WO2005077562A1

WO2005077562A1 - Method and apparatus for forming tapered steel pipe

Info

Publication number: WO2005077562A1
Application number: PCT/KR2004/001325
Authority: WO
Inventors: Young-Sik Lee
Original assignee: Han Young Machinerey Co, Ltd.
Priority date: 2004-02-16
Filing date: 2004-06-03
Publication date: 2005-08-25

Abstract

Disclosed herein is a method and apparatus for forming a tapered steel pipe, which has a constant inclination in a longitudinal direction thereof and is usable as a post of a street light or electric pole, by simply pulling an existing cylindrical or square steel pipe(10), having the same diameters at both ends thereof, into an angled or circular pipe having a desired shape by means of a traction device (50) while passing the steep pipe(10) through a pipe forming unit(40), instead of using a conventional method of successively bending steel plates. The present invention enables the tapered steel pipe to be more easily and simply manufactured through an automated system, resulting in considerable improvement in productivity and workability, and securing worker safety.

Description

Description METHOD AND APPARATUS FOR FORMING TAPERED STEEL PIPE Technical Field

[1] The present invention relates to a method and apparatus for forming a tapered steel pipe, and more particularly to a method and apparatus for forming a tapered steel pipe having a constant inclination in a longitudinal direction thereof and thus having different diameters at both ends thereof, the tapered steel pipe being obtained by reforming an existing steel pipe, and being usable as a post of a street light or electric pole.

[2] Background Art

[3] In general, steel pipes are produced by drawing predetermined lengths of a steel material, and the obtained respective steel pipes have the same diameter and shape.

[4] The steel pipes, according to their various different applications, are formed into various shapes. For example, when they are intended to be applied to road/street lights or electric poles as shown in Figs. 1 and 2, the steel pipes are formed into an upwardly tapered shape in order to secure their stable self-standing on the ground.

[5] For this, there has been proposed a steel pipe forming machine 100, as disclosed in Korean Patent Application No. 2003-40791. The disclosed steel pipe forming machine 100, as shown in Figs. 3 and 4, comprises: a material feeding unit 110 for the supply of a steel material (W), such as steel plates; a material transfer unit 120: 121 and 122 for transferring the steel material (W) from the material feeding unit 110 into the forming machine 100; a material setting unit 130 for setting the steel material (W) transferred from the material transfer unit 120 at a predetermined position so as not to be biased leftward or rightward; a material forming unit 140: 140a, 140b, 140c, and 140d for successively bending the steel material (W), which is set by the material setting unit 130, by means of a plurality of rollers; a joint compressing unit 150 for compressing both end joints of the steel material, which are bent in the material forming unit 140, so as to cause them to come into contact with each other; a welding unit 160 for welding the contact joints of the steel material; and a discharge unit 170 for transferring finished pipes out of the forming machine 100. With such a forming machine 100, a steel pipe, which is tapered by a constant inclination in a longitudinal direction thereof so as to have different diameters at both ends thereof, is obtained [6] However, since the above described steel pipe forming machine 100 is constructed to form a steel pipe by successively bending steel plates by means of a plurality of rollers as can be seen from Fig. 4, in order to achieve a finished product, there is a need of a plurality of the rollers having various different angles. Furthermore, when it is desired to form a circular pipe rather than an angled pipe, an increased number of the rollers have to be provided to successively bend the material little by little, resulting in excessive initial facility investment costs including manufacturing costs of the plurality of the rollers.

[7] Disclosure of Invention Technical Solution

[8] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method and apparatus for forming a tapered steel pipe which has a constant inclination in a longitudinal direction thereof, and is usable as a post of a street light or electric pole, by reforming an existing cylindrical steel pipe into an angled or circular pipe having a desired shape, rather than successively bending steel plates. Brief Description of the Drawings

[9] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[10] Figs. 1 and 2 are perspective views, respectively, illustrating a post of a general street light, and a general electric pole;

[11] Fig. 3 is an exemplary view illustrating the configuration of a conventional pipe forming machine;

[12] Fig. 4 is an exemplary view illustrating a steel pipe formed by the conventional pipe forming machine;

[13] Fig. 5 is a flow chart explaining a method for forming a tapered steel pipe in accordance with the present invention;

[14] Fig. 6 is a diagrammatic side view illustrating the general configuration of an apparatus for forming a tapered steel pipe in accordance with the present invention;

