JP2009287712A - Method of molding bellows pipe for exhaust pipe of automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of molding a bellows pipe for exhaust pipe of an automobile using a ferrite group stainless steel as a raw material by forming a raw pipe, which is formed by rolling a plate, with bellows. <P>SOLUTION: In manufacture of a multiple layer bellows pipe by rolling one metal plate several times so that a starting end and a terminal end are overlapped with each other and performing corrugated molding to the raw pipe having multiple layers of pipe walls, the metal plate formed from a ferrite group stainless steel having a yield point of 310-410 MPa, tensile strength of 420-550 MPa and YR of 80% or less is used to form the raw pipe by rolling the metal plate several times so as to mold the raw pipe having an outer diameter at 28-80 mmΦ, overlapping a starting end and a terminal end of the ferrite group stainless steel plate with each other with a margin within a range at >0° to ≤20°. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming a bellows pipe for an automobile exhaust pipe using ferritic stainless steel as a raw material, and particularly relates to an excellent flexibility without a welded portion.

  The bellows tube is characterized by a bellows-like structure that absorbs stress and mechanical vibration generated by thermal expansion and contraction. 1. A predetermined number of creases are formed in a single process by hydraulic forming using a ring-shaped movable mold; There is a method in which folds are made one by one in order by bulge molding using an elastic body (for example, Non-Patent Document 1).

  The former manufacturing method has a small number of steps, but has low productivity due to hydraulic molding. Further, the tool is complicated and cannot be shared between different product shapes, and the die cost is high. The latter may be a relatively simple mold, and the number of creases can be made freely by sequential processing, but the productivity is low.

  In general, the raw tube is manufactured by winding a thin steel plate into a cylindrical shape and then longitudinally seam-welding the end portion to form a thin-walled cylinder (for example, Patent Document 1). Since the part is hardened and the formability deteriorates, a metal flat plate is rolled over (for example, Patent Documents 2 and 3), or a single metal thin plate is wound in multiple layers so that the tube wall becomes a plurality of layers. Thus, it has been proposed to intermittently weld the outermost winding end edge (for example, Patent Document 4).

When the automobile exhaust pipe is a bellows pipe, austenitic stainless steel having excellent ductility and corrosion resistance is often used. Since austenitic stainless steel contains a large amount of Ni and is expensive, a ferritic stainless steel that has substantially the same ductility and corrosion resistance as austenitic stainless steel and does not contain Ni has been proposed for bellows pipes (for example, Patent Documents 5, 6, 7, and 8).
JP 58-28084 A JP-A-4-34284 Japanese Utility Model Publication No. 62-47720 Japanese Patent Laid-Open No. 3-79886 JP-A-7-268560 JP-A-8-176750 JP-A-8-188854 JP-A-9-125208 Plasticity and processing Vol. 32, No. 366, 818P

  However, although it is possible to manufacture a bellows pipe using ferritic stainless steel as a raw material, cracks are likely to occur in the welded part during bellows molding, and the manufacturing stability is inferior to that of austenitic stainless steel.

  In other words, ferritic stainless steel has higher weld strength than the base metal, and the HAZ part is softer than the base metal, reducing the austenite stabilizing elements such as C and N. As a result, uneven deformation is likely to occur due to the strength of the weld.

  On the other hand, in the case where the metal pipe is overlapped and wound so as to eliminate the welded portion of the raw tube, the hoop end edge portion is not in close contact with the hoop like the multilayer bellows tube described in Patent Document 2. The manufacturing process is complicated because it is necessary to take countermeasures such as a process of soldering the edge.

  Accordingly, the present invention provides a method for forming a bellows pipe for an automobile exhaust pipe made of ferritic stainless steel, using a cylindrical base pipe without performing longitudinal seam welding, with a flat plate being overwrapped. With the goal.

The object of the present invention can be achieved by the following means.
1. A method of manufacturing a multilayer bellows tube, in which a metal plate is wound a plurality of times so that the start end and end of the metal plate overlap each other, and a corrugated forming is performed on an element tube having a multilayered tube wall, the metal plate being a plate A ferritic stainless steel having a thickness of 0.2 to 0.5 mm, a yield point of 310 to 410 MPa, a tensile strength of 420 to 550 MPa, and a YR of 80% or less. The raw tube has an outer diameter of 28 to 80 mmΦ, The ferritic stainless steel flat plate is formed without being welded at the outermost winding end edge part by winding a plurality of times so that the overlap between the start and end of the ferritic stainless steel flat plate is 0 ° or more and 20 ° or less. A method for producing a multilayer bellows tube, which is characterized.

  According to the present invention, compared to austenitic stainless steel, it is possible to manufacture a bellows pipe for an automobile exhaust pipe made of an inexpensive ferritic stainless steel, which is extremely useful industrially.

  The manufacturing method of the bellows pipe according to the present invention defines the mechanical properties of ferritic stainless steel as a raw material, and the overlap between the start end and the end of the base pipe when wound several times is within a specific range. It is characterized by. Hereinafter, the present invention will be specifically described with reference to examples.

