Method of manufacturing fluid pressure cylinder

Abstract

To inexpensively provide a fluid pressure cylinder having a structure for sealing burrs on the inner peripheral side of a tube generated by friction welding.SOLUTION: Most of the cylinder end 20 has a diameter slightly smaller than the inner diameter of the tube 10, but a large-diameter portion 21 having the same diameter as the outer diameter of the tube 10 is formed at the friction-welded portion. Further, a cylindrical protruding portion 22 having a diameter smaller than the inner diameter of the tube 10 is formed from the end surface of the large diameter portion 21. When the tube 10 and the cylinder end 20 are joined together, a space 30 is formed between the inner peripheral surface of the tube 10 and the peripheral surface of the cylinder end 20 by the length of the protruding portion 22. An inner burr IB is formed from an end 31 of the space 30 on the cylinder end 20 side. Therefore, the inner burr IB is naturally accommodated inside the space 30 at the time of formation. After the joining of the tube 10 and the cylinder end 20 is completed, an O-ring 40 is fitted into the space 30 as a seal member.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a structure of a fluid pressure cylinder manufactured by friction welding, a jig used in manufacturing the fluid pressure cylinder, and a manufacturing method thereof. [Background technology]

[0002] Conventionally, when manufacturing a cylinder tube for a fluid pressure cylinder, a disk-shaped member is placed on one end of a cylindrical member, and the members are rotated while welding the boundary. However, when welding is performed in this manner, the welding points are limited to the outside of the cylinder tube and the cylindrical member, and there is a limit to the area that can be welded relative to the thickness of the members. In particular, as the cylinder becomes larger and the cylindrical member becomes thicker, the ratio of the joint area to the cross section decreases.

[0003] Furthermore, when joining components by welding, thorough control of welding quality must be exercised to prevent leakage of working fluid from the welded joints. However, if detailed inspections of the welded joints are carried out for this purpose, there is a problem that manufacturing costs increase.

[0004] Therefore, friction welding is used as a joining method that can join the entire cross section of a cylindrical member and can prevent the occurrence of welding defects. Friction welding is a method of joining two parts by bringing one part into contact with the other and rotating it at high speed while keeping the other stationary, generating frictional heat. This frictional heat heats up the parts, and then the rotation is stopped and the parts are pressed together with high pressure (upset pressure).

[0005] When joining cylindrical members by friction welding, burrs are generated on both the outer and inner peripheries due to the high pressure. The inside of a fluid pressure cylinder is divided into an extension side and a contraction side working fluid chamber by a packing fitted to the piston that slides in close contact with the piston. Therefore, burrs can damage the packing. Furthermore, if burrs peel off from the inner periphery during operation of the cylinder, they can damage the entire flow path of the working fluid. Therefore, it is desirable to remove burrs during the manufacturing process of the cylinder, but burrs on the inner periphery of the cylinder tube are difficult to remove because they are generated at a location away from the opening and are generated all around the circumference.

[0006] Therefore, the fluid pressure cylinder disclosed in Patent Document 1 forms a space in the disk-shaped member to contain burrs generated on the inner periphery of the cylinder, and further includes a flange portion (reference numeral 101 in Patent Document 1, Figure 2) to cover this space. The flange portion is sized to form a gap between it and the inner surface of the cylindrical member, but because the gap is narrow at 0.5 mm to 1 mm, burrs larger than the gap are prevented from entering the hydraulic oil chamber. Furthermore, if no gap is formed, frictional heat is generated in the flange due to the high speed rotation during joining, which can unexpectedly form a gap through which burrs can pass, resulting in defective products.

