KR940011851B1 - Small thick-walled composite metal tubing and process for producing the same - Google Patents

Abstract

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Description

Small-diameter, thick-walled metal tube and method of manufacturing the same

1 is a plan view of a small diameter and thick fuel injection tube of the present invention.

FIG. 2 is an enlarged cross-sectional view of a portion of FIG. 1;

3 is a cross-sectional view taken along the line A-A of FIG.

The present invention relates to a high-pressure fuel injection pipe for a fuel supply line of a diesel engine, in particular having a metallurgical press-fitted inner tube and an outer diameter, having an outer diameter of 30 mm or less, cavitation resistance and pressure resistance. A metal fuel injection tube having a small diameter and a thick wall, and a method of manufacturing the same.

In general, in a high pressure fuel injection tube of the above type, such as a diesel engine, the high pressure fuel has about 5 millisecond injection time, an internal pressure of 200-600 kg / cm ² (peak pressure) and a flow rate condition of 15 m / sec or less Under flow into the injection tube, one of the flow rate or internal pressure fluctuates frequently and rapidly.

For example, as can be seen in the tubing material for high pressure fuel pipes, this kind of polymeric metal pipe material is made of carbon steel sheets (JIS G3455 STS38) for large and small diameter high pressure pipes, each having a copper plating film provided in advance on the main surface of the polymerization. Press-fitting, followed by heat treatment to solder the copper plated film on the main surface of the polymerization as a filler, or drawing by inserting one of two tubes having different diameters into another tube And the step of press-fitting each other by, for example.

However, according to the former of these conventional processes, a complicated step is required because copper plating is required around the inner wall surface and the outer peripheral surface of the tube. If soldering is insufficient, the polymeric principal surfaces pressed-fit to each other will loosen, resulting in gaps that can break due to fatigue over time. However, if soldering is sufficient, only a limited degree of durability to vibration can be obtained as the base metal softens due to heating during soldering. Therefore, an excellent fuel injection pipe cannot be manufactured.

According to the latter in the conventional process, since the obtained form has a polymerized surface which simply press-fits, the polymerized main surface causes a loosening phenomenon that lowers the mechanical strength when the tube is used as a fuel injection tube. Vibration during engine rotation sometimes causes cracks or breakage.

In recent years, measures have been taken not only to increase horsepower but also to reduce NO _x to minimize the noisy smoke, and therefore tend to be particularly attentive to high pressure fuels. For example, there has been a need for high pressure fuel injectors that can be used under 1-2 millisecond injection times, flow rates of up to about 50 m / sec and internal pressure conditions of 600-1,000 kg / cm ² (peak pressure). As a result, under such severe use conditions, the high pressure fuel injection pipe requires (1) durability against fatigue due to repeated high pressure loads, (2) cavitation resistance, and (3) durability against vibration of the vehicle body. Therefore, safety measures against pipe cracking and breakage are very important.

For this purpose, as a countermeasure against excessive conditions, it is used as an inner tube of a high-pressure fuel injection tube of small diameter and thick wall pipe having a wall thickness of 25-40% with respect to the outer diameter, and the inner wall surface of the inner pipe has an overflow resistance. It has been proposed that the gap between the inner tube and the outer wall of the wall causing the breakage of the inner tube and / or the fuel leak is eliminated without having a wavefront irregular wave shape that generates the crack. Moreover, such an increase in the overflow resistance causes cavitation to cause cavitation corrosion of the inner wall of the inner tube, resulting in damage to the inner tube.

Nevertheless, fuel injection pipes for diesel engines which can be safely used under the above-mentioned harsh conditions have not been developed at present.

Therefore, it is an object of the present invention to provide a small diameter and thick wall fuel injection pipe for a diesel engine having excellent cavitation resistance and pressure resistance even under severe conditions.

