JPS62263804A - Method for preventing rolling crack of hard pipe body - Google Patents

Abstract

PURPOSE:To effectively and surely prevent a rolling crack by forming he working grooves of roll dies to a specific shape at the time of rolling a hard pipe body with a cold Pilger rolling mill. CONSTITUTION:The flattening rate (ODmax-ODmin)/ODminX100 of the working grooves 3, 3 of a pair of the upper and lower turnable roll dies 4, 4 having a mandrel 2 and the working grooves 3, 3 to roll the pipe body 1 to be worked is specified to <=3%. ODmax is the distance between the shoulder parts of the symmetrical working grooves 3, 3 and denotes the length in the major axis direction of the ellipse by the working grooves 3, 3. ODmin is the distance between the bottom parts of the symmetrical working grooves 3, 3 and denotes the length in the minor axis direction of the ellipse by the working grooves 3, 3. The center of the ellipse is positioned concentrical with the center of the mandrel 2 having a round section.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for rolling hard tubes made of Zr-Zr-based alloys, Ti-Ti-based alloys, etc. using a cold pilger rolling mill. This invention relates to a device that effectively and accurately prevents cracking phenomena occurring in a tube body.

(Prior art) Hard tubes made of Zr-Zr-based alloys, Ti-Ti-based alloys, etc. are rolled to the required thickness using a cold pilger rolling machine.
It is well known in the prior art to form a tube into a tubular body of a certain diameter, and the rolling process is carried out as shown in FIG. That is, in the figure, only the main structure for rolling forming is shown, but the tube 1 to be processed made of the above-mentioned metal material has its inner surface supported by a mandrel 2 having a perfect circular cross section. , symmetrical parts of the upper circumferential side and the lower circumferential side of the outer surface of the tubular body 1 are the mandrel 2
The die rolls 4, 4 are sandwiched between a pair of upper and lower rotatable die rolls 4, 4, each having a symmetrical machined groove 3゜3 concentric with the center of the ellipsoid as a circumferential concave groove.
The required diameter,
Since the tubular body is rolled and formed into a thick wall, the reason why the processed grooves 3, 3 are formed into flat ellipsoidal grooves is because of the side reliefs on both sides of the tubular body that are plastically deformed by the rolling process. This is for the sake of - <Problems to be Solved by the Invention> A problem that arises in the above-described rolling forming is that cracks 1a occur on the outer surface of the tubular body 1 to be processed, as illustrated in FIG. Cold pilger tube made of hard metal material
The reason why the above-mentioned rolling cracks occur during forming using a rolling mill is said to be due to the following reasons.

That is, the first reason is that in the pair of upper and lower roll dies 4.4 in FIG. In the groove shoulders B and B of the machined groove 3, the inner surface of the tube body 1 is not in contact with the outer peripheral surface of the mandrel 2,
It has not been directly processed by tools. However, since the tube body 1 is continuous, the material of the groove bottom A is extended forward, which means that a! #m In part B, the material is also pulled forward and extended by this, and the second reason is that
As mentioned earlier, the cross-sectional shape of the machining groove 3 of the roll die 4 is a flat elliptical shape for the side relief of the material, unlike the mandrel 2 (!I!I).
For this reason, the cross section of the tube body 1 during rolling is also flat, so
At this time, bending stress is applied to the groove shoulder B on the outer surface of the tube body 1, and thirdly, the tube body 1 is in the process of being rolled.
Since the groove shoulder B in is a tooth surface that does not come into contact with the tool, the first and second situations described above are added.
As shown in FIG. 4, cracking tends to occur near the groove shoulder B. Conventionally, methods for preventing such rolling cracks include firstly lowering the rolling speed (feed amount of tube 1, rotational speed of roll die 4 - number of strokes 7 minutes), and secondly reducing processing speed. The goal was to select a path schedule with a small pass schedule. Although all of these methods are effective in their own way, they all have a problem in that they reduce productivity.

(Means for Solving the Problems) Unlike the conventional means for preventing rolling cracks described above, the present invention reduces the rolling speed and reduces the processing rate by applying specific measures to the shape of the processed grooves in the roll die. It is possible to reliably prevent rolling cracks without the need to reduce the
A hard tubular body made of base alloy, etc. is rolled using a mandrel with a perfect circular cross section that supports the inner surface of the tubular body, and a pair of roll dies that have symmetrical processing grooves with an ellipsoidal shape that sandwich the symmetrical outer surface of the tubular body. When performing this, the processing groove of the roll die is adjusted to its oblateness ((ODmax −ODn+in)
/ ODwin X100) Rolling is performed with a groove shape of 3% or less.

