Note: Descriptions are shown in the official language in which they were submitted.
7~
MICROWAVI~ CURING OF RESIN
BACKG~OUND OF TIIE INVlillTlON
During the last five years, conservation of fuel and
energy has become of primary importance to industry. Oil, gas, and
5 electric power have increased in cost. The availability of oil and gas
has periodically become critical, forcing industry to either slow
down or stop. Coal is one of the United States' most availflble fuels,
but it lacks the convenience of oil or natural gas. Coal, however, is
a viable source for the production of electricity. Hydroelectric and
10 atomic power stations also contribute significantly to the production
of electric power. Therefore, it is probable that electric power will
be the most dependable source of power for the future.
When compared to gas or oil, electric heat is more ex-
pensive and is not preferred when alternatives exist. As shown in
15 Table 1, the cost of heating with electricity is a~out four times as
expensive as natural gas (as of March 1, 1979).
TI~BLE 1
COST
TYPE Btu/UNIT PER UNIT Btu/
OE FUE1 OF MEASURE (U.S. Currency~ $1.00
Electricity 3413 Btu/kWh $0.0282/kWh 121,028
Natural Gas 1000 Btu/Ft.3 0.2250/100 Ft3 444,444
Fuel Oil #2 140000 Btu/Gal. 0.5000/Gal. 280.000
Fuel Oil #6 144000 Btu/Gal. 0.2817/Gal. 511,182
When any form of energy is used to heat air in an ~ven
and, in turn, electrical parts passing through that hot air, the
efficiency of heat transfer is quite poor. The key to using electric
energy is in the efficient transferal of that energy to the parts ~eing
heated.
..~
~S'^~80~
Microwave technology for horne and industrial use has
been nvailable for 20 years. Yet industry has been slow to accept
and use microwave. Where metals were concerned, it seemed ob-
vious that they would reflect the microwaves and, therefore, would
S not heat.
S~MMARY O~ TH~ INVlE3NTION
Contrary to what would have been expected, it has now
been found that when armatures, stators, transformers and coils are
placed in a microwave field their temperatures increase at a surpris-
10 ing rate. This enables rapid cure of a varnish or enamel coating.
The microwave curing has been found to be effective whether the
metal is in coil form or in a laminate with a dielectric material
inbetween, e.g., in a capacitor configuration.
There can be employed as metals, the following; iron,
15 copper, silver, aluminum, nickel, zinc or alloys, e.g., steel. For
electrical purposes there usually is employed copper, aluminum and
electric~rade steel.
In the working examples below the microwave oven em-
ployed was mDdel SMC 1-33H of Despatch Industries, Inc. and des-
20 cribed in their catalogue 600-978 on pages 16-17.
For microwave curing, it was found that the ~eneral
ranges of 900 to 950 megahertz and 2400 to 2500 megahertz were
best suited. Based on these findings, equipment was employed which
had been set at 2450 megahertz with a variable power supply of 0 to
25 1 kWh(3.6x106 joules). A mode stirrer and turntable were included
in the oven to direct the microwave field randomly in the cavity.
Microwave energy is traditionally considered to be ap-
proximately 30 to 35% efficient. For every kWh of power drawn,
only 0.300 to 0.350 kWh~1.08x106 to 1.26x106 joules) arrives in the
30 cavity. These estimates were found to be quite accurate. Table 2
shows that the best efficiency is obtained when the demand is high
( ~ 50%). A recording ammeter, voltmeter, and power-factor meter
were used to determine how many kWh were used at each power set-
7l~
ting. At the same time, the number of kWh's delivered to the cavity
WAS accurately determined by measuring the heat rise in a predeter-
mined amount of w&ter. This value divided by the total power com-
ing into the oven determined the efficiency. Contributing to the
5 loss in efficiency was the use of motors for the mode stirrer,
turntable, and exhaust fans.
TABLEr. ~
(1) (2)
1 0 (Joules x 106)
In Oven % Efficiency
Total k Wh Cavity Calc.
