STEEL PIPE BENDING APPARATUS AND METHOD

Abstract: The present invention is carried out to supply a small sized and lightweight steel pipe bending apparatus so as to bring to construction sites, so as to keep thinning a thickness of the pipe at lower level and so as to obtain the pipe with a desired bending radius. The following apparatus realizes above-mentioned objectives of the present invention. A pipe bending apparatus comprises a heater (10, 11, 12) to heat a steel pipe (1) circularly around a center axis of the pipe, a tensile force applying mechanism (2, 3, 4, 5) to apply the tensile force on points of application which are located in the opposite directions from the circular heated portion, a variable controlling regulator (16, 19, 20) to control the tensile force variably, a transfer unit (7, 28, 31) to transfer the heated portion and the steel pipe relatively to the heater in the direction of the axis of the steel pipe and a controlling unit (14, 20) to control a velocity of the transfer.

Description: D E S C R I P T I O N STEEL PIPE BENDING APPARATUS AND METHOD Technical Field The present invention relates to an apparatus and a method for bending a steel pipe. Background Art FIG. 10 shows a conventional steel bending apparatus. A bending procedure according to this apparatus is carried out as follows: (1) As shown in FIG. 10 a steel pipe 51 to be bent is placed between a pair of support rollers 52 and rear end of the pipe facing a pusher 54 is held by a tail-stock 53. The front end of the pipe is held by an arm clamp 57 attached to a pivotal arm 56 which revolves the front end of the steel pipe 51 around a pivot 55. (2) Power is supplied to a heating coil 60 via a heating unit 62. Then as shown in FIG. 11, the steel pipe 51 is pushed through a pair of guide rollers 58 and 59 disposed right and left sides of the pipe by the pusher 54 in the direction of an axis of the steel pipe, is transferred toward heating coil 60 and is passed through the coil 60. In this way, the pushed steel pipe 51 is successively heated with induced current from the heating coil 60. Since the coil has a circular shape, the periphery of the steel pipe 51 is heated circularly around the axis of the pipe. As shown in FIG. 12, since the front side of the heated portion of the pipe is cooled successively by water 62 spouted from a plurality of holes h formed circularly on a circular channel 60a of the coil 60 so as to obtain a cooled circular portion c of the steel pipe 51, only a portion t having a width , of the steel pipe 51, virtually remains in a heated state. The locally heated portion t successively transfers toward the rear end of the pipe as the steel pipe 51 transfers forward. The temperature of the locally heated portion t is kept over a crystallization temperature of the pipe. In the case of a carbon steel pipe, for example, the heated zone having a predetermined width W in the direction of the steel pipe axis is kept between about 760 * 0 to 900°C. The front end of the steel pipe 51 is transferred forward by a successive pushing force from the pusher 54. However, since it is fixed by the arm clamp 57 attached to the pivotal arm 56, the steel pipe is forced to bend successively at the locally heated portion t. However, there are the following problems in the conventional steel pipe bending apparatus. (1) Since enough rigidity is necessary to cope with a bending moment of the steel pipe and with an applied restraining force to the steel pipe via the pivotal arm, a massive and huge pipe bending apparatus is required. Therefore, because of the interior portability of the apparatus, a large lot of pipes have to be bent at bending plants situated far from construction sites. Which is inevitably accompanied with the following drawbacks. CD At first, straight pipes are transported to a pipe bending plant and bent pipes are transported to construction sites by trucks or ships. Bent pipes occupy more voluminous space, namely, higher transportation costs are inevitable. (D It is difficult to adjust pipe bending schedules flexibly according to modified schedules or designs or additional orders which often occur at sites such as plants and pipelines construction sites etc. (2) According to the conventional method, since a compression force is imposed in the direction of the axis of the steel pipe due to the restraining force to the steel pipe moving forward via the pivotal arm, thinning a thickness of the pipe is prevented to a certain extent, but which is not satisfactory yet. In order to compensate such thinning thickness of the pipe, a one gage thicker pipe compared with a straight pipe to be connected with the bent pipe, is employed as the pipe for bending. Disclosure of Invention The present invention is carried out in view of the above-mentioned technical background to provide a steel pipe bending