METHOD AND APPARATUS FOR AUTOMATED COATING OF ELECTRICAL INSULATORS WITH A SILICONE COMPOSITION

METHODE ET APPAREIL PERMETTANT D'APPLIQUER AUTOMATIQUEMENT UN REVETEMENT A COMPOSE DE SILICONE SUR DES ISOLATEURS ELECTRIQUES

English Abstract

The present invention provides an automated continuous coating apparatus for coating industrial components such as porcelain, glass, and polymeric insulators. The apparatus consists of a several stage continuous inline operation. The stages are a cleaning operation, followed by drying and heating, coating, and curing.

French Abstract

La présente invention concerne un appareil d'application automatisée et continue de revêtement pour appliquer un revêtement sur des composantes industrielles comme la porcelaine, le verre et les isolants polymères. L'appareil comprend une opération en ligne, continue, comportant plusieurs étapes. Les étapes sont une opération de nettoyage, suivie du séchage et du chauffage, de l'application du revêtement et du durcissement.

Claims

Claims:
1. An apparatus for automatically coating an electrical insulator with a
silicone
elastomeric coating in a continuous inline operation the apparatus comprising:
a cleaning station for cleaning surfaces of the electrical insulator;
a drying and heating station to dry the surfaces of the electrical insulator
and
heat the surfaces of the electrical insulator to aid in adherence of a
silicone elastomeric
coating;
a supply of a curable silicone elastomeric composition;
a coating station to apply a coating of the curable silicone elastomeric
composition on the exposed surfaces of the electrical insulator, wherein the
coating
station comprises a robotic apparatus with a spray nozzle programmed to spray
the
curable silicone composition onto exposed surfaces of the electrical
insulator;
a curing station to accelerate the curing of the curable silicone elastomeric
composition, wherein the curing station comprises a chamber having an
atmosphere of
70-80% relative humidity at about 60° C. to accelerate curing of the
curable silicone
elastomeric composition on the surfaces of the electrical insulator; and
a conveying means for holding the electrical insulator and moving the
electrical
insulator through the automated apparatus, comprising a conveyor for conveying
the
electrical insulator through the stations, an electrical motor coupled to the
conveyer, and
a coupler for releasably coupling the electrical insulator to the electrical
motor, wherein
the electrical motor is configured to rotate the electrical insulator about a
vertical axis as
the electrical insulator passes through the stations.
2. The apparatus according to claim 1 wherein the curable silicone
elastomeric
composition is a one-part room temperature vulcanizable composition.
3. The apparatus according to claim 2 wherein the cleaning station comprises
one
or more nozzles dispensing steam, hot water or solvent onto the surfaces of
the
electrical insulator.
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4. The apparatus according to claim 3 wherein the cleaning station comprises a
plurality of nozzles dispensing blasts of hot water onto the surfaces of the
electrical
insulator to clean the surfaces of the electrical insulator.
5. The apparatus according to claim 4 wherein the drying and heating station
comprises a hot air blower blowing hot air over the surfaces of the electrical
insulator to
dry and heat the surfaces of the electrical insulator.
6. The apparatus according to claim 1, wherein the coating station is
maintained
with at least a partially nitrogen enriched atmosphere so as to prevent
skinning.
7. An apparatus for automatically coating an electrical insulator with a
silicone
elastomeric coating in a continuous inline operation the apparatus comprising:
a cleaning station for cleaning the surfaces of the electrical insulator;
a drying and heating station to dry the surfaces of the cleaned electrical
insulator
and heat the surfaces of the electrical insulator to aid in adherence of a
silicone
elastomeric coating;
a supply of a curable silicone elastomeric composition;
a coating station to apply a coating of the curable silicone elastomeric
composition on the exposed surfaces of the electrical insulator, wherein the
coating
station comprises a robotic apparatus with a spray nozzle programmed to spray
the
curable silicone composition onto exposed surfaces of the electrical
insulator;
a curing station to accelerate the curing of the curable silicone elastomeric
composition, wherein the curing station comprises a chamber having an
atmosphere
having a relative humidity within a preselected range at a preselected
temperature, the
humidity range and the temperature being selected to accelerate curing of the
curable
silicone elastomeric composition on the surfaces of the electrical insulator;
and
a conveying means for holding the electrical insulator and moving the
electrical
insulator through the automated apparatus, comprising a conveyor for conveying
the
electrical insulator through the stations, an electrical motor coupled to the
conveyer, and
a coupler for releasably coupling the electrical insulator to the electrical
motor, wherein
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the electrical motor is configured to rotate the electrical insulator about a
vertical axis as
the electrical insulator passes through the stations.
8. The apparatus according to claim 7 wherein the curable silicone
elastomeric
composition is a one-part room temperature vulcanizable composition.
9. The apparatus according to claim 8 wherein the cleaning station comprises
one
or more nozzles dispensing steam, hot water or solvent onto the surfaces of
the
electrical insulator.
10. The apparatus according to claim 9 wherein the cleaning station comprises
a
plurality of nozzles dispensing blasts of hot water onto the surfaces of the
electrical
insulator to clean the surfaces of the electrical insulator.
11. The apparatus according to claim 10 wherein the drying and heating station
comprises a hot air blower blowing hot air over the surfaces of the electrical
insulator to
dry and heat the surfaces of the electrical insulator.
12. The apparatus according to claim 7 wherein the preselected range is about
70-
80% relative humidity and the preselected temperature is about 60° C.
12

