AU614403B2

AU614403B2 - Method for making thin-walled metal tubes

Info

Publication number: AU614403B2
Application number: AU39170/89A
Authority: AU
Inventors: Shoji Inoue; Norimasa Miura; Takefumi Nakako; Yoshiaki Shimada; Akinobu Takezoe
Original assignee: Nisshin Seiko Co Ltd; Nisshin Steel Co Ltd
Current assignee: Nisshin Seiko Co Ltd
Priority date: 1988-09-09
Filing date: 1989-08-01
Publication date: 1991-08-29
Anticipated expiration: 2009-08-01
Also published as: KR900004425A; GB2222541A; AU3917089A; DE3922653A1; GB8919791D0; DE3922653B4; FR2636254A1; KR960007143B1; SE8902961D0; SE8902961L; FR2636254B1; GB2222541B; ZA894342B; JPH0275418A; JPH0729147B2; SE504310C2

Description

C Cur Ref: 277328 n 6%41 O FORIM AUSTRALIA Patents Act COMPLETE SPECIFICATION

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q h t An S 4* *8 4 Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Applicant(s): a a 4 4'a 4 oa @0 0 a Nisshin Seiko Kabushiki Kaisha No 4-1, Marunouchi 3-chome Chiyoda-ku Tokyo

JAPAN

ARTHUR S. CAVE CO.

Patent Trade Mark Attornerys Level 10, 10 Barrack Street SYDNEY NSW 2000 Address for Service: Sn:! Complete specification for n the invention entitled "Method for making thin-walled metal tubes".

The following statement is a full description of this invention, including the best method of performing it known to me:-

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SPECIFICATION

TITLE OF THE INVENTION METHOD FOR MAKING THIN-WALLED METAL TUBES BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for making thinwalled metal tubes having a t/D ratio of substantially 2 or lower wherein t is the thickness of a sheet and D is the outer diameter of a tube, which makes effective use of the pre-deformation of a metal 0ooo sheet to be caused by plastic bending afforded thereto.

Statement of the Prior Art bn, aMetal tubes have conventionally been fabricated on a continuous 00 line comprising the steps of forming metal sheets into tubes by successive widthwise bending with the use of a roll-forming machine comprising a tandem arrangement of a number of forming rolls, having a da caliber, or cage rolls, and joining together both side edges of the thus formed metal sheets by welding.

0 a However, the following problems arise, when it is intended to 0 00 °o0 0* make thin-walled metal tubes by such a conventional method. Since the thickness t of a starting metal sheet is much smaller than the outer 0 diameter D of a tube, it may not be subjected to sufficient plastic deformation until it is bent to the curvature radius of the end product. For that reason, the metal sheet undergoes so increased elastic deformation in the course of bending that increased springingback occurs while it leaves one roll and enters the next roll, thus resulting in insufficient bending of its side edges and leading to a possibility that edge bowing may occur due to increased edge stretching. In order to solve the problems, it has been proposed to increase the number of rolls to reduce such springing-back as much as possible. However, another problem with this proposal is that it takes some time for changing or regulation of the rolls due to less accommodativeness to sizes, and there is an increase in the time of contact of the metal sheet with the rolls by the time it is formed into the end tube, thus leading to a fear that surface flaws may occur.

As disclosed in Japanese Patent Laid-Open No. 62-176611, the present inventors have therefore proposed a method for making thinwalled metal tubes wherein a metal sheet is subjected on its side defining the inner side of the end tube to plastic bending with a 2009 0*o bending roll arranged perpendicularly to the lengthwise direction o 000 ooo0o0 until its lengthwise curvature is reduced to zero, said metal sheet is 0 0 0 widthwisely bent into a tubular form according to the curvature of the 00 0 end product by making use of the widthwise residual curvature resulting from said plastic bending, and said metal sheet is joined together at its side edges.

This method for fabricating thin-walled metal tubes makes a 4, breakthrough, since it is possible to produce a thin-walled metal tube without doing substantial damage to the surface of the metal sheet owing to a much decreased number of rolls. In order to carry out this method, however, it is required to effect plastic bending processings o: for giving increased plastic distortion to the side of a metal sheet defining the inner side of the end tube with the use of the rolls, having a small diameter, arranged perpendicularly to the lengthwise direction. Giving such increased plastic distortion inevitably needs to make the diameter of the bending rolls as small as possible.

