U.S. patent application number 10/593360 was filed with the patent office on 2007-08-02 for cooling method and manufacturing method of metal part and cooling apparatus for metal part.
This patent application is currently assigned to ORIENTAL ENGINEERING CO., LTD.. Invention is credited to Hiroyuki Hoshino, Hiromitsu Murakami, Satoshi Suda, Koichi Terasaka, Hideki Tsuge, Saburou Yamagata, Hideo Yokota.
Application Number | 20070175549 10/593360 |
Document ID | / |
Family ID | 35125091 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070175549 |
Kind Code |
A1 |
Yamagata; Saburou ; et
al. |
August 2, 2007 |
Cooling method and manufacturing method of metal part and cooling
apparatus for metal part
Abstract
A metal part is uniformly cooled by uniformly breaking a vapor
film formed when a cooling liquid vaporizes on a surface of the
metal part. Oscillations are applied to the vapor film formed on
the surface of the metal part, whereby the vapor film is broken
without the stirring of a cooling liquid 1. The cooling liquid 1 is
stirred after the vapor film begins to be broken, whereby bubbles
formed by the breakage of the vapor film are caused to diffuse in
the cooling liquid 1.
Inventors: |
Yamagata; Saburou; (Saitama,
JP) ; Murakami; Hiromitsu; (Saitama, JP) ;
Yokota; Hideo; (Kanagawa, JP) ; Suda; Satoshi;
(Kanagawa, JP) ; Hoshino; Hiroyuki; (Niigata,
JP) ; Tsuge; Hideki; (Tokyo, JP) ; Terasaka;
Koichi; (Kanagawa, JP) |
Correspondence
Address: |
Andrew R Basile;Young & Basile
3001 W Big Beaver Road
Suite 624
Troy
MI
48084
US
|
Assignee: |
ORIENTAL ENGINEERING CO.,
LTD.
TOKYO
JP
NIPPON OIL CORPORATION
TOKYO
JP
|
Family ID: |
35125091 |
Appl. No.: |
10/593360 |
Filed: |
April 7, 2005 |
PCT Filed: |
April 7, 2005 |
PCT NO: |
PCT/JP05/06872 |
371 Date: |
September 19, 2006 |
Current U.S.
Class: |
148/558 ;
148/712 |
Current CPC
Class: |
C21D 1/18 20130101 |
Class at
Publication: |
148/558 ;
148/712 |
International
Class: |
C21D 10/00 20060101
C21D010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2004 |
JP |
2004-113326 |
Claims
1. A cooling method of a metal part by immersing the heated metal
part in a cooling liquid, comprising the step of: appllying a
repeatedly varying pressure to a vapor film formed when the cooling
liquid vaporizes on a surface of the metal part, wherein the vapor
film is broken without the stirring of the cooling liquid.
2. The cooling method of a metal part according to claim 1, wherein
the step of repeatedly varying pressure to the vapor film includes
the step of applying oscillations to the cooling liquid.
3. The cooling method of a metal part according to claim 1, wherein
the step of repeatedly varying pressure to the vapor film includes
the step of changing a liquid-level pressure of the cooling
liquid.
4. The cooling method of a metal part according to claim 1, wherein
the step of repeatedly varying pressure to the vapor film includes
the steps of combining applying oscillations to the cooling liquid
and changing the liquid-level pressure of the cooling liquid.
5. The cooling method of a metal part according to claim 2, wherein
the step of applying oscillations to the cooling liquid includes
the step of using multiple oscillators.
6. The cooling method of a metal part according to claim 2, further
includes the step of adjusting at least either of the amplitude and
frequency of the oscillations according to the thickness of the
vapor film.
7. The cooling method of a metal part according to claim 2, further
including the step of adjusting at least either of the amplitude
and frequency of the oscillations according to the condition of the
cooling liquid.
8. A cooling method of a metal part according to claim 1, further
comprising the step of stirring the cooling liquid after the vapor
film begins to be broken and wherein bubbles formed by the breakage
of the vapor film are caused to diffuse in the cooling liquid.
9. The cooling method of a metal part according to claim 8, further
comprising the step of adjusting at least either of the intensity
of the stirring and the direction of a flow generated by the
stirring according to the condition of the cooling liquid and the
condition of the metal part in the cooling liquid.
10. A method of manufacturing a metal part, characterized in that
the manufacturing method comprises a step of heating a metal part
and a step of cooling the metal part after the heating thereof by
immersing the metal part in a cooling liquid, and in that in the
cooling step, by applying a repeatedly varying pressure to a vapor
film which is formed when the cooling liquid vaporizes on a surface
of the metal part, the vapor film is broken without the stirring of
the cooling liquid.
11. A cooling apparatus for a metal part, characterized in that the
cooling apparatus comprises means for cooling a metal part after
the heating thereof by immersing the metal part in a cooling
liquid, and in that the cooling apparatus applies a repeatedly
varying pressure to a vapor film which is formed when the cooling
liquid vaporizes on a surface of the metal part, and breaks the
vapor film without the stirring of the cooling liquid.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of cooling a metal
part by immersing the metal part in a cooling liquid, a
manufacturing method of a metal part by using this cooling method,
and a cooling apparatus for a metal part.
