Tube production machine

Abstract: A welding management apparatus for use with a tube production machine. A workpiece (1) fed from a roll of metal strip is formed in a tubular formation having side surfaces (1b,1c) opposite to each other. An upsetting pressure is applied to joint the opposite side surfaces of the workpiece at a jointing point. A high frequency power is supplied to the workpiece (1) to weld the opposite side surfaces (1b,1c) at the jointing point (1a) so as to produce a metal tube member. The welding management apparatus comprises a camera (40) positioned to have a visual field including the jointing point (1a) for producing a video signal (S₁) indicative of an image including an area luminous with a pre-arc produced in the visual field. An image processor (50) converts the video signal (S₁) into a luminance distribution pattern. An inference unit (60) is provided for inferring a defective welding condition based upon the luminance distribution pattern. The inference unit (60) includes an alarm unit (66) for producing an alarm when a defective welding condition is inferred.

Description: Background of the invention This invention relates to a tube production machine comprising means for forming a workpiece fed from a roll of metal strip in a tubular formation having side surfaces opposite to each other, a pair of squeeze rollers for providing an upsetting pressure to joint the opposite side surfaces of the workpiece at a jointing point, each of the squeeze rollers having a cylindrical shape with an annular groove in the side peripheral surface thereof to define a path for the workpiece along with the annular groove of the other squeeze roller, a roller holder for bearing each of the squeeze rollers, and means for supplying a high frequency power to the workpiece to weld the opposite side surfaces at the jointing point so as to produce a metal tube member. This invention also relates to a method for producing metal tubes. Tube production machines have been employed to produce a metal tube member by forming a workpiece fed from a roll of metal strip in a tubular formation having side surfaces opposite to each other, providing an upsetting pressure to butt the opposite side surfaces of the workpiece at a jointing point, and supplying a high frequency power to the workpiece to weld the opposite side surfaces at a welding point. Document BE-A-530,877 discloses a tube production machine of the kind mentioned above. It is known that squeeze rollers of tube production machines are supported at only one end by a shaft. The diameter of the supporting shaft is limited by the minimum diameter of the squeeze rollers. Consequently, for a high pressure on the workpiece the squeeze rollers of such tube production machines require a rather big size thereof and such known tube production machines cannot be used to produce small tubes. It is therefore an object of the invention to provide a tube production machine with smaller squeeze rollers which can bear high pressure forces. A further object of the present invention is to provide a tube production machine which can produce tubes having a diameter of 8 mm or less. A still further object of the present invention is to improve the method of producing a metal tube. These objects are achieved by a tube production machine of the above described kind which is characterized in that each of the squeeze rollers is a one-piece member having a cylindrical centre portion and upper and lower cylindrical end portions extending coaxially in opposite directions from the centre portion, the annular groove being formed in the side peripheral surface of the centre portion, and the upper and lower cylindrical end portions being formed for rotation in unison with the cylindrical centre portion, and in that the squeeze rollers are supported in the roller holder at their end portions. The improved method is achieved by the features of claims 4 and 5. Brief description of the drawings This invention will be described in greater detail by reference to the following description of preferred embodiments taken in connection with the accompanying drawings, in which: Fig. 1 is a fragmentary perspective view showing the welding section included in a conventional tube production machine; Fig. 2 is a sectional view showing a specified form of the squeeze roller arrangement; Fig. 3 is a plan view showing the squeeze roller arrangement of Fig. 2; Fig. 4 is an enlarged elevational view showing the squeeze roller included in the squeeze roller arrangement of Fig. 2; Fig. 5 is a fragmentary sectional view showing a modified form of the squeeze roller arrangement; Fig. 6 is a fragmentary plan view showing the squeeze rollers used in