RU2243045C2 - Method for calibrating rolls of pilger mills for rolling thin-wall tubes - Google Patents

Abstract

FIELD: rolled tube production, namely technological tools, particularly processes for calibrating rolls of pilger mills for rolling thin-wall tubes.

SUBSTANCE: method comprises steps of calibrating working portions of rolls having striker and polishing portion with angle of lengthwise outlet (both having the same angular and linear parameters) for forming variable grooved pass; making polishing portions of rolls with increased length values; determining said values according to expression

where Rr - rolling radius of roll in polishing portion, mm; α - angle of polishing portion of lower roll, °; m - metal feed value to deformation zone, mm; μ - elongation factor at rolling minimum thickness wall of tubes of given diameter; k = 0.25 - 0.30, coefficient whose less value is used for tubes with size 273 x 8 mm and large value is used for tubes 426 x 9 mm. Invention provides lowered allowance for wall and for outlet of tubes in tube rolling aggregates with pilger mills having relation D/S = 40 - 53 according to standard.

EFFECT: elimination of "corrugation" occurring in lower part of sleeve-tube, lowered cross wall thickness difference usually caused by non-complete rolling out of "corrugations" by upper roll.

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Description

The invention relates to pipe rolling production, in particular to a technological tool, in particular to a method for calibrating rolls of pilgrim mills for rolling thin-walled pipes.

The cross section of the pilgrim rolls has two main sections - idle and working, defined by the central angles Θ _xy and Θ _p . The working section of the rolls Θ _{p is} intended for the capture of metal by rolls, compression, calibration (formation of the geometric dimensions of the pipe) and smooth separation of the surface of the roll from the surface of the pipe. The idle portion of the rolls Θ _{xy is} designed to rotate the sleeve and feed it into the rolls (deformation zone). Two rolls form a caliber. When the rolls rotate, the diameter of the caliber changes from D _max to D _min (from zero point to polishing). The working part of the roll consists of three sections (striker, polisher and angle of longitudinal release), which correspond to the central angles Θ _b , Θ _p , Θ _pv . The angle Θ _b is called the striker or front cone, which produces the main deformation of the metal (sleeve). On the site Θ _{n the} pipe receives the final dimensions in diameter and wall thickness. Section Θ _pv is called the angle of longitudinal release, serves for the gradual (smooth) separation of the surface of the rolls from the surface of the pipe and reduce the "tubercles" on the pipes with increased feeds of metal (sleeve) into the deformation zone. A decrease in Θ _pv leads to the appearance of “knolls” on the pipes, i.e. longitudinal difference. The total increase in the working part Θ _{r of the} pilgrim rolls is limited by the rate of return of the sleeve by the feeding apparatus. In order for the feeding apparatus to ensure timely return and feed of the sleeve, it is necessary to have an angle of the idle part of the rolls of at least 150-160 °. Then Θ _p = Θ _b + Θ _n + Θ _pv ≤ 200-210 °. Practice has established the following limits of values of angles:

Θ _b = 60-90 °

Θ _n = 90-110 °

Θ _PV = 10-20 °

(Danilov F.A., Gleiberg A.Z., Balakin V.G. Hot rolling of pipes. M .: Metallurgizdat, 1962, p. 315). This practice and the calibration technology of the pilgrim mill rolls were distributed for rolling pipes with a ratio D / S ≤ 40, i.e. for rolling relatively thin-walled and thick-walled D / S≤ 10 pipes in the same rolls.

The closest technical solution is a method for calibrating rolls of pilgrim mills for rolling thin-walled and thick-walled tubes in different roll calibres (Auth. Certificate. USSR No. 358042. Pilgrim mill stream. OIPOTZ. No. 34, 1972 Aut. Certificate. USSR No. 554019. Roller pilgrim mill, OIPOTZ, No. 14, 1977, and Safyanov A.V., Osadchiy V.Ya. et al. Calibration of rolls of a pilgrim mill for rolling thin-walled pipes. TsNIICHM Bulletin, No. 15, p. 48-50, 1976. ) Calibration of rolls of pilgrim mills for rolling thin-walled pipes with a ratio D / S = 40-53 has the following parameters:

Θ _b = 90 °; Θ _n = 70 °; Θ _pv = 40 ° and Θ _pop.v. = 22 °

Θ _pop.v - the angle of the transverse release in the polishing area.

The introduction of this roll calibration made it possible to produce pipes with a size of 426 × 8 mm, that is, with a D / S ratio of 53, fully meeting the requirements of GOST 8732-78 in wall thickness on a TPA 8-16 "with pilgrim mills of OAO" ChTPZ ".

However, the known method for calibrating rolls of pilgrim mills for rolling thin-walled pipes has the following disadvantages. The practice of rolling thin-walled pipes with a D / S≥40 ratio in pilgrim installations shows that when the sleeve is rolled back by rolls, the upper roll starts to move away from the pipe from the beginning of the longitudinal outlet angle, and since the sleeve-pipe with the mandrel are simultaneously in the deformation zone ( rolls) and the chute of the pilgrim mill, then at the moment of separation of the upper roll, they (the pipe and the mandrel) under the weight of their weight are in contact with the lower roll until the centers of the blank section of the roll exit to the line. Due to the friction forces in the lower part of the pipe in front of the roll, i.e. between the sleeve-tube and the roll, a "corrugation" is formed. Values of "corrugations", i.e. their number, height and circumference of the pipe (angle) depend on the D / S ratio and weight (mandrel-tube-pipe), i.e. the thinner the wall, the larger the diameter of the pipe (the weight of the sleeve-pipe) and the weight of the mandrel, their number and size will increase. With subsequent feeds and tilts of the sleeve-pipe ≈ 90 °, the "corrugations" first fall into the outlets, and then at the top of the caliber of the upper roll. Since the polishing coefficient of the rolls is more than 2.0, they roll out with the end of the polisher and the beginning of the angle of longitudinal release, and the surface of the pipe turns out to be smooth, i.e. without the formation of a "wave". Large values of “corrugations” can lead to transverse sunsets on pipes, which is very rare, or to longitudinal delta, i.e. this volume of metal, falling at the end of the polishing section and the angle of longitudinal release of the upper roll, will roll into a thicker wall than the wall on the opposite side. And thus, the cycle is repeated for each feed, rolling, rolling in of the sleeve-tube with rolls with the formation of a “corrugation” in the lower part of the wave. To eliminate this phenomenon, it is necessary that both rolls are torn off from the sleeve-pipe simultaneously.