BACKGROUND ART
[0002] Quenching treatment and solid solution treatment are heat
treatments which involve immersing a metal part heated to a high
temperature into cooling liquids consisting of a mineral oil (a
quenching oil), water or an aqueous solution of water-soluble
coolant and the like, to rapidly cool the metal part. Although
these cooling liquids are excellent in the stability of cooling and
cost efficiency, the following point can be mentioned as a problem.
That is, the instant a metal part heated to a high temperature is
immersed in these cooling liquids, these cooling liquids vaporize
at an interface with the metal part, generating a film of vapor
(hereinafter called a "vapor film") on the surface of the metal
part. Because this vapor film retards the cooling of the metal
part, in particular, when the vapor film becomes partially stable
due to the shape of the metal part, the arrangement of the metal
part in a cooling tank, and the like, the metal part is not
uniformly cooled and deformation and soft spots (hardness
difference) occur in the metal part.
[0003] To solve this problem, a conventional practice has been to
stir a cooling liquid with a metal part immersed by means of
convection as strongly as possible, so that positive heat exchange
occurs at the interface between the vapor film and the cooling
liquid and the temperature of the surface of the metal part is
lowered, thereby rapidly breaking a vapor film.
[0004] In JP2003-286517A (hereinafter referred to as Patent
Document 1), there is proposed a method by which a cooling liquid
in which a metal part is immersed is stirred by oscillations and
jet flows, and horizontal and vertical flows are generated in the
cooling liquid, whereby a vapor film is broken and bubbles
generated from the broken vapor film are caused to diffuse in the
cooling liquid and disappear.
[0005] However, in the method described in Patent Document 1 above,
the cooling liquid is stirred when the vapor film is broken and,
therefore, strong flows are generated in the cooling liquid and
uniform breakage of the vapor film is apt to be hindered.
Therefore, this method described in Patent Document 1 has room for
further improvement in that a metal part is uniformly cooled.
[0006] Hence, the present invention has been made in view of the
above circumstances and has as its object the provision of a method
of uniformly cooling a metal part by uniformly breaking a vapor
film which is generated by the vaporization of a cooling liquid on
a surface of the metal part.
DISCLOSURE OF THE INVENTION
[0007] To solve this problem, the present inventors earnestly
devoted themselves to investigations and as a result they found out
that a vapor film formed by the vaporization of a cooling liquid on
the surface of a metal part is kept in a stable manner by the
pressure in the interior of the film, and that the vapor film can
be effectively broken by shattering the stability of this vapor
film.
[0008] That is, the present invention provides a cooling method of
cooling a metal part by immersing the heated metal part in a
cooling liquid, which is characterized in that by applying a
repeatedly varying pressure to a vapor film which is formed when
the cooling liquid vaporizes on a surface of the metal part, the
vapor film is broken without stirring the cooling liquid.
[0009] According to this cooling method, when a repeatedly varying
pressure is applied to a vapor film, the vapor film repeats
expansion and contraction and fluctuates, and the vapor film is
broken, with a portion where the film thickness has decreased due
to this fluctuation serving as an initiation point. At this time,
by applying a repeatedly varying pressure to the vapor film without
stirring the cooling liquid, weak flows like natural convection are
generated in the cooling liquid, but strong flows are not generated
as would be the case when the cooling liquid is stirred. For this
reason, the vapor film can be uniformly broken.
[0010] In the cooling method of the present invention, examples of
a method of applying a repeatedly varying pressure to the vapor
film include a method of applying oscillations to the cooling
method, a method of changing the liquid-level pressure of the
cooling liquid, and a method of performing the application of a
repeatedly varying pressure by combining these two methods. As a
method of applying a repeatedly varying pressure to the vapor film,
it is possible to mention also a method by which the metal part is
caused to swing. Furthermore, the pressure applied to the vapor
film may be continuously varied or it may be intermittently varied
like pulse oscillation.
[0011] In the cooling method of the present invention, a method of
applying oscillations to the cooling liquid is not especially
limited so long as it does not generate strong flows in the cooling
liquid, and examples of methods of applying oscillations to the
cooling liquid include, for example, a method which involves
providing an oscillator, such as an oscillating plate and a
rotating body, in a cooling tank, and causing the oscillating plate
to perform reciprocating motions or causing the rotating body to
perform rotational motions. Examples of a method of applying
oscillations to the cooling liquid also include a method which
involves providing multiple oscillators in the cooling tank and
causing these oscillators to oscillate. According to this method,
it is possible to apply oscillations due to the resonance by the
multiple oscillators to the cooling liquid and to apply
oscillations which are partially different within the cooling
tank.
[0012] Also in the cooling method of the present invention, when
the method which involves applying oscillations to the cooling
liquid is adopted as a method of applying a repeatedly varying
pressure to the vapor film, at least either of the amplitude and
frequency of the vibrations may be adjusted according to the
thickness of the vapor film.