However, the reductions in the diameter of the bending rolls give rise to a reduction in the bending rigidity of the bending rolls, so that deflection tends to occur axially. In order to prevent such deflection, it is therefore required that a metal sheet 4 to be processed be passed between an urethane rubber-lined roll 10 and a S- 2r 7 I I I 0 60 0a o Ia of 1 a a..

*at small-diameter bending roll 11 designed to force the metal sheet 4 against the roll '10, and said roll 11 be supported by a deflectionpreventing block 12 as shown in Figure 4.

As mentioned above, such a deflection-preventing block 12 makes up for the reduction in the bending rigidity of the small-diameter bending roll 11, thereby preventing its axial deflection. It is thus required that the block 12 be provided in its extreme end with a groove 12a having a radius substantially equal to that of the bending roll 11, which is then at least treated with a fluorine resin so as to reduce the friction with the bending roll 11, thereby preventing the occurrence of scuffing marks and assuring the smooth rotation of the bending roll 11. Furthermore, it is required that the metal sheet 4 be coated on its surface contacting the bending roll 11 with a lubricating oil so as to better the lubrication between the deflectionpreventing block 12 and the small-diameter bending roll 11.

In order to make metal tubes with such an arrangement, however, it is required that the small-diameter roll 11 be forced against the urethane rubber-lined roll 10 with large force so as to bend the metal sheet 4. Consequently, an extremely large pressure of contact occurs due to the small diameter of the bending roll 11. This causes that the deflection-preventing block 12 may be seized to the bending roll 11, the bending roll 11 may be flawed, or the bending roll 11 may be restrained from rotation, thus giving damage to the metal sheet 4. In order to prevent the occurrence of such phenomena, the block 12 and bending roll 11 are lubricated on their surfaces to reduce the friction therebetween. However, the lubricant penetrates in between the metal sheet 4 and the urethane rubber-lined roll 10, so that they slip relative to each other, or the metal sheet 4 moves in a zigzag direction. Moreover, when the lubricant it deposited onto the metal sheet 4, it has an adverse influence upon welding to be carried out in .3 Ii joining together the side edges of the metal sheet 4 to be joined into a metal tube. It is thus required that at least the regions of the metal sheet 4 to be welded be degreased. Cost problems also arise since not only are highly precise processings demanded for making the distribution of pressure of contact of the deflection-preventing block 12 with the small-diameter bending roll 11 as uniform as possible but also the parts involved have a short service life.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to a method for making thin-walled metal tubes in which a metal sheet is subjected =0 on its side defining the inner side of a metal tube to plastic bending with a small-diameter bending roll located perpendiuclarly to the lengthwise direction and is then bent back until its lengthwise curvature is reduced to zero, whereby said metal sheet is bent into a tubular form according to the curvature of the end product by making 0 0:o use of the widthwise residual curvature resulting from said plastic °o° 0 •o bending and bending-back, and said tubular form is joined together at their opposite side edges, said method being characterized in that it *0 0 0 is easily carried out at low costs without any need of post-treatments and makes it possible to effect plastic bending processings giving large plastic distortion.

In consequence of studies made to solve the above problems, it has now been found that a metal sheet is passed through a roll group comprising a feed roll in cylindrical form, a delivery roll in cylindrical form, which is in axial parallel to and spaced away from the feed roll by a gap G and rotates in the same direction as the feed roll, and a small-diameter bending roll defined by a floating roll located in the vicinity of and in axial parallel to the feed and delivery rolls and having a diameter larger than a length obtained subtracting from said gap G a length twice the thickness of the metal 4sheet to be bent, such that it is first fed along the feed roll, then guided through said gap G and bent along the bending roll, and finally guided back through said gap G.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, its preferred embodiment will now be explained in more detail with ,reference to the accompanying drawings, which are given for the purpose of illustration alone and in which: Figure I is a view illustrative of the principles of the method for making thin-walled metal tubes according to the present invention, 0:0000Fig-ure 2 is an enlarged view of a region shown at A in Figure 1,an 0 0 0 Fbn igressisg appsecdtoa vewtakenelnt telneBBofFg 0 0 DETAILED DESCRIPTION OF TH{E INVENTION Referring to the drawings, a feed roll 1 in cylindrical form is provided together with a delivery roll 2, again in cylindrical form, which is located in axial parallel to and spaced away by a gap G from the feed roll 1 and rotates in the same direction as the feed roll 1.