apparatus and a method having an excellent portability, having a good performance to minimize the thinning the thickness of the pipe during the bending procedure and having a flexible control on the bending radius. The present invention provides the following pipe bending apparatuses. (1) An apparatus of steel pipe bending comprises; a heating means to heat the steel pipe circularly around a center axis of the pipe, a cooling means to cool the heated portion of the pipe circularly around the center axis of the pipe, a tensile force applying means to apply the tensile force on points of application which are located in the opposite directions from the circularly heated portion, a variable controlling means to control the tensile force variably, a transfer means to transfer relatively the steel pipe and the heating means and the cooling means in a direction of the axis of the steel pipe and a controlling means to control the relative transfer velocity (hereinafter referred as "the first apparatus" ) . (2) An apparatus of steel pipe bending comprises; a heating means to heat the steel pipe circularly around an center axis of the pipe, a cooling means to cool the heated portion of the pipe circularly around the center axis of the pipe, a tensile force applying means to apply the tensile force on points of application which are located in the opposite directions from the circularly heated portion, a variable controlling means to control the tensile force variably, a transfer means to transfer relatively the steel pipe and the heating means and the cooling means in a direction of the axis of the steel pipe, a controlling means to control the relative transfer velocity and a scale to measure bent values stepwise according to a predetermined bending schedule (Hereinafter referred as "the second apparatus"). The present invention provides the following pipe bending methods. (1) A method of steel pipe bending comprises; forming a locally heated circular portion around a center axis of the steel pipe, relatively transferring the locally heated portion and the steel pipe in a direction of the center axis of the steel pipe and controlling the relative transfer velocity of the heated portion and the steel pipe during a bending procedure by applying a tensile force between two points of application which are located in the opposite directions from the heated portion along an eccentric axis of the steel pipe (Hereinafter referred as "the first method" ) . (2) A method of steel pipe bending comprises; forming a locally heated circular portion around a center axis of the steel pipe, relatively transferring the locally heated portion and the steel pipe in a direction of the center axis of the steel pipe, measuring actual bent values stepwise during a successive bending procedure according to a bending schedule where bent values are predetermined stepwise and controlling the relative transfer velocity of the heated portion and the steel pipe during the bending procedure by applying a tensile force between two points of application which are located in the opposite directions from the heated portion along an eccentric axis of the steel pipe according to a difference between the predetermined bent value and the actual bent value (hereinafter referred as "the second method" ) . Brief Description of Drawings FIG. 1 is a plan view with a partial cutout of a pipe bending apparatus according to a first embodiment of the present invention; FIG. 2 is a view for showing a pipe bending movement of the pipe bending apparatus according to the first embodiment; FIG. 3 is a plan view with a partial cutout of a pipe bending apparatus according to a second embodiment of the present invention; FIG. 4 is a view for showing a pipe bending movement of the pipe bending apparatus according to the second embodiment; FIG. 5 is a plan view of an essential part of the pipe bending apparatus according to the second embodiment; FIG. 6 is a plan view with a partial cutout of a pipe bending apparatus according to a third embodiment of the present invention; FIG. 7 is a plan view with a partial cutout of a modification of the pipe bending apparatus shown in FIG.6; FIG. 8 is a plan view with a partial cutout of a pipe bending apparatus according to a forth embodiment of the present invention; FIG. 9 is a view for showing a pipe bending movement of the pipe bending apparatus according to the forth embodiment; FIG. 10 is a plan view with a partial cutout of a conventional pipe bending apparatus; FIG. 11 is a view for showing a pipe bending movement of the conventional pipe bending apparatus; and FIG. 12 is an enlarged cross-sectional view of the heating coil in FIG. 10 in which a temperature distribution curve in the vicinity of a heated portion along an axis of the steel pipe is shown. Best Mode for Carrying Out of the Invention Hereinafter the