Pipe fittings and tubes with pipe fittings

Abstract

To provide a pipe joint and the like, which can obtain an initial axial force for setting corotation torque lower than an upper limit, when fastening and release are repeated.SOLUTION: A flare nut 1A comprises a zinc-based plated layer P1, and a resin coating layer 18 that is positioned on an outermost surface on the outside with respect to the zinc-based plated layer P1 and that includes a polyethylene-based substance, a lubricant and a solid particle. When an average plating thickness t of a joint, which is associated with the thickness of the zinc-based plated layer P1, is defined, the inequality, 2.1<t<19.7, is established.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pipe joint and a tube with a pipe joint. [Background technology]

[0002] It is well known that, for the purpose of preventing loosening or increasing axial force of threaded members such as standardized bolts and nuts, the surfaces of the threaded members are coated with lubricants or adhesives, or subjected to surface treatments such as plating. Also known is a technique for applying a resin coating to threaded pipe joints used in automobile brake tubes and the like (see, for example, Patent Documents 1 to 3).

[0003] When the tightening torque used to tighten a threaded member to a mating member is constant, the smaller the frictional force acting between the threaded member and the mating member, the greater the axial force. Therefore, surface treatments are applied to threaded members to reduce the frictional force. This allows a greater axial force to be obtained with the same tightening torque. This is true not only for standardized threaded members, but also for threaded pipe fittings. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-230099 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-299895 [Patent Document 3] European Patent Application Publication No. 2706277 Summary of the Invention [Problem to be solved by the invention]

[0005] When pipe fittings are used to connect metal tubing, an annular portion known as an ISO flare or double flare is formed at the end of the tube when the fitting is attached to the outer circumference of the tube. The annular portion protrudes radially outward and is larger than the inner diameter of the fitting, preventing the fitting from slipping out toward the end. Furthermore, because automotive piping tubes are bent to fit the layout of the vehicle's underside, the bent portion of the tube also prevents the fitting from slipping out in the direction away from the end. Therefore, when loosening a fitting to remove the tube and then returning it to its original state for maintenance or repair of various devices to which the tube is connected, the same fitting must be reused each time the tube is removed, unless the fitting is replaced along with the tube.

[0006] When a pipe joint is repeatedly tightened and released with the same tightening torque in order to reuse it, the axial force tends to decrease the more times this is done. Therefore, if a pipe joint is tightened with the same tightening torque when reused, the axial force will decrease as the axial force reduction rate increases, and there is a possibility that the desired joining strength will not be obtained in the reused pipe joint.

[0007] On the other hand, when fastening a pipe fitting, co-rotation, in which the tube rotates together with the pipe fitting, can occur. Co-rotation occurs when the frictional force between the annular portion of the tube and the pipe fitting exceeds the frictional force between the annular portion and the mating member. If the pipe fitting is fastened while the tube is fixed to prevent this co-rotation, a co-rotation torque is generated that twists the tube as a reaction force that prevents co-rotation. If the co-rotation torque is large, it can damage the tube. Furthermore, since the reaction force of the co-rotation torque acts in a direction that loosens the fastened pipe fitting, if co-rotation torque remains when the tube is attached to a vehicle, it can induce loosening of the pipe fitting due to vehicle vibration. Therefore, the upper limit of the co-rotation torque that can occur when fastening a pipe fitting is determined taking into account the strength of the tube and vehicle vibration.

[0008] The torque tends to be greatest when the pipe joint is first made up, decrease the next time it is used, and not change much with the number of uses thereafter. Therefore, if the torque is less than the upper limit when the pipe joint is first made up, the torque will not exceed the upper limit when the pipe joint is reused.

[0009] It is known that the purposes of applying zinc-based plating to pipe fittings are to improve corrosion resistance and to stabilize the preload by smoothing the surface on which the resin coating layer is to be formed. When the inventors of the present invention studied the reuse of pipe fittings, they found that the thickness of the zinc-based plating layer present inside the resin coating layer affects the rate of preload reduction due to reuse of the pipe fitting and the co-rotation torque at the time of initial make-up.

[0010] Therefore, one object of the present invention is to provide a pipe fitting and a tube with a pipe fitting that can obtain an initial axial force that keeps the co-rotation torque below an upper limit value when fastening and unfastening are repeated, and can keep the axial force reduction rate low. [Means for solving the problem]

[0011] The pipe fitting of the present invention is a pipe fitting that is attached to the outer periphery of a metal tube that has an annular portion provided at its end that protrudes outward in the pipe diameter direction, and that can connect the tube to a mating member by being fastened to the mating member while in contact with the annular portion, and that comprises a threaded portion that has a male thread formed thereon that meshes with a female thread provided on the mating member, a head portion that is provided on one end of the threaded portion and into which a tightening torque is input when fastening, a contact portion that is provided on the other end of the threaded portion and that presses the annular portion against the mating member while contacting the annular portion when fastening to the mating member, and ... threaded portion, the head portion, and the fastening portion. a zinc-based plating layer provided on the contact portion; and a resin coating layer located on the outermost surface outside the zinc-based plating layer and containing a polyethylene-based material, a lubricant, and solid particles; the threaded portion, the head, and the contact portion are each penetrated by a through hole extending in a direction parallel to the direction of advancement of the male thread during fastening; the male thread of the threaded portion has an outer diameter of 9.53 to 14.0 mm; the head has a first flat surface facing in the opposite direction to the direction of advancement and a second flat surface perpendicular to the first flat surface; the contact portion includes a contact surface that can come into contact with the annular portion and has an outer diameter of 4.98 to 8.It has an inner diameter of 44 [mm], includes a center line extending in the same direction as the through hole, and when counting the number of threads forming the male thread in a cross section orthogonal to the second plane of the head from the head side, the first thread is defined as the first thread, the second thread as the second thread, the third thread as the third thread, and the fourth thread as the fourth thread. In the cross section, a first region set on the first plane of the head, a second region set on the second plane of the head, a third region set on the trailing flank of the third thread, a fourth region set on the trailing flank of the fourth thread, and a fifth region set on the contact surface of the contact portion are defined. And, when calculating the arithmetic mean of the thicknesses of the zinc-based plating layer measured at seven points arranged in one direction at intervals of 10 [μm] within each of the regions from the first region to the fifth region, and taking the five calculated values as X1, X2, X3, X4, X5 for each of the first region to the fifth region, and when measuring the thicknesses of the zinc-based plating layer at the bottom of the valley between the second thread and the third thread, the peak of the third thread, the bottom of the valley between the third thread and the fourth thread, and the peak of the fourth thread in the cross section, and taking the four measured values as T1, T2, T3, T4, when defining the value obtained by (X1 + X2 + X3 + X4 + X5 + T1 + T2 + T3 + T4) / 9 as the joint average plating thickness t [μm], 2.1 < t < 19.7 holds.

[0012] The present invention provides a tube with a pipe fitting, which comprises: a metal tube having an annular portion at one end thereof that protrudes radially outward, and a bent portion at a position distant from the annular portion; and a pipe fitting that is attached to the outer periphery of the tube while being prevented from coming off by the annular portion and the bent portion, and that is fastened to a mating member while in contact with the annular portion, thereby connecting the tube to the mating member. The pipe fitting comprises a threaded portion having a male thread that meshes with a female thread provided on the mating member, a head portion provided on one end of the threaded portion and into which a tightening torque is input when fastened, and a head portion provided on the other end of the threaded portion that contacts the annular portion when fastened to the mating member. a contact portion for pressing the annular portion against the mating member; a zinc-based plating layer provided on the threaded portion, the head, and the contact portion; and a resin coating layer located on the outermost surface outside the zinc-based plating layer and containing a polyethylene-based material, a lubricant, and solid particles; the threaded portion, the head, and the contact portion are each penetrated by a through hole extending in a direction parallel to the direction of advancement of the male thread during fastening; the male thread of the threaded portion has an outer diameter of 9.53 to 14.0 mm; the head includes a first flat surface facing in the opposite direction to the direction of advancement and a second flat surface perpendicular to the first flat surface; the contact portion includes a contact surface that can come into contact with the annular portion and has a thickness of 4.98 to 8.It has an inner diameter of 44 [mm], includes a center line extending in the same direction as the through hole, and when counting the number of threads forming the male thread in a cross section orthogonal to the second plane of the head from the head side, with the first thread as the first thread, the second thread as the second thread, the third thread as the third thread, and the fourth thread as the fourth thread, respectively defined. In the cross section, a first region set on the first plane of the head, a second region set on the second plane of the head, a third region set on the trailing flank of the third thread, a fourth region set on the trailing flank of the fourth thread, and a fifth region set on the contact surface of the contact portion are defined. And, five calculated values obtained by calculating the arithmetic mean of the thickness of the zinc-based plating layer measured at seven points arranged in one direction at intervals of 10 [μm] within each of the regions from the first region to the fifth region are designated as X1, X2, X3, X4, and X5. When four measured values of the thickness of the zinc-based plating layer are measured at the bottom of the valley between the second thread and the third thread, the peak of the third thread, the bottom of the valley between the third thread and the fourth thread, and the peak of the fourth thread in the cross section and designated as T1, T2, T3, and T4, when the value obtained by (X1 + X2 + X3 + X4 + X5 + T1 + T2 + T3 + T4) / 9 is defined as the joint average plating thickness t [μm], 2.1 < t < 19.7 holds.