[0013] The thickness of the vapor film changes depending on the
size, temperature and shape of the metal part, the kind and
temperature of the cooling liquid, the pressure applied to the
liquid and the like. For example, when the vapor film is thick, it
is preferred to make the amplitude larger, and when the vapor film
is thin, it is preferred to make the frequency higher.
[0014] Furthermore, in the cooling method of the present invention,
when the method which involves applying oscillations to the cooling
liquid is adopted as a method of applying a repeatedly varying
pressure to the vapor film, at least either of the amplitude and
frequency of the oscillations may be adjusted according to the
condition of the cooling liquid.
[0015] The condition of the cooling liquid changes in the order:
(1) a vapor film stage at which a vapor film is present on the
surface of a metal part, (2) a boiling stage at which this vapor
film is broken and removed from the surface of the metal part, with
the result that the metal part is exposed and the cooling liquid
which comes into contact with this exposed surface boils, and (3) a
convection stage at which boiling comes to an end and convection
starts. For example, it is preferred to make the amplitude larger
in the former period of the vapor film stage at which a vapor film
exists in a stable manner and to make the frequency higher from the
latter period of the vapor film stage at which the vapor film
begins to be broken to before the transition to the boiling
stage.
[0016] In the cooling method of the present invention, the breakage
effect of the vapor film cannot be expected if the amplitude of
oscillations applied to the cooling liquid is too small; on the
other hand, if the amplitude is too large, the liquid surface of
the cooling liquid becomes wavy and in some cases strong flows are
generated. From this point of view, it is preferred that when
oscillations are applied by use of an oscillating plate, the
amplitude expressed by the swing width of the oscillating plate be
not less than 2 mm. When oscillations are applied by a pressure, it
is preferred that the amplitude expressed by an amount of change in
the pressure be not less than 1% (for example, not less than 100
Pa) of the pressure which is applied to the cooling liquid in the
state that the oscillations are not being applied.
[0017] If the frequency applied to the cooling liquid is too low, a
change in the pressure is gentle and the vapor film does not
fluctuate, with the result that the breakage effect of the vapor
film cannot be expected. On the other hand, if the frequency
applied to the cooling liquid is too high, the fluctuation of the
vapor film becomes too fine, with the result that the breakage
effect of the vapor film cannot be expected. From this point of
view, when an oscillating apparatus provided with a vibration motor
made by URAS TECHNO (trade name: URAS TECHNO VIBRATOR) is used, the
frequency of oscillations applied to the cooling liquid is
preferably 5 to 80 Hz, more preferably 20 to 30 Hz.
[0018] Furthermore, when oscillations applied to the cooling liquid
have a low frequency and a large amplitude, it is necessary to
prevent the liquid surface of the cooling liquid from becoming wavy
and, therefore, the construction of the cooling tank becomes
complex. When oscillations having a small amplitude and a high
frequency as ultrasonic waves are applied to the cooling liquid,
the fluctuation of the vapor film becomes too fine and, therefore,
the breakage effect of the vapor film cannot be expected.
[0019] In the cooling method of the present invention, it is
preferred that the cooling liquid be stirred after the vapor film
begins to be broken so that bubbles formed by the breakage of the
vapor film is caused to diffuse in the cooling liquid.
[0020] As a result of this, it is possible to cause the bubbles
formed from the broken vapor film to diffuse uniformly and rapidly
in the cooling liquid and disappear, with the result that the
cooling for a metal part may be performed uniformly and rapidly.
This stirring of the cooling liquid is effective particularly when
the rapid diffusion of bubbles is required, for example, in a case
where metal parts are cooled in a massive amount at a time, in a
case where metal parts having a large volume are cooled, and the
like.
[0021] Examples of a method of stirring the cooling liquid include
jet stirring and it is preferable to adopt a method by which a
uniform flow is formed in the cooling liquid from below upward. It
is preferred that the timing for starting the stirring of the
cooling liquid is synchronized with the point of time at which the
vapor film begins to be broken.
[0022] The stirring may be performed either after stopping the
application of a varying pressure to the vapor film or while
continuously applying a varying pressure. As for which method is
adopted, any one of the methods is selected according to the size,
kind, or quantity of a metal part to be cooled.
[0023] For example, when a metal part which is apt to be deformed
is cooled, in order to make gentle the cooling at the convection
stage of the cooling liquid, it is preferable to perform the
stirring after the application of a varying pressure to the vapor
film is stopped. That is, it is preferable not to apply
oscillations during the stirring of the cooling liquid. On the
other hand, in a case where metal parts are cooled in a massive
amount at a time and in a case where metal parts having a large
volume are cooled, in order to perform strong cooling even at the
convection stage of the cooling liquid, it is preferable to perform
the stirring, with a varying pressure applied to the vapor film.
That is, it is preferable to apply oscillations simultaneously with
the stirring of the cooling liquid.
