KR20080111922A - High pressure hydroformed multi-layer tube and manufacturing method there of tube using high pressure tube hydroforming - Google Patents

Abstract

A multi-layer steel pipe and a manufacturing method thereof are provided to deform the outer steel pipe with the expansion force of the inner steel pipe so that the pipes are mechanically bonded by the elastic recovery force. A manufacturing method of a multi-layer steel pipe includes the following steps. When water pressure is applied to an inner steel pipe, the inner steel pipe starts to expand(a). An outer steel pipe also expands by the expansion of the inner steel pipe as the inside and outer steel pipes contact(b). When entering the stabilized phase, the final shaping pressure is maintained(c). When the final shaping pressure is steadily fixed, the elasticity of the outer steel pipe is recovered by removing the water and the inner and outer steel pipes are uniformly bonded(d).

Description

High pressure hydroformed multi-layer tube and manufacturing method there of tube using high pressure tube hydroforming

Figure 1 shows an example of a multi-composite steel pipe using the high pressure hydraulic molding of the pipe according to the present invention, and also shows the main process of the manufacturing process for joining the inner tube and the exterior clearly.

Figure 2 shows an example of a manufacturing process diagram of a multi-composite steel pipe using the pipe high pressure hydraulic molding of the present invention.

3 is a molding perspective view (FIG. 3A) of a molding analysis program of a multi-composite steel pipe using the high pressure hydraulic molding of the present invention, and a mold photograph (FIG. 3B) and axial indentation of the multi-composite steel pipe using the high pressure hydraulic molding of the present invention. An example of a process (FIG. 3C) is shown.

Figure 4 is a preliminary analysis of thickness variation for forming analysis in the production of multi-composite steel pipe using the high pressure hydraulic molding of the pipe according to the present invention.

5 is a preliminary analysis of stress variation for structural analysis during manufacture of the present invention.

Figure 6 is an explanatory view showing the separation strength measurement of a multi-composite steel pipe using the high pressure hydraulic molding of the pipe according to the present invention.

7 shows an example of a molded valley diagram of an inner tube and an outer appearance of the present invention.

The present invention relates to a multi-composite steel pipe using a high pressure hydraulic molding pipe and a multi-composite steel pipe manufactured by the method of manufacturing the same, the inner steel pipe and the outer steel pipe by the high pressure hydraulic molding of the pipe by integral bonding of the surface of the internal and external steel pipe It is characterized in that it has a multi-bond structure.

In this case, high pressure hydraulic molding of pipe materials is made of various types of press molds to make complex parts. Instead of welding them, the material made in the form of a tube is placed in a mold having a cavity having a desired shape. It refers to a complex molding that is processed by pushing with high pressure. This process is a steel pipe processing technology with high material recovery and high productivity.

Commonly used double / multi-structured steel pipes are manufactured by shrinking adhesive or synthetic resin by filling between inner and outer steel pipes to bond or by heating or cooling the inner or outer steel pipes.

However, such a steel pipe has the following problems.

First, in the case of double or multiple steel pipes in which the inner and outer steel pipes are combined by filling an adhesive, the coupling performance of the inner / outer steel pipes is degraded by the loss of bonding performance due to chemical change depending on the ambient temperature or the environment.

Second, the productivity is poor because the process, such as surface treatment and solidification of the steel pipe for the adhesive coating or synthetic resin filling.

Third, the adhesive or the synthetic resin or the synthetic resin not only decomposes even after a long time, but also increases the manufacturing cost by using the adhesive or the synthetic resin.

Fourth, in order to bond by heat treatment, expensive heat treatment equipment is required, and if the length of the steel pipe is long, there is a problem in that all surfaces cannot be uniformly joined by heat treatment.

Therefore, the present invention does not use chemical fillers and adhesives to bond the inner steel pipe and the outer steel pipe, and also omits the heat treatment process. An object of the present invention is to provide a multi-composite steel pipe and a method of manufacturing the same, in which the external steel pipe is elastically and plastically deformed by the expansion force of the steel pipe, thereby being mechanically coupled by elastic recovery.

The present invention relates to a multi-composite steel pipe manufactured by the pipe high pressure hydraulic molding method as described above, and to a multi-composite steel pipe manufactured by the method of manufacturing the same, as shown in FIG. It is characterized by having a multi-composite steel pipe structure by bonding.

The outer circumferential surface of the inner steel pipe is expanded and plastically deformed by the high pressure hydraulic molding on the outer circumferential surface of the outer steel pipe, and the outer steel pipe is elastically restored when the pressure of the inner steel pipe is removed after the elastic and plastic deformation by the high pressure molding pressure generated in the inner steel pipe. And the external steel pipe is mechanically combined to make a continuous joining in the longitudinal direction of the outer peripheral surface of the inner / outer steel pipe.

