RU2163851C1 - Method for making heat exchange tubes - Google Patents

Abstract

FIELD: plastic metal working, namely manufacture of tubes secured to tube plates of heat exchange apparatuses at using effect of localized oriented plastic deformation of tube material. SUBSTANCE: method comprises steps of cutting off part of measured length of tube after straightening tube and trimming outer surfaces of tube ends; then forming tube portion with curvilinear generatrix turned to tube axis and placing tube end into opening of detachable die having outer and inner annular grooves on its inner surface; placing tube portion with curvilinear generatrix in front of inner annular groove of die; fixing tube against possible motion and forming on it annular protrusions at applying to tube end axial effort causing deformation of tube material and plastic yielding of material to annular grooves of die; simultaneously providing axial motion of die at rate equal to that of tube material deformation in order to make equal outer diameters of annular protrusions of tube at applying relatively small deforming efforts. EFFECT: enhanced efficiency. 8 dwg

Description

 The invention relates to the field of metal forming, in particular to the processes of fixing pipes in the tube sheets of heat exchangers using the effect of localized directional plastic deformed pipe material.

 There is a method of producing heat exchange pipes, in which a pipe made by one of the methods of metal forming is subjected to straightening, cutting to a measured length and then cleaning the external surfaces of the pipe ends to a given length (see OST 26-02-1015-85).

 The disadvantage of this method is that it does not provide for any change in the external smooth surface of the cleaned ends of the pipe, aimed at improving the occupancy of the volume of the annular grooves of the holes of the tube sheets. As a result, especially for tube bundles of the repair option, when there is an increased one-sided gap between the tube and the walls of the tube hole, the formation of a rolling joint with the required service characteristics is very problematic. And here it affects how the hardening of the pipe material takes place and the heterogeneity of the applied force to the inner surface of the pipe, causing trimming of its walls.

 There is also known a method of producing heat exchange pipes with external annular protrusions, including installing the end of the pipe in the hole of a detachable matrix having an external and internal annular grooves on the inner surface, fixing the pipe from possible movement and subsequent formation of annular protrusions on it by applying axial force to the pipe end, causing the deformation of the material of the pipe with ensuring its plastic flow into the annular grooves of the matrix (RU 2095180 C1, 10.11.1997, B 21 D 39/06 - prototype).

The main disadvantages of this method include:
the presence of a one-sided allowance for pipe material provided for filling the volumes of the annular grooves, which leads to the need to provide large deforming forces;
the sequence of filling volumes of the grooves from the outer to the inner, which determines the relatively worst geometric dimensions of the latter.

 The objective of the invention is to develop such a method for producing heat exchange pipes, which would ensure equal ring diameters in terms of external diameter under condition of relatively low deforming forces.

 The technical result is achieved by the fact that in the method for producing heat exchange tubes with external annular protrusions, including installing the end of the pipe in an opening of a detachable matrix having an outer and inner annular grooves on the inner surface, fixing the pipe from possible movement and subsequent formation of annular protrusions on it by applying to the end of the pipe axial force, causing the deformation of the material of the pipe with ensuring its plastic flow into the annular grooves of the matrix, according to the invention before by tapping the end of the pipe into the hole of the detachable matrix, straighten the pipe, cut a portion of the measured length, clean the surface of its ends and form a section on the pipe with a curvilinear generatrix facing the pipe axis, install the end of the pipe into the hole of the detachable matrix with the location of the pipe section with the curvilinear generatrix opposite the inner annular grooves of the matrix, and when forming the annular protrusions of the pipe, the matrix is axially moved at a speed equal to the rate of deformation of the pipe material.

 Implementation of the proposed method for producing heat exchange pipes allows the formation of external annular protrusions at the ends of the pipe with equal diameters at relatively low deforming forces.

 This is explained by the fact that, using the effect of variable pipe stiffness over the length subjected to axial compression, conditions are created for more efficiently filling the pipe material with the free volume of the internal (counting from the front surface of the matrix) ring grooves. For this, two allowances of pipe material are provided, respectively designed to fill the volumes of each of the annular grooves, and provide plastic flow of the processed material initially into the volume of the inner annular groove. A decrease in the deforming force is achieved by using a floating matrix forming active friction forces and sequential filling of the groove volumes.

 The invention is illustrated by drawings, where in FIG. 1 shows the tooling with the end of the heat exchanger tube placed in it before local crimping of the latter; in FIG. 2 - the stage of completion of the local crimping of the end of the heat exchange pipe; in FIG. 3 - the initial position of the end of the pipe (after partial distribution of its compressed portion) and technological equipment before forming annular protrusions on the outer surface of the pipe; in FIG. 4 - stage of plastic flow of the pipe material into the volume of the inner annular groove of the matrix, causing it to be fixed on the pipe; in FIG. 5 - the stage of filling the pipe material of the inner annular groove of the matrix; in Fig.6 is the stage of filling the outer annular groove of the matrix with pipe material; in FIG. 7 - stage calibration of the annular protrusions and the diameter of the holes in the pipe; in FIG. 8 - heat transfer tube with a thickened tip and annular protrusions having equal diameters.

 An embodiment of the invention is as follows.

