JPH0474086B2 - - 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 the productivity of an internally grooved tube with a simple device configuration.

(Background technology) Internally grooved tubes, which are heat transfer tubes with straight grooves or spiral grooves formed on the inner surface, are generally formed by rolling the tube to be processed using a rolling head with a grooved plug inserted inside. It is manufactured by. However, simply rolling the pipe to be processed using a rolling head does not result in a sufficient pipe shrinkage ratio, and it becomes necessary to roll the pipe with a small diameter, which significantly limits the rolling speed. be done.

Therefore, some proposals have been made to perform rolling on the pipe to be processed in a relatively large-diameter state, and then perform so-called dry drawing on the pipe to reduce its outer diameter to the desired size. ing.

However, since the conventional dry drawing was simply performed using one die, after the dry drawing, the pipe wall thickness of the pipe to be processed (pipe wall thickness at the bottom of the spiral groove; bottom wall thickness) There was a problem in which the pipe became significantly thicker than before dry drawing, and for this reason, when rolling the pipe to be processed, the pipe wall thickness was made to be thinner than the product standard by the amount of wall thickness increase due to dry drawing. , it becomes necessary to roll the pipe to be processed,
Correspondingly, the rolling speed of the tube to be processed decreases, resulting in a problem that the productivity of the internally grooved tube decreases.

On the other hand, in order to eliminate such problems, during the above-mentioned dry drawing, a rear tension is mechanically applied to the pipe to be processed using a drive roll or a drive caterpillar, and the workpiece is subjected to the mechanical rear tension. Dry drawing of processed pipes is also being considered. If the pipe to be processed is subjected to dry drawing under the action of rear tension, the increase in the wall thickness of the pipe can be effectively suppressed or prevented. By employing the tube, it is possible to improve the rolling speed and thereby improve the productivity of the internally grooved tube.

However, with this method, the cost of the device for applying backward tension to the pipe to be processed increases;
In addition to the large-scale construction of the drawing device as a whole, there are problems in that it is difficult to control the rear tension when the drawing speed fluctuates, and it is difficult to control the tube wall thickness at a constant level, so it is by no means desirable. Something happened.

It is also known that a plug mandrel is used to draw and shrink a rolled pipe without applying backward tension to the pipe. Although the pipe shrinking method for processed pipes makes it easy to control the pipe wall thickness, it has the problem that the drawing speed during drawing processing decreases significantly, especially when the pipe to be processed has a small diameter. However, there was a problem in that there were cases where such a method could not be adopted, and there were circumstances where it was said to be significantly inferior to the empty drawing method.

(Problem to be solved) The present invention has been made against the background of the above-mentioned circumstances, and the problem to be solved is a pipe to be processed in which a groove of a predetermined shape is formed on the inner surface. When shrinking the pipe by dry drawing, the increase in the wall thickness of the pipe to be processed can be effectively suppressed or prevented with a simple device configuration, and the productivity of the internally grooved pipe can be advantageously improved. It is an object of the present invention to provide a method for manufacturing an internally grooved tube.

(Solution Means) In order to solve this problem, in the present invention, a pipe to be processed having a groove of a predetermined shape formed on its inner surface is continuously emptied using a plurality of dies arranged in series. By drawing the pipe, the outer diameter of the pipe to be processed is reduced in stages while suppressing an increase in the wall thickness of the pipe.

(Specific configuration and operation) The present invention will be explained in more detail below with reference to the drawings.

That is, in the present invention, first, a pipe to be processed is prepared, in which a groove of a predetermined shape is formed on the inner surface of the pipe.For example, as shown in FIG. A tube 2 is rolled and prepared in a conventional manner using a rolling head 4 and a grooved plug 6. In this rolling process, the pipe to be processed 2 is shrunk at a predetermined shrinkage ratio, and at the same time, spiral fins 8 are formed on the inner surface of the pipe.
In other words, a spiral groove is formed.

In FIG. 1, reference numeral 10 denotes a floating plug that shrinks the pipe to be processed 2 by a predetermined amount between it and a die 12 provided upstream of the rolling head 4. It is connected to the grooved plug 6 and serves to hold the grooved plug 6 in a fixed position.

In addition, here, a type of rolling head 4 that presses balls 16 against the outer surface of the tube to be processed 2 is used, but it is also possible to use a type of rolling head that presses rollers against the outer surface of the tube to be processed 2. is also possible.

Next, as shown in FIG. 2, the tube to be processed 2 which has been subjected to the rolling process as described above is passed through at least two dies 18 having different forming dimensions.
(However, here, six dies 18 are shown) to perform dry drawing in order and reduce the diameter in stages to a desired final outer diameter. In this way, an internally grooved tube with a desired outer diameter is manufactured.

In this way, multiple dies 1 with different molding dimensions
8 to dry-draw the pipe 2 to be processed after rolling in a continuous and stepwise manner on the same line, when drawing with each die 18, the The pulling force from the die 18 acts on the tube 2 to be processed as a backward tension, effectively suppressing or obstructing the flow of the tube material in the radial direction during tube contraction. Compared to the case where the pipe to be processed 2 is subjected to dry drawing using the method, the rate of increase in the wall thickness of the pipe to be processed 2 (wall thickness at the bottom of the spiral groove; bottom wall thickness) can be significantly reduced. Moreover, it is even possible to reduce the wall thickness of the tube 2 to be processed. Therefore, during rolling processing, it has become possible to set the wall thickness of the pipe to be processed 2 larger than before, and it has become possible to further increase the rolling processing speed. This made it possible to improve the productivity of internally grooved tubes.