Figure 1 shows the main process of the process of the present invention. That is, when water pressure Pi is applied into the inner steel pipe as shown in FIG. 1 (a), the inner steel pipe 11 starts to expand, and as shown in FIG. 1 (b), the inner and outer steel pipes start to contact each other. The outer steel pipe is also affected by the expansion from the inner steel pipe and expands outward.

Finally, as shown in (c) of FIG. When the final molding pressure is uniformly and stably fixed, no further internal pressure fluctuations are eliminated. Then, as the water pressure is removed, the elasticity of the external steel pipe is restored as the water pressure (Pi) is removed, as shown in FIG. The appearance is closely bonded to the entire surface.

In addition, in the present invention, the inner steel pipe is mechanically frictionally coupled to the inner diameter outer circumferential surface of the outer steel pipe as shown in FIG. 1, but the inner steel pipe and the outer steel pipe have the same center, but are not elliptical, square, hexagonal. It may be manufactured to have a predetermined variety of shapes, such as octagon.

That is, an ellipse that is not circular, according to the shape of the pipe high pressure hydraulic forming mold having the same center so that the outer circumferential surface of the inner steel pipe and the inner circumferential surface of the outer steel pipe have the same joint surface, and have the same mechanical frictional force, and contact the outer steel pipe. It is characterized by including a variety of shapes, such as square, hexagon, octagon.

The inner and outer steel pipes are made of ferrous metals or nonferrous metals such as general carbon steel pipes, stainless steel pipes, aluminum pipes, copper (Cu) pipes, etc., and may be made of various materials with the same or different materials, and also internal steel pipes. Two or more steel pipes can be manufactured in multiple structures.

According to the present invention, a method for manufacturing a multi-composite steel pipe using high pressure hydraulic molding according to the present invention includes (i) inserting an inner steel pipe into an outer steel pipe after seating on a mold having a cavity having a constant tolerance and the outer diameter and length of the outer steel pipe. Mounting in the mold; (ii) applying a water pressure while gradually increasing the water pressure up to 850 bar in the inner steel pipe for several seconds (sec) and performing an axial indentation process to maintain the air tightness (FIG. 3C); and (iii) the inner steel pipe inside the inner steel pipe. To radially pressurize the inner steel pipe by high pressure water pressure (Fig. 1 (a)) and (iv) the inner and outer steel pipe by maintaining the final molding pressure as the inner pressure generated in the inner steel pipe. While the outer steel pipe is elastically deformed (Fig. 1 (b)) while maintaining the final molding pressure in this state to sufficiently elastically deform the inner and outer steel pipe (Fig. 1 (c)) (v) to remove the internal pressure Therefore, the inner steel pipe, the outer steel pipe is performed as a step of forming an elastic recovery (Fig. 1 (d)) all together.

When it exceeds 850 bar, the alignment and seating state of the inner and outer steel pipes in the mold becomes poor. First, apply hydraulic pressure up to 850 bar and check the seating, airtightness, etc. of the steel pipe in the mold until expansion of the internal steel pipe, and then perform plastic analysis and structural analysis through virtual molding test, and then apply plastic deformation to the final molding pressure of 1900 bar. Expand the inner steel pipe. If the final forming pressure exceeds 1900 bar, it exceeds the forming limit point, causing pipe breakage, breakage, and shape defects such as bursting. This final forming pressure depends on the type of steel, pipe diameter, thickness, and so on. On the other hand, as described above, the material of the inner and outer steel pipes can be used in a variety of material pipes having an iron or non-ferrous tube type according to the use, strength, and use environment. In addition, since the mold design / manufacturing, pipe outer diameter, thickness, and length can be applied in various ways, the expansion capacity of the steel pipe is derived from the elongation and forming limit curve of the pipe to be used and the value is applied to the molding analysis program. Molding test) is carried out to test whether or not proper molding is made during pipe hydraulic molding, and actual mold production and product manufacturing are performed.

As a 3D model design program, a multiplex pipe was designed based on FIG. 1.

Figure 2 shows a manufacturing process diagram of the present invention designed multiple composite steel pipe. According to the manufacturing process diagram, after the design, the elongation of the material and the limiting limit stone are applied to the molding analysis program, and the virtual molding test is performed to derive the appropriate pressure applied to the cavity, the shape, the dimensions, and the interior. To this end, it is important to calculate the expansion and elongation of the inner tube and the exterior according to the material. Thus, through the data collection and experiment, the elongation / molding limit curve results are obtained as shown in Table 4 and FIG. 6 as an example.

