RU2391162C2 - Method of fabricating thin-walled pipes - Google Patents

Abstract

FIELD: mechanics.

SUBSTANCE: invention relates to improvement of accuracy in dimensions of precision pipes sections, for instance from corrosion-resistant steels for shells of fuel elements in nuclear reactors. Method includes pipe drawing in cone draw die on fixed cylindrical mandrel. Stability of pipes dimensions and reduction of elastic and thermal deformation are provided by the fact that at first pipe billet is rolled and drawn without mandrel, and afterwards drawing of pipe is carried out in fixed cylindrical mandrel, when drawing coefficient along section of pipe λ makes 1.25≤λ≤1.48, at the same time coefficient of drawing along pipe wall λ_s makes 0.90λ≤λ_s≤0.94λ.

EFFECT: increased accuracy of precision pipes section dimensions.

Description

The invention relates to the production of pipes and can be used in the manufacture of thin-walled pipes from corrosion-resistant steels for the shells of fuel elements of nuclear reactors.

As a prototype, the method of drawing pipes on a fixed mandrel was selected (Perlin I.L., Yermanok M.Z. "The theory of drawing". M: Metallurgy, 1971, p.448), including drawing a pipe in a conical fiber on a fixed cylindrical mandrel.

The disadvantage of this method is the low accuracy of the pipe dimensions, with non-contact elasto-plastic deformations at the exit from the die, as well as associated with elastic and thermal deformations of the pipe after drawing. If the diameters of the calibrating die strip and the working surface of the mandrel are made equal to the nominal dimensions of the finished pipe, then the real pipe diameters are smaller than the nominal ones, and the wall thickness is larger than the nominal ones.

The technical problem to be solved by the claimed invention is directed is to increase the accuracy of cross-sectional dimensions of precision pipes.

This problem is solved by the fact that in the method of manufacturing thin-walled pipes, including drawing the pipe in a conical fiber on a fixed cylindrical mandrel, they first perform rolling and flawless drawing of the tube stock, and then draw on a fixed cylindrical mandrel, while the drawing coefficient over the pipe cross section λ is 1.25≤λ≤1.48, and the coefficient of drawing along the pipe wall λ _s is 0.90λ≤λ _s ≤0.94λ.

Rolling and flawless drawing, carried out before drawing the pipe on a fixed mandrel, allows to ensure the dimensional stability of the pipe and reduce elastic and thermal deformation at the stage of drawing the pipe on a fixed cylindrical mandrel.

The choice of the coefficient of extraction λ per passage of at least 1.25 is justified by the fact that in this case, the study of the structure of the pipe metal is achieved. With regard to pipes made of corrosion-resistant steels, this ensures that the austenitic grain size of the metal after subsequent heat treatment of the pipes is no more than 6 points, as well as the mechanical properties of the metal pipes are not lower than the norms regulated by current current technical conditions. The upper value of the coefficient of extraction per passage λ is limited by the elastic and thermal deformation of the pipe unloading after drawing.

The choice of λ no more than 1.48 is justified by the fact that this deformation of the pipe in this case does not bring the size of its inner diameter beyond the lower boundary of the tolerance field. The choice of the coefficient of extraction along the pipe wall λ _s = S ₀ / S of at least 0.90 λ is justified by the fact that in this case an almost complete “smoothing” of the surface of the pipe metal is achieved: a change in its topography and a decrease in roughness, which ensures submicron purity of the external and internal pipe surfaces. The choice of λ _{s of} more than 0.94λ is impractical due to the small gap between the inner surface of the billet pipe and the cylindrical surface of the mandrel, which leads to injection of lubricant into the zone adjacent to the center of compression of the pipe, the inflation of a thin-walled pipe before entering the fiber and, ultimately, to pipe break.

