RU2198052C2 - Method for making tubes with shaped outer ends - Google Patents

Abstract

FIELD: plastic metal working, possibly manufacture and repairing of tube bundles of heat exchange apparatuses. SUBSTANCE: method comprises steps of preliminarily forming calibrated portion by expanding tube end in order to receive its outer diameter exceeding diameter of opening of detachable die in closed state; realizing two-stage reduction of calibrated portion along length less than its initial length in order to form bearing portion and portion having first step arranged on tube end and second step; fixing tube against possible motion by reducing bearing portion due to applying radial effort to it; expanding tube along first step of bearing portion to diameter equal to that of second step; forming annular protrusion at applying axial compression effort to tube end. EFFECT: lowered deforming efforts. 5 dwg

Description

 The invention relates to the field of metal forming and, in particular, to processes for producing heat exchange tubes with profiled external ends using the effect of localized directed plastic flow of pipe material.

 A known method of producing heat exchange tubes with profiled endings, including installing the end of the pipe in the hole of a detachable matrix having annular grooves, fixing it from possible movement and the subsequent formation of annular protrusions on the outer surface of the pipe by applying compressive forces to its inner surface with mechanical rolling rollers (see RF patent for the invention 2160174, RU, C2, IPC B 21 D 39/06, Bull. 34 from 10.12.2000).

 The main disadvantage of the known method for producing pipes with profiled external ends is the fact that the annular protrusions on the outer surface of the pipe end are performed by reducing the wall thickness of the latter. Therefore, to avoid this drawback, before forming a profiled tip, in practice, a set of pipe wall thickness is carried out, which lengthens the process.

 There is also a method of producing heat exchange tubes with profiled external tips, including placing the end of the pipe in a detachable matrix, fixing it from possible movement and the subsequent formation of an annular protrusion by applying axial compressive force to the pipe end (RU, 2160175, C2, 10.12.2000, IPC B 21 D 39/06 - prototype).

 The disadvantage of this method is the need to use hydraulic presses with relatively large nominal forces, since the formation of annular protrusions is carried out by plastic flow of pipe material from the axial deforming force applied to its end.

 The objective of the invention is the development of such a method of producing heat exchange tubes with profiled external tips, which would be implemented relatively small in magnitude of the deforming pipe forces.

 The technical result is achieved by the fact that in the method for producing heat exchange pipes with profiled external tips, including placing the pipe end in a detachable matrix, fixing it from possible movement and subsequent formation of an annular protrusion by applying axial compressive force to the pipe end, according to the invention, previously at the pipe end by distributions form a calibrated section with an external diameter exceeding the diameter of the hole in the detachable matrix in its closed state, after which two-stage crimping of a calibrated section at a length shorter than its initial length, with the formation of a supporting pipe section, and a section having a first stage located at the end of the pipe, and a second stage, fixing the pipe from possible movement is carried out by crimping its supporting section by applying radial force to it after which they distribute the cavity of the pipe section in its first stage to a diameter equal to the diameter of the cavity of the second stage.

 The implementation of the proposed method allows to obtain heat transfer pipes with shaped ends in conditions where the use of hydraulic presses with relatively large deforming forces is not required.

 This is due to the fact that in the proposed method for producing pipes with profiled endings, an operation is introduced to form annular stiffness, which is subsequently located within the annular groove of the matrix, and the pipe is distributed with a conical punch of a minimum pipe cross section. The latter causes the plastic longitudinal bending of the generatrix pipe with filling mainly the free volume of the annular groove of the matrix. Subsequent calibration of the annular protrusion of the pipe when it is loaded at the end eliminates any discrepancy in the geometric dimensions of the annular protrusion of the pipe with respect to the geometric dimensions of the annular groove of the matrix.

 The invention is illustrated by drawings, in which Fig. 1 shows the initial position of the tooling and the end of the pipe with ring stiffness (marked by dots) before performing the pipe distribution operation with a conical punch, in Fig. 2 - the pipe distribution stage with the formation of a conical socket, in Fig. 1. 3 - end of the stage of pipe distribution with a conical punch, in FIG. 4 - the calibration stage of the annular protrusion axial deforming force applied to the end of the pipe, figure 5 - heat transfer pipe with a profiled outer tip.

 An embodiment of the invention is as follows. The heat exchange pipe 1, for example, of steel 10, before profiling the outer surface of its ends is subjected to preparatory operations: dressing, cleaning the outer surface of the ends to a metallic sheen and cutting to the best.

 Then the pipe is fixed from possible movement and, introducing a punch with an inlet conical section into its hole, they are distributed to a diameter exceeding the diameter of the split matrix in its closed state, forming a calibrated section. Next, a two-stage cascade crimping of the calibrated pipe section is carried out at a length shorter than its original length, thereby forming a supporting section. In this case, at the transition of the compressed sections of the pipe, ring stiffness is created in the form of a truncated cone (marked with dots).