[0007] Additionally, Patent Document 2 discloses a hydraulic cylinder having a structure in which tapered surfaces come into contact with each other to seal the space containing the burrs. To put it simply, the tapered surfaces are separated during rotation, but when upset pressure is applied, the tapered sections move closer to each other by an allowance, so the tapered surfaces also move closer to each other and finally come into close contact. As a result, the space containing the burrs is sealed, and the burrs are contained. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Utility Model Application Publication No. 4-87064 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-72160 Summary of the Invention [Problem to be solved by the invention]

[0009] The flange disclosed in Patent Document 1 has a gap between it and the inner peripheral surface of the cylinder, which means that burrs smaller than the gap can get into the hydraulic oil chamber. On the other hand, the cylinder disclosed in Patent Document 2 has tapered surfaces on the tube and the lid that are in close contact with each other, making it possible to contain burrs. However, ensuring a tight seal with this type of structure requires high-precision machining, such as machining the tapered surface with high dimensional accuracy and, further, accurately aligning the axial center during upset pressure application and applying uniform pressure around the entire circumference, resulting in high machining costs.

[0010] In view of the above circumstances, the present invention has an object to provide an inexpensive fluid pressure cylinder having a structure for sealing in burrs on the inner periphery of a tube that are generated by friction welding, and also an object to provide a jig used in manufacturing the fluid pressure cylinder, and a method for manufacturing a fluid pressure cylinder using the jig. [Means for solving the problem]

[0011] A first invention is a fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, wherein a cylindrical protrusion that protrudes into the tube and is coaxial with the tube is formed on the surface of the cylinder end that faces the inside of the tube, and a space that accommodates internal burrs generated by friction welding is formed between the inner surface of the tube and the circumferential surface of the protrusion, and the space is hermetically sealed by a sealing member.

[0012] A second invention is a fluid pressure cylinder characterized in that the diameter of the protrusion and the inner diameter of the tube described in the first invention are set so that the width between the protrusion and the inner surface of the tube is smaller than the cross-sectional width of the sealing member in an undeformed state.

[0013] A third invention is a fluid pressure cylinder according to the first invention, characterized in that the axial length of the protrusion is longer than the sum of the axial length of a burr formed in the space and the axial cross-sectional width of the sealing member.

[0014] A fourth invention is a fluid pressure cylinder according to the first invention, characterized in that a step portion is formed on the circumferential surface of the protruding portion so as to protrude radially outward from the protruding portion.

[0015] A fifth invention is the fluid pressure cylinder according to the fourth invention, characterized in that the stepped portion is a first stepped portion formed on the circumferential surface of the tip end portion of the protruding portion.

[0016] A sixth invention is a fluid pressure cylinder according to the fourth or fifth invention, characterized in that a second step portion is formed on the peripheral surface of the base side of the protrusion as the step portion.

[0017] A seventh aspect of the present invention is the fluid pressure cylinder according to the fourth aspect of the present invention, characterized in that the step portion is formed around the entire periphery of the protruding portion.

[0018] An eighth aspect of the present invention is the fluid pressure cylinder according to the fourth aspect of the present invention, characterized in that the step portion has a tapered shape.

[0019] A ninth invention is a fluid pressure cylinder characterized in that a step portion protruding toward the center is formed on the inner surface of the tube described in the first invention within the range in which the space is formed.

[0020] A tenth invention is a fluid pressure cylinder characterized in that, as the step portion described in the ninth invention, a third step portion is formed at a position on the inner surface of the tube that overlaps with the tip of the protrusion when viewed radially.

[0021] The eleventh invention is a fluid pressure cylinder according to the ninth or tenth invention, characterized in that the step portion is a fourth step portion formed at the end of the inner surface of the tube on the cylinder end side, closer to the axial center than the position where the inner burr is formed.

[0022] A twelfth aspect of the present invention is the fluid pressure cylinder according to the first aspect of the present invention, characterized in that the space is filled with a hardening filler over the entire area.

[0023] A thirteenth invention is a fluid pressure cylinder according to the first invention, characterized in that a groove is formed on the surface of the cylinder end facing the inside of the tube, surrounding the protrusion.

