FR2466485A1 - Microwave hardening of synthetic resins - coated on metal parts, e.g. oil-free satd. or oil-modified unsatd. polyester(s) - Google Patents

Abstract

Microwaves are used for hardening synthetic resins applied on metal parts present as a reel, esp. Cu reels, or as metal laminates enclosing a dielectric. Wire reel exposure to microwaves is also claimed, to soften a coating which bonds the reel wires. The reel wires pref. consist of Cu coated with a wire-lacquer and with a thermoplastic top-coat. The metal parts can be armature controls, stators, transformers, and magnetic reels. Microwaves impinging on a part are effectively converted to heat. Resin hardening time is shortened, e.g. to 15 min. as opposed to 1 hr on using electrically heated hot air. Energy consumption and costs are reduced.

Description

The present invention relates to a method of cooking insulating varnishes, applied to metal parts as armatures, stators, coils or other parts.

In the past five years the fuel and energy savings in the industry have become of paramount importance. The cost of oil, gas and electric power has increased significantly.

Oil and gas supplies are periodically critical, forcing the industry to stop or slow production. Coal is one of the most accessible fuels in the U.S., but it does not have the convenience of using petroleum or natural gas.

However, coal is an attractive source for generating electricity. Hydroelectric and atomic power stations also contribute a great deal to the production of electrical energy. This is why, it is likely that, in the future, electrical energy will be the source of power on which we can rely most.

 If we compare it to that supplied by gas or oil, electric heat is more costly, and it is not the solution chosen when another possibility exists. As shown in Table 1, the cost of heating by electricity is about 4 times higher than that of heating by natural gas (March 1979).

TABLE 1
Type of Kcal / unit-of-Cot' per Number of Kcal fuel measure unit per dollar (currency (US currency) ~~~~~~~~~~~~~
Electricity 860 Kcal / kWh 0.0282 / kWh 30,499.056
Natural gas 8.9 Kcal / like 0.0000795 / liter 111999.89 Oil N02 9324Kcal / liter 0.1321004 / liter 70560.00
Oil N6 95904Kcal / n 0.0744254 / lite 128817.86
When any form of energy is used to heat the air in an oven, and then electrical parts are passed through this hot air, the efficiency of heat transfer is very low. The key to the use of electrical energy lies in the efficient transfer of this energy to the rooms to be heated.

Microwave technology, for domestic and industrial use, has been known for 20 years. However, the industry has been reluctant to use them. Where metals are involved, it seemed obvious that there would be reflection from the microwaves, and therefore no heat.

However, it has been found quite the contrary that, if we place in a microwave field armatures, stators, transformers and coils, their temperatures increase at a surprising speed, which allows a rapid cooking of a coating of varnish or enamel. Microwave cooking is effective both when the metal is in the form of a coil and when it is in laminated form with a dielectric substance incorporated between the layers, as for example in the configuration of a capacitor.

The new method of baking a curable synthetic resin, deposited on a metallic piece in the form of a roll or laminate with a dielectric substance incorporated between the layers, is characterized in that, to cure the synthetic resin, energy from microwaves from 900 to 950 megahertz or from 2400 to 2500, and preferably 2450 megahertz.

As metals, iron, copper, silver, aluminum, nickel, zinc or alloys, for example steel, can be used. In general, for electrical parts, copper, aluminum and steel of electrical quality are used.

In the operating examples below, the microwave oven used is of the SMC 1-33H model from
Despatch Industries, Zinc, which is described in their catalog 600-978 on pages 16 and 17.

 It has been found that, for microwave curing, the most suitable frequency intervals are generally between 900 and 950 mega- and 2400 and 2500 megahertz. hertz From these observations, we use an equipment set to 2450 megahertz, with a variable power input from 0 to 1 kWh (3.6x106 joules).

An agitator and a turntable are placed in the oven to statistically direct the microwave field into the cavity.

 Microwave energy is usually considered to be 30-35% efficient. For each kWh of power involved, only 0.3 to 0.35 kWh (1.08 to 1.26x106 joules) arrives in the cavity. We find that these estimates are entirely correct. Table 2 indicates that the best efficiency is obtained when demand is high (more than 50%). To determine how many kWh are used for each power setting, an ampere meter, a voltmeter and a power factor meter, recorders, are used. At the same time, the number of kWh delivered to the cavity is precisely determined, by measuring the heating of a predetermined quantity of water. This value, divided by the total power going into the oven, determines the efficiency.Contributes to the loss of efficiency, the use of motors for the agitator, the turntable and the exhaust fans.