[15] Figs. 7 and 8 are a front view and a plan view, respectively, illustrating a pipe forming unit of the apparatus for forming a tapered steel pipe in accordance with a first embodiment of the present invention; [16] Figs. 9, 10, and 11 are front views illustrating alternative embodiments of the pipe forming unit in accordance with the first embodiment of the present invention;

[17] Fig. 12 is a front view illustrating a pipe forming unit in accordance with a second embodiment of the present invention;

[18] Fig. 13 is a plan view illustrating the pipe forming unit in accordance with the second embodiment of the present invention;

[19] Fig. 14 is a flow chart explaining a method for forming a tapered steel pipe in accordance with a third embodiment of the present invention;

[20] Fig. 15 is a diagrammatic plan view illustrating sequential steps of forming a steel pipe in a pipe forming unit in accordance with the third embodiment of the present invention;

[21] Fig. 16 is a rear view illustrating the configuration of the pipe forming unit shown in accordance with the third embodiment of the present invention; and

[22] Fig. 17 is a perspective view illustrating the general configuration of the pipe forming unit in accordance with the third embodiment of the present invention. Mode for the Invention

[23] Now, the configuration of the present invention will be explained in detail with reference to the accompanying drawings.

[24] Fig. 5 is a flow chart explaining a method for forming a tapered steel pipe in accordance with the present invention. Fig. 6 is a diagrammatic side view illustrating the general configuration of an apparatus for forming a tapered steel pipe in accordance with the present invention. Figs. 7 and 8 are a front view and a plan view, respectively, illustrating a pipe forming unit of the apparatus for forming a tapered steel pipe in accordance with a first embodiment of the present invention. Figs. 9, 10, and 11 are front views illustrating alternative embodiments of the pipe forming unit in accordance with the first embodiment of the present invention. Figs. 12 and 13 are a front view and a plan view, respectively, illustrating a pipe forming unit in accordance with a second embodiment of the present invention. Fig. 14 is a flow chart explaining a method for forming a tapered steel pipe in accordance with a third embodiment of the present invention. Fig. 15 is a diagrammatic plan view illustrating sequential steps of forming a steel pipe performed in a pipe forming unit in accordance with the third embodiment of the present invention. Fig. 16 is a rear view illustrating the configuration of the pipe forming unit in accordance with the third embodiment of the present invention. Fig. 17 is a perspective view illustrating the general configuration of the pipe forming unit in accordance with the third embodiment of the present invention.

[25] As can be seen from Fig. 5 shown as a flow chart for explaining a method for forming a tapered steel pipe in accordance with the present invention, the method of the present invention basically comprises a pre-forming step for preparing an existing steel pipe, which will be reformed into a tapered steel pipe having a constant inclination in a longitudinal direction thereof, and a main-forming step for tapering the prepared existing steel pipe, as a preform, by means of a pipe forming unit. In such a main-forming step, in order to enable the existing steel pipe to be reformed so that an outer peripheral surface thereof is tapered by a constant inclination in a longitudinal direction thereof, the existing steel pipe is pulled, in the same manner as drawing.

[26] The pre-forming step comprises: step S10 of removing the stress of an existing steel pipe 10 through a plastic forming; step S20 of compressing an outer peripheral surface of a front end region of the stress removed steel pipe 10 by means of compression rollers of a thermo-oαmpression unit 30 so as to form a cone-shaped portion 11, which is a diameter-reduced portion to be inserted into a pipe forming unit 40; and step S30 of fixedly assembling a clamp 13 to the cone-shaped portion 11 formed at the front end region of the steel pipe 10.

[27] A chemical treatment is adopted in the above step S10 for removing the stress of the existing steel pipe 10. Such a chemical treatment comprises the steps of: removing rust of the existing steel pipe 10 through a pickling treatment using sulfuric acid; coating a film for phosphate treatment on the outer peripheral surface of the pickled steel pipe; and applying a coating material for drawing onto the film coated steel pipe. In this way, as the stress of the existing steel pipe is removed, the existing steel pipe is allowed to be more easily reformed in the main-forming step.