Brief Description of the Drawings

[0015] For example, brake tubes in automobiles are used as piping to transmit pressure generated in the master cylinder to the brake units installed on each wheel. In many cases, an ABS unit or ESC unit is installed between the master cylinder and the brake units, and the brake tubes are also used to connect these units. Multiple brake tubes with different pipe diameters are selected to suit various conditions, such as the pressure resistance requirements between these units.

[0016] As shown in FIG. 1 , multiple brake tubes BT are bundled together using clamps C, made of resin, for example, and then bent according to the layout of the vehicle's bottom before being delivered to an automobile assembly line. Each brake tube BT is made of a double-wrapped tube made of a metal material such as steel, which has excellent pressure resistance, to withstand the brake operating pressure. For example, a brake tube with an outer diameter φ in the range of 4.76 to 8.00 mm is selected. Each brake tube BT is fitted with a flare nut FN that matches its outer diameter. On the automobile assembly line, workers tighten the flare nuts FN attached to each brake tube BT to each of the above units with a predetermined common tightening torque, thereby joining the brake tubes BT together.

[0017] The end of each brake tube BT is subjected to high-pressure terminal processing with a flare nut FN attached. Examples of high-pressure terminal processing include terminal processing that forms a ring-shaped portion Rp, such as the ISO flare specified by the International Organization for Standardization (ISO) or the double flare specified by the Japan Automotive Engineering Society (JASO). With the flare nut FN attached to the outer circumference of each brake tube BT, the terminal processing that forms the ring-shaped portion Rp and the bending process that forms the bent portion Bp are performed. Therefore, the flare nut FN is prevented from coming off the brake tube BT by the ring-shaped portion Rp and the bent portion Bp located away from the ring-shaped portion Rp.

[0018] (First form) FIG. 2 shows a flare nut 1A suitable for ISO flare. The flare nut 1A corresponds to an example of a pipe fitting of the present invention. The flare nut 1A is a hollow pipe fitting 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 on one end of the threaded portion 12, and a contact portion 14 provided on the other end of the threaded portion 12. The head portion 13, the threaded portion 12, and the contact portion 14 are passed through a through hole 10 extending in the direction of a 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. However, the through hole 10 can be replaced with, for example, a stepped through hole whose inner diameter changes at a predetermined point in the axial direction.

[0019] The male thread 12a formed on the threaded portion 12 is, for example, a metric coarse thread standardized by ISO, and engages with a female thread 12b (see Figure 4) formed on a mating member. However, the male thread 12a may also be modified to a metric fine thread of the same standard. Because fine threads have a smaller lead angle than coarse threads, modifying the threaded portion 12a to a fine thread can provide a flare nut that is less likely to loosen under the same axial force. Regarding the size of the threaded portion 12 of the flare nut 1A used for the above-mentioned brake tube BT, the larger the outer diameter of the attached tube, the larger the thread size tends to be. Unless there are special circumstances, the size of the threaded portion 12 is generally within the nominal diameter range of M10 to M14, i.e., an outer diameter of 10.0 to 14.0 mm. When inch threads are used on the flare nut 1A, threads within the nominal diameter range of 3 / 8 inch to 1 / 2 inch (approximately 9.53 to 12.7 mm) are typically used. Therefore, the male thread 12a that can be used in the flare nut 1A has an outer diameter within the range of 9.53 to 14.0 mm.

[0020] The head 13 is the portion to which tightening torque is input during tightening, and has a standardized hexagonal shape so that tightening can be performed with a common tool such as a flare nut wrench. The head 13 includes a hollow, circular flat surface 13a oriented in the axial direction and six side surfaces 13b with which the tool engages. The flat surface 13a corresponds to an example of a first flat surface, and each of the six side surfaces 13b corresponds to an example of a second flat surface. The size of the head 13 is selected to match the size of the threaded portion 12, but unlike the head of a standardized bolt, it is generally standardized to a certain extent to reduce the number of times tools need to be replaced.

[0021] The contact portion 14 is located at the right end of the flare nut 12 along the center line CL1 in FIG. 2, i.e., at the end of the flare nut 12 along the direction of travel of the male thread 12a during fastening. The contact portion 14 functions to press the annular portion 16 (see FIG. 3), formed as an ISO flare, against the mating member when fastened to the mating member. The contact portion 14 includes a contact surface 14a that contacts the annular portion 16 and a cylindrical portion 14b that extends from the threaded portion 12 toward the end. The boundary between the contact portion 14 and the through hole 10 is provided with a chamfered portion 10a that is inclined at approximately 45° relative to the center line CL1. The chamfered portion 10a reduces interference between the tube exterior and the flare nut 1A during fastening and reduces stress concentration at the boundary between the through hole 10 and the contact portion 14. The chamfered portion 10a has a conical surface whose ridgeline, as seen in a cross section taken along the center line CL1, is a straight line. The chamfered portion 10a may be replaced by a processed portion having a curved surface whose ridgeline is a curve drawn by one or more arcs that are convex toward the center.

[0022] The inner diameter of the contact portion 14 is determined by the inner diameter of the through hole 10. For example, the inner diameter d of the contact portion 14 is set to 4.98 mm when the outer diameter φ of the brake tube BT is 4.76 mm, 6.24 mm when the outer diameter φ is 6.0 mm, 6.59 mm when the outer diameter φ is 6.35 mm, and 8.29 mm when the outer diameter φ is 8.0 mm. The inner diameter d of the contact portion 14 is allowed to have an error of +0.15 mm, for example. Therefore, the inner diameter d of the contact portion 14 that can be used in the flare nut 1A is within the range of 4.98 to 8.44 mm.

[0023] As shown in Figure 3, the annular portion 16 is formed at the end of the brake tube BT. An example of the formation procedure is as follows: First, the resin coating layer BTa of the brake tube BT is peeled off circumferentially from the end over a predetermined range in the direction of the tube axis Tx. Next, the annular portion 16 is formed in an ISO flare shape, protruding outward in the tube radial direction perpendicular to the tube axis Tx from the end of the peeled portion BTb where the resin coating layer has been peeled off. Note that, depending on the resin material of the resin coating layer BTa, the annular portion 16 may be formed at the end of the brake tube BT without peeling off the resin coating layer BTa.

[0024] As an example of how to use the flare nut 1A, the case of connecting a brake tube BT to a master cylinder MC1 will be described with reference to Figure 4. The master cylinder MC1, which is an example of a mating member, has a housing 40. The housing 40 is formed with an insertion hole 41 into which the brake tube BT is inserted. The insertion hole 41 opens to the outside of the housing 40, and the opposite side of the opening communicates with a fluid passage 42 formed in the housing 40. The fluid passage 42 opens at a bottom 43 of the insertion hole 41. The bottom 43 is formed in a shape that is recessed toward the inside of the device so as to fit the shape of the annular portion 16 of the brake tube BT. The inner surface of the housing 40, in which the insertion hole 41 is formed, is formed with a female thread 12b that meshes with the male thread 12a of the flare nut 1A.

[0025] First, the flare nut 1A is moved away from the terminal, and the brake tube BT is inserted so that the annular portion 16 of the brake tube BT abuts against the bottom portion 43 of the insertion hole 41. Then, the flare nut 1A is moved toward the insertion hole 16, engaging the male thread 12a of the threaded portion 12 with the female thread 12b of the housing 40. When the flare nut 1A is rotated in the tightening direction, the contact portion 14 comes into contact with the annular portion 16. Then, when the flare nut 1A is tightened while the contact portion 14 is in contact with the annular portion 16, the contact portion 14 presses the annular portion 16 against the bottom portion 43. 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, transitioning from elastic to plastic deformation. This results in a fluid-tight connection between the brake tube BT and the master cylinder MC1. The connection force of the brake tube BT is determined by the maximum axial force acting during this tightening operation.

[0026] As shown in FIG. 5, the flare nut 1A is provided with a resin coating layer 18 to increase or stabilize the axial force during tightening, thereby firmly connecting the brake tube BT. The flare nut 1A has a zinc-based plating layer P1 formed on a metal base M1. Furthermore, a resin coating layer 18 is formed on the plating layer P1. The resin coating layer 18 is located on the outermost surface of the plating layer P1. Note that, as long as the resin coating layer 18 is located on the outermost surface, a different type of resin layer may be provided between the plating layer P1 and the resin coating layer 18. The plating layer P1 may be formed by zinc plating, zinc-iron alloy plating, or zinc-nickel alloy plating. In this embodiment, a zinc-nickel alloy plating layer is provided as the plating layer P1. The plating layer P1 is formed on the entire surface of the metal base M1. The plating layer P1 covers the surfaces of the thread portion 12, the head portion 13, and the contact portion 14, as well as the inner surface of the through hole 10 penetrating these portions.