  Table 1 shows the chemical composition and mechanical properties of the test steel, and Table 2 shows the evaluation results of the bellows pipe manufactured from the raw pipe made of the test steel shown in Table 1. The thickness of the test steel was all 0.25 mm.

  FIG. 1 schematically shows a cross-sectional shape of the raw tube. In the description, the “overlap” of the starting end and the end of the blank tube is expressed by a circumferential angle θ. The base tube is wound twice so that the portion of the overlap (circumferential angle θ: 0 to 30 °) is triple (however, if the circular angle θ is 0 °, it is double), then No welding (vertical seam welding or intermittent welding) was performed on the end edge of the outermost winding. In addition, an elementary tube in which the start end and end end do not overlap and a part of the circumference is single was also manufactured. The thickness of the raw tube was 0.25 mm, and the outer diameter was 60 mmΦ.

  Test steel No. 1 to 3 have a yield point of 310 to 410 MPa, a tensile strength of 420 to 550 MPa, and a YR of 80% or less. In Nos. 4 to 6, the yield point was 310 to 410 MPa, the tensile strength was 420 to 550 MPa, and the YR exceeded 80%. YR (%) is defined as yield point / tensile strength × 100.

  In bellows molding, a ring-shaped mold is placed outside the base tube, and the tube wall of the base tube is bulged outward from the inside by pressure using a liquid or urethane rubber or other elastic body as a medium. Compressed (shaft-pressed) to a ring-shaped mold placed outside.

  From Table 2, when the yield point of the test steel of the raw pipe is 310 to 410 MPa, the tensile strength is 420 to 550 MPa, and the YR is 80% or less, the hoop edge is in close contact with the pipe wall after the bellows molding (Test No. .1-8). On the other hand, when the yield point of the specimen steel of the base pipe is 310 to 410 MPa, the tensile strength is 420 to 550 MPa, and the YR exceeds 80%, the spring back is strong and the hoop edge is in close contact with the pipe wall after bellows molding. However, it was lifted (Test Nos. 9, 10, and 11).

  When the overlap is 30 °, the peak height of the bellows does not reach the target 9 mm, and when the single part is 45 °, fluid pressure leaks (Test No. 5), and the single part is 10 °. In the case of, cracks occurred (Test No. 6). The overlap is preferably 0 to 20 °.

  According to the present invention, a bellows tube is manufactured in which a ferritic stainless steel is overwrapped and a raw tube is a double tube (the overlapping portion of the start and end portions is a triple portion of 0 to 20 °). Is possible.

  In addition, the test steel No. Using a material with a plate thickness of 0.20 mm, double pipes and triple pipes with an outer diameter of 50 mmΦ were manufactured, and the possibility of manufacturing a target peak height of 9 mm was investigated by bellows molding by the method described above. .

  In any of the elementary pipes, the overlap between the start end and the end end is 20 °, and this portion is a triple tube (double if 0 °), a triple tube is quadruple (however, 0 ° In case of triple)). A bellows tube with a close hoop end edge that satisfies the target value of a peak height of 9 mm was produced from any of the elementary tubes.

  In addition, the test steel No. 3 using a material having a plate thickness of 0.30 mm as a base tube (outer diameter 55 mmΦ) of a double pipe and a welded pipe (double pipe with an inner pipe and an outer pipe as a welded pipe) In the bellows molding by the method, when the limit peak height at which cracking occurs was determined, cracks occurred at a peak height of 13.5 mm or more in the case of a double pipe, and in a welded pipe at a peak height of 12.0 mm or more Cracking occurred. In addition, the double tube was made into the bellows pipe | tube which made the overlap margin 10 degrees and the hoop edge part closely_contact | adhered.

  The thickness of the ferritic stainless steel used as the material is 0.2 mm or more from the viewpoint of manufacturing cost, 0.5 mm or less to prevent fatigue failure, and the raw pipe is a double pipe or triple pipe with an outer diameter of 28 to 80 mm. It is preferable that

  In order to ensure the amount of displacement absorbed by the bellows for an automobile exhaust pipe, it is preferable that the outer diameter is 28 mm or more, and the outer diameter is 80 mm or less in order to ensure rigidity.

  Although the bellows pipe according to the present invention has sufficient characteristics for an automobile exhaust pipe, the vacuum bellows pipe cannot be replaced from the viewpoint of airtightness.

The figure which is the schematic diagram of the cross-sectional shape of the raw tube which concerns on one Example of this invention, and is a figure explaining the overlap (circumferential angle (theta)) of a start end part and a termination | terminus part.

Claims (1)

  A method of manufacturing a multilayer bellows tube, in which a metal plate is wound a plurality of times so that the start end and the end of the metal plate overlap each other and the tube wall is multilayered, and the metal plate has a thickness of 0 .2 to 0.5 mm, Yield point is 310 to 410 MPa, Tensile strength is 420 to 550 MPa, YR is 80% or less ferritic stainless steel, the raw tube has an outer diameter of 28 to 80 mmΦ, and the ferrite The stainless steel flat plate is formed without being welded at the end edge of the outermost winding, after being wound a plurality of times so that the overlap between the start and end of the stainless steel plate is 0 ° or more and 20 ° or less. To manufacture a multilayer bellows tube.

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