JP2842225B2 - Upset processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an upsetting method for increasing the thickness of an end of a steel pipe.

[0002]

2. Description of the Related Art When connecting long steel pipes such as oil country tubular goods,
Install joints etc. on the screws formed on the inner and outer surfaces of the steel pipe end,
A method of connecting one after another is generally adopted. In this case, the end portion of the steel pipe P to secure the strength of the threaded portion, as shown in FIG. 6, often thickened portion P ₁ is formed.

In the upset process for forming such a thickened portion, conventionally, the end of the material 3 is heated in a heating furnace so as to have a temperature as uniform as possible in the axial direction.
(A) As shown in (b), a die 1 for forming the outer diameter of the thickened portion and a mandrel 2 for forming the inner surface are formed by hot forging.

[0004]

Meanwhile [0007], the thickened portion P ₁ formed by upset process as described above, since threading is performed, the thickened portion P ₁ the axial length of the predetermined Need to finish to length. This out outside upset length L ₁ is determined by the press allowance of the shape of the die 1 and the mandrel 2, the inner upset length L ₂ and the inner taper length L ₃ are die 1 shape and mandrel 2 It is not determined only by the pushing allowance, but also affected by the heating temperature and heating length of the pipe end. Therefore, in the upset processing, the heating condition of the pipe end is very important.

During the upset processing, the die 1 and the mandrel 2 come into contact with the heated pipe end to cool locally, and the deformation resistance changes due to the deformation history. The deformation process is very complicated.
For this reason, uniform heating in the axial direction as in the past is not necessarily optimal heating, and it is not always the case that the axial dimension of the thickened portion is long, or the thickening rate (thickness of material / thickness after upset processing). If the thickness) is large, the inner upset length L ₂ may not reach a predetermined size, there is a problem that often defects underfill or buckling occurs.

In Japanese Unexamined Patent Publication (Kokai) No. 61-276732, the heating temperature distribution in the middle portion of the pipe end thickening portion is gradually reduced from the tube end thickening portion side toward the steady thickness side of the pipe, and the upset is performed. Although a processing method is disclosed, this method is for controlling the shape of the tapered portion on the inner surface, and does not take into account the deformation in the process of increasing the thickness at the time of upsetting as in the present invention. Therefore, even if the wall thickness increase rate is large or the internal upset length is long by this method, only the shape control of the inner surface taper part can be performed, but the wall thickening deformation during the upset processing is the same as the conventional axial direction. As with uniform heating, defects such as underfill and buckling cannot be eliminated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides a predetermined upset dimension, particularly an inner upset length, without causing defects such as underfill and buckling. It is an object of the present invention to provide an upset processing method capable of performing an upset processing.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted a detailed investigation of the deformation process of a thickened portion when the conventional method of upsetting after uniform heating of the end is carried out by analysis and actual machine test. And found the following facts.

In the conventional uniform heating shown by the solid line in FIG. 1, the raw material 3 first contacts the outer tapered portion 1a of the die 1 as can be seen from the thickening process shown in FIGS. 8
(B)] Then, the blank 3 comes into contact with the entire surface of the die 1 (FIG. 8 (c)). After that, the meat increase is shown in FIG.
As shown in FIG. 3 (f), the material proceeds in order from the end, but the flow of the raw material 3 is hindered by the influence of friction with the mandrel 2, so that it is difficult to obtain a predetermined inner set-up length without defects. Has become.

The reason for this is that, as shown in FIG. 5B, the strain rate in the initial deformation process is highest at the pipe end, and the impact force at the initial stage of pushing the mandrel 2 is concentrated at the pipe end. This is because the pipe end is increased in thickness at an early stage and comes into contact with the mandrel 2. Therefore, if the pipe end is concentrated so that the wall thickness is intensively increased and contact with the mandrel 2 is suppressed at the initial stage, and processing is performed so that the wall thickness increases also from portions other than the pipe end and the wall thickness increases simultaneously in the axial direction. A predetermined inner upset length can be obtained without defects. In FIG. 5, the black portions have a strain rate of 8.8 to 12.3 (1 / sec), and the right hatched portions have a strain rate of 5.2 to 5.2.
8.8 (1 / sec), the point indicated by a dot has a strain rate of 1.7.
~ 5.2 (1 / sec), the blank part has a strain rate of 0.0 ~
1.7 (1 / sec).

[0011] upset machining method of the present invention has been made based on such knowledge, when to upset machining the ends of the steel pipe, maximum temperature and without a central portion of the pipe end the heating portion before processing, After the pipe end is heated with a chevron-shaped axial temperature distribution such that the temperature becomes lower as going from the center to both sides, upset processing is performed.

[0012]

[Action] upset machining method of the present invention, when upset machining the ends <br/> of steel pipe, maximum temperature and without a central portion of the pipe end the heating portion before processing, on both sides from the central portion After heating the pipe end with a mountain-shaped axial temperature distribution that becomes colder as it goes down, the upset processing is performed, which promotes the increase in wall thickness from the center in the heated pipe end, and the deformation resistance at the pipe end And the wall thickness increase occurs as simultaneously as possible in the axial direction.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The upset processing method of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing the heating temperature distribution at the pipe end in comparison with the raw material and the position of the steel pipe end after upset processing, and FIGS. 2 (a) to 2 (f) show the thickening process in the case of the method of the present invention. Figure showing step by step, FIG.
Is a schematic diagram of a heating furnace used when applying the method of the present invention,
FIG. 4 is an explanatory diagram of a temperature distribution of a pipe end heating portion when the method of the present invention is applied, FIG. 5 (a) is a diagram showing a strain rate of the tube end at the time of thickening in the method of the present invention, and FIG. FIG. 4 is a similar diagram for the method.

