JPH0141414B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method for forming spiral grooves on the inner surface of metal tubes such as heat transfer tubes, and particularly relates to a method for manufacturing spiral grooved tubes intended to improve productivity and form deep grooves. be. Generally, when manufacturing internally grooved pipes, a raw pipe with a large outer diameter is drawn, reduced in diameter, and drawn.
A continuous spiral groove is formed on the inner surface of the drawn pipe, but this method requires an extremely high drawing force because the resistance force due to the drawing process and the resistance force due to the groove process are combined. Therefore, it generates a large amount of heat and has the disadvantage that it is not possible to process thick materials or form deep internal grooves. This is because in the manufacturing process of such internally grooved pipes, the resistance force in the diameter-reducing grooving process and the resistance force in the internal grooving process are combined as described above, and the resistance force in the internally grooved process is combined as described above, and the purpose is only for general diameter reduction. This is because a significantly larger resistance force is generated compared to drawing processes, etc., and it is not possible to reduce the resistance force simply by combining existing drawing techniques, etc., so it is necessary to find the optimal combination that will reduce the drawing force the most. I need to look for it. For example, the approach plane 10 shown in FIG.
0 and a fixed die 102 having a bearing surface 101, and a floating plug 1 having an approach surface 103 and a bearing surface 104 parallel to the approach surface 100 and the bearing surface 101.
After reducing the diameter of the tube between the floating plug 105 and the floating plug 105, a grooved plug 107 is rotatably connected to the rear part of the floating plug 105 by a shaft 106. The diameter-reduced tube is compressed by discontinuous projections 108 provided on the inner diameter portion, and the inner surface thereof is pressed against the spiral groove on the outer periphery of the grooved plug 107 to form a groove. In this case, the approach surface 100 of the die 102
The tube cannot be drawn unless a large drawing force is applied due to the resistance force by the approach surface 103 on the floating plug 105 side and the resistance force by the bearing surfaces 101 and 104, and the discontinuous protrusion 108 is not drawn on the outer surface of the tube. Since the groove is created by rubbing and compressing the pipe, the discontinuous protrusion 10
8 and the outer periphery of the tube is large, and therefore, on top of the large drawing force caused by the fixed die 102 and floating plug 105, the resistance force caused by the discontinuous protrusions 108 is further added, so that the drawing force becomes even larger. It is not possible to process thick materials, and it is not possible to process grooves with complex shapes or deep unevenness. Another disadvantage is that long materials cannot be stably processed due to heat generation. Furthermore, in the conventional spiral grooved tube manufacturing apparatus, the grooved plug 107 having spiral grooves and protrusions formed on its outer circumferential surface is used as described above, and the tube is pressed against the grooved plug 107 to form a spiral groove on its inner surface. Because the drawing force in the direction of the tube axis is a combination of processing force parallel to the groove and frictional force perpendicular to the groove, it is necessary to create a so-called straight groove parallel to the tube axis. Compared to engraving, a large drawing force is required, making it difficult to process deep grooves and thin materials, and generates significant heat. However, spiral grooved tubes have better heat transfer performance than straight grooved tubes, and it is desired to develop a method for manufacturing spiral grooved tubes that does not have the above-mentioned disadvantages. The present invention has been made in view of the above-mentioned points, and its gist is a method of forming a spiral groove on the inner surface of a metal tube, in which a straight groove parallel to the tube axis is formed on the inner surface of the metal tube. A step of forming the straight grooved tube by cold drawing, a step of heating and softening the straight grooved tube, and a step of twisting the straight grooved tube around the tube axis after passing the softened straight grooved tube through a twisting area regulating means. The present invention provides a method for manufacturing a spirally grooved tube, the gist of which is a step of winding the tube. Next, embodiments embodying the present invention will be described with reference to the accompanying drawings starting from FIG. 2 to provide an understanding of the present invention. Here, FIG. 2 shows a process diagram of the entire spiral grooved pipe manufacturing apparatus that can be used directly to carry out the manufacturing method according to an embodiment of the present invention, and FIG. 3 shows an example of twist area regulating means. 4a and 4b are side sectional views showing the internal structures of a straight grooved tube and a spiral grooved tube, respectively, and FIGS. 5 and 6 are side sectional views showing the internal structure of a straight grooved tube and a spiral grooved tube, respectively. FIG. 7 is a side view showing a modification of the area regulating means. In FIG. 2, a hard long metal tube 1 is squeezed between a floating plug 2 and a die 3 surrounding it and undergoes cold drawing (thickening and diameter reduction) processing. The die 3 may be of a fixed type or a rotating spinning type that rotates around the tube axis. Behind the floating plug 2 (in the drawing direction shown by arrow 4), the floating plug 2
A grooved plug 5 is attached to the tube by a connecting rod 7, and the outer surface of the grooved plug 5 has grooves or protrusions 6 cut in a direction parallel to the tube axis. The grooved plug 5 is attached to the connecting rod 7 via bearings 8 and 9 so as to be able to rotate within the metal tube 1. Only one of the bearings 8 and 9 may be provided, in other words, it is a floating plug. It is sufficient if the grooved plug 5 is rotatable with respect to the plug 2. A compression device 10 is provided opposite the outer periphery of the grooved plug 5, and the compression device 10 presses the tube 1 against the outer periphery of the grooved plug 5 as shown by arrow P, and is attached to the inner surface of the tube 1 parallel to the tube axis. The compression element 11 has a straight groove carved therein. The compression element 11 can be composed of a fixed die, a rotating die, or a rolling device such as a rotatable ball or roller, and can be opened and closed at any timing by hydraulic means (not shown). Configure. The outer diameter D of the tube 1' exiting the die 3 is slightly larger than the outer diameter _d1 of the straight grooved tube 12 provided with straight grooves, and the compression device 10 causes a slight diameter reduction in the tube 1'. let As shown in FIG. 4a, the straight grooved tube 12 has a plurality of linear straight grooves 13 continuously carved in the tube axis direction on its inner surface, parallel to the tube axis. Next, the straight grooved pipe 12 was processed with grooves.