detailed embodiments of the present invention are described with reference to drawings . First embodiment FIG. 1 is a plan view with a partial cutout of a pipe bending apparatus according to a first embodiment and FIG. 2 shows a pipe bending movement of the pipe bending apparatus. An embodiment of the first method is realized by employing the pipe bending apparatus shown in FIGS. 1 and 2. In these figures, a reference numeral 1 represents a steel pipe, front and rear ends of which are clamped by a front cramping plate 2 and a rear cramping plate 3, respectively. A reference numeral T represents a tensile force application unit that applies a tensile force between the plate 2 and the plate 3. The unit T comprises a chain 4 and a hydraulic jack 5 which supplies the tensile force to the chain. A front end of the chain 4 is swingably attached to the front cramping plate 2 and a rear end of the chain is swingably attached to the hydraulic jack 5 is fixed to the rear cramping plate 3. The front and rear ends of the chain 4 are aligned in an eccentric axis line parallel to a central axis of the attached steel pipe 1. The both ends of the chain are served as application points of the tensile force applied to the chain 4 by the hydraulic jack 5. An adjustable wheel unit having a plurality of wheels, which is attached to the front cramping plate 2 to support the weight of the steel pipe may freely move on a horizontal floor Alternately, the front end of the pipe may be directly or indirectly laid on the wheel unit. A steel pipe transfer unit 7 to which the rear cramping plate 3 is fixed, may transfer along rails 9 laid on opposite supports 8 and extending in the direction of the axis of the steel pipe 1. A reference numeral 10 represents a heating coil which coaxially positioned around the steel pipe 1 to heat a periphery of the steel pipe 1 and a reference numeral 11 represents a heating unit. Via a coil holder 12, the heating coil 10 is supported by a frame of the heating unit 11 which is fixed to a support 13. The detailed structure and functions of the heating coil are similar to the conventional one shown in FIG. 12. The steel pipe transfer unit 7 may be electrically driven along the rails and its transfer velocity is manually adjustable by a velocity regulator 14 which may be operated by an operator with referring to a measured value from a velocity indicator 15 for the steel pipe transfer. The tensile force or tensility supplied from the hydraulic jack 5 to drag the chain 4 is manually adjustable by a tensile force regulator 16 with referring to a measured value from a tensile force indicator 17. The tensile force supplied from the hydraulic jack is adjustable by adjusting a drag velocity of the chain, since the tensile force and the drag velocity of the chain correlate with each other. In this embodiment, the drag velocity of the chain derived from the hydraulic jack 5 may be manually adjusted by a drag velocity regulator 18 with referring to a measured value from a tensile velocity indicator 19. A ratio of the drag velocity of the chain 4 to a relative velocity between the locally heated portion t (see FIG. 12) and the steel pipe 1 is adjusted by a velocity ratio regulator 20 and its measured value is displayed on a velocity ratio indicator 21. Heated temperature of the steel pipe 1 by the heating coil 10 and temperature of cooling water 62 for cooling the heated zone of the pipe 1 may be controlled by controlling means (which are not shown in figures). Herein after a steel pipe bending procedure is described according to the apparatus with the above- mentioned constitution. The steel pipe 1 is transferred forward by driving the steel pipe transfer unit 7 and the hydraulic jack 5 applies a predetermined tensile force to the chain 4. Thus, the steel pipe 1 is bent continuously at the locally heated portion t (see FIG. 12) which relatively transfers backward successively receiving a compression force in the direction of the eccentric axis of the steel pipe, since the both ends of the chain 4 are aligned on the eccentric axis. If the drag velocity of the chain 4 is increased (i.e. the tensile force is increased), a bent radius of the steel pipe can be decreased due to an increasing bent amount per unit time. On the other hand, if the drag velocity of the chain 4 is decreased (i.e., the tensile force is decreased), the bent radius of the pipe can be increased due to a decreasing bent amount per unit time. Alternately, if the transfer velocity of the steel pipe transfer unit 7 is decreased the bent radius of the pipe can be decreased due to the same reasons mentioned above. Consequently, if a ratio VI/V2, where VI is the drag velocity of the chain 4 and V2 is the transfer velocity of the steel pipe transfer unit 7, is increased, the bent radius is decreased, and vice versa. As described in the