JPH0474087B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a method for manufacturing an internally grooved tube, and particularly to a technique for improving productivity of an internally grooved tube. (Background Art) In general, an internally grooved tube, which is a heat transfer tube with a predetermined groove formed on its inner surface, is processed by rolling the tube to a rolling head to a first drawing ratio with a grooved plug inserted inside. After forming a predetermined groove on the inner surface of the tube to be processed, the rolled tube is rolled at a drawing die placed downstream of the rolling head. It is manufactured by drawing with a drawing rate of 2. However, in this conventional manufacturing method of internally grooved tubes, the drawing ratio of the tube to be processed is not necessarily sufficient, and for this reason, it is necessary to use a tube with a correspondingly smaller diameter as the tube to be rolled. As a result, the rolling speed of the pipe to be processed and, by extension, the production speed of internally grooved pipes were severely limited. On the other hand, in order to eliminate such problems, the pipe to be processed that has been drawn at the second drawing ratio is further subjected to dry drawing at a predetermined drawing ratio to improve the drawing ratio of the pipe to be processed. It has been considered to increase the diameter of the pipe to be rolled to improve the productivity of the internally grooved pipe. However, when dry drawing a pipe with a groove of a predetermined shape formed on the inner surface, the wall thickness of the pipe to be processed (bottom wall thickness at the bottom of the groove) increases significantly. There was a problem that caused a significant drop in the heat transfer performance of the internally grooved tube. In order to avoid such problems, if the pipe to be processed is made thinner by taking into account the thickness increase when forming the groove, production efficiency will not increase and problems such as rupture of the pipe to be processed will occur. It happens. (Problem to be solved) The present invention has been made against the background of the above, and the problem to be solved is the pipe wall thickness (bottom wall thickness) of the pipe to be processed.
This allows the tube to be processed to be reduced at a predetermined drawing ratio without significantly increasing the wall thickness of the pipe, and improves the productivity of internally grooved tubes without causing a significant decrease in heat transfer performance. It is an object of the present invention to provide a manufacturing method for an internally grooved tube that can be improved. (Solution Means) In order to solve this problem, in the present invention, a first groove is formed from the upstream side to the downstream side in the feeding direction of the pipe to be processed, the inner surface of which is formed with a groove of a predetermined shape. Place the capstan drum, the drawing die and the second capstan drum in order,
A drawing mechanism is configured to sequentially wind up the pipe to be processed on the first capstan drum, and
The pipe to be processed is let out from the first capstan drum so that the amount of winding on the first capstan drum is constant, and the workpiece is let out from the first capstan drum. After passing the tube through the drawing die, the tube is wound up by the second capstan drum, and the first With rear tension applied to the first capstan drum, the pipe to be processed fed out from the first capstan drum is drawn by the drawing die to shrink the pipe at a predetermined drawing ratio. It is. (Specific configuration and operation) The present invention will be described in more detail below based on the drawings. First, FIGS. 1 and 2 schematically show a specific example of an internally grooved tube manufacturing system for manufacturing an internally grooved tube to which the method of the present invention is applied. The manufacturing system is set up so that processing and drawing can be performed on the same line. That is, as shown in these figures, the internally grooved tube manufacturing system for manufacturing an internally grooved tube according to the method of the present invention moves the tube to be processed 2 from the upstream side to the downstream side in the feeding direction. The rolling head 4 includes a rolling head 4, a first drawing die 6, a first capstan drum 8, a second drawing die 10, and a second capstan drum 12 arranged in this order. Here, the rolling head 4 presses balls or rollers against the outer surface of the tube to be processed 2, rolls the tube to be processed 2 at a predetermined first drawing ratio, and grooves inserted into the inside of the tube to be processed 2. The first drawing die 6 is used to form a predetermined spiral groove, that is, a spiral fin 16, on the inner surface of the tube to be processed 2 using the attached plug 14, and the first drawing die 6 is used to perform the rolling process using the rolling head 4. The purpose is to draw the processed pipe 2 at a predetermined second drawing ratio, and the rolling process in the rolling head 4 and the drawing process in the first drawing die 6 are performed on the downstream side thereof. This is accomplished by the winding action of the tube to be processed 2 by the provided first capstan drum 8. Further, a second drawing die 10 provided on the downstream side of the first capstan drum 8 allows the workpiece tube 2 drawn by the first drawing die 6 to be drawn at a predetermined third drawing rate. The drawing process in the second drawing die 10 is performed by the winding action of the pipe to be processed 2 by the second capstan drum 12 provided on the downstream side. It will be done. By the way, in order to manufacture an internally grooved tube using such a manufacturing system from a raw tube to be processed 2 having a smooth inner surface, the tube to be processed 2 passed through the rolling head 4 and the first drawing die 6 must be The pipe to be processed is wrapped around the first capstan drum 8 a predetermined number of times, for example, 5 or 6 times, and the rotation of the capstan drum 8 causes the pipe to be processed to
After winding up the second drawing die 10
The tube to be processed 2 that is fed out from the first capstan drum 8 is wrapped around the second capstan drum 12 through the second capstan drum 1.