[28] The main-forming step comprises: step S40 of pushing the steel pipe 10 so that the front end region of the steel pipe 10, to which is assembled the clamp 13, is fitted in the pipe forming unit 40; step S50 of fixing a traction device 50, which is used to pull the steel pipe 10, to the clamp 13 of the steel pipe 10 fixed in the pipe forming unit 40; step S60 of pulling the steel pipe 10 in a longitudinal direction thereof by means of the traction device 50, so as to cause the steel pipe 10 to pass through the interior of the pipe forming unit 40; and step S70 of controlling the movement of press jigs 44, which are adapted to come into close contact with the outer peripheral surface of the steel pipe 10, so as to be radially moved along guide grooves 42 defined at the pipe forming unit 40, in proportion to a transfer speed (rate) of the steel pipe 10 passing through the pipe forming unit 40. [29] The above described method of the present invention enables the existing steel pipe to be reformed into a tapered steel pipe, having a desired size and shape, even by performing the method only once. However, in case that the existing steel pipe has a relatively large diameter, the method of the present invention may be repeatedly performed two or three times so that the diameter of the steel pipe is gradually reduced

[30] Now, referring to Fig. 6 illustrating the general configuration of an apparatus for forming a tapered steel pipe, having a constant inclination in a longitudinal direction thereof, in accordance with the present invention, the apparatus comprises a plastic forming unit 20, a thermo-oompression unit 30, a steel pipe transfer unit 35, a pipe forming unit 40, a traction device 50, a fixing frame 60, and a controller 70.

[31] The plastic forming unit 20 is adapted to remove the stress of the existing steel pipe 10, and the thermo-oompression unit 30 is adapted to partially compress the front end region of the stress removed steel pipe 10 so as to form a reduced-diameter portion, namely, the cone-shaped portion 11, adapted to be inserted into the pipe forming unit 40. The steel pipe transfer unit 35 is located at a rear side of the pipe forming unit 40, and has a cylinder 36, which is adapted to push a rear end of the steel pipe 10 into the pipe forming unit 40. The pipe forming unit 40 is constructed so that a plurality of press jigs 44, which are assembled in the radially arranged guide grooves 42 in a one to one ratio, reform the outer peripheral surface of the steel pipe 10 to have a desired shape, such as a rectangular, hexagonal, octagonal, circular shape, etc., in a state wherein they come into close contact with the outer peripheral surface of the steel pipe 10. The traction device 50 is positioned at a front side of the pipe forming unit 40, and is adapted to pull a front end of the steel pipe 10, in the same manner as drawing, so as to allow the steel pipe 10 to pass through the interior of the pipe forming unit 40. The fixing frame 60 comprises a pair of guides 61 and 62, which are arranged at both sides of the pipe forming unit 40, and are adapted to guide the transfer of the steel pipe 10. In addition, the guide 61 is used to fixedly support the steel pipe transfer unit 35, and the guide 62 is used to fixedly support the traction device 50. The controller 70 is used to control the operation of both the pipe forming unit 40 and the traction device 50.

[32] In the above described apparatus, the plastic forming unit 20 performs a plastic forming for removing the stress of the steel pipe 10, before the main-forming step, by making use of a chemical treatment effective to the removal of stress. As a result, the plastic forming processed steel pipe 10, as a preform, is allowed to be more easily reformed into a desired shape by means of the pipe forming unit 40. After obtained a completed tapered steel pipe, it can be again endowed with a required stress through a heat treatment, so as to maintain a required strength and stress thereof.

[33] After completing the plastic forming of the steel pipe 10, the stress removed steel pipe 10 is partially compressed at the front end region thereof by means of the thermo- oompression unit 30, so as to form the oone-shaped portion 11. The diameter of the cone-shaped portion 11 is gradually reduced toward the front end thereof, so as to be inserted into the pipe forming unit 40.

[34] The thermo-oompression unit 30, used to form the oone-shaped portion 11 at the front end region of the steel pipe 10, incorporates the compression rollers inside a body thereof. The compression rollers have inclinations suitable for securing them to come into contact with the outer peripheral surface of the steel pipe 10. With such a configuration, as the steel pipe 10 is forcibly pushed into the thermo-oompression unit 30 so that the front end region of the steel pipe 10 oomes into contact with the compression rollers, or as the compression rollers come into contact with the steel pipe 10 in a perpendicular direction thereto during rotation of the steel pipe 10, the steel pipe 10 is partially compressed at the front end region thereof. In this way, the oone- shaped portion 11, which has a gradually reduced diameter, is formed.

[35] To the oone-shaped portion 11 is fixedly assembled the clamp 13 for allowing the steel pipe 10 to be transferred in a longitudinal direction thereof by means of the traction device 50, which is also fixedly assembled to the clamp 13.

[36] Considering Figs. 7 and 8 illustrating the pipe forming unit 40 in detail, the pipe forming unit 40 takes the form of a universal chuck, and comprises a body 41, a plurality of the guide grooves 42: 42a, 42b, 42c,..., 44n, and 42n-l, a plurality of the press jigs 44:44a, 44b, 44c,..., 44n, and 44n-l, a rotating plate 45, and a driving motor 46.