is guided into an induction heating device (softening device) 14 using, for example, medium frequency or low frequency, where it is rapidly heated and softened. Conditions such as heating speed, heating temperature, and heating time are appropriately set within a preset range based on the running speed of the straight grooved tube 12, diameter, wall thickness, desired softening rate (ratio of hardness of the tube before and after softening), etc. be done. In other words, the straight grooved pipe 12 is in a hard state (H material) and then it is softened to make it half hard (1/2H material), or the half hard pipe is softened and turned into a quarter hard pipe (1/4H material). The optimal conditions are adopted depending on various situations, such as . The softened straight grooved tube 12' is then cooled to room temperature or warm temperature (50°C) by cooling means (not shown).
~200° C.), or if the softening temperature is not very high, it is introduced into the twisting region regulating means 15 as it is (particularly without being cooled). The twist area regulating means 15 is configured to prevent the pipe 1 from being twisted in the process in which the pipe 16 being twisted is sequentially wound around the winding shaft 18 of the winding device 17 during subsequent winding.
The twist of 6 is greater than the twist area regulating means 15 of the softening device 1.
It has the role of regulating the propagation in the direction of 4. Figure 3 shows die 1 as an example of twisting area regulating means.
9, the diameter d ₁ of the softened straight grooved tube 12' is reduced to the diameter d ₂ (d ₁ > d ₂ ) by dry drawing in the die 19. show. In this case, the purpose is not to increase the hardness by increasing the processing rate, but to correct (smooth) the minute irregularities on the outer surface of the grooved tube and to turn the tube 16 by twist winding, which will be described later. Tube 1 before 19
The main purpose is to restrict the range of twisting while holding the tube firmly so that it does not extend beyond 2'. Dice 19
is held in a tapered manner by the fixing unit 20, and remains in a fixed state during work. The rear half of the die 19 has a release surface 21 that is finished to be particularly smooth so as not to damage the rotating tube 16 and to ensure smooth rotation, and that is tapered toward the outlet. ing.
The processing rate of the tube with the die 19 is preferably 2 to 30%. In addition, the half-angle of rotation α of the tube 16 during twisting is 5 to 60.
degree range is ideal. FIG. 5 shows another example in which a friction roll 22 is used instead of the die 19. The softened straight grooved tube 12' is moved to a friction roll 22.
The material is wound 1 to 10 times around the material and then led to the next twisting and winding process. Tension control of the tube 16 during softening is performed using the clamping force (frictional force) between the wound tube and the surface of the friction roll 22.
Therefore, in this case, the friction roll 22 is driven by a motor (not shown) or the like, but conditions such as rotation speed are controlled by a control system with reference to the result of detecting the tension state of the tube 16. When the friction roll 22 is used as a drive system as described above, its main role is to control the tension and regulate the twisting range (range of L). Of course, it is also possible to use the roll as a driven system, and in this case, the main purpose is only to regulate the twisting region L. Figure 6 shows another example of the friction roll 22.
This is a case where the die 19' and the die 19' are combined. The friction roll 22 may be a drive system or a driven system, but in this case, the die 19' does not draw the tube 16 and has a hole diameter slightly larger than the diameter _d1 of the tube 16. Therefore, the die 19' functions to prevent the winding on the friction roll 22 from being affected by the degree of rotation of the tube during twisting. If the surface of the tube 16 is required to have considerable smoothness, the die 19' should have a structure (hole diameter ). Returning to FIG. 2, the tube exiting the twisting area regulating means 15 is twisted between there and the winding shaft 18 of the winding device 17 (twisting area). The turning of the tube 16 is achieved by sequentially winding the tube 16 in a coil shape along the axial direction of the winding shaft 18, so that the winding position on the winding shaft 18 reciprocates in the axial direction. The take-up device 17 itself is attached to a base 24 via a connecting rod 25, and the connecting rod 25 and the take-up device 17 are integrally fixed, and the connecting rod 2 is attached to the base 24.
