GB2222541A

GB2222541A - Method for making thin-walled metal tubes

Info

Publication number: GB2222541A
Application number: GB8919791A
Authority: GB
Inventors: Takefumi Nakako; Norimasa Miura; Shoji Inoue; Yoshiaki Shimada; Akinobu Takezoe
Original assignee: Nisshin Seiko KK; Nisshin Steel Co Ltd
Current assignee: Nisshin Seiko KK; Nippon Steel Nisshin Co Ltd
Priority date: 1988-09-09
Filing date: 1989-09-01
Publication date: 1990-03-14
Anticipated expiration: 2009-09-01
Also published as: GB8919791D0; SE504310C2; AU3917089A; DE3922653B4; SE8902961D0; FR2636254A1; KR900004425A; ZA894342B; DE3922653A1; JPH0275418A; GB2222541B; AU614403B2; KR960007143B1; FR2636254B1; SE8902961L; JPH0729147B2

Description

2222541 1 METHOD FOR MAKING THIN-WALLED METAL TUBES

Field of the Invention

The present invention relates to a method for making thin-walled 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 sheet to be caused by plastic bending afforded thereto.

Statement of the prior Art

Metal tubes have conventionally been fabricated on a continuous 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 rollers; having a caliber, or cage rollers. and joining together both side edges of the thus formed metal sheets by welding.

However. the following problems arise when it is intended to make thinwalled metal tubes by such a conventional method. Since the thickess t of a starting metal sheet is much smaller than the outer diameter D of 2 a tube. it may be not subjected to sufficient plastic deformation until it is bent to the curvature radius R(=D/2) of the end product. For that reason. the metal sheet undergoes so increased elastic formation in the course of bending that increased springing-back occurs while it leaves one roller and arrives at the next roller. 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 intrease the number of rollers 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 rollers due to less accommodativeness to sizes. and there is an increase in the time of contact of the metal sheet with the rollers by the time it is 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 bending roller arranged perpendicularly to the lengthwise direction until its lengthwise curvature is reduced to zero. said metal sheet is widthwisely bent into a tubular form r, 3 according to the curvature of the 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 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 rollers. In order to carry out this method, however, it is required to effect plastic bending processings 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 rollers having a small diameter, arranged perpendicularly to lengthwise direction. Giving such increased plastic distortion inevitably needs to make the diameter of the bending rollers as small as possible. However, the reductions in the diameter of the bending rollers give rise to a reduction in the bending rigidity of the bending rollers, 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 a urethane rubber-lined roller 10 and a small-diameter bending roller 11 designed to force the metal sheet 4 against the roller 10, and said roller 11 be supported by a deflectionpreventing block 12 as 4 shown in Figure 4.

As mentioned above. such a deflection-preventing block 12 makes up for the reduction in the bending rigidy of the small-diameter bending roller 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 roller 11. which is then at least treated with a fluorine resin so as to reduce the friction with the bending roller 11. thereby preventing the occurrence of scuffing marks and assuring the smooth rotation of the bending roller 11. Futhermore. it is required that the metal sheet 4 be coated on its surface contacting the bending roller 11 with a lubricating oil so as to better the lubrication between the deflection-preventing block 12 and the small- diameter bending roller 11.

In order to make metal tubes with such an arrangement, however, it is required that the small-diameter roller 11 be forced against the urethane rubber-lined roller 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 roller 11. This causes that the deflectionpreventing block 12 may be seized to the bending roller 11, the bending roller 11 may be flawed, or the bending roller 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 roller 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 roller 10, so that they slip relative to each other, or the metal sheet 4 moves in a zigzag direction. Moreover, when the lubricant is deposited onto the metal sheet 4. it has an adverse influence upon welding to be carried out in 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 distibution of pressure of contact of the deflection-preventing block 12 with the small-diameter bending roller 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 provide 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 roller. located perpendicularly 6 to its 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 the opposite side edges of said tubular form are subsequently joined together. said method being further characterised in that it is easily carried out at low costs without any need of posttreatments and in that it makes it possible to effect plastic bending processings giving large plastic distortion.

Furthermore. the present invention sets out to provide a method for making thin-walled metal tubes according to the appended claim 1. to which reference is hereby directed.

In consequence of studies made to solve the above problems. the present invention sets out to solve these problems, and others, by providing a method wherein a metal sheet is passed through a roller group comprising a feed roller in cylindrical form, a delivery roller in cylindrical form. which is axially parallel to and spaced away from the feed roller by a gap G and rotates in the same direction as the feed roller, and a smalldiameter bending roller defined by a floating 1 1 7 roller located in the vicinity of and axially parallel to the feed and delivery rollers and having a diameter larger than a length obtained by subtracting from said gap G a length twice the thickness of the metal sheet to be bent. such that it is first fed along the feed roller. then guided through said gap G and bent along the bending roller. and finally guided back through said gap G.

Brief DescriRtion of the Drawings For a better understanding of the present invention. its preferred embodiment. which is described by way of example, 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 1 is a view illustrative of the principles of the method for making thin-walled metal tubes according to the present invention; Figure 2 is an enlarged view of a region shown at A in Figure 1; Figure 3 is a sectional view taken along the line B-B of Figure 1; and 8 Figure 4 is a view of a conventional method for making thin-walled metal tubes. and is provided for illustrating the plastic bending processing applied to a metal sheet.