According to a first aspect of the present invention, a carbon steel pipe as an outer appearance and a stainless steel pipe as an inner tube press-fitted to a large diameter carbon steel pipe by a drawing process are formed, and the press-fitted polymerized surface of the inner and outer surfaces is metallurgically. The diffusion layer of at least one metal selected from the group consisting of Ni, Cr, Mo, Co, Al, Cu, or two or more alloys thereof, wherein at least an inner wall surface of the stainless steel pipe, which is an inner tube, is integrally formed A metal fuel injection pipe with a small diameter and a thick wall is provided.

According to a second aspect of the invention, a coating layer of at least one metal selected from the group consisting of Ni, Cr, Mo, Co, Al, and Cu or two or more metal alloys thereof is formed on a carbon steel pipe of an inner tube by a drawing process. Press-fitting a stainless steel pipe as an inner tube having the inner tube; and then heat-treating the inner tube and the polymerized surface of the outer tube by heat-treating the press-fitted inner tube and the outer surface obtained in a furnace or vacuum furnace in an oxygen-free atmosphere, and at least A method of manufacturing a metal fuel injection tube having a small diameter and a thick wall, which comprises forming a diffusion layer of the alloy or metal on an inner wall surface of an inner tube.

Other advantages, features and further objects of the invention will be apparent to those skilled in the art based on the following detailed description and the accompanying drawings which illustrate preferred embodiments incorporating the principles of the invention.

The principles of the present invention are particularly useful when implemented with a small diameter and thick-walled fuel injector (hereinafter referred to as "injection tube"), indicated by reference numeral 1, as shown in FIGS.

As shown in FIG. 2 and FIG. 3, the injection pipe 1 is a double metal pipe having an inner tube 12 inserted therein through the outer 11 and the outer 11, and has a diffusion layer 13 on the inner wall surface of the inner tube 12. As shown in FIG. Alternatively, the diffusion layer may be provided on the outer circumferential surface of the inner tube 12, that is, on the interface between the outer tube 11 and the inner tube 12.

In the present invention, carbon steel pipes (e.g., JIS G 3455 STS 38 and JIS G 3455 STS 42) are used in particular as external appearance 11 in terms of pressure resistance, while stainless steel pipes (e.g., JIS G 3459 SUS 304 TP, SUS 304 LTP) is used as inner tube 12 in terms of cavitation resistance.

Table 1 shows the chemical compositions of the carbon and stainless steels.

TABLE 1

Chemical composition of the inner and outer tubes

In order to safely pass the high-pressure fuel, it is preferable that the injection pipe 1 in the form of a double metal pipe has an outer diameter of 30 mm or less and its wall thickness is 25-40% of the outer diameter. The outer diameter and the thickness are easily defined from those commonly used in the art, and may be respectively defined at predetermined values.

In the manufacture of the high-pressure fuel injector 1, it is important that no gap should be generated between the outer and inner tubes, and that no wavefront undulation should be generated in the inner wall 14 of the injector. In other words, no through resistance should be generated on the fuel channel walls in terms of cavitation resistance.

From the point of view of the manufacturing process of the injection tube as a double gold tube, the gap between the inner tube and the outer tube and the irregular undulations on the inner wall surface 14 of the spray tube are press-fitted by the drawing process to reduce their diameter. And especially when the press-fitted outer and inner tubes are heat treated and then corrected by a straightening roller (double metal tubes are rapidly deformed during heat treatment). In order to maintain the actual conditions of the manufacturing process, it is important for the present inventors to limit the thickness of the inner tube 12 so as not to cause any irregularity between the inner wall surface of the injection pipe and any gap between the inner and outer surfaces. okay. For the injection pipe 1 of the present invention, it is preferable that the thickness of the stainless steel pipe as the inner pipe 12 is 1.5% to 8.5% with respect to the outer diameter of the entire double metal pipe. This is specified for the following reasons. If the thickness of inner tube 12 exceeds 8.5%, the tendency to cause a large gap between the inner tube and the outer tube is sharply caused by plastic deformation in the axial direction of the outer tube 11 due to correction during press-fitting after the drawing process and before diffusion by heat treatment. Increases. If the thickness of the inner tube 12 does not exceed 1.5%, the tendency to cause wavefront relief on the inner wall surface 14 of the flow path of the inner tube increases sharply due to the trace to the roll during calibration.

