JP2018001244A - Joining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a rupture in a joint from taking place before a rupture in a dented steel pipe body takes place, when a casing shoe and the dented steel pipe are joined by frictional pressure welding.SOLUTION: In a joining method, an end surface 502c of a dented steel pipe and an end surface 501c of a casing shoe different in material from the dented steel pipe are joined together by frictional pressure welding. The joining method satisfies the inequalities (101)-(103): t>t(101); D/D≥1.02 (102); and V/V≤2.05 (103).SELECTED DRAWING: Figure 11

Description

  The present invention relates to a joining method capable of preventing breakage at a joint portion before a breakage of a hollow steel pipe main body occurs when a casing shoe and a hollow steel pipe are joined by friction welding. .

  In excavation work such as tunnels for soft ground, civil engineering steel pipes are used to reinforce the natural ground on the tunnel excavation surface. Such a steel pipe for civil engineering is configured by connecting a plurality of steel pipes in the pipe axis direction. By placing the civil engineering steel pipe deeper in the ground, the natural ground is reinforced more firmly.

  However, a joint for joining a plurality of steel pipes in the pipe axis direction is often formed thinner than a thick part of the steel pipe or softened by welding or the like. Thereby, the intensity | strength of the said junction part can become lower than the intensity | strength of a steel pipe. Thereby, in excavation work, the joint may be broken by an impact force applied to the steel pipe for civil engineering. In order to prevent such breakage of the joint part, a technique related to joining for maintaining the strength of the joint part is required, and various techniques related to joining have been developed so far.

  In Patent Document 1 below, for a threaded joint for connecting a steel pipe, the threaded joint is thicker than the steel pipe body, or the threaded joint is made of a material harder than the steel pipe body. The technology about the part is disclosed. Such a technique can prevent the threaded joint from being broken. Patent Document 2 below discloses a technique for connecting a steel pipe for joint and a steel pipe with a recess by friction welding. With this technique, it is possible to obtain a civil engineering steel pipe having excellent joint strength without increasing the thickness of the joint steel pipe.

Japanese Unexamined Patent Publication No. 2011-7000 JP 2014-181551 A

  By the way, in excavation work such as a tunnel, a mirror bolt obtained by joining a steel pipe for civil engineering and a casing shoe that accommodates an excavation bit therein is used. The mirror bolt is driven against the tunnel excavation surface (mirror surface) to reinforce the natural ground and prevent the mirror surface from collapsing.

  In such a mirror bolt, a hollow steel pipe (for example, a dimple steel pipe) is often used instead of a normal straight steel pipe. A steel pipe with a depression is a steel pipe having a depression on the side surface of the pipe. By this depression, a high adhesion force with the ground of the steel pipe with the depression is exhibited. Therefore, it becomes possible to more reliably reinforce a natural ground having a ground having a low viscosity by using a mirror bolt to which a steel pipe with a recess is joined.

  The casing shoe used for the mirror bolt and the hollow steel pipe are joined by, for example, friction welding. By this friction welding, metal bonding between the members is promoted, and oxide film, dirt, adsorbed gas and the like existing on the metal surface are discharged to the outside. That is, since the two members are firmly coupled, the joint generated by the friction welding can have the same strength as the two members.

  However, the mirror bolt obtained by simply friction-welding the two members is friction-welded before the mirror bolt tube (steel tube with a recess) when impact force acts on the mirror bolt in excavation work or the like. There has been a problem that the produced joint portion is broken first.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to break the hollow steel pipe body with a hollow when the casing shoe and the hollow steel pipe are joined by friction welding. It is an object of the present invention to provide a new and improved joining method that makes it possible to prevent breakage at the joint before it occurs.

  In order to solve the above-described problem, according to an aspect of the present invention, there is provided a joining method of joining an end surface of a hollow steel pipe and an end surface of a casing shoe having a material different from the hollow steel pipe by friction welding. A joining method that satisfies the following formulas (101) to (103) is provided.

t _SA > t _P (101)
D _SA / D _PO ≧ 1.02 (102)
V _S / V _P ≦ 2.05 (103)

here,
t _SA : Thickness [mm] at the end face on the joining side of the casing shoe
t _P : Wall thickness [mm] of the above-described steel pipe with a recess
D _SA : outer diameter [mm] at the end face on the joint side of the casing shoe
D _PO : outer diameter [mm] at the end face of the steel pipe with the above-mentioned depression
V _S : Volume of the casing shoe [mm ³ ] from the end surface on the joint side of the casing shoe to a position of 15 mm in the tube axis direction.
_VP : Volume of the hollow steel pipe [mm ³ ] from the end surface on the joining side of the hollow steel pipe to a position of 15 mm in the pipe axis direction
It is.

The outer diameter of the casing shoe in the end surface of the joint side of the casing shoe to the position of length L _A in the tube axis direction may be the outer diameter D _SA of the end face of the bonding side of the casing shoe.

The inner diameter D _SI [mm] of the casing shoe may be equal to or less than the inner diameter D _PD [mm] at the deepest portion of the recess of the steel pipe with the recess.

  Either the casing shoe or the hollow steel pipe is rotated so that the end face of the casing shoe and the end face of the hollow steel pipe are rubbed together for a predetermined time, and the rotation is stopped within 0.1 second after the rotation is stopped. Upset thrust may be applied to the shoe and the hollow steel pipe in the tube axis direction.

  According to the said structure, when satisfy | filling the conditions of Formula (101)-(103), when the tensile load of a pipe-axis direction acts on the steel pipe with a hollow and casing shoe which were joined, before the fracture | rupture in a junction part arises In addition, it is possible to cause a break in the steel pipe main body with a recess. Therefore, the steel pipe with a recess joined by friction welding and the joint part of a casing shoe can have the intensity | strength more than a steel pipe with a recess, and the fracture | rupture in a junction part can be prevented.

  As described above, according to the present invention, when the casing shoe and the hollow steel pipe are joined by friction welding, it is possible to prevent the fracture at the joint before the hollow steel pipe main body breaks. Is possible.

