BENT PIPE

Abstract: A bent pipe (1) is made of a metal strip (2) having one edge in a straight line and the other edge in a curved line by winding it helically. A double fold (5) and a single fold (6) are formed along the straight edge and the curved edge, respectively. Then the metal strip (2) is wound helically so that the narrow portions will be in juxtaposition with one another.

Description: The invention relates to a method of producing a bent pipe or elbow for use at a corner portion of an airconditioning duct, an exhaust pipe, a drain pipe or the like. A method as defined in the preamble part of claim 1 has been known from US-A-4,704,885. Similar methods have been known from other documents. In these prior art methods, the metal strip which is to be helically wound has its two edges cut along undulating curved lines in symmectrical relation for defining the alternating wide and narrow portions. In making a metal strip having such a shape from a metal plate having straight edges, the edge portions cut out for forming the undulating edges are wasted, which increases the manufacturing costs. An object of the invention is to provide a method of the aforementioned type by which the bent pipe can be made from metal plate without producing any scrap. The method according to the invention is defined in the attached claim. With the method according to the invention a metal plate is cut along an undaluting longitudinal center line thus producing two metal strips of the required shape out of a single metal plate without wasting any material. Thus the manufacturing costs can be substantially reduced. Another advantage of the method according to the invention is that the use of a metal strip having one straight edge makes it easier to manufacture the forming rolls of a machine for producing the curved pipe. In this connection it is particularly advantageous to use the features of claim 2, whereby the more complicated forming of a double fold is made at the straight edge of the strip. Other features of the present invention will become apparent from the following description taken with reference to the accompanying drawings, in which: Fig. 1 is a side view of an apparatus for producing bent pipes according to the present invention; Fig. 2 is a sectional view taken along line A-A of Fig. 1; Fig. 3 is a sectional view taken along line B-B of Fig. 1; Fig. 4 is a sectional view taken along line C-C of Fig. 1; Fig. 5 is a sectional view taken along line D-D of Fig. 1; Fig. 6 is a sectional view taken along line E-E of Fig. 1; Fig. 7 is a sectional view taken along line F-F of Fig. 1; Fig. 8 is a sectional view taken along line G-G of Fig. 1; Fig. 9 is a perspective view of a portion of the same; Fig. 10 is a sectional view taken along line F-F of Fig. 1; Fig. 11 is a plan view of the metal strip; Fig. 12 is a plan view of a metal plate from which two metal strips are made; and Fig. 13 is a side view of the bent pipe made according to the present invention. Fig. 11 shows a strip of metal plate 2 for producing a bent pipe 1. This metal strip 2 has wide portions 2′ and narrow portions 2″ arranged alternately and has one of its longitudinal edges extending in a straight line and the other extending in a curved line. Each portion between adjacent troughs X-X will form an annular piece as a part of the peripheral wall of the bent pipe 1 when the metal plate 2 is wound helically so that the narrow portions will be in juxtaposition with each other. Thus, the straight edge of each annular piece at portion between X - X has a length substantially equal to the diameter of the bent pipe 1 multiplied by π. As shown in Fig. 12, two such metal strips 2 can be made by longitudinally cutting a single metal plate 3 in a curved line so as to form a pair of symmetrical portions. This will prevent the production of scrap. Next, it will be described how the bent pipe is produced, with reference to Figs. 1 - 10. The coiled metal plate 3 is drawn out into between a pair of first forming rolls 11 (Fig. 1) to form L-shaped bent portions 4 along both edges thereof by means of large-diameter annular plates 12 and small-diameter annular plates 13 provided at both ends of the respective forming rolls 11 (Fig. 2). As shown in Fig. 3, the bent portions 4 thus made are then formed into U-shaped double folds 5 by cooperation of annular ribs 15 and annular grooves 16 provided at both ends of a pair of second forming rolls 14. As shown in Fig. 4, after forming the double folds 5, the metal plate 3 is cut into two pieces by means of female and male rolls 18 and 20. The female roll 18 has the same diameter as that of the bent pipe 1 and is formed in its outer peripheral surface with a curved groove 17 whereas the male roll 20 is formed with a curved rib 19 having a sharp ridge line. Simultaneously with this cutting operation, the edges formed by cutting are pushed by the rib 19 into the groove 17 to form L-shaped single folds 6 along the edges. The female roll 18 and the male roll 20 are provided at both ends thereof with annular grooves 16 and annular ribs 15, respectively, similar to those of the second forming rolls 14. They serve to catch the double folds 5 therebetween, thus preventing lateral movement of the metal plate 3. The single folds 6 formed on the metal strips 2 cut from the metal plate 3 are bent obliquely toward the double folds 5 by means of an upper backing roll 21 (Fig. 5) cooperating with a lower third forming roll 25 in the shape of a rugby ball rotatably mounted on a bearing 24 secured to a slider 23 slidably mounted on a horizontal guide shaft 22. The backing roll 21 is formed at both ends thereof with annular ribs 26 which are adapted to be inserted into the double folds 5 to prevent lateral movement of the metal strips 2. As shown in Fig. 1, one of the metal strips 2 is then fed toward a helical winder 27 whereas the other is wound around a drum 28 to keep it in storage. Instead of storing it on the drum 28, it may be fed to another helical winder. As shown in Fig. 6, the double fold 5 formed on the metal strip 2 on its way toward the helical winder 27 is obliquely bent at its outer portion toward the single fold 6 by contact with forming surfaces 29′ on a pair of forming rolls 29. The metal strip 2 is then fed into between a pair of first and second rolls 30 and 31 (shown in Figs. 1 and 8) in the helical winder 27 and is bent by a third roll 32. It is then wound helically around the first roll 30. As shown in Fig. 10, the third roll 32 is slidably mounted on a guide shaft 34 protruding from a support member 33 and is formed in its outer peripheral surface with an annular groove 35 in which the single fold 6 engages so that the roll 32 will reciprocate as the width of the metal strip 2 increases and decreases. As shown in Fig. 8, there is provided a reciprocating roll 36 having its peripheral surface in contact with the metal strip 2 along its curved edge so as to be moved backwards when it is in contact with the crests or protruding portions of the curved edge and to move forward when it is in contact with the valleys or recessed portions of the curved edge. Thus the metal strip 2 is always biased forward by the roll 36 so that the double fold 5 and the single fold 6 can automatically get into engagement with each other. As shown in Figs. 8 and 9, there are provided an arm 38 pivotally mounted and adapted to be pivoted around a pin 37 by the contact between a rolling element 39 provided at the bottom end of the arm 38 and a cam 40 provided on the outer peripheral surface of the second roll 31. A first slider 42 coupled to the arm 38 through a link 41 has a front end face tapered at an angle of 45°. A second slider 43 supporting the reciprocating roll 36 has a rear end face 44 tapered at an angle of 45° and kept in contact with the tapered surface on the first slider 42. The second slider 43 is pulled rearwards by a spring 45. Thus, the reciprocating roll 36 can make a sliding movement. The single fold 6 and the double fold 5 kept in engagement with each other are pressed flat when they pass between the first roll 30 and the second roll 31. The bent pipe 1 thus made is cut by an abrasive cut-off machine 46. In cutting the pipe, the number of crests on the curved edge of the metal strip 2 is detected by a sensor (not shown). When the number of crests counted reaches a predetermined number, the operation of the helical winder 27 will be stopped and the abrasive cut-off machine 46 be reciprocated to cut the pipe. As shown in Figs. 1 and 7, a pair of fifth forming rolls 48 are provided ahead of the fourth forming rolls 29 to form on the metal strip 2 fold lines 1′ extending longitudinally across the maximum-width points of the wide portions 2′ (Fig. 11) and in parallel to the straight edge. The fold lines 1′ serve to eliminate wrinkles formed, depending upon its material, on the metal strip 2 at the maximum-width points of the wide portions 2′. They also serve to increase the strength of the bent pipe 1. Also, because the metal strip 2 has one of its edges extending straight, the other curved edge is longer than the straight one. Thus the first roll 30 on which the metal strip 2 is wound helically should have a smaller diameter at the portion where the curved edge touches than the portion where the straight edge does. This will assure that the length of the curved edge will be shrinked to that of the straight edge when the metal strip is wound helically.