The upset processing method of the present invention
In the up-set processing, the pipe end heating portion before processing is adjusted, for example, by adjusting the resistance of each coil 4a of the high-frequency induction heating furnace 4 as shown in FIG. 3 to obtain a temperature distribution as shown by an imaginary line in FIG. That is, the heating central portion (the portion in the material) has the highest temperature A, for example, 1200 ° C., and the lower the temperature from the heating central portion toward both sides, that is, the tube end and the raw tube side, that is, the temperature B at the tube end is 20 from the maximum temperature A
After heating at a lower temperature of 0 to 400 ° C., for example, at a mountain-shaped axial temperature distribution of 900 ° C., upset processing is performed.

After heating the temperature distribution of the pipe end heating portion with the above-described angle-shaped axial temperature distribution and performing upset processing, first, the material 3 is formed into the outer surface tapered portion 1a of the die 1 and the parallel portion 1b (material). 3 (FIG. 2 (b)), and thereafter the wall thickness increases not only at the pipe end but also in the entire axial direction [FIG. 2 (c) to FIG.
(E)]. Then, in the final stage, the entire surface comes into contact with the mandrel 2 at a stretch to finish the processing [FIG. 2 (f)].

That is, according to the method of the present invention, the temperature is lowered at the pipe end to increase the deformation resistance, thereby avoiding intensive wall thickening and promoting the wall thickening at the center of heating.
As shown in FIG. 5A, the strain rate does not increase intensively at the pipe end, and the wall thickness increases almost uniformly in the axial direction. As a result, there is no influence of friction with the mandrel 2 in the wall thickness increasing process. Therefore, if and inner upset length L ₂ longer, even when the thickness increase rate greater, can be obtained without defects predetermined upset length of such buckling or underfill.

By the way, the maximum temperature A at the center of heating is
After heating at 1200 ° C. and heating at a tube-shaped axial temperature distribution such that the temperature B at the pipe end becomes 900 ° C., an I · EUE type upset as shown in FIG. After comparing the method and the product processed by the conventional method with the same upset processing after uniformly setting the temperature of the heated part to 1200 ° C., the product processed by the conventional method showed a variation in the inner upset length. Many were less than the prescribed length. In addition, even when a predetermined length is obtained, a defect such as an underfill may occur.

On the other hand, the product processed by the method of the present invention has an average upset length that is about 18% longer on average than that processed by the conventional method, and has a variation range of about 30%.
% And less than the conventional method. Further, the occurrence rate of underfill and buckling was 0%, and a predetermined upset length could be obtained without defects.

It should be noted that in the present embodiment, the I as shown in FIG.
-Although the description has been given of the case where the present invention is applied to the EUE type upset processing, it is also applicable to all forging processing in which the mandrel is pushed in to increase the pipe end of the material as in the IEU type upset processing shown in FIG. Applicable. Further, the heating temperature distribution may not be a mountain shape having a sharp angle as shown by the imaginary line in FIG. 1 but may be a smooth mountain shape as shown by the solid line or the broken line in FIG.

[0020]

As described above, according to the upset processing method of the present invention, the central portion of the pipe end heated portion before processing is set to the highest temperature, and the lower the temperature becomes from the center to both sides, the lower the temperature becomes. Heating the pipe end with the temperature distribution in the axial direction and then performing the upset processing promotes the increase in wall thickness from the central part in the heated pipe end, increases the deformation resistance at the pipe end, and is almost uniform in the axial direction. As a result, the meat is not affected by friction with the mandrel during the meat increasing process. Therefore, when the inner upset length is long,
Even when the rate of wall thickness increase is large, a predetermined upset length can be obtained without defects such as buckling and underfill.

[Brief description of the drawings]

FIG. 1 is a diagram showing a heating temperature distribution at a pipe end in comparison with a raw material and an end position of a steel pipe after upset processing.

FIGS. 2 (a) to 2 (f) are diagrams sequentially showing the process of increasing the thickness in the case of the method of the present invention.

FIG. 3 is a schematic view of a heating furnace used when applying the method of the present invention.

FIG. 4 is an explanatory diagram of a temperature distribution of a tube end heating portion when the method of the present invention is applied.

FIG. 5 (a) is a diagram showing a strain rate of a pipe end at the time of thickening in the method of the present invention, and FIG.

FIG. 6 is a diagram illustrating an example of upset processing;
(A) shows the I.EUE type, and (b) shows the IEU type.

FIGS. 7A and 7B are diagrams for explaining an upset processing method in order;

8 (a) to 8 (f) are diagrams sequentially showing a process of increasing the thickness in the case of the conventional method.

[Explanation of symbols]

 1 Dice 2 Mandrel 3 Material

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-276732 (JP, A) JP-A-4-351241 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B21J 1/06 B21J 5/08

Claims (1)

(57) [Claims] Upon 1. A to upset machining the ends of the steel pipe, maximum temperature and without a central portion of the pipe end the heating portion before processing, low temperature become such chevron axial extent Yuku on both sides from the central portion An upset processing method comprising heating a pipe end at a temperature distribution and then performing upset processing.