[0024] Furthermore, in the cooling method of the present invention,
it is preferable to adjust at least either of the intensity of the
stirring and the direction of a flow generated by the stirring
according to the condition of the cooling liquid and the condition
of the metal part in the cooling liquid.
[0025] At the boiling stage of the cooling liquid, it is preferable
to cause the bubbles formed from the broken vapor film to diffuse
uniformly and rapidly in the cooling liquid and disappear. For this
reason, it is preferable to perform strong stirring from the later
period of the vapor film stage at which the vapor film begins to be
broken to before the transition to the convection stage. Also, in a
case where the longitudinal direction of a metal part is arranged
toward a vertical direction in the cooling liquid, it is preferable
to ensure that the direction of flows generated by stirring is a
vertical direction and in a case where the longitudinal direction
of a metal part is arranged toward a horizontal direction in the
cooling liquid, it is preferable to ensure that the direction of
flows generated by stirring is a horizontal direction.
[0026] Incidentally, the cooling method of the present invention
can be favorably used in the quenching treatment and solid solution
treatment of metal parts.
[0027] The present invention also provides a method of
manufacturing a metal part, which is characterized in that the
manufacturing method comprises a step of heating a metal part and a
step of cooing the metal part after the heating thereof by
immersing the metal part in a cooling liquid, and in that in the
cooling step, by applying a repeatedly varying pressure to a vapor
film which is formed when the cooling liquid vaporizes on a surface
of the metal part, the vapor film is broken without stirring the
cooling liquid.
[0028] According to this manufacturing method, the uniformity of
the cooling of a metal part is improved and the deformation or the
soft spots thereof become less apt to occur. Therefore, it is
possible to obtain a high-accuracy and high-quality metal part.
[0029] Incidentally, in the manufacturing method of the present
invention, in the same way as with the above-described cooling
method, examples of a method of applying a repeatedly varying
pressure to the vapor film includes a method of applying
oscillations to the cooling method, a method of changing the
liquid-level pressure of the cooling liquid, a method of performing
the application of a repeatedly varying pressure by combining these
two methods, and a method of fluctuating a metal part.
[0030] Also, as a method of applying oscillations to the cooling
liquid, in the same way as with the above-described cooling method,
it is possible to mention a method by which one or multiple
oscillators are caused to oscillate.
[0031] Furthermore, in the manufacturing method of the present
invention, when the method of applying oscillations to the cooling
liquid is adopted as a method of applying a repeatedly varying
pressure to the vapor film, in the same way as with the
above-described cooling method, at least either of the amplitude
and frequency of the oscillations may be adjusted according to the
thickness of the vapor film and the condition of the cooling
liquid.
[0032] Moreover, in the manufacturing method of the present
invention, it is preferred that the cooling method includes
stirring the cooling liquid after the vapor film begins to be
broken so that bubbles formed by the breakage of the vapor film is
caused to diffuse in the cooling liquid. At this time, in the same
way as with the above-described cooling method, it is preferable to
adjust at least either of the intensity of the stirring and the
direction of a flow generated by the stirring according to the
condition of the cooling liquid and the condition of the metal part
in the cooling liquid.
[0033] Furthermore, the present invention provides a cooling
apparatus for a metal part, which is characterized in that the
cooling apparatus comprises means for cooling a metal part after
the heating thereof by immersing the metal part in a cooling
liquid, and in that the cooling means applies a repeatedly varying
pressure to a vapor film which is formed when the cooling liquid
vaporizes on a surface of the metal part, and breaks the vapor film
without stirring the cooling liquid.
[0034] According to this cooling apparatus, the uniformity of the
cooling of a metal part is improved and the deformation or the soft
spots thereof become less apt to occur. Therefore, it is possible
to obtain a high-accuracy and high-quality metal part.
[0035] Incidentally, in the cooling apparatus of the present
invention, in the same way as with the above-described cooling
method, examples of a method of applying a repeatedly varying
pressure to the vapor film includes a method of applying
oscillations to the cooling method, a method of changing the
liquid-level pressure of the cooling liquid, a method of performing
the application of a repeatedly varying pressure by combining these
two methods, and a method of fluctuating a metal part. Furthermore,
the pressure applied to the vapor film may be continuously varied
or it may be intermittently varied like pulse oscillation.
[0036] Also, in the cooling apparatus of the present invention, as
a method of applying oscillations to the cooling liquid, in the
same way as described above, it is possible to mention a method by
which one or multiple oscillators are caused to oscillate.
[0037] Furthermore, in the cooling apparatus of the present
invention, when the method of applying oscillations to the cooling
liquid is adopted as a method of applying a repeatedly varying
pressure to the vapor film, in the same way as described above, at
least either of the amplitude and frequency of the oscillations may
be adjusted according to the thickness of the vapor film and the
condition of the cooling liquid.
