result. And, if necessary, the measurement result can be output to output means such as a display.

(2) Test method Using the axial force measuring device 100 shown in FIG. 12, an unused sample S is attached to an unused test tube T, and the above-described fastening operation is performed, and then the tightening operation unit 101 A release operation is performed to release the connection of the test tube T to the test member TM by loosening the fastening of the sample. When the detected value of the load cell 117 returned to the initial value (for example, 0.0 [kN]), it was determined that the connection of the test tube T was released. As an example, the tightening torque at the time of tightening by the tightening operation unit 101 is set to a value within the range of 12.0 [Nm] to 22.0 [Nm], eg, 17.0 [Nm]. The above operation was defined as the first tightening test, and the tightening test including the tightening operation, the measurement of the axial force, and the release operation was repeated without exchanging the test tube T and the sample S for a total of 5 times. In each fastening test, the axial force and the co-rotating torque were obtained as measured values by the axial force measuring device 100 and recorded. An interval between each fastening test was set to 60 [sec] as an example.

The number of repetitions of the tightening test was determined based on the limit of the number of times the brake tube of the automobile was removed during the period from the time the car was new to the time the car was scrapped. We estimated the limit based on a discrete probability distribution with the frequency of brake tubes removed as a random variable. Here, assuming three elements, the ABS unit, the master cylinder, and the brake unit, as mating members to which the brake tube is connected, and assuming that the flare nut will always be reused in the event of failure of these three elements, failure of the three elements We considered the probability of occurrence, the number of brake tube joints, average values from new to scrap, and other parameters. From this, it was estimated that the number of times the brake tube was removed was 6 or more than 6 times with a negligibly low probability. Therefore, the number of repetitions of the fastening test was set to 5 times, which is less than 6 times.

(3) Axial force reduction rate As a parameter for evaluating changes in axial force due to repeated fastening tests on the same flare nut, an axial force reduction rate α [kN/time] was defined by Equation 1 below.

α=-( _Fn - _F1 )/(n-1) ...... 1

Here, F ₁ [kN] is the initial axial force, which is the maximum axial force generated in the first fastening test. F _n [kN] is the n-th axial force that is the maximum axial force generated in the n-th fastening test (where 1<n<6). However, Expression 1 is conditioned on the fact that 0<F _n <F _{n- 1} holds, where F n-1 is the (n-1)-th axial force generated at the (n-1)-th time. Therefore, α>0.

As described above, in this test, the number of repetitions was set to n= ₅ , which is less than 6 times. can be rewritten as

α=−(F ₅ −F ₁ )/4…………1′

3. Test Results and Evaluation The test results of the fastening test performed in the manner described above are shown in FIGS. 13A and 13B.

(1) Evaluation Criteria Each sample was evaluated according to the following criteria a and b based on the mechanical properties of the flare nut.
・Criterion a Initial axial force F ₁ is less than 14.0 [kN] ・Criterion b Axial force decrease rate α is less than 1.75 [kN/time]

The criterion a defines the upper limit of the initial axial force _F1 . This upper limit was determined based on the upper limit of co-rotating torque. The upper limit of the co-rotating torque is determined in consideration of the strength of the tube and the vibration of the vehicle, and is 1.0 [Nm] as an example. The co-rotating torque and the axial force are correlated, and the axial force corresponding to the upper limit value of the co-rotating torque is uniquely determined. The axial force is 14.0 [kN] as an example. The co-rotational torque was maximum at the initial fastening accompanied by plastic deformation of the annular portion formed in the tube, and decreased after reuse of the flare nut, and tended not to change much depending on the number of reuses. Therefore, when the axial force meets the criterion a, it is guaranteed that the co-rotating torque will be less than the upper limit even when reused. The lower limit of the initial axial force _F1 is set so as to secure the coupling force required for the tube even if the axial force decreases when the flare nut is reused. For example, the lower limit of the initial axial force _F1 is preferably 10.0 [kN], more preferably 11.0 [kN], and even more preferably 12.0 [kN]. That is, the initial axial force F ₁ is preferably 10.0<F ₁ <14.0, more preferably 11.0<F ₁ <14.0, and even more preferably 12.0<F ₁ <14.0.