(See Table 2 on the next page)
TABLE 2
(1) (2)
% of total efficiency of kWh kWh in% Effica
of power put into play 6 city cavity
(joules x 10) oven x 106) 2 X 100
(joules x 106) T7
calculated from
the increase
temperature
water ture
O (position 0.699 (2.516) 0 (0)
waiting)
10 0.754 (2.714) 0.053 (0.191) 7.0
20 0.967 (3.481) 0.152 (0.547) 15.7
30 1.118 (4.025) 0.268 (0.965) 24.0
40 1.328 (4.781) 0.350 (1.260) 26.4
50 1.528 (5.501) 0.462 (1.663) 30.2
60 1.738 (6.257) 0.570 (2.052) 32.8
70 1,985 (7,146) 0.715 (2,574) 36.0
80 2.262 (8.143) 0.800 (2.880) 35.4
90 2.576 (9.274) 0.880 (3.168) 34.2 100 3.062 (11.023) 1.080 (3.888) 35.3
Secondary efficacy has been found to be
that is to say the conversion of microwave energy into
heat in electrical parts, does more than compensate
ser the initial efficiency from the source to the cavity.

The process according to the invention can be used
to harden any thermosetting resin, deposited on
a metal coil or a metal laminate with
dielectric substance between its layers. So can we
operate with all the conventional resins used to coat metals, for example electrical conductors
ques, in the form of enamels and insulating varnishes.
for example use hardenable polyesters prove
from a diol, such as ethylene glycol, propylene glycol,
neopentyl glycol, tetramethyl-2,2,4,4 cyclobutanediol, 1,3, butanediol-1,4, of a polyol containing at least 3 hydroxyl groups, such as glycerin, tris isocyanurate (2-hydroxyethyl), trimethylolpropane , and a polycarboxylic acid, such as benzophenone dicarboxylic acid4,4 ', terephthalic acid, isophthalic acid, imide of dicarboxylic acid prepared from trimellitic anhydride and oxy- or methylene-dianiline, o-phthalic acid, adipic acid, trimellitic acid, trimesic acid.

Other thermosetting resins are also suitable, such as phenol-formaldehyde, cresol-formaldehyde, phenol-furfural, melamine-formaldehyde resins; epoxy resins, for example bisphenol A-epichlorohydrin, glycerin-epichlorohydrin; unsaturated polyesters, for example obtained from glycols similar to those mentioned above, and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaoonic acid, with or without other polycarboxylic acids such as adipic acid, succinic, terephthalic acid, isophthalic acid, o-phthalic acid, and an unsaturated monomer such as styrene, diallyl phthalate, tert-butylstyrene, methyl methacrylate, methyl acrylate, vinyl toluene, and the like.

Thus, can we use the thermosetting resins described in US Pat. Nos. 3,338,743 to
Laganis, No. 3,342,780 by Meyer, No. 3,425,866 by Meyer, No. 3,108,083 by Laganis, No. 3,249,578 by Meyer, No. 3,312,573 by Sheffer, No. 3,296,024 by Jordan, No. 4,016,330 by Laganis , No. 3,523,820 to Sheffer, No. 4,073,826 to Galkiewicz; n 4 105 639 from Laganis, n 4 1197> 58 from Keating, n 4 133-787 from Laganis, n 2 982 754 from Sheffer, n 3 479 307 from Laganis, n 3480 589 from Jordan, n0'3 498 940-de Laganis, $ n 3,646 3; 4 from Jordan, n 2,889,304 from Sheffer, n 4,196,109 from Laganis.

 In the present description, unless otherwise indicated, the parts and percentages are given by weight.

 The only figure in the appended drawing represents a diagram showing how 5 winding coils are arranged in the oven cavity.

In the following are described preferred embodiments of the invention, but which do not limit the scope thereof, as well as, by way of comparison, tests with other modes of heating.

In the first test, 5 small stators weighing about 340 g each are used. The total weight of copper is estimated at around 450 g. The stators of the first set are varnished and fired by means of a microwave source, while those of the second set are varnished and fired by electric heating of hot air.

 As the same microwave oven is also capable of heating by forced air, heated with electricity, it is used for the 2 sets of stators. In this way we eliminate many of the uncontrolled variables that would come into play if we operated with different ovens. it is interesting to note that, when the parts are heated in an electric hot air oven, it seems that the iron heats preferably over the copper coil. However, with microwaves, the opposite happens. The winding temperature is always higher than that of the iron (see table 3).