(Function) According to the technical means of the present invention, as shown in FIG. roll 4,
4, the ellipsoidal and symmetrical machined groove 3.3
Oblateness ratio ((ODmax - ODmin) 1
By setting 0Dmin xlOO) to 3% or less, it is possible to suppress the flatness of the processed tube 1 whose outer surface is symmetrically held between the processed grooves 3, 3 to the same value. Suppressing the flattening ratio of the beaten tube 1 to a specific range prevents rolling cracks from occurring during rolling of the tube 1 by the mandrel 2 and the roll die 4°4. As is clear from the relationship diagram between the aspect ratio and rolling cracks shown in Figure 2, by setting the aspect ratio to 3% or less, rolling cracks can occur at all processing rates. It has been confirmed that there is no such thing.

That is, in the same figure, the horizontal axis shows the processing rate (%), and the vertical axis shows the above-mentioned flatness ratio ((ODmax - ODmin)/
ODmin Both are safe areas that do not cause cracks.
On the other hand, if it is 3% or more, it is a rolling crack risk area where cracking occurs at all processing rates.That is, according to the machined groove shape of the present invention with an aspect ratio of 3% or less, Zr -
Hard tubes made of Zri alloy, Ti-Ti base alloy materials, etc.
It is possible to reliably prevent rolling cracks that tend to occur when rolling with a cold pilger rolling mill.

(Embodiment) In the embodiment shown in FIG. 1, the mandrel 2 and the roll die 3 having the ellipsoidal groove 3 belong to a mechanism completely similar to that in a conventionally known cold pilger rolling mill. This is omitted from illustration in its entirety. Oblateness ((ODmax - ODmin) 10
ODmax in Dmin is the distance between the groove bottoms A and A in the symmetrically machined groove 3.3, and indicates the length in the short axis direction of the ellipse formed by the machined groove 3.3, and the center of the ellipse is the center of the mandrel 2 with a perfect circular cross section. considered to be concentric.

(Effects of the Invention) In the present invention, when a hard tube body made of the exemplified metal material is rolled by a cold pilger rolling mill, the reasons for rolling cracks that occur in the tube body (the problems to be solved by the invention first) are explained. As a result of considering the above three reasons (factors), we focused on the flat state of the workpiece tube 1 during rolling as the most effective and easily controllable parameter. By devising the groove shape of the ellipsoidal processed grooves 3, 3 in the roll dies 4, 4 that cause the occurrence of rolling cracks, and by making the groove shape have a specific oblateness, the oblateness of the tube body can be adjusted to a range that does not cause rolling cracks. The major feature is that it suppresses the occurrence of rolling cracks, and the results shown in Figure 2 are the results of actual conditions for tube bodies made of Zr-Zr base alloys and Ti-Ti base alloys, where such rolling cracks occur frequently. is exemplified, but in any case, the oblateness ((ODmax - ODm
By setting in ) / ODmin There is no need to decrease productivity by reducing the processing rate or reducing the processing rate, and it is possible to effectively and accurately obtain rolled tubes without defects, eliminate yield loss due to rolling cracks, and efficiently achieve high quality. It has a great advantage in that it can produce products of.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main part of an embodiment of the present invention, FIG. 2 is a graph showing the relationship between rolling cracks and processing rate in a product according to the same embodiment, and FIG. 3 is a sectional view of the main part of rolling in the prior art. FIG. 4 is an explanatory diagram of the occurrence of isopressure grinding. 1... Pipe body to be processed, 2... Mandrel, 3... Machining groove, 4... Roll die. , Patent applicant: Kobe Steel, Ltd. Figure 4 (cm) Figure 7 Figure 3

Claims (1)

[Claims] (1) Rolling of hard tubes made of Zr-Zr-based alloys, Ti-Ti-based alloys, etc. is carried out using a mandrel with a perfect circular cross section that supports the inner surface of the tube and an ellipsoidal mandrel that holds the symmetrical outer surface of the tube. When performing this using a pair of roll dies having symmetrical machining grooves, the machining grooves of the roll dies have an oblateness of {
(ODmax-ODmin)/ODmin×100}3
A method for preventing rolling cracks in a hard tube, characterized by rolling with a groove shape of less than %.