96 Power (Joulesx 106) On Water (2) X 100
Output_ Drawn ~e~ m
.
150(Standby) 0.699(2.516) 0(0)
0.754(2.714) 0.053(0.191) 7.0
0.967(3.481) 0.152~0.547) 15.7
1.118~4.~25) 0 268(û.965) 24.0
1.328(4.781) 0.350(1.260) 26.4
20 50 1.5a8(5.501) 0.462(1.663) 30.2
1.738(fi.257) 0.570(2.052) 32.8
1.985(7.146) 0.715(2.574) 36.0
2.262(8.143) 0.800(2.880) 35.4
2.576(9.274) 0.8~0(3.168) 34.2
25 100 3.062(11 023) 1.080(3.888) 35.3
It has been found that the secondary efficiency (the
conversion of microwave energy to heat in the electrical parts) more
than compensates for the initial inefficiency from source to cavity.
This process of the present invention can be used to
30 cure any thermosetting resin on a metal coil or metal laminate with
a dielectric material inbetween. Thus there can be used any of the
conventional resins employed for coating metals, e.g., electrical
conductors in the form of insulating varnishes and enamels. Thus for
example there can be employed curable polyesters from a dihydric
35 alcohol such as ethylene glycol, propylene glycol, neopentyl glycol,
2,2,4,4-tetramethyl-1,3-cyclobutanediol, butanediol-1,4 and a poly-
hydric alcohol containing at least three hydroxyl groups, e.g.,
57~ 5
glycerine, tr~s (2-hydroxyethyl) isocyanurate, trimethylolpropane,
and a polychrboxylic acid, e.g., 4,4'~enzophenone dicarboxylic acid,
terephthalic flcid, isophthalic acicl, the imide dicarboxylic acid
prepared from trimellitic anhydride with oxydianiline or methylene
5 dianiline, o-phthalic acid, adipic acid, trimellitic acid, trimesic acid.
There can also be employed other thermosetting resins
such as phenol-formaldehyde, cresol-formaldehyde, phenol-furfural,
melamine-formaldehyde, epoxy resins, e.g., bisphenol A-epichlor-
hydrin, glycerine-epichlorhydrin, unsaturated polyesters, e.g., from
10 glycols such as those mentioned above with an unsaturated dicar-
boxylic acid, e.g., maleic acid, fumaric acid or itaconic acid with or
without other polycarboxylic acids, e.g., adipic acid, succinic acid,
terephthalic acid, isophthalic acid, o-phthalic acid and an unsatur-
ated monomer such as styrene, diallyl phthalate, t~utyl styrene,
15 methyl methacrylate, methyl acrylate, vinyl toluene, etc.
Thus there can be used any of the thermosetting resins
set forth in Laganis U.S. patent 3,338,743, Meyer U.S. patent
3,342,780, Meyer U.S. patent 3,4259866, Laganis, U.S. patent
3,108,083, Meyer U.S. patent 3,249,578, Sheffer U.S. patent
3,312,573, Jordan U.S. patent 3,296,024, Laganis U.S. patent
4,016,330, Sheffer U.S. patent 3,523,820, Galkiewicz U.S. patent
4,073,826, Laganis U.S. patent 4,105,639, Keating U.S. patent
4,119,758, Laganis U.S. patent 4,133,787, Sheffer U.S. patent
2,982,754, Laganis U.S. patent 3,479,307, Jordan U.S. patent
3,480,589, Laganis U.S. patent 3,498,940, Jordan U.S. patent
3,646,374, Sheffer U.S. patent 2,889,304 and Laganis U.S. Patent
4,196,109.
BRIE~ DESCRIPTION O~ THE DRAWING
The single figure of the drawings is a diagram showing
30 how five coil bobbins were positioned in the cavity of the furnace.
Unless otherwise indicated all parts and percentages are
by weight.
131 S~7t~)S
D~SCRIPTION OF TEIE PREFERRED EMBODIMEN'rS ANI)
COMPAR~SON WITH OTHER ~ORMS OF ~I13A~NG
The first test used five small stators weighing appr~>xi-
mately 340 grams each. The total copper weight was estimated at
5 about 450 grams. The first set of stators was varnished and cured
using a microwave source, while the second set was v~rnished and
cured using electric hot air heating.