 (See Table 3 on the next page).

TABLE 3
CYCLE - with microwave kWh (Joules)
Com Production Duration - kWh temperature
(mn) external C (Joules
of Iron Hoar- x10)
powers used,
sance
Preheating 2 60% 82 93 0.058 -
(0.209)
Diving 0.5 0% - - 0.006 -
(0.022)
Drainage 5 0% - - 0.058 -
(0.209)
Cooking N 1 5 70% 116 132 0.165 light
is lying
(0.594) sticky
Cooking N32 5 70% 132 149 0.165 Rolls
ment ten
dre
(0.594) no peas
seux Muscooking 5 60% 149 160 0.145 Whole
cooked
(0.522)
Total 22.5 0.597
(2.149)
CYCLE - with electrically heated oven (Temperature
from the oven at 1630C) / Forced air, on average 3.805 kWh
(13.698 x 106 Joules)
Duration Temperature kWh Commen
(mn) external C (Joules keep quiet
Rolled Iron- x 106)
Lements used
Preheating 2 52 49 0.127 -
(0.457)
Diving 0.5 - - 0.032 -
(0.115)
Draining 5 - - 0.317 -
(1,141)
Cooking N01 15 93 71 0.951 wet
(3,424)
Cooking N 2 15 121 104 0.951 wet
(3,424)
TABLE 3 (continued)
Duration Temperature kWh Commen
(mn) external OC (Joules shut up
Iron Enmu- x106)
lemerits useful
Sés Cooking N03 15 127 113 0,951 Sticky
(3,424) Baking 15,135,116 0.951 Rolls
(3,424) ten
dres, no
sticky Cooking N05 15 149 135 0.951 cooked
3,424
Total 82.5 5.231
(18,832)
This table 3 shows that the parts, cooked by microwave, have winding temperatures about 14 C higher than those of iron. it follows that the microwave cooking is much better, because the varnish applied cooks better on the surfaces in the immediate vicinity of the windings, and it is precisely there that one wishes to have the best cooking.

A second point to take into consideration is that, when heating by electric hot air ovens, the rods of the electric heating resistors are heated first. there follows a transfer of heat by the air circulating in the surroundings. Then, this hot air must heat the walls of the oven and maintain the temperature. The hot air exiting through the ventilation system is a total loss. Finally, when the oven is not used, the same number of calories are expended per hour. On the whole, from the heating rods to the parts finally treated, in the hot air electrical system, there are many losses of efficiency.

With microwaves, there is no heat transfer by air. More precisely, the microwaves that arrive on the room are efficiently converted into heat. The air and the oven walls are not heated. The quantity of air expelled to the outside can be reduced since it only suffices to expel the solvent vapors from the heating unit. Finally, when the oven is not in use, the microwave electronics can be put in the reserve position, where the energy consumption is very low. Obviously, saving time is the most important thing. The conventional forced hot air heating system requires 82 minutes and 30 seconds from start to finish for satisfactory cooking to be carried out, while microwave cycles require only 22 minutes and 30 seconds in total. If we only compare the cooking periods, it only takes 15 minutes with the microwaves against 1 hour and 15 minutes for the forced hot air electric system.

 An economic comparative study of the 5 stators is presented in Table 4. Certain assumptions have been made to present the corresponding values for natural gas, an oil (fuel NO 2) and a second oil (fuel NO 6). ). The values for electric heating by hot air have been measured with precision. The number of kWh, used for electric hot air heating, is converted into Kcal / kWh (see table 1). Then the expenses for gas and oil are calculated, assuming that the same number of Kcal is used, to bring the temperature of the oven to the same value (1630C). Table 4 indicates that the numbers of Kcal used for electric heating (hot air oven), heating with natural gas or heating with two oils are equivalent.

The amount of electricity consumed for microwave heating has been precisely measured, and is reported in Tables 3 and 4.

