FIELD OF THE INVENTION
The present invention relates to a micro wave assisted fast drying
process for porcelain insulators, which is environment friendly and
facilitates drastic reduction in cycle time resulting in lower cost of
processing and lower rejection.
OBJECT OF THE INVENTION
- the object of the invention is to develop an improved method of
drying porcelain insulator.
- the another object of the invention is to reduce the drying cycle of
porcelain insulators in the range of 70 - 80% of the conventional
process
- further object of the invention is to reduce the consumption of
energy in the range of 20 - 40% of that conventional process.

- also the object of the invention is to reduce the percentage of
rejection of finished porcelain insulators.
- still another object of the invention is to retain all the electrical
and mechanical properties of the insulators after such fast drying
process.
- yet another object of the invention is to develop an environ-
friendly method for drying of porcelain insulators in replacement of
fossil fuel.
PRIOR STATE OF THE ART
Although microwave drying of clay bodies has been reported, not
much data available in the literature regarding the effect of
temperature on the moisture removal by microwave drying of
Porcelain insulators. Further, a major resistance from the production
group regarding the effect of fast microwave drying on the green
properties of the product has not been reported in the literature.

This is very important since ceramics are prone to generate defects
during fast water removal. The green defects can lead to
catastrophic failure during sintering. Further the drying of Indian
porcelain insulator using microwave energy has not been attempted.
This technology is appropriate due to ever raising cost for fuels.
BACKGROUND OF THE INVENTION
The manufacturing of porcelain insulator involves mainly three steps:
forming, drying, and firing. After forming they are dried in order to
achieve the critical moisture level below which there will not be
further shrinkage of the porcelain body during drying. The large
proportion of the selling price of these items represents energy costs.
While ceramic producers have always had a high awareness of
energy costs, they are increasingly motivated to act, as energy prices
increase and global competition intensifies. More than 70% of
energy in ceramics manufacturing is accounted for the drying and
firing process, with oil and gas as the predominant fuels.

The conventional drying of large ceramic components is a time-
consuming process and involves a combination of natural drying and
tunnel drying. Typically, for a porcelain insulator of >15 Kgs. of
weight, a natural drying of 5-7 days followed by tunnel drying of 5-7
days are required to remove ~ 17% moisture. Very fast drying by
conventional methods are not possible due to the defect generation
during fast removal of water from the wet core through the dried
surface. Porcelain manufacturing is a traditional process utilizing a
mixture of natural raw materials like clay and quartz and synthetic
raw materials like alumina. The conventional drying process has
many limitations including the high drying time, large space
requirement, low turnover and high manpower requirement. All
these factors lead to high cost of the product which is not feasible to
survive in the today's competitive market. In addition, there is a
threat to these industries due to the environmental pollution arising
from the burning of fossil fuels during processing. Therefore, a need
arises to develop a fast, efficient and environment friendly process
which suitably replace the conventional technology of drying in a

commercial scale. Microwave drying has proven to be such a
technology for the further growth of these industries.
To tackle this problem, an alternative method is microwave heating.
This is a most promising technology over the conventional one with
an advantage of time and energy savings. The process enables high
rate of heating resulting in product. Further, materials will
experience the minimization of grain growth leading to improved
mechanical strength. The volumetric heating will avoid any
temperature gradient inside body. The process is based on clean
electrical energy and thus is an environmental friendly technology.
The microwave drying of profiled porcelain insulators is complicated.
The profile of the insulator can be varied from uniform shaded core
to differential shaded core. The difference in moisture level in core
and shade poses problem in uniform drying in a conventional
process. However, because of the volumetric heating nature of the
microwave process, similar problems can be minimized with proper

control in humidity and drying rate during drying of these
components. Microwave drying of ceramic components is fairly a
new technology in ceramics industry.
DETAIL PISCRIPTION OF THE PREFERRED EMBODIMENT
According to the present invention, there is provided an improved
environment-friendly energy saving microwave process for fast drying
of shaped porcelain components in air from raw materials consisting
of Feldspar, washed clay, raw clay, quartz, alumina and other
additives comprising drying shaped component first in open air and
then in a microwave furnace using a suitable assembly in humid
condition inside the chamber; maintaining drying cycle in the furnace
from 10 - 15 hrs.; resulting a fully dried product with < 1% residual moisture, comparable mechanical properties like bend strength and
Modulus of elasticity and surface microstructure with those obtained
by conventional dried samples.