The reference b defines the upper limit of the axial force decrease rate α. For example, if the axial force decrease rate α is 1.75 [kN/time] or more, even if the flare nut is tightened with the same tightening torque as the initial tightening, the axial force may fall below the lower limit value when reused. many. The lower limit of this axial force is set based on the lower limit of the coupling force required for the brake tube. By conforming to the criterion b, it is possible to prevent the axial force from falling below the lower limit even when the flare nut is reused and tightened with the same tightening torque as the initial tightening. As a result, even when the flare nut is reused, it is possible to secure the coupling force required for the brake tube. It should be noted that the smaller the axial force decrease rate α, the better, provided that α>0.

(2) Evaluation Results Evaluation results are shown in FIGS. 14A and 14B. In these figures, each sample is arranged in order from the smallest to the largest unit area mass w, and the acceptable samples that meet both criteria a and b and those that do not meet at least one of these criteria a and b. The failed samples that were found were summarized. In FIGS. 14A and 14B, "y" indicates that the criteria a or b is met, and "n" indicates that the criteria are not met. In addition, "YES" is indicated when both criteria a and b are met, and "NO" is indicated when at least one of criteria a and b is not met.
(3) Discussion As can be understood from FIGS. 14A and 14B, whether the criteria a and b are appropriate depends on the mass per unit area w regardless of whether the coating agent is different or not. As the unit area mass w increases, the initial axial force _F1 generally increases while the axial force reduction rate α tends to decrease. Conversely, as the unit area mass w becomes smaller, the initial axial force _F1 generally decreases while the axial force decrease rate α tends to increase. It was found that if the mass per unit area w is too large, criterion a fails, and if the mass per unit area w is too small, criterion b fails. An overview of the acceptable samples shows that the mass per unit area w of the acceptable samples is within the range of 0.79<w<10.07. The smaller the initial axial force _F1 is, the less damage to the tube can be achieved while securing the necessary coupling force for the tube. Considering the mass production of flare nuts, it is advantageous in terms of production costs to use as little coating agent as possible. Therefore, when considering not only the mechanical properties but also the damage to the tube and the production cost of the flare nut, the upper limit of the unit area mass w is preferably less than 9.00 [g/m ² ], for example. Less than 0.50 [g/m ² ] is more preferable, and less than 6.00 [g/m ² ] is even more preferable. That is, the unit area mass w is preferably 0.79<w<9.00, more preferably 0.79<w<7.50, and still more preferably 0.79<w<6.00.

If the unit area mass w is within any of the above ranges, the mechanical properties required for the flare nut are satisfied. However, it has been found that if the unit area mass w is too small, the mechanical properties of the flare nut are satisfied, but there is a problem in the corrosion resistance of the flare nut during reuse.

B: Corrosion test Corrosion test confirmed the relationship between the corrosion resistance of the flare nut and the unit area mass w.

(Sample preparation)
A predetermined number of flare nuts having the same size and shape but different unit area mass w were prepared, and the above fastening test was performed on these flare nuts. It was created. As an example, the first sample group in which the fastening test was tried once and removed from the test tube, the third sample group in which the same test was tried three times and removed from the test tube, and the same test were tried five times. A fifth sample group was prepared by removing from the test tube with In addition, as a comparative example, a group of unused comparative samples having the same dimensions and shape as those of the test sample group and having different unit area masses w were prepared.

(Test method and results)
A corrosion test was performed on each test sample group and each comparative sample group. This test conforms to the salt spray test specified in JASO 104-86. Summarizing the test results, it was found that there is a relationship shown in FIG. 15 between corrosion resistance and unit area mass. The vertical axis in FIG. 15 represents the time [hr] from the start of the test to the occurrence of white rust, which means the corrosion resistance of the flare nut. The horizontal axis of FIG. 15 is the unit area mass w that correlates with the thickness of the resin coating layer.