[0038] Furthermore, in the cooling apparatus of the present
invention, it is preferred that the above-described cooling means
stir the cooling liquid after the vapor film begins to be broken so
that the bubbles formed by the breakage of the vapor film are
caused to diffuse in the cooling liquid. At this time, it is
preferable to adjust at least either of the intensity of the
stirring and the direction of a flow generated by the stirring
according to the condition of the cooling liquid and the condition
of the metal part in the cooling liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a schematic configuration diagram showing an
example of a cooling apparatus used in a cooling method of a metal
part related to the present invention;
[0040] FIG. 2 is a diagram showing pressure changes occurring in
the cooling liquid when an oscillation device is actuated in the
cooling apparatus of this embodiment;
[0041] FIG. 3 is a diagram showing pressure changes occurring in
the cooling liquid when a stirrer is actuated in the cooling
apparatus of this embodiment;
[0042] FIG. 4 is a schematic configuration diagram showing another
example of a cooling apparatus used in a cooling method of a metal
part related to the present invention;
[0043] FIG. 5 is a diagram showing cooling curves on the side
surfaces of round bar test pieces made of stainless steel subjected
to cooling treatments No. 1 to No. 4; and
[0044] FIG. 6 is a diagram showing cooling curves on the side
surfaces of round bar test pieces made of stainless steel subjected
to cooling treatments No. 5 and No. 6.
BEST MODE FOR CARRYING OUT THE INVENTION
[0045] An embodiment of the present invention will be described
below with reference to the drawings.
[0046] In this embodiment, a description will be given of a case
where metal parts are manufactured by using a cooling apparatus for
a metal part related to the present invention.
[0047] FIG. 1 is a schematic configuration diagram showing an
example of a cooling apparatus used in a cooling method of a metal
part related to the present invention.
[0048] As shown in FIG. 1, this cooling apparatus is equipped with
a cooling tank 2 which contains a cooling liquid 1, a container 3
which houses metal parts, two oscillation devices 10, a stirrer 20,
and a controller 30. In the upper part of this cooling apparatus,
there is arranged a heating device 40 which heats the metal parts.
And the container 3 which houses metal parts heated by this heating
device 40 is immersed in the middle part of the cooling tank 2 by
use of an elevator apparatus not shown in the figure.
[0049] The oscillation device 10 is equipped with one oscillating
plate 11 and a drive unit 12 which oscillates this oscillating
plate 11 with a prescribed amplitude and a prescribed frequency.
This oscillating plate 11 is disposed near the side surface of the
container 3 in the cooling tank 2 perpendicularly, with the plate
surface thereof facing the container 3. When this oscillation
device 10 is actuated, the oscillating plate 11 performs horizontal
reciprocal motions and oscillations 4 are generated. The
oscillations 4 are applied to the cooling liquid 1. By adjusting
each of the frequencies and amplitudes of the two oscillation
devices 10, it is possible to apply oscillations generated by the
resonance of the two oscillating plates 11 or oscillations which
differ on both sides of the container 3.
[0050] The stirrer 20 is equipped with a propeller 21 which is
disposed, with a shaft thereof facing a vertical direction,
multiple flow regulating plates 22, and a drive unit 23 which
controls the rotational motions of the propeller 21, all these
three members being present sideways from the oscillating plate 11
in the cooling tank 2. By actuating this stirrer 20, the propeller
21 performs rotations and the cooling liquid 1 is stirred, with the
result that in the cooling liquid 1, upward flows are generated
which move along the flow regulating plate 22 from below the
container 3 upward.
[0051] The controller 30 is disposed outside the cooling tank 2,
and constructed so as to control the timing for actuating the drive
unit 12 of the oscillation device 10 and the drive unit 23 of the
stirrer 20. Also, the controller 30 is constructed so as to control
the drive unit 12 of the oscillation device 10 according to the
thickness of the vapor film or the condition of the cooling liquid
1 and, at the same time, so as to control the drive unit 23 of the
stirrer 20 according to the condition of the cooling liquid 1 or
the condition of metal parts in the cooling liquid 1.
[0052] A strain-gauge pressure sensor was installed in the cooling
tank 2 of this cooling apparatus and pressure changes occurring in
the cooling liquid 1 within the cooling tank 2 were measured in a
case where the oscillation device 10 and the stirrer 20 are
individually actuated.
[0053] FIG. 2 is a graph showing pressure changes occurring in the
cooling liquid when the oscillating plate of the oscillation device
is actuated under such a condition that the frequency is 40 Hz.
FIG. 3 is a graph showing pressure changes occurring in the cooling
liquid when the stirrer is actuated under such a condition that
upward flows generated in the cooing liquid amount to a flow rate
of 30 m.sup.3/h. In this graph, the fluctuation width of the
electromotive force of the sensor on the ordinate indicates the
magnitude of the amount of change in the pressure (a relative
value) and a numerical value of the electromotive force of the
sensor indicates the intensity of a flow generated in the cooling
liquid (a relative value).
[0054] As shown in FIGS. 2 and 3, when the oscillation device 10
was actuated, such pressure changes that the electromotive force of
the sensor became 0.02 V or so occurred repeatedly in the cooling
liquid, whereas pressure changes scarcely occurred in the cooling
liquid when the stirrer 20 was actuated.
