U.S. patent application number 16/164230 was filed with the patent office on 2019-04-25 for lubricating oil for press working.
This patent application is currently assigned to TOYOTA BOSHOKU KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA BOSHOKU KABUSHIKI KAISHA. Invention is credited to Kazuyuki HIRATA, Naoki KATO, Ryota SASAKI.
Application Number | 20190119599 16/164230 |
Document ID | / |
Family ID | 65996715 |
Filed Date | 2019-04-25 |
United States Patent
Application |
20190119599 |
Kind Code |
A1 |
SASAKI; Ryota ; et
al. |
April 25, 2019 |
LUBRICATING OIL FOR PRESS WORKING
Abstract
A lubricating oil for press working contains a base oil and a
fat or oil-containing additive and a calcium-containing additive
added to the base oil. The proportion of the fat or oil-containing
additive with respect to the whole volume of the lubricating oil
for press working is 10 to 30%. The proportion of the
calcium-containing additive with respect to the whole volume of the
lubricating oil for press working is 5 to 15%.
Inventors: |
SASAKI; Ryota; (Toyota-shi,
JP) ; HIRATA; Kazuyuki; (Toyota-shi, JP) ;
KATO; Naoki; (Kariya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA BOSHOKU KABUSHIKI KAISHA |
Aichi-ken |
|
JP |
|
|
Assignee: |
TOYOTA BOSHOKU KABUSHIKI
KAISHA
Aichi-ken
JP
|
Family ID: |
65996715 |
Appl. No.: |
16/164230 |
Filed: |
October 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10M 2221/00 20130101;
C10M 169/041 20130101; C10M 2219/044 20130101; C10M 2207/40
20130101; C10M 2203/003 20130101; C10M 2203/04 20130101; C10M
169/04 20130101; C10M 159/04 20130101; C10M 137/06 20130101; C10N
2040/24 20130101; C10N 2030/02 20130101; C10M 141/08 20130101; C10M
2223/042 20130101; C10M 2219/044 20130101; C10N 2010/04 20130101;
C10M 2219/044 20130101; C10N 2010/02 20130101; C10M 2219/044
20130101; C10N 2010/02 20130101; C10M 2219/044 20130101; C10N
2010/04 20130101 |
International
Class: |
C10M 169/04 20060101
C10M169/04; C10M 159/04 20060101 C10M159/04; C10M 137/06 20060101
C10M137/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2017 |
JP |
2017-206307 |
Claims
1. A lubricating oil for press working, comprising: a base oil; and
a fat or oil-containing additive and a calcium-containing additive
added to the base oil, wherein a proportion of the fat or
oil-containing additive with respect to the whole volume of the
lubricating oil for press working is 10 to 30%, and a proportion of
the calcium-containing additive with respect to the whole volume of
the lubricating oil for press working is 5 to 15%.
2. The lubricating oil for press working according to claim 1,
wherein the calcium-containing additive comprises a calcium
petroleum sulfonate.
3. A lubricating oil for press working, comprising: a base oil; and
a fat or oil-containing additive and a sodium-containing additive
added to the base oil, wherein a proportion of the fat or
oil-containing additive with respect to the whole volume of the
lubricating oil for press working is 10 to 30%, and a proportion of
the sodium-containing additive with respect to the whole volume of
the lubricating oil for press working is 5 to 20%.
4. The lubricating oil for press working according to claim 3,
wherein the sodium-containing additive comprises a sodium petroleum
sulfonate.
5. The lubricating oil for press working according to claim 1,
wherein the fat or oil-containing additive comprises a phosphate
ester.
6. The lubricating oil for press working according to claim 3,
wherein the fat or oil-containing additive comprises a phosphate
ester.
Description
BACKGROUND
[0001] The present invention relates to a lubricating oil for press
working.
[0002] When workpieces such as separators for fuel cells are press
worked, to properly form the shapes of workpieces and the like by
press working, a lubricating oil is applied to metallic materials
as raw materials of workpieces such as separators so as to form an
oil film to reduce friction during press working on the surface of
the metallic materials. As the metallic materials when separators
of fuel cells are press worked, hard materials such as titanium are
usually used. Further as the lubricating oil, a lubricating oil in
which various types of additives are added to a base oil to meet
requirements for the lubricating oil is used.