TABLE 4
Microwave oven
electric fase waves
Weight of the 5 pieces 1700 g 1772 g
Approximate weight
copper 465 g 487 g
Enrou caliber
AWG 30 gauge copper elements AWG 30 gauge (0.302mm) (0.302mm)
(P) (P)
Varnish used A4UANEL 600 AQUANEL 600
(Polyester to (Polyester to
water) water)
Economic data (see fuel prices in
Table t)
Kcal 6 Cobt for cooking
(Joules x 10) the 5 pieces
consumed (US Currency)
Electric 0.513 (Microwave) (2.150) * 0.01684
Electric 4,499 0.14751 (oven) (18.835)
Natural gas 4,499 (oven) (18,835) 0.04017
Oil N02 4,499 0.06376 (oven) (18.835)
Oil n6 * 4,499 0.03492 (oven) (18.835)
* N06 fuel is generally used in boilers for steam production or heating of heat exchanger liquid. No attempt has been made to correct this value based on the efficiency of the heat exchange.

The comparison of the expenses necessary to cook the 5 pieces is very striking. The amount of energy consumed (number of Kcal) is much less when using microwave heating. Even the savings in expenses compared to natural gas are very clear.

The main factor acting on the low cost is the relatively short time necessary to bake the varnish on the parts.

 AQUANEL 600 is a water-modified polyester insulating varnish, manufactured according to the process described in U.S. Patent No. 4,196,109 mentioned above. It is a mixture of an oil-modified alkyd resin made from tall oil fatty acids, dipropylene glycol, trimethylol propane, isophthalic acid and trimellitic anhydride, and of a formaldehyde-salicylic acid-bisphenol Ap-tert-butylphenol resin, of hexamethyl ether or of hexamethylol melamine (Resimene X-745) and of dimethylethanolamine, in a mixture of 2-butoxyethanol (butyl cellosolve) and of water, and which has a viscosity of the order of 3 poises.

In the following experiment, two armatures of automobile alternator are used. The two pieces have a total weight of 5.4 kg. In Table 5 we can compare the results obtained by microwave cooking on the one hand, and cooking with hot air, electric, forced.

In order to adjust the heat rise in the oven, the power input is varied. A rapid increase in temperature is obtained by increasing the power. A reduction in this (for example 17g) can maintain the temperature or slow its increase. As can be seen in Table 5, the microwave cooking period (cooking 1, 2, 3 and 4) only totals 17 minutes and results in complete cooking, while conventional heating gives attenuated cooking even after 60 minutes of stay in the oven.

The economic data relating to this test are presented in table 6. The saving achieved with microwaves compared to natural gas, is not / marked only in the first study. The smallest number of Kcal consumed is nevertheless important.

TABLE 5
KWh microwave heating (Joules)
Production time - Temperature kWh Commen
(mn) external C (Joules shut up
x 106)
then- used
sance
Preheating 5 70% 49 0.165 -
(0.594)
Diving 0.5 0% - 0.006 -
(0.022)
Draining 5 0% - 0.058 -
(0.209)
Cooking N01 5 80% 88 0.189 light
(0.680) ment
piss
Cooking N02 5 90% 132 0.215 light
(0.774) ment
sticky
Cooking N03 5 90% 154 0.215 gel ten
(0.774) dre no
sticky
Cooking N04 2 90% 160 0.086 cooked
(0.309)
Total 27.5 0.934
(3.362)
Electric oven heating (oven temperature
at 163 C) / forced air on average 3.891 kWh (14.008
x106 Joules
Duration Temperature kWh Commen
(mn) external C (Joules keep quiet
x 106
used
Preheating 5 54 0.324 -
(1,166)
Diving 0.5 - 0.032 -
(0.115)
Draining 5 - 0.324 -
(1,166)
Cooking N 1 30 127 1,946 sticky
(7.006)
Cooking N 2 30 146 1,946 cooking
(7.006) tender
Total 70.5 4.282 no peas
(15,415) seux
TABLE 6
Heating by Heating by
microwave electric oven
Weight of 2 pieces 5580 g 5444 g
Rectangular caliber
re copper (2.286 x 3.81 mm) (2.286 x 3.81 mm)
Varnish used AQUANEL W 600 AQUANEL
(polyester to (polyester to
water) water)
Economic data (see fuel cost,
in table 1)
Kcal Cooking cost
(Joules x 106 of 2 pieces
used (US currency)
Electric (microwave) 0.806 (3.374) 0.0264
Electric 3,683 (15,418) 0.12075 (heating by
oven)
Natural gas 3,683 (15,418) 0.03288 (heating by
oven)
Oil N02 3,683 (15,418) 0.05219 (heating by
oven)
Oil N06 * 3,683 (15,418) 0,02859 (heating by
oven)
* N06 fuel is generally used in boilers for steam production or heating of heat exchanger liquid. No attempt has been made to correct this value based on the efficiency of the heat exchange.