The aim of the proposed method is to eliminate the formation of "corrugations" in the lower part of the sleeve tubes when they roll back rolls, reducing the lateral difference in the pipes formed due to incomplete rolling of the "corrugations" by the upper roll, and therefore reducing the tolerance on the wall and the release of pipes on the TPA with pilgrim mills with the ratio D / S = 40-53 in accordance with GOST 8732-78.

This goal is achieved by the fact that in the known method for calibrating rolls of pilgrim mills for rolling thin-walled pipes, including the calibration of the working sections of the rolls, consisting of a hammer, polishing section and the angle of the longitudinal output, forming a variable caliber and having the same angular and linear parameters polishing sections of the upper rolls perform increased length, the values of which are determined from the expression

L _V.V. = π · R _K · α / 180 + k · m · μ,

where R _k is the rolling radius of the roll in the polishing section, mm;

α is the angle of the polishing section of the lower rolls, deg .;

m is the amount of metal supply to the deformation zone, mm;

μ is the drawing coefficient during rolling of the smallest wall thickness of pipes of a given diameter;

k = 0.25-0.30 - coefficient, the smaller value of which is taken for pipes of size 273 × 8, and the larger for pipes of 426 × 9 mm.

A comparative analysis of the proposed solution with the prototype shows that the inventive method for calibrating rolls of pilgrim mills for rolling thin-walled pipes is characterized in that the polishing sections of the upper rolls perform an increased length, and their values are determined from the expression

L _V.V. = π · R _K · α / 180 + k · m · μ.

This allows us to conclude that the proposed method meets the criterion of "novelty."

Comparison of the proposed method, not only with the prototype, but also with other solutions in the art, did not reveal the signs that distinguish the claimed method from the prototype, which allows us to conclude that the criterion of "significant differences".

The method has been tested and carried out on a tube-rolling installation with 8-16 pilgrim mills of OAO ChTPZ when calculating copiers and manufacturing rolls of a pilgrim mill with 383 and 432 mm calibers for rolling thin-walled pipes with a diameter of 377 and 426 mm. For the experiment, one pair was manufactured new rolls calibrated by the existing technology and the proposed method. Data on the technical parameters of the upper rolls made by the existing technology and the proposed method, and the values of the relative transverse difference and thin-walled pipes 377 × 9 and 426 × 9 mm in size are shown in the table: 50 pipes of 377 × 9 and 426 × 9 mm in size were rolled in these rolls. After rolling, the wall thickness was measured on each pipe from the seed end and the pilgrim head at 8 points around the perimeter. The average relative difference in each pipe and batch was determined. The table shows that the average relative lateral difference in pipes 377 × 9 mm in size, rolled in rolls calibrated by the existing technology, was 27.0%, and in rolls on offer the proposed method 24.9%, i.e. a decrease in lateral difference by 7.8% was obtained. All pipes measuring 377 × 9 mm, rolled in pilot rolls, meet the requirements of GOST 8732-78 of increased accuracy on the wall (± 12.5%), and in rolls manufactured using the existing technology, only 73.5%. The average relative lateral difference on pipes with a size of 426 × 9 mm, rolled in rolls manufactured by the existing technology, was 27.4%, and on pipes rolled in rolls made by the proposed method, 25.1%, i.e. a decrease in the average transverse difference ≈ by 8.4% was obtained. All 426 × 9 mm pipes rolled in rolls calibrated according to the existing technology meet the requirements of GOST 8732-78 for wall thicknesses of usual accuracy (+ 12.5 / -15.0%) and only 47.3% of pipes of high accuracy. All 426 × 9 mm pipes rolled in pilot rolls correspond to the usual accuracy, and 87.4% of the pipes have increased accuracy.

Thus, the use of the proposed method for calibrating rolls of pilgrim mills for rolling thin-walled pipes of size 377 × 9 and 426 × 9 mm will reduce the relative lateral difference by an average of ≈ 8.0%, and therefore will make it possible to produce pipes of size 377 × 9 mm corresponding to the requirements of GOST 8732-78 of increased accuracy in wall thickness, and the output of pipes with a size of 426 × 9 mm of increased accuracy in the wall should be increased from 47.0 to 87.0%, i.e. 1.85 times.

Claims (1)

1. A method of calibrating rolls of pilgrim mills for rolling thin-walled pipes, comprising calibrating the working sections of the rolls, consisting of a striker, a polishing section with a longitudinal angle of production, forming a variable caliber and having the same angular and linear parameters, characterized in that the polishing sections of the upper rolls perform increased lengths, while the lengths of the polishing sections of the upper rolls are determined from the expression

where R _to - rolling radius of the roll on the polishing section, mm; α is the angle of the polishing section of the lower roll, deg .; m is the amount of metal supply to the deformation zone, mm; μ is the drawing coefficient during rolling of the smallest wall thickness of pipes of a given diameter; k = 0.25-0.30 - coefficient, the smaller value of which is taken for pipes of size 273x8, and the larger for pipes of 426x9 mm.