The present invention will be better understood by the narrated
description for an embodiment below with reference to the
accompanying figures and a table in which
Figure 1 represents the green porcelain components which were
experimented in this study for microwave drying (Initial
moisture content: 15-18%, final moisture content after
drying : < 1%).
Figure 2 represents the assembly used in drying the porcelain
insulators inside a microwave furnace.
Figure 3 represent the weight loss as a function of time for both
type of porcelain insulators subjected to microwave drying
Table 2 represents the time required to dry the porcelain
components in a microwave furnace compared to that in
a conventional manner.

The present invention provides an improved method for the
microwave firing of commercial grade and indigenously available
porcelain insulator components.
In a conventional commercial process, the raw materials are
intimately mixed with wet mixing in a ball mill followed by filter
pressing to obtain the cakes of desired hardness. These cakes are
used for further shaping of actual porcelain insulators, components
initially undergo natural drying in air at room temperature followed
by tunnel drying at a high temperature. The dried components are
sintered in a conventional gas/oil fired kiln at high temperatures
exceeding 1200 C.
In the improved method, the shaped components were directly dried
in a microwave furnace by avoiding the natural drying as the first
step used in conventional process. Figure 2 depicts a schematic of
samples (figure 1) placed in a microwave furnace for drying. The
temperature was measured with a K-type thermocouple after

switching off the microwave power at different intervals. The
advantage of this method is that the temperature on the sample will
not go beyond a temperature range of 60-70 deg C, which otherwise
will develop defects during processing. Further, the moisture level
was controlled by the introduction of blowing air inside the chamber
during drying process. Figure 3 represents the weight loss as
function of time for both type of porcelain insulators subjected to
microwave drying. Table 2 represents the time required to dry the
porcelain components in a microwave furnace compared to that in a
conventional manner.
The x-ray diffraction of the dried product is compared with that
obtained by conventional method (Figure 4) of a combination of
natural drying and tunnel drying at 130° C. Since, porcelain does not
undergo any phase change below 150° C, there was no change in
peak pattern observed confirming that microwave drying will not
change the composition of the component. The microstructure of the
dried product (Figure 5) after drying by the new method also

confirmed that there is no drastic change in surface morphology from
other processes. The Infrared Thermography test results (Figure 6)
on the dried products by both the methods indicate that, the product
dried by new method shows better thermal distribution compared to
its conventional counterpart. The Mechanical properties of the dried
products by the new methods revealed slightly better values
compared to those processed by conventional methods (Table 2).
Both three point bend strength and Young's modulus were measured
on the dried samples and compared. Further, the three point bend
strength data of a large number of samples were used to calculate
the reliability of the material after drying by both the processes. It
was observed that the Weibull Modulus (m) of the product dried by
the new method resulted significantly higher value (m = 15.6)
Compared that of 9.3 in the conventionally dried samples (Figure 7).
30 samples were used for this experimental analysis. All these
results indicate that the products dried by the new method will either
give comparative results or sometimes better results than the

conventionally dried products in addition to the energy and cost
savings and environment friendly nature of the technology.
The invention is illustrated with testing results wherein:
Figure 4 shows the x-ray diffraction patterns of conventionally
dried and new method of drying porcelain components in
air
Figure 5 shows the optical micrographs on the dried surface of the
porcelain components which were dried by both
conventional and the new method
Figure 6 shows the infrared thermographic image analysis of a disc
insulator after drying both by conventional and hew
method.
Figure 7 shows the theoretical calculation of Weibull Modulus from
the experimental data of three point bend strength of
dried products from both the methods

Table 1 shows the three point bend strength and Modulus of
Elasticity data of the product dried by the new method
and compared with those obtained from the conventional
dried products.
Two types of insulators were used for experiments in the new
method: solid core bus bar insulators weighing ~ 15-20 Kgs and
possessing an initial moisture level of ~ 15-17 % and disc insulator
weighing ~ 8-10 Kgs and with similar initial moisture content. The
experiments were carried out in a 6 kW Microwave furnace. An
assembly was created as depicted in figure 2 in order to avoid
moisture loss from the chamber during drying and uniform heating of
the products during the volumetric drying as achieved by the
application of microwave energy. The Air circulation was carried out
with the help of an outside blower.
In the new method, an insulator was kept in the drying chamber
after the turning operation. For the experimentation, a thermocool
enclosure was prepared which was covered with glass wool blanket
around it. The inside of thermocool was covered with Polymer sheets.
With this arrangement, the uniformity in temperature and humidity
inside the chamber could be properly maintained, which is most
essential for drying such items. The sample with 17 % initial

