RU2417849C2 - Pipe cold roll mandrel - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to pipe rolling and may be used in pipe cold rolling at roll stands. Proposed mandrel comprises stem and working section with cross section decreasing from said stem generating variable-taper curve, the taper at the end of squeezing section being equal to that of gage development. Mandrel working section features generatrix taper K₀ matching that of gage tape in compliance with inequality K_T<K₀<K_p(1+2f), where f is pipe wall thickening in reduction zone vs diametre reduction in said zone; K_t is mandrel tape at the end of squeezing section equal to that of gage development in that zone, and K_p is gage development taper at the start of working section.

EFFECT: higher quality of pipe inner surface, ruling out of fold formation thereon and rejects, reduced metal consumption.

1 ex, 2 dwg

Description

The invention relates to pipe rolling production and can be used in cold rolling of pipes on roll mills.

Known mandrels for cold rolling pipes having a working section with a curvilinear generatrix (USSR AS No. 659216, BI No. 16, 1979 and No. 761043, BI No. 33, 1980). The disadvantage of these mandrels is the low quality of the inner surface of the pipes, since the profile of the mandrel is not consistent with the profile reamer caliber at the beginning of the working section, which can lead to increased thickening of the pipe wall in the reduction zone and the formation of wrinkles on the inner surface. Another disadvantage of the mandrels listed is the low accuracy of the pipes due to inconsistency of the mandrel profile with the gauge sweep profile at the end of the compression section, which leads to the formation of a longitudinal difference.

The closest in technical essence to the proposed one (prototype) is a mandrel for cold rolling of pipes, containing a shank and a working section with a circular cross section decreasing from the shank and forming in the form of a curve with a variable taper, which at the end of the crimp section is equal to the taper of the gauge sweep (see article An automated method for calculating calibrations of the working tool of the KhPT mills / V.G. Mironov, V.I. Ryabushkin, B.Ya. Mitberg, etc. // Steel. 1988. No. 6. P. 61). The advantage of the prototype, unlike analogues, is the consistency of the mandrel and caliber profiles at the end of the working section, which increases the accuracy of the pipes. The disadvantage of the prototype is the low quality of the inner surface of the pipes, since the profile of the mandrel is not consistent with the profile of the reamer gauge at the beginning of the working section, which can lead to increased thickening of the pipe wall in the reduction zone and the formation of wrinkles on the inner surface.

The technical task of the invention is to improve the quality of the inner surface of the manufactured pipes. The technical problem is solved due to the fact that the taper of the forming mandrel at the beginning of the working section K _{0 is} made consistent with the taper of the sweep of the caliber in accordance with the inequality

where K _t - the taper of the mandrel at the end of the crimp section, equal to the taper of the sweep gauge;

To _p - taper sweep caliber at the beginning of the working section.

f is the coefficient connecting the thickening of the pipe wall in the reduction zone with compression in diameter.

The essence of the invention lies in the fact that the profile of the mandrel is consistent with the profile of the caliber scan at the beginning of the working section, which improves the quality of the inner surface of the pipes by eliminating the increased thickening of the pipe wall in the reduction zone and eliminating the possibility of wrinkling on the inner surface.

Figure 1 shows a mandrel for cold rolling pipes, containing a shank 1 and a working section 2 with decreasing round cross-section from the shank and forming in the form of a curve with a variable taper, which at the end of the crimp section is equal to the taper of the sweep of the caliber K _t , and at the beginning of the crimp plot K ₀ is selected by the formula (1). The taper of the mandrel of the cold rolling mills is usually characterized by the slope of the generatrix in this section, therefore, in Fig. 1, the taper at the beginning of the working section (section I) K ₀ = tgα ₀ , and at the end of the crimping section (section II) K _t = tgα _T .

The rational taper of the mandrel at the beginning of the working section is determined by condition (1), to derive this condition, we use figure 2, which shows the section of the rolled pipe with an initial outer diameter D ₀ and wall thickness S ₀ corresponding to the reduction zone l ₁ . Taking the generators of the caliber and the mandrel in the zone l _{1 in} straight lines, we define the taper of the mandrel K ₀ = tgα ₀ . Consider the rectangle ABCD, the equality of sides AB = CD is expressed by the relation

where Δ is the gap for inputting the mandrel; ΔS - wall thickening in the reduction zone; ΔD _p - compression in diameter in the reduction zone; Δd _p - reduction of the diameter of the mandrel in the reduction zone.

Dividing both sides of expression (2) by l ₁ and performing the transformations, we obtain

- коэффициент, связывающий утолщение стенки трубы в зоне редуцирования с обжатием по диаметру.Where

- coefficient connecting the thickening of the pipe wall in the reduction zone with compression in diameter.

The coefficient f can be taken f = 0.75S ₀ / D ₀ (see the book by Shevakin Yu.F. Calibration and efforts in cold rolling of pipes. M: Metallurgizdat, 1963, p. 188, formula (89)).

From the expression (3) it follows that K ₀ ≠ K _p (1 + 2f), since the clearance for entering the mandrel Δ cannot be equal to 0. Also, there cannot be K ₀ > K _p (1 + 2ƒ), since Δ and l ₁ are positive numbers. Thus, the right-hand side of inequality (1) is justified. The validity of the left-hand side of inequality (1) is explained by the fact that at K ₀ ≤ K _{T the} forming mandrel will be either rectilinear or convex, which makes it difficult for the pipe to come off the mandrel and can cause metal to stick to the mandrel.

As an example, consider the implementation of a mandrel for rolling pipes along the route 55 × 6.3 → 25 × 3 mm (initial and final diameter and wall thickness of the pipe). For pipe rolling, the caliber of the cold pipe rolling mill was used, having a taper at the beginning of the working section K _p = 0.1, and at the end of the crimping section K _t = 0.023. The taper of the mandrel at the beginning of the working section was performed according to the relation (1), taking the coefficient f = 0.75 · 6.3 / 55 = 0.086:

0.023 <K ₀ <0.1 · (1 + 2 · 0.086) or

0/023 <K ₀ <0.117.

Assigned To ₀ = 0.05.

Along the length of the crimp section, the taper of the mandrel was made variable, varying from K ₀ = 0/05 to K _t = 0,023 according to the linear law.

As a result of rolling, pipes with a good quality of the inner surface without sunsets and creases, as well as without longitudinal delta, were obtained.

The technical result of the claimed invention is to obtain high-quality cold-rolled pipes. Industrial experiments performed in the pipe rolling shop of one of the plants showed that rolling on the inventive mandrel eliminates the folds on the inner surface of the pipes, as well as reduce metal consumption for the manufacture of calibers by 20-30% compared with the prototype.

Claims (1)

A mandrel for cold rolling pipes containing a shank and a working section with a circular cross section decreasing from the shank and forming in the form of a curve with a variable taper, which at the end of the crimping section is equal to the taper of the reamer gauge, characterized in that it is made with a taper forming To ₀ , consistent with the taper of the sweep of the caliber in accordance with the inequality K _t <K ₀ <K _p (1 + 2f),
Where

- the coefficient connecting the thickening of the pipe wall ΔS in the reduction zone with compression in diameter ΔD _p in this zone;
To _t - the taper of the mandrel at the end of the crimp section, equal to the taper of the reamer caliber at the end of the crimp section;
To _p - taper sweep caliber at the beginning of the working section.

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