2, and then unwound from the second capstan drum 12 and sent to an inspection process or the like. Then, a tensile force is applied to the tube to be processed 2 by the winding action caused by the rotation of the first capstan drum 8, and the tube to be processed 2 is rolled by the rolling head 4 and the first drawing die 6. and drawing processing, and the second capstan drum 1
A tensile force is applied to the pipe to be processed 2 by the winding action caused by the rotation of the capstan drums 8 and 12, and the pipe to be processed 2 is drawn by the second drawing die 10. Adjust the rotation speed and
A predetermined backward tension is applied to the portion of the pipe to be processed 2 to be drawn by the second drawing die 10. In addition, in FIG. 1, 18 is the pipe to be processed 2.
This is a tension measuring device that measures the rearward tension by detecting the displacement of the degree of warpage of the capstan drum 18. Adjustments will be made based on the tension measurement results. That is, here, the first capstan drum 8, the second drawing die 10, and the second capstan drum 12 constitute a drawing mechanism according to the present invention. If the internally grooved tube is manufactured in this way, the tube to be processed 2 is rolled at the rolling head 4 at the first drawing rate by the winding action of the first capstan drum 8. A grooved plug 14 is formed on the inner surface of the pipe to be processed 2.
A predetermined spiral groove (fin 16) can be formed in the same way as in the conventional method, and the pipe to be processed 2 that has been rolled by the rolling head 4 is then drawn to a second drawing rate by the first drawing die 6. In addition, the pipe to be processed 2 drawn with the first drawing die 6 can be further drawn with the second drawing die 10 at a third drawing rate. It is possible to further shrink the tube by drawing.
At that time, based on the rear tension applied to the tube to be processed 2, the plastic flow of the tube wall of the tube to be processed 2 in the radial direction is well suppressed, and the wall thickness of the tube to be processed 2 (helical This makes it possible to effectively suppress the increase in the bottom wall thickness of the groove. As described above, according to the method of the present invention, the tube to be processed 2 is shrunk at the first drawing ratio in the rolling head 4 and then shrunk at the second drawing ratio in the first drawing die 6.
can be further shrunk at the third drawing ratio while effectively suppressing the increase in pipe wall thickness using the second drawing die 10 to produce an internally grooved pipe.
By increasing the diameter of the tube to be processed 2 (original tube) during rolling processing without causing a significant decrease in heat transfer performance, the rolling speed of the tube to be processed 2 can be increased, and the final product can be improved. This makes it possible to improve the productivity of internally grooved tubes. Further, in the manufacturing system of this embodiment, as described above, the rolling head 4 performs the rolling process, the first drawing die 6 performs the first drawing process, and the second drawing die 10 performs the second drawing process. This can be done on the same line, which has the advantage of greatly simplifying the internally grooved tube manufacturing system compared to the case where they are done on separate lines. In this embodiment, a so-called seamless pipe in which grooves are formed by a rolling head 4 and a grooved plug 14 is used as the pipe to be processed 2, but a plate material with grooves on one side may also be used. Of course, it is also possible to apply the present invention to a so-called internally grooved welded pipe, etc., which is formed by bending a pipe and welding the butted ends. In addition to a spiral shape, a straight groove or the like may also be adopted. Furthermore, in this embodiment, a drawing mechanism consisting of a drawing die 10 and a capstan drum 12 is simply provided on the downstream side of the first capstan drum 8, and the pipe to be processed 2 is drawn in three stages. However, two or more sets of drawing mechanisms as in the above example are provided downstream of the first capstan drum 8, and the pipe to be processed 2 is compressed in four or more stages. The tube may be contracted by Examples of the present invention are shown below in order to clarify the present invention more specifically, but the present invention is not limited in any way by the description of the examples, and the present invention It should be understood that other embodiments may be implemented without departing from the spirit thereof. (Example) A tube with internal grooves as shown in FIG. 1 was manufactured using a ball-pressing type rolling head 4 that rolls a tube 2 to be processed using balls, and W-shaped drawing dies 6 and 10. Configured the system. In this internally grooved tube manufacturing system, the second drawing die 1
The aperture rate at 0 (third aperture rate) is 12%, 20%, 25
%, and the ratio of the rear tension to the breaking force of the pipe to be processed 2 (=backward tension/breaking force) to each breaking condition to manufacture an internally grooved pipe, and at that time, the second drawing The amount of change in the tube wall thickness (bottom wall thickness of the spiral groove): tf of the tube to be processed 2 before and after drawing with the die 10 was measured. The measurement results are shown in FIG. The outside diameter of the tube to be processed 2 before drawing with the second drawing die 10 (after the drawing with the first drawing die 6) is 7.94 mm, and the tube wall thickness: tf is 0.31 mm. Ta. From the measurement results shown in FIG. 3, when the drawing ratio of the second drawing die 10 is set to around 10%, the backward tension/breaking force is within a relatively wide range of about 0.1 to 0.6, and the workpiece tube 2 Pipe wall thickness: When increasing the wall thickness of tf by simple dry drawing (backward tension/breaking force = 0
It is recognized that the rear tension / Breaking force is 0.1~0.3
It is recognized that within a certain range, the amount of increase in the tube wall thickness (tf) of the tube to be processed 2 can be suppressed to approximately 1/2 or less (approximately 0.01 mm or less) of that in the case of simple dry drawing. From this, the manufacturing method of the internally grooved tube according to the present invention can greatly suppress the reduction in heat transfer performance due to the increase in the tube wall thickness: tf, while significantly increasing the drawing ratio of the tube to be processed 2. Improve to
It has now been recognized that the productivity of internally grooved tubes can be greatly improved. Furthermore, FIG. 4 shows the results of measuring the amount of change in the height of the fins 16 before and after drawing of the pipe to be processed 2 drawn as described above.
