JPS6156746A - Expanding method of seamless steel tube - Google Patents

Abstract

PURPOSE:To product the material yield and large tubes efficiently and reduce the cost by inserting a seamless steel material into a sticky mantrel with a head tube diameter and reducing a thickness of the tube diameter while heating the spot subsequently in the vicinity of a taper part. CONSTITUTION:A seamless steel material 1 is inserted into a mandrel 1, where a taper part 22 and a parallel plug part 22 are provided with slopes on their edge, and a mandrel edge part 2 is fixed and supported by a chack 4. A material 1 is pushed by a pusher head 5 and a high frequency heating coil 3 around and in the vicinity of the taper 22 and the material 1 are heated by a ring-like gas burner, and tube diameter reducing thickness is discharged from a plug part 21 to reduce the deforming resistance and facilitate tube diameter reducing with less resistance. If a peripheral steel of the plug 21 is pressed, a tube diameter becomes more homogeneous and better. A smaller edge of the plug part 21 prevents the resistance by cooling shrink of the steel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention particularly relates to a method for manufacturing thin-walled, large-diameter seamless steel pipes that are difficult to directly manufacture by roll piercing and hot extrusion methods.

[Prior art]

For example, steel pipes and joints for piping related to nuclear power generation are required to have no welds. If there is a welded part, it is necessary to inspect that part during regular inspections, which not only poses a safety problem as work is performed in a contaminated environment, but also extends the period when the machine is stopped for regular inspections. It is from.

It goes without saying that so-called seamless steel pipes are suitable for such uses.

Incidentally, in the case of such uses, a pipe having a considerably large diameter and a thin wall is required, but the above-mentioned seamless steel pipe has the disadvantage that it is difficult to make a thin-walled, large-diameter pipe.

In other words, relatively large-diameter seamless steel pipes are usually made by the so-called roll perforation rolling method (M/Sessmann method), but this is originally a method of manufacturing large quantities of pipes by continuous pipe manufacturing.
Current equipment is designed to efficiently manufacture pipes based on the dimensional range of products in demand, so pipes with too large a diameter, specifically over 430 mm, are not manufactured. It is no longer possible to manufacture it.

Another method for producing seamless steel pipes is hot extrusion (mluhar), which allows the production of considerably larger diameter pipes that cannot be produced manually. However, this method also uses t/D (t
: wall thickness, D: outer diameter) is restricted (e.g. outer diameter 450mm
Then t/D: 25%, same (at 800mm, t/D≧1
(limited to 1%), and there is a regret that thin-walled products cannot be manufactured. The Erhardt method is a method for reducing the diameter of a kelp-shaped material obtained by hard pressing by inserting a mandrel into its inner cavity and passing it through a die while applying force to the bottom. There is a risk of breakage.

There are three methods for obtaining thin-walled, large-diameter pipes that cannot be directly produced using the Erhardt method. First, a large-diameter pipe is drawn out using the Erhardt method, and its inner and outer surfaces are machined to make it thinner.
Next, we used the same Erhardt method to create an internally tapered tube with a thicker wall on the bottom side to prevent bottom breakage, and finished it by machining in the same way.Finally, we used the Mannesmann method or the hot extrusion method. The third method is to cold-reduce and expand the diameter of a seamless steel pipe using a cored metal.

However, the former two methods are not only inferior in terms of material yield and manufacturing cost because they are finished by machining, but also have problems in terms of productivity because the Erhardt method itself is not efficient. However, there is a disadvantage that a special tapered mandrel must be prepared.

Specifically, the third method for thinning and expanding the diameter is to attach a tapered core metal (9) with a tapered tip to a steel pipe (1) that is placed on a base plate (8), as shown in Figure 9. This is a method of pushing in, but there is a limit to the amount of diameter expansion (processing degree) per one time.
Depending on the required product diameter, the tube may need to be expanded several times, which is not an efficient method. However, as the number of processing increases, the number of softening treatments and lubrication treatments also increases, which poses an economical problem.

[Purpose of the invention]

The present invention enables the production of thin-walled, large-diameter pipes that cannot be directly manufactured using the Mannesmann method or the Erhardt method without machining, and is efficient and capable of achieving an extremely large amount of pipe expansion per operation. This provides an economical method for expanding seamless steel pipes.