Pipe production ext. 6.6 × 0.20 includes the following operations:

Rolling at the mill ХПТ-90 100 × 12 → 78 × 8.5 Turning, boring 78 × 8.5 → 77 × 7 Rolling at the mill KhPT-55 77 × 7 → 41 × 3.6 Rolling at the mill KhPT-32 41 × 3.6 → 20 × 1.41 Rolling at the KhTPR mill - 15 ÷ 30 20 × 1.41 → 17 × 0.90 Rolling at the KhTPR mill - 15 ÷ 30 17 × 0.90 → 15 × 0.40 Augmented dragging 15 × 0.40 → 12 × 0.43 → 8.5 × 0.47 Rolling at the KhPTZ mill - 8 ÷ 15 8.5 × 0.47 → 7.52 × 0.26 Drawing on a fixed mandrel 7.52 × 0.26 → ext. 6.6 × 0.20

The method is as follows:

In the manufacture of seamless cold-formed especially thin-walled pipes from corrosion-resistant steel EI-847 according to TU 14-159-293-2005 for the cladding of fuel rods of nuclear reactors with dimensions: inner diameter 6.6 mm, with wall thickness 0.2 mm and with internal tolerances with a diameter of ± 0.020 mm and a wall thickness of ± 0.030 mm, we used a tube billet obtained with a KhTPR 8-15 with an outer diameter of D ₀ = 7.590 ... 7.727 mm and a wall thickness of S ₀ = 0.254 ... 0.266 mm. For finishing block the passage in the fixed cylindrical mandrel with a die diameter used sizing girdle D _ox = 7.033 mm _OD mandrel diameter D = 6.622 mm. The coefficient of exhaustion over the cross section of the pipe was λ = 1,365. As a result, pipes were obtained in the range of internal diameters from 6.594 mm to 6.608 mm, wall thicknesses from 0.203 mm to 0.211 mm. The obtained cross-sectional dimensions of pipes of a sufficiently large batch fully fit into the tolerance fields regulated by TU 14-159-293-2005. Pipes of such accuracy show high manufacturability in the implementation of reactor assemblies.

Extra-thin-walled pipes made of steel EI-847 according to TU 14-159-293-2005 with an inner diameter of the finished pipe of 11.6 mm and a wall thickness of 0.2 mm with the same tolerances as for pipes ext. ,66.6 × 0.2 mm, was made by short-drawing drawing from the workpiece with an outer diameter of 12.796 ... 12.905 mm and a wall thickness of 0.276 ... 0.286 mm. A die with a diameter of 12.063 mm and a mandrel with a diameter of 11.643 mm were used. The coefficient of drawing along the cross section was λ = 1.410, and the coefficient of drawing along the wall was λ _s = 0.94λ. After drawing and cooling the pipes, the inner diameter of the batch of elongated pipes ranged from 11.595 mm to 11.612 mm, and the wall thickness of the pipe from 0.210 mm to 0.214 mm.

The assigned hood is the most statistically significant parameter, since it determines both the drawing force, which determines the non-contact hood, and the deformation heating of the pipes during drawing, and, consequently, the magnitude of the elastic and thermal deformation of the pipes after drawing.

Pipes with the same finished dimensions, stretched from the same workpieces according to the prototype method, when the sizes of the dies and mandrels coincided with the nominal dimensions of the finished pipes, all without exception went beyond the minus tolerance field and the wall thickness beyond the plus tolerance field.

Thus, the proposed method provides higher dimensional accuracy of especially thin-walled pipes, in particular, of corrosion-resistant steels for nuclear reactors.

Claims (1)

A method of manufacturing thin-walled pipes, including drawing a pipe in a conical fiber on a fixed cylindrical mandrel, characterized in that they carry out rolling and flawless drawing of a pipe billet, after which they draw on a fixed cylindrical mandrel with an extraction coefficient over the pipe cross section λ of 1.25≤λ ≤1.48, and the coefficient of extraction along the pipe wall λ _{s of} 0.90λ≤λ _s ≤0.94λ.