embodiment, when a bending procedure of the steel pipe is executed by applying the tensile force to the two points of application aligned on the eccentric axis of the steel pipe 1, the bent radius of the steel pipe 1 can be controlled to be predetermined value, for example according to a bending curve depicted on a floor, since the above-mentioned tensile velocity (i.e. tensile force) and the relative velocity of the above-mentioned locally heated portion and the pipe can be controlled. Such a bending procedure may be made in a real time continuously or intermittently by manually adjusting at least one of the regulators 14,16,18,20 according to the measured value or values displayed on the respective indicator or indicators 15,17,19,21. In the first embodiment, during the bending procedure, thinning the thickness of the pipe is suppressed, since the steel pipe is compressed in the longitudinal direction by applying the tensile force between the two points of the application along the eccentric axis of the steel pipe. In addition, in the first embodiment, since the steel pipe can be bent by employing the tensile force application unit, it is possible to render the pipe bending apparatus smaller and lighter. Thus, it is not necessary to prepare a massive and heavy apparatus to cope with a huge bending moment as seen in the conventional pushers (to apply pressing force) and pivotal arms. Therefore the present invention enables the pipe bending apparatus to be portable and to be set up on construction sites more easily. Second embodiment FIGS. 3 and 4 show an apparatus according to a second embodiment. An embodiment of the second method is realized by the steel pipe bending apparatus in the second embodiment. The steel pipe bending apparatus in the second embodiment employs the same apparatus in the first embodiment except having an additional measuring instrument (hereinafter referred as "scale") S, indicators 23, and a measuring instrument 24. The scale revolves according to the bending procedure of the steel pipe 1 and measures expanded or contracted value of a telescopic rod assembly or arm of the scale S in accordance with a revolved angle θ so as to measure a bent value (hereinafter referred as "actual bent value") of the steel pipe 1 in a real time continuously or intermittently. The indicator 23 displays bent value, the measuring instrument 24 determines a revolved angle of the scale S, and the indicator 25 displays a revolved angle of the scale S. Except instruments and indicators relevant to the scale S, the pipe bending apparatus has the same configuration as the first embodiment. Since in FIGS. 3 and 4, the same reference numerals are used to represent the same or similar manners and units as in FIG. 1, a detailed explanation of the apparatus is omitted. The above-mentioned scale S comprises a cylinder 22a and a sliding rod 22b built in the cylinder 22a so as to ensure expandable movement. A distal end of the rod 22b is pivotably attached to a circular metal fitting 26 secured to the outer periphery of the front end of the steel pipe 1 via a shaft B fixed to the fitting so as to revolve relatively to the fitting 26. A proximal end of the cylinder 22a is pivotably attached to the frame of the heating unit 11 via a shaft A fixed to the frame so as to revolve relatively to the frame. The scale S revolves around the shaft A in accordance with the bending procedure of the steel pipe 1 by keeping its length constantly or variably, and the shaft B plays an outermost revolving point of the scale S. A reference numeral C represents a center line in the diameter direction of the heating coil 10 perpendicular to an axis line or central axis C2 of the steel pipe 1 on a parallel plane to the floor. The revolving center A is aligned on the extended line of Cι« In FIG. 3, a cross point D where the axis line C2 and the center line Ci are crossed with each other is a bending initiation point of the steel pipe 1. As shown in FIG. 3, before bending, the scale S is arranged at a position with a revolved angle a (hereinafter referred as "initial position") from the center line Ci and at this stage the revolving point B is situated ahead of the above-mentioned cross point D on the axis line C2. In this embodiment the initial angle a is set at a predetermined angle, for example, 20 degrees. The above-mentioned "actual bent value" is expressed as an extended or contracted value of the scale S at a revolved angle θ of the scale when the length of the scale S at the initial position is set zero. The extended or contracted value is displayed on the indicator 23. The revolved angle θ of the scale S is determined by the measuring instrument 24 and then the determined value θ is displayed on the indicator 25 By employing the steel bending apparatus with above-described constitution according to the second embodiment, for