JPS6072602A - Rolling method of metallic pipe by compensating its rear-end speed - Google Patents

Abstract

PURPOSE:To compensate the rear-end speed of a metallic pipe and to improve the dimensional accuracy of the pipe by increasing the speed of a roll by a prescribed amount or decreasing the speeds of suceeding rolling rolls by a prescribed amount each, when the rear end of pipe is bitten by the roll during rolling. CONSTITUTION:In a mandrel mill rolling, deformations and crops are produced at the front and rear ends of a rolling material 2'. When the rear end crop is bitten by a rolling roll, the speed of said roll is increased by a prscribed amount or the speeds of succeeding rolling rolls excluding the biting roll are decreased by a prescribed percentage each. It this way, the read end speed is compensated at the time when the pipe 2' is rolled by rolls 1 by disposing a mandrel 3 in the pipe 2', and the dimensional change of pipe 2' in its longitudinal direction is prevented.

Description

Detailed Description of the Invention (Industrial Field of Application) Seamless steel pipes are manufactured using, for example, a push-drilling machine that presses a square piece of steel into a roll having a circular hole to form a hollow blank pipe;
An inclined roll rolling machine that further reduces the wall thickness of this hollow tube,
Furthermore, this is carried out using a mandrel mill that continuously reduces the wall thickness by inserting a mandrel into the tube, a stretch reducer, etc. that reduces the outer diameter after heating the tube again.

The present invention uses a so-called mandrel mill, ie, a seamless steel pipe manufacturing process.

The present invention relates to a method of rolling a metal tube using a continuous rolling mill having a plurality of rolling stands each driven in series and a mandrel, and more particularly to a method of rolling a metal tube with trailing end speed compensation.

(Problems with the prior art) In general, what is important in continuous rolling mills in all fields is the balance of the material speed of each stand.
Between the two stands, it is necessary to match the material exit velocity of the first stand and the material entry velocity of the second stand. If this does not match, a tension or compression force is applied to the material, causing a dimensional change in the longitudinal direction.

In particular, in the mandrel mill according to the present invention, since the mandrel exists inside the tube, it is known that the material speed changes during rolling depending on the rolling method, and care must be taken when setting the speed.

There are three main methods for this mandrel mill, depending on the restraint state of the mandrel during rolling.

The first is the full floating mandrel mill method in which the mandrel is rolled freely without restraint, the second is the semi-floating mandrel mill method in which the mandrel is rolled at a constant speed, and the third is the second method in which the mandrel is rolled at a constant speed. There is a method in which the restraint of the mandrel is released in the latter stage of rolling and rolling is performed freely.

In the first method, since it is inevitable that the mandrel speed changes during rolling, the state of speed balance between each stand changes with the rolling stage, and compressive force acts on the material between the stands as a so-called stomach phenomenon. Measures have been taken to partially increase the outer diameter.

In the second method, since the mandrel speed remains constant, such a phenomenon does not occur, and a product having uniform dimensions in the longitudinal direction is said to be obtained. Furthermore, in the third method, it may be considered that an intermediate dimensional change between the two occurs.

(Object of the Invention) The present invention mainly relates to the above-mentioned second and third rolling methods, and was made in order to obtain further dimensional accuracy.

That is, the inventors believe that the second. Although it is true that the third rolling method can produce products with higher dimensional accuracy than the first rolling method, there are still other problems that partially worsen the dimensional accuracy. I discovered something. This will be explained next.

Generally, when rolling a steel pipe or the like, unsteady deformation occurs at the leading end and the trailing end f, so that a so-called crop occurs, and the trailing end in particular has a shape as shown in FIG. As shown in Fig. 2(b), this crop is rolled protruding outside the hole shape, so the rolling load increases significantly and the motor rotation speed decreases, which causes the rear stand I unit, the reed When the material wall thickness is the same, the tendency becomes more pronounced as the thinner the tube is rolled.

That is, when such a phenomenon occurs between two stands, when the trailing end crop passes T through the first stand, the speed of the exit material decreases due to the decrease in the rotational speed of the first stand. On the other hand, since the inlet velocity of the second stand is constant, tension is created in the inter-stand material, resulting in dimensional changes such as a reduction in tube diameter.

(Construction and Effect of the Invention) The present invention has been carried out for the purpose of solving the above problems and obtaining a constant size and shape in the longitudinal direction.

That is, in the basic song, while the trailing end of the material is passing through each stand, the rotation speed is increased to compensate for the decrease in rotation speed due to the increase in load, and the tension is reduced. Alternatively, it is sufficient to control T so that a slight compressive force is obtained.

The gist of the present invention is to provide a continuous rolling mill train having a plurality of rolling mills arranged in series and driven individually, and a method of rolling a metal tube using a mandrel, in which a trailing end crop of the tube is rolled by the rolling mill. When the rolling rolls of any rolling mill in the machine train are bitten, the speed of the rolling rolls of that rolling mill is increased by a predetermined amount relative to the steady speed, or the rolling of all rolling mills except this rolling mill is stopped. This is a method for rolling a metal tube with trailing end speed compensation, characterized in that the roll speed is lowered by a predetermined percentage relative to a steady speed.

The actual procedure is to use a rolling load meter, etc. on each stand to detect jamming, detect tail removal, or detect the position of the material to predict the time when the trailing edge of the material will pass through each stand, and then set the time in advance. It is only necessary to output the rotation speed change signal that has been set. It's a size.

Whether to increase the speed of a passing stand or to reduce the speed of other stands may be selected depending on the ease of implementation of the equipment. Furthermore, it is not necessarily necessary to target all stands for changing the number of revolutions, depending on the degree of influence on the final dimensional change.

Just choose.

(Example) As an example, a case will be described in which semi-floating mandrel rolling is performed in a rolling mill consisting of four stands.

Table 1 shows examples of implementation conditions.

Table 1 Also, Fig. 3 shows the cases in which rear end speed compensation is implemented (in the case of the present invention and in normal rolling (conventional method) without implementation).

The changes in longitudinal outer diameter were compared.

From the figure, it can be seen that when rear end speed compensation is performed, a uniform outer diameter is obtained in the longitudinal direction.

(Effects of the Invention) According to the present invention, it has become possible to prevent changes in rotational speed due to increased load on the rear end crop during mandrel mill rolling, and to obtain uniform dimensions in the longitudinal direction.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the cropped shape of the rear end of the tube. FIG. 2(a) is a sectional view showing the rolling state of the steady portion, ゛(t) is a sectional view showing the rolling state of the crop, and FIG. 3 is a graph showing the dimensional change in the longitudinal direction of the tube in the example. 1 is the roll, 2.2' is the material, and 3 is the mandrel. Patent applicant Representative patent attorney Tomoyuki Yafuki (and 1 other person) Fig. 1 Fig. 2 (α) (l:l) Fig. 3 Continuation of page 1 @ Inventor Ken Kintoki - Hatto to Kitakyushu City 1-1-1 Edamitsu, Nippon Steel Corporation Yawata Steel Works

Claims (1)

[Claims] arranged in series. In a continuous rolling mill row having a plurality of individually driven rolling mills and a method of rolling a metal tube using a mandrel, the rear end crop of the tube is bitten by the rolling roll f of any of the rolling mills in the rolling mill row. When you're hiding,
The rolling mill speed is increased by a predetermined amount relative to the steady speed, or the rolling roll speeds of all subsequent rolling mills except the rolling mill are respectively reduced by a predetermined percentage relative to the steady speed. A method for rolling metal tubes with trailing end speed compensation.