[37] The body 41 is perforated with a center through bore 411 having a relatively large diameter. The guide grooves 42 are defined at one-side surface of the body 41 so that they radially extend from the center through bore 411 to an outer peripheral surface of the body 41 so as to communicate with the center through bore 411. The press jigs 44 are assembled to the guide grooves 42, respectively, so that they oome into contact with the outer peripheral surface of the steel pipe 10 so as to press it. The rotating plate 45 is positioned inside the body 41, and has spiral gears 451, which are adapted to engage with gears 441 of the press jigs 44. The driving motor 46 is assembled inside the body 41, and is adapted to provide a rotating force required to rotate the rotating plate 45. The operation of the driving motor 46 is controlled by the controller 70. [38] Preferably, the number of the guide grooves 42 defined at the body 41, and the press jigs 44 assembled to the guide grooves 42 in a one to one ratio is at least four and less than twelve, respectively, in order to enable them to be selectively used in proportion to the number of workpieces. The press jigs 44 are assembled to the rotating plate 45 operated by the driving motor 46, so that they cooperate with each other.

[39] When viewed from an upper surface of the body 41, the press jigs 44, which are assembled inside the body 41 so as to oome into contact with the outer peripheral surface of the steel pipe 10, are arranged in parallel two rows, which are spaced apart from each other by a certain distance in a forward or rearward direction, in order to prevent interference between adjacent press jigs 44. In addition, the press jigs 44 arranged in the two rows are alternately assembled in the respective guide grooves 42. In this way, the press jigs 44 can uniformly compress the outer peripheral surface of the steel pipe 10 with a more effectively distributed compression force.

[40] Although it is explained in the above description that the press jigs 44 cooperate with each other by means of the rotating plate 45, if necessary, they may independently operate by respective driving motors. In addition, in consideration of wear occurring during forming of the steel pipe 10, it is preferable that the respective press jigs 44 are divided into two portions, namely, a portion adapted to oome into contact with the steel pipe 10, and a portion formed with the gears 441 to engage with the spiral gears 451 of the rotating plate 45, and these two portions are assembled by a separate fastening member 443. This enables partial exchange of a worn or damaged portion.

[41] The controller 70 controls a rotating speed of the rotating plate 45 as well as the driving motor 46, in proportion to the transfer rate (speed) of the steel pipe 10 passing through the pipe forming unit 40, thereby allowing the respective press jigs 44, which cooperate with the rotating plate 45, to radially move along the guide grooves 42.

[42] The traction device 50, for pulling the steel pipe 10, comprises a traction rope 51, such as a steel wire or cable, chain conveyor, or the like, and a rotating drum 52, to which one end of the traction rope 51 is fastened. The rotating drum 52 is adapted to be rotated according to the operation of a driving motor. As the traction rope 51 is wound around the rotating drum 52, the steel pipe 10 is pulled and moved in a longitudinal direction thereof.

[43] The traction device 50 and the pipe transfer unit 35, which are positioned at both sides of the pipe forming unit 40, are fixed to the guides 61 and 62 of the fixing frame 60 so that they are aligned in parallel to each other. [44] Fig. 9 shows an alternative embodiment of the pipe forming unit wherein four press jigs are assembled so as to form a square pipe, Fig. 10 shows another alternative embodiment of the pipe forming unit wherein eight press jigs are assembled so as to form an octagonal pipe, and Fig. 11 shows yet another alternative embodiment of the pipe forming unit wherein twelve press jigs are assembled so as to form a substantially circular pipe.

[45] Reference is now made to Figs. 12 and 13, which are a front view and a plan view, respectively, illustrating a pipe forming unit in accordance with a second embodiment of the present invention. As can be seen from Figs. 12 and 13, the pipe forming unit of the present embodiment, designated as reference numeral 80, comprises fixing brackets 81, which are equally spaced apart from one another along a circumference of the pipe forming unit 80. In the present embodiment, there are four fixing brackets 81. These fixing brackets 81 are integrally connected to one-side ends of hinge logs 82 by making use of fixing pins 83, respectively. The other-side ends of the hinge logs 82 are adhered to forming jigs 84 of the pipe forming unit 80 in a one to one ratio. The forming jigs 84 oome into contact at their outer peripheral surfaces with press jigs 85 so as to vertically move the press jigs 85 according to their rotation.