[0024] A fourteenth invention is a seal member temporary placement jig for temporarily placing a seal member for sealing a space of a fluid pressure cylinder, in which a tube and a cylinder end are joined by friction welding, the surface of the cylinder end facing the inside of the tube is provided with a cylindrical protrusion that protrudes into the tube coaxially with the tube, and a space for accommodating internal burrs generated by friction welding is formed between the inner peripheral surface of the tube and the peripheral surface of the protrusion, the seal member temporary placement jig comprising: a handle that is longer than the axial length of the tube; and a seal holding part that holds the seal member, the seal holding part being fixed to one end of the handle, and a shape holding part that holds the shape of the seal member in a circular shape when viewed in the axial direction, at the part opposite to where the handle is fixed.

[0025] A fifteenth aspect of the present invention is a seal member insertion jig for inserting a seal member into a fluid pressure cylinder in which a tube and a cylinder end are joined by friction welding, a cylindrical protrusion that protrudes into the tube coaxially on a surface of the cylinder end facing the inside of the tube, and a space for accommodating internal flash generated by friction welding is formed between the inner peripheral surface of the tube and the peripheral surface of the protrusion, while holding the space so as not to fall off, the seal member insertion jig comprising: a handle made of a round bar material that is longer than the axial length of the tube; a pipe that is longer than the axial length of the tube but shorter than the handle and has an inner diameter that can be fitted with the handle and rotated; and a half of the protrusion. a stopper portion having a length greater than the radius of the protrusion and less than the radius of the inner peripheral surface of the tube, the stopper portion having a surface shaped to fit along the end face of the protrusion; and an insertion portion having a length greater than the radius of the protrusion and less than the radius of the inner peripheral surface of the tube, the tip of which has a convex portion shaped to be able to enter the space and having a length greater than the length from the end face of the protrusion to the location in the space where the sealing member is positioned; one of the stopper portion and the insertion portion is fixed to one end of the handle, and the other is fixed to one end of the pipe, the handle is fitted into the pipe, and the stopper portion and the insertion portion are capable of relative rotation around the handle as an axis.

[0026] The sixteenth invention is a sealing member insertion jig, characterized in that the anti-slip portion described in the fifteenth invention is fixed to the handle, and the insertion portion is fixed to the pipe, and when the handle is fitted into the pipe, the anti-slip portion and the insertion portion can be displaced relative to each other along the axial direction of the handle.

[0027] a cylindrical projection formed on a surface of the cylinder end facing the interior of the tube and projecting into the tube coaxially with the tube; an annular gap for accommodating internal burrs formed by friction welding between the inner peripheral surface of the tube and the outer peripheral surface of the projection; and the annular gap sealed with a seal, the method comprising: a preparation step of preparing the cylinder end in which the axial length of the projection is longer than the sum of the axial length of the internal burr formed by friction welding and the axial length of the seal; a friction welding step of coaxially friction-welding the tube and the cylinder end to form an annular gap between the inner peripheral surface of the tube and the outer peripheral surface of the projection, the annular gap being capable of accommodating the internal burr and into which the seal can be attached; and a seal member insertion step of attaching the seal to the annular gap to contain the internal burr in the annular gap. an annular gap for accommodating internal burrs formed by friction welding between the inner circumferential surface of the tube and the outer circumferential surface of the protrusion; and a method for manufacturing a fluid pressure cylinder comprising: a tube and a cylinder end joined by friction welding; a cylindrical protrusion formed on a surface of the cylinder end facing the interior of the tube, the cylindrical protrusion protruding into the interior of the tube and being coaxial with the tube; an annular gap for accommodating internal burrs formed by friction welding between the inner circumferential surface of the tube and the outer circumferential surface of the protrusion; and a friction welding step of friction-welding the tube and the cylinder end coaxially to form an annular gap between the inner circumferential surface of the tube and the outer circumferential surface of the protrusion, the annular gap being capable of accommodating the internal burrs and allowing attachment of the seal. [Effects of the Invention]