From the figure, the drawing rate of the second drawing die 10 is
It has been found that the amount of decrease in fin height can be kept sufficiently small within the range of 0.1 to 0.3 of the rear tension/breaking force, not only when it is relatively small at around 10%, but also when it is relatively large at around 20%. From this, it is recognized that according to the inventive method, a decrease in heat transfer performance due to a decrease in fin height is sufficiently suppressed. On the other hand, outer diameter: D ₀ is 11.9 mm, pipe wall thickness: t is 0.36 mm
Using the circular tube as the master tube of the tube to be processed 2, using the internally grooved tube manufacturing system configured as described above,
60 fins 16 with an apex angle of 56° and a height of 0.15mm are formed on the inner surface of the tube with a lead angle of 18°.The inner surface has an outer diameter of 7mm and a wall thickness: tf of 0.27mm. Grooved tubes were manufactured. At that time, the drawing speed of the processed tube (inner grooved tube) 2 from the second drawing die 10 was measured, and the drawing speed was 48 m/min, and a similar inner grooved tube was manufactured using the conventional method. It was confirmed that the productivity could be improved by about 20% compared to the drawing speed (approximately 40 m/min). In addition, the feed speed, outer diameter, and tube wall thickness (t, tf) of the processed tube 2 in each region shown in FIG. 1 are as follows:
The results are shown in Table 1 below, and it was confirmed that the increase in tube wall thickness (tf) due to the drawing process using the second drawing die 10 was suppressed to 0.1 mm. In addition, the drawing rate at each processing position (first to
The third reduction rate) is as shown in Table 2 below.

【table】

[Table] (Effects of the invention) As is clear from the above explanation, according to the method of the present invention, the pipe wall thickness (bottom wall thickness at the bottom of the groove) of the pipe to be processed which is grooved can be increased. It is possible to shrink the tube by drawing at a predetermined reduction rate while suppressing the inner wall thickness well. The effect of improving the productivity of attached pipes can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing an example of an internally grooved tube manufacturing system suitable for implementing the method of the present invention, and FIG. 2 shows a more concrete version of the system in FIG. 1. It is an explanatory diagram. FIG. 3 is a graph showing an example of the measurement results of the amount of change in the tube wall thickness before and after drawing with the second drawing die of the internally grooved tube manufactured according to the method of the present invention, and FIG. , similarly,
7 is a graph showing an example of a measurement result of the amount of change in fin height. 2: Workpiece pipe, 4: Rolling head, 6: First drawing die, 8: First capstan drum, 1
0: Second drawing die, 12: Second capstan drum, 14: Grooved plug, 16: Fin.

Claims (1)

[Scope of Claims] 1 A first cap stand drum, a drawing die, and a second cap stand drum, a drawing die, and a second cap stand are arranged from the upstream side to the downstream side in the feeding direction of a pipe to be processed, the inner surface of which is formed with a groove of a predetermined shape. A drawing mechanism is configured by arranging stand drums in order so that the pipe to be processed is wound up in sequence on the first cap stand drum, and the amount of winding on the first cap stand drum is constant. After the pipe to be processed is fed out from the first capstan drum and the pipe to be processed fed out from the first capstan drum is passed through the drawing die, the pipe to be processed is fed out from the first capstan drum. Winding it up with the capstan drum, and applying a backward tension on the first capstan drum under the action of a tensile force based on the winding action of the second capstan drum. . A method for producing an internally grooved tube, characterized in that the tube to be processed fed out from the first cap stand drum is drawn by the drawing die and contracted at a predetermined drawing ratio.