JPS59129777A - Formation of thick metallic pipe having small diameter - Google Patents

Abstract

PURPOSE:To improve the cavitation erosion resistance of the inner wall of a thick metallic pipe having a small diameter without deteriorating the flexibility by forming a carburized hardened surface layer in the inner wall of the pipe. CONSTITUTION:A carburizer is filled into a thick metallic pipe having a small diameter, and the inner wall of the pipe is carburized by heating in a prescribed gaseous atmosphere in a furnace. Quenching and tempering are then carried out to form a carburized hardened surface layer in the inner wall of the pipe. The surface hardness of the inner wall is increased, and the cavitation erosion resistance is improved without deteriorating the flexibility of the pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a method of forming thick-walled, narrow-diameter metal tubes for high-pressure piping.

Because high-speed, high-pressure fuel is pumped through the fuel injection pipe that connects the fuel injection pump and the injection valve of a diesel engine, local boiling occurs on the inner surface of the pipe due to a drop in static pressure. As a result, erosion is induced by the impact pressure generated when the bubbles collapse, causing the inner surface of the pipe to become rough and rough, and sometimes cracks may also occur. This is particularly noticeable when using fuel with a low boiling point such as alcohol fuel. Carbon steel pipes for high pressure piping (STS-38, 42, 49) are generally used as high-pressure piping.
etc.) are often used, and their hardness is from lv180 to
230, which is relatively soft and the cavitation erosion is promoted. Therefore, in order to ensure pressure resistance, it is necessary to increase the wall thickness of the pipe, or to replace it at regular intervals depending on the conditions of use.The former hinders weight reduction, and the latter requires time and effort for maintenance. There are some inconveniences.

The advantage of making a thick-walled, thin-diameter high-pressure pipe is that the inner tube, which is located at the innermost side of a polymerized metal tube made of thick-walled, thin-diameter pipes press-fitted together to form a flow path, has a tensile strength of 48 kg/mm or more, and the pipe material Thick-walled, narrow-diameter metal pipe material made from special steel pipes with a ratio of 1.5% to 8.5% of the product outer diameter (Japanese Patent Laid-Open No. 56
-62614) has been proposed. However, such thick-walled, small-diameter metal tubes require large equipment for pressure-fitting and polymerization, and are expensive.

The present invention has been made in view of the above-mentioned problem, and it forms a carburized hardened layer on the inner wall surface of a thick-walled, small-diameter metal tube for pumping high-speed, high-pressure liquid, thereby increasing the hardness of the inner wall surface of the tube and improving cavitation resistance. The present invention provides a method for forming a thick-walled, narrow-diameter metal tube.

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As mentioned above, FIG. 1 shows a cross section of a carbon steel pipe for high pressure piping that connects an injection pump and an injection valve of a diesel engine, and this steel pipe 1 has, for example, a length of about 400+nn+, an outer diameter of about 6mm, It is a thick-walled, narrow-diameter metal tube with an inner diameter d of about 1 mm, and a hole la of the tube 1 is filled with two predetermined amounts of powdered carburizing agent. At this time, the carburizing agent 2 is filled in a loose manner, that is, in a loose manner, without being compressed, so that scum can penetrate into the holes 1a, as will be described later. Carburizing agent 2
is composed of, for example, carbon mixed with 10 to 20% carburizing accelerator. Alternatively, apply this carburizing agent 2 to the inner diameter d of the pipe 1.
It may also be formed into a wire shape with a smaller diameter and inserted into the hole 1a by loosely fitting it. The outer surface of the tube 1 is coated with copper plating or the like to prevent a carburized layer from forming on the outer surface of the tube 1.

Next, the tube 1 is placed in a furnace 4 in a scum atmosphere 3 made by mixing a predetermined gas that does not decarburize or oxidize, such as phthane, and air, and is heated and carburized, followed by quenching and tempering. An example of each of these conditions is shown in Table 1. For example, carburizing is performed by leaving it for about 1.5 hours at a temperature of 870 degrees C (7), followed by quenching at a temperature of 800 to 850 degrees C for about 30 minutes, and then carburizing at a temperature of 400 to 430 degrees C. Tempering is carried out for about 40 minutes under these conditions. As a result, carburized hardened Ji41b of about 0.1 to 0.4 mm was formed on the inner wall surface of the tube 1. Then, the inner wall surface 1b of the tube 1 remains quenched.
The hardness of the inner wall surface 1b of the tube 1 after tempering is about 380 to 490 IIv.

That is, since it becomes too hard if it is quenched, it is tempered to form an appropriate carburized layer. Further, since the outer surface of the tube 1 is copper plated as described above, it is not carburized, and the flexibility of the tube 1 is increased.

FIG. 2 shows another embodiment of the present invention, in which a gas mixture 6 of carburizing RX gas and ammonia is formed by a gas adjustment device 5, and this mixed gas 6 is connected to a pipe 7.9 and a connection (not shown). A thick-walled, thin-diameter metal tube 8 is placed inside the heating furnace 4 via a metal fitting, with both ends thereof slightly protruding outside the furnace 4.
The tube 8 is connected in communication with both ends of the pore 8a to be supplied into the hole 8a, and the tube 8 is heated to carburize its inner wall surface 8a, followed by quenching and tempering as described above. Table 2 shows these conditions. That is, carbonitriding was performed by leaving it for about 2.5 hours at a temperature of 800 degrees Celsius.
Hardening is performed for about 30 minutes at a temperature of 0 to 830 degrees Celsius, and tempering is performed for about 40 minutes at a temperature of 400 to 430 degrees Celsius.