[0027] The plating layer P1 may be subjected to a chemical conversion treatment. In this case, the plating layer P1 includes a chemical conversion treatment layer on its outer surface. However, depending on the composition of the chemical conversion treatment layer, it may be difficult to confirm even with a microscope. This chemical conversion treatment layer enhances adhesion between the plating layer P1 and the resin coating layer 18. The chemical conversion treatment layer may contain metal atoms selected from titanium, zirconium, molybdenum, tungsten, vanadium, manganese, nickel, cobalt, chromium, and lead. Furthermore, some of these metal atoms may be contained in the chemical conversion treatment layer as compounds such as oxides. The chemical conversion treatment layer may be a chromium-free chemical conversion treatment layer. The chemical conversion treatment process for forming the chemical conversion treatment layer may be a reactive or coating type, and may be either a trivalent chromium chemical conversion treatment or a chromium-free chemical conversion treatment.

[0028] The plating layer P1 is formed by electrolytic plating. The untreated nut with the exposed metal base M1 is immersed in a plating bath containing zinc and nickel ions. The thickness of the coating deposited on the metal base M1 of the untreated nut is controlled by adjusting at least one of the current density (defined as the current per unit area) and the treatment time during the plating process.

[0029] In electrolytic plating, the current density varies depending on the shape of the product being plated, resulting in inconsistent coating thickness. For example, if the product being plated includes not only areas with minimal shape variation, such as flat or cylindrical surfaces, but also areas with significant shape variation, such as convex corners or sharp points, the coating thickness will vary across each area. In the case of flare nut 1A, the thickness of plating layer P1 varies when comparing the crest and root of the thread on thread portion 12 and when comparing the crest and contact surface 14a of contact portion 14. For example, when comparing the thickness of plating layer P1 between the crest of thread on thread portion 12 and the contact surface 14a of contact portion 14, the thickness at the crest tends to be smaller than the thickness at the contact surface 14a.

[0030] As described below, it has been found that the mechanical properties of the flare nut 1A change depending on the thickness of the plating layer P1. However, because the thickness of the plating layer P1 varies depending on the location of the flare nut 1A, it is not possible to accurately evaluate the correlation between the thickness of the plating layer P1 and mechanical properties such as axial force. Therefore, the thickness of the plating layer P1 is quantitatively controlled or managed using the average plating thickness of the joint, which is calculated using a predetermined method, as described below.

[0031] The resin coating layer 18 is formed in a coating region R (see FIG. 2 ), which includes at least the surfaces of the threaded portion 12 and the contact portion 14. As an example, the coating region R is set on the entire surface of the flare nut 1A. That is, the coating region R is set on the surfaces of the threaded portion 12, the head portion 13, and the contact portion 14 of the flare nut 1A, as well as on the inner circumferential surface of the flare nut 1A penetrated by the through hole 10. The resin coating layer 18 includes a polyethylene-based substance, a lubricant, and solid particles. The resin coating layer 18 is formed by applying a coating agent C containing these components to the coating region R. For example, the polyethylene-based substance may be polyethylene or a polyethylene copolymer. For example, the lubricant may be polyethylene wax, molybdenum disulfide, graphite, or boron nitride, or any combination thereof. The lubricant may be solid or liquid. For example, the solid particles may be silicon dioxide, silicon nitride, or titanium nitride, or any combination thereof.

[0032] The resin coating layer 18 is formed, for example, by a dip coating method. Instead of this method, the resin coating layer 18 may be formed by, for example, a spray method in which a coating agent is finely divided and sprayed. This spray method is suitable for forming the resin coating layer 18 partially on the flare nut 1A. The friction coefficient of the resin coating layer 18 is smaller than that of the plating layer P1.

[0033] (Second form) FIG. 6 shows a flare nut 1B suitable for a double flare. The flare nut 1B corresponds to an example of a pipe joint of the present invention. The flare nut 1B is a hollow pipe joint formed with a through hole 20 into which a tube can be inserted. The flare nut 1B includes a threaded portion 22 with a male thread 22a, a head portion 23 provided on one end of the threaded portion 22, and a contact portion 24 provided on the other end of the threaded portion 22. The head portion 23, the threaded portion 22, and the contact portion 24 are passed through a through hole 20 extending in the direction of a center line CL2. In the case of the flare nut 1B, the through hole 20 has a shape with a constant inner diameter in the axial direction. However, the through hole 20 can be replaced with a stepped through hole whose inner diameter changes at a predetermined point in the axial direction, for example.

[0034] The male threads 22a formed on the threaded portion 22 have the same specifications as the male threads 12a provided on the threaded portion 12 of the flare nut 1A of the first embodiment, and the male threads 22a that can be used in the flare nut 1B have an outer diameter within a 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 head 23 includes a hollow, circular flat surface 23a oriented in the axial direction and six side surfaces 23b with which a tool engages. The flat surface 23a corresponds to an example of a first flat surface, and any one of the six side surfaces 23b corresponds to an example of a second flat surface. The specifications of the contact portion 24 are also the same as those of the contact portion 14 of the flare nut 1A, and the contact portion 24 that can be used in the flare nut 1B has an inner diameter d within a range of 4.98 to 8.44 mm.

[0035] The contact portion 24 is located at the right end of the flare nut 1B along the center line CL2 in FIG. 6, in other words, at the end of the flare nut 1B in the direction of travel of the male thread 22a during fastening. The contact portion 24 functions to press the double-flared annular portion 26 (see FIG. 7) against the mating member while contacting the annular portion 26. In the case of the flare nut 1B, the contact portion 24 is located near the end of the threaded portion 22. The flare nut 1B does not have a distinct cylindrical portion like the cylindrical portion 14b (see FIG. 2) of the flare nut 1A. However, some flare nuts suitable for double flares include a cylindrical portion equivalent to the cylindrical portion 14b. The contact portion 24 has a conical contact surface 24a with an inclination angle of approximately 42° relative to the axial direction.

[0036] As shown in Figure 7, the annular portion 26 is formed at the end of the brake tube BT. An example of the formation procedure is as follows: First, the resin coating layer BTa of the brake tube BT is peeled off circumferentially from the end over a predetermined range in the direction of the tube axis Tx. Next, a double-flared annular portion 26 is formed at the end of the peeled portion BTb where the resin coating layer BTa has been peeled off, protruding outward in the tube radial direction perpendicular to the tube axis Tx. Note that, depending on the resin material of the resin coating layer BTa, the annular portion 26 may be formed at the end of the brake tube BT without peeling off the resin coating layer BTa.

[0037] An insertion hole 51 having the structure shown in FIG. 8 is formed in the mating member to which the brake tube BT, which has the annular portion 26 formed therein, is coupled. For example, the insertion hole 51 is formed in a master cylinder MC2, which is an example of a mating member. The insertion hole 51 opens to the outside of the housing 50, and the opposite side of the opening communicates with a fluid passage 52 formed in the housing 50. The fluid passage 52 opens to a bottom 53 of the insertion hole 51. The bottom 53 is formed in a shape that protrudes toward the outside of the device so as to fit 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 circumferential surface of the housing 50, in which the insertion hole 51 is formed. The coupling of the brake tube BT using the flare nut 1B is similar to that in the case of the flare nut 1A, and therefore a description thereof will be omitted.

[0038] As shown in FIG. 9 , a resin coating layer 28 is provided on the flare nut 1B. In the flare nut 1B, a zinc-based plating layer P2 is formed on a metal base material M2. Furthermore, a resin coating layer 28 is provided on the plating layer P2. The resin coating layer 28 is located on the outermost surface of the plating layer P2. Note that, as long as the resin coating layer 28 is located on the outermost surface, a different type of resin layer may be provided between the plating layer P2 and the resin coating layer 28. The plating layer P2 may be formed by zinc plating, zinc-iron alloy plating, or zinc-nickel alloy plating. In this embodiment, a zinc-nickel alloy plating layer is provided as the plating layer P2. The plating layer P2 is provided on the entire surface of the metal base material M1. The plating layer P2 covers the surfaces of the thread portion 22, the head portion 23, and the contact portion 24, as well as the inner surface of the through hole 20 penetrating these. The plating layer P2 may include a chemical conversion layer on its outer surface. As in the first embodiment, the plating layer P2 is formed by electrolytic plating, and the resin coating layer 28 is formed by dip coating, for example. The coefficient of friction of the resin coating layer 28 is smaller than the coefficient of friction of the plating layer P2. [Example]

[0039] For the above-mentioned flare nuts 1A and 1B, repeated tightening and loosening using the same tightening torque tended to result in a decrease in preload during tightening as the number of repetitions increased. Furthermore, the tightening test described below revealed that the thickness of the zinc-based plating layer is a factor affecting the preload reduction rate. Since no significant differences were found between flare nuts 1A and 1B in the tightening test results, the test results conducted on flare nut 1A are disclosed below.

