Note: Descriptions are shown in the official language in which they were submitted.
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HYDRAULIC FLUID AND METHOD OF
PREVENTING VAPOR PHASE CORROSION
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Patent
Application No.
61/092,483, filed August 28, 2008, incorporated herein by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to water-glycol (W/G)-based hydraulic
fluids and to
the prevention of vapor phase corrosion attributed to use of a W/G-based
hydraulic fluid.
More particularly, the present invention is directed to a W/G-based hydraulic
fluid containing
an ammonium salt as a vapor phase corrosion inhibitor. The hydraulic fluids
can be used in a
variety of practical applications, including food-related applications.
BACKGROUND OF THE INVENTION
[0003] Hydraulic fluids are used as a power transmitting medium for a variety
of practical
applications. These hydraulic fluids must meet stringent performance criteria,
such as
thermal stability, fire resistance, low susceptibility to viscosity changes
over a wide range of
temperatures, good hydrolytic stability, and good lubricity.
[0004] Several hydraulic fluids are based on mineral oils. These hydrocarbon-
based fluids
met the performance criteria, and did not pose a significant corrosion problem
because the
fluids were essentially free of water. Hydrocarbon-based hydraulic fluids
however do pose a
potential fire hazard. Several present-day hydraulic fluids therefore are
based on water-
glycol mixtures, which overcome the fire hazard concerns, but corrosion of
metal parts
becomes a significant problem.
[0005] The W/G-based hydraulic fluids contain significant amounts of water.
The water
level in some fluids can be as high as 60%, by weight, and typically is at
least 35%, by
weight. The presence of a high percentage of water in the fluid, when heated
to operating
temperatures of 150 F or higher in a hydraulic system and in the presence of
air/oxygen,
creates ideal conditions for corrosion of metal parts made of non-stainless
steel or cast iron.
[0006] Various additives are included in W/G-based hydraulic fluids to inhibit
corrosion of
metal parts. For example, morpholine and other alkyl alkanolamines have been
used as a
vapor phase corrosion inhibitors in industrial, nonfood-related applications.
However, a need
still exists for the inclusion of a useful inorganic vapor phase corrosion
(VPC) inhibitor in a
WIG-based hydraulic fluid, and particularly for a W/G-based hydraulic fluid
for use in food-
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related applications. Presently, no commercial VPC inhibitor designed for a
W/G-based
hydraulic fluid meets the requirements of the Food and Drug Administration
(FDA) for use in
food-related applications.
SUMMARY OF THE INVENTION
100071 The present invention is directed to W/G-based hydraulic fluids that
inhibit the
vapor phase corrosion of exposed metal surfaces. More particularly, the
present invention is
directed to a W/G-based hydraulic fluid comprising an ammonium salt as a VPC
inhibitor.
The present fluids are suitable for use in food-related applications. Prior
W/G-based
hydraulic fluids used in food-related applications did not contain a VPC
inhibitor, and
therefore lacked an important performance property. The present W/G-based
hydraulic fluids
overcome this unsolved problem.
[00081 Therefore, one aspect of the present invention is to provide a W/G-
based hydraulic
fluid that inhibits corrosion of exposed metal surfaces caused by vaporization
of the hydraulic
fluid. A present W/G-based hydraulic fluid comprises an ammonium salt as a VPC
inhibitor.
[00091 Still another aspect of the present invention is to provide a method of
inhibiting,
retarding, or preventing the vapor phase corrosion of exposed metal surfaces
caused by a
hydraulic fluid comprising incorporating an effective amount, e.g., about
0.05% to about 1%,
by weight, of an ammonium salt in a W/G-based hydraulic fluid.
[00101 Another aspect of the present invention is to provide a W/G-based
hydraulic fluid
comprising:
(a) about 25% to about 50%, by weight, of a glycol;
(b) about 0.5% to about 8%, by weight, of a partially neutralized aliphatic C6-
C16
carboxylic acid;
(c) about 15% to about 40%, by weight, of a polyalkylene glycol;
(d) about 0.05% to about 1%, by weight, of an ammonium salt;
(e) a sufficient amount of a buffering alkali to provide a reserve alkalinity
of at
least about 20 ml;
(f) 0% to about 0.5%, by weight, in total, of one or more of a defoamer, a
dye, and
a metal deactivator; and
(g) about 25% to about 50%, by weight, water.