(Discussion)
As shown in FIG. 15, as a tendency of overall corrosion resistance, it can be seen that the larger the unit area mass w is, the more the corrosion resistance is improved. Then, when each test sample group and the comparison sample group are compared, in the region where the unit area mass w is 1.20 or less, each test sample group has a similar unit area mass w as compared to the comparison sample group. White rust tends to occur in a short time. That is, in the region where the unit area mass w is 1.20 or less, the corrosion resistance is lowered by reuse. When each test sample group is compared in the same region, there is a tendency that the greater the number of repetitions, the lower the corrosion resistance. These tendencies are remarkable when the unit area mass w is in the range of 0.40 to 1.00.

On the other hand, it can be seen that there is no significant difference in corrosion resistance with respect to the unit area mass w between each test sample group and the comparative sample group in the region where the unit area mass w exceeds 1.20. That is, in the region where the unit area mass w exceeds 1.20, the corrosion resistance does not change depending on the number of times of reuse. Therefore, when the unit area mass w exceeds 1.20, even when the flare nut is reused, it is possible to ensure the same corrosion resistance as when it is used for the first time. If the unit area mass w exceeds 1.20, the same corrosion resistance as when used for the first time can be secured, but in order to reliably obtain corrosion resistance comparable to that when used for the first time, the unit area mass w exceeds 1.50. more preferably over 1.80, even more preferably over 2.00.

C: Summary Summarizing the results of the above fastening tests and corrosion resistance tests, it is clear that in order to satisfy the mechanical properties required of flare nuts and to ensure the same level of corrosion resistance when reused as when used for the first time, fastening The condition obtained by the test: 0.79<w<10.07 and the condition obtained by the corrosion resistance test: 1.20<w must be satisfied. Therefore, at least Equation 2 below must hold for the unit area mass w.

1.20<w<10.07 ……2

The present invention is not limited to the above embodiments and can be implemented in various forms. In each of the above embodiments, the flare nut is used for the metal brake tube, but the use of the flare nut is not limited to the brake tube. For example, various metal tubes such as vapor tubes can be used. Each of flare nuts 1A and 1B is merely an example of a pipe joint used to join metal tubes. The present invention differs from the illustrated shape as long as the male thread has an outer diameter of 9.53 to 14.0 [mm] and the contact portion has an inner diameter of 4.98 to 8.44 [mm]. It can also be applied to flare nuts.

The coating region R according to each of the above embodiments is set on the entire surface of the flare nut, that is, on the entire surface of the threaded portion, the head, and the contact portion, and on the inner peripheral surface of the flare nut penetrated by the through hole. . However, setting the coating area to the entire surface is only an example. For example, the coating area may be limited to the surface of the threaded portion and the surface of the contact portion. In this case, the inner peripheral surface and head surface of the flare nut penetrated by the through hole are excluded from the coating area. Moreover, the coating region is not limited to be set on the entire surface of the threaded portion and the contact portion. For example, a coating area may be set on a portion of each surface of the threaded portion and the contact portion. In this case, as an example, the coating area may be set to preferably 40% or more, more preferably 60% or more, and even more preferably 80% or more of the surface of the threaded portion. Also, the coating area may be set to preferably 40% or more, more preferably 60% or more, even more preferably 80% or more of the surface of the contact portion. As noted above, the surface of the threaded portion refers to the surface of the threaded area that actually or is intended to mate with the female thread. Also, the surface of the contact portion means a contact surface that actually contacts the annular portion or is scheduled to contact the annular portion.

In each of the above embodiments, the resin coating layer 18 is provided on the surface 17 provided with the zinc-based plating layer P1, and the resin coating layer 28 is provided on the surface 27 provided with the zinc-based plating layer P2, but these are only examples. . For example, the present invention may be implemented in a form in which a surface of a pipe joint is made of a base metal that is not subjected to chemical surface treatment such as plating, and a resin coating layer is provided on the surface. Also in this form, the coefficient of friction of the resin coating layer is smaller than the coefficient of friction of the surface, which is the base metal.