It is a schematic diagram which shows the mirror bolt which concerns on this embodiment. It is an expanded cross-sectional photograph of the junction part of the mirror bolt in which the junction part fracture | rupture produced by the tension test. It is an expanded sectional photograph of the junction part of the mirror bolt joined by friction welding on the same conditions as the mirror bolt shown in FIG. It is a cross-sectional photograph for explaining the definition of the distance between two surfaces D (mm) and the inclination angle θ (°) of the first joint surface. It is a graph which shows the relationship between the fracture | rupture result of each test body, the distance D between two surfaces, and inclination-angle (theta). It is a figure which shows an example of the friction welding simulation model by FEA. It is a figure which shows an example of each model structure of the casing shoe which has the conventional shape, and a steel pipe. It is a figure which shows an example of the maximum temperature distribution at the time of the shape change in the junction part of the casing shoe and steel pipe of a conventional model after the friction welding analysis by FEA. It is a figure which shows an example of each model structure of the casing shoe and steel pipe which have the shape of full thickness in the edge part by the side of joining. It is a figure which shows an example of the maximum temperature distribution at the time of the shape change in the junction part of the casing shoe and steel pipe of a full thickness model after the friction welding analysis by FEA. It is a figure which shows an example of each model structure of the casing shoe and the steel pipe with which the shape of the edge part by the side of joining was improved. It is a figure which shows an example of the maximum temperature distribution at the time of the shape change in the junction part of a casing shoe and a steel pipe of an improved model after the friction welding analysis by FEA. It is a graph showing the relationship between the outer diameter ratio _D SA _{/ D PO} and inclination angle theta. It is a figure for demonstrating the definition of the volume of the edge part vicinity of the casing shoe in a contact part, and the edge part vicinity of a steel pipe. Is a graph showing the relationship between the volume ratio V _{S /} V _P and dihedral distance D. It is a figure for showing the conditions which the joining method concerning this embodiment fulfills. It is an expanded sectional photograph of the junction part of the mirror bolt produced by joining the casing shoe which satisfy | fills Formula (1)-(3), and the steel pipe with a dent by friction welding. It is an enlarged sectional view of a joint portion for explaining the relationship between inner diameter D _PD at the deepest portion of the recess of the inner diameter D _SI and depression-steel pipe ends of the joint side of the casing shoe. It is a figure which shows an example of the maximum temperature distribution at the time of the shape change in the junction part of the casing shoe and the steel pipe after the friction welding analysis by FEA with respect to an improved model at the time of shortening an interval.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, the duplicate description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<< 1. Background of the invention >>
<1.1. Configuration of mirror bolt>
First, with reference to FIG. 1, the structure of the mirror bolt 1 which concerns on one Embodiment of this invention is demonstrated. FIG. 1 is a schematic diagram showing a mirror bolt 1 according to the present embodiment.

  As shown in FIG. 1, a mirror bolt 1 according to the present embodiment includes a casing shoe 2 and a steel pipe 3 with a recess. The casing shoe 2 and the hollow steel pipe 3 are joined via a joint 4 made by friction joining.

  The casing shoe 2 is a hollow tubular member. The casing shoe 2 is provided at the tip of the mirror bolt 1 and abuts against the unexcavated ground at the time of construction related to the reinforcement of the natural ground. As a result, the rod that is inserted into the casing shoe 2 and includes the excavation bid at the tip is protected. During the excavation process using the excavation bid, the casing shoe 2 is greatly affected by excavation, and therefore, it is preferable that the casing shoe 2 be formed of a material having excellent mechanical properties such as tensile strength. The casing shoe 2 according to the present embodiment is made of, for example, SCM435 chrome molybdenum steel.

  The hollow steel pipe 3 is a steel pipe having irregularities on the surface of the pipe body, and is used for the purpose of increasing the adhesion between the steel pipe and earth and sand. In FIG. 1, a dimple steel pipe is illustrated as an example of the hollow steel pipe 3. This hollow steel pipe 3 is not limited to a dimple steel pipe, but may be a stepped steel pipe, for example. In addition, the steel pipe 3 with a dent which concerns on this embodiment is the carbon steel pipe for general structures of STK400, for example.

  The blowout in FIG. 1 shows a cross-sectional view of the casing shoe 2 and the hollow steel pipe 3 in the vicinity of the joint 4. Immediately after the friction welding, burrs containing oxides or impurities extruded by the upset process are generated on the inner side surface and the outer side surface of the joint portion 4, but the burrs are appropriately removed after the friction welding. Therefore, as shown in the balloon, generally, in the mirror bolt 1 after friction welding, the outer diameter of the casing shoe 2 at the end face on the joining side of the casing shoe 2 and the hollow steel pipe at the end face on the joining side of the steel pipe 3 with the depression. The outer diameter of 3 is the same.

  Although omitted in FIG. 1, the end of the hollow steel pipe 3 with a recess that is different from the contact surface with the casing shoe 2 is joined to another steel pipe. For joining with other steel pipes, for example, a threaded joint or the like is used. As such a threaded joint, for example, a pin / box type threaded joint that directly cuts a screw may be provided at the end of the recessed steel pipe 3, but the recessed steel pipe 3 has a different cross section. Therefore, it is difficult to ensure the joint strength. Therefore, as a threaded joint that is attached to the end of the steel pipe 3 with a recess, a threaded joint that is attached by joining a joint that has been cut separately from the pipe body to the end of the steel pipe 3 with a recess by friction welding or the like. It is preferable to use it. For the friction welding of the threaded joint to the hollow steel pipe 3, for example, a joining method disclosed in Patent Document 2 may be used.

  A rod (not shown) is inserted into the mirror bolt 1 according to the present embodiment, and an excavation bit (not shown) is attached to the tip of the rod. Excavation is performed when the excavation bit applies an impact to the natural ground in a state where the mirror bolt 1 is driven in the natural ground.

