CA1059738A

CA1059738A - Method of producing a high pressure fuel injection pipe

Info

Publication number: CA1059738A
Application number: CA266,215A
Authority: CA
Inventors: Masayoshi Usui
Original assignee: Usui Kokusai Sangyo Kaisha Ltd
Current assignee: Usui Kokusai Sangyo Kaisha Ltd
Priority date: 1976-11-22
Filing date: 1976-11-22
Publication date: 1979-08-07

Abstract

ABSTRACT OF THE DISCLOSURE:

A steel blank pipe is first subjected to the step of cutting off the hair crack layer portion including the black skin layer of the inner peripheral wall surface of the blank pipe. Thereafter, the steel blank pipe is repetitively subjected to the process of pipe drawing and the process of annealing within a non-oxidizing-hearth.

Description

~59'73~

This invention relates to a method of producing a high pressure fuel injection pipe often used as a fuel supply line for a Diesel internal combustion engine~
In the prîor art method of producing such a type of injection pipe, a steel blank pipe whose inner peripheral wall surface has a black skin layer and hair crack layer portion of the order of 0.1 to 0.15 mm in thickness has immediately been repe~

titively subjected to the process of dil~tion of thepipe length or drawing and theprocess of annealing within anon-oxidizing environmen~.
According to this method, however, numberless crack layers which have grown into a black skin layer have remained in the finished pipe of desired final diameter, so ~at the roughness of the inner peripheral wall surface of the finished pipe has been 8S or higher (see the photograh of Figure 2B of the accom-panying drawings) and the black skin layer has been peeled off by the internal fluid pressure and :in addition, the numberless crack layers so grown have further been grown with the use of the pipe, thus resulting in deteriorated resistance to pressure of the pipe which have often led to fractures or breakage of the pipe during the use thereof.
It is an object of the present invention to prevent the hair crack layer including the black skin layer from remaining in the inner peripheral wall surface of a finished injection pipe of desired final diameter and thereby provide a smooth inner peripheral wall surface of such pipe.
It is another object of the present invention to prevent fractures or breakage which would otherwise result from the growth of the hair crack caused by the process of pipe drawing being repetitively effected, to thereby prevent the deterioration of the resistance to pressure of the pipe, thus providing a strong fuel injection pipe which has a high anti-pressure strength.

l~S973t3 According to the present invention, there is provided a method of producing a high pressure fuel injection pipe comprising the steps of cutting off the hair crack layer portion including the black skin layer of the inner peripheral wall surface of a steel blank pipe, and thereafter repetitively subjecting the steel blank pipe to the process of pipe drawing the process of annealing within a non-oxidizing hearth, thereby forming a finished pipe.
The invention will become more fully apparent from the following detailed description of an embodiment thereof taken in conjunction with the accompanying drawings.
Figure 1 is a prespective view of an injection pipe produced by the method according to the prior art.
Figure 2A is an enlarged cross-sectional view taken along line I-I of Figure 1.
Figure 2B is a photograph (X-200) taken of the cross-section of the injection pipe shown in Figure 2A.
Figure 3 is a perspective view of an injection pipe produced by the method of the present invention.
Figure 4A is a cross-sectional view taken along line II-II of Figure 3.
Figure 4B is a photograph (X-200) taken of the cross-section of the injection pipe shown in Figure 4A.
To achieve the above objects, according to the present invention, a steel blank pipe _ is first subjected to the step of cutting off a hair crack layer portion 1 including the black skin layer of the inner peripheral wall surface of the blank pipe, and thereafter the steel blank pipe is repetitively subjected to the process of pipe drawing and the process of annealiny within a non-oxidizing hearth, thereby forming a finished pipe. By doing so, it is possible to eliminate the above-noted disadvantages peculiar to the prior art method and provide a strong fuel injec-tion pipe which is free of fracture and has a high anti-pressure strength, as shown in the photograph of Figure 4B.

- 2 -5~3!3 An example of the method according to the present invention will be shown belowO
Blank pipe .~O material: STS 35; outer diameter: 34 . Omm;
inner diameter- 24.4m; length: 2750mm;
wall thickne~s: 4.8mm Cutting tool ... Beisner type deep hole drilling machine Model ~MF2-3000 (made by Fuji Works, ~td.~
Cutting conditions ... number of revolutions: 1000 r.~.m.; feed speed: 600 mm/min.;
cutting allowance: 0.3mm Blank pipe before drawing... outer inner wall diameter diameter thickne~s 34.Omm 25.Omm 4.5mm 1st dilation ... 27.0mm19.4mm ~.8mm 2nd dilation ... 21~0mm14.0mm 3~5mm 3rd dilation ... 16.Omm9.6mm 3.2mm 4th dilation ... 12.0mm6.2mm 2.9mm 5th dilation .. , 9.0mm 4.0mm 2.5mm 6th dilation ... 6.0mm2.0mm 2.0mm Annealing wa~ effected before each step of pipe drawing and within a non-oxidiæing hearth of nitron gas at a temperature of 900C for 15 (fifteen) minutes. ~he ~tate of the i~ner periph-eral wall surface wa~ such that the surface roughness wa~ 3S or less and hair crack was eub~tantially inappreoiable (see the photograph of ~igure 3).
Throughout the drawingæ, xeference ¢haracter a deæign-ates the steel blank pipe and numeral 1 denotes the hair crack layer portion including the black skin layer.
B

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of producing a high pressure fuel injection pipe comprising the steps of cutting off the hair crack layer portion including the black skin layer of the inner peripheral wall surface of a steel blank pipe, and thereafter repetitively subjecting said steel blank pipe to the process of pipe drawing and the process of annealing within a non-oxidizing hearth, thereby forming a finished pipe.

2. A method of producing a high pressure fuel injection pipe, comprising:
a) providing a steel pipe having an inner diameter, an outer diameter and a wall thickness each dimensioned greater than desired in a finished pipe;
b) removing the hair crack layer portion including the black skin layer of the radially inner wall of the pipe;
c) drawing the pipe to effect a reduction in the inner diameter, outer diameter and wall thickness;
d) annealing the pipe in a non-oxidizing environment; and e) repeating steps (c) and (d) above until the desired dimensions of the finished pipe are obtained.

3. A method of claim 2 wherein said dimensional reduction is accomplished in not less than four steps.

4. A method of claim 3 wherein said annealing is accomplished in a non-oxidizing hearth of nitrogen gas.

5. A method of claim 2 wherein said annealing is accomplished in a non-oxidizing hearth of nitrogen gas.