the tube production machine; Fig. 7 is a fragmentary elevational view showing the squeeze rollers used in the tube production machine; Fig. 8 is a graph of tube diameter versus squeeze roller diameter; Fig. 9 is a graph of tube diameter versus V throat angle; Fig. 10 is a perspective view showing a modified form of the squeeze roller arrangement; Fig. 11 is a plan view of the squeeze roller arrangement of Fig. 10; and Fig. 12 is a sectional view of the squeeze roller arrangement of Fig. 10. DETAILED DESCRIPTION OF THE INVENTION As schematically shown in Fig. 1 a known tube production machine, generally designated by the numeral 10, employs forming rollers arranged in a number of stages to form a workpiece 1 fed from a roll of metal strip in a tubular formation. A pair of squeeze rollers 13a and 13b are positioned on the opposite sides of the workpiece 1 and they provide an upsetting pressure to joint the opposite side surfaces of the workpiece 1 at a jointing point 1a just upstream of a point intermediate between the squeeze rollers 13a and 13b. A heating coil 12 is positioned to surround the workpiece 1 at a position upstream of the jointing point 1a. The heating coil 12 is supplied with a high frequency power to produce a highly concentrated, rapidly alternating magnetic field so as to induce an electric potential in the workpiece 1. This electric potential causes heating because of I 2 ·R losses at a welding point just downstream of the jointing point 1a where the opposite side surfaces 1b and 1c of the workpiece 1 are welded. The V-shaped gap, which is defined near the jointing point 1a by the opposite side surfaces 1b and 1c of the workpiece 1, is referred to as a V throat. The heating coil 12 is powered from a high frequency power source 20. Referring to Figs. 2 to 5 there is illustrated a first embodiment of the tube production machine of the invention. In this embodiment, the tube production machine employs a pair of squeeze rollers 70 each of which is a one-piece member having a cylindrical center portion 70a and upper and lower cylindrical end portions 70c and 70d extending coaxially from the upper and lower surfaces of the cylindrical center portion 70a. The cylindrical end portions 70c and 70d have a diameter somewhat shorter than the diameter D SQR of the cylindrical center portion 70a. The cylindrical center portion 70a is formed in its side peripheral surface with an annular groove 70b. The squeeze rollers 70 are juxtaposed in parallel with each other so as to applying an appropriate upsetting pressure to the curved workpiece 1 passing the space defined by the annular grooves 70b of the respective squeeze rollers 70. The squeeze rollers 70 are supported on separate roller holders 72 each of which has upper and lower rigid arms 72a extending in spaced-parallel relation to each other. The upper and lower rigid arms 72a are formed near their ends with coaxial holes 72b for receipt of the upper and lower end portions 70c and 70d. The squeeze roller 70 is supported rotatably between the upper and lower arms 72a with its upper and lower end portions 70b and 70c inserted in the respective holes 72b. The roller holders 72 are bolted on respective sliders 74 mounted for sliding movement on a roller stand (not shown). A conventional sliding mechanism, for example, of the type including a screw rod 76, is provided to move the sliders 74 toward and away from each other so as to adjust the distance between the squeeze rollers 70 and thus the upsetting pressure applied to the workpiece 1. This arrangement can reduce the size of the squeeze rollers 70 without any reduction in their strength. It is, therefore, possible to place the squeeze rollers 70 closer to the induction coil 12 without interference of the squeeze rollers 70 with the induction coil 12 so as to improve the welding heat efficiency. It is also possible to produce small-diameter tubes having a diameter of 8 mm or less for which the conventional apparatus cannot be used. It is preferable to avoid induction heating of the squeeze rollers 70 by making the squeeze rollers of an insulating material such as ceramics. It is also preferable to provide bushes 78 for bearing the squeeze rollers 70, as shown in Fig. 5. The busties 78 may be made of special bearing metal or the like. Referring to Figs. 6 and 7, a small-diameter tube is produced while the curved workpiece 1 passes between the squeeze rollers 70. It is now assumed that the squeeze rollers 70 has a maximum diameter D SQR and the small-diameter tube has a diameter Dp. If the squeeze roller diameter D SQR increases, the distance ℓ v of the induction coil 12 from the welding point 1a intermediate between the squeeze rollers 70 