For the most distinctive feature of the invention, at least the inner wall surface of the inner tube 12 has a diffusion layer of at least one metal or two or more metal alloys thereof selected from the group consisting of Ni, Cr, Mo, Co, Al, Cu. . Alternatively, the diffusion layer may be provided on the outer wall surface of the inner tube 12, that is, the boundary surfaces adjacent to each other between the inner tube 12 of the outer tube 11, and in the case of metal or alloy, diffused around the boundary between the outer tube 11 and the inner tube 12, Make sure that the pipes are firmly bonded.

In order to form the above-mentioned diffusion layer of the metal or alloy, the coating of the metal or alloy is previously formed by plating or the like on the inner wall surface 14 of the inner tube 12, and the outer tube 11 and the inner tube 12 are heat-treated after being press-fitted. The inner tube may be manufactured by using a stainless hoop or strip steel sheet (coated for forming the inner tube) previously coated with the above-described metal or alloy by plating or pressing, and then heat-treated to form a diffusion layer of the metal or alloy. have. The method of forming the diffusion layer is not limited to the described example.

Forming the above-described metal or alloy coating on the inner wall surface or inner wall surface of the inner tube 12 and the outer wall surface can be accomplished by chemical plating. Moreover, the thickness of the coating is not particularly limited and may be usually 1-20 탆.

In the present invention, after the outer tube and the inner tubes 11 and 12 are press-fitted, the outer tube and the inner tubes 11 and 12 are joined together in a metallurgical unit, so that the outer tube and the inner tubes 11 and 12 are vacuum furnaces or no acid. Heat treatment is carried out in a reducing or reducing atmosphere. By the heat treatment at that time, a diffusion layer is formed simultaneously.

After the press-fitting described above, the heat treatment conditions in a vacuum furnace or a reducing atmosphere furnace may be any conditions sufficient to integrate the adjacent interface between the outer tube and the inner tube metallurgically, and are usually performed at 700-1200 ° C. for 1-30 minutes.

The small diameter and thick wall fuel injection tube of the present invention has the following results.

(i) Since the Ni diffusion layer is formed around the inner wall surface of the inner tube, an inner wall surface having a high hardness is obtained, thereby improving cavitation resistance and pressure resistance.

(ii) Since the press-fitted polymeric surfaces of the outer (carbon steel) and inner (stainless) steels are firmly bonded to each other by diffusion, these two tubes are hardly separated during bending and press working. In general, when a gap is formed between the outer tube and the inner tube, the inner tube may be broken in a short time due to the rapid pressure fluctuation of the high pressure fuel. However, according to the present invention, such a gap does not occur.

(iii) In general, in the manufacture of this type of fuel injection pipe, irregular undulations occur on the inner wall surface of the inner pipe due to the processing force, in particular, the processing force applied during the straightening of the pipe in the final process, and thus the cavitation resistance Lowers. However, in the arrangement of the present invention, it is possible to improve the cavitation resistance and the pressure resistance because any irregular undulation of the inner wall surface of the inner tube can be prevented by limiting the thickness of the inner tube.

EXAMPLE

An embodiment of the present invention will now be described. However, the present invention is not limited to these specific examples.

Example 1

As an external appearance, a carbon steel pipe of STS 38 (outer diameter of 10 mm and inner diameter of 5 mm) is used. As the inner tube, a stainless steel tube of SUS 304 (outer diameter 5 mm, inner diameter 0.5 mm) having a Ni plating layer having a thickness of 7 µm on the inner wall surface is used.

After the external appearance and the inner tube are purified, in particular, impurities such as users and carbon scale are removed from the outer circumferential surface of the inner tube and the outer circumferential surface of the outer tube, and then the inner tube is inserted into the outer tube. Then, by drawing on a drawing bench, the outer and inner tubes are mutually fitted to obtain a double metal tube having a diameter of 6.35 mm and an inner diameter of 2.0 mm.