Since the same microwave oven was alss capable of
heating by electric forced hot air, it was used for both sets of
10 stators. In this way there was eliminated many of the uncontrolled
variables which would have occurred if a different oven had been
used. One noteworthy observations is that, when parts were heated
in an electric hot air oven, the iron appeared to heat preferentially
compared to the copper coil. With microwave, however, the oppo-
15 site was true. The coil temperature was always hotter than that ofthe iron. (See Table 3).
Table 3 shows that the microwave cured parts have coil
temperatures approximately 25F ( 14C) higher than that of the
iron. Thus, microwave curing is significantly better because the
20 applied varnish will cure best on the areas adjacent to the coils.
This is exactly where the best cure is wanted.
A second point to be considered is that, when heating
with electric hot air ovens, the electrical resistance heating rods are
energized first. This is followed by heat transfer to the air moving
25 past them. NeXt, the hot air must heat the walls of the oven and
maintain that temperature. The hot air must also heat the incoming
parts. Hot air in the venting system (exhaust) is a total loss.
Finally, when the oven is not in use, the same number of Btu's are
expended per hour. Altogether, from the heating rods to the finally
3 0 processed parts, many inefficiencies exist in an electric hot air
system.
5~
TABLe 3
___
CYCLE- Microwave (kWh (Joules) Varies)
kWh
Power (Joules
Time Out Temp.Out(E~`/C) x loD)
(Min.) Put Iron ~ Coils Used Comment
Preheat 2 60% 180/82 200/93 0.058
(0.209)
Dip 0.5 0% -- -- 0.006
1 0 (0.022)
Drain 5 0% -- -- 0.058
(0.209)
Bake #1 5 70% 240/116 270/132 0.165 Slightly
(0.594) tacky
Bake #2 5 70% 270/132 300/149 0.165 Tack-free
(0.594) coils soft
Bake t~3 5 60% 300/149320/160 0.145 Fully
(0.522) cured
Totals 22.5 0.597
(2.1~9)
CYCLE - Electric Heating Oven (~ven Temp. at 325F
¦163~C)/Forced Air/3.805 kWh (13.698 x 10 Joules) Avg.)
kWh
(Joules
Time Temp.Out(F/~C) x 106)
(Min.) Iron Coils Used Comment
Preheat 2 125/52 120/49 0.127
(0.457)
Dip 0.5 -- -- 0.032
(0.115)
Drain 5 -- ~ 0.317
(1.141)
Bake #1 15 200/93 160/71 0.951 Wet
(3.424)
Bake #2 15 250/121 220/104 0.951 Wet
(3.424)
(35
Bake #3 15 260/127 235/113 0.951 Tacky
(3.42~)
Bake #4 15 275/135 240/116 0.951 Tack-free
(3.424) coils soft
5 Bake #5 15 300/149 275/135 0.951 Cured
(3.4~4)
Totals 82.5 5.231
(18.832)
With microwave, there is no heat transferal by air.
10 Rather, the microwave which falls on the part is converted effi-
ciently to heat. The oven walls and air do not heat. The amount of
air exhausted to the outside can be reduced since it is only necessary
to sweep solvent vapors away from the hot unit. Finally, when the
oven is not in use, the microwave electronics may be put on "stand-
15 by" where very little energy is consumed. Obviously, the most dra-
matic saving is in time. The conventional heating system of forced
hot air required 82.5 minutes from beginning to end in order to
effect a satisfactory cure, but the microwave cycles totalled only
22.5 minutes. Comparing the bake cycles only, microwave curing
20 required only 15 minutes versus one hour and lS minutes for the
electric forced hot air system.