Claims: A method of producing a bent pipe, comprising the steps of a) providing a strip (2) of sheet metal having a curved undulating edge defining alternating wide portions (2′) and narrow portions (2″) of the strip; b) helically winding the strip (2) to a bent tube shape wherein the wide portions (2′) of the strip are juxtaposed on one side of the tube shape and the narrow portions (2″) are juxtaposed on the opposite side of the tube shape; and c) joining the adjacent edges of the helical metal strip together to form the bent pipe, characterized in that said metal strip (2) has one straight edge and one undulating curved edge and is obtained by cutting a single elongate metal plate (3) having two straight longitudinal edges along an undulating curved longitudinal line so as to form a pair of symmetrical strips (2). A method according to claim 1, characterized in that a double fold (5) is formed along a straight edge and a single fold (6) is formed along the undulated edge of the metal strip (2), and the edges of the metal strip (2) are joined by engaging said single fold (6) and said double fold (5) together.

Inventors: TAKASUGI, TAMOTSU,
Applicants: FUJI KUCHO KOGYO KABUSHIKI KAISHA, KABUSHIKI KAISHA DUCT SANGYO, KABUSHIKI KAISHA OKADA SEISAKUSHO, TAKASUGI, TAMOTSU
Application year: 1990
Main classification: F16L43
IPC codes: B21C37, F16L43, B21D19