[0003] Then, it has been discovered that the kinematic viscosity
(fluidity) of the lubricating oil has an influence on whether the
shapes of workpieces are properly formed through press working. In
detail, when the kinematic viscosity of a lubricating oil is
excessively low (fluidity is excessively high), the strength of an
oil film to be formed on the surface of a metallic material during
press working is weakened to generate so-called oil film shortage
during press working, resultantly causing perforation and the like
in the workpieces. On the other hand, when the kinematic viscosity
of a lubricating oil is excessively high (fluidity is excessively
low), an oil film formed on the surface of a metallic material
becomes a hindrance to press working, and surface shapes of
workpieces are incapable of being formed into intended shapes.
Hence, it is desired that the kinematic viscosity of a lubricating
oil be in such a proper range (for example, 50 to 70 mm.sup.2/s)
that the kinematic viscosity is not excessively low or excessively
high under the normal temperature (for example, 40.degree. C.)
condition.
[0004] In Japanese Patent No. 5306724, it is stated that an organic
carbonate is added to a base oil of a lubricating oil. The organic
carbonate has lowered kinematic viscosity at high temperatures.
That is, the organic carbonate has such a property that its
kinematic viscosity is low at high temperatures as compared with
the kinematic viscosity of the base oil and the like. Hence, by
heating a metallic material and a die for press working and
maintaining them at a high temperature, the kinematic viscosity of
an oil film (lubricating oil) to be formed on the surface of the
metallic material during press working can be regulated at a value
in the above proper range through the use of the above property of
the organic carbonate added to the lubricating oil.
[0005] In this case, however, the metallic material and the die
must be heated and maintained at a high temperature as described
above, and it is thus undeniable that the energy consumption at
this time brings about a rise in the production cost of
workpieces.
[0006] Then, even if the kinematic viscosity of a lubricating oil
is regulated at a value in a proper range for press working, the
value is not always optimum for application of the lubricating oil
to a metallic material. That is, from the viewpoint of application
of the lubricating oil to the metallic material, uniform
application of the lubricating oil cannot be performed due to an
excessively high kinematic viscosity.
[0007] Although electrostatic application is conceivably used as a
method of efficiently uniformly applying a lubricating oil, an
additive for providing the lubricating oil with conductivity must
be added to a base oil in order to carry out such electrostatic
application. If the amount of the additive added to the base oil is
not suitable, however, such risks arise that the lubricating oil
cannot be provided with a conductivity necessary for the
electrostatic application and that the washability of the
lubricating oil is worsened when workpieces are washed after press
working.
[0008] It is an objective of the present invention to provide a
lubricating oil for press working, the lubricating oil providing a
kinematic viscosity suitable for press working without being heated
at a high temperature and being capable of achieving efficient
uniform electrostatic application without worsening
washability.
SUMMARY
[0009] In accordance with one aspect of the present disclosure, a
lubricating oil for press working is provided that contains a base
oil and a fat or oil-containing additive and a calcium-containing
additive added to the base oil. A proportion of the fat or
oil-containing additive with respect to the whole volume of the
lubricating oil for press working is 10 to 30%. A proportion of the
calcium-containing additive with respect to the whole volume of the
lubricating oil for press working is 5 to 15%.
[0010] In accordance with another aspect of the present disclosure,
a lubricating oil for press working is provided that contains a
base oil and a fat or oil-containing additive and a
sodium-containing additive added to the base oil. A proportion of
the fat or oil-containing additive with respect to the whole volume
of the lubricating oil for press working is 10 to 30%. A proportion
of the sodium-containing additive with respect to the whole volume
of the lubricating oil for press working is 5 to 20%.
[0011] Other aspects and advantages of the present disclosure will
become apparent from the following description, taken in
conjunction with the accompanying drawings, illustrating exemplary
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The disclosure may be understood by reference to the
following description together with the accompanying drawings:
[0013] FIG. 1 is a cross-sectional view illustrating a manner of
use of a lubricating oil when a separator of a fuel cell is press
worked;
[0014] FIG. 2 is a cross-sectional view illustrating a manner of
use of the lubricating oil when a separator of a fuel cell is press
worked;
[0015] FIG. 3 is a graph showing the test results of an evaluation
test on the kinematic viscosity;
[0016] FIG. 4 is a graph showing the test results of an evaluation
test on the added amount of a fat or oil-containing additive;
[0017] FIG. 5 is a graph showing the test results of an evaluation
test on the added amount of a calcium-containing additive;
[0018] FIG. 6 is a graph showing test results of an evaluation test
on the added amount of a sodium-containing additive; and
[0019] FIG. 7 is a table showing the test results of a washing
test.