Detailed Description of the Invention

Referring to the drawings. a feed roller 1 in cylindrical form is provided together with a delivery roller 2. again in cylindrical form, which is located axially parallel to and spaces away by a gap G from the feed roller 1 and rotates in the same direction as the feed roller 1. A small-diameter bending roller 3 is defined by a floating roller which is located in the vicinity of the two rollers 1 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 roller group comprising the feed and delivery rollers 1 and 2 and the floating roller. i.e. the smalldiameter bending roller 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 roller 1. then guided through the gap G and bent along the bending roller 3. and is finally guided back through the gap It is understood that the term "metal sheet 411 referred to herein is meant to include not only conventionally j 1 9 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 deflector roller 5 is used to deflect the delivery direction of the metal sheet 4 which has been subjected on its side defining the inner side of the end tube to plastic bending. with said plastic bending arrangement located in the direction perpendicular to the lengthwise direction, and has been guided back through the gap G and has been bent back until its lengthwise curvature is reduced to zero. A seam guide roller 6 is provided to position the opposite side edges of the metal sheet 4, now in tubular form, just below a welding torch, which sheet has been widthwisely bent according to the specifications for the curvature of the end product by making use of the residual widthwise curvature thereof resulting from the plastic bending and bending-back occurring with the plastic bending arrangement and the deflector roller 5. respectively. A squeeze roller 7 is provided to put the opposite side edges of the tubular metal sheet 4 leaving the seam roller 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 roller 7. A urethane rubber-lined pinch roller 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 roller 1 of the plastic bending arrangement. guided through the gap G defined between the feed roller 1 and the delivery roller 2, and subjected on its side defining the inner side of the end tube to plastic bending with the small- diameter bending roller 3 in the direction perpendicular to the lengthwise direction. The metal sheet 4 is then drawn out while a line connecting the axial center of the feed roller 1 with that of the delivery roller 2 is forwardly inclined toward the outlet side of the plastic bending arrangement through a certain amount of angle larger than 00 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 roller 2. The metal sheet 4 subsequently changes its direction of advancement, and is fed through the deflector roller 5. by which it is bent back until its lengthwise curvature is reduced to zero, to the seam guide roller 6 spaced from the deflector roller 5 by a distance in excess of about 10 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 resulting from plastic bending and 11 bending-back according to the curvature of the end product, thereby obtaining a tubular product. The opposite side edges of the tubular product are positioned by the seam guide roller 6. After leaving the squeeze roller 7, the metal sheet 4. now in tubular form, is welded together at its side edges by the welding torch B. Finally, the metal tube product is carried and discharged out along the urethane rubber- lined pinch roller 9.

Examples

Example 1

Feed and delivery rollers 1 and 2, each of 35mm in radius and 100mm in length, with a gap G of 3.Omm located therebetween, were used with a small-diameter bending roller 3 of 2.Omm in radius and 110mm in length and a plastic bending arrangement wherein a line connecting the axial center of the feed roller 1 with that of the delivery roller 2 is inclined toward the squeeze roller 7 at an angle of 300. A deflector roller 5 was spaced a distance of 600mm from the squeeze roller 7. and the bottom bed surface of the deflector roller 5 was located at a position higher than the height from the bed surface of the squeeze roller 7 to the tubes bottom by 15mm. With the use of such an 12 arrangement. the metal sheet of an SUS 304-BA material coil having a thickness of 0.15mm, a width of 89.38mm and a yielding point of 32Kgflmm 2 was formed into a welded tube havingan outer diameter of 28.6mmo. Consequently. thin-walled welded tubes of stainless steel could be continuously made. which excelled in geometry. surface properties and welding quality.

Example 2

Feed and delivery rollers 1 and 2, each of 35mm in radius and 100mm in length, with a gap G of 4.Omm defined therebetween, were used with a small-diameter bending roller 3 of 2.5mm in radius and 110mm in length and a plastic bending arrangement wherein a line connecting the axial center of the feed roller 1 with that of the delivery roller 2 is inclined toward the squeeze roller 7 at an angle of 300. A deflector roller 5 was spaced a distance of 600mm from the squeeze roller 7. and the bottom bed surface of the deflector roller 5 was located at a position higher than the height from the bed surface of the squeeze roller 7 to the tube's bottom by 15mm. With the use of such an arrangement, the metal sheet of a pure titanium coil having a thickness of 0.2mm, a width of 89.22mm and a yielding point of 23 Kgf/mm 2 was formed into a welded tube having an outer diameter of 26.6mm4). Consequently, thin-walled welded t 13 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 has such various merits as enumerated below. and is thus of great industrial value.

1. since it is unnecessary to lubricate the small-diameter bending roller 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 small-diameter bending roller 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 rollers have a prolonged service life. Thus, considerable improvements in productivity are achieved on account of removed shutting down of the production line for roller replacement, 4. Since it uses highly precise processing and does not 14 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 roller, defined by a floating roller making use of a commercially available "polishing round rod', and changing of the gap defined between the two cylindrical rollers. 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, cermaic 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 scope of the invention.

Claims

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 roller located perpendicularly to its 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 the opposite sides edges of said tubular form are subsequently joined together; wherein:said metal sheet is passed through a roller group comprising a feed roller in cylindrical form, a delivery roller in cylindrical form. which is axially parallel to and spaced away from said feed roller by a gap G and rotates in the same direction as said feed roller. and a small-diameter bending roller defined by a floating roller located in the vicinity of and axially parallel to said feed roller and said delivery roller. which bending roller has 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; and wherein said metal sheet is first fed along said feed roller. then guided through said gap G and bent along said bending roller, and finally guided back through

16 said gap g.

1 A 1 Published 1990 atThePateritOfft0s. State House. 86;? L Fl9hHolburn. L4ndonWClR4TP- Further copies maybe obtAintdfrom The PlLtentOMce. liles Branch. St Mary Cray. Orpu4wn, X3n,. ialm 3RD. Printed by Multiplex tachniques ltd. St Mary Cray. IrAnt. Com 1:87