[0028] According to the present invention, it is possible to provide at low cost a fluid pressure cylinder having a structure for sealing in burrs on the inner peripheral side of a tube generated by friction welding. It is also possible to provide a jig used in manufacturing the fluid pressure cylinder and a method for manufacturing a fluid pressure cylinder using the jig. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a vertical cross-sectional view of a hydraulic cylinder according to a first embodiment. [Figure 2] 5A to 5C are diagrams illustrating a friction welding process for the hydraulic cylinder according to the first embodiment. [Figure 3] 5A to 5C are diagrams illustrating a friction welding process for the hydraulic cylinder according to the first embodiment. [Figure 4] 5A to 5C are diagrams illustrating a friction welding process for the hydraulic cylinder according to the first embodiment. [Figure 5] FIG. 2 is an enlarged view of part A shown in FIG. [Figure 6] 1A is a front view showing a first jig, and FIG. 1B is a side view showing the first jig. [Figure 7] 1A is a front view showing a second jig, and FIG. 1B is a side view showing the second jig. [Figure 8] 10A and 10B are a front view and a side view, respectively, showing a third jig. [Figure 9] 10A is a front view and FIG. 10B is a side view of the second jig attached to the third jig. [Figure 10] 5A to 5C are diagrams illustrating a procedure for fitting an O-ring according to the first embodiment. [Figure 11] 5A to 5C are diagrams illustrating a procedure for fitting an O-ring according to the first embodiment. [Figure 12] FIG. 2 is an enlarged view of a portion corresponding to portion A in FIG. 1 according to a second embodiment. [Figure 13] FIG. 2 is an enlarged view of a portion corresponding to portion A in FIG. 1 according to a second embodiment. [Figure 14] 1. FIG. 5 is an enlarged view of a portion corresponding to portion A in FIG. 1, showing a modified example of the second embodiment. [Figure 15] FIG. 10 is an enlarged view of a portion corresponding to portion A in FIG. 1 according to a third embodiment. [Figure 16] FIG. 10 is an enlarged view of a portion corresponding to portion A in FIG. 1 according to a third embodiment. [Figure 17] FIG. 10 is an enlarged view of a portion corresponding to portion A in FIG. 1, showing a modified example of the third embodiment. [Figure 18] FIG. 10 is an enlarged view of a portion corresponding to portion A in FIG. 1 according to a fourth embodiment. [Figure 19] FIG. 10 is an enlarged view of a portion corresponding to portion A in FIG. 1 according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, identical or similar parts are denoted by identical or similar reference numerals, and redundant explanations are omitted. It should be noted that the drawings are schematic. Therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual ones, and the drawings also include parts where the relationship between dimensions and ratios differ. Furthermore, the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the materials, shapes, structures, markings, etc. of component parts to the following embodiments. In the following embodiments, a hydraulic cylinder, which is an example of a fluid pressure cylinder, will be described as having an axial direction fixed along the left-right direction, with the cylinder end located on the left side and the tube located on the right side.

[0031] First Embodiment (Overall structure of hydraulic cylinder) First, the overall structure of the hydraulic cylinder will be described with reference to FIG. The hydraulic cylinder 1 has a cylinder end 20, which serves as a lid, friction-welded to one axial end of a tube 10, which is a cylindrical member. Although not shown in the figure, a cylinder rod equipped with a piston is inserted, and then a cylinder head, through which the cylinder rod passes, is bolted to the other end of the tube 10. Since the present invention relates to the structure around the joint between the tube 10 and the cylinder end 20, in the following explanation, explanations of parts other than the peripheral parts between the tube 10 and the cylinder end 20 joined by friction welding will be omitted.

[0032] (Cylinder end structure) Next, the structure of the cylinder end 20 will be described with reference to FIG. Most of the cylinder end 20 has a diameter slightly smaller than the outer diameter of the tube 10, but a large-diameter portion 21 with the same diameter as the outer diameter of the tube 10 is formed at the end on the tube 10 side, which is the friction-welded portion. In addition, a cylindrical protrusion 22 with a diameter smaller than the inner diameter of the tube 10 is formed on the surface of the large-diameter portion 21 facing the inside of the tube 10, in a position coaxial with the other portions. Note that when the cylinder end 20 is joined to the tube 10, the tube 10 and the cylinder end 20 are coaxial, and therefore the protrusion 22 and the tube 10 are also coaxial.