DETAILED DESCRIPTION
[0020] When a workpiece such as a separator of a fuel cell is press
worked, a lubricating oil for press working according to the
present invention is applied to the surface of a metallic material
as a raw material of the workpiece, and thereby forming an oil film
on the surface of the metallic material to reduce friction during
press working. A lubricating oil containing a base oil and a fat or
oil-containing additive and a calcium-containing additive added to
the base oil, or a lubricating oil containing a base oil and a fat
or oil-containing additive and a sodium-containing additive added
to the base oil is used as such a lubricating oil. A mineral oil
functioning as a carrier to support dissolution and dispersion of
various types of additives is used as the base oil. Further, a
stainless steel, titanium, a titanium alloy or the like is
conceivably used as the metallic material.
[0021] Then, the above-mentioned fat or oil-containing additive,
calcium-containing additive, and sodium-containing additive each
will be described in detail.
[0022] [Regarding Fat or Oil-Containing Additive]
[0023] The fat or oil-containing additive is for reinforcing the
oil film strength and thereby improving the load resistance of the
lubricating oil. The fat or oil-containing additive preferably
contains at least a phosphate ester, and may contain, in addition
to the phosphate ester, at least one of castor oil fatty acid ester
derivatives, and mineral oils.
[0024] The phosphate ester is for providing a lubricating oil with
a wear prevention effect, and for improving workability by
formation of an iron phosphate-based compound film. The castor oil
fatty acid ester derivatives are oiliness improvers and have a
polar group. That is, the castor oil fatty acid ester derivatives
are for imparting, to the lubricating oil, adsorbability and
penetrability to the metal surface and for forming a firmer
lubricating oil film than the mineral oil (base oil). The castor
oil fatty acid ester derivatives also have an effect of improving
solubility of other additives. As a mineral oil contained in the
fat or oil-containing additive, in consideration of improvement in
miscibility when the fat or oil-containing additive is added to a
base oil, it is preferable to use the same mineral oil as used for
the base oil.
[0025] [Regarding Calcium-Containing Additive]
[0026] The calcium-containing additive is for making the
conductivity of the lubricating oil to be a value in a proper range
(for example, 1,000 to 100,000 pS/m) for electrostatic application.
By making the conductivity of the lubricating oil be a value in the
proper range for electrostatic application by adding such a
calcium-containing additive, the lubricating oil can be efficiently
uniformly applied to a metallic material through electrostatic
application. The calcium-containing additive preferably contains at
least a calcium petroleum sulfonate, and may contain, in addition
to the calcium petroleum sulfonate, at least one of calcium
hydroxide, calcium carbonate and mineral oils.
[0027] The calcium petroleum sulfonate is for providing the
lubricating oil with a cleaning dispersing effect of causing the
metal salt to collect undissolved components generated in the
lubricating oil and avoiding mutual contacting of the undissolved
components. If a highly basic calcium petroleum sulfonate is used,
since acidic components produced by deterioration of the
lubricating oil are neutralized, adverse influences, such as
generation of rusts, by the acidic components can be suppressed.
The calcium hydroxide is for providing the lubricating oil with
basicity. The calcium carbonate is for improving lubricity of the
lubricating oil by becoming a fine solid lubricant. As a mineral
oil contained in the calcium-containing additive, in consideration
of improvement in miscibility when the calcium-containing additive
is added to a base oil, it is preferable to use the same mineral
oil as used for the base oil.
[0028] [Regarding Sodium-Containing Additive]
[0029] The sodium-containing additive is also for making the
conductivity of the lubricating oil be a value in the proper range
for electrostatic application. Also in the case where the
conductivity of the lubricating oil is a value in the proper range
for electrostatic application by adding the sodium-containing
additive in place of the calcium-containing additive, the
lubricating oil can be efficiently uniformly applied to a metallic
material through electrostatic application. The sodium-containing
additive preferably contains at least a sodium petroleum sulfonate,
and may contain, in addition to the sodium petroleum sulfonate, at
least one of mineral oils and water.
[0030] The sodium petroleum sulfonate is obtained by neutralizing a
sulfonic acid with sodium hydroxide, and easily dissolves in water
and functions as an emulsifier or a rust preventive for the
lubricating oil. As a mineral oil contained in the
sodium-containing additive, in consideration of improvement in
miscibility when the sodium-containing additive is added to a base
oil, it is preferable to use the same mineral oil as used for the
base oil.
EXAMPLES
[0031] Examples of the lubricating oils for press working according
to the present invention will now be described.
