JPS6224828A - Mandrel for expanding tube - Google Patents

Abstract

PURPOSE:To prevent the inside surface of a finished tube from waving and to improve both dimensional accuracy and quality by specifying the radius of curvature of the circular arc part of the work plane of a mandrel. CONSTITUTION:A mandrel is classified in a mandrel body 1a and a top plug which consists of a tapered part 20 and a straight part 21. The work plane M of the tapered part 20 is made up of a tapered plane m1 is the front stage and a tapered plane m2 in the rear stage and an intermediate circular arc plane m0 adjoining the planes m1 and m2. The circular arc plane m0 has a proper shape capable of connecting the tapered plane m1 in the front stage and the tapered plane m2 in the rear stage smoothly. The radius R of curvature of the plane m0 is larger than the inside radius r0 of a blank tube. In this way, the inside surface of a finished tube is prevented from waving.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement in the shape of a tip plug of a mandrel for expanding a metal pipe, for example, a steel pipe, and more specifically to improving the shape of the tip plug of a mandrel for expanding a metal pipe, such as a steel pipe. This invention relates to a mandrel that prevents the occurrence of undulation in the axial direction.

[Conventional technology]

For example, large-diameter, thin-walled, seamless steel pipes are required for nuclear power generation-related piping, but thin-walled, large-diameter pipes that meet these requirements can be produced using conventional methods such as the roll perforation rolling method (Mannesmann method), Hot punching method (Erhardt method)
It is actually difficult to directly produce it by such a method, and even if it could be produced, there would be a big disadvantage in terms of production yield and efficiency.

As a method of manufacturing such a thin-walled, large-diameter tube, there is a method of expanding the tube using a mandrel. That is, as shown in Fig. 6, a mandrel f1+ having a thickened plug part (2) at its tip is used, the tube ful obtained by the above manufacturing method is inserted into this as a material, and the rear end ( The tube is expanded by pushing the tube (UL is the tip σ) and passing through the plug part (2) in order by pressing the U with the bushing head (3) (hereinafter referred to as the mandrel tube expansion method).This process In principle, this is done hot by placing a heating means (fc) such as a high-frequency coil near the plug part (2), but depending on the conditions, cold work is also possible.

[Problem that the invention seeks to solve]

However, this mandrel tube expansion method has a problem with the dimensional accuracy of the product. One of the problems is that, as shown in FIG. 7, the expanded tube U), especially the inner surface 1), has a wavy shape in the axial direction, and the inner diameter is not stable in the axial direction.

The purpose of the present invention is to improve the dimensional accuracy and quality of a pipe as a product by the mandrel expansion method by preventing the above-mentioned inner surface waving phenomenon, and to provide a mandrel that meets such purpose. There is a particular thing.

[Means for solving the problem] The general structure (shape) of the mandrel used in the mandrel tube expansion method is as follows. That is, as shown in FIG. 8, the mandrel (1) is first divided into a mandrel main body αω and a tip plug portion (2). The tip plug portion (2) consists of a thickened tip portion (21 straight body portion + 211), the thickened tip portion continues from the main body αa, and the straight body portion (21
+ is connected to the large diameter side of the thick part ■. The machined surface h) of the thickened part (2) is formed as a tapered surface, which is usually divided into the front stage Gut) and the rear stage GT12), and the taper angle (θαθ2) of the rear stage GT12) is greater than that of the front stage U1). is set so that it is larger.

The tube (ul) is set in the mandrel body (1a) from the rear end can' side, and is pushed through the plug part (2) at the tip from here. The processing by the plug part (2) is to substantially expand the pipe in the thickened part, and then to expand the pipe in the straight part C.
This is done by refining the old material and adjusting its shape.

The reason why the front thickening part circle is divided into the first stage (Gut) and the second stage G112) is to prevent excessive deformation force from acting on the material at the start of machining.
The slope (taper angle (θ1)) is set smaller.

The inventors of the present invention thought of preventing the above-mentioned phenomenon of internal waving of the finished tube by adjusting the shape of the plug part of the mandrel, and conducted detailed experiments and studies on the shape of the plug part. As a result, we found the following facts.