Figure 3 shows the analysis of the virtual molding results in the molding analysis program. As described above, if the outer diameter of the inner steel pipe is too close to the inner diameter of the outer steel pipe or is excessively separated from each other and the gap is large, there will be a burst or unmolding during the high pressure hydraulic molding of the pipe, which will prevent mechanical friction coupling between the inner and outer steel pipes. Can be. On the contrary, if the gap between the outer steel pipe and the mold is too close, there is no elastic deformation and mechanical friction is not achieved. If the gap is too large, uneven molding is likely to occur in the circumferential direction, resulting in thickness deviation or defective product. easy.

Therefore, as shown in FIGS. 3 and 4, the optimal internal / external material selection and the specifications (dimensions) of the internal / external material pipes should be adjusted in advance through virtual molding experiments.

Through the above process, the pipe high pressure hydraulic molding die is designed / manufactured. Figure 4 shows the tube high pressure hydraulic molding die of the present invention. The inner steel pipe is inserted into the outer steel pipe in the mold, and the upper and lower molds are fastened by using a press, and then the axial press-in cylinders are contacted at both ends of the inner steel pipe, respectively (Fig. 3c). After filling up the pressure slowly. At this time, the axial indentation cylinder to maintain the airtightness of the inner steel pipe by pushing both ends of the inner steel pipe.

FIG. 6 is a molding limit curve created based on Specimen 1 of Table 3 in Examples to be described later. FIG. The result of molding analysis is shown and the figure on the right is the thickness change of the outer / inner steel pipe. The molding analysis is performed by changing the thickness, and accordingly, the molding operation is performed by finding the most suitable value. Here, the molding limit curve is a curve representing the boundary between the fracture zone and the unsafe zone during molding. The lower part of the molding curve indicates the safety zone, and the upper part of the curve indicates the fracture zone. The black spots and the black area portions of FIG. 6 represent the area ranges in which safe and good molding is obtained as a result of the molding analysis comparison according to the embodiment of the present invention.

Before performing the high pressure hydraulic molding, the amount of thickness change to be obtained is examined through preforming analysis as shown in FIG. 4.

As shown in FIG. 5, the structural analysis can be known through the structural analysis of high stress value at low stress by analyzing and examining the stress change amount of the external steel pipe and the internal steel pipe through preliminary structural analysis.

In other words, the elongation and molding limit curves according to the materials are generally obtained through tensile tests and applied to the molding analysis program during preforming analysis.

In the present invention, it is important to select the outer diameter and the thickness of the inner steel pipe so that the inner steel pipe is 5% or less in the outer steel pipe for the efficient and stable multi-steel pipe joint, and the results of the long-term research and testing were confirmed. When more than 5% expansion was made, shape defects and surface defects frequently occurred, and expansion ratios of about 1% to 5% were generally applied according to steel grade (material), dimensions (steel pipe diameter, etc.) and elongation.

On the other hand, the gap between the outer steel pipe and the mold maintains a 0.2 ~ 1.0mm gap, and when the final molding pressure is closely adhered to the mold, the elasticity is recovered. Therefore, the expansion capacity, elongation, and molding limit curve are not considered. If it is kept below 0.2 mm, the elastic surface will not be deformed and the molding surface will be poor. If the gap is more than 1.0 mm, the pipe will be cracked or unevenly formed, resulting in thickness variation and poor shape. it's difficult. Finally, the final check whether the internal / external steel pipe joints are well done, the present invention is to perform the following test.

1) Penetration test

Penetration test is a non-destructive testing method that is effective for the detection of cracks and discontinuous defects on the surface. It is a test that detects defects opened on the surface by penetrating the penetration liquid into the defect by using capillary phenomenon of liquid.

The test method is to observe the location, size and indication of the defect using chemicals of three kinds of penetrant, developer, and cleaning solution.

2) Ultrasonic test

3) Eddy Current Test

On the basis of the accompanying drawings will be described in more detail as an embodiment of the present invention.

Example

The mechanical properties of Table 1 and Chemical Compositions of Table 2 were selected from the materials of the inner and outer steel pipes, and their elongation and forming limit curves were derived.

Table 1. Mechanical Properties of Internal and External Steel Pipes

Table 2. Chemical Composition of Internal and External Steel Pipes

Table 3. Example of Mechanical Properties of Multiple Composite Steel Pipes

As described above, the inner steel pipe and the outer steel pipe having the specifications of Tables 1 and 2 were manufactured. When the pressure of the water in the inner steel pipe is increased, the water pressure gradually increases to 850 bar for several seconds (sec) as shown in FIG. Increase the pressure and press up to 1900 bar to complete the molding. The total time required was around 20 seconds.