[Structure of the invention]

That is, the present invention uses a seamless steel pipe obtained by a roll perforation rolling method or a hot extrusion method as a raw material, and comprises a tapered portion whose diameter gradually increases toward the tip side and a parallel portion continuing from the large diameter end. A plug having an outer surface is inserted into a mandrel with a tip at its tip, from its proximal end side and pushed toward the tip, and is passed through the plug while being sequentially locally heated by a heating means provided near the plug to expand the diameter and reduce the thickness. This article focuses on a method for expanding seamless steel pipes that is characterized by performing the following steps.

Hereinafter, the method of the present invention will be explained specifically and in detail based on the drawings.

Figure 1B) is a conceptual diagram of the tube expansion method of the present invention, in which (1) is the raw tube, (2) is the mandrel, (3) is the heating means, (4)
is a chuck, and (5) is a putunya head.

The mandrel (2) consists of a mandrel body (20) and a plug (21+) attached to the tip of the body.The mandrel body (201) has a diameter slightly smaller than the inner diameter of the raw pipe (1) used, and its length is The plug (21) should be at least somewhat thicker than the length of one raw tube.The plug (21) is connected to the mandrel body (mandrel), and basically has a taper part whose diameter gradually increases toward the tip. It has an outer surface consisting of a parallel portion (231) that continues to the end.The shape of the plug will be described in more detail later.

The heating means (3) is provided so as to extend from the tip of the mandrel main body to the taper part of the plug, and also partially extend from the parallel part of the plug. As a heating means, a high frequency coil is suitable, and this is connected to a mandrel (2) as shown in the figure.
It is set up so that it concentrically surrounds.

The chuck (4) grips and fixes the proximal end (h side) of the mandrel (2), and the pusher head (5) grips and fixes the proximal end (h side) of the mandrel (2), and the pusher head (5) grips and fixes the proximal end (h side) of the mandrel (2). This is to push the raw tube toward the tip of the mandrel by applying it to the mandrel.

The tube expanding method of the present invention is carried out using such an apparatus as follows.

The wall thickness and outer diameter of the raw pipe (1) to be used are determined based on the required product dimensions (target pipe manufacturing dimensions) and in consideration of sizing by pipe expansion as described below. The raw tube may be made by either the Mannesmann method or the hot extrusion method. Since the Mannesmann method is more advantageous in terms of economy, it is desirable to use this method for products within the size range that can be manufactured by this method.

The raw pipe (1) is inserted into the mandrel (2), which has been subjected to internal lubrication treatment if necessary, from its proximal end () side, and the proximal end of the mandrel (2) is gripped by the chuck (4). After fixing, a pusher head (5) is set on the rear end (1') of the raw tube (1) to propel the raw tube (1) toward the tip of the mandrel (2).

Then, the raw tube (1) that has been pushed by the butt/ear head (5) and has come to the tip of the mandrel body @) is heated by the heating means (3) sequentially from the tip as it advances, and the plug ( 21) to perform wall thinning and tube expansion processing. (Refer to the dashed line diagram) 1 This raw pipe is processed at the rear end (1') of the raw pipe.
) is stopped once before it is applied to the plug +211, and here, as shown in the same figure (b), the next raw pipe (10) is inserted into the preceding material (
After 1), set in the same manner and push the rear end (1σ) of the subsequent blank tube (111Il) with the head (5) to further push the preceding material (1) that is currently being processed forward, and complete the remaining processing. Once completed, the tube is discharged from the tip of the mandrel.By repeating this operation cycle, the tube is expanded one after another.

Now, although the specific method of the present invention is as described above, the shape of the plug of the mandrel used in the method of the present invention will be described in detail here.

FIG. 2 shows a preferred example of the above plug. As mentioned above, a plug consists of a tapered part and a parallel part, but in the illustrated plug, the taper part is first divided into two parts, the front stage (22g) and the rear stage (z2b), and the taper angle (θ1) of the front stage is the same as that of the rear stage. It is formed larger than that of (σ2). And the parallel part (231 is the front stage ■ω, the middle part (23b
), Rear stage G23c) (+) 3 Ic vignetting, middle stage diameter ('DD) is slightly larger than that of the front stage and rear stage ■0■υ.

The dimensions and functions of each part of the plug will be described in detail below.