An economic comparison of the five stators is shown in
Table 4. Certain assumptions were made in order to present values
corresponding to natural gas, oil (Fuel #2) and oil (Fuel ~6). The
25 values for electric hot air heating were accurately measured. The
number of kWh's used in the electric hot air heating was converted
to Btu/kWh ~see Table 1~. Then the costs for g~as and oil were calcu-
lated, assuming the same number of Btu's would be used to heat the
oven temperature to the same temperature ~325 F/163 ) in this
3Q case. Table 4 shows the Btu's used for electric (hot air oven), natur-
al gas, and the two oils as equivalent. The electricity used in micro-
wave heating has been accurately measured and is shown in both
Tables 3 and 4.
3'7~3()S
TABL~3 4
ELECTRIC
MICROWAVE HEATING OVEM
Weight of the
Five Parts 170 g 1772 g
Approx. Wt. of
Copper 465 g 487 g
Gauge of Copper
in Windings 30 AWG(0.302mm) 30 AWG(0.302mm)
10 Varnish Used AQUANEL(~)600 AQUANEL~7600
Water-borne ( Wate~borne
Polyester) Polyester)
ECONOMICS (See Fuel Cost Table 1 for Conversion Information.)
Btu's Cost To
(Joules x 106) Cure 5
Used Parts (U S. Currency)
Electric
(Microwave) 2,038(2.150) $0.01B84 -
Elec tric
(Heating Oven) 17,853(18.835) 0.14751
Natural Gas
(Heating Oven) 17,853(18.835) 0.04017
Oil Fuel #2
(Heating Oven) 17,853(18.835) 0.06376
25 Oil Fuel #6*
(Heating Oven) 17,853(18.835) 0.03492
*Fuel #6 is generally used in boilers for producing steam or
heating a heat-exchange liquid. No attempt has been rnade to
correct this value based on the heat-exchange efficiency.
The comparison of the costs to eure five parts is quite
dramatic. l'he amount of energy consumed (number of Btu's) was
significantly less when microwave heating was employed. Even the
cost saving compared with natural gas is quite significant. The
primary factor influeneing the low cost is the relatively short time
35 necessary to cure the varnish on the parts.
Aquane~00 is a water borne modified polyester insula-
ting varnish made in accordance with the above identified Laganis
Patent 4,196,109. It is a mixture of an oil modified alkyd resin made
7~(~5
from tall oil fatty acids, dipropylene glycol, trimethylol propane,
isophthalic acid and trimellitic anhydride and a p t-butylphenol-
bisphenol A-salicylic acid-formaldehyde resin, hexamethyl ether or
hexamethylol melamine (Resimene X-745) and dimethylethanolamine
S in a mixture of 2-butoxyethanol (butyl Cellosolve) and water and has
a viscosity tGardner-Holdt) of K-M.
In the next experiment two autornobile alternator armrl-
tures were used. The two parts had A combined weight of l2 pounds
(5.4 kilograms). Again a comparison was made between microwave
10 curing and electric forced hot air. (See Table 5).
In order to control the heat rise in the oven, the power
input was varied. By increasing the power, a rapid increase in
temperature was realized. A reduction in power (e.g., by l096) could
maintain temperature or slow the temperature rise. As can be seen
15 in Table 5, the microwave baking cycle (bakes #l, #2, ~3, and ~4)
totalled only 17 minutes and gave a complete cure, while conven-
tional heating yielded a soft cure even after 60 minutes in the oven.
The economics for this trial are presented in Table 6.
The cost saving of microwave over natural gas is not as drarnatic as
20 that shown in the first study. The smaller-number of Btu's consumed
is nonetheless significant.