 In the following experiment, a large stator is used as the test piece. It weighs just over 4.5 kg. Table 7 shows the operating conditions for two different kinds of microwave cooking, as well as for a conventional, electric, forced hot air system. In cycle A (microwave), power is applied slowly over a long period of time. In cycle B, on the other hand, the temperature rise takes place quickly over a short period.

This modification is carried out in order to show the possible variations when using microwave cooking. In the two cycles A and B, the cooking time is much shorter than when operating by the conventional method.

 This experience also shows that the thermosetting properties of the varnish are clearly dependent on the temperature. The higher the temperatures above 1350C, the shorter the total cooking time. In the parts which take 30 minutes to reach 1180-1210C (see the paragraph of Table 7 concerning electric heating), only the solvent has been removed, and there is only a very slight thermal cure in the polymer. In cycle B (microwave) the temperature reaches 1630C after 20 minutes. At this time all the solvent has been removed and crosslinking is well underway.

TABLE 7
CYCLE A - Microwave
Production time - Temperature kWh Commen
(mn) external C (Joules keep quiet
of x 10
then- used
sance
Preheating 5 70% 74 0.165 -
(0.594)
Diving 0.5 0% - 0.006 -
(0.022)
Draining 5 0% - 0.058 -
(0.209)
Cooking N01 20 70% 116 0.0662 wet
(2.383)
Cooking N02 15 70% 127 0.496 sticky
(1,786)
Cooking N03 15 80% 149 0.566 no
(2,038) sticky
TABLE 7 (continued)
Duration Produc- Temperature kh Commen
(mn) external C (Joules keep quiet
x 106)
then-- used
sance ~~~~~~~~~~~ ~~~~~~~~
Cooking N 4 5 88% 160 0.210 cooked
(0.756)
Total 65.6 2.163
(7.787)
CYCLE B - Microwave
Preheating 5 70% 74 0.175 -
(0.630)
Diving 0.5 0% - 0.006 -
(0.022)
Draining 5 0% - 0.058 -
(0.209)
Cooking N01 10 80% 104 0.329 light
(1,184) ment
sticky
Cooking N02 10 90% 163 0.423 no
(1,523) sticky
Cooking N03 3 90% 177 0.127 cooked
(0.457)
Total 33.5 1,168
(4.205)
CYCLE C - Heating by electric oven (temperature
oven temperature (1630C) / forced air on average
3.953 kWh (14.231 x 106 Joules)
Duration Temperature kWh Commen
(mn) external C (Joules keep quiet
w 106)
used
Preheating 5 54 0.329 -
(1.184)
Diving 0.5 - 0.032 -
(0.115)
Draining 5 - 0.329 -
(1.184)
Cooking N01 30 118 1,977 wet
(7.117)
TABLE 7 (continued)
Duration Temperature kWh Com
(mn) external C (Joules men
x10) shut up
useful
his
Cooking N02 30 135 1,977 sticky
(7.117)
Cooking n 3 30 143 1,977 no
(7,117) sticky cooking
Total 100.5 (23,836) tender
What is interesting to compare is the number of Kcal expended during the two microwave cookings. In principle, in the first study (Cycle
A of table 7), -one does not obtain the optimal condition (power production) for the fastest cooking. However, conditions, similar to those indicated for cycle A, may be desirable for certain applications. Cycle A (microwave) is more expensive than heating with natural gas, while cycle B is less expensive than gas.

Table 8 shows the energy consumption and the economic data for each of these tests.

TABLE 8
Microwave Electric Oven
Workpiece weight 4,753 g 4,753 g
Wire size 22 AWG (0.643mm) 22 AWG (0.643mm)
18-1 / 2 AWG (1.00mm) 18-1 / 2 AWG (1, oemn)
Varnish used AQUANEL R 600 AQUANEL R 600
(Polyester to (Polyester to
water) 11 water)
Economic data
Kcal Cost of cooking
(Joules x 106) sound of 5 pieces
used (US currency)
Electric (Microwave Cycle A) 1,860 (7,788) # 0.06099
TABLE 8 (continued)
Kcal 6 Cost of cooking
(Joules x106) 5-piece sound
used (US currency) Electric trique (cycle B, microwave) 1.004 (4.2055) t 0.03294
Electric
(heated oven) 5.694 (23.840) 0.18671
Natural gas
(heated oven) 5.694 (23.840) 0.05084
Oil N02
(heated oven) 5.694 (23.840) 0.08070
Oil N061
(heated oven) 5.694 (23.840) 0.04421
N06 fuel is generally used in boilers for steam production or heating of heat exchanger liquid. No attempt has been made to correct this value based on the efficiency of the heat exchange.