<1.2. Problems related to friction welding and fracture of joints>
The casing shoe 2 and the hollow steel pipe 3 according to the present embodiment are joined by friction welding as described above. In friction welding, first, the contact surfaces of two members are rubbed together at high speed, and frictional heat is generated at the end portion on the joining side of the casing shoe 2 and the hollow steel pipe 3 to melt the surface metal (friction). Exothermic treatment). Then, the two members are joined by applying an upset thrust (compression force) in the tube axis direction (upset process). By this friction welding, metal bonding between members is promoted, and an oxide film, contaminants such as dirt, adsorbed gas and the like existing on the metal surface are discharged to the outside. Thereby, the joint part produced | generated by friction welding can have a comparable strength as two base materials.

  In this friction welding, not only members of the same kind of metal but also members of different kinds of metal can be joined. Therefore, the present inventors made a mirror bolt 1 by joining the casing shoe 2 and the hollow steel pipe 3 using friction welding, and applied the mirror bolt 1 to ground reinforcement for tunnel excavation work.

  However, when the ground work for tunnel excavation work is reinforced using the mirror bolt 1 obtained by friction welding, the joint 4 of the mirror bolt 1 breaks due to the impact load during excavation by the excavation bit. There were some examples. Therefore, in order to investigate the cause of the breakage of the joint 4, the present inventors conduct a tensile test in the tube axis direction on the plurality of mirror bolts 1 and break the tubular body of the hollow steel tube 3 (tubular breakage). Or examination about the phenomenon of fracture (joint fracture) in joint 4 was performed.

  The inventors first observed the state of the joint 4 of the mirror bolt 1 in which the joint 4 was broken. FIG. 2 is an enlarged cross-sectional photograph of the joint portion 4 of the mirror bolt 1 in which the joint portion is broken by the tensile test. In FIG. 2, it can be seen that a fracture surface 40 is generated at the joint 4 between the casing shoe 2 and the hollow steel pipe 3.

  Next, the inventors observed the joint 4 of the mirror bolt 1 that was friction-joined under the same conditions as the mirror bolt 1 in which the joint fracture occurred. FIG. 3 is an enlarged cross-sectional photograph of the joint 4 of the mirror bolt 1 joined by friction welding under the same conditions as the mirror bolt 1 shown in FIG. As shown in FIG. 3, it can be seen that two joint surfaces (first joint surface 41 and second joint surface 42 from the side closer to the casing shoe 2) exist separately in the joint portion 4. Moreover, it turns out that the 1st joining surface 41 is the state which inclines in the main body direction of the casing shoe 2 from the inner surface to the outer surface of the hollow steel pipe 3 with a hollow (in this specification, the state of this inclination is referred to as "outside. Defined as "tilted").

  Such separation of the joint surface and inclination to the outside have been observed, for example, in a joint portion formed by friction welding between a hollow steel pipe disclosed in Patent Document 2 and a threaded joint that is the same material as the hollow steel pipe. Absent. On the other hand, when the hollow steel pipe 3 is simply friction-welded with the hollow steel pipe 3 and the casing shoe 2 which is a different material, the separation of the joint surfaces as shown in FIG. It was confirmed that there was an inclination to The inventors inferred that when there is such separation of the joint surfaces and inclination to the outside, the strength of the joint 4 is reduced and breakage is likely to occur.

  Therefore, the present inventors have quantitatively evaluated the separation of the two joint surfaces and the inclination of the first joint surface 41 described above, and have verified the conditions when the joint fracture occurs in the mirror bolt 1. FIG. 4 is a cross-sectional photograph for explaining the definition of the distance between two bonding surfaces (distance between two surfaces) D (mm) and the inclination angle θ (°) of the first bonding surface 41. As shown in FIG. 4, the distance D between the two surfaces is a distance parallel to the tube axis of the first joint surface 41 and the second joint surface 42 at the thickness center of the steel tube 3 with the recess. Further, the inclination angle θ is a value indicating an inclination angle of the first joint surface 41 in the main body direction of the casing shoe 2 with respect to the surface 43 orthogonal to the tube axis direction. This inclination angle θ is a positive value in the case of an outward inclination as shown in FIG. 4, and is negative in the case of an inward inclination (inclination toward the main body of the casing shoe 2 from the outer surface to the inner surface). Become.

  The present inventors perform a tensile test on a plurality of specimens of the mirror bolt 1, and the results of the fracture of each specimen by tension, as well as the distance D between the two surfaces measured based on the definition shown in FIG. The relationship of the inclination angle θ of the first bonding surface 41 was verified. FIG. 5 is a graph showing the relationship between the fracture result of each specimen, the distance D between two surfaces, and the inclination angle θ. ○ indicates a plot of the specimen fractured at the tubular body of the hollow steel pipe 3, and × indicates a plot of the specimen fractured at the joint 4.

  As shown in FIG. 5, all the specimens having the distance D between the two surfaces of 0.5 mm or less and the inclination angle θ of 8 ° or less obtained a result of tubular fracture. Accordingly, the mirror bolt 1 is obtained by friction-welding the casing shoe 2 and the hollow steel pipe 3 so that the distance D between the two surfaces at the joint 4 is 0.5 mm or less and the inclination angle θ is 8 ° or less. It is considered that breakage at the joint 4 can be avoided more reliably.

  Therefore, the present inventors have used FEA (Finite Element Analysis; FEA) as a joining method by friction welding for producing the joint 4 in which the distance D between the two faces is 0.5 mm or less and the inclination angle θ is 8 ° or less. Finite element analysis). Specifically, the present inventors have conducted various studies on the shape of the end portion on the joining side of the casing shoe 2 and have found the shape that satisfies the above conditions. Hereinafter, conditions of the joining method according to the present embodiment based on the analysis result by FEA will be described.

<< 2. Conditions of joining method according to this embodiment based on analysis result by FEA >>
<2.1. Analysis conditions>
The inventors of the present invention constructed and analyzed a friction welding simulation model by FEA, and examined the reason why separation of the joint surface and inclination to the outside occur in the joint portion 4 based on the analysis result. Moreover, the present inventors examined the conditions of the joining method that can prevent the occurrence of breakage at the joint 4 produced by friction welding based on the analysis result. First, FEA analysis conditions will be described.