This occurs because the winding device 5 and the winding device 17 integrated therewith are structured to be driven to rotate at a preset rotational speed. The winding shaft 18 is rotationally driven by a drive system 26 such as a motor. Turning of the winding device 17 and accompanying grooved tube 16
The grooved tube 16 is twisted around its tube axis by the rotation of the grooved tube 16, and the magnitude of the twist angle is mainly determined by the winding speed _V1 of the winding shaft 18 and the connecting rod 2.
It is selected by appropriately combining the circumferential rotational speed V ₂ of the tube based on the rotation of 5. Also, depending on the degree of tempering (hardness) of the tube 16, a slight spring back may occur, and the torsion angle may change slightly when the tube is loosely coiled afterward, but this should be determined through experiments in advance. When processing almost rigid pipes,
There is no problem if the twisting conditions (twisting speed, etc.) are set in consideration of such a springback rate. The more completely flexible the tube, the less springback needs to be considered. For example, Table 1 shows an example, and when wound on the winding shaft 18, 0 degrees (soft), 1 degree (1/4
If the twist angle is as large as the pipe), it will become loose.

[Table] When the tube has the desired twist angle. In the case of the conventional manufacturing method of the spirally grooved tube shown in Fig. 1, since the grooving and spiraling are performed at the same time, the deformation resistance of the tube material is large, and when drawn at high speed, the thinner the tube, the more likely it will break. This increases the risk of ducting. In this respect, in the present invention, since the grooving is only straight grooving, the grooving in the grooved plug 5 can be performed very smoothly on the pipes one after another. That is, since there is no large resistance during groove machining, high-speed machining is possible in this grooved portion. There is no problem with the subsequent rapid heating as long as the pipe is not extremely large in diameter, as the current low frequency induction type rapid heating equipment can sufficiently handle the pipe running speed. There are no particular factors that adversely affect the tube running speed in the twist area regulating means 15, and the spirally grooved tube can be manufactured at a desired speed, so that the manufacturing speed can be increased. As the winding device 17, a well-known device used in conventional normal drawing can be used, and there is no particular problem in terms of performance. As described above, the present invention provides a method for forming a spiral groove on the inner surface of a metal tube, which includes a step of forming a straight groove parallel to the tube axis on the inner surface of the metal tube by cold drawing, and a method for forming a spiral groove on the inner surface of a metal tube. It is characterized by comprising the steps of heating and softening the tube, and passing the softened straight grooved tube through a twisting area regulating means, and then winding it up while twisting it around the tube axis. Since this is a method for manufacturing a spiral grooved tube, the spiral grooves are not carved all at once using a grooved plug having a spiral groove or a protrusion on the outer periphery, as in the conventional method for manufacturing a spiral grooved tube. After forming a straight groove, the entire tube is rotated around the tube axis, so the resistance of groove machining is low.
Thin-walled tubes can also be easily grooved, and for the same reason, deep grooves and high-speed machining are possible, and the problem of heat generation is also solved. In addition, if you understand the various conditions of the softening process and twist winding process of straight grooved pipes in advance through experiments, and set the conditions according to the tempering (hardness), even hard and thin metal pipes can be processed. A grooved tube with an accurate helical angle can be obtained without variations in the helical angle due to spring back, etc., and furthermore, a twisting area regulating means is provided between the softening step and the twisting winding step.
Grooving processing can be stably performed without affecting the previous process due to twisting of the pipe.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a device used in a conventional method for manufacturing a spiral grooved tube, and FIG. 2 is a process diagram of the entire manufacturing device that can be used directly to implement a manufacturing method according to an embodiment of the present invention. Figures 3 and 3 are side sectional views showing an example of twisting area regulating means, Figures 4a and b are side sectional views showing the internal structures of a straight grooved tube and a spiral grooved tube, respectively. FIG. 6 is a side view showing a modification of the twisting area regulating means that can be used in the same embodiment. Explanation of symbols, 1... Metal tube, 2... Floating plug, 3... Dice, 5... Grooved plug, 6... Groove or protrusion, 10... Compression device, 1
2, 12'...Straight grooved tube, 13...Straight groove, 14...Softening device, 15...Twisted area regulating device, 16...Spiral grooved tube, 17... Winding device.

Claims (1)

[Claims] 1. A method for forming a spiral groove on the inner surface of a metal tube, which includes a step of forming a straight groove parallel to the tube axis on the inner surface of the metal tube by cold drawing, and heating and softening the straight grooved tube. and a step of winding the softened straight grooved tube while twisting it around the tube axis after passing through a twisting area regulating means. .