[0040] 1. Test sample (1) Preparation of test samples As shown in Fig. 10, a plurality of samples with different joint average plating thicknesses t [μm] were prepared for three types of flare nuts having different shapes and sizes. As an example of the plating layer of each sample, a zinc-nickel alloy plating layer was adopted. Further, the joint average plating thickness t was made different from each other by adjusting at least one of the current density and the treatment time during the plating process of each sample. That is, the parameters for controlling the joint average plating thickness t are the current density and the treatment time.

[0041] The resin coating layer of each sample contains the above-described polyethylene-based substance, lubricant, and solid particles, and is formed by adhering either one of two types of coating agents C1 and C2 having different viscosities at 25 [°C] to the coating region. The dip coating method was adopted as the method for forming the resin coating layer. Regarding the thickness of the resin coating layer, the thickness was managed using the unit area mass w [g / m 2 , which is described later and correlates with the thickness. The unit area mass w of each sample is adjusted within the range of 0.79 < w < 10.07.

[0042] (2) Joint average plating thickness Due to the characteristics of electrolytic plating, the thickness of the plating layer is not uniform depending on the part of the flare nut. It has been found that the thickness of the plating layer affects the mechanical properties of the flare nut such as the axial force. Therefore, the joint average plating thickness t [μm] is used to quantitatively control or manage the thickness of the plating layer. The joint average plating thickness t is calculated as follows.

[0043] Fig. 11A shows a cross-section of the flare nut 1A passing through the center line CL1 and orthogonal to any two of the six side surfaces 13b of the head 13. The thickness of the plating layer at each part appearing in this cross-section is measured to calculate the joint average plating thickness t.

[0044] (a) Thread R constituting the male thread 12a i(where i = 1, 2, 3, 4...) are counted from the head 13 side, and the first thread is defined as the first thread R1, the second thread as the second thread R2, the third thread as the third thread R3, and the fourth thread as the fourth thread R4.

[0045] (b) The following five regions Ar i (where i=1, 2, 3, 4, 5) (b1) First area Ar1 The first area Ar1 is an area set on the flat surface 13a of the head 13. As shown in FIG. 11A, the first area Ar1 is defined by a distance r from the center line CL1 to the inner circumferential surface of the through hole 10. 11 The distance from the center line CL1 to the side surface 13b is r 12 In this case, r1=(r 11 +r 12 ) / 2 away from the target point, and is set within a circle with a radius of 100 μm. (b2) Second area Ar2 The second area Ar2 is an area set on the side surface 13b of the head 13. As shown in Fig. 11A, when the distance from the flat surface 13a to the end of the side surface 13b is L2, the second area Ar2 is set within a circle with a radius of 100 [µm] and centered at a position that is L2 / 2 away from the flat surface 13a. (b3) Third area Ar3 The third area Ar3 is set within a circle with a radius of 100 μm, centered at the midpoint of the following flank of the third thread R3. (b4) Fourth area Ar4 The fourth area Ar4 is set within a circle with a radius of 100 μm, centered at the midpoint of the trailing flank of the fourth thread R4. (b5) Fifth area Ar5 The fifth region Ar5 is a region set on the contact surface 14a of the contact portion 14. As shown in FIG. 11A, the fifth region Ar5 is defined by a distance from the center line CL1 to the inner circumferential surface of the through hole 10 (the inner diameter of the contact portion 14) defined as r 51 The distance from the center line CL1 to the outer circumferential surface of the contact portion 14 is r 52 Then, from the center line CL1, r5 = (r 51 +r 52) / 2 away from the center line CL2 of the contact surface 24a of the contact portion 24. In the case of the flare nut 1B, the first region Ar1 to the fourth region Ar4 are the same as those of the flare nut 1A, but the fifth region Ar5 is set as shown in FIG. 11B. FIG. 11B shows a portion of a cross section of the flare nut 1B that passes through the center line CL2 and is perpendicular to any two of the six side surfaces 23b of the head 23. In this case, the fifth region Ar5 is set within a circle with a radius of 100 μm that is centered at the midpoint of the contact surface 24a of the contact portion 24 that appears in this cross section.

[0046] (c) Each area Ar set in (b) above i As shown in FIG. 11C, the thickness of the plating layer was measured at seven points p1 to p7 arranged in one direction at 10 μm intervals, and the arithmetic mean of these seven measured values ​​was defined as an area Ar i This calculates the five regions Ar i Obtain five calculated values ​​X1, X2, X3, X4, and X5 corresponding to the above.

[0047] (d) The thickness of the plating layer is measured at the root M1 between the second thread R2 and the third thread R3, the crest M2 of the third thread R3, the root M3 between the third thread R3 and the fourth thread R4, and the crest M4 of the fourth thread R4. Four measurement values ​​T1, T2, T3, and T4 corresponding to these portions M1 to M4 are obtained.

[0048] (e) Calculate the joint average plating thickness t based on the following formula 1. t=(X1+X2+X3+X4+X5+T1+T2+T3+T4) / 9 ……1

[0049] (f) To measure the thickness of the plating layer, first, the actual flare nut 1A or 1B is cut longitudinally using a cutting machine. During this cutting, the cutting position of the cutting blade is slightly offset radially from the center line to prevent excessive grinding beyond the center line of the actual nut during the polishing process described below. This ensures a polishing allowance and results in a measurement piece slightly larger than half the size. Next, the measurement piece is molded in resin to cover it. The orientation of the cut surface of the measurement piece is kept visible even after molding. Next, the resin-molded measurement piece is flat-ground using a grinding machine until the cross section including the center line shown in Figure 11A or 11B is revealed. Then, each portion of the polished cross section is imaged at 1000 to 2500 times magnification using, for example, the digital microscope described below, and the thickness of the plating layer is measured based on the image. Model number: OLYMPUS DSX 510 Manufacturer: Olympus Corporation

[0050] (3) Calculation of unit area mass The thickness of the resin coating layer correlates with the mass of the substance attached to the coating area. Therefore, as a physical quantity correlated with the thickness of the resin coating layer, the value obtained by dividing the mass difference between the presence and absence of the resin coating layer by the surface area of ​​the coating area is called the mass per unit area w [g / m 2 The unit area mass w was used to quantify the thickness of the resin coating layer.

[0051] 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 resin coating layer was formed by the total surface area of ​​the flare nut. Conversely, the unit area mass w may also be calculated by dividing the mass difference between the mass of the flare nut on which the resin coating layer was formed and the mass of the flare nut after the resin coating layer was removed by the total surface area of ​​the flare nut. One method for removing the resin coating layer is, for example, immersing the flare nut on which the resin coating layer was formed in a high-temperature organic solvent, then washing the immersed flare nut with a separately prepared organic solvent for cleaning and drying it. Organic solvents that can dissolve polyethylene, such as benzene and decalin, can be used as the organic solvent for immersing the flare nut. The immersion time and drying time are set to a degree that allows the flare nut to be considered identical to the flare nut before the resin coating treatment. For example, the immersion time in the organic solvent may be 5 hours, and after washing with the organic solvent for cleaning, the drying time may be 1 hour. The flare nut from which the resin coating layer has been removed by this treatment can be considered the same as the flare nut before the resin coating treatment.

[0052] The total surface area of ​​the flare nut was calculated using the surface area calculation function included in the CAD software based on the design drawing data of the flare nut. Using this function, the surface area of ​​any area of ​​the flare nut can be calculated. Note that although there may be slight differences in the calculated surface area depending on the CAD software, these differences can be ignored when calculating the unit area mass w, which is calculated to two decimal places. Similarly, the error between the value calculated by the CAD software and the value calculated based on the measurement data obtained by three-dimensionally measuring the external dimensions of the actual product is also negligible.

[0053] (4) Sample number As shown in Figure 10, the samples were given sample numbers #101 to #209 to distinguish them from one another. The first digit of the sample numbers corresponds to the type of coating agent C1 or C2.

[0054] 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 shows a schematic diagram of the axial force measuring device 100. A test tube T corresponding to a 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 its tube axis Tx coincides with the reference axis SAx. A flare nut sample S is attached to the test tube T, and a test annular portion TR is formed at the end of the test tube T. The axial force measuring device 100 performs a tightening operation on the sample S until a predetermined tightening torque is reached, connecting the test tube T to a test member TM corresponding to the mating member. The axial force measuring device 100 measures the axial force and other physical quantities of the sample S during the tightening operation.

[0055] The axial force measurement device 100 includes a frame 101, which is installed, for example, on the floor of a test room. The frame 101 of the axial force measurement device 100 is provided with a clamping operation unit 102 that performs a clamping operation on the sample S, a mating member holding unit 103 that holds a test member TM, and a tube holding unit 104 that holds a test tube T. The clamping operation unit 102, the mating member holding unit 103, and the tube holding unit 104 are provided on the frame 101 so as to be aligned in the direction of the reference axis SAx.

[0056] The tightening operation unit 102 includes a tool 110 that is fitted onto the head of the sample S, a motor 111 that drives the tool 110 to rotate around the reference axis SAx, and a tightening torque sensor 112 that outputs a signal corresponding to the driving resistance of the tool 110.