Tl~BLF. 5
CYCLE - Microwave (kWh (Joules) Varies)
kWh
Power (Joules
Time Out Temp.Out x l06~
(Min.~ Put (F/C) Used Comment
Preheat 5 70% 120/49 0.165
(0.594)
30 Dip 0.5 0% -- 0.006
(0.022)
Drain 5 0% -- 0.058
(0.209)
~.157~
Bake ~1 5 80% 190/88 0.189 Slightly
(0.680) tacky
Bake #2 5 90% 270/132 0.215 Slightly
(0.774) tacky
Bake #3 5 9096310/ 154 0.215 Tack-free
(0.774 soft gel
Bnke #4 2 90% 320/160 0.086 Cured
(0.3093
Totals 27.5 0.934
(3.362)
CYCLE - Electric Heating Oven (Oven Temp. at 325~ F
~/Forced Air/3.891 kWH (14.008 x 106 Joules)Avg.)
kWh
(Joules
Time Temp.Out x lo6)
(Min.) ( F/ C) Used _omment
Preheat 5 130/54 0.324 - --
(1.166)
Dip 0.5 -- 0.032
(0.115)
Drain 5 -- 0.324
(1.166)
Bake #1 30 260/127 1.946 Tacky
(70006)
25 Bake #2 30 295/146 1.946 Tack-free
(7.006) soft cure
Totals 70.5 4.282
(15.415)
TABLR fi
ELECTRIC
MICROWAVE HEATING OVEN
Weight of the
Two Parts 5580 g 5444 g
Rectangular 90 x 150 rnils. 90 x 150 mils.
Copper Gauge (2.286 x 3.81mm) (2.286 x 3.81mm)
Varnish Used AQUANEI~60û AQUAMEL 600
( ~Vater-borne ( Water~borne
1 0 Polyester) Polyester)
ECONOMICS (See Fuel Cost Table 1 for Conversion Information.)
Btu's Cost To
(Joules x 106) Cure 2
Used Parts (U.S. Currency?
. . _ .
15Electric
(Microwave) 3,198(3.374) $0.0264
Electric
(Heating Oven) 14,614~15.418) 0.12075
Natural Gas
20l(Heating Oven) 14,614(15.418) û.03288
Oil Fuel #2
(Heating Oven) 14,614(15.418) 0.05219
Oil Fuel #6*
(Heating Oven) 14.614(15.418) 0.02859
~Fuel #6 is generally used in boilers for producing stream or
heating a heat-exchange liquid. No atternpt has been made to
correct this value based on the heat-exchange efficiency.
In the next experiment, one large stator w~s used as the
test piece. It weighed slightly over ten pounds. Table #7 presents
two different conditions for microwave curing, as well as the con-
ventional electPic forced hot air system. In Cycle A (microwave),
the power was applied slowly over a period of time. In Cycle B, the
temperature was increased quickly for a shorter period of time.
This modification was made to demonstrate the variations possible
when microwave curing is used. In both Cycles A and B, the baking
times im~olved were much shorter than by the conventional method.
7~ 5
12
l'his exp~3riment also demonstrates that the thermoset-
t;ng properties of the varnish are significantly dependent on the
temperature. The faster one obtains ternpe~atures above 275F
(135C), the shorter the overall cure time. In the parts which took
30 minutes to reach 245 - 250~ (118 - 121~C~ (see Electric Heatin~
portion of Table 7), only the solvent had been driven off ~nd very
little thermosetting had oc~urred in the polymer. In Cycle B (micr~
wave), the temperature reached 325F (163C) after twenty min-
utes. By that time all solvent had been driven off and chemical
crosslinking was well underway.
TABLE 7
_YCLE A - Microwave (kWh (Joules) Varies)
kWh
Power (Joules
Time Out Temp.Out x 106~
~Min.) Put ( F/ C) Used Comment
Preheat 5 70% 165/74 0.165
-- (0.594
Dip 0.5 0% -- 0.006
2 0 (0.022)
Drain 5 0% ~ 0.058
(0.209)
Bake #1 20 70% 240/116 0.0662 Wet
(2.383)
Bake #2 15 70% 260/127 OA96) Tacky
(1.786)
Bake #3 15 80% 300/149 0.566 Tack-free
(2.038)
Bake ~4 5 88% 320/160 0.210 Cured
_ (0.756)
Totals 65.6 2.163
(7.787)
13 .~S7~S
_LE B - Microwave (kWh (Joules) Varies)
Preheat 5 70% 165/74 0.175
(0.630)
Dip 0.S 0% -- 0.006
(0.022)
Drain 5 0% -- 0.058
(0.209)
Bake #1 10 80% 22D/104 0.329 Slightly
(1.1~4) tacky
Bake t~2 10 90% 325/163 0.423 Tack-free
(1.523)
Bake #3 3 90% 350/177 0.127 Cured
(0.457)
Total 33.5 1.168
(4.205)
CYCLE - Electric Heating Oven (Oven Temp. at 325 F
(163C~/Forced Air/3.953 kWh (14.231 x 106 Joules)Avg.)
