JPH05200413A - Method for preventing roll burning in seamless steel tube rolling - Google Patents

Abstract

PURPOSE:To eliminate roll burning in seamless steel tube rolling and to prevent roll slip. CONSTITUTION:Lubricating effect of cooling water is decreased and burning of rolling powder to a roll is reduced by stopping cooling water supply to the roll for several seconds during rolling, especially, before a base stock runs out of rolls. In this way, roll slip is eliminated. Especially, this method can be suitably applied to seamless steel tube rolling that a rolling base stock of a high alloy steel contg. Cr of >=13% is rolled by Mannesmann mandrel mill process or Mannesmann plug mill process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing seizure of rolls in the rolling of seamless steel pipes, particularly in the case of perforating a rolling material and stretching and rolling.

[0002]

2. Description of the Related Art As a typical manufacturing method of seamless steel tube rolling, a Mannesmann plug mill method consisting of an indentation piercing rolling mill, two drawing rolling mills, a plug mill, and a rolling mill train such as a reeler mill to a sizer mill, and a piercer
The Mannesmann-mandrel mill method including a mandrel mill train and a rolling mill train such as a stretch reducer is widely known.

These manufacturing methods are selectively used according to the outer diameter of the product. Generally, the former has an outer diameter of 7 in. As mentioned above, the latter is 7 in. It is customary to apply below.

In these rolling processes, depending on the material to be rolled, seizure of the surface of the rolled roll causes occasional external flaws and even roll slip. Particularly, when the latter roll slip occurs, seizure is exponential. However, in some extreme cases, rolling becomes impossible.

These tendencies are remarkable when the rolled material is a material with less scale generation on the surface, and when the hot deformation resistance is high, for example, 13% Cr steel or 22% Cr steel.

In particular, these phenomena are remarkable in the piercer and the stretching rolling machine shown in FIG. 2, that is, in the inclined rolling machine in which the rolls a and b are inclined with respect to the material M to be rolled, such as the elongator mill.

For this reason, conventionally, measures such as rolling ordinary steel before and after rolling high alloy steel and applying a lubricant to prevent seizure have been taken. The chance is limited, and the latter has the problem of increasing slip if the kind and amount of lubricant used are not appropriate for the rolled material.

Further, in order to prevent the occurrence of this slip,
The rolling roll may be subjected to so-called knurling in which a shallow groove pattern is engraved, but the sufficient effect cannot be obtained.

This is because powder generated by abrasion during rolling, that is, rolled material particles are transferred to the roll surface and grow by repeated abrasion, and even if this is a knurled roll, its groove is seized by seizure. It is because it is buried and it is not possible to maintain an appropriate surface condition.

Further, in order to improve the seizure resistance of the roll, it was also studied to increase the amount of graphite contained in the metal structure of the roll.

This is intended not to aim at the lubricating effect of graphite but to prevent the transfer of the seizure particles, but it has not yet achieved a sufficient effect.

As described above, the problem of roll slip in the case of rolling a high alloy seamless steel pipe is not actually solved, whereas in the case of a high alloy, the roll exchange is performed in the rolling of 12,000 ordinary steels. The reality is that frequent roll changes are performed every 200 to 300 rolls, which significantly impedes productivity.

[0013]

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to find means for reducing roll slip and minimizing roll change during seizure during seamless steel pipe rolling. ..

[0014]

DISCLOSURE OF THE INVENTION The present invention is based on the knowledge that rolling troubles due to roll slip in rolling of seamless steel pipe are extremely small when the temperature of the rolling material is low, that is, so-called low heat rolling.

The low heat rolling is, for example, due to a trouble in a succeeding rolling mill or the like, the rolling material is made to stand by in front of the inclined rolling machine, and as a result, the material temperature is 50 to 100 compared with the steady rolling.
It means rolling in a state of being lowered by about ℃.

That is, according to the present invention, when the rolling material is rolled by the rolling rolls, the supply of the cooling water to the rolls is temporarily stopped at a part from the biting of the material into the rolls to the slipping out. Was achieved.

The temporary stop of the supply of the cooling water to the rolls can be suitably applied to the rolling of the seamless steel pipe in which the high alloy rolling material containing 13% or more of Cr is rolled by the Mannesmann mandrel mill method or the Mannesmann plug mill method. The supply of cooling water to the rolls in the inclined rolling mill such as a piercer or an elongator mill is temporarily stopped for a certain period of time before the material slips out.

[0018]

The roll cooling water in the rolling of the seamless steel pipe is originally performed to prevent heat scratches and cracks of the rolls, and it does not matter much if the cooling water supply is stopped in the low heat rolling region. ..