Taper part> The former stage G22a) with a large taper angle (θ1) is where most of the tube expansion process is performed. θl is determined by the heating status of the material at the relevant location, the deformation resistance of the material, the required amount of pipe expansion, the amount of wall thickness change,
Laws are regulated as appropriate due to equipment constraints on material pressing force. -Although it cannot be said already, about 10° x θ1 x 15° is appropriate. Further, the length of this front part (/1) may be set to 0.8 times the length of the entire tapered part.

In addition, depending on the material heating condition, a part of the same portion (22a) on the mandrel body (20) side may have a taper angle of θ1 as described above.
The amount of processing may be kept relatively small at the initial stage of processing, when the deformation resistance has not yet sufficiently decreased, by appropriately creating a smaller portion.

Next, the latter stage (22b) of the tapered part serves to moderate the straightness of the material expanded in the previous stage C2ω, and to make the inner surface of the material overflow into the following parallel part 123). The taper angle (θ2) of this part needs to be much smaller than the above-mentioned θ1, and specifically, it can be said that about 2°<θ2<5° is optimal.

The length 12) of the same part is the length 11 of the front stage (22a).
) is 0.2 x total length of the taper part 1e)).

<Parallel part> The front stage (23a) is a part for correcting deformation of the tube expanded at the taper part @. The pipe passing through the tapered part @ is subjected to forces that cause it to become oval or bend due to heating temperature, uneven distribution of lubricant, uneven thickness, etc., so the deformation caused by this is corrected. The diameter (Ilk) of this portion is determined so that the pipe expansion by the next middle stage (23b) will be an appropriate amount (approximately 2 factors). In reality, it will be approximately equal to the inner diameter of the product tube.

The middle stage (23b) is a part where the pipe that has proceeded through the previous stage (23a) is finally slightly expanded to correct roundness and bending, and to ensure the product size takes into account the amount of heat shrinkage. It is. Therefore, the diameter (DO) of this portion is set to a size that takes into account the amount of heat shrinkage in the inner diameter of the product. An appropriate tube expansion rate for this middle stage C23b) is 2 degrees of variety.

The latter stage Cl23c) serves to prevent the occurrence of bending and deterioration of the roundness during the cooling process of the tube. In relation to the heating means (3), this part is provided so that the tube shows a temperature drop, and its diameter (Da) is set at the middle stage (3).
The inner diameter of the tube processed in step 23b) is made slightly smaller than the inner diameter when it contracts due to the material temperature difference between the middle stage and the front position of the part. If the diameter (DC) is about the same as that of the middle stage (23b), the pipe will seem to embrace the latter stage (03C), which will hinder the processing of the subsequent pipe.

According to the method of the present invention as described above, it is possible to secure a very large amount of pipe expansion, specifically up to 200 tubes, in one processing.

In the method of the present invention, the dimensional change in thickness reduction or length reduction accompanying pipe expansion is basically proportional to the amount of pipe expansion. Figure 3,
Figure 4 shows an example of experimental data showing this tendency (
The dashed line in the figure indicates the range of data variation. )this is,
This relationship was determined by keeping the inclination condition of the taper portion of the mandrel constant. Thickness loss and shrinkage due to tube expansion also have a large effect on the shape of the mandrel used and the heat pattern of heating the raw tube. There is a tendency that the higher the temperature, the smaller the thinning and the larger the shrinkage rate.

By the way, what about the present invention? At the rear stage (23c) of the parallel part of the plug, that is, at the final stage of the plug, as shown in FIG.
A spinning copying roller (6) that rotates and moves circularly on the outer circumferential surface of the AI is installed, and by continuously spinning the tube after the tube expansion process is completed, uneven thickness can be corrected and the wall thickness can be made even thinner. It is also possible to try to achieve this. In addition, by using this spinning process, it is also possible to create thick-walled stepped pipes as required.

Also, depending on the material and other conditions of the pipe to be processed, the pipe may be machined by an annular nozzle (7) surrounding the pipe (1) immediately after leaving the plug (21) as shown in Figure 6. It is also effective in ensuring quality to prevent bending (due to the tube's own weight, difference in cooling speed, etc.) during the tube cooling process by performing forced cooling by spraying water or air evenly around the tube. That's true.

Furthermore, before processing, the wall thickness of each raw tube is measured using ultrasonic waves, etc., and based on the information on the raw tube, heating means (3
) by controlling the pattern of heating in the axial and circumferential directions of the pipe, it is possible to improve the accuracy of product wall thickness, correct uneven thickness, prevent the occurrence of new uneven thickness due to processing, and even suppress bending. It is possible. If the heating means is a high-frequency coil, the axial heating pattern adjusts the amount of power supplied to the coil, and the circumferential pattern adjusts the positional relationship (eccentricity) of the center of the coil with respect to the center of the tube. By doing so, each can be changed arbitrarily.

