JPH02182311A - Method for preventing wall thickness deviation in hot rolled steel tube - Google Patents

Abstract

PURPOSE:To prevent deviations in wall thickness without influence of twist of a stock by performing reduction rolling by locally and forcedly cooling thick parts in the peripheral direction of a tube in a roll stand consisting of plural rolling rolls. CONSTITUTION:A hexagonal inside shape is generated in a stand incorporating three rolls. Thick wall parts in sides of the hexagonal shape are locally and forcedly cooled to increase deformation resistance and deviation amounts are reduced because a wall thickness of corner parts of the hexagonal shape is relatively increased in a stage of drafting an outside diameter. Respective thick wall parts in sides of the hexagonal shape correspond to positions of caliber edge E of respective rolls in a 1st stand 1 and caliber bottoms B of a 2nd stand 2. Nozzles 12 of a circular-shaped colling water head 11 provided with the nozzles 12 at 60 deg. intervals are arranged in respective stands to correspond with the bottoms B and edges E of a roll caliber to cool locally and forcedly thick wall parts in the peripheral direction. Hence, generation of deviations in wall thickness in the peripheral direction is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for preventing thickness deviation in the circumferential direction of a steel pipe when hot reducing rolling the steel pipe.

[Conventional technology] Conventionally, when hot steel pipes are reduced and rolled, 20
A plurality of roll stands incorporating 1- or 30-ru are arranged in series, and steel pipes heated to 1300°C to 900°C are sequentially reduced and rolled.

For example, in the case of a typical 30-roller, as shown in Figure 1, the first stand 1 has three rolls LA, LB, and HIC arranged at 120@, and then the first stand 1 has three rolls LA, LB, and HIC arranged at 120@, and then a 2
For example, 20 stands, such as stand 2.
The stands are arranged in series with a phase shift of 60''.

In this case, the steel pipe is subjected to reduction rolling while alternating the direction of reduction by 60 degrees, resulting in hexagonal inner surface angularity as shown in FIG. 2, and uneven thickness in the circumferential direction.

Therefore, various measures to prevent uneven thickness have been studied. For example, in JP-A No. 62-19920, by arranging 30-hole stands with their phases substantially shifted by 30 degrees, the uneven amount of thickness can be reduced by making the inner surface of a dodecagon square. A technique for relatively reducing the amount is disclosed. or,
Japanese Patent Laid-Open No. 61-49709 discloses a technique for preventing uneven thickness by forcibly cooling the thick portion in the circumferential direction of the tube in the first half of a large number of stands arranged.

[Problem to be Solved] However, although the first measure described above reduces equipment modification costs, it still requires considerable costs. Furthermore, in the second measure, the material is twisted within the rolling mill row, so it is difficult to say that the result is sufficiently achieved.

The purpose of this invention is to provide a method for preventing thickness unevenness in hot rolled steel pipes that can prevent uneven thickness with low equipment costs.
This is the subject.

[Means for Solving the Problems] A method for preventing wall thickness deviation of a hot rolled steel pipe according to the present invention involves arranging a plurality of roll stands each consisting of a plurality of rolling rolls in series and sequentially reducing the outer diameter of the hot rolled steel pipe to a predetermined outer diameter. In the process of manufacturing the steel pipe, the thick part in the inner circumferential direction of the pipe is locally forcedly cooled and reduced throughout the entire drawing process.

[Function] By locally forcibly cooling the thick portion in the circumferential direction of the tube throughout the entire drawing process, uneven thickness can be prevented without being affected by twisting of the material within the rolling mill row.

[Example] For example, in the case of a stand incorporating a 30-rule, a hexagonal lining as shown in FIG. 2 results. Therefore, the deformation resistance of the material is increased by locally forcibly cooling the thick portions of the hexagonal sides. As a result, in the process of reducing the outer diameter, the thickness of the hexagonal corner portions is relatively increased. In this way, the amount of uneven thickness is reduced.

By the way, the thick part of the hexagonal side shown in FIG.
Caliber Edge E of each roll of the first stand 1 shown in the figure
and corresponds to the position of the caliber bottom B of the second stand 2. Therefore, as shown in Fig. 3, every 60 @ nozzles 12
A nozzle of a circular cooling water header 11 provided with is arranged in each stand in correspondence with the bottom B and edge E of the roll caliber to locally cool the thick part in the circumferential direction. This results in
Uneven thickness in the circumferential direction can be prevented.

When a 15A (outside diameter 21.7 mm, wall thickness 2.8 m) steel pipe was tested according to the second measure, the thickness unevenness rate was 0.
．． Although it was possible to improve by 5%, the method of the present invention resulted in 1.
We were able to improve this by 2-1.6%.

Furthermore, as shown in Fig. 4, the nozzles 12 are arranged at 120° intervals.
The cooling water headers 13 having the same configuration may be arranged at the front and rear of each stand with a phase shift of 60''.

In addition, in the above embodiment, a cooling water header is provided for each stand, but for example, 2 or 3 cooling water headers are provided throughout the entire drawing process.
A cooling water header may be provided for each stand for cooling.

[Effects of the Invention] The method for preventing thickness unevenness in hot-rolled steel pipes of the present invention is as described above, and is capable of preventing wall thickness unevenness in the circumferential direction with relatively low equipment cost and without being affected by the twisting of the material during reduction rolling. can be prevented.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are explanatory diagrams of the arrangement of the 30-ru stand, Figure 2 is an explanatory diagram of the hexagonal lining, and Figure 3 is an example of a cooling water header used in the method of the present invention. An explanatory diagram showing
FIGS. 4(a) and 4(b) are explanatory diagrams of other examples of cooling water headers. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] In the process of manufacturing a steel pipe with a predetermined outer diameter by sequentially reducing the outer diameter of a hot-worked steel pipe by arranging a plurality of roll stands consisting of a plurality of rolling rolls in series, the wall thickness in the circumferential direction of the pipe increases throughout the drawing process. A method for preventing uneven thickness of a hot-rolled steel pipe, which is characterized by locally forced cooling and reduction rolling of a portion.