moisture level was dried at a microwave power level of 0.4-0.6 kW.
The temperature on the sample was measured initially in every 30
min. using a K-type thermocouple after switching off the microwave
power. The surface temperature was maintained at a maximum of
80° C in order to avoid damage in a long run. The microwave power
is switched off if the temperature exceeds 60° C and put On again
below this temperature. This ON and OFF cycle continued and the
weight of the samples was measured after a certain interval to check
the presence of moisture content in the product. The air circulation
during drying was carried out by connecting an air blower through a
duct into the microwave furnace. The air circulation assisted in
maintaining uniform temperature and humidity inside the drying
chamber so that drying was volumetric and coinciding with
volumetric heating of water by microwave radiation during drying.
The drying cycle was followed as per the curve obtained in figure 3.
It was observed that the drying rate slowed down and temperature
build up on the sample increased with increase in time. Therefore,
frequent measurement of temperature is essential in order to
maintain a peak temperature below 80°C during the later state of
drying. In all cases, the residual moisture after completion of drying
was <1%. The enclosure was further modified to PVC pipe enclosure
with glass wool insulation to further minimize the temperature
difference on the product inside the enclosure.

The dried products obtained by the new method were characterized
by different analytical techniques, as already discussed. Further, few
samples were also sent for sintering by conventional method at a
peak temperature of 1220 - 1240 C. The products were tested as
per the conventional mechanical electrical tests and all the results
were passed. The required phases were also formed after sintering
as tested by x-ray diffraction. Few pieces were also dispatched to
the customer alongwith the standard lots. This experiment further
builds up confidence that the samples dried by the new fast method,
did not deteriorate and can give improved product with required
phase content on sintering by conventional method.
The main advantages of the new and improved process are:
a) The improved method is extremely fast process and less energy -
intensive without affecting the properties of the component. This
translates into very low cost for the processing of such materials in
an industrial scale.
b) The new method produces dried components which have similar
or better properties than those of their conventionally processed
counterparts.

c) The dried products obtained by the new method are more reliable
as revealed by the higher value of the Weibull modulus than its
conventionally processed counterparts.
d) The new method is environment - friendly in nature and thus
avoids the depletion of natural resources like fossil fuels.
The invention as narrated herein with an embodiment and illustrated
with test results should not be ready and construed in a restrictive
manner as various adaptations, changes and modifications are
possible within the limit and scope of the invention as defined and
encompassed in the appended claims.
TITLE a novel environment-friendly microwave assisted
method for fast drying of porcelaininsulators
SUMMARY OF THE INVENTION
To achieve the objects, and purpose of the present invention, a
method has been developed which allows drying of porcelain
components using an environment friendly process. The processing
has been carried out using a microwave furnace operating at 2.45
GHz frequency. This method enables reduction of cycle time by 70 -
80% and reduction in energy cost by 20 - 40% over conventional

method. Further, the properties of the dried products as measured
by "different analytical techniques were shown to be either
comparable or in some cases better than their conventional
counterparts. The process is environment friendly since it does not
use the ever depleting fossil fuels for processing. The technology
developed here can be scaled up on a commercial scale in drying
porcelain materials in a cost-effective manner.

WE CLAIM
1 An improved method of fast drying of high voltage porcelain insulators with
core and shed structure in a microwave operated apparatus, comprising
drying porcelain components in the microwave apparatus at controlled
temperature,
circulating air through a duct inside the apparatus to control humidity and
volumetric heating of the components, characterized in that an uniform
temperature and humidity is maintained inside the chamber to prevent
development of temperature gradient inside the insulator body during
moisture removal leading to improved mechanical properties, and in that
the drying cycle is maintained for 12-18 hrs till final moisture content of the
components reaches < 1%
2 A method as claimed in claim 1, wherein the peak drying temperature
does not exceed 80°C

ABSTRACT

TITLE : "AN IMPROVED METHOD OF FAST DRYING OF HIGH VOLTAGE
PORCELAIN INSULATORS WITH CORE AND SHED STRUCTURE IN A
MICROWAVE OPERATED APPARATUS"
An improved method of fast drying of high voltage porcelain insulators with core
and shed structure in a microwave operated apparatus, comprising drying
porcelain components in the microwave apparatus at controlled temperature,
circulating air through a duct inside the apparatus to control humidity and
volumetric heating of the components, characterized in that an uniform
temperature and humidity is maintained inside the chamber to prevent
development of temperature gradient inside the insulator body during moisture
removal leading to improved mechanical properties, and in that the drying cycle
is maintained for 12-18 hrs till final moisture content of the components reaches
< 1%