JPH0739931A - Method for locally thickening tube - Google Patents

Abstract

PURPOSE:To manufacture a thickened tube by a simple method using a general purpose device. CONSTITUTION:The thickened tube without wrinkles is manufactured by heating and cooling a tube 101 while moving a coil 8 and cooling ring 9 along the tube 101 at a constant speed and swaging the tube by lowering a press slide 2 while increasing or decreasing a swaging pressure to a specific pressure by repeating turning on or off of the power supply for a oil pump so that a swaging speed at which an index value that is obtained from a heating state and swaging speed is made smaller than the critical index value.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for thickening a part of a pipe.

[0002]

2. Description of the Related Art A joint is generally used for a bent portion or a branched portion of a pipe, but in order to reduce cost, a bent pipe may be used without using the joint. If the pipe is bent in order to manufacture such a bent pipe, the wall thickness of the bent portion becomes very thin, which causes a problem in strength. For this reason, a local thickening method is used in which the thickness of the bent pipe is increased in advance in order to make the thickness of the bent pipe uniform.

Such a conventional local thickening apparatus is shown in FIG.
Shown in. The steel pipe 101 is held by the clamp 21, and the coil 24 through which electricity flows and the cooling ring 25 that jets water are moved along the longitudinal direction of the steel pipe 101 to locally cool the periphery of the steel pipe 101 to a predetermined temperature. While heating with high frequency induction. At the same time, the press machine 22 applies a predetermined pressure to the clamp 21 via the bearing 23 to the steel pipe 101.
When added in the direction orthogonal to the axis of
Since a pressure is applied to the steel pipe 101 in a direction parallel to the axis of the steel pipe 101, the heated portion of the steel pipe 101 is compressed (hereinafter referred to as upsetting) and the wall thickness is increased.

FIG. 5 shows the correlation between the pressure and upset amount and the processing time in this case. The pressure increases rapidly up to 0.5 minutes,
After that, it increased slightly, and after 1.5 minutes, the specified pressure (10
Reaching 0 kgf / cm ² ). On the other hand, the upset amount increased sharply to 0.5 minutes, and then gradually increased and decreased to 1.2
After 5 minutes, the amount of increase is constant. That is, in the initial stage of processing, the amount of increase in the upsetting amount (hereinafter, this is referred to as upsetting speed) is large.

[0005]

In the above-described local thickening method, the steel pipe 101 is rapidly increased in pressure to a predetermined value.
In addition, the upsetting speed of the steel pipe 101 is higher in the initial stage of machining than in the end stage of machining. Therefore, as shown in FIG. 6, wrinkles 101b are likely to occur in the thickened portion 101a that was heated in the initial stage of processing,
It becomes a problem in use.

As a solution to such a problem, Japanese Patent Publication No. 2-7738 discloses that a stepping cylinder is controlled by a control device so that the upsetting speed is always constant. However, this requires the use of expensive equipment in order to maintain a constant upsetting speed,
It is very difficult to thicken a pipe at low cost.

In view of the above, an object of the present invention is to provide a method for locally increasing the thickness of a pipe by which a thickness-increasing pipe can be manufactured by a simple method by using a widely used device. .

[0008]

In order to solve the above-mentioned problems, the present invention is to locally increase the wall thickness of a pipe by locally installing the pipe while locally heating the pipe. In the processing method, the index value obtained from the heating state and the upsetting speed was set up while increasing or decreasing the upsetting pressure to a predetermined pressure so that the upsetting speed becomes smaller than the limit index value obtained in advance. is there.

[0009]

In the method for locally increasing the wall thickness of a pipe having the above-described structure, the upsetting pressure is increased or decreased to a predetermined pressure so that the index value becomes smaller than the limit index value. Is not increased rapidly, and the tube is not wrinkled.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for locally thickening a pipe according to the present invention will be described with reference to the drawings. FIG. 2 shows a schematic configuration of an apparatus used when applying the method.

As shown in FIG. 2, a press slide 2 which is vertically movable is provided above the press head 1 so as to face it. A hydraulic cylinder (not shown) that moves the press slide 2 up and down is attached to the press slide 2. A hydraulic pump (not shown) for sending oil to the hydraulic cylinder is connected to the hydraulic cylinder.
This hydraulic pump can adjust the hydraulic pressure to the hydraulic cylinder by switching the power on / off.