[0057] The mating member holder 103 holds the test member TM using a first jig 103a and a second jig 103b, which are divided in the direction of the reference axis SAx. The test member TM is divided in the direction of the reference axis SAx, with one first part TMa held by the first jig 103a and the other second part TMb held by the second jig 103b. The first part TMa has a threaded hole 115 with an internal thread 115b that mates with the external thread of the sample S. The second part TMb has a bottom 116 against which the test annular portion TR of the test tube T is pressed. When the threaded hole 115 and the bottom 116 are concentrically butted together, they form a hole shape corresponding to the insertion holes 41 and 51 described above. The first jig 103a and the second jig 103b can hold the first part TMa in a state in which the threaded hole 115 and the bottom 116 of the second part TMb are concentrically butted together. The first jig 103a 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 butted against each other and with the load cell 117 interposed therebetween.

[0058] The tube holding portion 104 is equipped with a fixing mechanism 118 that clamps a fixed position set at a predetermined distance (e.g., 0.3 m) from the end of the test tube T, and a co-rotating torque sensor 119 that outputs a signal corresponding to the torque generated around the reference axis SAx in the fixing mechanism 118.

[0059] When the tightening operation unit 101 tightens the sample S, the sample S advances while engaging with the internal thread 115b formed in the first part TMa of the test member TM, and the test ring portion TR is pressed against the bottom portion 116 formed in the second part TMb. This causes a force to act on the first part TMa and the second part TMb, pulling them apart 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 is therefore immovable in the direction of the reference axis SAx. Meanwhile, the second part TMb is held by the second jig 103b and is constrained in the direction of the reference axis SAx via the load cell 117. Therefore, the load acting on the second part TMb corresponds to a reaction force to the axial force of the sample S, and the detected value of the load cell 117 can be treated as a measured value of the axial force. In other words, the axial force of the sample S can be measured directly based on the output signal of the load cell 117, without relying on a calculation based on the tightening torque. The signals from the tightening torque sensor 112, the load cell 117, and the co-rotation torque sensor 119 are input to the control device 120. The control device 120 may be, for example, a personal computer. The control device 120 performs predetermined processing on the input signals from each sensor, stores data in which the axial force and co-rotation torque correspond to the tightening torque input to the sample S as measurement results, and can output the measurement results to output means such as a display as needed.

[0060] (2) Test method Using the axial force measurement device 100 shown in FIG. 12, an unused sample S was attached to an unused test tube T and the above-described fastening operation was performed. Then, a release operation was performed to loosen the fastening of the sample using the fastening operation unit 101 and release the connection of the test tube T to the test member TM. The test tube T was determined to have been released when the detected value of the load cell 117 returned to its initial value (e.g., 0.0 kN). The fastening torque applied by the fastening operation unit 101 during fastening was set to a value ranging from 12.0 Nm to 22.0 Nm, e.g., 17.0 Nm. This operation constituted the first fastening test. This fastening test, including the fastening operation, measurement of axial force, etc., and release operation, was repeated a total of five times without replacing the test tube T and the sample S. In each fastening test, the axial force and co-rotational torque were measured and recorded using the axial force measurement device 100. The interval between each fastening test was, e.g., 60 seconds.

[0061] The number of times the fastening test was repeated was determined based on the limit of the number of times a vehicle's brake tubes are removed between the time the vehicle is new and the time it is scrapped. Although vehicle brake tubes are not removed frequently, the limit was estimated based on a discrete probability distribution in which the number of times they are removed is a random variable. Here, we assumed that the brake tubes are connected to three components: the ABS unit, the master cylinder, and the brake unit. Based on the premise that the flare nut must be reused in the event of a failure in any of these three components, we considered the probability of failure of the three components, the number of brake tube connection points, the average value of the period from the time the vehicle is new to the time it is scrapped, and other parameters. Based on this, we estimated that the probability of the brake tube being removed six or more times is negligibly low. Therefore, the number of times the fastening test was repeated was set at five, less than six.

[0062] (3) Axial force reduction rate The axial force reduction rate α [kN / cycle] was defined by the following equation 2 as a parameter for evaluating the change in axial force due to repeated tightening tests on the same flare nut. α=-(F n -F1) / (n-1)……2

[0063] Here, F1 [kN] is the initial axial force which is the maximum axial force generated in the first fastening test. F n [kN] is the nth axial force which is the maximum axial force generated in the nth (where 1 < n < 6) fastening test. However, in Equation 2, when the (n - 1)th axial force generated at the (n - 1)th time is F n-1 , the condition is that 0 < F n < F n-1 holds. Therefore, α > 0.

[0064] As described above, in this test, since the number of repetitions was set to n = 5 which is less than 6, Equation 2 for defining the axial force reduction rate α can be rewritten as the following Equation 2' when the axial force at the 5th time is F5. α = -(F5 - F1) / 4………2'

[0065] 3. Test Results and Evaluation The test results of the fastening test conducted as described above are shown in FIG. 13.

[0066] (1) Evaluation Criteria Each sample was evaluated according to the following Criteria a and Criteria b based on the mechanical properties of the flare nut. · Criterion a The initial axial force F1 exceeds 10.0 [kN] and is less than 14.0 [kN]. · Criterion b The axial force reduction rate α is less than 1.75 [kN / rev].

[0067] [[ID=3S]] Criterion a defines the range of the initial axial force F1. The upper limit of criterion a is determined based on the upper limit of the torque. The upper limit of the torque is determined taking into account the strength of the tube and vehicle vibration, and is, for example, 1.0 [Nm]. The torque and the axial force are correlated, and the axial force corresponding to the upper limit of the torque is uniquely determined. For example, this axial force is 14.0 [kN]. The torque is greatest during initial tightening, which involves plastic deformation of the annular portion formed on the tube. It tends to decrease after the flare nut is reused and change little with the number of reuses. Therefore, by ensuring that the axial force is below the upper limit of criterion a, the torque remains below the upper limit even after reuse. On the other hand, the lower limit of criterion a is set so that the required connecting force of the tube can be maintained even if the axial force decreases when the flare nut is reused. For example, this axial force is 10.0 [kN]. Therefore, by ensuring that the axial force exceeds the lower limit of criterion a, the required connecting force of the tube can be maintained even after reuse.

[0068] Criterion b specifies the upper limit of the preload reduction rate α. For example, if the preload reduction rate α is 1.75 kN / cycle or higher, the preload will often fall below the lower limit when the flare nut is reused, even if it is tightened with the same tightening torque as when it was initially tightened. This lower limit is set based on the lower limit of the connecting strength required for the brake tube. By complying with Criterion b, it is possible to avoid the preload reduction rate falling below the lower limit when the flare nut is reused, even if it is tightened with the same tightening torque as when it was initially tightened. This ensures that the connecting strength required for the brake tube can be maintained even when the flare nut is reused. Note that the smaller the preload reduction rate α, the better, provided that α>0.

[0069] (2) Evaluation results The evaluation results are shown in Fig. 14. In this figure, each sample is arranged in order from the one with a smaller joint average plating thickness t to the one with a larger joint average plating thickness t, and the qualified samples that meet both of the criteria a and b and the unqualified samples in which at least one of these criteria a and b does not meet are grouped together. In Fig. 14, the cases where the criteria a or b are met are denoted as "y", and the cases where they do not meet are denoted as "n", respectively. Also, the case where both of the criteria a and b are met is denoted as "YES", and the case where at least one of the criteria a and b does not meet is denoted as "NO", respectively.

[0070] (3) Discussion As can be understood from Fig. 14, whether the criteria a and b are met depends on the joint average plating thickness t regardless of the difference in the coating agents. As the joint average plating thickness t increases, generally the initial axial force F1 and the axial force reduction rate α tend to decrease. Conversely, as the joint average plating thickness t decreases, generally the initial axial force F1 and the axial force reduction rate α tend to increase. It has been found that when the joint average plating thickness t is too large, the criterion a does not meet, and when the joint average plating thickness t is too small, the criterion b does not meet.

[0071] Looking at the qualified samples, the joint average plating thickness t of the qualified samples falls within the range of 2.1 < t < 19.7. The smaller the initial axial force F1, the more the damage to the tube can be reduced while ensuring the bonding force required for the tube. Also, considering the mass production of flare nuts, it is more advantageous in terms of production cost that the thickness of the plating layer is as small 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, as the upper limit value of the joint average plating thickness t, for example, less than 16.0 [μm] is preferable, less than 1 _ 4.0 [μm] is more preferable, and less than 12.0 [μm] is even more preferable. That is, the joint average plating thickness t is preferably 2.1 < t < 16.0, more preferably 2.1 < t < 14.0, and even more preferably 2.1 < t < 12.0.

[0072] The present invention is not limited to the above embodiments and can be embodied in various forms. In the above embodiments, the flare nut is used with a metal brake tube, but the flare nut is not limited to brake tubes. For example, it can also be used with various metal tubes, such as vapor tubes. Each of the flare nuts 1A and 1B is merely an example of a pipe joint used to connect metal tubes. The present invention can also be applied to flare nuts with shapes different from those shown in the drawings, 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.

