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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to cleaning electrical contacts from traces
of contaminants so that good contact can be made between electrically
conducting surfaces. Particularly, it pertains to use of terpene
hydrocarbons and ketone blends as an environmentally safer substitute for
Freon 11 and Freon 13 for the cleaning of printed wiring circuit boards,
etc.
2. Background Art
The electrical power industry has traditionally employed solvent based
cleaning agents to remove traces of dirt and moisture from their
equipment. In any electrical field it is very important that no
contaminants remain behind on such contact surfaces because this can cause
dangerous arcing and serious damage to both equipment and its operators.
For this reason, for many years solvent based cleaners, such as 1,1,1
Trichloroethane have been utilized to perform such tasks. This material
was frequently used because of its high dielectric strength and its very
fast evaporation rate. However, because of its high toxicity and hazard to
the environment, an alternative method is now deemed necessary. 1,1,1
Trichloroethane upon inhalation causes a drastic in drop blood pressure,
can be the cause of unconsciousness and even death when inhaled in large
amounts. This product is also known to cause damage to the kidneys, liver,
spleen, and blood can occur when ingested.
On the other hand, Freon 11 and Freon 13 which are chlorofluorocarbons
evaporate very quickly but are very destructive to the ozone layer of the
atmosphere and thus are no longer considered acceptable because of their
destructive effect on the environment.
Newly developed hydrochlorofluorocarbons liquids are ozone safe but contain
chlorine and fluorine which are not safe to the water supplies and soil.
For these reasons, as well as their extremely high cost, it makes them
unacceptable for this use.
Many other solvents have also been tried as electrical contact cleaners and
circuit board cleaners, such as isopropyl/acetone mixtures which are
extremely flammable, and non-biodegradable thus making them unacceptable
for use as a cleaning aid. Alcohols also may carry moisture into a system
and cause corrosion problems. Alcohols also are not good at dissolving
oils and thus do not clean well. Petroleum distillates such as mineral
spirits do not evaporate quickly and in general are very flammable and
therefore dangerous to use.
SUMMARY OF THE INVENTION
In the electrical power industry it is common practice to employ a solvent
to remove moisture from "hot sticks" which are fiberglass probes used to
check high voltage circuits for current flow. It has been determined that
cyclohexanone is a solvent which is highly effective in removing moisture
from surfaces because it has a 2.3% solubility in water and can remove
such moisture leaving the "hot sticks" dry and safe for use. It has also
been found that cyclohexanone is an extremely useful cleaner for home
electrical meters which need to be cleaned with an appropriate drying
solvent so as to make them ready for use again.
An important feature of the use of cyclohexanone is its relatively high
flash point of 116 degrees Fahrenheit (open cup) and 141 degrees
Fahrenheit (closed cup). While this is not as good as Freon or
hydrochlorofluorocarbon solvents which are non-flammable, it is
sufficiently good so as to allow for safe handling. Other non-halogenated
solvents having flash points which are much lower, such as
acetone-isopropyl alcohol mixtures which typically have flash points of
-10 degrees Fahrenheit (open cup). Thus these solvents have been found
unacceptable for safe usage. Cyclohexanone has an evaporation rate of 0.38
(while water is typically 1). With this fast evaporation rate for
cyclohexanone, it is best for this application because too fast an
evaporation rate will not be able to dissolve all contaminants. On the
other hand, cyclohexanone evaporates leaving no residue behind, thus
leaving the surface system completely clean and ready for use. See TABLE
#1.
Cyclohexanone has a dielectric strength of 28 KV or 28,000 volts which
makes it a safe solvent for use around electrical equipment. Because of
this high value, it is unlikely a flashover will occur in most situations.
In accordance with American Society for Testing Materials Standard D8577 a
cell containing two disk electrodes was utilized. The solvents were run in
triplicate. If the results varied by more than 2 KV, the test cell was
cleaned and flushed with the contact cleaner product before retesting. See
TABLE #2.
Because Dipentene is a natural product extracted from trees (a terpene), it
is attackable by bacteria found in nature. Therefore, Dipentene may be
considered as biodegradable within 28 days.
TABLE #1
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Product Evaporation Residue
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Hydrochlorofluorocarbon
Fast None
Dipentene/ketone blend
Moderately Fast*
None
Naptha Slow None
alpha-phenanthrene
Slow Trace
D-limonene Slow Trace
mineral spirits Slow None
1,1,1 Trichloroethane
Fast None
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Evaporation rates are judged as follows:
0-30 seconds
Very Fast
31-60 seconds
Fast
61-90 seconds
Moderately Fast
*Most desirable
91-150 seconds
Moderate
>150 seconds
Slow
TABLE #2
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Dielectric Strength
ASTM D8577
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Hydrochlorofluorocarbon
16
Dipentene/ketone blend
28
Naptha 18.5
alpha-phenanthrene
22.5
D-limonene 12
mineral spirits 21
1,1,1 Trichloroethane
26
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Corrosion tests have also determined that oxidation is a potential hazard
of all contact cleaners. Tests with strips of copper and steel measuring
1" wide by 6" long by 20 mil thick were buffed on a belt sander to remove
any oxide films. Fifty milliliters of solvent was placed in a cylindrical
Pyrex glass container and the strips were placed in so that 75% of the
surface was immersed in the solvent. A sample container filled with tap
water was used as a control for test. This would ensure that there were no
alloys in the metal strips that would prevent oxidation. The opening of
the sample containers were sealed with cork stoppers to reduce
evaporation. All of the solvents found tested in TABLES 1 and 2 were found
to be non-corrosive.