Description

CA 02537740 2006-02-27
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TITLE: METHOD AND APPARATUS FOR AUTOMATED COATING OF
ELECTRICAL INSULATORS WITH A SILICONE COMPOSITION
FIELD OF THE INVENTION
The present invention is directed to an automated
continuous coating apparatus and method and in
particular, to a coating apparatus for coating components
such as, high voltage line insulators with silicone
rubber coatings, more particularly with one component
room temperature vulcanizable (RTV) silicone rubber.
BACKGROUND OF THE INVENTION
Components utilized in industrial structures are
frequently exposed to a corrosion environment and must be
protected. For example, insulators utilized in
electrical utilities such as suspension insulators in
high voltage power transmission lines are designed to
keep to a minimum, current discharge under normal
conditions. However, when the insulator surface becomes
contaminated, leakage current can develop along the
surface of the insulator. The amount of this leakage
current depends upon the voltage stress and conductivity
of the film or contaminant on the surface of the
insulator. The leakage currents can incur or cause
arcing on the surface of the insulator which can have
serious effects upon the insulator surface such as the
formation of free carbon and non-volatile semiconductor
materials. It may eventually result in a conducting path
forming across the surface of the insulator and
effectively shorting out the insulator.
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The outer surface of the electrical insulator is the most
important part of the insulator as this is the part that
is subjected to the effects of electrical voltage stress,
leakage currents and weathering. When the surface of the
high voltage insulator is exposed to moisture such as
rain or fog in combination with contaminated atmospheres
as are found in industrial locations, the surface may be
subject to extensive corrosion unless protected in some
way from exposure to the corrosive atmosphere. Other
potentially corrosive environments include along sea
coasts where salt spray is found and in areas where
agricultural chemicals are widely distributed.
More and more electrical utilities are switching toward
the use of a one component room temperature vulcanizable
(RTV) silicone rubber coating for these high voltage line
sulators. By coating the surface of the insulator with
the electrically non-conductive material, the coating
provides for improved insulation that is arc resistant,
hydrophobic and resistant to the stresses imposed upon
such electrical insulators. This results in increased
tin of the insulator between scheduled maintenance as
well as increased overall life of the insulator.
Examples of such coatings are shown for example in the
applicant's prior US patents and applications,
specifically 6,833,407 issued December 21, 2004;
6,437,039 issued August 20, 2002; 5,326,804 issued July
5, 1994; 2004/0006169 published Jan. 8, 2004 and
2003/0113461 published June 19, 2003.
In addition to electric insulators, other components for
industrial structures would also benefit from the
automated application and method such as that of the
present invention.
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These insulators are manually coated on the ground and
strung on the overhead transmission lines. This is not
only labour and cost intensive, but also time consuming,
especially for industrialized countries. Thus, there
remains a need for a cost effective rapid method of
coating a large number of insulators.
SUMMARY OF THE INVENTION
The present invention provides an automated continuous
coating apparatus for coating industrial components such
as porcelain, glass, and polymeric insulators with a
silicone elastomeric coating. The apparatus consists of