[0073] Zinc-based plating includes zinc-nickel alloy plating, zinc plating, zinc-iron alloy plating, etc. To satisfy the mechanical properties required of the flare nut, the average joint plating thickness t should be within the above range. Therefore, the type of zinc-based plating can be selected depending on the corrosion resistance required for the flare nut's intended use.

[0074] The coating region R in each of the above embodiments is set on the entire surface of the flare nut, i.e., on the entire surfaces of the threaded portion, head portion, and contact portion, as well as on the inner circumferential surface of the flare nut penetrated by the through hole. However, setting the coating region on the entire surface is merely an example. For example, the coating region may be limited to the surface of the threaded portion and the surface of the contact portion. In this case, the inner circumferential surface of the flare nut penetrated by the through hole and the surface of the head are excluded from the coating region. Furthermore, the coating region does not necessarily have to be set on the entire surface of the threaded portion and the contact portion. For example, the coating region may be set on only a portion of the surface of the threaded portion and the contact portion. In this case, as an example, the coating region may be set on preferably 40% or more of the surface of the threaded portion, more preferably 60% or more, and even more preferably 80% or more. Furthermore, the coating region may be set on preferably 40% or more of the surface of the contact portion, more preferably 60% or more, and even more preferably 80% or more. The surface of the threaded portion refers to the surface of the thread-forming area that actually engages with the female thread or is intended to engage with the female thread. The surface of the contact portion means a contact surface that actually contacts the annular portion or is intended to contact the annular portion.

[0075] The inventions that can be identified from the above-described embodiments and their modified examples are disclosed below. Note that, to facilitate understanding of the disclosed inventions, the reference symbols and figure numbers used in the description of the above-described embodiments are written in parentheses, but the inventions are not limited to the shapes, structures, etc. of the components shown in the drawings.

[0076] The pipe fitting of the disclosed invention is a pipe fitting (1A, 1B) that is fitted to the outer periphery of a metal tube (BT) that has an annular portion (Rp, 16, 26) that protrudes outward in the pipe diameter direction at its end, and that can connect the tube to a mating member (MC1, MC2) by being fastened to the mating member while in contact with the annular portion, and that comprises a threaded portion (12, 22) on which a male thread (12a, 22a) is formed that meshes with a female thread (12b, 22b) provided on the mating member, a head (13, 23) provided on one end of the threaded portion and into which a tightening torque is input when fastening, a contact portion (14, 24) provided on the other end of the threaded portion and that presses the annular portion against the mating member while contacting the annular portion when fastening to the mating member, zinc-based plating layers (P1, P2) provided on the threaded portion, the head, and the contact portion, and a contact portion (15, 16) on an outer side of the zinc-based plating layer and a resin coating layer (18, 28) located on the outermost surface of the male screw, the resin coating layer (18, 28) including a polyethylene-based substance, a lubricant, and solid particles, the threaded portion, the head, and the contact portion are each penetrated by a through hole (10, 20) extending in a direction parallel to the direction of advancement of the male screw during fastening, the male screw of the threaded portion has an outer diameter of 9.53 to 14.0 [mm], the head includes a first plane (13a, 23a) facing in the opposite direction to the direction of advancement and a second plane (13b, 23b) perpendicular to the first plane, the contact portion includes a contact surface (14a, 24a) that can come into contact with the annular portion, has an inner diameter of 4.98 to 8.44 [mm], includes a center line (CL1, CL2) extending in the same direction as the through hole, and in a cross section (cross section of FIG. 11A or FIG. 11B ) perpendicular to the second plane of the head, a thread (R 1 ) constituting the male screw i) When counting the number from the head side, the first thread is defined as the first thread (R1), the second thread as the second thread (R2), the third thread as the third thread (R3), and the fourth thread as the fourth thread (R4). In the cross-section, a first region (Ar1) set on the first plane of the head, a second region (Ar2) set on the second plane of the head, a third region (Ar3) set on the trailing flank of the third thread, a fourth region (Ar4) set on the trailing flank of the fourth thread, and a fifth region (Ar5) set on the contact surface of the contact portion are defined. And, five calculated values obtained by calculating the arithmetic mean of the thickness of the zinc-based plating layer measured at seven points arranged in one direction at intervals of 10 [μm] within each of the first region to the fifth region are taken as X1, X2, X3, X4, X5. When four measured values of the thickness of the zinc-based plating layer are taken as T1, T2, T3, T4 at the bottom valley (M1) between the second thread and the third thread, the peak (M2) of the third thread, the bottom valley (M3) between the third thread and the fourth thread, and the peak (M4) of the fourth thread in the cross-section, when the value obtained by (X1 + X2 + X3 + X4 + X5 + T1 + T2 + T3 + T4) / 9 is defined as the joint average plating thickness t [μm], 2.1 < t < 19.7 holds.

[0077] According to this pipe joint, for the joint average plating thickness t correlated with the thickness of the zinc-based plating layer provided on the pipe joint, 2.1 < t < 19.7 holds. Therefore, when tightening and loosening are repeated, an initial shaft force with a circumferential torque less than the upper limit value can be obtained, and the shaft force reduction rate can be suppressed low.

[0078] In one aspect of the pipe joint of the disclosed invention, a test member (TM) corresponding to the mating member and a test tube (T) having a test annular portion (TR) corresponding to the annular portion with the same outer diameter as the tube are prepared. A fastening operation of fastening the test member with a predetermined fastening torque in a state of contacting the test annular portion, and a releasing operation of loosening the fastening after the fastening operation to release the connection of the test tube are included. When the fastening test including these operations is repeated n times (where 1 < n < 6), the maximum axial force generated in the first fastening test is defined as the initial axial force F1 [kN], and the maximum axial force generated in the nth fastening test is defined as the nth axial force F n [kN]. When the value obtained by -(F n - F1) / (n - 1) is defined as the axial force reduction rate α [kN / rev], 0 < α < 1.75 may be satisfied. According to this aspect, regarding the axial force reduction rate α, since 0 < α < 1.75 is satisfied, the reduction of the axial force during reuse can be suppressed, and a desired coupling force can be obtained during reuse even when fastening with the same fastening torque as during the first use.

[0079] In this aspect, the tube is a brake tube used for an automobile brake pipe. When the fastening torque is within the range of 12.0 to 22.0 [Nm], 10.0 < F1 < 14.0 may be satisfied. In this case, since it is guaranteed that the upper limit value of the circumferential torque is not exceeded, it is possible to prevent loosening of the pipe joint while avoiding damage to the brake tube.

[0080] The tube with pipe fitting of the disclosed invention comprises a metal tube (BT) having an annular portion (Rp, 16, 26) at its end that protrudes radially outward and a bent portion (Bp) at a position spaced apart from the annular portion, and a pipe fitting (1A, 1B) that is attached to the outer periphery of the tube while being prevented from coming off by the annular portion and the bent portion, and that is fastened to a mating member while in contact with the annular portion, thereby connecting the tube to the mating member. The pipe joint includes a threaded portion (12, 22) on which a male thread (12a, 22a) is formed to mesh with a female thread (12b, 22b) formed on the mating member, a head (13, 23) provided on one end of the threaded portion and into which a tightening torque is input when fastening, and a contact portion (14, 24) provided on the other end of the threaded portion and for pressing the annular portion against the mating member while contacting the annular portion when fastening to the mating member, and a contact portion (14, 24) formed on the threaded portion, the head, and the The screw thread has a zinc-based plating layer (P1, P2) provided on the contact portion, and a resin coating layer (18, 28) located on the outermost surface outside the zinc-based plating layer and containing a polyethylene-based substance, a lubricant, and solid particles. The threaded portion, the head, and the contact portion are each penetrated by a through hole (10, 20) extending in a direction parallel to the direction of advancement of the male thread during fastening. The male thread of the threaded portion has an outer diameter of 9.53 to 14.0 mm, and the head is , a first plane (13a, 23a) facing in the opposite direction to the advancing direction and a second plane (13b, 23b) perpendicular to the first plane, the contact portion includes a contact surface (14a, 24a) that can come into contact with the annular portion, has an inner diameter of 4.98 to 8.44 [mm], includes center lines (CL1, CL2) extending in the same direction as the through hole, and has a thread (R 1 , CL 2 ) that constitutes the male screw in a cross section of the head that is perpendicular to the second plane (the cross section of FIG. 11A or FIG. 11B ). i) When counting the number from the head side, the first thread is defined as the first thread (R1), the second thread is defined as the second thread (R2), the third thread is defined as the third thread (R3), and the fourth thread is defined as the fourth thread (R4). In the cross-section, a first region (Ar1) set on the first plane of the head, a second region (Ar2) set on the second plane of the head, a third region (Ar3) set on the trailing flank of the third thread, a fourth region (Ar4) set on the trailing flank of the fourth thread, and a fifth region (Ar5) set on the contact surface of the contact portion are defined. And, five calculated values obtained by calculating the arithmetic mean of the thickness of the zinc-based plating layer measured at seven points arranged in one direction at intervals of 10 [μm] in each of the regions from the first region to the fifth region are designated as X1, X2, X3, X4, and X5. When four measured values obtained by measuring the thickness of the zinc-based plating layer at the bottom valley (M1) between the second thread and the third thread, the peak (M2) of the third thread, the bottom valley (M3) between the third thread and the fourth thread, and the peak (M4) of the fourth thread in the cross-section are designated as T1, T2, T3, and T4, when a value obtained by (X1 + X2 + X3 + X4 + X5 + T1 + T2 + T3 + T4) / 9 is defined as the joint average plating thickness t [μm], 2.1 < t < 19.7 holds.