[46] Meanwhile, although it is shown in the above description that the pipe forming unit 40 takes the form of a universal chuck, hereinafter, a roller type pipe forming unit 90 in accordance with a third embodiment of the present invention will be introduced.

[47] Such a roller type pipe forming unit 90 comprises: a frame 91 having a guide 97 attached at a steel pipe entrance side thereof for preventing deformation of the steel pipe 10; a driving gear 92 mounted at a lower side of the frame 91; a driving motor 93 having a driving shaft 98 fixedly inserted into the center of the driving gear 92; a pair of driven gears 94 positioned at one side of the driving gear 92 so as to cooperate with the driving gear 92; a pair of shafts 95 eccentrically mounted to the driven gears 94, respectively; and a pair of adjoining forming rollers 96 fitted around the shafts 95, respectively. Each of the forming rollers 96 is externally defined in a circumferential direction thereof with a tapered forming groove portion 961.

[48] The pipe forming method in accordance of the present embodiment of the present invention comprises the pre-forming step, and the main-forming step using the pipe forming unit 90.

[49] Similarly to the previous embodiment, the pre-forming step comprises: step SI 00 of removing the stress of the existing steel pipe 10 through a plastic forming; step S200 of compressing an outer peripheral surface of the front end region of the stress removed steel pipe 10 by means of compression rollers of the thermo-oompression unit 30 so as to form the oone-shaped portion 11, which is a diameter-reduced portion to be inserted into the pipe forming unit 90; and step S300 of fixedly assembling a clamp 80 around the oone-shaped portion 11 formed at the front end region of the steel pipe 10.

[50] In the present embodiment, the main-forming step comprises: step Sl-00 of pushing the rear end of the steel pipe 10 so that the front end of the steel pipe 10, around which is assembled the clamp 80, to be inserted into the pipe forming unit 90; step S500 of fixing the traction device 50, which is used to pull the steel pipe 10, to the clamp 80 of the steel pipe 10 fixedly fitted in the pipe forming unit 90; step S600 of pulling the steel pipe 10 in a longitudinal direction thereof by means of the traction device 50, which is connected with a driving unit, so as to cause the steel pipe 10 to pass through the pipe forming unit 90; and step S700 of forming the outer peripheral surface of the steel pipe 10 passing through the pipe forming unit 90.

[51] As can be seen from the above description, the present invention achieves an angled or cylindrical pipe having a desired shape by simply pulling the existing steel pipe 10, which has a circular or square sectional shape and has the same diameter as at both ends thereof, by means of the traction device 50, in a similar manner to a drawing process, so as to pass through the pipe forming unit 40. This has an advantage of considerably simplifying the manufacture of the steel pipe.

[52] In brief, in the pre-forming step, after the existing steel pipe 10 is primarily processed to remove the stress thereof, the oone-shaped portion 11 is formed at one end region of the steel pipe 10, and then the clamp 13 is fixed to the oone-shaped portion 11. In the following main-forming step, after the traction rope 51 of the traction device 50 is connected to the clamp 13, assembled to the one end of the steel pipe 10, the steep pipe 10 is pulled in a longitudinal direction thereof so as to pass through the interior of the pipe forming unit 40 by means of the traction device 50. At the same time with such a passage of the steel pipe 10 through the pipe forming unit 40, the press jigs 44 of the pipe forming unit 40, which are arranged to oome into close contact with the outer peripheral surface of the steel pipe 10, are controlled so as to be gradually spread out in a radial direction along the guide grooves 42. Thereby, the steel pipe 10 is tapered by a constant inclination in a longitudinal direction thereof while passing through the pipe forming unit 40, and thus has different diameters at both ends thereof. Industrial Applicability

[53] As apparent from the above description, the present invention provides a method and apparatus for forming a tapered steel pipe, which has a constant inclination in a longitudinal direction thereof, and is usable as a post of a street light or electric pole, by reforming only an outer peripheral surface of an existing cylindrical steel pipe into an angled or circular pipe having a desired shape, rather than successively bending steel plates, thereby enabling the tapered steel pipe to be more easily and simply manufactured through an automated system, resulting in considerable improvement in productivity and workability. Such an automated system also contributes to worker safety.

[54] Further, according to the present invention, since an inclination value on the outer peripheral surface of the tapered steel pipe is variable by controlling the operation of press jigs of a pipe forming unit or forming rollers of a roller type pipe forming unit, the steel pipe can be easily formed into various shapes. Furthermore, by virtue of the fact that such a control of the pipe forming unit is easily achieved, it is possible to produce uniform finished products and thus improve quality of the products, and to reduce manufacturing cost. This has an effect of enhancing international competitiveness in overseas markets.