  FIG. 6 is a diagram illustrating an example of a simulation model 10 relating to friction welding by FEA. The simulation model 10 includes a casing shoe model 20 (hereinafter simply referred to as a casing shoe 20), a steel pipe model 30 (hereinafter simply referred to as a steel pipe 30), and a clamp model 90. One end surface in the tube axis direction of the casing shoe 20 is in contact with one end surface in the tube axis direction of the steel pipe 30. A region in the vicinity of the contact surface is defined as the contact portion 50. Further, the outer surface of the steel pipe 30 is in contact with the inner surface of the clamp model 90. These models are tube-axisymmetric solid models, and the portions other than the contact portion 50 between the casing shoe 20 and the steel pipe 30 are each formed of a uniform solid. Further, the parts of the casing shoe 20 and the steel pipe 30 included in the abutting portion 50 are used to analyze in more detail the heat and stress that can be generated by the friction welding between the casing shoe 20 and the steel pipe 30 as shown in the following figure. In addition, it is composed of finer solids.

In addition, the constant regarding the dimension used in the simulation using the following FEA is as follows.
The length L _S (mm) of the casing shoe 20 in the tube axis direction = 84 mm.
Length L _P (mm) of the steel pipe 30 in the tube axis direction = 500 mm.
The outer diameter D _SO (mm) of the casing shoe 20 at a position separated from the end surface on the joining side of the casing shoe 20 by a length L _A (mm) or more in the tube axis direction = 82.6 mm.
Inner diameter D _SI (mm) at the end surface on the joining side of the casing shoe 20 = 62.56 mm.
The outer diameter D _PO (mm) of the steel pipe 30 = 76.3 mm.
The thickness t _P (mm) of the steel pipe 30 is 4.5 mm.

In the following analysis using the FEA, the outer diameter D _SA (mm) and the wall thickness t _SA (within a length L _A (mm) in the tube axis direction from the end surface on the joining side of the casing shoe 20 according to the analysis target. mm), and the length L _a in the tube axis direction from the end face of the bonding side of the casing shoe 20 is appropriately changed as a parameter. Note that the wall thickness t _SA on the end surface on the joining side of the casing shoe 20 is required to be larger than the wall thickness t _P of the steel pipe 30. This is because, when the steel pipe 30 is a hollow steel pipe, the end face on the joining side of the casing shoe is used as the end face on the joining side of the steel pipe 30 even when the outer diameter and the inner diameter of the steel pipe 30 change depending on the presence or absence of the recessed face. This is to ensure contact.

In the FEA according to the present embodiment, a temperature-stress coupled analysis was performed on the friction welding. The frictional heat generated by friction welding is proportional to the reaction force at the node of the contact surface (abutting surface). Specifically, Joule heat generated by friction welding is 27 J / (sec · mm ² ). Further, it is assumed that the material of the casing shoe 20 is SCM435 and the material of the steel pipe 30 is STK400. In the FEA according to the present embodiment, known physical property values such as tensile strength, yield stress, fracture toughness, specific heat and the like of these materials are input as analysis parameters.

  The friction welding process in FEA includes a frictional heat generation process and an upset process. In the frictional heat generation process, either the casing shoe 20 or the steel pipe 30 is rotated to generate frictional heat based on sliding on the contact surface between the casing shoe 20 and the steel pipe 30, and the frictional heat generation causes the two members to contact each other. The part near the contact surface softens. At that time, a compressive force is applied in the tube axis direction. In the FEA, the behavior related to the heat of each member due to frictional heat generated by rotational sliding is simulated. The frictional heat generation step is performed for a predetermined time (for example, 5 to 15 seconds). The relative rotation suddenly stops at the end of the frictional heat generation process, and the upset process is executed after an interval (time from the stop of the rotation at the end of the frictional heat generation process to the start of the upset process) is provided. . In the upset process, a compressive force higher than the compressive force applied in the frictional heat generation process is applied to the two members in the tube axis direction. Note that the interval between the frictional heat generation step and the upset step is 0.55 seconds in the FEA according to the present embodiment.

<2.2. Analysis of conventional model>
First, the analysis result of the friction welding using the casing shoe of the conventional model will be described. FIG. 7 is a diagram showing an example of each model configuration of a casing shoe 51a and a steel pipe 52a having a conventional shape. The casing shoe 51a shown in FIG. 7 is referred to as a “conventional model”. As shown in FIG. 7, the end surface 501a on the joining side of the casing shoe 51a is in contact with the end surface 502a on the joining side of the steel pipe 52a. Moreover, the casing shoe 51a has the same outer diameter as the steel pipe 52a in the end surface 501a on the joining side. That is, the outer peripheral surface of the casing shoe 51a and the outer peripheral surface of the steel pipe 52a are continuous in the tube axis direction on the contact surface. The friction welding using the conventional model casing shoe 51a was analyzed. In this analysis, D _SA = 76.3 mm, t _SA = 6.87 mm, and L _A = 16 mm.

  FIG. 8 is a diagram showing an example of the shape change and the maximum temperature distribution at the time of upsetting in the joint portion of the casing shoe 51a and the steel pipe 52a of the conventional model after the friction welding analysis by FEA. Referring to FIG. 8, it can be seen that the abutting surface (contact surface) 53a is inclined outward. It can also be seen that the ridge line 54a of the temperature distribution is located on the steel pipe 52a side with respect to the abutting surface 53a. The ridge line 54a of this temperature distribution is considered to correspond to an upset surface in which shearing in the radial direction occurs during upset processing because the softening of the metal member due to frictional heat is considered to be most promoted. That is, the ridge line 54a of the temperature distribution corresponds to the upset surface 54a. The abutting surface 53a and the upset surface 54a are considered to correspond to, for example, the first joining surface 41 and the second joining surface 42 of the joining portion 4 shown in FIG. That is, these results reproduce the state of the joint 4 of the mirror bolt 1 as shown in FIG. 3, for example. The inventors first examined the inclination of the abutting surface 53a from the analysis result shown in FIG.