[0081] According to this tube with a pipe joint, it is possible to provide a tube provided with a pipe joint that can ensure the mechanical properties required during reuse.

[0082] In one aspect of this tube with a pipe joint, a test member (TM) corresponding to the mating member and a test tube (T) having a test annular portion (TR) corresponding to the annular portion with the same outer diameter as the tube are prepared. A fastening operation of fastening the test member with a predetermined fastening torque in a state of contacting the test annular portion, and a releasing operation of releasing the fastening after the fastening operation to release the connection of the test tube are included. When the fastening test including these operations is repeated n times (where 1 < n < 6), the maximum axial force generated in the first fastening test is defined as the initial axial force F1 [kN], and the maximum axial force generated in the nth fastening test is defined as the nth axial force F n [kN]. When the value obtained by -(F n - F1) / (n - 1) is defined as the axial force reduction rate α [kN / turn], 0 < α < 1.75 may hold. According to this aspect, regarding the axial force reduction rate α, since 0 < α < 1.75 holds, the reduction of the axial force during reuse can be suppressed, and a desired coupling force can be obtained during reuse even when fastening with the same fastening torque as during the first use.

[0083] In this aspect, the tube is a brake tube used for an automobile brake pipe. When the fastening torque is within the range of 12.0 to 22.0 [Nm], 10.0 < F1 < 14.0 may hold. In this case, since 10.0 < F1 < 14.0 holds for the initial axial force F1, it is guaranteed that the upper limit value of the circumferential torque is not exceeded, and it is possible to prevent loosening of the pipe joint while avoiding damage to the tube used for the brake pipe.

[0084] Another pipe fitting of the disclosed invention is a pipe fitting (1A, 1B) that is fitted to the outer periphery of a metal tube (BT) that has an annular portion (Rp, 16, 26) that protrudes outward in the pipe diameter direction at its end, and that can connect the tube to a mating member (MC1, MC2) by being fastened to the mating member while in contact with the annular portion, and that comprises a threaded portion (12, 22) having a male thread (12a, 22a) that meshes with a female thread (12b, 22b) provided on the mating member, a head (13, 23) that is provided on one end of the threaded portion and into which a tightening torque is input when fastening, a contact portion (14, 24) that is provided on the other end of the threaded portion and that presses the annular portion against the mating member while contacting the annular portion when fastening to the mating member, zinc-based plating layers (P1, P2) provided on the threaded portion, the head, and the contact portion, and a portion outside the zinc-based plating layer. and a resin coating layer (18, 28) located on the outermost surface of the male screw side, the resin coating layer (18, 28) including a polyethylene-based substance, a lubricant, and solid particles, the resin coating layer (18, 28) including a polyethylene-based substance, a lubricant, and solid particles, the threaded portion, the head, and the contact portion are each passed through a through hole (10, 20) extending in a direction parallel to the direction of advancement of the male screw during fastening, the male screw of the threaded portion has an outer diameter of 9.53 to 14.0 [mm], the head includes a first plane (13a, 23a) facing in the opposite direction to the direction of advancement and a second plane (13b, 23b) perpendicular to the first plane, the contact portion includes a contact surface (14a, 24a) that can come into contact with the annular portion, has an inner diameter of 4.98 to 8.44 [mm], includes a center line (CL1, CL2) extending in the same direction as the through hole, and in a cross section (cross section of FIG. 11A or FIG. 11B ) perpendicular to the second plane of the head, the thread (R iWhen counting the number of from the head side, the first thread is defined as the first thread (R1), the second thread is defined as the second thread (R2), the third thread is defined as the third thread (R3), and the fourth thread is defined as the fourth thread (R4). In the cross-section, a first region (Ar1) set on the first plane of the head, a second region (Ar2) set on the second plane of the head, a third region (Ar3) set on the trailing flank of the third thread, a fourth region (Ar4) set on the trailing flank of the fourth thread, and a fifth region (Ar5) set on the contact surface of the contact portion are defined. And, five calculated values obtained by calculating the arithmetic mean of the thickness of the zinc-based plating layer measured at seven points arranged in one direction at intervals of 10 [μm] within each of the first region to the fifth region are denoted as X1, X2, X3, X4, X5. In the cross-section, the bottom valley (M1) between the second thread and the third thread, the peak (M2) of the third thread, the bottom valley (M3) between the third thread and the fourth thread, and the peak (M4) of the fourth thread. When four measured values of the thickness of the zinc-based plating layer at each of them are denoted as T1, T2, T3, T4, the value obtained by (X1 + X2 + X3 + X4 + X5 + T1 + T2 + T3 + T4) / 9 is defined as the joint average plating thickness t [μm]. And, a test member (TM) corresponding to the mating member and a test tube (T) having a test annular portion (TR) corresponding to the annular portion with the same outer diameter as the tube are prepared. A fastening operation of fastening the test member with a fastening torque within the range of 12.0 to 22.0 [Nm] in a state of contacting the test annular portion, and a releasing operation of releasing the fastening after the fastening operation to release the connection of the test tube are included. When the fastening test is repeated n times (where 1 < n < 6), the maximum axial force generated in the first fastening test is defined as the initial axial force F1 [kN], and the maximum axial force generated in the nth fastening test is defined as the nth axial force F n [kN]. When the value obtained by -(F n - F1) / (n - 1) is defined as the axial force reduction rate α [kN / turn], the range of the joint average plating thickness t is set so that 10.0 < F1 < 14.0 and 0 < α < 1.75 are satisfied.

[0085] According to this pipe joint, for the axial force reduction rate α, 0 < α < 1.75 holds. Therefore, the reduction of the axial force during reuse can be suppressed, and even when tightened with the same tightening torque as during the first use, the desired coupling force can be obtained during reuse. Moreover, since 10.0 < F1 < 14.0 holds for the initial axial force F1, it is guaranteed that the upper limit value of the rotation torque is not exceeded, and it is possible to prevent loosening of the pipe joint while avoiding damage to the tube used in the brake pipe.

[0086] In one aspect of this pipe joint, the range of the joint average plating thickness t may be 2.1 < t < 19.7. According to this aspect, when tightening and releasing are repeated, it is possible to obtain an initial axial force with the rotation torque below the upper limit value, and to keep the axial force reduction rate low.

[0087] The method for measuring the plating thickness of a pipe fitting of the disclosed invention is applied to a plated pipe fitting that is attached to the outer periphery of a metal tube (BT) that has an annular portion (Rp, 16, 26) protruding outward in the pipe diameter direction at its end, and that is fastened to a mating member (MC1, MC2) while in contact with the annular portion, thereby being able to connect the tube to the mating member. The pipe fitting comprises a threaded portion (12, 22) having a male thread (12a, 22a) that meshes with a female thread (12b, 22b) provided on the mating member, a head portion (13, 23) provided on one end of the threaded portion and into which a tightening torque is input when fastened, and a contact portion (14, 24) provided on the other end of the threaded portion that comes into contact with the annular portion and presses the annular portion against the mating member when fastened to the mating member, and and plating layers (P1, P2) provided on a thread portion, the head, and the contact portion, wherein the thread portion, the head, and the contact portion are each penetrated by a through hole (10, 20) extending in a direction parallel to the direction of advancement of the male screw during fastening, the male screw of the thread portion has an outer diameter of 9.53 to 14.0 [mm], the head includes a first plane (13a, 23a) facing in the opposite direction to the direction of advancement and a second plane (13b, 23b) perpendicular to the first plane, the contact portion includes a contact surface (14a, 24a) that can come into contact with the annular portion and has an inner diameter of 4.98 to 8.44 [mm], includes center lines (CL1, CL2) extending in the same direction as the through hole, and in a cross section (cross section of FIG. 11A or FIG. 11B ) perpendicular to the second plane of the head, a thread (R 1 ) constituting the male screw i) counting from the head side, the first thread is defined as the first thread (R1), the second thread as the second thread (R2), the third thread as the third thread (R3), and the fourth thread as the fourth thread (R4), respectively, and in the cross section, a first region (Ar1) is set on the first flat surface of the head, a second region (Ar2) is set on the second flat surface of the head, a third region (Ar3) is set on the trailing flank of the third thread, a fourth region (Ar4) is set on the trailing flank of the fourth thread, and a fifth region (Ar5) is set on the contact surface of the contact portion; The method includes the steps of: acquiring five calculated values ​​X1, X2, X3, X4, and X5 for each of the first to fifth regions by calculating the arithmetic mean of the thickness of the plating layer measured at seven points spaced apart in one direction at [μm] intervals; acquiring four measured values ​​T1, T2, T3, and T4 by measuring the thickness of the plating layer at the root (M1) between the second thread and the third thread, the crest (M2) of the third thread, the root (M3) between the third thread and the fourth thread, and the crest (M4) of the fourth thread on the cross section; and acquiring a calculated value based on the formula: (X1+X2+X3+X4+X5+T1+T2+T3+T4) / 9 as the joint average plating thickness t [μm].