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[0011] Another aspect of the present invention is to provide a W/G-based
hydraulic fluid
having a reserve alkalinity of at least about 20 ml. in order to extend the
useful life of the
hydraulic fluid.
[0012] These and other aspects of the present invention will become apparent
from the
following detailed description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWING
[0013] Fig. 1 contains photographs of cast iron plates exposed to vapors of a
comparative
W/G-based hydraulic fluid (left side) or to vapors of a present WIG-based
hydraulic fluid
containing an ammonium salt (right side).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The present invention is directed to W/G-based hydraulic fluids. W/G-
based fluids
are widely used because they are fire resistant. A present W/G-based hydraulic
fluid can be
used in a variety of practical applications, especially including food related
applications. In
accordance with an important feature of the present invention, exposed metal
surfaces resist
vapor phase corrosion caused by evaporation of W/G-based hydraulic fluid at
elevated
operating temperatures.
[00151 A W/G-based hydraulic fluid of the present invention inhibits, retards,
and/or
prevents corrosion of exposed metal surfaces. Corrosion of a metal surface is
inhibited,
retarded, or prevented when a metal surface is visually less oxidized by
vapors of a W/G-
based hydraulic fluid containing an ammonium salt compared to the amount of
visual
oxidation of an identical metal caused by an identical W/G-based hydraulic
fluid that is free
of, or essentially free of, an ammonium salt.
[0016] A W/G-based hydraulic fluid that is "essentially free" of an ammonium
salt
contains less than about 0.05%, by weight, of an ammonium salt. Corrosion of a
wide variety
of metal surfaces can be inhibited, retarded, or prevented using a composition
and method of
the present invention. For example, corrosion can be inhibited on metal
surfaces, including,
but not limited to, iron, titanium, aluminum, copper, zinc, nickel, cobalt,
chromium,
magnesium, and other metals. The composition and method of the present
invention also can
be used to protect alloys such as, but not limited to, steel.
[0017] A W/G-based hydraulic fluid of the present invention comprises:
(a) about 25% to about 50%, by weight, of a glycol;
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(b) about 0.5% to about 8%, by weight, of a partially-neutralized aliphatic C6-
C16
carboxylic acid;
(c) about 15% to about 40%, by weight, of a polyalkylene glycol;
(d) about 0.05% to about 1%, by weight, of an ammonium salt;
(e) a sufficient amount of a buffering alkali to provide a reserve alkalinity
of at
least about 20 ml;
(f) 0% to about 0.5%, by weight, in total, of one or more of a defoamer, a
dye, and
a metal deactivor; and
(g) about 25% to about 50%, by weight, water.
A present hydraulic fluid is suitable for use in a variety of practical
applications, including
food-related applications. The present W/G-based hydraulic fluids inhibit,
retard, and/or
prevent vapor phase corrosion of exposed metal surfaces attributed to use of
these hydraulic
fluids.
[00181 An important feature of the present invention is an ability to use a
present hydraulic
fluid in food-related applications. Currently no commercial VPC inhibitors are
approved by
the FDA for prevention of VPC resulting from the use of a hydraulic fluid.
After extensive
research, suitable corrosion inhibitors were found that also could be used in
compositions for
use in incidental food contact lubricants (21 C.F.R. 178.3570).
[00191 A present hydraulic fluid comprises about 25% to about 50%, by weight,
of a
glycol. In preferred embodiments, a present hydraulic fluid comprises about
30% to about
45%, by weight, and more preferably about 35% to about 40%, by weight, of a
glycol. A
glycol is included in the composition as an antifreeze and diluent, and to
provide some
viscosity control. The glycol can be, for example, ethylene glycol, propylene
glycol,
butylene glycol, pentylene glycol, hexylene glycol, diethylene glycol,
dipropylene glycol,
dihexylene glycol, triethylene glycol, tripropylene glycol, trihexylene
glycol, and mixtures
thereof. Other similar glycols also can be used.
[0020] A present hydraulic fluid also contains about 0.5% to about 8%, and
preferably
about 1 % to about 6%, by weight, of a partially-neutralized aliphatic C6-C16
carboxylic acid,
linear or branched. The partially neutralized C6-C16 carboxylic acid acts as a
boundary
lubricant to improve performance of the W/G-based hydraulic fluid, especially
with respect
wear resistance and sludge solubility.