[0032] FIGS. 1 and 2 each show a manner of use of a lubricating oil
when a separator of a fuel cell is press worked. As shown in FIG.
1, by applying the lubricating oil to a plate-shaped metallic
material 1 as a raw material for forming the separator, oil films 2
are formed on the surfaces of the metallic material 1. Then, as
shown in FIG. 2, on the press worked metallic material 1
(separator), a groove 3 is formed, which is used for forming a flow
path for a fluid, such as a fuel gas, an oxidizing gas, or a
coolant, to be used in a fuel cell to flow therethrough. As
described above, the press worked separator is washed after press
working. The washing removes the lubricating oil applied in press
working, and the like from the separator.
[0033] Then, an evaluation test on the kinematic viscosity and an
evaluation test on the amount of a fat or oil-containing additive
added to determine the added amount of the fat or oil-containing
additive with respect to a base oil in a lubricating oil will be
described in detail.
[0034] [Evaluation Test on Kinematic Viscosity]
[0035] The kinematic viscosity (fluidity) on the lubricating oil
for forming oil films 2 on the surfaces of a metallic material 1 in
press working has an influence on whether the shape of a separator
can be properly formed through press working. Hence, aiming at
determining a suitable kinematic viscosity of the lubricating oil
when the separator was press worked, the following evaluation test
on the kinematic viscosity was carried out.
[0036] In the evaluation test on the kinematic viscosity, with use
of each one of a plurality of lubricating oils having different
kinematic viscosities at normal temperature, individually, a
metallic material 1 was press worked. Then, the number of defective
products in the separators after the press working was counted for
each lubricating oil.
[0037] FIG. 3 shows the test results of the evaluation test on the
kinematic viscosity. In this test, as a result of counting the
numbers of defective products in a plurality of lubricating oils
having kinematic viscosities of 30, 50, 55, 70, and 100 mm.sup.2/s,
respectively, it was found that when the kinematic viscosity was 30
mm.sup.2/s or lower, and when the kinematic viscosity was 100
mm.sup.2/s or higher, the number of the defective products
increased.
[0038] This is because when the kinematic viscosity of the
lubricating oil is as low as 30 mm.sup.2/s or lower (high in
fluidity), the strength of the oil film 2 (FIG. 1) formed on the
surface of the metallic material 1 decreases and so-called oil film
shortage occurs on portions enclosed by the broken lines in FIG. 2
during press working, and perforation and the like occur in the
separator. On the other hand, when the kinematic viscosity of the
lubricating oil is as high as 100 mm.sup.2/s or higher (low in
fluidity), the oil film 2 (FIG. 1) formed on the surface of the
metallic material 1 prevents press working and it is impossible to
form the surface shape of the separator into an intended shape. In
detail, as indicated by the long dashed double-short dashed lines
in FIG. 2, the depth of the groove 3 in the press worked separator
is insufficient. Consequently, the number of defective products
increases also when the kinematic viscosity of the lubricating oil
is as high as 100 mm.sup.2/s or higher.
[0039] As is clear from the test results of the evaluation test on
the kinematic viscosity, the proper range of the kinematic
viscosity at normal temperature of a lubricating oil for press
working is 50 to 70 mm.sup.2/s, and the optimum value of the
kinematic viscosity is 55 mm.sup.2/s.
[0040] [Evaluation Test on Added Amount of Fat or Oil-Containing
Additive]
[0041] With use of each one of a plurality of lubricating oils
having different added amounts of the fat or oil-containing
additive, that is, having different proportions of the fat or
oil-containing additive with respect to the whole volume of the
lubricating oil, individually, the metallic material 1 was press
worked at normal temperature. Then, the number of defective
products in the separators after the press working was counted for
each lubricating oil.
[0042] FIG. 4 shows the test results of the evaluation test on the
added amount of a fat or oil-containing additive. In this test, a
plurality of lubricating oils having proportions of 0, 10, 20, 30,
and 50% of a fat or oil-containing additive with respect to the
whole volume of the lubricating oil, respectively, were prepared.
Then, as a result of counting of the number of defective products
for each lubricating oil, it was found that when the proportion of
the fat or oil-containing additive was 0% and when the proportion
of the fat or oil-containing additive was 50% or higher, the number
of defective products increased.
[0043] This is presumably for the following reasons. That is, when
the added amount of the fat or oil-containing additive is reduced
and the proportion of the fat or oil-containing additive approaches
0%, the strength of the oil film 2 (FIG. 1) formed on the surface
of the metallic material 1 decreases and the oil film shortage
occurs on portions enclosed by the broken lines in FIG. 2 during
press working, and perforation and the like occur in the separator.