As another embodiment of the present invention, the final pressure was formed by applying an injection pressure of about 8.3 mm up to 650 bar and an injection pressure of up to 16.9 mm until the maximum molding pressure was maintained for about 3 seconds. Next, as shown in Figure 4 to increase the water pressure over 13 seconds to 850bar, and pressurized up to 1,190bar to complete the molding. At this time, the elastic and plastic deformation is caused by the axial load generated by the inner steel pipe of the outer steel pipe, and after the pressure of the inner steel pipe is removed, elastic recovery is applied to stress the inner steel pipe, and mechanical friction coupling between the inner and outer steel pipes is performed. Was formed.

An example thereof is shown in Table 4.

Table 4.

In addition, the elongation of the general carbon steel pipe is shown in Table 5 as an example.

Table 5.

In order to cut the product through the above process to the desired length and to check the integrity of the inner and outer steel pipes, the final inspection stages of the product are non-collapse test (ECT + UT), fracture test (flange test) and fracture test (Crush Test). ), The flattening test (Flattening Test), the breakdown test (Fig. 6) through the mechanical properties of the composite steel pipe Table 3. The product multiple composite steel pipe with excellent performance was developed.

According to the present invention, a conventional double / multi-structured steel pipe is used by filling adhesive or synthetic resin between an inner steel pipe and an outer steel pipe to bond or by using a shrinkage using a method of heating or cooling the inner or outer steel pipe. Instead of high pressure hydraulic molding of the pipe, the inner steel pipe is tightly expanded to the outer steel pipe for plastic deformation, and the external steel pipe is elastically and plastically deformed by the expansion force of the inner steel pipe and mechanically combined to provide excellent bonding strength. Since the synthetic resin is not required separately, manufacturing cost is reduced and workability and productivity are improved.

In addition, the material of the inner steel pipe and the outer steel pipe can be used in various combinations according to the use, and there is an advantage that the product of various shapes can be manufactured according to the shape of the pipe high pressure hydraulic molding mold cavity.

Claims (4)

The inner and outer steel pipes are placed in the mold without chemical fillers, adhesives, and heat treatments, and the elongation and limit curves are drawn at room temperature, and the values are preformed (virtual molding). Experiment) to apply high pressure hydraulic molding and apply water pressure in the inner steel pipe, and close the inner steel pipe to the outer steel pipe under the airtightness to make plastic deformation, and elastic steel plastic deformation by elastic expansion of the inner steel pipe to elastic recovery. Method of manufacturing a multi-composite steel pipe, characterized in that by mechanically joining the internal steel pipe and the external steel pipe by integrally multiple. The method of claim 1, wherein the manufacturing of the multiple composite steel pipe comprises the steps of seating in the mold after the inner steel pipe is inserted into the outer steel pipe after seating on the mold having a cavity having a constant tolerance and the outer diameter and length of the outer steel pipe; Applying a hydraulic pressure while gradually increasing the pressure of the inner steel pipe to 850 bar for several seconds and performing an axial indentation process for maintaining airtightness; Applying a high pressure water pressure of up to 1900 bar radially from the inside of the inner steel pipe to expand the inner steel pipe to plastic deformation; Elastically deforming the outer steel pipe by maintaining the final molding pressure as the inner pressure generated in the inner steel pipe; The method of manufacturing a multi-composite steel pipe, characterized in that the inner steel pipe, the outer steel pipe to the elastic recovery by removing the internal pressure. According to claim 1 or 2, wherein the mold and the outer steel pipe is maintained between the gap of 0.2 ~ 1.0 mm and then close to the mold at the final molding pressure to remove the pressure to recover the elasticity of the steel pipe, The method of manufacturing a multi-composite steel pipe, characterized in that for calculating the outer diameter and thickness of the inner steel pipe so that the inner steel pipe is 5% or less expansion pipe in the outer steel pipe. The inner steel pipe and the outer steel pipe according to claim 1 are concentric so as to be frictionally coupled with the same mechanical frictional force at the joining surface in the longitudinal direction, and have an elliptical shape, not in the shape of a garden steel pipe having the same center. , Square, hexagonal, octagonal, and various shapes, and the inner steel pipe and the outer steel pipe, respectively, or use a ferrous or non-ferrous metal steel pipe, such as ordinary carbon steel pipe, stainless steel pipe, aluminum pipe, copper (Cu) pipe, or The internal steel pipe and the external steel pipe are each composed of the same kind of material or different materials, and the multiple steel composite pipe, characterized in that the internal steel pipe and the external steel pipe can be manufactured in a double or more than three or more multi-structure.

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