[0055] Flows generated in the cooling liquid 1 the oscillation
device 10 were weak compared to those occurred at the actuation of
the stirrer 20. From this fact it could be ascertained that when
the oscillation device 10 is actuated, a repeatedly varying
pressure is applied to the cooling liquid 1 without the generation
of strong flows, whereas by the actuation of the stirrer 20, a
varying pressure is not applied although strong flows are formed in
the cooling liquid 1.
[0056] FIG. 4 is a schematic configuration diagram showing another
example of a cooling apparatus used in a cooling method of a metal
part related to the present invention.
[0057] As shown in FIG. 4, this cooling apparatus is equipped with
a cooling tank 2 containing a cooling liquid 1, a container 3 which
houses metal parts to be subjected to cooling treatment, a gas
introduction pipe 5 which introduces a gas into the cooling tank 2,
a gas exhaust pipe 6 which exhausts the gas from the cooling tank
2, a stirrer 20 in which a propeller 21 is disposed sideways in the
cooling tank 2, with a shaft thereof facing a vertical direction,
and a controller 50 disposed outside the cooling tank 2. And in the
same way as with the cooling apparatus shown in FIG. 1 described
above, the container 3 which houses metal parts heated by a heating
device 40 is immersed in the middle part of the cooling tank 2.
Incidentally, the same numerals refer to the same parts as those of
the cooling apparatus shown in FIG. 1 described above, and
description of these parts are omitted.
[0058] The gas introduction pipe 5 can introduce a gas into the
cooling tank 2 by use of a solenoid valve 5a connected to the
controller 50.
[0059] The gas exhaust pipe 6 can discharge the gas in the cooling
tank 2 by use of a solenoid valve 6a connected to the controller
50.
[0060] The controller 50 is constructed so as to continue
introducing a gas into the cooling tank 2 by opening the solenoid
valve 5a of the gas introduction pipe 5 and repeatedly perform the
opening and closing the solenoid valve 6a of the gas exhaust pipe
6. As a result of this, it is possible to change the pressure on
the liquid level of the cooling liquid 1 which has entered the
cooling tank 2. Also, the controller 50 is constructed so as to
start the actuation of the stirrer 20 at the point of time when the
vapor film begins to be broken.
[0061] Furthermore, the controller 50 is constructed so as to
control the gas volume introduced from the gas introduction pipe 5
and the timing for the opening and closing of the solenoid valve 6a
of the gas exhaust pipe 6 according to the condition of the vapor
film and the cooling liquid 1 and so as to control a drive unit 23
of the stirrer 20 according to the condition of the cooling liquid
1 and metal parts in the cooling liquid 1.
[0062] By use of the cooling apparatus of the above-described
construction, the cooling of metal parts was performed by a method
corresponding to the embodiment of the present invention and by a
method corresponding to a conventional method.
[0063] Round bar test pieces made of stainless steel (metal parts)
having a diameter of 12 mm, which had been heated to 830.degree.
C., were immersed in a quenching oil (a cooling liquid) 1 at
70.degree. C. and cooled by the methods of No. 1 to No. 5 shown
below. Incidentally, in Nos. 1 to 3 and Nos. 5 and 6, cooling was
performed by use of the cooling apparatus shown in FIG. 1 described
above (hereinafter called "the first cooling apparatus"), and in
No. 4, cooling was performed by use of the cooling apparatus shown
in FIG. 4 shown above. Incidentally, the amplitude of oscillations
4 applied to the quenching oil 1 in the first cooling apparatus is
expressed by the swing width of the oscillating plate 11.
Incidentally, each cooling method is automatically performed by the
execution of the arithmetic processing stored beforehand in the
controllers 30, 50.
[0064] In No. 1, first, the oscillation device 10 was actuated,
whereby the oscillating plate 11 was caused to oscillate with a
frequency of 40 Hz and an amplitude of 4 mm, and the oscillations
were applied to the quenching oil 1 for 2 seconds. Next, the
oscillation device 10 was stopped and simultaneously the stirrer 20
was actuated, whereby the quenching oil 1 was jet-stirred by upward
flows at a flow rate of 30 m.sup.3/h.
[0065] In No. 2, the oscillation device 10 was actuated, whereby
the oscillating plate 11 was caused to oscillate with a frequency
of 40 Hz and an amplitude of 4 mm, and the oscillations were
applied to the quenching oil 1.
[0066] In No. 3, the oscillation device 10 was actuated, whereby
the oscillating plate 11 was caused to oscillate with a frequency
of 40 Hz and an amplitude of 4 mm, and simultaneously the stirrer
20 was actuated, whereby the quenching oil 1 was jet-stirred by
upward flows at a flow rate of 30 m.sup.3/h.
[0067] In No. 4, the solenoid valve 5a was opened and the nitrogen
gas from the gas introduction pipe 5 was continued to be introduced
into the cooling tank 2. With the liquid-level pressure of the
quenching oil 1 kept at 0.12 MPa, the opening and closing of the
solenoid valve 6a of the gas exhaust pipe 6 was performed twice per
second for a duration of 15 seconds, whereby the pressure applied
to the liquid level was repeatedly varied.