  As shown in FIG. 8, it is considered that the outward inclination of the abutting surface 53a is caused by the end surface 502a of the steel pipe 52a riding on the end surface 501a of the casing shoe 51a. The present inventors cause the inclination to the outside because the end face 502a of the steel pipe 52a is more likely to slip in the outer diameter direction than in the inner diameter direction when a compressive load is applied in the pipe axial direction during friction welding. I thought it was. This is because the deformation resistance of the casing shoe 51a in the outer diameter direction is smaller than the deformation resistance in the inner diameter direction. Since the end surface 502a of the steel pipe 52a slides in the outer diameter direction, it is difficult to apply a surface pressure in the tube axis direction, so that it is considered that a sufficient bonding strength by friction welding cannot be obtained.

<2.3. Analysis of full thickness model>
Based on the above examination results, the present inventors examined the shape of the casing shoe so as not to cause the inclination of the abutting surface based on the above analysis results. FIG. 9 is a diagram showing an example of each model configuration of the casing shoe 51b and the steel pipe 52b having a full thickness shape at the end portion on the joining side. The casing shoe 51b shown in FIG. 9 is referred to as a “full thickness model”. Unlike the conventional model shown in FIG. 7, the outer diameter of the joint shoe end face 501b of the full thickness model casing shoe 51b is the same as the outer diameter of the other portion of the casing shoe 51b, and is larger than the outer diameter of the steel pipe 52b. large. The inventors of the present invention have conceived that slippage in the outer diameter direction of the end surface 502b of the steel pipe 52b during friction welding can be suppressed by increasing the thickness of the casing shoe 51b in the end surface 501b on the joining side in the outer diameter direction. The friction welding using the full thickness model casing shoe 51b was analyzed. In this analysis, D _SA = 82.6 mm (= D _SO ) and t _SA = 10.02 mm. In the full thickness model, L _A = 0.

  FIG. 10 is a diagram illustrating an example of the shape change and the maximum temperature distribution at the time of upsetting in the joint portion of the casing shoe 51b and the steel pipe 52b of the full thickness model after the friction welding analysis by FEA. Referring to FIG. 10, the abutting surface 53b is substantially orthogonal to the tube axis direction, and no outward inclination is seen. For this reason, in the full-thickness model, it became clear that the slip in the outer diameter direction of the end surface 502b of the steel pipe 52b is suppressed. On the other hand, it can be seen that the upset surface 54b is located closer to the steel pipe 52b than the abutting surface 53b, as in the example shown in FIG. That is, the abutting surface 53b and the upset surface 54b are separated.

  The present inventors thought that the cause of the separation of the abutting surface 53b and the upset surface 54b is the difference in heat capacity between the casing shoe 51b and the steel pipe 52b. The size of the heat capacity of the member is proportional to the size of the region where heat is diffused, that is, the size of the volume where heat is diffused. Frictional heat generated on the contact surface, which is a sliding surface, diffuses to each of the casing shoe 51b and the steel pipe 52b. Here, in the case of the full thickness model, the volume on the casing shoe 51b side in the vicinity of the end portion on the joining side is larger than the volume on the steel pipe 52b side. In this case, the heat capacity on the casing shoe 51b side is also larger than the heat capacity on the steel pipe 52b side. Then, the heat removal from the frictional heat becomes more remarkable on the casing shoe 51b side than on the steel pipe 52b side. Therefore, the maximum temperature distribution during upsetting can be located on the steel pipe 52b side. When an upset process is performed at the joint having this temperature distribution, shearing occurs along the ridgeline of the temperature distribution as described above, so that the upset surface 54b is formed on the steel pipe 52b side.

  Two problems can arise when the upset surface is formed separately from the abutting surface. One is that since the upset surface is formed on the steel pipe side, the upset thrust is not transmitted to the counterpart member, and the metal bonding between the respective members is not sufficiently promoted, so that defects are likely to occur on the upset surface. The other is that impurities such as an oxide film present on the abutting surface due to shearing by the upset process are not discharged to the outside. That is, when the upset surface is formed separately from the abutting surface, the bonding strength between the casing shoe and the steel pipe can be deteriorated.

  In summary, from the results of analysis by FEA, the frictional welding between the casing shoe and the steel pipe is such that the abutting surface is inclined outward and the abutting surface and the upset surface are formed separately, so that the joining strength is sufficient. The present inventors have found a mechanism that cannot be obtained. That is, in order to perform friction welding that can ensure high bonding strength, it is required to simultaneously suppress the inclination of the abutting surface and the separation of the abutting surface and the upset surface. As a result of analysis by FEA, the present inventors have found that in order to suppress the inclination of the outside of the abutting surface, it is required to increase the deformation resistance in the outer diameter direction of the end portion of the steel pipe. Further, the present inventors have found that in order to suppress separation between the abutting surface and the upset surface, it is required to reduce the difference in heat capacity between the casing shoe and the steel pipe.

  The inventors of the present invention diligently studied the above problems and developed the shape of the end portion of the casing shoe capable of reducing the difference in heat capacity while increasing the deformation resistance in the outer diameter direction of the end portion of the steel pipe. Hereinafter, the shape of the improved model of the casing shoe used for the joining method according to the present embodiment will be described.

<2.4. Analysis of improved model>
FIG. 11 is a diagram showing an example of each model configuration of the casing shoe 51c and the steel pipe 52c in which the shape of the end portion on the joining side is improved. The casing shoe 51c shown in FIG. 11 is referred to as an “improved model”. Casing shoe 51c improvement model, as shown in FIG. 11, the size of the outer diameter is formed to be a D _SA over a length L _A from the end face 501c of the joint side in the axial direction of the tube. In this improved model, the outer diameter _{D SA} is set larger than the outer diameter _{D PO} in the end face 502c of the steel pipe 52c. Friction welding was analyzed using this improved model of the casing shoe 51c. In this analysis, D _SA = 77.3 mm (= D _PO +1 mm), t _SA = 7.37 mm, and L _A = 16 mm.

  FIG. 12 is a diagram showing an example of the shape change and the maximum temperature distribution at the time of upset in the joint part of the improved model casing shoe 51c and the steel pipe 52c after the friction welding analysis by FEA. Referring to FIG. 12, the abutting surface 53c is substantially orthogonal to the tube axis direction, and no outward inclination is seen. It can also be seen that the distance between the two surfaces of the abutting surface 53c and the upset surface 54c is shorter than the distance between the two surfaces using the full thickness model casing shoe shown in FIG.