example, a 90 degree bending procedure where the shaft A is set as the revolution point of the scale S and a bending radius R is set as a distance between the cross point D and the revolution point A of the scale S (i.e., shaft A), is executed as follows. ( 1 ) A bending schedule table as shown in Table 1 where the length of the scale S is exhibited in relation to the revolved angle θ of the scale S is prepared beforehand. The length of the scale S at the angle θ (1 to 90 degrees) in the Table 1 means the scheduled value expressed in mm when the value is set zero at the initial position. Table 1 (2) In the same way as in the first embodiment, the steel pipe 1 is successively bent by driving the steel pipe transfer unit 7 so as to transfer the steel pipe forward and applying the tensile force to the chain 4 from the hydraulic jack 5 with referring to the Table 1. As shown in FIG. 4, the steel pipe 1 is continuously bent at the heating portion t (FIG.12) which successively transfers backward receiving applied compression force in the direction of the eccentric axis line of the pipe. (3) During the bending procedure, if the actual bent values displayed on the indicator 23 are, for example, values in Table 2, the above-mentioned tensile velocity VI from the hydraulic jack 5 and the transfer velocity V2 of the steel pipe transfer unit 7 are controlled so that the actual bent values attain the same values as scheduled ones. This controlling may be accomplished by a manual while looking the indicator 23, or an automatic manner using a CPU including a memory and/or inputting means for a scheduled bending figure, (not shown) connected between the scale S and the regulators 14, 16, 18, 20 to actuate the regulator according to a signal showing a measured bending angle, outputted from the scale. Table 2 Since the actual bent value, for example, +1 means that the actual bending amount is less than the scheduled one, the adjustment is made by increasing the above-mentioned tensile velocity VI, decreasing the transfer velocity V2 or increasing the ratio (V1/V2). When the actual bent value shows -1, the opposite controlling measure is taken. In the bending procedure depicted in FIGS. 3 and 4, the center of the bending radius R is set at the revolving center A of the scale S. However, the bending radius of the steel pipe 1 can be increased by setting the center of the radius at E situated on the extended center line Ci of the heating coil 5 apart from the revolving center A of the scale S so as to obtain the bent pipe with a larger radius Rj_ as shown in FIG. 5. In order to obtain the bent steel pipe 1 with radius R]_, the scheduled bent values are prepared, for example, as shown in Table 3. Scheduled bent values are exhibited in the table, when a distance between the revolving center A and the bent initiating point D is set 200 mm and bent radius R^ is set 500 mm. The scheduled bent values are increased as revolved angles θ are gradually increased up to 90 degrees. Table 3 Though not shown in figures, the center of the bending radius of the steel pipe 1 can be set on the extended center line Ci at the same side of the heating coil apart from the revolving center A. If the bending radius is gradually increased or decreased at the bending initiation point and ending point, fluctuation of the thickness of the bent pipe in the vicinity of these points can be made more moderate. In this case the bending procedure is executed in the same way as described above. Third embodiment FIG. 6 illustrates an apparatus according to a third embodiment of the invention. The embodiment of the second method is realized by the steel pipe bending apparatus in the third embodiment. The above-mentioned steel pipe bending apparatus in the second embodiment is constituted so that the heating coil 10 is fixed and the steel pipe 1 is transferred. In the third embodiment, on the other hand, the steel pipe bending apparatus is constituted so as that the steel pipe 1 is fixed and the heating coil is transferred along the steel pipe. Namely, the bending apparatus is constituted such that the rear cramping plate 3 is fixed to a support 27 and the heating coil 10 is attached to a coil transfer unit 28 and transferred by along the steel pipe 1. A transfer velocity of the coil transfer unit 28 is controlled by a velocity regulator 29 of the unit referring displayed value on an indicator 30 of the transfer velocity. Other configuration is virtually the same as the second embodiment. Also the bending procedure is carried out in the same way as in the second embodiment. The above-mentioned coil transfer unit 28 transfers on the steel pipe 1, but the coil may be transferred by another type of a coil transfer unit 31 having wheels runing on a rail 33 fixed to a support 32 as shown in FIG. 7. In this case, the transfer velocity of the coil