kWh
(Joules
Time Temp.Out x 106~
(Min.) ( F/ C) Used Comment
Preheat 5 130/54 0.329
(1.184)
~ip 0.5 -- 0.032
(0.115)
Drain 5 -- 0.329
(1.184)
Bake #1 30 245/118 1.977 Wet
(7.117)
Bake #2 30 275/135 1.977 Tacky
(7.117)
Bake #3 30 290/143 1.977 Tack-free
(7.117) soft cure
Totals 100.5 (23.836~
~:~57~ S
1~
An interesting comparison is the nurnber of Btu's used in
the two microwave cures. Basically, in the first study (Cycle A in
Table 7), the optimum condition (power output) was not obtained for
the fastest cure. However, conditions such as those shown in Cycle
5 A could be desirRble in certain applications. Cycle A (microwave)
cost more than the estimated cost for natural gas, while Cycle B
was less expensive than gas. Table 8 shows the economics and
energy consumption for each of the trials.
TABLE 8
ELECTRIC
_CROWAVE HEATING OVEN
Weight of Part 4753 g 4753 g
Gauge o Wire 22 AWG(0.643mm) 22 AWG(0.643mm)
18-1/2 AWG(l.OOmm) 18-l/2 AWG(l.OOmm)
Varnish Used AQUANEL 600 AQUANEL 600
( Water-borne ( Water-borne
Polyester) Polyester)
ECONOMICS (See Fuel Cost Table 1 for Conversion Information
Btuts Cost To
2 0 (Joules x 106) Cure 5 Parts
Used (U.S. Currencv)
___
Electric
(Microwav~Cycle A~ 7,3B2(7.788) $0.0609g
Electric
(Microwave-Cycle B) 3,986(4.2055) 0.03294
Electric
(Heating Oven) 22,597(23.840) 0.18671
NaturPl Gas
(Heating Oven) 22,5~7(23.840) 0.05084
Oil Fuel #2
lHeating Oven) 22,597(23.840) 0.08WO
Oil Fuel #6*
(Heating C)ven) 22,597(23.840) 0.04421
*Fuel #6 is generally used in boilers for producing ~team or
heating a heat-exchange liquid. No attempt has been made to
correct this value based on the heat-exchange e~iciency.
7~3()~i
Thus, it is clear that electrical parts may be heated ef-
ficiently in a microwave oven. Two other basic tests were con~
ducted to further enhance the understanding of microwaYe.
First, a solid block of steel was placed in the oven; it
had little or no temperature rise. Howev0r, there was definitely an
increase in temperature when a stator core containing no copper WQS
placed in the oven. The temperature increase (74F/41C) was not
as high as when copper windings were present.
While not being limited to any theory one explanation of
the reason why microwave curing of thermosetting synthetic resins
on metal coils or laminates is successful is that when a high fre~
quence R-F field impinges on a metallic loop (i.e., be it a plane
metallic sheet or a loop of wire)3 a circulating current is induced
which attempts to oppose the applied magnet component of the R-P
field. The magnitude of this current will depend on the magnitude
of the R-F field and the effective resistance of the metal. For wire
coils, the capacitive coupling completes the loop allowing resistive
heating of the wire in relation to wire size and number of turns. For
laminations, the existence of magnetic versus the copper case ex-
2 0 plains the heating observed in the lflminant structure. The still
lower heating observed in a solid block relates to the increased skin
eff ect.