Thus, by the size of the outer diameter over the length L _A of the tube axis direction from the end surface of the joint side of the casing shoe processing the shape of the end of the casing shoe so that D _SA, the abutment surface It was suggested that it is possible to suppress outward inclination and separation of the abutting surface and the upset surface. Based on the knowledge obtained from the analysis results of the friction welding using the three models of the above-described casing shoes, the present inventors have developed a casing shoe for satisfying predetermined conditions for the inclination angle θ and the distance D between two surfaces. Further study was made on the shape of the.

<2.5. Study of tilt angle θ>
The inventors of the present invention first examined the friction welding conditions for the inclination angle θ to be 8 ° or less. As described above, the inclination to the outside of the end portion of the steel pipe at the joint after friction welding is considered to be due to the low deformation resistance at the abutting surface with the casing shoe. For this reason, it is considered that the deformation resistance can be increased by making the outer diameter _DSA on the joining shoe end face larger than the outer diameter _DPO of the steel pipe. Accordingly, the present inventors have ratio of the outer diameter D _SA of the end face of the joining of the casing shoe to the outside diameter D _PO of the steel tube (outer diameter ratio _{D SA /} D _PO) as a parameter, the end face of the outer diameter side joined from case of friction welding using a casing shoe is D _SA across the tube axis direction to the length L _a, were analyzed for the inclination angle θ of the abutment surface.

As analysis conditions for the inclination angle θ according to the present embodiment, the range of the outer diameter ratio D _SA / D _PO is 1.00 to 1.08, and the length L _A is 4 mm or 16 mm. FEA was performed using these values, and analysis results were obtained.

FIG. 13 is a graph showing the relationship between the outer diameter ratio D _SA / D _PO and the inclination angle θ. As shown in the graph of FIG. 13, even when the length _{L A} of any 4mm and 16 mm, the outer diameter ratio _D SA _{/ D PO} ≧ 1.02, that the inclination angle θ is 8 ° or less indicates It was done. The inclination angle θ tends to decrease as the outer diameter ratio D _SA / D _PO increases. This is presumably because the deformation resistance of the end face of the casing shoe against the slip of the end face of the steel pipe in the outer diameter direction increases as the outer diameter ratio D _SA / D _PO increases.

<2.6. Examination of distance D between two surfaces>
Subsequently, the present inventors examined the friction welding conditions for the distance D between the two surfaces to be 0.5 mm or less. As described above, it is considered that the separation between the abutting surface and the upset surface is caused by a difference in heat capacity between the vicinity of the end portion of the casing shoe and the vicinity of the end portion of the steel pipe. Therefore, it is required to set the shape of the end portion of the casing shoe so as to minimize the difference in heat capacity between the vicinity of the end portion of the casing shoe and the vicinity of the end portion of the steel pipe. As a result of various studies, it has been clarified that the relationship between the volume in the vicinity of the end portion of the casing shoe and the volume in the vicinity of the end portion of the steel pipe is mainly influenced in order to reduce the difference in heat capacity. That is, by setting the shape of the casing shoe so that the ratio of the volume in the vicinity of the end portion on the joining side of the casing shoe to the volume in the vicinity of the end portion on the joining side of the steel pipe is not more than a predetermined ratio, the distance D between the two surfaces The present inventors have thought that it is possible to reduce the value of.

  FIG. 14 is a view for explaining the definition of the volume in the vicinity of the end portion of the casing shoe and the vicinity of the end portion of the steel pipe in the contact portion 50d. The casing shoe 51d and the steel pipe 52d shown in FIG. 14 are radial sectional views. Referring to FIG. 14, the region of the casing shoe from the end surface 501d on the joining side of the casing shoe 51d to the position 15 mm in the tube axis direction is S, and the position 15 mm in the tube axis direction from the end surface 502d on the joining side of the steel pipe 52d. Each region is defined with P as the region of the steel pipe. In FIG. 14, the region S and the region P are shown in a two-dimensional cross section, but the region S and the region P are cylindrical regions formed around the tube axis. The value of “15 mm” that defines the above two regions is a range in which frictional heat generated by friction welding extends from the end surface 501d (502d) on the joining side of the casing shoe 51d and the steel pipe 52d in the tube axis direction. It is a value based on various analysis results. That is, by setting the shape of the casing shoe so that the volume ratio is reduced in the region within 15 mm from the end surface 501d (502d) on the joining side, the difference in heat capacity is reduced and the distance D between the two surfaces is reduced. I think it can be done.

The volume of the region S and the region P was set to V _S and V _P , respectively, and the relationship with the distance D between the two surfaces was evaluated using the volume ratio V _S / V _P as a parameter. As analysis conditions for the distance D between two surfaces according to the present embodiment, the outer diameter ratio D _SA / D _PO was 1.02, 1.04, 1.06, and the total thickness (1.085). The length _{L A} was 4 mm, 8 mm, 16 mm, and a 32 mm. The volume ratio _V S / _{V P} is determined by the value of the outer diameter ratio _D SA _{/ D PO,} and the length _{L A.}

  In FEA, the distance D between the two surfaces was the distance in the tube axis direction between the joining surface at the thickness center of the steel pipe, the temperature distribution during upsetting, and the ridgeline.

FIG. 15 is a graph showing the relationship between the volume ratio V _S / V _P and the distance D between two surfaces. As shown in the graph of FIG. 15, when the volume ratio V _S / V _P ≦ 2.05, the distance D between the two surfaces was 0.5 mm or less. Further, as the volume ratio V _S / V _P decreases, the distance D between the two surfaces tends to decrease. This is considered because the difference in heat capacity between the vicinity of the end portion of the casing shoe and the vicinity of the end portion of the steel pipe becomes smaller as the volume ratio V _S / V _P decreases.