Further, by using the processing method of the present invention, it is also possible to obtain a stepped pipe or a pipe with a reducer by stopping the expansion of a single pipe at an intermediate stage and removing it from the mandrel.

〔Effect of the invention〕

Next, examples of the present invention will be described.

Using a seamless steel pipe (obtained by the Mannesmann method) with the material and dimensions (nominal) shown in Table 1 as a raw material, and aiming at the product dimensions and expansion ratio shown in the same table, the pipe was manufactured according to the present invention as shown in Fig. 7. Hot thinning tube expansion processing was performed using a mandrel (2) equipped with plugs (21) of various dimensions.

As for the heating means, a high frequency coil (3) was arranged in two stages so as to have a positional relationship with the mandrel as shown in FIG.

The processing conditions are such that the heat pattern (tube axis direction) is as shown in Figure 8 (
The horizontal axis representing the position in the mandrel axis direction corresponds to Fig. 7)
Others are shown in Table 2. In this example, the mandrel itself was preheated by a high frequency coil (3) before the start of molding.

Table 1 Table 2 Twelve product tubes were obtained by such tube expansion processing, and the product dimensions, uneven thickness, straightness (bending), and roundness (ovality) were as follows.

1) Product dimensions Outer diameter: 394. ．． 1 to 395.5 mark f, wall thickness 215.2
~16.7 marks! 1+) Thickness unevenness: Equal circumferential positions ta+~(h
) is the ratio of the difference between the maximum and minimum wall thicknesses to the target thickness, with a maximum of 12.7%, a minimum of 5.5 inches, and an average of 9.3%.

111) Straightness, the amount of bending (δ) of the tube with respect to the reference plane

1 roundness: the same cross section of the pipe (4 directions (first
The ratio of the difference between the maximum and minimum outer diameter measured in the direction of the dashed line in Figure 0) to the target outer diameter, maximum 1.3%, minimum 0.5%,
Average 0.8%.

This result shows that the method of the present invention can produce thin-walled, large-diameter pipes of stable quality.

As is clear from the above explanation, the method of the present invention uses seamless steel pipes manufactured by the Mannesmann method or hot extrusion method as raw materials to create large diameter pipes by hot thinning pipe expansion processing, and does not require machining. In addition to having a good material yield, the amount of diameter expansion per step can be set extremely large, making it possible to manufacture large diameter pipes economically and efficiently. Reduce costs and improve production efficiency in manufacturing seamless large-diameter pipes of approximately 430 a+m or more, as well as thin-walled large-diameter pipes with an outer diameter of approximately 430 mm or more and a t/D of less than 5%, which cannot be directly manufactured using the Erhard method. It has an extremely large contribution to make.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram showing the tube expanding method of the present invention, Fig. 2 is a diagram illustrating the preferred shape of the mandrel plug used in the method of the present invention, and Figs. 3 and 4 are diagrams based on the present invention. Figure 5 is a schematic explanatory diagram showing a state in which the method of the present invention is combined with spinning processing, which shows experimental data showing the tendency of dimensional changes in thinning and shrinkage due to pipe expansion processing.
The old one is a vertical side view, and (b) is a front view. FIG. 6 is an explanatory diagram of a method of cooling a tube immediately after the tube expansion process according to the present invention is completed, in which (a) is a longitudinal side view and (b) is a front view. 7th
The figure is an explanatory diagram showing the mandrel and heating means (high-frequency coil) used in the embodiment of the present invention, Fig. 8 is a diagram showing the heat pattern of material heating in the same embodiment, and Fig. 9 is a diagram showing the conventional tube expansion method. FIG.

Claims (1)

[Claims] (1) A seamless steel pipe obtained by roll piercing rolling or hot extrusion is used as a raw material, and the outer surface consists of a tapered part whose diameter gradually increases toward the tip and a parallel part continuing to the large diameter end. The plug is inserted into a mandrel with a plug at its tip from the proximal end side and pushed toward the tip, and the plug is passed through the plug while being locally heated sequentially by a heating means provided near the plug to expand the diameter and reduce the thickness. A method for expanding seamless steel pipes.