should be increased to avoid the interference of the squeeze roller 70 with the induction coil 12. The greater the distance ℓ v , the greater the resistance of the electric path extending from the induction passage 12 to the welding point 1a. As a result, the ratio of the current flowing to the welding point 1a to the current circulating through the workpiece 1 in the direction of the circumference of the curved workpiece 1 increases. Consequently, the welding heat produced at the welding point 1a decreases for the same power applied to the induction coil 12. In addition, the workpiece 1 is softened by the heat conducted over the entire area of the workpiece so that the V throat cannot be maintained at a constant angle . The inventors have discovered an acceptable range of the squeeze roller diameter D SQR from tests conducted to change the squeeze roller diameter D SQR for workpieces having various widths ranging from 11 mm to 25 mm. The test results are illustrated in Fig. 8. As can be seen from the test results, it is preferable that the squeeze roller diameter D SQR be in an acceptable range defined by first and second lines La1 and Lb1. The first line La1 is presented as 5.5 x Dp and the second line Lb1 is presented as 2.5 x Dp. Assuming now that the tube diameter Dp is 6.35 mm, the acceptable range of the squeeze roller diameter D SQR extends from 15.9 mm to 32.9 mm. Assuming now that the tube diameter Dp is 4 mm, the acceptable range of the squeeze roller diameter D SQR extends from 10.1 mm to 20.8 mm. If the squeeze roller diameter D SQR is greater than the acceptable range, the distance ℓ v is too long. If the squeeze roller diameter D SQR is less than the acceptable range, the squeeze rollers 70 will have an insufficient strength against the reaction force produced in response to an upsetting pressure applied to the workpiece 1. A seam guide 3 is placed between the opposite side surfaces 1b and 1c of the workpiece 1 to increase the angle  of the V throat so as to shorten the distance Lsg. The inventors have discovered an acceptable range of the V throat angle  from tests conducted to change the V throat angle  for workpieces having various widths ranging from 11 mm to 25 mm. The test results are illustrated in Fig. 9. As can be seen from the test results, it is preferable that the V throat angle  be in an acceptable range defined by first and second lines La2 and Lb2. The first line La2 is presented as 1.5 x Dp and the second line Lb2 is presented as 0.6 x Dp. Assuming now that the tube diameter Dp is 6.35 mm, the acceptable range of the V throat angle  extends from 4.06° to 8.83°. Assuming now that the tube diameter Dp is 4 mm, the acceptable range of the V throat angle  extends from 2.56° to 5.56°. If the V throat angle  is greater than the acceptable range, the wrinkles or deformations occur on the opposite side surfaces 1b and 1c of the workpiece 1. If the V throat angle  is less than the acceptable range, pre-arc occurs in the V throat of the workpiece 1 to degrade the welding quality. Referring to Figs. 10 to 12 there is illustrated a second embodiment of the tube production machine of the invention. In this embodiment, the squeeze rollers 70 are supported in a cassette holder 80. The cassette holder 80 includes a lower member 80a and an upper member 80b fixed on the lower member 80a to form a box-shaped holder. The upper and lower members 80a and 80b are formed near their centers with a pair of coaxial holes 80c for receipt of the upper and lower end portions 70c and 70d. The squeeze roller 70 is supported rotatably between the upper and lower members 80a and 80b with its upper and lower end portions 70b and 70c inserted in the respective holes 80c. The cassette holder 80 is fixed on a roller stand by means of bolts 86 extending through bolts holes 82 formed in the upper and lower members 80a and 80b. Thus, the distance between the squeeze rollers 70 are fixed at a predetermined appropriate value. The numeral 88 designates a cutout formed in the upper member 80a intermediate between the holes 80c. The cutout 88 is effective to monitor the welding point 1a therethrough and escape spatters therethrough. This arrangement can reduce the size of the squeeze rollers 70 without any reduction in their strength. It is, therefore, possible to place the squeeze rollers 70 closer to the induction coil 12 without interference of the squeeze rollers 70 with the induction coil 12 so as to improve the welding heat efficiency. It is also possible to produce small-diameter tubes having a diameter of 8 mm or less for which the conventional apparatus cannot be used. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the scope of the appended claims.