transfer unit 31 controlled by a velocity regulator 34 with referring to a measured value displayed on a velocity indicator 35 of the coil transfer velocity. In this case the bending procedure is also executed in the same way as the second embodiment. Forth embodiment FIGS. 8 and 9 illustrate fourth embodiment of the present invention. The embodiment of the second method is realized by the steel pipe bending apparatus in the forth embodiment. The pipe bending apparatus in the forth embodiment employs an extendable scale Si in place of the scale S in FIG. 3. The other configuration is the same as the second embodiment as shown in FIG. 3. One end of a rod 36 constituting the scale Si is pivotably attached to the circular fitting 26 via a shaft F so as to revolve around the shaft, the other end of the rod is inserted in a cylinder 37 . One end of the cylinder is attached to a rail 39 mounted on a support 38 via a slider 40 so as to slide along the rail. The rail 39 is fixed to the support 38 parallel to the central axis C2 of the steel pipe l,and the scale S j _ is attached to the rail 39 to be parallel to the center line Ci of the heating coil. The rail 39 in this embodiment is served as a guide rail for scale S during the bending procedure as shown in FIG. 9, and also as a measuring instrument to determine a transferred distance of the scale Si by using a conventional position detecting means. An "actual bent value" in the forth embodiment is expressed as an extended value of scale Si according to a transferred distance L of the scale Si along the rail 39 when the length of the scale S before the bending procedure is set zero as shown in FIG. 8. The extended value of the scale Si is displayed on an indicator 41. The transferred distance L of the scale Si, determined by the measuring instrument (rail) 39, is displayed on an indicator 42 to display the transferred distance. By employing the steel bending apparatus with the above-mentioned constitution where a bending radius R2 is set as a distance between a center point A on the extended center line Ci and the initiation point D of the bending on the steel pipe 1, a 90 degree bending of the steel pipe 1 is executed as follows. ( 1 ) A bending schedule table as shown in Table 4 where a length of the scale Si is given in relation to a transferred distance L of the scale Si is prepared beforehand. In this Table, scheduled bent values are exhibited when the bending radius is set 500 mm. The length of the scale Si in relation to the transferred distance L means the "scheduled bending value" expressed in mm of the steel pipe 1 when the length of the scale Si is set zero before the bending. Table 4 (2) The steel pipe 1 is successively bent by driving the steel pipe transfer unit 7 so as to transfer the steel pipe forward and applying the tensile force to the chain 4 from the hydraulic jack 5 with referring to the table, in the same way as the first embodiment. The steel pipe 1 is continuously bent at the heating portion t that successively transfers backward receiving compression force in the direction of the eccentric axis line of the pipe. (3) During the bending procedure, if the "actual bent values" displayed on the indicator 41 are, for example, values in Table 5, the above-mentioned tensile velocity VI of the hydraulic jack 5 and the transfer velocity V2 of the steel pipe transfer unit 7 are manually controlled so that the "actual bent values" attain the same values as scheduled ones. Table 5 For example, if the difference is +1.3, namely, it means the actual bent amount is less than the scheduled one, either a measure to increase the tensile velocity VI, a measure to decrease the transfer velocity V2 or a measure to increase the ratio (V1/V2) is employed. If the difference is -2.0, namely it means the actual bent is more than the scheduled one, the opposite controlling measure is taken. The bending schedules in the embodiments 2 to 4 mentioned above may be stored in recording media as computer programs so as to execute computer controlled bending procedures, like the first embodiment. As explained, above-mentioned constitutions according to the present invention attain, the following effects. (1) The bending procedure of metal elongated members such as pipes or rods, for example made of steel can be executed on construction sites in accordance with a progress of the construction, since the present invention realizes a small sized, lightweight and portable steel pipe bending apparatus. (2) Thinning thickness of the steel pipe during the bending procedure can be kept to a lower extent, since the compression force is applied in the longitudinal direction of the steel pipe by the tensile force applying means . (3) Bending accuracy of the steel pipe can be improved, since the bending amount of the steel pipe is controlled successively and stepwise.