Inventions (hereinafter referred to as disclosed inventions) that can be specified from the above embodiments and modifications thereof will be disclosed below. In order to facilitate understanding of the disclosed invention, the reference numerals and figure numbers used in the description of the above embodiments are shown in parentheses, but the shapes, structures, and the like of the illustrated configurations are not limiting.

The pipe joint of the disclosed invention is attached to the outer periphery of a metal tube (BT) having annular portions (16, 26) protruding radially outwardly at the ends thereof, and is attached to the outer periphery of a metal tube (BT) in contact with the annular portion. A pipe joint capable of coupling the tube to the mating member by being fastened to the member (MC1, MC2), wherein male threads (12a, 22a) mesh with female threads (12b, 22b) provided on the mating member. is formed at the threaded portion (12, 22), and the end portion on the traveling direction side of the male screw at the time of fastening, and the annular portion is attached to the mating member while being in contact with the annular portion at the time of fastening to the mating member. and a resin coating layer (18, 28) provided in a coating region (R) including the surfaces of the threaded portion and the contact portion, the threaded portion and each of the contact portions is penetrated by a through hole (10, 20) extending in a direction parallel to the traveling direction, and the male screw has an outer diameter of 9.53 to 14.0 [mm] and the contact portion has an inner diameter of 4.98 to 8.44 [mm], the resin coating layer contains a polyethylene-based substance, a lubricant and solid particles, and the resin coating layer 0.79<w<10.07 is established when the value obtained by dividing the mass difference due to the presence or absence of the coating region by the surface area of the coating region is defined as the unit area mass w [g/m ² ].

According to this pipe joint, 0.79<w<10.07 holds for the unit area mass w, which correlates with the thickness of the resin coating layer provided on the pipe joint. , the initial axial force that makes the co-rotating torque less than the upper limit can be obtained, and the axial force decrease rate can be kept low.

In one aspect of the disclosed invention, a test member corresponding to the mating member and a test tube having the same outer diameter as the tube and a test annular portion corresponding to the annular portion are prepared, and the test annular portion A fastening test including a fastening operation of fastening to the test member with a predetermined fastening torque while in contact with the n When the number of times is repeated (where 1<n<6), the maximum axial force generated in the first fastening test is defined as the initial axial force F ₁ [kN], and the maximum axial force generated in the nth fastening test is defined as As the n-th axial force F _n [kN], when the value obtained by −(F _n −F ₁ )/(n−1) is defined as the axial force decrease rate α [kN/times], 0<α< 1.75 may hold. According to this aspect, since 0<α<1.75 is established for the axial force decrease rate α, it is possible to suppress the decrease in the axial force at the time of reuse, and it is possible to fasten with the same tightening torque as at the time of the first use. However, the desired bonding strength can be obtained at the time of reuse.

The tube with a pipe fitting of the disclosed invention is a metal tube ( BT), and is attached to the outer periphery of the tube in a state of being retained by the annular portion and the bent portion, and is fastened to the mating member (MC1, MC2) in a state of contact with the annular portion, whereby the A tube with a pipe fitting, comprising a pipe fitting (1A, 1B) capable of coupling the tube to the mating member, wherein the pipe fitting has a male thread that meshes with a female thread (12b, 22b) provided on the mating member. Threaded portions (12, 22) having (12a, 22a) formed thereon, and an end portion on the traveling direction side of the male thread at the time of fastening, and the annular a contact portion (14, 24) for pressing the portion against the mating member; and a resin coating layer (18, 28) provided in a coating region (R) including each surface of the threaded portion and the contact portion. In addition, each of the threaded portion and the contact portion is penetrated by a through hole (10, 20) extending in a direction parallel to the advancing direction, and the male thread is 9.53 to 14.0 [ mm], and the contact portion has an inner diameter of 4.98 to 8.44 [mm], and the resin coating layer contains a polyethylene-based substance, a lubricant, and solid particles, In addition, when the value obtained by dividing the mass difference due to the presence or absence of the resin coating layer by the surface area of the coating region is defined as the unit area mass w [g/m ² ], 0.79<w<10.07 This is a tube with a pipe fitting that satisfies

According to this tube with a pipe joint, it is possible to provide a tube with a pipe joint that can ensure the mechanical properties required for reuse.