[0021] The aliphatic C6-C16 carboxylic acid can be one or more of hexanoic
acid,
heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid,
undecanoic acid,
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myristic acid, pentadecanoic acid, palmitic acid, tridecanoic acid, 2-
ethylhexanoic acid, and
2-propylhexanoic acid, for example. Preferred C6-C16 carboxylic acids contain
six to ten
carbon atoms. A neutralizing agent is added to the W/G-based fluid in a
sufficient amount to
neutralize at least a portion of the carboxyl groups of the C6-C16 carboxylic
acid.
100221 The aliphatic C6-C16 carboxyl acid is neutralized with neutralizing
agent, typically
an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide,
lithium
hydroxide, or a mixture thereof. A preferred neutralizing agent is potassium
hydroxide. The
neutralizing agent is added in a sufficient amount to neutralize at least
about 50%, and
preferably at least about 60%, and up to about 99%, but less than 100%, of the
carboxyl
groups of the C6-C16 carboxylic acid.
[00231 A present W/G-based hydraulic fluid also contains about 15% to about
40%, by
weight, of a polyalkylene glycol. In preferred embodiments, the polyalkylene
glycol is
present in an amount of about 20% to about 30%, by weight, of the fluid. The
polyalkylene
glycol serves as a thickener to provide a desired viscosity.
[00241 The identity of the polyalkylene glycol is not limited, and several
commercial
polyalkylene glycols are available for use in a present W/G-based hydraulic
fluid. The
polyalkylene glycol typically is a copolymer of ethylene oxide (EO) and
propylene oxide
(PO), in a ratio of EO to PO of about 10 to 1 to about I to 10. Homopolymers
of EO and PO,
i.e., polyethylene glycol and propylene glycol, also can be used as the
polyalkylene glycol.
The polyalkylene glycols have a molecular weight of at least about 5,000,
typically in excess
of about 10,000, up to about 200,000, for example. One polyalkylene glycol or
a mixture of
polyalkylene glycols can be used in a present W/G-based hydraulic fluid.
[00251 One commercial class of polyalkylene glycol useful in the present W/G-
based fluid
is the PLURASAFE products, available from BASF Corp., Floral Park, NJ. An
example of
a useful PLURASAFE product is PLURASAFE WT 90000 H, a composition containing
60% by weight of methyl-oxirane polymer with oxirane (CAS No. 9003-11-6) and
40% by
weight water. PLURASAFE WT 90000 H is approved for incidental food contact.
Other
useful PLURASAFE products are WS-660, WS-2000, WS-5100, WT-1400, WT-9150, and
WT-150,000. Each of these PLURASAFE products is approved for incidental food
contact.
[00261 In accordance with an important feature of the present invention, a
present WIG-
based hydraulic fluid comprises a sufficient amount of an ammonium salt to
inhibit, retard,
and/or prevent the vapor phase corrosion of a metal surface exposed to vapors
of a W/G-
based hydraulic fluid. Typically, the W/G-based fluid contains about 0.05% to
about 1%, by
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weight of the ammonium salt. In preferred embodiments, the WIG-based fluid
contains about
0.1% to about 0.8%, and more preferably, about 0.15% to about 0.6%, by weight
of an
ammonium salt.
100271 The identity of the ammonium salt is not particularly limited. However,
the
ammonium salt must be water soluble in the amount added to the hydraulic fluid
and must
permit vaporization of ammonia at operating temperatures to protect exposed
metal surfaces
from VPC. Suitable ammonium salts include, but are not limited to, ammonium
hydroxide,
ammonium carbonate, ammonium acetate, and mixtures thereof. Each of these
ammonium
salts is approved as a food additive for human consumption.
[00281 Another component of a present W/G-based hydraulic fluid is a
sufficient amount
of a buffering alkali to provide a reserve alkalinity of at least about 20 ml.
Hydraulic fluid
wear performance is directly related to fluid pH, and accordingly the pH is
maintained at a
sufficiently high value. A buffering alkali controls the reserve alkalinity,
pH, and acidity of
the hydraulic fluid. Reserve alkalinity is reported as the volume (in
milliliters) of 0.1 M
hydrochloric acid required to titrate 100 ml of a W/G-based hydraulic fluid to
pH 5.5.
