JPH01202311A - Method for expanding steel pipe in punched pipe - Google Patents

Abstract

PURPOSE:To reduce working cost by forming a bottomed raw pipe by a flat roll and a mandrel into a special-shaped cross section and then manufacturing a pipe by a punching mandrel and a ring die. CONSTITUTION:The bottomed raw pipe is formed and prepared by Erhard perforation-push bench punching. The pipe stock is rolled by a pipe rolling mill provided with a plurality of flat rolls 1 and a complete round mandrel 2 to form a bottomed pipe M having an elongated inner circumference and special-shaped cross section. In this case, the outer diameter of the mandrel 2 is set to be so large that it can enter the pipe stock. Continuously, the bottomed pipe M having a special-shaped cross section is punched and manufactured by a mandrel 3 having an outer diameter equal to the inner diameter of a desired pipe and finished by passing through a ring die. Since the desired inner and outer diameters are worked after the length of the inner circumference of the raw pipe is elongated previously, the press power can be reduced. Besides, since the times of heating are reduced, the total pipe manufacturing cost is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for expanding a steel pipe in punching pipe manufacturing, and more specifically, to a method for expanding a steel pipe in a punching process, and more specifically, to a method for expanding a steel pipe in a tube punching process, and more specifically, it relates to a method for expanding a steel pipe in a punching process. Regarding processing methods.

[Conventional technology]

The punching pipe manufacturing method is to manufacture seamless copper pipes by Erhardt drilling and push bench punching.

In the tube punching method, the inner diameter of the tube to be manufactured is usually determined by the diameter of the hole drilled with the Erhardt punching press. That is, the manufacturable range is defined by the diameter of the mandrel possessed by the punching press.

In the case of extruded pipes, the following pipe expansion process is performed to meet the demand for an inner diameter size that exceeds the manufacturable range after carrying out the above two steps.

As shown in FIG. 3, a punching mandrel 3 having an outer diameter larger than the inner diameter is press-fitted into a bottomed tube M that has passed through a bush bench, and in this state, punching with a ring die is performed as usual. The inner diameter is expanded by a predetermined amount by press-fitting the mandrel, and the outer diameter (thickness) is adjusted by passing the ring die through i11.

[Problem to be solved by the invention]

However, in this method, a large pressing force is required for expanding the tube by press-fitting the mandrel, and as a result, the diameter expansion cap per operation is limited6.
In a 1500T press, the limit for ordinary steel is an increase of 50 m in diameter, and for stainless steel etc., this is limited to an increase of 15 to 30 meters.

Therefore, when a large amount of diameter expansion is required, it is necessary to secure the specified amount of diameter expansion in several steps, and the mandrel is changed and the work is repeated, which is a tedious task. However, it is necessary to prepare a large number of mandrels with different diameters, and if hot working is required, there is a disadvantage that heating must be performed each time the work is performed.

The object of the present invention is to provide a method for expanding a tube in a punched tube manufacturing process that solves such problems as much as possible.

[Means for Solving the Problems] The present invention is characterized in that a bottomed tube obtained by the Erhardt drilling/push bench punching process is expanded in the following two steps [1] and [2]. This article focuses on the method for expanding steel pipes in punched pipe manufacturing.

■ As shown in Figure 1, a bottomed tube with an irregular cross-section with an extended inner circumference is produced using a tube rolling mill equipped with a plurality of flat rolls arranged axially symmetrically and a perfectly circular mandrel 2. M
(periphery stretching process).

■ As shown in Figure 3, a punching mandrel 3 whose outer circumference is longer than its inner circumference is press-fitted into the bottomed tube M with an irregular cross section to enlarge the inner diameter, and in this state, the tube is punched using a ring die. (diameter expansion process).

[For production]

In the method of the present invention, first, in the rolling step (2), the inner circumferential length of the bottomed tube as a raw material is elongated by a predetermined amount.

At this time, the cross-sectional shape of the tube becomes irregular as shown in FIG. 2, for example.

Next, in step (2), this bottomed tube M having an irregular cross section is first made into a shape with a perfect circle on the inner periphery by press-fitting with a mandrel.