[0033] The diameter of the protrusion 22 is set so that the width of a space 30 formed between the protrusion 22 and the inner circumferential surface of the tube 10 (described later) is narrower than the cross-sectional width of an O-ring 40 serving as a sealing member. The axial length of the protrusion 22 is longer than the sum of the axial width of an inner burr IB, which will be described later, and the cross-sectional width of the O-ring 40.

[0034] (Friction welding process) Next, the friction welding process of the tube 10 and the cylinder end 20 will be described with reference to FIGS. As shown in Fig. 2, in the friction welding process, first, the tube 10 is fixed and the cylinder end 20 is rotated at high speed. Then, as shown in Fig. 3, the large diameter portion 21 of the cylinder end 20, which is rotating at high speed, is brought into contact with the tube 10, generating frictional heat at the contact point TP. At this time, the protrusion 22 rotates without coming into contact with the tube 10.

[0035] When the contact point TP reaches a temperature suitable for welding due to frictional heat, the rotation of the cylinder end 20 is stopped and an upset pressure is applied by pressing it strongly against the tube 10, as shown in FIG. The upset pressure joins the tube 10 and the large diameter portion 21 of the cylinder end 20, but parts of the tube 10 and the cylinder end 20 are pushed inward and outward in the radial direction, forming outer burrs OB and inner burrs IB that contain impurities and have an umbrella-shaped cross section, as shown in Figure 5.

[0036] (Structure of burr-enclosed part) Next, the structure of the enclosed portion of the inner flashing IB will be described with reference to FIG. When the tube 10 and the cylinder end 20 are joined together, a space 30 is formed between the inner peripheral surface of the tube 10 and the peripheral surface of the cylinder end 20, the space 30 being the length of the protruding portion 22. Furthermore, an inner burr IB is formed from the end 31 of the space 30 on the cylinder end 20 side. Therefore, the inner burr IB is naturally accommodated inside the space 30 when it is formed.

[0037] After the tube 10 and the cylinder end 20 are joined together, an O-ring 40 is fitted into the space 30 as a sealing member. The O-ring 40 has a cross-sectional width larger than that of the space 30, and deforms when fitted, thereby adhering closely to the inner peripheral surface of the tube 10 and the peripheral surface of the protrusion 22, sealing the space 30 and containing the inner flash IB. Thereafter, the outer flash OB is removed, completing the friction welding.

[0038] After removing external flash OB, a cylinder head is bolted to the end of the tube 10 opposite the cylinder end 20, and piping is installed to complete the hydraulic cylinder 1. After that, the hydraulic cylinder 1 is attached to industrial machinery or the like, and the interior is filled with hydraulic oil. When the hydraulic cylinder 1 begins to be used in this way, hydraulic pressure is applied to the O-ring 40 so that it is intermittently pressed against the end 31. This pressure prevents the O-ring 40 from falling off. Furthermore, because hydraulic oil leaking from the O-ring 40 flows into the space 30, albeit in small amounts, after a certain amount of time has passed since the hydraulic cylinder was put into operation, the interior of the space 30 will also be filled with hydraulic oil.

[0039] (Structure of manufacturing jig) 6 to 9, a description will be given of a jig for fitting the O-ring 40, which is a sealing member, into the space 30. Note that line BB in Fig. 6 indicates a cross section of the first jig 50 in Fig. 10, and line CC in Fig. 9 indicates a cross section of the second jig 60 in Fig. 11.

[0040] The first jig 50 is a jig for temporarily placing a sealing member, and is used to hold the O-ring 40, move it to the fitting position, and temporarily place it there. The second jig 60 and the third jig 70 are combined to form a seal member insertion jig. The second jig 60 has a stopper that prevents the O-ring 40, temporarily placed in the fitting position, from coming off the protrusion 22 during fitting, and the third jig 70 has an insertion part that fits the O-ring 40 to a predetermined position in the space 30.