a several stage continuous inline operation. The stages
are a cleaning operation, followed by drying and heating,
coating, and curing.
An aspect of the invention provides an apparatus for
automatically coating an industrial component with a
silicone elastomeric coating in a continuous inline
operation, the apparatus comprising:
a conveying means for holding the industrial
component and moving the component through the automated
apparatus;
a cleaning station for cleaning the surfaces of the
component;
a drying and heating station to dry the surface of
the cleaned component and heat the surface of the
component to aid in adherence of a silicone elastomeric
coating;
a coating station to apply a coating of a curable
silicone elastomeric composition on the exposed surfaces
of the component; and
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a curing station to accelerate the curing of the
silicone elastomeric composition.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention are
illustrated in the attached drawings in which:
Figure 1 is a schematic view of a first embodiment of a
continuous coating apparatus of the present invention;
Figure 2 is a perspective view of a preferred embodiment
of the conveying apparatus of the present invention;
Figure 3 is a perspective view of a preferred embodiment
of a spray nozzle arrangement for coating of the present
invention;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
20The present invention is directed to an automated
continuous coating apparatus for coating industrial
components such as porcelain, glass or polymeric
insulators with a silicone coating composition. The
apparatus consists of a several stage continuous inline
operation as illustrated in Figure 1. The first stage of
the apparatus is cleaning and set up for ensuring that
the surface of the insulator is free from any materials
such as oils, grease, dust or other soils which may
interfere with the adherence of the silicone coating to
the insulator surface. The cleaning of the insulator may
be accomplished by any of the methods commonly utilized,
such as steam cleaning, hot water spray, hot water
blasts, solvent wiping or dry ice blasting. Preferably
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the cleaning operation utilizes either steam cleaning or
hot water blasting. In order to improve the cleaning
efficiencies, detergent and other washing aids may be
added to the cleaning solutions to help in the removal of
organic materials or other soils from the surface of the
insulator. Once the insulator has been washed with the
cleaning solution, it is preferably rinsed with a clean
steam or hot water blast.
Once the insulator has been cleaned, it then passes to a
drying and heating apparatus where any moisture remaining
on the insulator is evaporated in this apparatus.
Preferably the apparatus moves heated air across the
surface of the insulator to improve the drying and
heating. Most preferably this is accomplished by the use
of a hot air blower blowing air at approximately 40 C to
150 C, preferably 40 C to 80 C, more preferably about
60 C through the apparatus. During the drying stage, the
insulator is also heated to a desired temperature level.
This heating of the insulator aids in the application and
curing of the silicone composition to the surface of the
insulator.
Once the insulator has been dried and heated, it passes
through a coating apparatus in which the surface of the
insulator is coated with a uniform coating of a silicone
composition. The silicone composition is preferably as
taught in our previous patents and applications,
specifically 6,833,407 issued December 21, 2004;
6,437,039 issued August 20, 2002; 5,326,804 issued July
5, 1994; particularly the one part RTV compositions shown
in U.S. Patent 5,326,804 issued July 5, 1994.
This coating may be accomplished by many/