 After which the pipe 1 is installed (Fig. 1) with its profiled end in the hole of the split matrix 2 containing three segments. An annular groove of a trapezoidal cross section is made in the cavity of the matrix. Note that the largest diameter of the cavity of the matrix is less than the outer diameter of the supporting portion of the pipe. The correct installation of the pipe is controlled by placing its end in the end plane of the matrix.

 The pipe is fixed from possible movement by closing the segments of the matrix with a clip 3, while informing the matrix of the necessary stiffness (indicated in Fig. 1 by arrows). The closure of the matrix segments leads to a decrease in the outer diameter of the supporting section of the pipe by the crimping operation and explains the appearance of axial support forces, which will eliminate the pipe deformation outside the matrix during the formation of the annular projection.

 A stepped punch 4 is introduced into the hole of the pipe with a conical inlet section. Moving the punch in the axial direction, the pipe end is initially distributed over a length ranging from the end to the ring stiffness (Fig. 2). A bell is formed with a certain taper angle, almost equal to the taper angle of the inlet section. As practice shows, at this stage, one can neglect the deformation of ring stiffness in the radial direction. The subsequent movement of the punch in the axial direction leads to non-contact deformation of the pipe with a longitudinal bend of the forming pipe relative to the inner edge of the annular groove. The latter causes the filling of the ring stiffness of the free volume of the annular groove (figure 3). At this point, a large step of the punch reaches the end of the pipe and begins the calibration stage of the annular protrusion, when any deviations of the geometric dimensions of the annular protrusion from the geometric dimensions of the annular groove are eliminated (Fig. 4).

 The pipe extracted from the tooling has on the outer surface an annular protrusion of a trapezoidal (or any arbitrary shape) cross-section with an external diameter equal to the diameter of the crimped calibrated section. The plastic flow of the pipe in the annular groove of the matrix leads to hardening of the processed material, which is reflected in the allocation of the hardened zone by points. The profiled tip also has a calibrated hole diameter, which is very important at the stage of fixing the pipe in the hole of the tube sheet.

 The described operations are performed at the second end of the pipe.

 A pilot test of the developed method took place when profiling the outer surfaces of the ends of the pipes of steel 10.

 Pipes prepared for profiling with the initial geometric cross-sectional dimensions: 24.9 • 9.8 mm were distributed by a rigid punch with a conical inlet cone 10 mm long, up to the outer diameter of the calibrated pipe section - 25.4 mm. The length of the calibrated section was 30 mm.

 Then, the calibrated pipe section over a length of 20 mm was cascaded in a two-stage matrix, which caused the pipe to deform in the first stage to an external diameter of 24.3 mm, and in the second stage to an external diameter of 23.8 mm. The width of the ring stiffness was 2 mm.

 When fixing the pipe in a detachable 3 - segment matrix, the calibrated pipe section was crimped from a diameter of 25.4 mm to a diameter of 25.3 mm. A double-acting hydraulic horizontal press of the design of OOO Yukos Oil and Gas Repair and Repair Plant LLC was used as technological equipment.

 Profiled endings had an outer diameter of the annular protrusion of 25.3 mm, the outer diameter of the pipe web was 24.3 mm, the diameter of the hole in the second stage was 18.4 mm. The height of the annular protrusion was 0.5 mm, its large base was 4.0 mm, and the small base was 2.0 mm.

 The tooling was made of U8A tool steel with a hardness of HRC after hardening of at least 56 units and with precision of executive dimensions according to the 9th grade. Trapezoidal annular grooves in the tooling matrix were made with the following geometric dimensions: small base - 2 mm; large base - 4 mm; depth - 0.5 mm.

 The step punch had a diameter of a small step - 18.4 mm, a diameter of a large step - 24.3 mm.

 The formation of annular protrusions on the pipe was carried out on a double-acting hydraulic horizontal press designed by Repair and Mechanical Plant of the Yukos Oil Company LLC at forces not exceeding 0.3 MN, which ensured full reproduction of the required geometric dimensions of the annular protrusions of the trapezoid cross section.

 It has been established that the operation of forming the outer annular protrusions of the trapezoidal cross-section by combining the bending deformation of the pipe and its axial compression with the calibration operation ensures their geometric dimensions guaranteed by technological equipment, performance stability for any steels and alloys.

 The invention is applicable in the manufacture of tube bundles of heat exchangers for oil refining, petrochemical, gas and other industries.

Claims (1)

 A method of producing heat exchange pipes with profiled external tips, including placing the pipe in a detachable matrix, fixing it from possible movement and then forming an annular protrusion by applying axial compressive force to the pipe end, characterized in that a calibrated section is formed at the pipe end by distribution with an external with a diameter exceeding the diameter of the hole in the detachable matrix in its closed state, after which a two-stage crimping of the calibrated section at d and less than its original length, with the formation of the supporting section of the pipe, and a section having a first stage located at the end of the pipe, and a second stage, the pipe is fixed from possible movement by crimping its supporting section by applying radial force to it, after which they are distributed the cavity of the pipe section in its first stage to a diameter equal to the diameter of the cavity of the second stage.

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