[0088] This measurement method allows the average joint plating thickness t to be obtained based on measurements of the plating layer thickness at multiple locations on a pipe joint. The thickness of the plating layer is not uniform throughout the pipe joint. However, this thickness affects the pipe joint's mechanical properties, such as axial force. By using the average joint plating thickness t as a parameter representing the thickness of the pipe joint's plating layer, the correlation between plating layer thickness and mechanical properties can be accurately evaluated without being affected by spatial variations in plating layer thickness. For example, when mass-producing plated pipe joints, using the average joint plating thickness t to control the plating layer thickness makes it possible to accurately estimate the mechanical properties, such as axial force, of each individual pipe joint.

[0089] The zinc-based plating layer P1 or P2 in each of the above embodiments corresponds to an example of the plating layer of the disclosed invention. The disclosed invention does not require the presence or absence of a resin coating layer outside the plating layer. Therefore, the disclosed invention can also be applied to pipe fittings in which the plating layer is located on the outermost surface. [Explanation of symbols]

[0090] 1A, 1B flare nut (pipe joint) 10, 20 through holes 12, 22 Threaded section 12a, 22a male thread 13, 23 head 13a, 23a Flat surface (1st plane) 13b, 23b side (second plane) 14, 24 contact area 14a, 24a contact surface 16 ISO flare (annular section) 18, 28 Resin coating layer 26 Double flare (annular part) BT Brake Tube (Tube) FN flare nut MC1, MC2 master cylinder (mating component) P1, P2 zinc-based plating layer T Test Tube TM Test Member TR test loop

Claims

1. A pipe joint is provided in which an annular portion protruding radially outward is attached to the outer periphery of a metal tube provided at an end thereof, and the pipe joint is fastened to a mating member in a state of contact with the annular portion, thereby connecting the tube to the mating member, a threaded portion having a male thread formed thereon that meshes with a female thread provided on the mating member; a head portion provided on one end side of the threaded portion and into which a tightening torque is input when the threaded portion is fastened; a contact portion provided on the other end of the threaded portion, the contact portion contacting the annular portion and pressing the annular portion against the mating member when fastened to the mating member; a zinc-based plating layer provided on the thread portion, the head portion, and the contact portion; a resin coating layer located on the outermost surface outside the zinc-based plating layer and containing a polyethylene-based substance, a lubricant, and solid particles; Equipped with The thread portion, the head portion, and the contact portion are each penetrated by a through hole extending in a direction parallel to the direction of advancement of the male screw during fastening, The male thread of the threaded portion has an outer diameter of 9.53 to 14.0 mm, the head includes a first plane oriented in a direction opposite to the traveling direction and a second plane perpendicular to the first plane, the contact portion includes a contact surface that can contact the annular portion and has an inner diameter of 4.98 to 8.44 mm; In a cross section including a center line extending in the same direction as the through hole and perpendicular to the second plane of the head, when the number of threads constituting the male screw is counted from the head side, the first thread is defined as the first thread, the second thread is defined as the second thread, the third thread is defined as the third thread, and the fourth thread is defined as the fourth thread, In the cross section, a first region set on the first plane of the head, a second region set on the second plane of the head, a third region set on a trailing flank of the third thread, a fourth region set on a trailing flank of the fourth thread, and a fifth region set on the contact surface of the contact portion are defined; and The arithmetic mean of the thickness of the zinc-based plating layer measured at seven points arranged in one direction at intervals of 10 μm in each of the first to fifth regions was calculated for each of the first to fifth regions, and five calculated values ​​were calculated as X １ , X ２ , X ３ , X ４ , X ５ and four measured values ​​of the thickness of the zinc-based plating layer at the root between the second thread and the third thread, the crest of the third thread, the root between the third thread and the fourth thread, and the crest of the fourth thread in the cross section were defined as T １ , T ２ , T ３ , T ４ In this case, (X １ +X ２ +X ３ +X ４ +X ５ +T １ +T ２ +T ３ +T ４ ) / 9 is defined as the joint average plating thickness t [μm], A pipe fitting in which 2.1<t<19.7 is satisfied.

2. 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 a fastening test including a fastening operation of fastening the test member to the test member with a predetermined tightening torque while in contact with the test annular portion, and a release operation of loosening the fastening after the fastening operation to release the connection of the test tube is repeated n times (where 1<n<6), and the maximum axial force generated in the first fastening test is defined as an initial axial force F １ [kN], and the maximum axial force occurring in the n-th fastening test is the n-th axial force F ｎ [kN], -(F ｎ -F １ 2. The pipe joint of claim 1, wherein when the value obtained by (n-1) is defined as the preload reduction rate α [kN / cycle], the relationship 0<α<1.75 holds.

3. The tube is a brake tube used in brake piping of an automobile, and the tightening torque is within a range of 12.0 to 22.0 [Nm]. 10.0<F １ 3. The pipe joint according to claim 2, wherein the following relationship holds true:

4. a metal tube having an annular portion at an end thereof that protrudes radially outward, and a bent portion at a position spaced apart from the annular portion; a pipe fitting that is attached to an outer periphery of the tube in a state where the tube is prevented from coming off by the annular portion and the bent portion, and that is fastened to a mating member in a state where the pipe fitting is in contact with the annular portion, thereby being able to connect the tube to the mating member; A tube with a pipe fitting, The pipe joint comprises: a threaded portion having a male thread formed thereon that meshes with a female thread provided on the mating member; a head portion provided on one end side of the threaded portion and into which a tightening torque is input when the threaded portion is fastened; a contact portion provided on the other end of the threaded portion, the contact portion contacting the annular portion and pressing the annular portion against the mating member when fastened to the mating member; a zinc-based plating layer provided on the thread portion, the head portion, and the contact portion; a resin coating layer located on the outermost surface outside the zinc-based plating layer and containing a polyethylene-based substance, a lubricant, and solid particles; The thread portion, the head portion, and the contact portion are each penetrated by a through hole extending in a direction parallel to the direction of advancement of the male screw during fastening, The male thread of the threaded portion has an outer diameter of 9.53 to 14.0 mm, the head includes a first plane oriented in a direction opposite to the traveling direction and a second plane perpendicular to the first plane, the contact portion includes a contact surface that can contact the annular portion and has an inner diameter of 4.98 to 8.44 mm; In a cross section including a center line extending in the same direction as the through hole and perpendicular to the second plane of the head, when the number of threads constituting the male screw is counted from the head side, the first thread is defined as the first thread, the second thread is defined as the second thread, the third thread is defined as the third thread, and the fourth thread is defined as the fourth thread, In the cross section, a first region set on the first plane of the head, a second region set on the second plane of the head, a third region set on a trailing flank of the third thread, a fourth region set on a trailing flank of the fourth thread, and a fifth region set on the contact surface of the contact portion are defined; and The arithmetic mean of the thickness of the zinc-based plating layer measured at seven points arranged in one direction at intervals of 10 μm in each of the first to fifth regions was calculated for each of the first to fifth regions, and five calculated values ​​were calculated as X １ , X ２ , X ３ , X ４ , X ５ and four measured values ​​of the thickness of the zinc-based plating layer at the root between the second thread and the third thread, the crest of the third thread, the root between the third thread and the fourth thread, and the crest of the fourth thread in the cross section were defined as T １ , T ２ , T ３ , T ４ In this case, (X １ +X ２ +X ３ +X ４ +X ５ +T １ +T ２ +T ３ +T ４ ) / 9 is defined as the joint average plating thickness t [μm], A tube with a pipe fitting that satisfies the condition 2.1<t<19.

7.

5. 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 a fastening test including a fastening operation of fastening the test member to the test member with a predetermined tightening torque while in contact with the test annular portion, and a release operation of loosening the fastening after the fastening operation to release the connection of the test tube is repeated n times (where 1<n<6), and the maximum axial force generated in the first fastening test is defined as an initial axial force F １ [kN], and the maximum axial force occurring in the n-th fastening test is the n-th axial force F ｎ [kN], -(F ｎ -F １ 5. The tube with pipe fitting according to claim 4, wherein when the value obtained by (n-1) / (n-1) is defined as the axial force reduction rate α [kN / cycle], the relationship 0<α<1.75 is satisfied.

6. The tube is a brake tube used in brake piping of an automobile, and the tightening torque is within a range of 12.0 to 22.0 [Nm]. 10.0<F １ 6. The tube with pipe fittings according to claim 5, wherein the relationship <14.0 holds true.

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