[0068] In No. 5, the quenching oil 1 was allowed to undergo natural
convection.
[0069] In No. 6, the stirrer 20 was actuated, whereby the quenching
oil 1 was jet-stirred by upward flows at a flow rate of 30
m.sup.3/h.
[0070] And in the cooling process of Nos. 1 to 6, the temperature
on the side surface of a round bar test piece made of stainless
steel was measured and a cooling curve of each test piece was
prepared. The results are shown in FIGS. 5 and 6.
[0071] FIG. 5 shows cooling curves on the side surfaces of round
bar test pieces made of stainless steel cooled under the conditions
of No. 1 to No. 4. FIG. 6 shows cooling curves on the side surfaces
of round bar test pieces made of stainless steel cooled under the
conditions of No. 5 and No. 6.
[0072] As shown in FIG. 5, in the No. 1 method which involves
performing cooling by jet stirring of the quenching oil 1 after the
application of oscillations to the quenching oil 1, in 1.9 seconds
after the immersion of a test piece in the quenching oil 1, a
change occurred from gentle cooling to abrupt cooling. This point
of change is called a "characteristic point."
[0073] In both the No. 2 method which involves performing cooling
by applying oscillations to the quenching oil 1 and the No. 3
method which involves performing cooling by jet stirring the
quenching oil 1 simultaneously with the application of oscillations
to the quenching oil 1, a characteristic point was observed in 2.7
seconds after the immersion of test pieces in the quenching oil
1.
[0074] In the No. 4 method which involves performing cooling by
repeatedly varying the liquid-level pressure of the quenching oil
1, a characteristic point was observed in 2.7 seconds after the
immersion of a test piece in the quenching oil 1.
[0075] It might be thought that because in No. 2, the quenching oil
1 is not jet-stirred after the application of oscillations to the
quenching oil 1, it takes time for the bubbles formed by the
breakage of a vapor film to diffuse, with the result that the point
of time at which a characteristic point is observed lags behind
that of No. 1.
[0076] Also, it might be thought that because in No. 3, cooling is
performed by jet-stirring the quenching oil 1 simultaneously with
the application of oscillations to the quenching oil 1, strong
flows are generated in the cooling liquid and uniform breakage of a
vapor film is impeded, with the result that the point of time at
which a characteristic point is observed lags behind that of No.
1.
[0077] Furthermore, it might be thought that because in No. 4, the
quenching oil 1 is not jet-stirred after the varying of the
liquid-level pressure of the quenching oil 1, it takes time for the
bubbles formed by the breakage of a vapor film to diffuse, with the
result that the point of time at which a characteristic point is
observed lags behind that of No. 1.
[0078] On the other hand, as shown in FIG. 6, in the No. 5 method
which involves cooling by the natural convection of the quenching
oil 1, a characteristic point was observed in 3.8 seconds after the
immersion of a test piece in the quenching oil 1. In the No. 6
method which involves cooling by jet-stirring the quenching oil 1,
a characteristic point was observed in 3.5 seconds after the
immersion of a test piece in the quenching oil.
[0079] From the above results, it became apparent that a metal part
can be rapidly cooled by breaking a vapor film without the stirring
of the quenching oil 1 and stirring the quenching oil 1 after the
vapor films begins to be broken.
[0080] The characteristic point of No. 1 was a temperature about
20.degree. C. higher than the characteristic points of No. 2 to No.
4 and this temperature was about 50.degree. C. higher than the
characteristic points of Nos. 5 and 6. From the results, when
cooling is performed under the condition of No. 1, it could be
ascertained that the breakage of a vapor film is caused by the
shattering of the stability of the vapor film, and is not due to a
drop of the surface temperature of a metal part.
[0081] Subsequently, metal parts were subjected to carburizing
treatment and cooling thereafter was performed by the method of the
present invention and by a conventional method. Dimensional changes
of the metal parts before and after the heat treatment were
investigated as follows.
[0082] First, ring-shaped materials made of SCM420 (outside
diameter: 70 mm, inside diameter: 55 mm, axial length: 40 mm) were
prepared. The ring-shaped materials were arranged in a furnace
which had been brought into a reducing atmosphere by adding alcohol
dropwise at 920.degree. C., with the axial direction of the
materials aligned in a vertical direction. Next, while propane gas
being added into this furnace in a reducing atmosphere, carburizing
treatment was performed for 60 minutes, with the carbon
concentration of the atmosphere kept at 0.8%. Next, the temperature
of the ring-shaped materials was lowered to 850.degree. C. in the
furnace in a reducing atmosphere.
[0083] Next, the ring-shaped materials were transferred from the
heating device 40 shown in FIG. 1 into the cooling tank 2. This
cooling tank 2 contains a quenching oil (a cooling liquid) 1 at
70.degree. C., and the area above the quenching oil 1 is held in a
nonoxidizing atmosphere. The ring-shaped materials were immersed in
this quenching oil 1. And cooling was performed under the
conditions of No. 10 to No. 15.