Claims: A tube production machine comprising means for forming a workpiece (1) fed from a roll of metal strip in a tubular formation having side surfaces (1b, 1c) opposite to each other, a pair of squeeze rollers (70) for providing an upsetting pressure to joint the opposite side surfaces (1b, 1c) of the workpiece (1) at a jointing point (1a), each of the squeeze rollers (70) having a cylindrical shape with an annular groove (70b) in the side peripheral surface thereof to define a path for the workpiece (1) along with the annular groove (70b) of the other squeeze roller (70), a roller holder (72) for bearing each of the squeeze rollers (70), and means for supplying a high frequency power to the workpiece (1) to weld the opposite side surfaces (1b, 1c) at the jointing point (1a) so as to produce a metal tube member, characterized in that each of the squeeze rollers (70) is a one-piece member having a cylindrical centre portion (70a) and upper and lower cylindrical end portions (70c, 70d) extending coaxially in opposite directions from the centre portion (70a), the annular groove (70b) being formed in the side peripheral surface of the centre portion (70a), and the upper and lower cylindrical end portions (70c, 70d) being formed for rotation in unison with the cylindrical centre portion (70a), and in that the squeeze rollers (70) are supported in the roller holder (72) at their end portions (70c, 70d). The tube production machine as claimed in claim 1, wherein the roller holder (72) includes first and second sections for bearing the respective squeeze rollers (70), the first and second sections being mounted for sliding movement toward and away from each other to position the squeeze rollers (70) at an adjustable distance. The tube production machine as claimed in claim 1, where the roller holder (72) is a single member for supporting the squeeze rollers (70) at a predetermined distance. A method for producing metal tubes by forming a workpiece (1) fed from a roll of metal strip in a tubular formation having side surfaces (1b, 1c) opposite to each other, providing an upsetting pressure by a pair of squeeze rollers (70) of a tube production machine as defined by claim 1 to butt the opposite side surfaces (1b, 1c) of the workpiece (1) at a jointing point (1a) and supplying a high frequency power to the workpiece (1) to weld the opposite side surfaces (1b, 1c) at the jointing point (1a), characterized in that the squeeze rollers (70) have a diameter (D SQR ) set within a range defined by first and second lines (La1, Lb1), the first line (La1) being presented as 5.5 x Dp, the second line (Lb1) being presented as 2.5 x Dp where Dp is the diameter of the tube to be produced. A method for producing metal tubes by forming a workpiece (1) fed from a roll of metal strip in a tubular formation having side surfaces (1b, 1c) opposite to each other, providing an upsetting pressure by a pair of squeeze rollers (70) of a tube production machine as defined by claim 1 to butt the opposite side surfaces (1b, 1c) of the workpiece (1) at a jointing point (1a) and supplying a high frequency power to the workpiece (1) to weld the opposite side surfaces (1b, 1c) at the jointing point (1a), characterized in that the opposite side surfaces (1b, 1c) make an angle (Θ) set within a range defined by first and second lines (La2, Lb2), the first line (La2) being presented as 1.5 x Dp, the second line (Lb2) being presented as 0.6 x Dp, where Dp is the diameter of the tube to be produced. Method according to claim 5, wherein the squeeze rollers (70) have a diameter (D SQR ) set within a range defined by third and fourth lines, the third line being presented as 5.5 x Dp, the forth line being presented as 2.5 x Dp, where Dp is the diameter of the tube to be produced.

Inventors: ISHIZAKA YUJI, KIMURA HIROYASU, MASUDA OSAMU, TAKASHI KATANOSAKA, ISHIZAKA, YUJI, KIMURA, HIROYASU, MASUDA, OSAMU, TAKASHI, KATANOSAKA, ISHIZAKA, YUJI, C/O K.K. MEIDENSHA, Kimura, Hiroyasu, c/o K.K. Meidensha, Masuda, Osamu, c/o K.K. Meidensha, Takashi, Katanosaka, c/o K.K. Meidensha
Applicants: MEIDENSHA ELECTRIC MFG CO LTD, KABUSHIKI KAISHA MEIDENSHA
Application year: 1993
Main classification: B23K13
IPC codes: H05B6, B23K13