[0041] As shown in FIG. 6, the first jig 50 has a rod-shaped handle 51 and a disk-shaped seal holding portion 52 at the tip thereof, the disk-shaped seal holding portion 52 having approximately the same diameter as the inner diameter of the tube 10. A groove 53 having approximately the same diameter as the outer diameter of the protrusion 22 is formed on one surface of the seal retaining portion 52. The groove 53 guides the seal retaining portion 52 so that the protrusion 22 fits therein and the O-ring 40 is positioned appropriately. Furthermore, the surface of the seal retaining portion 52 on which the groove 53 is formed is provided with a shape retaining portion 54 for maintaining the circular shape of the O-ring 40. The shape retaining portion 54 is formed along the entire circumferential surface of the groove 53, with the center side protruding in the axial direction and forming a surface that is obliquely oriented radially outward. Therefore, the shape retaining portion 54 comes into contact with the inner circumferential side of the O-ring 40, maintaining the O-ring 40 in its circular shape.

[0042] One end of handle 51 is fixed to the center of the surface of seal retaining portion 52 opposite to the surface on which shape retaining portion 54 is provided. Handle 51 is formed longer than tube 10 so that the entire first jig 50 is not housed inside tube 10 when O-ring 40 is fitted into space 30.

[0043] 7, the second jig 60 has a round bar handle 61 and a flat plate-shaped anti-detachment portion 62 at the tip of the handle 61. The wide surface of the anti-detachment portion 62 is rectangular, and the side opposite to the side to which the handle 61 is fixed is formed in an arc shape with a diameter larger than the outer diameter of the protrusion 22 and smaller than the inner diameter of the tube 10.

[0044] 8, the third jig 70 has a pipe-shaped handle 71 that is longer than the tube 10 but shorter than the handle 61 of the second jig, and an insertion part 72, which is a plate with a convex part 73 formed so that the longitudinal section is L-shaped, fixed to the tip of the handle 71. The convex part 73 is formed in a range between an arc with a diameter larger than the radius of the protrusion 22 but smaller than the tube 10, and an arc with approximately the same diameter as the tube 10, so that it can enter the space 30. The convex part 73 also protrudes from the surface of the insertion part by a distance equal to or greater than the length from the end face of the protrusion 22 to the position in the space 30 where the O-ring 40 is disposed. The inner diameter of the handle 71 of the third jig 70 is approximately equal to the diameter of the handle 61 of the second jig, and when the handle 61 of the second jig 60 is inserted into the handle 71 of the third jig 70, the insertion portion 72 becomes integrated with the anti-detachment portion 62 so as to cover a portion of the anti-detachment portion 62, as shown in Figure 9.

[0045] By integrating the second jig 60 and the third jig 70, the third jig 70 can rotate relative to the anti-detachment portion 62 with the handle 61 as the rotation axis. In addition, the third jig 70 can also be displaced relative to the anti-detachment portion 62 along the axial direction of the handle 61.

[0046] (O-ring fitting procedure) Next, with reference to FIGS. 10 and 11, a method for manufacturing the hydraulic cylinder 1 in which the O-ring 40 is fitted into the space 30 using a first jig 50, a second jig 60, and a third jig 70 will be described. First, grease is applied to the seal holding portion 52 of the first jig 50, and the O-ring 40 is attached and held while maintaining its circular shape. Then, the first jig 50 is inserted from the cylinder head side of the tube 10, and a seal member temporary placement step is performed in which the O-ring 40 is placed at the opening of the space 30. After placement, the first jig is rotated while being pressed to peel off the O-ring 40 from the seal holding portion 52 , and the first jig 50 is pulled out from the inside of the tube 10 .

