CS260898B1 - Method of tubes production by means of hot rolling in draught reducing plant - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for the production of tubes by hot rolling on a three-roller drawing machine. This is a tensile reduction of the tubes in the reduction plant, which not only allows the diameter of the starting tube to be reduced, but also provides a reduction in the wall thickness of the starting tube during the reduction.

Three-roller tension reducers equipped with either common or individual drive of rolling stands are used for tensile reduction of tubes. The speed of the rollers in the individual rolling stands is usually adjustable within a certain range. The number of racks of the tension reducer is usually different, depending on the technological conditions of production and the dimensions of the starting and final tubes. 24 to 30 stands are most commonly used. In each rack there are three rollers 1 (Fig. 1) whose speed and hence the rolling speed is adjustable so that it allows the application of axial tension in the tube to be reduced. The starting tube from the rolling mill is heated to the necessary inlet temperature for the tensile reduction, usually in a stepper furnace. During the actual reduction, the starting tube passes through the individual stages of the reducing plant in such a way that in each of them the outer diameter of the tube is reduced and the wall thickness is reduced according to the drawn tension conditions. The calibration of the reducer and the tension adjustment are important not only for its correct operation and for achieving the required reduction in wall diameter and thickness, but also to guarantee conditions in which the tubes do not tear or create grooves or other defects on the outer surface of the tubes.

E.g. the calibration used on a 24-stand three-cylinder thrust reducer with differential drive and two-engine drive allows an overall maximum reduction of 76.7% to date. This calibration is characterized by the caliber's ovality, given the magnitude of the caliber opening y (Fig. 1). The current calibration uses the opening size given by this expression:

Ύ> = 0,3 (Oj ..! - where:

Dj - is the diameter of the tube behind the stand

Dj_i - is the diameter of the pipe in front of the stand

Dj = 2. Rj

With the required drawing range from 0 = 22 mm (or 1/2 “) up, this requires two pipe diameters, 0 = 108 mm and 0 = 89, and simultaneously two separate calibration series. The calibration used up to now does not allow the use of higher diameter reduction in the rack, and this justifies the need for two different calibration series. This solution has a number of disadvantages, including:

- higher charge price for tube production 0 = 89 mm, - lower output and labor productivity in tube production 0 = 89 mm, - lower yield when using a starting tube 0 = 89 mm, - need for two different calibration series, - reduced power to roll - more cuts per tonne of production and higher cuts.

These disadvantages are eliminated by the method for producing pipes by hot rolling in a stretch reducing using a calibration range of the opening size caliber that respects Propagation material being formed in the gauge, depending on the quality of the molding material, stroke size, and the size reduction of the diameter when the opening size is given by y _t (Djj - Dj), where Dj is the outside diameter of the pipe downstream of the i-th stand, Dj_i is the outside diameter of the pipe upstream of the i-th stand, and is a constant, according to the invention, they roll at a value of 0.33 to 0.40.

The solution of the present invention is based on a change of the calibration line of the drawing machine and the calibration of the cylinders of the individual racks so that the average reduction of up to 81.0% can be achieved in 24 racks. The distribution of the reducers between the racks makes it possible to obtain such a drawing number that the pipes in the reducer are not torn. In order to achieve increased diameter reductions in the racks without causing tube defects, the calibration of the rollers has been changed so that the opening of the y-gauge (except for the inlet and end racks) is within the following range:

y j = (0.33 to 0.40). (Dj_i - DJ

An exemplary embodiment of the rolling process according to the invention is shown in the accompanying drawing.

When forming a tube in the caliber of a tensile reducer, material propagation occurs and the formed material, Figure 1, flows toward the edges of caliber 2 of the reduction cylinders 1. Determining the magnitude of the material propagation value in the caliber when reducing the tubes in a three-roller reducer is important to increase the diameter reduction. gauge under axial thrust. The aim is to prevent defects from the edges of the rollers on the tube surface. It has been verified that the minimum opening of the gauge must respect the size of the gauge, which depends on the pipe diameter Dj, the wall thickness of the pipe Sj, the magnitude of the axial thrust characterized by the traction number Z _{i (} magnitude of diameter reduction in caliber and correction constant K _k) . reducing the heat to the quality of the molded material, the number of rollers in the stand of the reducer and the amount of draft.

Minimum opening of the gauge is given by:

Yi min.

b — D,

Metal spread rate indicator: mi = (0,72 - 1,15 Si / DJ - 0,52. Z; + K _k

Caliber ovality coefficient:

gi (100 liUj

100 — ZlD ° / o f

K _k = 0.28.

It follows from the above equations that mj = 0.60; gi = 1.050; bj = 51.57 mm;

Yi min. ⁼ 1.24.

Caliber width:

bi = gi. Dj

Actual value of opening, expressed as a reduction in diameter in caliber:

y, i = a (Dj_i-- EJ

The tensile reduction criterion without the occurrence of defects on the surface of the tubes is met if:

Yi> Yimn.

In equations it means:

0D% - reduction in diameter in caliber in percent, and - constant characterizing opening of caliber,

KV - correction constant, which has a mean value of 0.28 at a three-roller reduction mill when rolling carbon steel tubes. Example of calculation:

Calibration series 0 j 08 - 0 22 mm, 11th stand.

Is given:

D; = 49.11 mm;

D i = 52.94 mm;

Sj - 2.89 mm; D,% = 7.8;

Zi = 0.64;

For a = 0.30, y _f = 1.15 <y; _min ....

... not compliant

For a = 0.33, yi = 1.26> yj _min ....

... compliant.

In a similar way, a value of at least 0.33 is based on all calibers of the calibration line of the traction reducer operating with increased reduction in the rack.

An example of the use of this method of hot rolling tube production in a 24-axis thrust reducer is the production of tubes in the manufacturing range < 7 > This production range required two initial pipe dimensions of 0 108 mm and 0 89 mm in the original reduction process, corresponding to two diameters of the initial billets of 0 120 mm and 0 105 mm. The use of a single tube diameter of 0 108 mm for the entire production range makes it possible to use the initial billets of only 0 120 mm, rolled on a continous mill from a single heat, while the originally used diameter 105 mm. re-heating and rolling on the HCC coarse mill, to 0 105 mm.

Introducing a new method of tensile reduction of pipes will bring metal savings in the production of billets, energy savings for heating, increased yield and metal consumption during pipe rolling, reduced end waste of pipes, increased output and labor productivity, reduced batch preparation costs and reduced metal waste in the batch preparation plant as a result of reduced shear.

Claims (1)

SUBJECT Method of production of tubes by hot rolling in a tensile mill using a calibration series with a caliber opening size which respects the spread of the formed material in the caliber depending on the quality of the formed material, the size of the drawing and the size reduction diameter, where the opening size is given by OF THE INVENTION Yi = a. D 1 - D 1, where D 1 is the outside diameter of the pipe downstream of the i-th stand, D 1 is the outside diameter of the pipe upstream of the i-th stand, and is a constant characterized in that the pipes are rolled at a = 0.33 to 0 , 40.