METHOD OF PRODUCING A HIGH PRESSURE FUEL INJECTION PIPE

METHODE POUR FABRIQUER DES TUYAUX D'INJECTION DE COMBUSTIBLE A HAUTE PRESSION

English 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.

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.

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.
- 1 -
13

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