Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~B~5
DEVIC~ FOR AUTO.~I~.~IC ADD-rTION OF A CORROSION
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INHIBITOR TO A COOLAM~ S~ST~M
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Descri~t~on
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The cooling system of an automotive vehicle
;nvolves the circulation of a li~uid coolant through
the enqlne ~lock of an ;nternal combust~on englne and
then through a heat exchanger or radiator ~y a nump
operated ~ the engine. T~e coolant removes heat from
t~e engine block during operation, and the radiator
cools the heated coolant by a forced air flow through
the radiator and around a plurality of tubes therein
carr~Iing the coolant. In view of the temperature
extremes in many parts of the countr~, the conventional
coolant is an approximately 50-50 mixture of ethylene
glycol with water.
Presently, automotive radiators are formed of
copper and/or bras-s, and the ethylene glycol, ~ith a
s~all percentage of diethylene glycol, is diluted ~7ith
water to make a 50% or lower concentration of glycol
depending on the desired freezing point protection.
?lost manufacturers or distributors of ethylene glycol
also add corrosion inhibitors to the solution; ~hich
inhibitors are usually a mixture of one or more lnorganic
salts, such as phosphates, horates, nitrates, nitrites,
2S silicates and arsenates, and an organic compound, such
as henzotriazole, tolyltriazole, or mercapto~enzothiazole,
to prevent copper corrosion. ~he solution ls generally
buffered ,o a pEr of 8~10 to reduce ixon corrosion and
to neutralize any glycolic acid formed in the oxidation
30 OI ethylene gl~col.
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Most manufacturers of ethylene ~lycoi recommend a
maximum of one or two years' service for th~ir antiL~eeZe,
however, the average car owner does not follow the
owner's ~anual instructions to maintain -2'' F. pro-
tection or check the coolant -to see if it is rusty or
dirty. r~any owners only add water when the antifreeze
is lost through leakage or hose breakage. In normal
passenger car service, 25% of the cars require coolant
system servicing a~ter one year; and after two years,
this rises to 50~. Wit~ a conventional copper-brass
radiator, it is extremely important that the antifreeze
mixture contains 50-55~ of the correctly inhibited
ethylene glycol. A reduction to 33~O ethylene ~lycol
67% water will increase metal corrosion significantly.
This is especially important with higher temperature
coolant systems which are becoming more common with the
increased use of emission controls.
At the present time, a concerted effort is being
made by the automobile manufacturers to increase gas
mileage to federally legislated standards by size and
weight reduction of the automobiles. To provide weight
reduction, lightweight metals and plastics are heing
substituted for present day heavier metal components.
One such area is in the use of aluminum in place of
copper and brass for automotive radiators. Aluminum
provides a high heat transfer capability, however,
there have been problems in dimensional stability,
corrosion resistance, and in the manufacture of the
aluminum structure.
In particular, the corrosion problems discussed
previously are considerably accentuated for aluminum
radiators and, where corrosive water is used to replace
the proper ethylene glycol-water mixture due to leakage
3~3
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or hose breakage during operation of the vehicle,
corrosion of the aluminum radiator is consi~erably more
rapid and destructive. Thus, the present invention
provides for automatic replacement of the corrosion
inhibitor to avoid the corrosion problems.
The present invention comprehends the provision of
a device designed to automatically add a suitable
corrosion inhi~itor to the coolant in an engine cooling
system in the event t~at the operator replaces lost
ethylene glycol solution ~ith water. The device is
designed as a hydrometer with a solid or liquid in-
hibitor in the hollow upper tube or stem above the
weighted end. The hydrometer could be placed in the
coolant overflow tank or, if small enough, in the
radiator tank. As the specific gra~ity of the coolant
decreases due to the addition of water, the hydrometer
tube will gradually drop until the inhibitor is contacted
by the coolant solution.