1A, 1B Flare nut (pipe joint)
10, 20 through holes 12, 22 threaded portions 12a, 22a male screws 14, 24 contact portion 16 ISO flare (annular portion)
18, 28 Coating layer 26 Double flare (annular part)
BT brake tube (tube)
FN Flare nut MC1, MC2 Master cylinder (mating member)
R coating region T test tube TM test member TR test annulus

Claims (3)

An annular portion protruding radially outward is attached to the outer periphery of a metal tube provided at the end, and the tube is fastened to the mating member while being in contact with the annular portion. A coupleable pipe fitting,
a threaded portion formed with a male thread that meshes with a female thread provided on the mating member;
a contact portion provided at an end portion of the male screw on the traveling direction side during fastening, for pressing the annular portion against the mating member while being in contact with the annular portion during fastening to the mating member;
a resin coating layer provided in a coating region including each surface of the threaded portion and the contact portion;
Each of the threaded portion and the contact portion is penetrated by a through hole extending in a direction parallel to the advancing direction, and the male screw has an outer diameter of 9.53 to 14.0 [mm]. and the contact portion has an inner diameter of 4.98 to 8.44 [mm],
The resin coating layer contains a polyethylene-based material, a lubricant, and solid particles, and
When the value obtained by dividing the mass difference due to the presence or absence of the resin coating layer by the surface area of the coating region is defined as the unit area mass w [g/m ² ], 0.79 < w < 10.07 is established. pipe fittings. A test member corresponding to the mating member and a test tube having the same outer diameter as the tube and a test annular portion corresponding to the annular portion are prepared, and in a state of contact with the test annular portion, a predetermined When a fastening test including a fastening operation of fastening to the test member with a fastening torque and a releasing operation of releasing the coupling of the test tube by loosening the fastening after the fastening operation is repeated n times (however, 1 <n<6), let the maximum axial force generated in the first fastening test be the initial axial force F ₁ [kN], and let the maximum axial force generated in the nth fastening test be the n-th axial force F _n [ kN], when the value obtained by -(F _n - F ₁ )/(n-1) is defined as the axial force decrease rate α [kN/time], 0 < α < 1.75 is established. Item 1 pipe joint. A metal tube provided with an annular portion protruding radially outwardly at an end thereof and having a bent portion at a position spaced apart from the annular portion;
Attached to the outer periphery of the tube in a state of being retained by the annular portion and the bent portion, and fastened to the mating member while being in contact with the annular portion, the tube can be coupled to the mating member. a pipe joint;
A tube with a fitting, comprising
The pipe joint is
a threaded portion formed with a male thread that meshes with a female thread provided on the mating member;
a contact portion provided at an end portion of the male screw on the traveling direction side during fastening, for pressing the annular portion against the mating member while being in contact with the annular portion during fastening to the mating member;
a resin coating layer provided in a coating region including each surface of the threaded portion and the contact portion;
Each of the threaded portion and the contact portion is penetrated by a through hole extending in a direction parallel to the advancing direction, and the male screw has an outer diameter of 9.53 to 14.0 [mm]. and the contact portion has an inner diameter of 4.98 to 8.44 [mm],
The resin coating layer contains a polyethylene-based material, a lubricant, and solid particles, and
When the value obtained by dividing the mass difference due to the presence or absence of the resin coating layer by the surface area of the coating region is defined as the unit area mass w [g/m ² ], 0.79 < w < 10.07 is established. pipe fittings.

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