Further, the cooling water supplied to the rolls has a kind of lubricating effect, and depending on the rolling conditions, the lubricating effect of the cooling water rather causes slipping, and an appropriate metal touch (contact) between the rolls and the rolled material is caused. It has been confirmed that this phenomenon occurs more often when the material is slipping out of the bottom of the material than when the material is caught. Therefore, it was confirmed that stopping for several seconds before slipping out of the material is the most effective.

Of course, since the heat load is large during rolling, it is not possible to stop water supply at all stages during rolling from the viewpoint of roll protection from heat scratches and cracks.
Therefore, the timing of using the roll cooling water is important, and the roll surface can be kept sound.

When the rolled material slips out, it is considered that the rolling occurs in the so-called unsteady region at the end of the rolled material, and slip occurs because the roll grip (holding) length of the rolled material is short.

That is, the unexpectedly simple method of temporarily stopping the cooling can maintain the roll surface in a proper and sound state, which greatly reduces the slip due to the seizure of the roll and remarkably extends the life of the roll. I knew I could do it.

Further, it is preferable to apply a method of stopping the cooling supply even at the time of biting, if necessary, because of concern about biting failure due to cooling at the pipe end.

[0024]

EXAMPLE 76.4Φ × 18., Heated to 1250 ° C.
0 × 3500 mm STKM13A (C: 0.5%, S
i: 0.2%, Mn: 0.5%, P: 0.0025% or less, S: 0.008% or less) Indentation piercing mill-drawing mill-plug mill-reeler mill-Manesmann consisting of sizer mill -Rolled by a plug mill rolling method.

FIG. 1 shows an example of application of the cooling water stopping method in a drawing rolling mill in comparison with the conventional method. In the conventional method, cooling water is supplied from the start of pushing to the start of biting of the material in the rolling mill, but at the same time as the start of biting, the cooling water supply was stopped for a few seconds, and then the cooling water was supplied again.
On the other hand, in the method of the present invention, the cooling is stopped for a few seconds before the rolling is completed, that is, when the so-called blank of the material is removed. In the figure, the cooling water supply period is indicated by diagonal lines, and the cooling water stop period is indicated by white spaces.

As a result, as described above, the slip between the rolling roll and the raw material is reduced, the advancing efficiency of the rolled material is improved, and as a result, the rolling time is shortened (T). Table 1 shows the results obtained by arranging each condition and the like at this time into numerical values.

In Table 1, in the comparative example as the conventional method, rolling is performed without stopping the supply of cooling water at the time of biting (no primary stop), and in the method of the present invention, cooling water is stopped for 3 seconds immediately before slipping out. It is a thing.

As can be seen from Table 1, the forward efficiency is calculated from the actually measured value of the actual rolling time with respect to the theoretically predicted rolling time (without slip). That is, in the conventional method, the advancing efficiency is 86 to 89%, whereas in the method of the present invention, it reaches 93.4%, which is about 3 in rolling time.
It will be shortened in seconds.

[0029]

[Table 1]

[0030]

The present invention has the following effects.

(1) It is possible to remarkably prevent the slip due to the seizure of the roll, and to extend the conventional roll changing timing to about twice.

(2) Therefore, productivity can be improved by reducing the roll unit consumption and the roll replacement frequency.

(3) Rolling cycle time is shortened because there is little roll slip.

(4) By reducing the roll slip, surface defects of the product are reduced.

[Brief description of drawings]

FIG. 1 shows a roll cooling water supply timing during rolling in which the method of the present invention and the conventional method are compared.

FIG. 2 shows a rolling condition of a raw material in a typical inclined roll rolling mill.

[Explanation of symbols]

 a, b Roll M Rolled material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuji Kuno 1-1 No. 1 Tobita-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture New Nippon Steel Corporation Yawata Works

Claims (6)

[Claims] 1. Roll seizure prevention in seamless steel pipe rolling, in which the supply of cooling water to the roll is temporarily stopped at a part from the biting of the material into the roll to the slipping out when rolling the material to be rolled. Method. 2. A method for preventing roll seizure in seamless steel pipe rolling, wherein the rolling material according to claim 1 is an alloy having less surface scale generation and high hot deformation resistance. 3. A method for preventing roll seizure in seamless steel pipe rolling, wherein the rolling material according to claim 1 is a high Cr steel high-alloy alloy containing 13% or more of Cr. 4. A method for preventing roll seizure in seamless steel pipe rolling, wherein the supply of cooling water to the roll according to claim 1 is temporarily stopped for a certain period of time before slipping out of the rolling material. 5. A method for preventing roll seizure in seamless steel pipe rolling, wherein the supply of cooling water to the roll according to claim 1 is temporarily stopped during a certain period of time before the rolling material is caught and before the rolling material slips out. 6. A method for preventing roll seizure in seamless steel pipe rolling, wherein the cooling water to the roll according to claim 1 is temporarily stopped in a piercer or an elongator mill.