A small-diameter bending roll 3 is defined by a floating roll which is located in the vicinity of the two rolls I and 2 and in parallel to the axes thereof and has a diameter larger than a length obtained by subtracting from the gap G a length twice the thickness of a metal sheet 4. A roll group comprising the feed and delivery rolls 1 and 2 and the floating roll, the small-diameter bending roll 3 will hereinafter be referred to as the plastic bending arrangement. In the plastic bending arrangement, the metal sheet 4 is first fed along the feed roll 1, then guided through the gap G and bent along the bending roll 3, and is finally guided back through the gap G. It is understood that by the term "metal sheet 4" to be formed into a thinwalled metal tube and referred to herein is meant not only conventionally cold-rolled metal sheets but also metal sheets polished on at least one side by mirror polishing or hair line polishing or surface-treated at least on one side by etching, chemically chromatic processings, ceramic coating, plating or chemical coating. A o.aro deflector roll 5 is used to deflect the delivery direction of the metal sheet 4 which has been subjected on its side defining the inner tside of the end tube to plastic bending with said plastic bending 0 O O0 a: arrangement located in the direction perpendicular to the lengthwise direction and guided back through the gap G and to bend the metal sheet 4 back until its lengthwise curvature is reduced to zero. A seam guide roll 6 is provided to position the opposite side edges of the metal sheet 4, now in tubular form, just below a welding torch, o 0 o 0 0 which sheet has been widthwisely bent according to the curvature of the end product by making use of the residual widthwise curvature o o O thereof resulting from the plastic bending and bending-back occurring with the plastic bending arrangement and the deflector roll a respectively. A squeeze roll 7 is provided to put the opposite side edges of the tubular metal sheet 4 leaving the seam guide roll 6 in alignment with each other. A welding torch 8 is provided to weld together the side edges of the tubular metal sheet 4 just after it leaves the squeeze roll 7. A urethane rubber-lined pinch roll 9 is provided to deliver the metal tube 4 having its side edges welded together by the welding torch 8, As the metal sheet 4 is passed through the arrangement of such a structure as mentioned above, it is bent along the feed roll 1 of the plastic bending arrangement, guided through the gap G defined between the feed roll I and the delivery roll 2, and subjected on its side defining the inner side of the end tube to plastic bending with the small-diameter bending roll 3 in the direction perpendicular to the lengthwise direction. The metal sheet 4is then drawn out while a line connecting the axial center of the feed roll I with that of the delivery roll 2 is forwardly inclinded toward the outlet side of the plastic bending arrangement through a certain amount of angle larger than 0* so as to prevent any reduction in the residual stress of the metal sheet 4, which may otherwise be caused by its reverse bending occurring at the time when it leaves the delivery roll 2. The metal 0 0A 044 sheet 4 subsequently changes its direction of advancement, and is fed a 0 0 through the deflector roll 5, by which it is bent back until its 00 0 44 0 0 0 4 lengthwise curvature is reduced to zero, to the seam guide roll 6 spaced from that deflector roll 5 a distance in excess of about times the diameter of the metal tube to be made. In the meantime, the metal sheet 4 is widthwisely bent by the widthwise residual curvature 0 resulting from plastic bending and bending-back according to the 08 curvature of the end product, thereby obtaining a tubular product.

The opposite side edges of the tubular product is positioned by the seam guide roil 6. After leaving the squeeze roll 7, the metal sheet 4, now in tubular form, is welded together at its side edges by the welding torch 8. Finally, the metal tube product is carried and discharged out along the urethane rubber-lined pinch roll 9.

Examples .xample 1 The feed and delivery rolls 1 and 2, each of 35 mm in radius and 100 mm in length, with a gap G of 3.0 mm located therebetween, were used with the small-diameter bending roll 3 of 2.0 mm in radius and 110 m= in length and the plastic bending arrangement wherein a line connecting the axial center of the feed roll I with that of the delivery roll 2 is inclined toward the squeeze roll 7 at an angle of The deflector roll 5 was spaced a distance of 600 mm from the squeeze roll 7, and the bottom bed surface of the deflector roll 5 was located at a position higher than the height from the bed surface of the squeeze roll 7 to the tube's bottom by 15 mm. With the use of such an arrangement, the metal sheet of an SUS 304-BA material coil 'having a thickness of 0.15 mm, a width of 89.38 mm and a yielding point of 32 Kgf/mm 2 was formed into a welded tube having an outer o diameter of 28.6 mm6. Consequently, thin-walled welded tubes of o" stainless steel could be continuously made, which excelled in o geometry, surface properties and welding quality.

