JPS6046805A - Control method of mandrel mill - Google Patents

Abstract

PURPOSE:To round properly a pipe at a final stand by adjusting the deviation of an actual reaction from a roll reaction obtained previously and forming the shape of caliber of stand into a specifically elliptical shape instead of a completely round one, in manufacturing a seamless steel pipe by a mandrel mill. CONSTITUTION:In a continuous rolling of 7-8 passes, constituted of several sets of a pair of rolling rolls (a) having each a semicircular caliber and a mandrel (c) inserted into the hollow part of a blank rolling pipe (b); the rolls (a) having each a caliber provided with a relief part (d) having a 15-30 deg. relief angle (e) in the vicinity of a roll flange instead of a completely round caliber, are used excepting the rolls (a) at a final stand, to form the pipe (b) into a pipe having a completely round cross section at the final stand. In this case, the rolling reduction is adjusted in accordance with the deviation of an actual roll reaction of stand from the previously obtained roll reaction in order to properly round the pipe at the final stand, thereby manufacturing a seamless steel pipe free from a flow caused by the mandrel drawing and a defective shape.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method of controlling a mandrel mill (semi-floating mandrel mill or full-floating mandrel mill), which is a continuous rolling mill used, for example, in seamless cableless pipe manufacturing.

(Prior Art) A mandrel mill is one of the processes for manufacturing seamless steel pipes, and is arranged as the next step of a drilling machine or a drawing machine following it, and a drawing machine is arranged as a subsequent step. As shown in Fig. 1, such a mandrel mill consists of a set of rolls a, each having a semicircular hole shape, and a hollow part 1 of a rolled stock pipe.
The rolled blank tube is rolled to a desired outer diameter and wall thickness by continuous rolling of 7 to 8 passes using a mandrel C inserted at L7.

In a mandrel mill, rolling is performed with the mandrel inserted into the rolled material, so the mandrel must be removed from the rolled material when continuous rolling is completed. To make this possible (C), in a mandrel mill, the cross section of the rolled material during the rolling process is not a perfect circle (as shown in Figure 2, a relief part di with a relief angle ef is provided near the roll flange to make it elliptical, The total circumference is made larger than the outer circumference of the mandrel, and at the final stand, it is shaped into a perfect circular cross section as shown in FIG. 3, and a gap f is completely formed between the inner wall surface of the rolled material l) and the outer circumferential surface of the mandrel C.

Since mandrel mill rolling is continuous rolling, the speed lance collapses during rolling due to temperature variations and variations in the lubrication status due to the lubricant applied to the mandrel, creating tension between the stands. Changes may occur. For this reason, on the final stand (round-up stand) that shapes the cross section into a perfect circle, excessive round-up or insufficient round-up is performed, resulting in poor pulling when pulling the mandrel from the rolled material, resulting in damage to the surface of the mandrel and the rolled material. The occurrence of flaws on the inner surface and the defective product shape remain in the drawing machine of the subsequent mill, resulting in a negative impact such as a significant deterioration of quality.

(Objective and Structure of the Invention) The present invention has been made for the purpose of solving the problems described in -H. This characteristic is achieved by inserting a mandrel into the inside of the tube to be rolled and rolling the tube completely continuously using a substantially circular caliber row made up of a pair of rolls driven 1-1. Final stand that forms a gap in between (round-up stand)
In order to enable proper round-up, it is necessary to detect the deviation in the reaction force of the stand in advance and adjust the roll reduction accordingly for the next material or during rolling. This is the aforementioned mandrel mill control method in which the caliber shape is not a perfect circular caliber but a caliber with a relief angle of 15 to 30 degrees.

The contents of the present invention will be explained in full detail in Section 1 below.

During mandrel mill rolling, in actual operation, due to temperature variations and the condition of the lubricant applied to the mandrel, speed imbalance between the rolled materials or during rolling occurs (1) tension between stands occurs, resulting in the ellipse shown in Figure 2. Among the shapes, the shape of the roll flange portion changes, and the inner circumferential length of the rolled material changes.

When the space between the stands becomes a compression IC, the flange shape tends to protrude and a large circumference is obtained, and when the space between the stands becomes tensile, the flange shape approaches the mandrel side and the circumference becomes small. As a result, in the roundup stand,
When the circumference is large, excessive round-up occurs and the number of rolling edges increases, and when the circumference is small, round-up is insufficient and the number of rolling edges decreases.

In the present invention, the roll reaction force for proper roundup is determined in advance through full theoretical calculation or experiment, and the difference between the roll reaction force of the roundup stand during rolling and the predetermined appropriate roll reaction force is detected, and the appropriate value is determined. By returning to , you always get the correct roundup.

The constant pressure control of the round-up stand is carried out by changing the gap between the stunt rolls, but in some cases, when the caliber shape is a perfect circle, the elliptical shape of the cross section of the rolled material becomes conspicuous due to geometric reasons. In order to prevent this and obtain a better shape, it is recommended to provide a relief part with a caliber relief angle of 15 to 300. If the relief angle is less than 15°, there is no effect, and if it is more than 30°, the roundness will be impaired. In addition, it is necessary to connect the relief parts smoothly so that there are no steps.

(Example) Examples will be described below.

As an example, outer diameter 60.5mN + wall thickness 5. A case in which a steel pipe of Q mN is continuously rolled on four stands with a total mandrel diameter of 48 will be explained. Table 1 shows an example of the implementation conditions.

Table 1 As an example of the results, Table 2 shows a comparison of the mandrel pulling force and the outer diameter after rolling when the rolling blade of the roundup stand is appropriate and when the rolling reduction is large.

6- It can be seen that when controlled to an appropriate value, the pulling force is small and can be pulled out smoothly, and the roundness is also good.

(Effects of the Invention) As described above, the present invention eliminates troubles during drawing, improves the durability of the mandrel, improves the quality of the final product, and has extremely great practical value.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a general mandrel mill rolling method, Figure 2 is a diagram showing the cross-sectional shape of a mandrel mill after intermediate stand rolling, and Figure 3 is a diagram showing the cross-sectional shape of a round-up hole after rolling. ing. a...Rolling roll, b...Rolled material, C...Mandrel, d...° roll relief section, e..."'-le relief angle, f... Mandrel outer peripheral surface and rolled material Gap between inner wall surface.

Claims (1)

[Claims] 1. In mandrel mill rolling, in which a tube is continuously rolled by a substantially circular caliber row composed of a pair of driven rolls, and a mandrel is inserted into the tube to be rolled, the mandrel The final stand for forming a gap (round-up) between the rolled material and the rolled material was prepared in advance to enable proper round-up. A control method for a mandrel mill, characterized in that a deviation in the reaction force of the stand with respect to the roll reaction force is detected, and adjustment is made accordingly during roll rolling of the next material or during rolling. 2. The method for controlling a mandrel mill according to claim 1, wherein the caliber shape of the stand (C is not a perfect circular caliber but a caliber having a relief angle of 15 to 300 mm).