On the other hand, when the added amount of the fat or
oil-containing additive is increased and the proportion of the fat
or oil-containing additive approaches 50% or higher, the strength
of the oil film 2 (FIG. 1) formed on the surface of the metallic
material 1 increases and the oil film 2 prevents press working and
it is impossible to form the surface shape of the separator in an
intended shape. That is, as indicated by the long dashed
double-short dashed lines in FIG. 2, the depth of the groove 3 in
the press worked separator is insufficient and the number of
defective products increases.
[0044] As is clear from the test results of the evaluation test on
the added amount of the fat or oil-containing additive, the
proportion of the fat or oil-containing additive with respect to
the whole volume of the lubricating oil for press working is
preferably in the range of 10 to 30%, and more preferably 20%.
[0045] As is clear from the test results of the evaluation test on
the kinematic viscosity and the evaluation test on the added amount
of the fat or oil-containing additive, it is presumed that in the
lubricating oil for press working, when the added amount of the fat
or oil-containing additive with respect to the base oil is
established so that the proportion of the fat or oil-containing
additive with respect to the whole volume of the lubricating oil is
10 to 30%, the kinematic viscosity of the obtained lubricating oil
is a value in the proper range for press working. As is clear from
the above-mentioned test results of the evaluation test on the
kinematic viscosity, the proper range used herein is 50 to 70
mm.sup.2/s in the normal temperature environment.
[0046] Then, a detailed description will be made on an evaluation
test on the added amount of the calcium-containing additive to
establish the added amount of the calcium-containing additive with
respect to the base oil in the lubricating oil, an evaluation test
on the added amount of the sodium-containing additive to establish
the added amount of the sodium-containing additive with respect to
the base oil, and a washing test.
[0047] [Evaluation Test on Added Amount of Calcium-Containing
Additive]
[0048] In the evaluation test on the added amount of a
calcium-containing additive, a plurality of lubricating oils having
different added amounts of the calcium-containing additive, that
is, having different proportions of the calcium-containing additive
with respect to the whole volume of the lubricating oil were
prepared, and the conductivities of the lubricating oils were each
measured.
[0049] FIG. 5 shows the test results of the evaluation test on the
added amount of the calcium-containing additive. In this test, a
plurality of lubricating oils having proportions of, respectively,
0, 5, 10, and 15% as of the calcium-containing additive with
respect to the whole volume of the lubricating oil were prepared.
Then, as a result of measurement of conductivities of the
lubricating oils, it was found that for the respective lubricating
oils having proportions of the calcium-containing additive of 5,
10, and 15%, the conductivity became a value in the proper range
(1,000 to 100,000 pS/m) for electrostatic application.
[0050] [Evaluation Test on Added Amount of Sodium-Containing
Additive]
[0051] In the evaluation test on the added amount of the
sodium-containing additive, a plurality of lubricating oils having
different added amounts of the sodium-containing additive, that is,
having different proportions of the sodium-containing additive with
respect to the whole volume of the lubricating oil were prepared,
and the conductivities of the lubricating oils were each
measured.
[0052] FIG. 6 shows the test results of the evaluation test on the
added amount of the sodium-containing additive. In this test, a
plurality of lubricating oils having proportions of 0, 5, 10, 15,
and 20%, respectively, with respect to the whole volume of the
lubricating oil were prepared. Then, as a result of measurement of
conductivities of the lubricating oils, it was found that for the
respective lubricating oils having proportions of the
sodium-containing additive of 5, 10, 15, and 20%, the conductivity
became values in the proper range (1,000 to 100,000 pS/m) for
electrostatic application.
[0053] [Washing Test]
[0054] In the washing test, a plurality of lubricating oils having
different added amounts of the calcium-containing additive (that
is, having different proportions of the calcium-containing additive
with respect to the whole volume of the lubricating oil), and a
plurality of lubricating oils having different added amounts of the
sodium-containing additive (that is, having different proportions
of the sodium-containing additive with respect to the whole volume
of the lubricating oil) were prepared. Then with use of each one of
these lubricating oils, individually, the metallic material 1 was
press worked; and the separators after the press working were
washed for a certain time (for example, for 7 minutes) by an alkali
washing machine, and thereafter, dried in a drier. Then, the number
of lubricating oil stains on each separator after the drying was
counted individually; and the washability of each lubricating oil
was evaluated based on the number of the lubricating oil
stains.