°o Example 2 The feed and delivery rolls I and 2, each of 35 mm in radius and 100 mm in length, with a gap G of 4.0 mm defined therebetween, were used with the small-diameter bending roll 3 of 2.5 mm in radius .0 and 110 mm in length and the plastic bending arrangement wherein a o o line connecting the axial center of the feed roll 1 with that of the o o0 delivery roll 2 is inclined toward the squeeze roll 7 at an angle of 0 a on The deflector roll 5 was spaced a distance of 600 mm from the squeeze roll 7, and the bottom bed surface of the deflector roll 5 was 0 o o located at a position higher than the height from the bed surface of the squeeze roll 7 to the tube's bottom by 15 mm. With the use of such an arrangement, the metal sheet of a pure titanium coil having a thickness of 0.2 mm, a width of 89.22 mm and a yielding point of 23 Kgf/mm 2 was formed into a welded tube having an outer diameter of 28.6 mm Consequently, thin-walled welded tubes of pure titanium could be continuously fabricated, which were found to excel in geometry, surface properties and welding quality.

The method for making thin-walled metal tubes according to the present invention have such various merits as enumerated below, and is i- 1 0 4 00*p 009 0 It j 0 00 0 00 0r #0 0 01900 0009 b1 0 00 3 thus of great industrial value.

1. Since it is unnecessary to lubricate the small-diameter bending roll and the metal sheet so as to subject the latter to plastic bending, the metal sheet is always kept so clean that a poor welding problem is avoidable when welding together its side edges and any degreasing step can be dispensed with.

2. Since it is unlikely that the metal sheet and/or the smalldiameter bending roll may be flawed by slippage, the quality of the resulting thin-walled metal tubes are remarkably improved.

3. Since it is unlikely that the metal sheet may move in a zigzag direction, the rolls have a semi-infinite service life. Thus, considerable improvements in productivity are achieved on account of removed shutting down of the production line for roll replacement.

4. Since it needs highly precise processings and does not need to use any deflection-preventing blocks having a short service life in making the metal sheet, the present method is feasible at low costs.

5. Since changing of bend radii is also achievable by changing of the small-diameter bending roll defined by a floating roll making use of a commercially available "polishing round rod" and changing of the gap defined between the two cylindrical rolls, the method of the present invention is very advantageous in view of cost.

6. A metal sheet subjected on at least one side to mirror polishing or hair line polishing or a metal sheet surface-treated on at least one side by etching, chemical chromatic processings, ceramic coating, plating or chemical coating may be used without a fear of damaging that treated side.

It is understood that the above described method and the above examples are simply illustrative of the application of principles of the invention and many other modifications may be made without departing from the spirit and scope of the invention.

Claims

1. A method for making thin-walled metal tubes in which a metal sheet is subjected on its side defining the inner side of a metal tube to plastic bending with a small-diameter bending roll located perpendicular to the lengthwise direction and is then bent back until its lengthwise curvature is reduced to zero, whereby said metal sheet is bent into a tubular form according to the curvature of the end product by making use of the widthwise residual curvature resulting from said plastic bending and bending-back, and said tubular form is ,a joined together at their side edges, wherein: a said metal sheet is passed through a roll group comprising o. a feed roll in cylindrical form, a delivery roll in U 0 o* cylindrical form, which is in axial parallel to and spaced away from said feed roll by a gap G and rotates in the same direction as said feed roll and a small-diameter bending roll defined by a floating roll located in the vicinity of and in axial parallel to said o i feed and delivery rolls and and having a diameter larger than a length obtained by subtracting from said gap G a length twice the thickness of said metal sheet to be bent, such that it is first fed along said feed roll then guided through said gap G and bent a« along said bending roll and finally guided back through said gap G.

2. A method for making thin-walled metal tubes substantially as herein described. DATED the 31st day of July, 1989 NISSHIN SEIKO KABUSHIKI KAISHA By Its Patent Attorneys ARTHUR S. CAVE CO.