Then, by the subsequent punching process, the outer diameter is made into a perfect circle, and at the same time, the wall thickness is adjusted to a predetermined thickness.

That is, in the method of the present invention, the circumferential length of the tube is lengthened in advance in preparation for tube expansion, and as a result, the pressing force required for tube expansion is greatly reduced.

As a result, compared to the conventional method for the same amount of diameter expansion, the press force is smaller than that required by the conventional method, which reduces wear and damage to the mandrel during press-fitting. The contact surface pressure with the material is reduced, resulting in better performance.

In addition, with the same allowable press force, the amount of diameter expansion per press can be significantly increased, which not only simplifies the tube expansion work but also reduces the number of mandrels to be held, and further reduces the number of heating cycles in the case of hot working. Based on this reduction, the fuel consumption rate will be reduced.

The method of the present invention will be explained in more detail below.

○ Circumferential length stretching process A bottomed tube (hereinafter simply referred to as a raw tube) obtained through the basic process of punching tube manufacturing (Erhardt drilling - push bench punching) is used as a raw material, and the inner circumferential length is extended by roll rolling. FIG. 1 shows an example of a tube rolling mill used in this process.

In the figure, l is a flat roll, 2 is a mandrel, M
indicates a bottomed tube being processed. Four flan rolls 1 form a set and are arranged around the pipe feed line at axially symmetrical positions, with the roll axis perpendicular to the pipe feed line.

On the other hand, like a normal bushing bench, the mandrel 2 is provided so as to be movable forward and backward along the pipe feed line (in a direction perpendicular to the plane of the paper), and the forward and backward movements are performed by a drive mechanism not shown.

In such a device, the raw tube is set at the tip side of the mandrel 2, and as the mandrel moves, it is sent to the center position of the four rolls. The mandrel 2 used is one that can fit into the inner hole of the raw pipe. The fed raw tube passes between four rolls from the tip side as the mandrel 2 feeds it out, and in the process of passing, the outer surface is supported by the mandrel 2 on the inner side. The sides are pressurized from all sides and processed. Through this processing, the raw tube is formed into a bottomed tube M having an irregular cross-section as shown in FIG. In other words, the thickness of the raw pipe is frozen to the thickness ta at the four mouth-corresponding parts a,
Material corresponding to the thickness reduction flows from the raw tube portion corresponding to each portion in both the axial direction and the circumferential direction. The material flowing to both sides in the circumferential direction gathers in the area where the rolls do not come into contact, increasing the thickness of the turning part and swelling the outer periphery, and forming a recessed part C with a width W on the inner periphery, where a thickness tb is formed. Create a corner part. As a result of this material movement, the outer peripheral surface of the tube has four rounded corners. By press-fitting the mandrel, it is only necessary to arrange the inner surface shape of the tube into a circular shape, which means that the required press can be kept to a minimum. However, the amount of diameter expansion does not necessarily have to be this way, and can be set arbitrarily within a range where the press force required for mandrel press-fitting is within an allowable level for the equipment.

Note that the four rolls may be rotated as a result of the punching movement by the mandrel 2 during processing, or may be forcibly driven.

The inner peripheral surface of the roll 1 is formed as a cylindrical surface with an inner diameter corresponding to the diameter of the mandrel as a whole due to the presence of the mandrel, but concave portions C are created at locations corresponding to the four corners of the outer peripheral surface. It takes shape. Here, the inner circumferential length is ensured to be extended by an amount corresponding to the formation of the recessed portion C.

It is advantageous for the amount of extension of the inner circumference to be as close to the inner circumference of the tube as possible on the smaller side than the inner circumference of the tube to be obtained by the tube expansion process. As long as the inner circumferential length required in this step is substantially secured, in principle, any number of rolls l can be used as long as it is a plurality of rolls, but it is practical to knead up to four rolls. If the number is too large, it becomes difficult to obtain the effect of extending the inner circumference length, and the original purpose is diminished. In the case of two or three wires, there is no problem in this sense. FIG. 4 shows a tube forming shape when two rolls are used to punch out a blank tube that has been punched out with a 90 degree phase shift. Note that the reference numerals in this figure correspond to the four rolls shown in FIG. 1 above.