<2.7. Summary of casing shoe shape>
In the above, the joining conditions between the casing shoe and the hollow steel pipe for preventing breakage at the joint have been described with reference to the analysis conditions and analysis results of the FEA shown in FIGS. From the FEA analysis result described above, the friction angle of the casing shoe and the hollow steel pipe satisfying the expressions (1) to (3) described below is such that the abutting surface inclination angle θ is 8 ° or less, and A mirror bolt having a joint portion having a distance D between two surfaces of 0.5 mm or less can be reliably produced. Thereby, the tensile strength of the junction part of a mirror bolt is securable. Therefore, when an impact force is applied to the mirror bolt, it is possible to prevent the joint from being broken before the tube breaks. In addition, FIG. 16 is a figure for showing the conditions which the joining method which concerns on this embodiment satisfy | fills. As shown in FIG. 16, the outer diameter ratio D _SA / D _PO ≧ 1.02 (formula (2)) and the volume ratio of the casing shoe and the hollow steel pipe used in the joining method according to the present embodiment. By satisfying the condition of V _S / V _P <2.05 (formula (3)) (range indicated by the region 100 in FIG. 16), breakage at the joint can be prevented.

t _SA > t _A (1)
D _SA / D _PO ≧ 1.02 (2)
V _S / V _P ≦ 2.05 (3)

FIG. 17 is an enlarged cross-sectional photograph of the joint 63 of the mirror bolt 1 produced by joining the casing shoe 61 satisfying the expressions (1) to (3) and the hollow steel pipe 62 by friction welding. The outer diameter _{D SA} of the end face of the joining side of the front friction welding of the casing shoe 61 is _77.3mm (D PO + 1mm), the length _{L A} is 16 mm. The outer peripheral portion of the end surface on the joining side of the casing shoe 61 shown in FIG. 17 is cut out together with the removal of burrs generated by the friction welding, but before the friction welding, the casing shoe 61 is as shown in FIG. End shape. As shown in FIG. 17, the abutting surface 64 is not greatly inclined outward, and the distance between the abutting surface 64 and the upset surface 65 (distance D between the two surfaces) is compared with the example shown in FIG. And it is getting shorter. Specifically, the inclination angle θ of the abutting surface 64 is 4.8 °, and the distance D between the two surfaces is 3.2 mm. Therefore, the inclination angle θ and the distance D between the two surfaces of the joint portion of the mirror bolt 1 shown in FIG. 17 satisfy both the conditions of the inclination angle θ and the distance D between the two surfaces so as not to cause the joint fracture. .

In the example shown in FIGS. 11 and 14, the shape of the end portion of the bonding side of the casing shoe, over a length L _A in the axial direction of the tube from the end surface of the joint side, the outer diameter of the casing shoe has the formula (2) It was to be shaped such that D _SA satisfying, the present invention is not limited to such an example. For example, of the shape of the end portion of the bonding side of the casing shoe, if D _SA the outside diameter of the end face satisfies the equation (2), the shape of toward the main body of the casing shoe from the end face, wherein the (3) When satisfy | filling, it does not specifically limit. For example, the shape of the end portion of the casing shoe may be a tapered shape that extends along the tube axis direction from the end portion toward the main body side. The end portion of the casing shoe may have a flange shape extending in the outer diameter direction. Further, the outer peripheral portion of the end surface of the casing shoe may be provided with a curvature. In addition, as long as Expression (3) is satisfied, the casing shoe can take various shapes from the end to the main body.

However, since the casing shoe is a member having high hardness such as SCM435, quality degradation such as cracking may occur depending on the difficulty of processing. Therefore, the shape of the end of the casing shoe to satisfy equation (3), the outer diameter of the joint casing shoe over a length L _A in the axial direction of the tube from the end face of the casing shoe satisfies the equation (2) D _SA It is preferable that it is the shape which is.

<< 3. Other joining conditions >>
Next, further joining conditions of the joining method by friction welding according to the present embodiment will be described.

<3.1. Condition of inner diameter of hollow steel pipe>
In the joining method according to the present embodiment, the inner diameter D _SI [mm] of the end portion on the joining side of the casing shoe is preferably equal to or less than the inner diameter D _PD [mm] at the deepest portion of the hollow of the hollow steel pipe. Figure 18 is a cross-sectional view of a joint portion for explaining a relationship between the inner diameter D _PD at the deepest portion of the recess of the inner diameter D _SI and depression-steel pipe ends of the joint side of the casing shoe. Referring to FIG. 18, the end surface 701 of the casing shoe 71 is in contact with the end surface 702 of the indented portion 73 of the indented steel pipe 72. At this time, if D _SI ≦ _DPD , the end surface 702 of the hollow portion 73 of the hollow steel pipe 72 is surely brought into contact with the end surface 701 of the casing shoe 71. Thereby, about the steel pipe with a hollow which has the end surface cut | disconnected and produced | generated in arbitrary positions, the friction welding with a casing shoe end surface can be performed reliably. Moreover, it can prevent that the rod etc. which penetrate the inside of the casing shoe 71 and the steel pipe 72 with a dent physically interfere with the dent part 73.

<3.2. Shortening the interval between the frictional heating process and the upset process>
In the joining method according to the present embodiment, it is further preferable to further shorten the interval between the frictional heat generation step and the upset step. As a result, the upset process is performed before the temperature of the joint portion on the abutting surface after the frictional heat generation process is greatly reduced, so that the metal flow due to the upset process increases. As a result, the upset surface can be brought closer to the abutting surface. That is, the strength of the joint can be further increased.

  The present inventors analyzed using FEA when the interval was set to 0.05 seconds, and evaluated the state of the joint after friction welding. FIG. 19 is a diagram showing an example of the shape change and the maximum temperature distribution at the time of upset in the joint part of the improved model casing shoe and steel pipe after the friction welding analysis by FEA when the interval is shortened. As shown in FIG. 19, it can be said that the distance between the two surfaces of the abutting surface 53 e and the upset surface 54 e is further reduced as compared with FIG. 12. Therefore, it is considered that the joint can be further strengthened by further shortening the interval between the frictional heat generation process and the upset process.