[0055] FIG. 7 shows the test results of the washing test.
[0056] In this test, the proportion of the fat or oil-containing
additive was set to 20% in any of lubricating oils A to G. Then, to
the lubricating oil B, the lubricating oil C, and the lubricating
oil D, the calcium-containing additive was added, and the
proportions of the calcium-containing additive were set to be 5,
10, and 15%, respectively. Further, to the lubricating oil E, the
lubricating oil F, and the lubricating oil G, the sodium-containing
additive was added, and the proportions of the sodium-containing
additive were set to be 5, 10, and 20%, respectively.
[0057] The washability of each of the lubricating oils A to G was
evaluated in 5 ranks of [1] to [5] based on the above number of the
lubricating oil stains. In this evaluation, in 5 ranks, it is
indicated that [1] is the worst washability, and as the value of
the rank increases from [2] to [5] through [3] and [4], the
washability becomes better. A lubricating oil having the value of
[3] or higher among the lubricating oils A to G can be used as a
lubricating oil for press working.
[0058] As is clear from the test results, among the lubricating
oils B to D, which had the calcium-containing additive added
therein, the lubricating oil exhibiting the worst washability was
the lubricating oil B. This is conceivably because the
emulsification action of the lubricating oil was reduced due to
that the proportion of the calcium-containing additive was as low
as 5%. On the other hand, when the proportion of the
calcium-containing additive was set to be higher than 15%, the
proportion of the calcium-containing additive became too high and
worsening of the washability was observed.
[0059] Therefore, in the case where the calcium-containing additive
is added in order to make the conductivity of the lubricating oil
to be a value in the proper range for electrostatic application, in
consideration of the washability of the lubricating oil, the
proportion of the calcium-containing additive with respect to the
whole volume of the lubricating oil is preferably set to be a value
in the range of 5 to 15%, and more preferably 10%.
[0060] Further as is clear from the above test results, among the
lubricating oils E to G, which had the sodium-containing additive
added therein, the lubricating oil exhibiting the best washability
was the lubricating oil F, and the lubricating oil G exhibited
washability worse than the lubricating oil F, and had a usable
washability only in the lowest level. Further, as is clear from the
test results of the evaluation test on the added amount of the
sodium-containing additive, the proportion of the sodium-containing
additive must be set to be at least 5%, like the lubricating oil E,
in order to provide a conductivity necessary for electrostatic
application.
[0061] Therefore, in the case where the sodium-containing additive
is added in order to make the conductivity of the lubricating oil
to be a value in the proper range for electrostatic application, in
consideration of the washability and the conductivity of the
lubricating oil, the proportion of the sodium-containing additive
with respect to the whole volume of the lubricating oil is
preferably a value in the range of 5 to 20%, and more preferably
10%.
[0062] As is clear from the above, in the lubricating oil for press
working, when the fat or oil-containing additive is added to the
base oil so that the proportion of the fat or oil-containing
additive with respect to the whole volume of the lubricating oil is
10 to 30%, the kinematic viscosity of the lubricating oil is a
value in the proper range for press working of 50 to 70 mm.sup.2/s
at normal temperature.
[0063] In the lubricating oil for press working, in the case where
the calcium-containing additive is added to the base oil, by adding
the calcium-containing additive so that the proportion of the
calcium-containing additive with respect to the whole volume of the
lubricating oil is 5 to 15%, the conductivity of the lubricating
oil can be a value in the proper range for electrostatic
application of 1,000 to 100,000 pS/m. Hence, the lubricating oil
can be efficiently uniformly applied through electrostatic
application. Further when the proportion of the calcium-containing
additive is set to be 5 to 15% as in the above, the washability
when workpieces are washed after press working never worsens.
[0064] Further, in the lubricating oil for press working, instead
of adding the calcium-containing additive to the base oil, a
sodium-containing additive may also be added. In this case, by
adding the sodium-containing additive so that the proportion of the
sodium-containing additive with respect to the whole volume of the
lubricating oil is 5 to 20%, the conductivity of the lubricating
oil can be a value in the proper range for electrostatic
application of 1,000 to 100,000 pS/m. Hence, the lubricating oil
can be efficiently uniformly applied through electrostatic
application. Further when the proportion of the sodium-containing
additive is set to be 5 to 20% as in the above, the washability
when workpieces are washed after press working never worsens.
[0065] The present examples and embodiments are to be considered as
illustrative and not restrictive, and the invention is not to be
limited to the details given herein, but may be modified within the
scope and equivalence of the appended claims.
* * * * *