 Operations are performed on the heat-exchange pipe in order to prepare its surface for the subsequent formation of annular protrusions: straightening the pipe, a segment of its measured length and cleaning the outer surface of the ends to a metallic luster. Next, the pipe 1 (Fig. 1) is placed at one of its ends in the container 2. The latter has a working cavity made in the form of a step with a minimum diameter made to fit the movement relative to the diameter of the pipe 1. The pipe 1 is fixed from possible movement by application of radial pressure to its outer surface (shown by arrows). In the formed gap between the pipe 1 and the side surface of the cavity of the container 2, a sleeve of elastic material, for example, polyurethane grade SKU 7L, is installed. A three-stage punch 4 is introduced into the hole of the pipe 1, the small step of which is smaller than the diameter of the hole of the pipe 1, the middle stage has a diameter made with a minimum clearance with respect to the diameter of the pipe 1, and the diameter of the large stage is equal to the outer diameter of the pipe 1. On a large stage of the punch 4, place sleeve punch 5, the outer diameter of which is made with a minimum clearance with respect to the diameter of the cavity of the container 2 (Fig. 1).

 Applying axial force to the end face of the punch 5 (Fig. 2), cause it to move in the axial direction, reducing the length of the sleeve 3. Changing the cross section of the sleeve 3 leads to the appearance of radial pressure (shown by arrows) on the outer surface of the end of the pipe 1, which leads to the formation of a section with a curved generatrix facing the axis of the pipe 1. The depth of the section with a curved generatrix is determined by the difference between the radius of the hole in the pipe 1 and the radius of the small step of the punch 4. The length of the generatrix of the curved section is specified by remescheniem punch sleeve 4 relative to the bottom surface of the cavity of the container 2.

 The pipe 1 by its section with a curvilinear generatrix (Fig. 3) is installed in the hole of a matrix 6 that is detachable along the generatrix, which has the possibility of axial movement relative to the thick-walled holder 7 made of hardened steel enclosing it. The pipe 1 is fixed from possible movement by the clamp 8. In the hole of the matrix 6, annular grooves (N 1 and N 2) of a trapezoidal cross section are made. A section of the pipe 1 with a curvilinear generatrix is installed in the matrix 6 so that its inner edge (point A) is located above the inner edge of the groove N 2, and the end face of the matrix 6 is placed at some distance from the clamp 8. A step punch 9 is inserted into the hole of the pipe 1, causing a partial distribution of its compressed area, and the appearance of contact pressure (shown by arrows). The large step of the punch 9 has a diameter equal to the average diameter of the pipe 1 (Fig. 3).

 The application of axial force to the punch 9 ensures the distribution of the pipe 1, its bending relative to the outer edge of the annular groove and, as a result, the movement of point A into the volume of the annular groove N 2. From the moment the volume of the annular groove N 2 is filled (Fig. 4), the material of the pipe 1 is observed joint movement of the punch 9 and the matrix 6. As a result of the latter moving on its outer surface (behind the outer edge of the groove N 2), friction forces arise (Fig. 5), directed towards the groove N 2 (shown by arrows). The material of the pipe 1 from the lower allowance (located between the end face of the matrix 6 and the clamp 8) with plastic flow fill the gap between the small step of the punch 9 and the matrix 6 (Fig. 6). The final stage is the calibration stage of the annular protrusions, realized by extruding the pipe material from the upper allowance (from the working end of the punch 9) into the free volumes of the grooves of the matrix 6 (Fig. 7). The heat exchange tube has a thickened tip with equal diameters of the annular protrusions (Fig. 8).

 A pilot test of the developed method took place upon receipt of steel (steel 20) pipes with profiled external endings. The initial geometric dimensions of the pipe were: external diameter 25 mm, wall thickness 2.5 mm. The pipe was previously locally crimped on a hydraulic press with polyurethane in die tooling to an external diameter of 23.8 mm. The compressed sections of the pipe had a length of 13 mm, located at a distance of 8 mm from its end.

 Partial distribution of the pipe in the compressed sections of its length was carried out by a stepped punch having a diameter of a small step of 18.6 mm.

 Ring protrusions were obtained by cold extrusion in a floating matrix. With an outer diameter of the annular protrusions equal to 25 mm, the height of the annular protrusions was 0.51 mm (for the depth of the annular grooves of the pipe hole in 0.5 mm), and their base was equal to the width of the annular groove of 3.0 mm The distance between the protrusions is 10.5 mm. The diameter of the pipe hole after the formation of the annular protrusions was 18.4 mm.

 The tooling for the production of pipes with external annular endings and its fastening in the pipe holes was made of U8A tool steel with a hardness of HRC after hardening of at least 56 units and accuracy of executive dimensions according to the 7th grade.

 The formation of annular protrusions on the pipe was carried out on a special hydraulic machine with forces not exceeding 5 MN, which ensured full reproduction of the required geometric dimensions of the annular protrusions of the trapezoidal cross section.

 It is established that the formation of annular protrusions with equal diameters ensures the formation of the required residual pressure on the contact surface of the annular protrusions with annular grooves of the pipe hole when fixing the pipe. The latter provides enhanced service characteristics of milling joints; significantly increases the overhaul mileage of the tube bundle, subject to the possibility of repeated use of tube sheets. Tests for pulling the pipe out of the tube sheet revealed that the deforming force of the pipe is limited by the tensile strength of its original section.

 The density of the compounds ensured their 100% suitability for production requirements.

 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 tubes with external annular protrusions, including installing the end of the pipe in an opening of a detachable matrix having an external and internal annular grooves on the inner surface, fixing the pipe from possible movement and subsequent formation of annular protrusions on it by applying axial force to the pipe end causing deformation material of the pipe with ensuring its plastic flow in the annular grooves of the matrix, characterized in that before installing the end of the pipe into the hole of the detachable ma the pipes make the straightening of the pipe, cutting a part of the measured length, cleaning the outer surface of its ends and forming a section on the pipe with a curved generatrix facing the pipe axis, installing the pipe end in the hole of the split matrix is carried out with the location of the pipe section with a curved generatrix opposite the inner ring groove of the matrix, and when forming annular projections of the pipe, the matrix is axially moved at a speed equal to the rate of deformation of the pipe material.

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