<< 4. Summary >>
Heretofore, the method for joining the casing shoe and the hollow steel pipe according to the present embodiment has been described. As described above, simply joining the casing shoe and the hollow steel pipe by friction welding results in fracture at the joint after friction welding when the mirror bolt obtained by joining is placed during ground reinforcement construction. Sometimes occurred. The cause of the fracture of the joint portion includes the inclination of the friction welding in the joint portion to the outside of the abutting surface and the separation of the abutting surface and the upset surface.

  Therefore, in this embodiment, first, when the inclination angle θ of the abutting surface is 8 ° or less and the distance between the abutting surface and the upset surface (distance D between the two surfaces) is 0.5 mm or less. It was clarified that no breakage occurred at the joint.

Next, it was clarified that the inclination angle θ of the abutting surface can be suppressed by increasing the deformation resistance of the end of the steel pipe by the end of the casing shoe. Then, when the ratio of the outer diameter _{D SA} of the end face of the joining of the casing shoe to the outside diameter _{D PO} of the steel tube (outer diameter ratio _D SA _{/ D PO)} satisfies the equation (2), the inclination angle of the abutment surface θ It was clarified that the angle can be set to 8 ° or less.

Next, it was clarified that the separation of the abutting surface and the upset surface can be suppressed by lowering the heat capacity of the end portion of the casing shoe. And the ratio (volume ratio V _S / V _P ) of the volume in the vicinity of the end portion on the joining side of the casing shoe with respect to the volume in the vicinity of the end portion on the joining side of the steel pipe satisfies the formula (3), so It was clarified that can be made 0.5 mm or less.

  That is, by using a casing shoe having an end structure that satisfies the conditions of the expressions (1) to (3) for friction welding, it is possible to prevent breakage at the joint, and the tube body before breakage at the joint. Breaking can be realized. Therefore, according to this embodiment, it is possible to provide a mirror bolt that does not break at the joint. The invention shown in the above embodiment can be applied to casing shoes and hollow steel pipes having various pipe diameters and thicknesses as long as the conditions of the formulas (1) to (3) are satisfied.

  Next, examples of the present invention will be described. In addition, the following Examples are only the example conditions adopted in order to confirm the feasibility and effects of the present invention, and the present invention is not limited to the conditions of the following Examples.

  A plurality of types of casing shoe specimens are joined to a hollow steel pipe (in this case, a hollow steel pipe satisfying formula (1) is used), and each specimen satisfies the conditions of formula (2) and formula (3). In addition to determining whether or not to satisfy, a tensile test was performed to confirm the fracture mode when a tensile load was applied to each specimen in the tube axis direction.

Table 1 shows conditions of each specimen according to Examples and Comparative Examples of the present invention, outer diameter ratio D _SA / D _PO , volume ratio V _S / V _P , inclination angle θ, distance between two surfaces D, and tube axis The fracture | rupture form when a tensile load is provided to a direction is shown.

  For example, Comparative Example 3 corresponds to the case where the conventional model casing shoe shown in FIG. 7 is used, and Comparative Example 1 corresponds to the case where the full thickness model casing shoe shown in FIG. 9 is used. .

  As shown in Table 1, Examples 1 to 15 of the present invention satisfy the conditions of the formulas (1) to (3). As a result, any of the specimens of Examples 1 to 15 was broken at the tube, not at the joint. Therefore, it can be said that the joint has ensured a strength higher than the tensile strength of the tube. On the other hand, Comparative Examples 1 to 21 do not satisfy at least one of the conditions of Formula (2) or (3). For example, Comparative Examples 1, 3, 4, 9, 10, 17, and 18 do not satisfy Expression (2). Moreover, the comparative examples 2, 5-8, 11-17, and 19-21 do not satisfy | fill Formula (3). As a result, breakage occurred at the joints.

  From the above test results, by satisfying the conditions of the expressions (1) to (3), the inclination of the joining surface to the outside and the separation between the joining surface and the upset surface are suppressed to a predetermined threshold value or less. Therefore, it can be said that it was proved that the strength of the joint portion was ensured and that the fracture at the pipe body could be realized before the fracture at the joint portion.

  Furthermore, since Examples 13 to 15 satisfy the condition that the interval between the frictional heat generation process and the upset process is 0.1 second or less, the distance D between the two surfaces is generally larger than that of the other examples. It can be said that it has become shorter. Therefore, it is considered that by setting the interval to 0.1 second or less, it is possible to further suppress the reduction in the strength of the joint and more reliably prevent the joint from breaking.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

1 Mirror Bolt 2, 61 Casing Shoe 3, 62 Steel Pipe with Recess 4, 63 Joint

Claims (4)

A joining method for joining the end face of the hollow steel pipe and the end face of the casing shoe having a material different from the hollow steel pipe by friction welding,
A joining method that satisfies the following formulas (101) to (103).

t _SA > t _P (101)
D _SA / D _PO ≧ 1.02 (102)
V _S / V _P ≦ 2.05 (103)

here,
t _SA : Thickness [mm] at the end face on the joining side of the casing shoe
t _P : Wall thickness [mm] of the steel pipe with the depression
D _SA : outer diameter [mm] at the end face on the joining side of the casing shoe
D _PO : outer diameter [mm] at the end surface of the hollow steel pipe
V _S : Volume of the casing shoe [mm ³ ] from the end surface on the joint side of the casing shoe to a position of 15 mm in the tube axis direction.
V _P : Volume [mm ³ ] of the steel pipe with recesses from the end surface on the joining side of the steel pipe with recesses to a position of 15 mm in the pipe axis direction.
It is. The outer diameter of the casing shoe at the end face of the bonding side of the casing shoe to the position of length L _A in the tube axis direction, an outer diameter D _SA of the end face of the bonding side of the casing shoe, according to claim 1 Joining method. 3. The joining method according to claim 1, wherein an inner diameter D _SI [mm] of the casing shoe is equal to or less than an inner diameter D _PD [mm] at a deepest portion of the recess of the steel pipe with the recess. Rotating either the casing shoe or the hollow steel pipe and rubbing the end face of the casing shoe and the end face of the hollow steel pipe for a predetermined time,
The joining method according to any one of claims 1 to 3, wherein an upset thrust is applied in a tube axis direction to the casing shoe and the hollow steel pipe within 0.1 seconds after stopping the rotation. .