As a result, approximately 0.1 to 0.4
A carburized hardened layer 8b of about mm was formed on the inner wall surface of the tube 8. Then, the inner wall surface 8 of the tube 8 remains quenched in the same manner as described above.
The hardness of a was about 6601+ν or more, and the hardness after tempering was about 380 to 490 Hν.

Since the mixed waste 6 is passed through the surface and the tube 8, the furnace 4
The atmosphere inside the pipe 8 may be similar to that of
The outer surface is not carburized and its flexibility is increased.

The carburized hardened layer formed on the inner wall surface of the thick-walled, thin-diameter metal tube 1.8 has a certain effect even if it is about 0.1 mm thick, but if it is 0.2-0. It is best to form the carburized layer to a thickness of about 4 mm, and in view of the flexibility of the metal tube, the hardness of the carburized layer is optimally about It v 380 to 490.

As a result, a carburized layer of a desired thickness can be formed on the inner wall surface of a thin tube having an inner diameter of about 1 to 2 mm, and its hardness can be increased, so that cavitation resistance can be improved.

In the embodiment shown in FIG. 2, the case has been described in which both ends of the tube 8 are projected outside the heating furnace 4 so that the tube 8 and each pipe 7.9 can be easily connected, but this is not limited to this. Of course, the entire tube 8 may be housed in the heating furnace 4 as long as the mixed gas is allowed to pass through the pores 8a of the tube 8 instead of through the pores 8a.

As explained above, according to the present invention, a carburizing agent is filled or inserted into a thick-walled, thin-diameter metal tube through which high-speed, high-pressure liquid is pumped, and the carburizing agent is heated and carburized in a furnace with a predetermined gas atmosphere, or A diameter metal tube is heated, and ammonia scum is added to a carburizing atmosphere in the metal tube to aerate the scum, which carburizes the inner surface of the tube. After that, quenching and tempering are performed to carburize and harden the inner wall surface of the tube. It becomes possible to form a layer and harden the surface of the inner wall surface of a small diameter tube with an inner diameter of about 1 mm or more without losing the flexibility of the metal tube, improving the resistance to cavitation erosion. The lifespan and reliability of high-pressure piping can be extended and the reliability can be improved, and it can be applied regardless of the metal material.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the method for forming a carburized layer on the inner surface of a thick-walled, narrow-diameter metal tube according to the present invention, and FIG. 2 is a diagram showing another embodiment of the present invention. ■, 8...Thick-walled thin metal tube, 2...Carburizing agent, 4...
・Heating furnace, 5... gas adjustment device, 6... mixed gas,
7.9... Connection pipe. Applicant: Diesel Kiki Co., Ltd. Agent Patent Attorney: Toshihiko Watanabe Procedural Amendment (Spontaneous) March 1, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi 1. Indication of Case: 1988 Patent Application No. 003740 2. Name of 95 Akira Method of Forming Thick-Walled and Small-diameter Metal Tubes 3, Relationship with the Amendment Case Patent Applicant Address 3-6-7 Shibuya, Shibuya-ku, Tokyo Name (33
3) Diesel Kiki Co., Ltd. Representative: Mochizuki-4, Agent address: 301 Sunshine Koken Plaza, 3-2-4 Higashiikebukuro, Toshima-ku, Tokyo Address: 170 Telephone: 03 (983) 0926 Name: Patent attorney (8188) Toshihiko Watanabe 5, Subject of amendment 6, Contents of amendment (2) Page 5, line 2, r660Hv and rH
Corrected to v660J. (3) Line 4 of the same page r380-490 [-(vJ is corrected to II-(v 380-490J). (4) Line 10 of the same page [Adjustment device Correct to J. (5) ``660Hv'' on page 6, line 5 of the same page is rl
-1v Corrected to 660J. (6) Page 6, line 6 “380-490) (v
Correct J to rl-(v380-490j. (7) On page 6, line 8, correct the phrase ``whatever it is'' to ``whatever''.

Claims (1)

[Claims] 1. A carburized hardened layer is formed on the inner wall surface of a thick-walled, small-diameter metal tube for pumping high-speed, high-pressure liquid to increase the hardness of the inner wall surface and improve cavitation resistance. Method for forming thick-walled, small-diameter metal tubes. 2. The carburized hardened layer is formed by filling or inserting a carburizing agent into the thick-walled, small-diameter metal tube, heating and carburizing it in a furnace with a predetermined gas atmosphere, and then quenching and tempering. A method for forming a thick-walled, narrow-diameter metal tube according to claim 1. 3. The carburized layer is formed by heating the thick-walled, small-diameter metal tube and passing a gas prepared by adding ammonia gas into a carburizing atmosphere through the metal tube to carburize the inner surface of the tube, followed by quenching and quenching. A method for forming a thick-walled, narrow-diameter metal tube according to claim 1, characterized in that the metal tube is formed by performing a return process.