■G- for mandrel tube expansion method uses low heat and low pushing force.
In order to improve the inner surface properties of processed tubes, it is customary to use a lubricant between the outer surface of the mandrel (1) and the inner surface of the tube (UL). Behavior is involved. Now, the thick part of the plug part■
The diameter increase rate (gradient) at the connection position (A) of the material passing through it (considering UL, the thickened part is on the machined surface, front stage 1) and rear stage GT 12) is at the front in the direction of material movement. Since the material (U) will increase transitionally to the side
The contact surface pressure between the outer surface of the mandrel and the outer surface of the mandrel increases significantly beyond the above-mentioned position A (B), and as a result, near the position A, the material tends to float up from the outer surface of the mandrel, creating a gap (sl) between the two. During processing, this void (
Lubricant is drawn into Sl from the front stage (mo side) one after another as the material is loaded, but this lubricant is drawn into the rear stage (m2).
Since the contact pressure on the side is very high, it gradually accumulates there.

In this way, the pressure within the gap gradually increases until it balances with the surface pressure on the downstream side.1. Immediately after the pressure within the gap exceeds the above-mentioned surface pressure, the lubricant ruptures and is ejected to the subsequent stage, resulting in a phenomenon in which the pressure within the gap suddenly decreases. This behavior of the lubricant, from internal pressure rise to bursting, is repeated periodically during pipe expansion according to the continuous pushing operation of the pipe, resulting in varying degrees of lubricant state in the subsequent stage G112). Such changes in processing conditions cause the inner surface of the finished tube to wave.

■In order to prevent the inner surface waving phenomenon, adjust the shape near the connection position (A) of the front stage (mt) and rear stage ←2) of the machined surface of the thickened part to create a gap (Sl) between it and the material (u). In other words, make a radius near the above connection position as shown by the symbol Gn0) in Figure 1 so that it smoothly connects to both sides of the front stage Buddha 1) and the rear stage (m2). I can think of seven.

The appropriate value of this radius of curvature (m0) depends on the inner diameter of the raw pipe (ul) to be processed, and the radius of curvature should be larger than the inner radius (rO) of the raw pipe. This effectively prevents the inner surface waving. That is, by setting such a curvature, the generation of the void (S) in the thickened portion is avoided, and fluctuations in processing conditions due to lubricant rupture, which is the cause of inner surface undulation, are prevented.

The present invention is based on the investigation of the above facts,
In other words, the feature of the tube expansion mandrel according to the present invention is that, in the thickened end of the tip plug part, the machined surface whose slope becomes gradually steeper toward the tip side is arranged as a circular arc surface, or the whole is formed into a single circular arc surface or a double circular arc surface. It is composed of arcuate surfaces that are smoothly connected as a whole, and the radius of curvature (2) of the arcuate surface portion is set to be larger than the inner radius (r0) of the raw pipe used.

Specific examples of the mandrel of the present invention will be described in detail below.

FIG. 1 shown above shows the most basic example of the mandrel of the present invention.

The basic structure of the mandrel of the present invention is also the same as that of the conventional mandrel described above. That is, the mandrel is first divided into a mandrel main body (1a) and a tip plug part (2). The diameter (d) of this mandrel body (1a) is slightly smaller than the inner diameter (2xr0) of the raw tube (ul) to be expanded. +211, the thickened part (to) connects to the mandrel main body (1a), and its diameter (drrL) gradually increases from the main body diameter (dl) toward the tip side, and the straight body part (2Il It is a form with a .

Now, in the example shown in the same figure, the thickened part (processed surface of the mausoleum) ((
R) are smoothly connected by a circular arc surface (m0). That is, the processing surface ((R) is two tapered surfaces G11l) GT12 at the front stage and the rear stage) is set, and these (M) are connected by a circular arc surface (ma).

To explain each part of the above-mentioned machining surface, firstly, the pre-stage tapered surface Gnt) continuing from the mandrel body (1a) is designed to prevent sudden excessive force from acting on the material at the start of machining, as mentioned earlier. The taper angle (θ1) is considerably smaller than that of the later stage Gn 2), which will be described later. Specifically, the material properties of the materials used (
(deformability, etc.) and is determined so that the deformation force at the start of machining is within a reasonable level. In the case of steel pipes, the appropriate value varies depending on the pipe diameter, but is generally around (3 to 20).

The part from the arcuate surface Gn 0) following the first stage @1) to the tapered surface (m2) of the second stage functions as a place where full-scale processing is applied to the tube processed in the first stage.