Furthermore, in the case of two rolls, the expansion of the raw pipe may be restricted by using a guide that faces in a direction perpendicular to the direction in which the raw pipe is pressed by the rolls l.

○ The diameter expansion process is exactly the same as the general pipe expansion process. It consists of a mandrel press-fit as shown in FIG. 3 and a tube made by punching with a ring die in that state.

In the mandrel press-fitting, the diameter of the bottomed tube M obtained in the previous step and having an irregular cross-section as shown in FIG. 2 is expanded to make the inner surface a perfect circle.

The mandrel 3 used has an outer diameter that matches the inner diameter of the tube to be obtained.

In this process, the cross section of the outer diameter also approaches a perfect circle.

The subsequent punching tube manufacturing is performed by press-fitting the mandrel 3 to the bottom of the bottomed tube M having an irregular cross-section as shown in FIG. 3, and then passing the tube as it is through a ring die. Through this step, the bottomed tube M having an irregular cross-section is finished to have a perfectly circular outer shape, and at the same time, the wall thickness is reduced.

The ring die to be used is determined according to the outer diameter of the target product.

In the method of the present invention, tube expansion is performed through the processes described above.

Next, the effects of the present invention will be explained by giving specific examples.

A raw tube with an outer diameter of 1271 mm and an inner diameter of 80 mm was rolled using a mandrel with an outer diameter of 74 mm using a four-roll rolling mill shown in Figure 1 to obtain a bottomed tube with an irregular cross-section as shown in Figure 2. . Rolling was performed three times, each time with a phase shift of 45°. The dimensions of the bottomed tube with an irregular cross section are ta = 6.5w, tb = 11m,
W=12 mm, and distance between opposite sides of the outer surface=87 fi.

Further, the inner circumferential length at this time was 250 fl, which was 7.5% longer than the outer circumferential length of the mandrel.

This bottomed tube with an irregular cross-section was expanded in diameter using a mandrel having an outer diameter of 79 mm, and then punched through a ring die having an inner diameter of 97 mm to obtain a product with an outer diameter of 97 mm and a wall thickness of 9 mm.

The pressing force required for the mandrel engineering at this time is the pressing force when a true circular bottomed tube with an inner diameter of 74 fins, no concave parts, and an equal cross-sectional area is expanded using a mandrel with an outer diameter of 19 wm. It was 80%.

〔Effect of the invention〕

As detailed above, the method of the present invention can effectively reduce the press force required for mandrel press-fitting in the expansion process of steel pipes associated with tube punching, and can limit the amount of expansion per one time. will be significantly eased. As a result, even when a large diameter expansion is required, the number of machining operations can be reduced, the number of mandrels to be owned can be reduced, and even when performing hot working, fuel consumption can be reduced by reducing the number of times of heating. In addition to this, many other effects can be expected, such as reducing wear and tear on the press-fitting mandrel and improving the internal properties of the product.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram (front view) showing an example of a pipe rolling machine used in the circumferential length stretching process based on the present invention, and Fig. 2 shows the processing status of the pipe in the same process and the pipe shape after processing. A sectional view, FIG. 3 is an explanatory view showing the mandrel press-fitting process in the diameter expansion process, and FIG. 4 is a view showing the cross-sectional shape of the tube when the circumferential length is stretched using two rolls. In the figure, 1: flat roll, 2: mandrel (for tube rolling mill), 3X mandrel (for press-fitting and punching). Figure 3 Figure 1

Claims (1)

[Claims] (1) Steel pipe expansion process in punched pipe production, which is characterized by expanding the bottomed base pipe obtained by the Erhardt drilling/push bench punching process in the following two steps [1] and [2] Law. [1] A tube rolling mill with a plurality of flat rolls arranged axially symmetrically and equipped with a perfectly circular mandrel is used to obtain a bottomed tube with an extended inner circumferential length and an irregular cross-section. [2] A punching mandrel having an outer circumference longer than its inner circumference is press-fitted into the bottomed tube of irregular cross-section to enlarge the inner diameter, and in this state, the tube is punched using a ring die.