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different processes. In one process, the coating is
applied by a dip coating wherein the insulator is dipped
in a bath of silicone material to allow the material to
cover and adhere to the surface of the insulator.
Preferably in order to maintain the uniformity of the
coating on the insulator, the insulator may be rotated at
a speed sufficient to provide for the desired coating
level on the insulator surface. The viscosity of the
silicone composition is also controlled to allow the
composition to coat the entire surface of the insulator.
When utilizing dip coating, the dipping area is
maintained under a nitrogen atmosphere to avoid skinning
of the surface of the silicone composition.
The silicone composition may also be applied to the
surface of the insulator by a spray means. This may be
accomplished utilizing one or more spray nozzles
directing the composition at the surface of the insulator
to coat the surface with the uniform coating of the
composition. Preferably, in order to uniformly coat the
entire surface of the insulator, the insulator may be
rotated such that the spray of the composition from the
nozzle coats the entire surface of the insulator. More
preferably, in order to coat both the upper and lower
surfaces of the insulator, at least two nozzles are
provided in the spray apparatus, one above the path of
the insulator through the apparatus, and one below the
path of the insulator through the apparatus. In some
circumstances with some configurations of insulators, it
may also be advantageous to provide more than one nozzle
at one or both of the upper and lower surfaces of the
insulator as illustrated in Figure 3. Alternatively, a
robotic apparatus utilizing a single spray nozzle
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programmed to spray the exposed surfaces of the insulator
may be utilized.
Once the silicone composition has been applied to the
surface of the insulator, the silicone coating is then
allowed to cure. Preferably, in order to increase the
curing of the silicone composition, the coated insulator
is placed in a curing chamber, such as an oven for one
part RTV silicone coatings, to decrease the amount of
time required for the coating to cure. Preferably for
RTV systems the curing chamber or oven is maintained at
approximately 60 C with 70-80% relative humidity. For
other cure systems such as a radiation cure system, for
example UV cure, the oven is provided with a suitable
radiation source, for example UV lighting to initiate and
accelerate the curing. In these applications, the oven
may also be supplied with a nitrogen atmosphere. For
coatings utilizing a volatile solvent, a flash oven with
an explosion proof chamber is provided prior to the
curing chamber to remove the volatile components. By
providing the curing chamber or part of the system, the
standard curing time is greatly reduced. For example,
the standard curing time of several hours for a one-part
RTV silicone is reduced to less than one hour. This
allows the insulator to have an improved quality and
consistency of the coating thickness combined with an
increased hourly production rate of coated insulators to
cut down the production costs significantly.
Once the coated insulator has properly cured, the
insulators are then inspected and packaged for shipping
to the final customers.
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The automated coating line of the present invention
utilizes a conveyor system to move the insulators through
each of the stages of the operation. Preferably, the
conveying apparatus utilized also allows for rotation of
the insulator through the stages to allow for uniform
treatment of the surface of the insulator as described
above. In one embodiment, this is accomplished by
providing a rotating means to rotate the insulators at a
slow rate such as an electric motor as illustrated in
Figure 2. The insulator is releasably clamped to the
rotation means to which holds onto the insulator during
its motion through these stages of the coating apparatus.
The electric motors and clamps are disposed along a
conveyor means to move through the stages of the
apparatus.
Other means of providing the conveying and rotation of
the insulators through the apparatus may also be provided
such as, for example, a dual-speed belt or chain drive
such that the clamp for the insulator is connected to a
gear driven simultaneously by the two belts or chains as
the belts or chains are travelling at different rates of
speed in the same direction. The gear and attached
insulator rotates as it moves along the line.
Alternatively, if each of the cleaning and coating
stations are provided with robotic spray apparatus, it
may not be necessary to rotate the insulators throughout
the apparatus.
The following example is used to illustrate a preferred
embodiment of the present invention, but the invention is
not limited to this embodiment.
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In a preferred embodiment of the automated coating
apparatus of the present invention, the conveying
apparatus moves the insulators along at a speed of
approximately 5 metres per minute while rotating the
insulators at a rotation speed of 12 revolutions per
minute. The insulator is washed in the washing station
for approximately 1 minute followed by 1 minute drying
time. The insulator is then coated in the spray booth
for about 5 seconds before travelling to the curing
chamber in which it is heated at 60 C for 20 minutes to
cure the coating on the insulator. The insulator is then
wrapped in the packaging. The apparatus of the present
invention allows for a high throughput coating of
electrical insulators with a throughput of approximately
500 insulators coated for every hour of operation. This
results in significant labour and cost savings for
coating of the high voltage insulators.
Although various preferred embodiments of the present
invention have been described herein in detail, it will
be appreciated variations may be made thereto without
departing from the spirit of the invention.
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Representative Drawing