In the second trial, coils wound around plastic bobbins
were used. These pieces heated very well. In this study, wires of
four different gauges were used (35, 31, 30, and 23 AWG/0.160,
0.274, 0.302, and 0~643 mm, respectively~. For all the runs, the
output power was kept constant at 4096 (approximately 0.350 kWh
(1.26 x lo6 ~oules) in the cavity). All trials were run for a period of
one minute. Five bobbins of each wire gauge were placed on the
turntable such that each would pass through a different area in the
cavity while being rotated.
~1 ~S7~)5
16
This is illustrated in the drawing.
In Table 9, Trial # I shows copper weights for Iully
wound bobbins, while Trial #2 corresponds to copper weights after
several turns of the winding had been removed. The column
5 "Temperature After Two Minutes" ~.ndicates the approximate tem-
peratures after waiting two minutes for the parts to come to
equi~ibrium. (See Table 9).
~:~57~3S
17
TABL~ 9
36 AWG (0.160mm~
TRIAL # 1
.
COPPER TEMPERATURR TEMPERAT~
HEIGHT DN RB~ O~ A~T~R
~CH C IL(~ CH~C) 2 M~N.~C)
a) 27.6 275/135 200/93
b) 27.4 275/135 200/93
c) 27.3 310/15~ 200/g3
d) 26.7 260/127 200/93
e) 27.3 260/127 200/93
Avg. 27.3 276/136 ~7
31 AWG (0.274mm)
TRIAL ~1
a) ~~~~ 39.7 190/88 165/74
b) 40.8 225/107 165/74
c) 41.3 225/107 165/74
d) 41.2 195/91 165/74
e) 39.1 195/91 165/74
Avg. 40-4 ~7~ 165/74
30 AWG (0.302mm)
TR~AL $ 1
a) 49.7 185/85 165/74
b) 49~5 200/93 160/71
c) 49.5 205/96 165/7~
d) 50.0 175/7g 155/68
e) 49.6 170/77 155/68
Avg. 49.7 187786 160/71
30 TR~AL # 1
a) 93.7 135/57 125/52
b) 93.7 140/80 125/52
c) 93.6 135/57 125/52
d) 93.9 145/63 130/54
e) 93 6 140/60 124/52
Avg. 93.7 139/59 126/52
~7~)5
18
TABL~ 9(Continued)
6 A W G (0.160m m~
TRIAL #2
COPP~R TEM PERATUR~ T~MP~RAllUR~
HEIG~T IN RIS~ O]~ A~T~R
EAC H COIb(~) ~A CEl~ F ~ C) 2 ~ P~ C?
a) 19.4 ~320/160 260/127*
b) 19.4 >320/1~0 260/127*
c) 19.3 ~320/1~0 260/127
d) 18.3 ~320/lB0 260/127*
e) 19.3 ~I20/160 260/127*
Avg. 19.1 ~ 320/160 2ffOrl27*
31 A W G (0.274m m)
.. ..
TRIAL #2
~J 21.4 320/160 200/93
b) 21.4 280/138 210/99
c) 21.0 250/121 200/93
d) 23.1 320/160 205/96
e) 21.1 250/121 180/82
~vg. 21.2 284/140 199/93-
30 A W G (0.302 m m?
TRIAL #2
a) 29.7 270/132 200/93
b) 29.5 250/121 200/93
c) 29.5 240/116 200/93
d) 29.9 220/104 190/88
e) 29.6 210/99 190/88
Avg. 29.6 ~ ~~4 196i91
23 A W G (0.643 m m~
TR~AL #2
a) ` ~ 43.7 220/104 180/83
b) 43.7 225/107 175/79
c) ~3.6 230/110 lgO/82
d) 43.9 210/99 180/82
e) 43.4 210/99 170/77
Avg. 43.7 219/104 177/8i
* Only run fcr 30 seconds using 36 A W G due to plastic melting.
~7;1~5
19
For tr;als using approximately the same weight of cop-
per, the heat rise is about the ~QMe (compare 30 AWG (0.302mm)/
Trial #1 with 23 AWG (0.643mm/Trial #2). If these values were
plotted using the average weight values for the x-axis and the aver-
age temperature rise (using either the initial readings or the rea~
ings after two minutes) on the y-axis, the curve would be near
hyperbolic.