A pressing jig 3 having a flat upper surface is attached to the upper surface of the press head 1. On the lower surface of the press slide 2, there are attached pressure jigs 4 whose lower surface is inclined so that the thickness becomes thicker on both right and left ends in FIG. A clamp 5 for holding the pipe 101 is provided between the pressing jig 3 and the pressing jig 4, and the lower surface of the clamp 5 is formed to be flat corresponding to the upper surface of the pressing jig 3. The upper surface of the clamp 5 is inclined so that the thickness increases toward the center so as to correspond to the lower surface of the pressing jig 4. A bearing 6 is provided between the pressure jig 3 and the clamp 5. A bearing 7 is provided between the pressure jig 4 and the clamp 5.

That is, the vertical pressure applied by the press slide 2 is converted by the pressure jig 4, the bearing 7, and the clamp 5 so as to upset the pipe 101 in a direction parallel to the axis of the pipe 101. is there.

A coil 8 is provided in an annular shape along the outer circumference of the pipe 101. A high-frequency power supply device (not shown) is connected to the coil 8 via a cable (not shown), and the coil 8 is adapted to perform high-frequency induction heating on the peripheral surface portion of the tube 101 adjacent to the inner peripheral surface thereof. A cooling ring 9 for spraying water onto the pipe 101 is provided on the left side of the coil 8 in FIG. 2 along the outer periphery of the pipe 101. The coil 8 and the cooling ring 9 are attached to a slide (not shown) and are movable along the longitudinal direction of the pipe 101.

Here, the coil 8 at a predetermined heating temperature
Fig. 3 shows the correlation between the index value expressed by the ratio of the upsetting speed to the moving speed and the thickness increase rate. As shown in FIG.
The larger the index value, the higher the rate of thickness increase. Index value is 0.3
If it exceeds, wrinkles will occur in the thickened portion of the pipe. That is, when the exponent value exceeds a predetermined value (here, 0.3), wrinkles occur, but if the exponent value is a predetermined value (hereinafter, referred to as a limit exponent value), Wrinkles do not occur.

From the above, in order to manufacture the thickened pipe with the above-mentioned apparatus, the pipe 101 is held in the clamp, and the pipe 101 is heated and cooled by the coil 8 and the cooling ring 9 to a predetermined temperature. . The coil 8 and the cooling ring 9 are moved at a constant speed by the slide, the hydraulic pump is operated, and the press slide 2 is lowered. At this time, the power supply of the hydraulic pump is repeatedly turned on and off so that the index value becomes a setting speed smaller than the limit index value, and the installation pressure is increased and decreased to a predetermined pressure.

That is, as shown in FIG. 1 showing the correlation between the pressure and the upset amount at this time and the processing time, the pressurization is repeated up and down to a predetermined value (100 kgf / cm ^{2 in} this example). The upsetting speed should not be sharply increased.

As a result, the above-mentioned index value does not exceed the limit index value, and wrinkles do not occur in the manufactured thickened pipe.

[0019]

As described above, in the method for locally increasing the wall thickness of a pipe according to the present invention, installation is performed while increasing or decreasing the upsetting pressure to a predetermined pressure so that the upsetting speed is such that the index value becomes smaller than the limit index value. Since the wrinkles do not occur in the pipe even if the upsetting speed is not kept constant, the thickened pipe can be manufactured by a simple method using a general-purpose device.

[Brief description of drawings]

FIG. 1 is a correlation diagram of pressure and upset amount and processing time when the method for locally thickening a pipe according to the present invention is applied.

FIG. 2 is a schematic configuration diagram of an apparatus when the method is applied.

FIG. 3 is a correlation diagram between an index value and a thickness increase rate at a certain predetermined heating temperature.

FIG. 4 is a conventional pipe local thickening device.

FIG. 5 is a correlation diagram of pressure and upset amount and processing time when a conventional method is applied using the apparatus.

FIG. 6 is a cross-sectional view of a tube processed by the conventional method.

[Explanation of symbols]

 1 Press head 2 Press slide 3 Pressurizing jig 4 Pressurizing jig 5 Clamp 6 Bearing 7 Bearing 8 Coil 9 Cooling ring 101 Tube

Claims (1)

[Claims] 1. A method for locally increasing the wall thickness of a pipe by locally installing the pipe while locally heating the pipe to locally increase the wall thickness of the pipe. A method for locally increasing the wall thickness of a pipe, which comprises increasing and decreasing the upsetting pressure to a predetermined pressure so that the upsetting speed becomes smaller than a limit index value obtained in advance.