[0047] Next, the second jig 60 is inserted into the tube 10. At this time, the handle 71 of the third jig 70 may be fitted into the handle 61 of the second jig 60 beforehand. The second jig 60 is then pushed in until the retaining portion 62 comes into contact with the tip surface of the protrusion 22. With the retaining portion 62 in contact with the tip surface of the protrusion 22, the third jig 70 is used to perform the sealing member insertion step of fitting the O-ring 40 into the space. Then, this step is performed for the entire circumference while the third jig 70 is rotated around the handle 71 as an axis, thereby completing the fitting of the O-ring 40 into the space 30.

[0048] Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. In the following description of each embodiment, only the differences from the first embodiment will be described, and the description of the similarities will be omitted.

[0049] In the cylinder end 20 according to this embodiment, a first step 23 that protrudes radially outward is formed on the circumferential surface of the tip portion of the protruding portion 22. The first step 23 is formed between the tip portion of the protruding portion 22 (FIG. 12) and the position where the end of the burr is formed (FIG. 13). At the time of manufacturing the tube, a member is added to compensate for the length (extrusion allowance) that is reduced by the formation of the burr during friction welding.

[0050] The protruding portion 22 may have a shape that includes a first step portion 23 on the tip side and a second step portion 24 on the large diameter portion 21 side. 12 and 13, the first step portion 23 is a radially protruding portion, but in the application of the present invention, the first step portion 23 does not necessarily have to have such a structure. For example, as shown in Fig. 14, a structure in which the first step portion 23 is formed on the tip side and the second step portion 24 is formed on the base side, and a groove for fitting an O-ring 40 into the protruding portion 22 may be formed.

[0051] (Effects of the second embodiment) The first step 23 formed on the protruding portion 22 restricts the movement of the O-ring 40 fitted in the space 30. Therefore, when the first step 23 is formed on the tip side of the protruding portion 22, it has the effect of preventing the O-ring 40 from coming off, and when it is formed on the cylinder end side, it prevents the O-ring 40 from being pushed in excessively. Preventing the O-ring 40 from coming loose improves the ability to contain internal burrs IB. Also, the O-ring 40 is susceptible to pushing-in pressure due to hydraulic oil pressure inside the tube 10, which can cause it to come into contact with burrs and be scratched or cut. Therefore, by forming the first step 23 on the cylinder end side, damage to the O-ring 40 can be prevented.

[0052] The first step 23 and the second step 24 do not necessarily need to be formed continuously over the entire circumferential surface of the protruding portion 22, but may be formed by removing a portion of the circumference or by forming the first step 23 and the second step 24 at a predetermined interval on the circumferential surface. In this case, fitting and replacing the O-ring 40 becomes easier.

[0053] Third Embodiment A third embodiment of the present invention will be described with reference to FIGS. The tube 10 according to this embodiment is formed with a third step 11 that protrudes radially toward the center within the range where the space 30 is formed on the inner circumferential surface.

[0054] Furthermore, a fourth step 12 may be formed on the end of the tube 10, closer to the axial center than the position where the inner burr IB is formed. This corresponds to the second step 24 in the second embodiment, and restricts movement of the O-ring 40 so that it does not come into direct contact with the inner burr IB.

[0055] As shown in Figure 15, the third step portion 11 may be formed at any position within the range 13 that overlaps with the tip of the protrusion 22 when viewed from the radial direction, and the position can be changed depending on the size and shape of the O-ring 40. Moreover, the tube 10 may have a structure including both the third step portion 11 and the fourth step portion 12.

[0056] In this embodiment, the third step 11 is formed to protrude toward the axial center, but the tube 10 does not necessarily have to have such a structure when applying the present invention. For example, the third step may be formed by processing into a tapered shape as shown in Figure 17. Alternatively, a groove as shown in Figure 14 may be formed on the side of the tube 10.

[0057] (Effects of the third embodiment) The third step portion 11 is formed on the tube 10 side, but has the same effect as the first step portion 23 and the second step portion 24 described in the second embodiment.

[0058] <Fourth embodiment> A fourth embodiment of the present invention will be described with reference to FIG. The hydraulic cylinder 1 according to this embodiment differs from the first to third embodiments in that, after friction welding, an O-ring 40 is not fitted into the space 30. Instead, the space 30 is filled with a hardenable filler 41.