Claims: C L A I M S 1. An apparatus for bending a metal elongated member (1) comprising: heating means (10, 11, 12) to heat a peripheral portion (t) of the elongated member (1) having a central axis (C2); and bending means for bending the elongated member at its heated peripheral portion to form a bending portion characterised in that said bending means comprises: tensile force applying means (2, 3, 4, 5) to apply a tensile force on two points which are located in the opposite directions from said heated portion of the elongated member and displayed from the central axis of the elongated member so that the elongated member is applied with the tensile force along the central axis; first controlling means (16, 19, 20) to control said tensile force; transfer means (7; 28; 31) to transfer relatively said elongated member and said heating means in a direction of the central axis of said elongated member; and second control means (14, 20) to control said relative transfer velocity. 2. The apparatus according to claim 1, characterised in that said transfer means transfers cooling means (60) for cooling the heated peripheral portion (t)of said elongated member, in relative to the elongated member. 3. The apparatus according to claim 1 or 2, characterised in that said first control means includes means for measuring the tensile force applied on two points of the elongated member and indicating the measured tensile force in a real time. 4. The apparatus according to any one of claims 1 to 3, characterised in that said second control means includes means for measuring the relative transfer velocity of the elongated member and heating means, and indicating the measured relative transfer velocity in a real time. 5. The apparatus according to any one of claims 1 to 4, characterised in that said tensile force applying means includes a first attachment (2) attached to one end of the elongated member, a second attachment (3) attached to the other end of the elongated member, a jack mechanism (5) fixed to the second attachment, and a chain (4) having one end connected to the first attachment at one of said two point and the other end connected to the jack mechanism at the other of said two point, wherein the jack mechanism drags the elongated member in the central direction. 6. The apparatus according to claim 5, characterised by further comprising third control means (18) for controlling a drag velocity. 7. The apparatus according to any one of claims 1 to 6, characterised by further comprising measuring means (S) for measuring the bending radius of bent portion of the elongated member in a continuous or intermittent real time so that at least one of said first and third control means is controlled according to the measured bending radius during a bending process, 8. The apparatus according to claim 7, characterised in that said measuring means includes a telescopic rod assembly (22a, 22b; 36, 37) which measure actual bent values of the bending portion of the elongated member by expanding or contracting according to the actual bent radius of the bending portion. 9. The apparatus according to claim 8, characterised in that said measured actual bent values value are compared with scheduled bent values and at least one of said first and third control means may be controlled according to the difference values between the actual vents values and scheduled bent values. 10. The apparatus according to claims 1, characterised in that said metal elongated member is a steel pipe. 11. A method of bending a metal elongated member comprising the steps of forming a locally heated circular portion on the elongated member; transferring the locally heated portion of said elongated member in a direction of a central axis thereof; bending the heated portion of the elongated member by applying a tensile force and/or dragging force between two points of application which are located in the opposite directions from said heated portion along an eccentric axis of said elongated member; and controlling at least one of said tensile force, dragging force and a transition velocity of the heated portion. 12. The method according to claim 11, characterised by further comprising a step of measuring bent radiuses of the bent portion of the elongated member, so that said controlling step is accomplished by the measured bent radiuses in a continuous or intermittent time during the bending step.

Inventors: SATOH TORU, SATOH, TORU
Applicants: SATOH TORU, SATOH, TORU
Application year: 2001
Main classification: B21D7
IPC codes: B21D7