[00291 In preferred embodiments, a sufficient amount of a buffering alkali is
present to
provide a residual alkalinity of at least about 22 ml, and more preferably at
least about 25 m],
up to a reserve alkalinity of about 35 ml. At this reserve alkalinity level,
the useful life of the
W/G-based fluid has sufficient buffering capabilities to maintain the pH of
the fluid at about
9 or higher, e.g., about 10 to about 12, and avoid large, rapid pH
fluctuations. Preferably, the
pH of the hydraulic fluid is maintained at about 9 to about 11. Useful
buffering alkalis
therefore include, but are not limited to carbonates, bicarbonates, borates,
tetraborates,
phosphates, and mixtures thereof. The buffering alkali can be added as the
sodium or
potassium salt, for example.
[0030] A W/G-based fluid of the present invention further comprises optional
ingredients
known to persons skilled in the art of hydraulic fluids. These optional
ingredients include a
defoamer, a dye for leak detection, and a metal deactivator to prevent
corrosion of metal in
contact with the liquid W/G-based hydraulic fluid. These optional ingredients
are present, in
total, in an amount of 0% to about 0.5%, by weight, of the fluid. Suitable
metal deactivators
include the IRGAMET class of metal deactivators available from CIBA, such as
IRGAMET' 30, 39, 42, BTZ, and TTS. The defoamer is typically a silicone-based
defoamer.
[00311 The carrier of the W/G-based hydraulic fluid is water, which is present
in an
amount of about 25% to about 50%, by weight of the fluid. The water preferably
is deionized
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(DI) water because calcium and magnesium ions present in potable water can
react with fluid
additives causing a floc or precipitate to form, and adversely effect fluid
performance. To
prolong the fluid and component life, water included in the W/G-hydraulic
fluid should have
a maximum total hardness of 5 parts per million (ppm).
[0032] A composition of the present invention is prepared by simply admixing
composition ingredients until a homogeneous solution is provided. Typically,
the water, an
alkali hydroxide (e.g., potassium hydroxide), and ammonium carbonate are
premixed,
followed by the addition of the C6-C16 carboxylic acid. This addition
typically is followed by
addition of the glycol and the polyalkylene glycol, followed by the addition
of all remaining
hydraulic fluid ingredients.
[0033] To demonstrate the W/G-based hydraulic fluids of the present invention,
and their
ability to inhibit, retard, and/or prevent corrosion of exposed metal surfaces
from VPC, the
following hydraulic fluids were prepared and tested for corrosion inhibition.
Comparative Example (prior art)
Range Typical
(wt%) (wt%)
Deionized Water 30-35 34.0
90% Solid Potassium Hydroxide (KOH) 0.6-1.2 1.0
Propylene Glycol, Standard Grade (1) 35-45 39.8
Hexanoic Acid 1.5-3.0 2.7
PLURASAFE WT-90,000 H Fluid 18.25 22.5
(Polyalkylene glycol)
IRGAMET 39 Fluid (Tolutriazole
compound for metal deactivation) 0.01-0.05 trace
MAZU DF-210S (Silicone defoamer) 0.05-0.25 0.1
[0034] This comparative example is free of a VPC inhibitor, and is similar to
W/G-based
hydraulic fluids presently sold commercially.
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Examples
Preferred
Range
(wt%)
Deionized Water 30-35
90% Solid KOH 0.6-1.2
Ammonium Salt 0.05-.5
Hexanoic Acid 1.5-3.0
Propylene Glycol, Standard Grade 35-45
PLURASAFER
-'WT-90,000 H Fluid 18-25
IRGAMET 39 Fluid 0.01-0.05
MAZU DF-210S 0.05-0.25
Sodium Carbonate 0.1-0.4
1 Typically ammonium carbonate, ammonium hydroxide, ammonium acetate, or
mixtures thereof, on a 100% active basis.