[55] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[56]

[57]

[58]

Claims

[1] A method for forming a tapered steel pipe having a constant inclination in a longitudinal direction thereof comprising: a pre-forming step, comprising the steps of: removing the stress of an existing steel pipe through a plastic forming; compressing an outer peripheral surface of a front end region of the stress removed steel pipe by means of compression rollers of a thermo-oompression unit so as to form a oone-shaped portion, the oone-shaped portion having a gradually reduced diameter capable of being inserted into a pipe forming unit; and fixedly assembling a clamp to the oone-shaped portion of the steel pipe; and a main-forming step, comprising the steps of: pushing a rear end of the steel pipe so that the front end region of the steel pipe, to which is assembled the clamp, is inserted into the pipe forming unit; connecting a traction device, which is used to pull the steel pipe, to the clamp of the steel pipe inserted in the pipe forming unit; pulling the steel pipe in a longitudinal direction thereof by means of the traction device, so as to cause the steel pipe to pass through the interior of the pipe forming unit; and controlling the movement of press jigs, which are adapted to oome into close contact with the outer peripheral surface of the steel pipe, so as to be radially moved along guide grooves defined at the pipe forming unit, in proportion to a transfer speed of the steel pipe passing through the pipe forming unit, whereby the outer peripheral surface of the steel pipe is formed to have a constant tapered inclination in the longitudinal direction thereof while passing through the interior of the pipe forming unit.

[2] An apparatus for forming a tapered steel pipe comprising: a plastic forming unit for removing the stress of an existing steel pipe; a thermo-oompression unit for partially compressing a front end region of the stress removed steel pipe so as to form a oone-shaped portion having a gradually reduced diameter capable of being inserted into a pipe forming unit; a steel pipe transfer unit located at a rear side of the pipe forming unit for pushing a rear end of the steel pipe so as to allow the front end region of the steel pipe to be inserted into the pipe forming unit; the pipe forming unit having a plurality of press jigs, which are assembled in radially arranged guide grooves, respectively, and are adapted to compress an outer peripheral surface of the steel pipe to have a desired shape; a traction device for pulling a front end of the steel pipe 10, in the same manner as drawing, so as to allow the steel pipe to pass through the interior of the pipe forming unit; a fixing frame having a pair of guides disposed at both sides of the pipe forming unit for fixedly supporting the steel pipe transfer unit and the traction device, respectively; and a controller for controlling both the pipe forming unit and the traction device.

[3] The apparatus as set forth in claim 2, wherein the pipe forming unit includes: a body perforated with a center through bore having a relatively large diameter; the guide grooves radially defined at one-side surface of the body to communicate with the center through bore; the press jigs assembled to the guide grooves, respectively, and adapted to oome into contact with the outer peripheral surface of the steel pipe; a rotating plate positioned inside the body, and having spiral gears, which are adapted to engage with gears of the press jigs; and a driving motor assembled inside the body, and adapted to provide a rotating force required to rotate the rotating plate, whereby, under the control of the controller, the driving motor rotates the rotating plate in proportion to a transfer speed (rate) of the steel pipe passing through the pipe forming unit, so that the respective press jigs, adapted to cooperate with the rotating plate, radially move along guide grooves.

[4] The apparatus as set forth in claim 2, wherein the pipe forming unit includes: fixing brackets equally spaced apart from one another along a circumference of the pipe forming unit; hinge logs each being connected at one end thereof to an associated one of the fixing brackets by making use of a fixing pin; forming jigs to which the other end of each hinge log is adhered in a one to one ratio; and press jigs coming into contact at their one-side ends with the forming jigs, respectively, so as to be vertically moved according to rotation of the forming jigs.

[5] The apparatus as set forth in claim 2, wherein the pipe forming unit includes: a frame having a guide attached at a steel pipe entrance side thereof for preventing deformation of the steel pipe; a driving gear mounted at a lower side of the frame; a driving motor having a driving shaft fixedly fitted into the center of the driving gear; a pair of driven gears positioned at one side of the driving gear so as to cooperate with the driving gear; a pair of shafts eccentrically inserted and fixed to the driven gears, respectively; and a pair of adjoining forming rollers fitted around the shafts, respectively. [6] The apparatus as set forth in claim 5, wherein each of the forming rollers has a tapered forming groove portion defined along an outer peripheral surface thereof.