The taper angle (θ2) of the latter stage is determined according to the material properties, the required amount of pipe expansion, and taking into account the equipment constraints on the pressing force of the raw pipe. The taper angle of the previous stage (θ1) should be larger than the taper angle (θ1) of the previous stage and below the limit taper angle for the occurrence of battering based on material properties, and the pressing force of the raw pipe should be within the constraints from the equipment perspective, and the pressure of the previous stage ( mt) and the length Clm of the entire machined surface (b) including the arcuate surface Gn0) described below
') shall be designed to a length that does not cause any inconvenience in terms of equipment, workability, productivity, etc. Generally speaking, the above l! It is advantageous for the length of m to be shorter from all aspects, so in practice, this taper angle (θ2
) should be set as large as possible. In the case of steel pipes, the taper angle (θ2) at the turn is approximately 10° to 25°. The large diameter side end of this latter stage (m2) will be connected to the processing surface of the straight body part (2D), which will be described later.

The arc surface (m0) is both the front and rear Taber surfaces (m 1)
It has a shape that smoothly connects Gn 2) (M), and its radius of curvature 8) is larger than the inner radius of the raw pipe (r0).

The size of the radius of curvature (R1 is based on the knowledge of the inventors mentioned above, and if it is smaller than the inner radius of the raw pipe (r0), the material (u
A gap similar to that shown in FIG. 7 (S) above is also observed between the lubricant and lubricant, and as in the past, lubricant accumulates and ruptures occur repeatedly, and the phenomenon of internal undulation cannot be prevented. By making this equal to or larger than the inner radius of the raw pipe (r0), the abnormal behavior of the lubricant caused by the above-mentioned void fs) can be effectively eliminated, making it possible to obtain a product with a stable shape without inner surface undulations. It is.

The most preferable range of this radius of curvature is 2×r
.

Above, particularly good results can be obtained within this range.

The upper limit of the radius of curvature of this arcuate surface is not intentionally set. This is because the radius of curvature (R) is as thick as possible (there is no problem even if it is.) The arcuate surface is made between the front stage -θ and the rear stage GT12 while maintaining the condition of smooth connection to both. As the radius of curvature B) of u0) increases, the proportion occupied by the arcuate surface increases, and the range of the tapered surface GTII) GT12) becomes compressed, and finally the entrance end of the thickened portion ■■ 5, or the exit end (2
The range of the arcuate surface 0) extends to the position 0'). Since it is geometrically impossible to increase the radius of curvature R) beyond 2, the upper limit of the radius of curvature is determined there. In other words, the upper limit of the radius of curvature (R1) will change depending on how the thermal theory front and rear stages (m Lm2 ) are set, but once the setting is decided, it will be specified automatically. However, there is no decrease in the effect of preventing internal pruning, and in fact, there is a tendency for it to improve.

When the radius of curvature @) of the circular arc surface (m 0) is increased to its maximum limit, the following special form will be derived.

(2) As shown in Figure 2, there is no front stage (mt), and the arcuate surface Gn0) starts directly from the entry side end (20') of the thickened end.

The initial slope of the arcuate surface (the tangential slope at the inlet end (20') of the thickened portion) conforms to the slope of the previous stage described above, that is, the taper angle (θ1).

■As shown in the same figure (b), there is no rear stage θ, and the arcuate surface 0) reaches directly to the protruding end of the thickened part (■).
Leads to 1. Final slope of the arc surface (outgoing end of the thickened part (2
The tangential gradient at ) is the latter taper angle (θ2
).

■It is a combination of ■ and ■ above, and the first stage GnL) is also the second stage ←
There is no ρ, and the entire machined surface is composed of a single circular arc surface GTIω. The initial slope and final slope of the arc surface are the same as in part a.

In each of the above examples, the number of arcuate surfaces is one, but the thickened end circle can also be configured with a plurality of arcuate surfaces, and an example of this is shown below.

b) As shown in Figure 2)), the tapered surface is shaped in three steps (m 0 (
m 2) and 3), or higher in some cases, and a circular arc surface Gno-1) (mo-2
).

In this case, the above conditions are applied to all arcuate surfaces.

→This is a development of the above A) using the same concept as in the case of one circular arc surface, and the radius of curvature (R) of the circular arc surface U0) is increased to expand its range and the tapered surface Gnt)Gn
2) A form in which one or more of (m3) is missing. As a very special case of this example, a form formed by a plurality of circular arc surfaces having different radii of curvature can be considered.