[00351 The ammonium salts tested were ammonium hydroxide, ammonium acetate,
and
ammonium carbonate. Each ammonium salt is listed as a food additive for human
consumption. The first test was performed using a W/G-based hydraulic fluid,
i.e., the
typical example above containing 0.5%, by weight, ammonium hydroxide, about
40%
propylene glycol, about 22.5% PLURASAFE' WT-90,000 H, about 0.2% sodium
carbonate,
and about 3.5% partially neutralized capric acid. This corrosion inhibition
test utilized three
cast iron plates suspended over 100 ml of hydraulic fluid in a cylindrical
jar. The top of the
jar was covered with a cork having an opening for condensing tube. The jar was
placed in a
constant temperature bath set at 150 F, and the sample was heated for 96
hours. The cast
iron plates were observed visually for rust and corrosion. No visible
corrosion was observed
on any plate. A separate test using a control jar containing an identical
hydraulic fluid, but
containing no ammonium hydroxide (e.g., Comparative Example 1) resulted in
heavy rust on
all three cast iron plates.
[00361 This test was repeated with W/G-based hydraulic fluids containing
ammonium
carbonate or ammonium acetate. No corrosion was observed on any of the cast
iron plates in
either test.
[00371 Figure 1 illustrates the corrosion inhibition effects of a present,
commercially
available W/G-based hydraulic fluid. The photograph of the cast iron plate on
the left shows
substantial vapor phase corrosion, whereas the cast iron plate on the right is
free of vapor
phase corrosion. The panel on the left was subjected to vapors of a W/G-based
hydraulic
fluid free of an ammonium salt, whereas the panel on the right was subjected
to vapors of an
identical W/G-based fluid, but containing 0.5%, by weight, ammonium hydroxide.
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[0038] Presently, no commercial W/G-based hydraulic fluid is suitable for food
related
uses because no food grade VPC additives have been available for such fluids.
In testing
various compounds approved for a direct food additive as a VPC inhibitor, it
was found that
only ammonium salts provided sufficient VPC protection, as demonstrated in the
following
Table 1.
Table 1
Vapor Phase corrosion Test a 145 F
Products Tested VPC Test VPC Test VPC Test
24 hrs 48 hrs 96 hrs
Standard Fluid 1), no VPC additive Fail Fail Fail
Standard Fluid with Sodium Nitrite Pass Fail Fail
Standard Fluid with Ammonium Hydroxide, FCC Pass Pass Pass
Standard Fluid with Ammonium Acetate, FCC Pass Pass Pass
Standard Fluid with Ammonium Carbonate FCC Pass Pass Pass
Standard Fluid with Sodium Carbonate FCC Fail Fail Fail
Commercial non-food Grade fluid Pass Pass Pass
Typical Comparative Example from above
[0039] Table 1 shows that hydraulic fluids containing no VPC inhibitor, or
containing
sodium nitrite or sodium carbonate, did not pass the VPC test for 48 hours or
96 hours.
Sodium nitrite passed the 24 hour test, but this length of time is
insufficient for practical fluid
applications. Hydraulic fluids containing ammonium hydroxide, ammonium
acetate, or
ammonium carbonate each passed the 96 hour VPC test. This VPC inhibition is
attributed at
least in part to volatilizing of ammonia, which imparts VPC inhibition to
exposed metal
surfaces. Tests using standard corrosion inhibitors, such as benzotriazole and
polyquaternary
compounds, failed to impart VPC inhibition because such compounds are not
volatile under
the operating conditions of the hydraulic fluid.
[0040] To further improve performance of a present W/G-based hydraulic fluid,
the
reserve alkalinity is increased to greater than 20 ml by the addition of a
buffering alkali.
Reserve alkalinity is important to increase the useful life of the fluid.
Hydraulic fluids having
a low reserve alkalinity start exhibiting high wear in a shorter period of
time.
[0041] In this test, sodium carbonate (0.5%, by weight) was added to a W/G-
based
hydraulic fluid containing 0.25%, by weight, ammonium carbonate. The addition
of sodium
carbonate increased the reserve alkalinity from 15 m] to 22.5 ml. The W/G-
based hydraulic
fluid was operated at standard conditions of 150 F, and 1500 and 1750 psi. A
pump test
performed using the procedure of ASTM D2882 show on average wear one replicate
tests of
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less than 70 mg wear. The ASTM D2882 test is conducted at 2,000 psi (13.8 MPa)
for 100
hours and eight gallons per minute (30.6 L/min) in a Sperry Vickers V-1040
vane pump.
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