Next, the double metal tube is heat-treated at 1,100 ° C. for 5 minutes in a continuous heat treatment furnace in an oxygen-free atmosphere, and the inner and outer polymerized surfaces are bonded to each other metallurgically integrally, and the Ni-plated layer is formed in the inner tube. It diffuses around the wall surface to form a diffusion layer rich in Ni component, excellent fatigue strength and high warning. The desired continuous process, such as forming the obtained double metal pipe for a connection head part, was performed. As a result, a high-pressure fuel injection pipe for a diesel engine was obtained, and this pipe was superior in pressure resistance as well as cavitation resistance as compared with the conventional pipe. Specifically, in the single-piece injection tube (conventional) made of STS 38 annealed with the outer diameter and thickness described above, the cavitation corrosion test was conducted under injection conditions in which the pressure waveform in the tube generating cavitation corrosion was 0.6 mm or less. All. As a result, cavitation corrosion hardly occurred on the inner wall surface of the single-layer injection pipe. Moreover, the fatigue resistance property was increased by 2.4 times compared with the conventional pipe. In the bending fatigue test, considered the "5.8 bending fatigue test" of the so-called JA SOM 104 "brake tube test method", the seismic resistance increased by 15%.

Example 2

A double metal tube was obtained in the same manner as in Example 1 except that the stainless tube as the inner tube was made of a stainless hoop (strip steel plate). In particular, the inner tube was formed by forming a 1-micron-thick Ni-plated layer and a 6-micron-thick Cr-plated layer on the stainless hoop, followed by shaping the stainless hoop plated on the tube and finally plug-drawing the tube. Further, an attempt was made to obtain an inner tube from a clad strip steel sheet having a Ni layer of the same thickness. The high pressure fuel injection tube was obtained from the obtained double metal tube, and this tube was excellent in cavitation resistance and pressure resistance like the tube of Example 1.

Claims (9)

(a) a carbon steel pipe as an external appearance, and (b) a stainless steel pipe as an inner pipe press-fitted into a carbon steel pipe having a large diameter by a drawing process, wherein the externally pressurized polymerized surface of the inner pipe is metallurgically integrated with each other. And a diffusion layer of at least one metal or alloy thereof selected from the group consisting of at least Ni, Cr, Mo, Co, Al, and Cu on the inner wall surface of the stainless steel pipe of the inner tube. This small, thick walled metal fuel injection tube. The metal fuel injection tube according to claim 1, wherein the metal fuel injection tube has an outer diameter of 30 mm or less. The metal fuel injection tube of claim 1, wherein the metal fuel injection tube has a thickness of 25% to 40% of an outer diameter of the metal fuel injection tube. The metal fuel injection tube according to claim 1, wherein the stainless steel pipe as the inner tube has a thickness of 1.5% to 8.5% of the outer diameter of the metal fuel injection tube. (a) Pressing a stainless steel pipe as an inner pipe having a coating layer of at least one metal or alloy thereof selected from the group consisting of Ni, Cr, Mo, Co, Al, and Cu in the carbon steel pipe as an external appearance by a drawing process. And (b) heat-treating the press-fitted inner tube and the outer tube obtained in an oxidizing atmosphere or in a vacuum furnace to perform diffusion bonding of the polymerized surface of the inner tube and the outer tube, and then at least the metal on the inner wall of the inner tube. Or a small diameter and thick walled metal fuel injection tube comprising forming a diffusion layer of an alloy. The production method according to claim 5, wherein the heat treatment is performed at 700 to 1200 ° C in the non-oxidizing atmosphere or in a vacuum furnace. The manufacturing method according to claim 5, wherein the metal fuel injection pipe has an outer diameter of 30 mm or less. The method of claim 5, wherein the metal fuel injection pipe has a thickness of 25% to 40% of an outer diameter of the metal fuel injection pipe. The method according to claim 5, wherein the stainless steel pipe as the inner pipe has a thickness of 1.5% to 8.5% of the outer diameter of the metal fuel injection pipe.

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