SU770577A1 - Method of screw tube rolling - Google Patents

Description

The invention relates to pipe production and relates to the production of seamless hot-rolled pipes in rolling mills.

There is a known method of rolling tubes in a five-roll helical rolling mill, including the deformation of a hollow billet on a mandrel into a pipe with variable wall thickness and a constant outer diameter, moved in a 10th period of unsteady rolling process in the radial direction by driven working rolls and guide lines [ί]. According to this method, a change in wall thickness is carried out ~ 15 peat dilution rolls in the rolling process. To compensate for the increase in the outer diameter and in order to keep it constant, guide rails are simultaneously reduced. The coefficient of 20 ovalization decreases. Opposite movement of rolls and rulers relative to the rolling axis makes it possible to use this method when rolling only thick-walled sleeves (tubes) with ϋ / 5 <12, which is associated with the deformation features characteristic of this gauge: the cross-section rolling is small and practically independent from compression on the wall;

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therefore, the change in the outer diameter has the same sign as the change in wall thickness.

When rolling with variable compression of thin-walled pipes (gklz) with ϋ / 5> 12, the nature of the deformation of the metal in the deformation zone changes. The tangential deformation increases significantly, the magnitude of which depends on the compression along the wall. Greater compression (corresponding to pipe sections with a thinner wall) causes greater tangential deformation, leading to an increase in the outer diameter of the pipe, which makes subsequent processing difficult, for example, in a calibration mill. _with

In connection with the indicated displacement (in different directions relative to the axis of rolling) of the work rolls and guide rulers in the radial direction when rolling thin-walled pipes with variable wall thickness does not allow the outer diameter to be kept constant, which is a disadvantage of this method.

The aim of the invention is the provision of rolling pipes with the ratio of diameter to wall thickness of more than 12 with a constant outer diameter and variable compression on the wall.

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For this, according to the proposed method, helical rolling of tubes, including the deformation of a hollow billet on a mandrel in a caliber formed by two rolls and guide rails, periodically simultaneously moving L., the radial direction, the displacements and the rolls are reported in the same direction with speeds whose ratio is 1 / 2 ratio of the diameter of the pipe to the thickness of its wall. This makes it possible to produce thin-walled break-in tubes with a constant diameter.

The essence of the method lies in the deformation of the hollow billet on the mandrel rolls and rulers. When rolling without moving the rulers, a change in 15 compression along the wall due to the radial movement of the rolls leads to a change in the outer diameter, the relative value of which is about half as much as the change in the relative compression of the wall.

To keep the outer diameter constant, it is necessary to reduce the perimeter of the gauge accordingly by an amount that is twice as small as the change in the relative wall compression.

Since the movement of the rolls is insignificant (2-5% of the wall thickness), the practically necessary reduction of the caliber perimeter is achieved by moving the lines. In this case, only one of the axes of the gauge decreases, and therefore the relative displacement

• rulers should be doubled,

/ than the relative perimeter change. This condition is satisfied if 35

the ratio of the speeds of movement of the rulers and rolls is equal to half the ratio of the diameter of the pipe to the thickness of its wall.

The above range of 40.accompression change equal to 2-5% is chosen from the following considerations. The magnitude of reductions limited to the lower limit of the interval (up to 2%) give a slight change in the outer diameter of the pipes 45 during rolling with fixed rulers and do not complicate the subsequent processing, for example, in a calibration mill. Therefore (for such a change in compression) there is no need to limit the growth of the outer diameter of the pipes by radial movement of the rulers.

If the change in compression exceeds the upper limit (more than 5%), then in this case the movement of the rulers required to limit the growth of the outer diameter reaches a significant value, which leads to a significant decrease in the ovality coefficient in the deformation center and a decrease in the stability of the process. In addition, the proportional nature of the dependence of the increment of the outer diameter of the pipe on the change in compression along the wall changes.

Thus, the proposed process can be used with screw ι

when rolling thin-walled tubes, when a relatively small change in compression along the wall is essential, these conditions are most characteristic of rolling mills.

An example. The method can be used in the production of thin-walled irreducible pipes on automatic installations in the process of rolling rollers on rolling mills.

The end sections of pipes on a length equal to 2-3 diameters, usually have an increased lateral varicosity, which makes it difficult to roll at minus tolerances along the wall thickness. So, in the case of full use of the negative tolerance field at the ends of the pipes in the middle part, it is used incompletely or not at all. Its effective use can be achieved by reducing the wall thickness in the middle part of the pipe when rolling in rolling mills by an amount equal to half the difference between the actual values of the thickness of the end sections and the middle part of the pipe.

When rolling tubes of 146x x8 mm in a tube-rolling installation

"350" YuTZ possible value of reducing the wall thickness of the middle part of the pipe according to experimental data is 0.3 mm; the length of the end sections with increased granular wall thickness is 0.5 m.

Reducing the wall thickness while maintaining the outer diameter is achieved by the same radial movement of the rolls and guide lines by the existing drives of the pressing devices of the rolling mills. Pipe dimensions: 154x8.0 mm, set in the rolling mill, outgoing 162x7.5 mm in the middle part and 162 * x7.8 mm at the ends.

Rolling in the rolling mill is as follows. ·

The pipe is set into the mill, and the distance between the rollers and the rulers is set according to the current rolling table: 152 and 170 mm respectively When rolling the front end of a pipe 0.5 m long with an average wall thickness of 7.8 mm and an outer diameter of 162 mm, rolls are reduced to 0 , 6 mm and rulers on 6,4 mm, and roll a part of a pipe with decreasing from 7.8 to

7.5 mm wall thickness and a constant outer diameter equal to 162 mm) then roll the middle part of the pipe with a reduced wall thickness of 162x7.5 mm. When diluting the rolls to 0 "6 mm and 6.4 mm rulers, roll a part of the pipe with a wall thickness increasing from 7.5 mm to 7.8 mm and a constant outer diameter equal to 162 mm. Roll the rear end of the pipe 0.5 m long with an average

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wall thickness of 7.8 mm and an outer diameter of 162 mm, after which the pipe is issued “of the mill.

Rolling on the proposed method allows to reduce the average weight of one meter of pipe and get savings in metal.

Claims (1)

Claim Method of helical rolling of tubes, including the deformation of a hollow billet on a mandrel in a caliber formed by double rollers and guide bars, periodically simultaneously moving in the radial direction <0 In order to ensure rolling of pipes of constant outer diameter with a ratio of diameter to wall thickness of more than 12 and variable compression along the wall, the movement of the rulers and rolls is reported in the same direction with speeds whose ratio is 1/2 the ratio of the diameter of the pipe to thickness of its wall.