In further experiments other classes of insulating
varnish were applied to 1" bobbin-wound coils to note the effect of
microwave. In all cases the applied liquid varnish advanced to either
a cured state or partially cured state after 4 minutes nt ~0% power
(0.350KWH). The finQl temperature on the part was in exeess of
300 F indicating;
1) all the solvent had been removed - thus allowlng the
part temperature to exceed 260F.
2) The part temperature was well within the traditionally
established cure temperature range.
The individual results are given below:
5~eneric Condition of
Varnish Used Classification Temp. Cure
ISC)LITE~)299I Unsaturated 300 F Cured
(uncat~lyzed) polyester
ISOI,ITE~) 2991 Unsaturated 300 F Cured
(Cat. With 1% polyester
(TBP)
ISONEL 32E50 Phenolic Mod. 300F Cured
Polyester
ISOPOXY~433~50A Phenolic Mod. 300F (:ured
Epoxy
Dow~DC-997 Silicone 200F Tacky
In the case of the DC-997, this condition of tacky is not
unexpected since silicones traditionally require 4 times the time
necessary to cure a phenolic~modified polyester.
,~0
7~
Isolite(a'299I is an unsatur~ted polyester-reactive uns~-
turated monomer composition made from a polyester made from
dimerized fhtty acids (Empol@~1018), propylene glycol and maleic
anhydride and vinyl toluene as the unsaturated monomer. To this
Sthere is ~dded glyceryl tris~l2-hydroxystearate) as a thixotropic
agent and Resimene X-745. The Isolite'~'299I has about 60% solids in
vinyl toluene as the solvent. There are also present a small amount
of hydroquinone and t-butyl catechol as polymeriz~tion inhibitors.
It is completely surprising that this resin composition
10cures without a catalyst.
Isolite'~'299I catalyzed with 1% tert butyl peroxide (TBP)
is the same as Isolit~9299l except there is added 1% of TE~P based on
the weight of the resin solution prior to applyng the product to the
wire.
15Isonel~32E5C is a phenolic modified polyester insulating
varnish comprising a polyester made from tall oil fAtty acid, tri-
methylolethane, isophthalic acid, soybean oil and glycerine and a
phenolic resin made from bisphenol A, P-alkylphenol and formalde-
hyde dissolved in a mixture of xylene and mineral spirits to give a
20product having about 50% solids. (It has a viscosity of l~0-245 cps
at 77% solids in this solvent.)
Isopoxy(~433-50A is an insulating varnish particularly
suited for hermetic application made from a phenolic resin ~nd
Epon~1007 (bisphenol A-epichlorhydrin) dissolved in a mixture of
25n-butanol, monomethyl ether of propylene glycol and xylene having a
solids content of about 50% at a viscosity of T-V.
Dow~ DC-997 is a silicone resin containing insulating
varnish.
In another aspect of the present invention there can be
30prepared bondable wire by the process of the present invention.
Bondable wire is wire e.g. copper wire, coated with an enamel, e.g.
polyvinyl formal (Formvar) or a polyamid~imide-polyester and over-
coated with polyvinyl butyral (Butvar) or other thermoplastic poly-
mer, e.g. a linear polyester such as polyethylene terephthalate (e.g.
35Dacron). The bondable wire is preformed into a coil and then expo~
2 1 ~'~S~OS
ed to microwave energy to heat the product and make the thermo
plastic overcoat flow and hond adjacent layers of coil.
In a specific example employing bondable copper wire
wherein the copper was coated with Formvar and overcoated with
5 phenolic modified Butvar (p-phenylphenol-formaldehyde modified
polyvinyl butyral) and the wire coil wound on a plastic bobbin was
placed in a microwave oven at a power output of 0.268 kWh. At I
minute in the oven the temperature of the coil was 315F and at 2
minutes the overcoat had softened and bonded strand to strand.