The present invention also comprehends the provision
of a device to add corrosion inhibitor automatically to
a coolant solution where a hydrometer has an upper tube
with small openin~s therein at a level opposite the
corrosion inhibitor. To provide for gradual additions,
separators may be placed between levels of corrosion
inhibitor so that the device will be operative over an
extended period of time.
One way;of carrying out the invention is described
in detail below with reference to drawings which illustrate
only one specific embodiment, in which:-
J/~ 3
Figure l is a side elevational ~iew with aportion broken away of a hydrometer containing corrosion
inhibitor.
Figure 2 is a side elevational vlew with a portion
broken away of the hydrometer with separakors between
inhibitor layers.
Referring more particularly ~o the disclosure in
the drawin~ wherein are shown illustrative embodiments
of the present invention, Figure 1 discloses a hydrometer
lO of conventional shape with an elongated tubular stem
ll terminating in an enlarged bulbous lower end 12
wherein a suita~le weight 13, such as steel shot, is
located.
The tubular stem has a graduated scale 14 thereon
to indicate speci~ic gravity of the coolant and a
plurality of small openings 15 in the stem generally
opposite a quantity of a suitable corrosion inhibitor
16 located within the stem and resting on a glass
separator 17. Assuming that the hydrometer lO is placed
in the overflow tank for the radiator (not shown) where
temperatures are unlikely to exceed 200 F., at the
proper specific gravity for the ethylene glycol-water
mix, the stem ll containing the corrosion inhibitor
will not contact the coolant. As water is added to the
coolant system to replace the loss of coolant, the
hydrometer will gradually drop as the specific gravity
decreases until the coolant can pass through the
openings 15 to contact the inhi~itor 16 and a portion
of it or all of it will dissolve, depending on the
contact area, which in turn depends on the water-
ethylene glycol concentration.
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As more specifically shown in the table, the
speci~ic gravity o~ the coolant will vary with con-
centration and temperature:
TAsLE I
S Volume Percent Solution Specific Gravity t/60F. in air
Ethylene Freezing Pt. O O
GlycolWater F. 60F. 150 F.200 F.
__
50-33.5 . 1.080 1.05G1.030
60-ll.0 1.064 1. 0371.018
10 30 70 ~.3 1.050 1. 0241.005
8015.7 1.034 1.0100.992
9024.6 1.020 0.9970,980
0 10032.0 1.004 0.9820. 966
Considering the data in this table, assuming the
15 hydrometer lO is located in the overflow tank at
approximately 200F., a 50-50 mixture ~Till have a
specific gravity of 1.030 and no inhibitor will con-tact
the coolant. However, if the specific gravity decreases
to 1. 020 through the addition of water, the hydrometer
20 will drop allowing part of the solid inhibitor to
dissolve. As the coolant dissolves the solid material,
the weight of the hydrometer may initially increase and
then decrease as the solid dissolves and is replaced by
water. To overcome this, a separator 17 is located
25 between each level 18,19,20 of inhibitor as shown in
Figure 2.
The weight of the inhibitor 16 is dependent on its
solid density. ~ixed powdered inhibitors can be compacted
to increase their density by compression molding. For
30 an average coolant volume of about 15 liters, requiring
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0.1% inhibitor for me-tal protection, the weight of
inhibitor needed ~ill be 15 grams. To increase the
inhibitor weight, it is necessary to increase the cross
sectional area of t~e hydrometer. For example, to
illustrate a simple case, assume the hydrometer is a
cylinder which sinks to a depth "a" in water and a
depth "x" in an ethylene glycol-water mixture of 50-50.
Let the weight of the cylinder be m and its cross
sectional area A.
lO Then mg = AapOg = Axpg
where pO = density of water, p = density
of ethylene glycol mixture and
g = the acceleration due to gravity.
This equation shows that as m increases, A must increase
for everything else to remain the same. In the hydro-
meters of both Figures l and 2, a rubber stopper 21
closes the open end of the stem 11.