[0084] In No. 10, the oscillation device 10 was actuated, whereby
the oscillating plate 11 was caused to oscillate with a frequency
of 40 Hz and an amplitude of 4 mm, and the oscillations were
applied to the quenching oil 1 for 60 seconds.
[0085] In No. 11, the oscillation device 10 was actuated, whereby
the oscillating plate 11 was caused to oscillate with a frequency
of 60 Hz and an amplitude of 2 mm, and the oscillations were
applied to the quenching oil 1 for 60 seconds.
[0086] In No. 12, the oscillation device 10 was actuated, whereby
the oscillating plate 11 was caused to oscillate with a frequency
of 40 Hz and an amplitude of 4 mm, and simultaneously the stirrer
20 was actuated, whereby the quenching oil 1 was jet-stirred by
upward flows at a flow rate of 30 m.sup.3/h for 60 seconds.
[0087] In No. 13, first, the oscillation device 10 was actuated,
whereby the oscillating plate 11 was caused to oscillate with a
frequency of 40 Hz and an amplitude of 4 mm, and the oscillations
were applied to the quenching oil 1 for 2 seconds. Next, the
oscillation device 10 was stopped and simultaneously the stirrer 20
was actuated, whereby the quenching oil 1 was jet-stirred by upward
flows at a flow rate of 30 m.sup.3/h for 60 seconds.
[0088] In No. 14, the stirrer 20 was actuated, whereby the
quenching oil 1 was jet-stirred by upward flows at a flow rate of
30 m.sup.3/h for 60 seconds.
[0089] In No. 15, the quenching oil 1 was allowed to undergo
natural convection and a ring-shaped material was immersed in this
quenching oil 1 for 5 minutes.
[0090] And for each of the ring-shaped materials after the cooling
treatment, outside diameters and out-of-roundness were measured in
both end portions and middle portion in the axial direction, and
changes in the outside diameter and out-of-roundness before and
after the heat treatment were investigated. The results are shown
in Table 1.
[0091] In Table 1, the numerical values of outside diameter marked
with "+" mean that the size increased after the heat treatment, and
the numerical values marked with "-" mean that the size decreased
after the heat treatment. Maximum differences in dimensional
changes between top end, middle and bottom end are also shown in
Table 1. The smaller the maximum difference in outside diameter,
the smaller the deformation difference in the axial direction of a
ring-shaped material after the heat treatment.
[0092] As shown in Table 1, in the methods of Nos. 10 to 13 which
involve performing cooling by applying oscillations to the
quenching oil 1, the maximum difference in outside diameter was
small compared to the method of No. 14 which involves performing
cooling by the jet-stirring of the quenching oil 1 and the method
of No. 15 which involves performing cooling by the natural
convection of the quenching oil 1.
[0093] Among the methods of No. 10 to No. 13, the maximum
difference in outside diameter was very small in No. 13 which
involves performing cooling by the jet-stirring of the quenching
oil 1 after the application of oscillations to the quenching oil 1.
In No. 11 which involves performing cooling by the application of
oscillations having a high frequency and a small amplitude to the
quenching oil 1, the effect of oscillations was small and showed
that the maximum difference in outside diameter was large compared
to Nos. 10, 12 and 13.
[0094] In Nos. 10 to 13, changes in out-of-roundness were small
compared to No. 14 which involves performing cooling by the
jet-stirring of the quenching oil 1, and out-of-roundness of the
same degree as in No. 15 which involves performing cooling by the
natural convection of the quenching oil 1 was obtained.
[0095] From the above results, it became apparent that by breaking
a vapor film without stirring a quenching oil and by stirring the
quenching oil after the vapor film begins to be broken, the
nonuniformity of axial deformation of an obtained metal part can be
improved. TABLE-US-00001 TABLE 1 Method of Change in outside
diameter (.mu.m) Change in out-of-roundness (.mu.m) quenching Top
Bottom Top Bottom treatment end Middle end Difference end Middle
end Difference 10 +9 +1 +34 33 37 26 41 35 11 -14 -3 +25 39 43 29
35 36 12 +6 +4 +36 32 41 33 40 38 13 +12 +8 +31 23 42 29 36 36 14
-28 -7 +32 60 53 34 45 44 15 -27 -10 +21 48 45 27 37 36
INDUSTRIAL APPLICBILITY
[0096] According to the present invention, a repeatedly varying
pressure is applied to a vapor film formed on the surface of a
metal part and the vapor film is broken without the stirring of a
cooling liquid, with the result that strong flows are not generated
in the cooling liquid. Therefore, it becomes easy that the vapor
film is uniformly broken. Hence, the uniformity of the cooling of
the metal part is improved and the deformation or the soft spots
thereof become less apt to occur. As a result of this, it becomes
easy to obtain high-accuracy and high-quality metal parts.
* * * * *