SU1574317A1 - Method of producing bent tubes - Google Patents

Abstract

The invention relates to the processing of metals by pressure, in particular to pipe bending (T), preferably for a small radius (R = 1 ... 1.5 diameter of the workpiece) from pearlitic steels and ferritic steels. The purpose of the invention is to improve the quality of the product. The method includes induction heating, settlement, bending and subsequent cooling of the bent portion. Heating is carried out in two stages. First, T is heated to Ac temperature ₁ - / 200 ... 250 / ° C with ensuring a temperature gradient of 50 ... 70 ° C along wall thickness T. Then, in addition, in the deformation zone, T is heated to a temperature on the outer surface of Ac ₃ . Ac ₁ and Ac ₃ values are temperatures of critical points of phase transformation of the metal. The method allows to obtain bent T without cracks and other defects with high quality metal that does not require additional heat treatment. 2 Il.

Description

The invention relates to the processing of metals by pressure, in particular, to the bending of pipes for a small radius (R 1 is 1.5 times the diameter of the workpiece) and can be used in various areas of mechanical engineering in the processing of billets made of pearlitic steels and ferritic steels undergoing and the transformation.

The aim of the invention is to improve the quality of products.

FIG. 1 shows a device for carrying out flexible pipes by the proposed method; in fig. 2 is a diagram of temperature distribution over the wall thickness of the pipe in the deformation zone.

Curves 1-3 show the distribution with known methods, 4 - with the proposed.

The pipe 1 (Fig. 1) along the guide rollers 2 is pushed by the pusher 3 into the inductor 4 and

preheated to Aci- (200 - 250 ° C) temperature with holding at this temperature until a temperature gradient across the wall thickness of 50-70 ° C is obtained. Then pipe 1 by pusher 3 is moved through inductor 5 and secured with the front end in the turntable 6. 5, heating up the narrow juice of the 7 bend area (deformation zone) to a temperature not higher than Asz (Fig. 2). After the required heating temperature in the deformation zone is reached, water spray cooling is turned on and a longitudinal compressive force P is applied to the pipe through the pusher 3, and the braking torque Mt is applied to the rotary carrier. Under the action of these forces, the pipe is continuously and sequentially moved through inductors 4 and 5 at a speed V, a flexible pipe is carried out at an angular velocity (O for a given radius

cl

but

with

curvature with simultaneous draft in the deformation zone.

The result is a bent pipe of the required geometry with high quality metal.

Example. It is necessary to bend a pipe with a diameter of 530 mm and a wall thickness of 28 mm from 15GS steel to a radius of 850 mm. Bending was performed on the mill UZTM-TVCh 820 with local induction heating of the pipe. The current frequency during induction heating is 500 Hz, the heating power is 250-260 kVA, and the bending speed V is 0.2 m / s.

On the pipe pre-marked area to be flexible. Then the pipe was installed in the mill and its rear end was fixed in the push carriage (pusher). An auxiliary inductor was turned on and the bending area was heated to 450 ° C with an initial exposure in the order of 8-10 minutes to ensure a temperature difference across the wall thickness of 50-70 ° C. After that, the heated section was moved to the main inductor and the pipe was fixed with a front end in a bending mechanism (cage) of the mill. The main inductor was turned on and a narrow strip of the pipe was heated to 870 ° C for 5-8 min. Then the sprayer water cooling was turned on and, with continuous and sequential movement of the pipe through the inductors (auxiliary and main), it was bent at a predetermined angle with simultaneous application of the calculated longitudinal compressive force (75 tf) and braking torque (10 tfm) to it . As the pipe progresses through the included inductors (auxiliary and main), it is uniformly heated in the hearth throughout the wall thickness up to 820-870 ° C.

As a result, the product was obtained - a bent pipe - without cracks with the required geometrical parameters (wall thinning - 20%, cross section ovality - 5%) and mechanical characteristics of the metal (carbon dioxide, 2 35-37 kgf / mm2, (7c 60-65 kgf / mm2, d 30-35%, at 65-70% and ak 7-9 kg cm / cm2), not inferior to the characteristics of the metal of the original pr - mby pipe (ao, 2 32-35 kgf / mm2, 5c 52-57 kgf / mm2, (5 35%, / 70% and ak 7 kgcm / cm2),

Thus, the proposed method allows to obtain bent pipes without cracks and other defects with high quality metal that do not require additional heat treatment after bending with local induction heating and water cooling of the bent portion.

Claims (1)

The invention method for producing bent pipes, mainly with a bending radius of 1-1.5 diameters of the billet, of pearlitic and ferritic-grade steels undergoing a-5-y transformation, including heating, slumping and bending, followed by intensive cooling of the bent y- An aka, characterized in that, in order to improve the quality of the product, heating is carried out in two stages: first, the pipe is heated to Aci - 200 - 250 ° C with ensuring a temperature gradient of 50 - 70 ° C over the wall thickness, and then in the deformation zone of the pipe tionary is heated to a temperature not higher ASP on the outer surface, and wherein Aci ASP - temperature critical points of phase transformation of the metal. figure 1 t ° s FIG. 2