According to the method of the present invention, as described above,
Suppressing the increase or thinning of the tube wall thickness when the tube 2 to be processed is shrunk after the rolling process can be achieved simply by continuously empty drawing the tube 2 to be processed using a plurality of dies 18. Since this can be achieved by mechanically applying rear tension to the pipe to be processed 2, the equipment cost is lower and more compact, and its manufacture and maintenance are also extremely easy. It became.

Note that, according to the method of the present invention, each die 1
The rear tension during the dry drawing at step 8 and the rate of change in the wall thickness of the pipe 2 to be processed due to the dry drawing are determined by the number of dies 18 used and the number of dies 18 applied to the pipe 2 to be processed.
It is possible to control the rate of change over a relatively wide range based on the combination of the tube shrinkage rate or the shape of each die 18, and the rate of change is
Since the lubrication conditions in step 8 can be stably controlled by controlling them to a constant value, there is an advantage that the tube wall thickness can be easily and extremely stably controlled to a desired thickness.

In addition, in the method of the present invention, the die 18 whose molding dimensions have changed due to wear can be reused with corrected dimensions, except for the maximum molding dimension, so in this sense as well, it is economical. There are some advantages that are said to be advantageous.

Incidentally, Figures 3 and 4 respectively show a circular tube with an outer diameter of 15.88 mm and a tube wall thickness of 0.665 mm as the workpiece tube 2.
The number of dies 18 used is changed from 1 to 6 stages to dry draw the pipe 2 to be processed, and the relationship between the shrinkage ratio of the pipe 2 to be processed and the drawing load during the dry drawing, and These figures show the results of measuring the relationship between the shrinkage ratio and the wall thickness of the pipe 2 to be processed, and as is clear from these figures, if a plurality of dies 18 are used, it is easier to use just one die 18. Compared to the case, the rate of increase in the wall thickness of the tube to be processed 2 can be significantly suppressed, and especially when three or more dies 18 are used, the wall thickness of the tube to be processed 3 can be reduced. You can even do that. From this, when a pipe with internal grooves provided with spiral fins 8 on the inner surface is used as the pipe to be processed 2, and the pipe to be processed 2 is subjected to dry drawing with two or more dies 18, the pipe to be processed is It is easily inferred that the rate of increase in the bottom wall thickness at the bottom of the spiral groove of the pipe to be processed 2 can be significantly reduced or reduced compared to the case where the pipe 2 is simply drawn with one die 18. It is.

FIG. 5 also shows a workpiece tube (inner grooved Pipe) 2 from the outer diameter of 9.52mm to 7.0
The measurement results of the bottom wall thickness, fin height, and total wall thickness (bottom wall thickness + fin height) of the pipe to be processed 2 when the pipe is shrunk to an outer diameter of mm when a single die 18 is used. As is clear from the figure, if only a single die 18 is used, it is inevitable that the bottom wall thickness of the pipe to be processed 2 will be significantly increased. However, in the case of dry drawing according to the present invention using a six-stage die 18, only the outer diameter of the pipe to be processed 2 can be reduced well without changing the bottom wall thickness or the fin height. It is recognized that it can be controlled.

Although the present invention has been described in detail above, the present invention is not limited in any way by the above description, and it goes without saying that the present invention can be implemented in modes other than the above without departing from the spirit thereof.

For example, the pipe to be processed may be a pipe in which grooves are formed on the inner surface using a grooved plug and a rolling head as described in the examples, or a plate material with grooves formed on one side by rolling. It may be a so-called internally grooved welded pipe in which the abutted ends are welded to each other, and it is also possible to use a die 18 with seven stages or more in the dry drawing process. be.

(Effects of the Invention) As is clear from the above description, the present invention is advantageous in that when a tube to be processed having a groove of a predetermined shape is formed on the inner surface is shrunk to a desired size, the tube is covered with a plurality of dies arranged in series. Since the pipe to be processed is continuously drawn by air, it has an extremely simple and inexpensive device configuration, and can suppress or prevent thickening of the pipe to be processed, while maintaining a good quality of the pipe to be processed. Therefore, by increasing the thickness of the pipe to be processed, the rolling speed during rolling processing can be made faster than before, and the productivity of internally grooved pipes can be advantageously increased. It can be improved. Moreover, according to the method of the present invention, the tube wall thickness of the final product can be accurately maintained at a constant value by simply controlling the lubrication of each die at a constant level during dry drawing, making it possible to control the tube wall thickness. It also has the advantage of being extremely easy.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional explanatory view for explaining the step of forming grooves by rolling on the inner surface of a pipe to be processed prior to application of the method of the present invention, and FIG. FIG. 2 is a cross-sectional explanatory diagram for explaining an example of a drawing operation. Fig. 3 is a graph showing the fluctuation state of the drawing force of the circular tube during dry drawing as the number of dies used changes, and Fig. 4 shows the fluctuation state of the drawing force during dry drawing as the number of dies used changes. It is a graph which shows the fluctuation state of the pipe wall thickness of a circular pipe. Figure 5 shows
Comparing the fluctuation state of the wall thickness of the internally grooved pipe that was dry drawn according to the method of the present invention and the fluctuation state of the pipe wall thickness of the internally grooved pipe that was dry drawn according to the conventional method. This is a graph showing. 2: Pipe to be processed, 4: Rolling head, 6: Grooved plug, 8: Fin, 18: Die.

Claims (1)

[Claims] 1. A pipe to be processed having grooves of a predetermined shape formed on its inner surface is continuously subjected to dry drawing using a plurality of dies arranged in series, while suppressing an increase in the wall thickness of the pipe to be processed. , a method for manufacturing an internally grooved tube, characterized by reducing its outer diameter in stages.