Dipentene/ketone should be sprayed on copper and other conductive surfaces
which may be found in electrical contacts on meters, cables, transformers,
switches, relays and fiberglass "hot sticks". The solvent should then be
allowed to evaporate leaving the surface clean and ready for use.
Effective removal of dust and spot free cleaning of circuit board and
electronic components can be accomplished by using Dipentene/ketone as a
cleaning aid. The Dipentene/ketone needs to be free of particulates and
moisture before dipping or spraying printed circuit boards or electronic
components. This can be accomplished by filtering the cyclohexanone
through a 0.1 um millipore filter to remove any particulates which may
cause contamination of electronic components. A standard cellulose drying
filter which was pre-dried in an oven at 110 degrees Centigrade can be
used to remove any moisture from the Dipentene/ketone blend.
The printed circuit boards should be sprayed or dipped into the
Dipentene/ketone solvent and allowed to air dry for at least 15 minutes to
allow all of the solvent to evaporate completely. A drying oven may also
be used to force dry the solvent from the desired surface. A temperature
of 60 degrees Centigrade is satisfactory to speed the drying process. The
printed circuit board or electronic components cleaned in this process
will now be free of dirt and moisture and ready for implementation.
Blending ketones with other solvents such as Dipentene can reduce the cost
of using ketones as an electrical contact cleaner.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention teaches a solvent selected from the terpene
hydrocarbon and ketone group and with best results obtained
Dipentene/methyl isoamyl ketone as a replacement for 1,1,1 trichloroethane
and chlorofluorocarbon solvent as an electrical contact cleaner. To
practice the invention, material may be utilized for proper cleaning of
rubber gloves, fiberglass "hot sticks", electric meters, switches, relays,
transformers, cables, and circuit boards. The material to be effective
must have a 1-3% solubility in water, have a flashpoint of 118 degrees
Fahrenheit (closed cup), and must not dissolve synthetic cable insulation.
The solvent should also have a dielectric strength of at least 25,000
volts, and an evaporation rate of at least 0.40 (where water is employed
as a standard at the rate of 1.0). The solvent must also evaporate
completely, leaving behind no residue and contain no halogens.
Usage of the above described solvents would be similar to those described
in the following when as an example to prevent arcing on rubber gloves it
is considered to be desirable to prepare a 90:10 blend of Dipentene and
methyl isoamyl ketone (MIAK), then carefully hold a pair of linemen's
rubber gloves typically made of ethylene propylene diamine monomer, or
EPDM) and pour the Dipentene/methyl isoamyl ketone mixture over their
outside surface until they are completely covered with solvent. After this
is completed, the solvent is allowed to evaporate completely, with the
procedure repeated every 20 minutes as long as work is being performed on
high voltage equipment.
Another example, to prevent arcing on fiberglass "hot sticks" used in
checking high voltage circuits, a 90:10 blend of Dipentene and methyl
isoamyl ketone is prepared with the solvent poured over a fiberglass "hot
stick", pouring the solvent over the entire surface of the stick until it
is soaked. After this the solvent is permitted to evaporate completely,
the procedure being repeated every 20 minutes as long as work is being
performed on high voltage equipment.
Another use for the present solvent includes the removal of grease from
high voltage cables is facilitated by preparing the 90:10 blend of
Dipentene and methyl isoamyl ketone, opening the insulation on the cable
until the copper conductor is exposed. At this point the solvent blend is
poured onto the exposed conductive surface, after which excessive cable
grease is wiped off along with the solvent mixture with a clean rag until
the surface is free of grease.
To clean transformer contacts of contaminants which may cause arcing is
accomplished by again preparing a 90:10 blend of Dipentene and methyl
isoamyl ketone. After this occurs, the cable is detached from the cable
terminals, a generous amount of the solvent is sprayed onto the
transformer terminals and onto the cable connectors. At the completion of
this step, excess solvent is wiped off with a clean rag until the surfaces
are clean of contaminants. After this, it is appropriate to reattach the
clean cable connectors to transformer terminals. This procedure is
repeated for electrical contacts on electric meters, switches, relays or
other high voltage electrically conductive surfaces.
To clean printed circuit boards of dirt and other contaminants, again a
90:10 blend of Dipentene and methyl isoamyl ketone is mixed, after which
the 90:10 blend is passed through a 0.1 micron filter to remove
particulates. The circuit boards are then dipped into the solvent in a
circulating chamber for 1-5 minutes. After this period, the circuit boards
are removed from the solvent and the solvent is allowed to evaporate for
about 15 minutes with the cleaned circuit boards being placed in an oven
preheated to 60 degrees Centigrade for 5 minutes to speed evaporation of
the solvent.
It should also be noted that other ketones, such as acetone, methyl ethyl
ketone, methyl isobutyl ketone and cyclohexanone may also be used as a
substitute for methyl isoamyl ketone in the above examples.
Other terpene hydrocarbons such as alpha-pinene, beta-pinene, nonal,
octanal, para-menthadiene, para-cymene and turpentine may be used as a
substitute for Dipentene in the above examples.
It should be noted that while several uses of the embodiments of the
present invention have been shown, it will be obvious to those skilled in
the art that numerous modifications to the processes disclosed herein may
be made without departing from the spirit of the present invention which
shall be limited only the scope of the claims appended hereto.
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