Next, regarding such a thickened part, near the exit end C2 (R) (final stage), there is a slope (taper angle μ )) may be given as a finished surface and connected to the straight body part (211) through this.In other words, the small tapered surface (n) of The material portion (u2) is the subsequent portion passing through the thickened portion (
Due to the force (moment force) that tries to continue expanding the tube from u3), there is a tendency for the straight body to be lifted from the outer surface of the closed body, but the finished surface (nl) alleviates this tendency. It is expected that the inner surface of the material will be aligned along the straight body part (2υ outer surface) to further stabilize the finished dimensions.This tapered surface (the slope of nl is 1710
Below, 3/40 or less is particularly effective, and its axial length is 0. It is desirable to set it to IXD (D is the diameter of the straight body part + 211) or more.

Note that, instead of the single tapered surface described above, this portion may be formed by a multi-step tapered surface or an arcuate surface whose slope gradually decreases toward the exit side, and in this case, the same conditions are taken into consideration.

Finally, the straight body part ■D is the part where final refinement is applied to the tube (ul) that has been processed at the thickened end, and is mainly used to correct roundness and bending. Its diameter (Dl) teeth,
There are no particular restrictions on the diameter (the same as or slightly smaller than the target finished inner diameter, and the length), but from the perspective of straightening effectiveness, it is desirable to set it equal to or greater than the diameter (Dl), and it also improves handling and tooling. In terms of cost, etc., it is better to set it to about 2XD at the longest.

With the dimensions of each part shown in Figure 4, the thickened part ■ The front stage of the machined surface (
m t ) and the rear stage GTI2). ) Using mandrels with various radius of curvature 8), a steel pipe with an inner diameter of 204 ann/m and a wall thickness of 17.5 mm was used to expand the mandrel (number of expanded pipes per mandrel type: 10), and the inner surface was corrugated. When we investigated the occurrence situation, the results were as shown in Figure 5.

As is clear from the figure, the frequency of occurrence of internal undulations was 5096, but R = 102mm (=r0
), it decreases to 30 coefficients, R = 204 mm (roX
2), there was no such occurrence, confirming the effectiveness of the present invention.

〔Effect of the invention〕

As is clear from the above description, the mandrel of the present invention is
It reduces and even completely prevents the phenomenon of internal waving of finished pipes during mandrel expansion, and it greatly contributes to improving the dimensional accuracy and quality of mandrel expansion products.

[Brief explanation of the drawing]

FIG. 1 is a side view showing the structure of a tube expansion mandrel according to an embodiment of the present invention, FIG. 2 U) to U) are upper half side views showing other embodiments of the mandrel of the present invention, and FIG. 3 4 is a side view showing an embodiment of the mandrel of the present invention, which has a finishing surface at the last stage of the thickened end of the plug part; FIG. 4 is a diagram showing the dimensions of each part of the mandrel used in the mandrel expansion experiment; Fig. 5 is a diagram showing the results of the experiment, Fig. 6 is a schematic diagram explaining the mandrel pipe expansion method, Fig. 7 is a partially cutaway perspective view showing the state of internal waving of the finished pipe in mandrel pipe expansion, and Fig. 8 is a side view for explaining a conventional example of a tube expansion mandrel and the mechanism of occurrence of the above-mentioned inner surface undulation,
It is. In the figure 1 = mandrel, 1a: mandrel body, 2 nib lug section, 2o: thickened end section, 21: straight body section, 3: pusher head Fig. 1 Fig. 2 Fig. R Inner radius Fig. 6 Fig. 8 Fig. 7

Claims (1)

[Claims] (1) A mandrel having a thickened plug part (2) at the tip, through which a metal tube is pushed and passed through for pipe expansion processing, wherein the tip plug part (2) is the point where the pipe is substantially expanded. It consists of a thickened part (20) and a straight body part (21) which is a fine processing part following it, and the thickened part (20) starts at the entrance end (20') of the part and turns towards the exit side. It has a machined surface (M) with a steep slope, and the machined surface is partially arranged with an arcuate surface, or the whole is composed of a single arcuate surface or a double arcuate surface, and the whole is smoothly connected. , the radius of curvature (R) of the circular arc surface portion is the inner radius (r_
A mandrel for expanding tubes, characterized in that the size is set to be larger than 0).