[0059] The hardening filler 41 filled inside the space 30 is a resin that hardens when dried or the like, and is integrated with the inner burr IB in the space 30. This prevents the inner burr IB from falling off, and also prevents metal particles from being mixed into the hydraulic oil.

[0060] (Effects of the fourth embodiment) Furthermore, the side of the hardened hardenable filler 41 that is exposed to the inside of the tube 10 has a flat shape and a uniform thickness. Therefore, partial shedding is less likely to occur than with the inner burrs IB, and small pieces or particles of the hardened filler are rarely mixed into the hydraulic oil. Even if a portion of the filler peels off, damage to the inside of the tube 10 can be prevented by adjusting the components of the hardening filler to a material softer than the inner burrs IB. Furthermore, since the inner burrs IB do not come into direct contact with the working fluid, deterioration of the inner burrs IB can be prevented, and they can also be prevented from falling off.

[0061] Fifth Embodiment Next, a fifth embodiment of the present invention will be described with reference to FIG. In the cylinder end 20 according to this embodiment, a groove 25 is formed in the large diameter portion 21. Due to the formation of the groove 25, a space 30 is expanded inside the cylinder end 20 after friction welding.

[0062] (Effects of the fifth embodiment) Groove 25 expands space 30, making it possible to form a portion on the large diameter portion 21 side that is equal to the wall thickness of the tube. In addition, by moving the cylinder end side edge of space 30 toward large diameter portion 21, an area that is flush with the inner circumferential surface of tube 10 is formed, so that the portion where burrs are formed is flush. Due to the above factors, the tube 10 and the cylinder end 20 are heated to approximately the same temperature during the heating process, which makes it easier to set the joining conditions and results in a good joining state. [Explanation of symbols]

[0063] 1...hydraulic cylinder, 10...tube, 11...third stage portion, 20...cylinder end, 21...large diameter portion, 22...protruding portion, 23...first stage portion, 30...space, 40...O-ring, 41...hardening filler, 50...first jig, 60...second jig, 70...third jig, TP...contact portion, OB...external burr, IB...internal burr

Claims

1. A method for manufacturing a fluid pressure cylinder, comprising: a tube and a cylinder end joined by friction welding; a cylindrical protrusion that protrudes into the tube and is coaxial with the tube is formed on a surface of the cylinder end facing the interior of the tube; an annular gap that accommodates internal burrs generated by friction welding is formed between an inner peripheral surface of the tube and an outer peripheral surface of the protrusion; and the annular gap is sealed by a seal member, a preparation step of preparing the cylinder end in which the axial length of the protrusion is formed to be longer than the sum of the axial length of the inner burr generated by friction welding and the axial length of the seal member; a friction welding process in which the tube and the cylinder end are coaxially friction-welded to form an annular gap between an inner peripheral surface of the tube and an outer peripheral surface of the protruding portion, the annular gap accommodating the inner burr and allowing the seal member to be attached; a seal member inserting step of fitting the seal member into the annular gap to seal the internal burr in the annular gap.

2. A method for manufacturing a fluid pressure cylinder, comprising: a tube and a cylinder end joined by friction welding; a cylindrical protrusion that protrudes into the tube and is coaxial with the tube is formed on a surface of the cylinder end facing the interior of the tube; an annular gap that accommodates internal burrs generated by friction welding is formed between an inner peripheral surface of the tube and an outer peripheral surface of the protrusion; and the annular gap is sealed by a seal member, a preparation step of preparing the cylinder end in which the axial length of the protrusion is formed to be longer than the sum of the axial length of the inner burr generated by friction welding and the axial length of the seal member; and a friction welding step of coaxially friction-welding the tube and the cylinder end to form an annular gap between the inner peripheral surface of the tube and the outer peripheral surface of the protruding portion, the gap accommodating the inner burr and allowing the seal member to be attached.

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