 It is therefore clear that electrical parts can be efficiently heated in a microwave oven. Two other fundamental tests are carried out to further enhance the understanding of the use of microwaves.

First, a solid block of steel is placed in the oven: there is little or no rise in temperature. However, when a stator core that does not contain copper is placed in the oven, there is a marked increase in temperature. This increase (410C) is not as high as when copper coils are present.

A possible explanation for the reason why microwave curing of thermosetting synthetic resins on metal coils or laminates is successful, would lie in the following fact: when high frequency RP fields strike a metal circuit ( that is to say a flat metal sheet or a loop of wire), a current is induced, which tries to oppose a magnetic component applied to the RF field. The intensity of this current depends on the intensity of the RF field and the effective resistance of the metal. For the wire windings, the coupling in capacity completes the loop allowing the heating by resistance, according to the dimension of the wire and of the number of winding turns, In the case of laminated products, the existence of magnetism with respect to copper explains the heating observed in this structure. The even lower heating observed in a solid block is related to the increased skin effect.

 In the second test, windings made around plastic coils are used.

These parts heat very well. During this study, we use wires of different calibers (AWG 35, 31, 30 and 23, i.e. 0.160, 0.274, 0.302, and 0.643 mm). For all these tests, the production power is kept constant at 40%, notably around 0.35 kWh, or 1.26 X 106 joules, in the cavity. All operations are carried out for 1 minute. 5 spools of each wire size are placed on the turntable in such a way that each one passes, during the rotation, in a different zone of the cavity. This is illustrated in the accompanying drawing.

 In table 9, test N01 indicates the weights of copper for the coils whose winding is complete, while test 2 indicates the weights of copper for coils from which several turns of the winding have been removed. The column "Temperature after 2 minutes" represents the approximate temperature after waiting for 2 minutes, allowing the parts to reach equilibrium.

TABLE 9
36 AWG (0.160 mm)
Test N01
Weight of copper Increase Temperature
in each of tempera- after 2 mi
winding ture C nutes C (g)
a) 27.6 135 93
b) 27.4 135 93
c) 27.3 154 93
d) 26.7 127 93
e) 27.3 127 93 average 27.3 136 93
31 AWG (0.274mm)
Test N01
a 39.7 88 74
b) 40.8 107 74
c 41.3 107 74
d 41.2 91 74
e 39.1 91 74 average 40.4 97 74
30 AWG (0.302mm)
Test N01
a 49.7 85 74
b 49.5 93 71
c) 49.5 96 74
d) 50.0 79 68
e) 49.6 77 68 average 49.7 86 71
23 AWG (0.643 mm)
Test N 1
a) 93.7 57 52
b) 93.7 60 52
c) 93.6 57 52
d) 93.9 63 54
e) 93.6 60 52 average 93.7 59 52
TABLE 9 (continued)
36 AWG (0.160 mm)
Test N02
Weight of copper Increase Temperature
in each of temperature- after 2 mi
winding (q) re C nutes C
a) 19.4> 160 127 *
b) 19.4> 160 127 *
c) 19.3> 160 127 *
d) 1934> 160 127 *
e) 19.3> 160 127 average 19.1> 160 127 *
31 AWG (0.274mm)
Test N02
a 21.4 160 93
b) 21.4 138 99
c) 21.0 121 93
d) 23.1 160 96
e) 21.1 121 82 average 21.2 140 93
30 AWG (0.302mm)
Test N02
a 29.7 132 93
b) 29.5 121 93
c) 29.5 116. 93
d 29.9 104 88
e 29.6 99 88 average 29.6 114 91
23 AWG (0.643mm)
Test N02
a 43.7 104 83
b 43.7 107 79
c 43.6 110 82
d) 43.9 99 82
e) 43.4 99 77 average 43.7 104 81 t In the case of 0.16 mm wire, we only operate for
30 seconds because the plastic melts.

For tests using approximately the same weight of copper, the temperature increase is almost identical (compare test N01, caliber 0.302 mm, with test N02 caliber 0.643 mm). If these values were translated graphically, using the average weight values for the x-axis, and the average temperature increase (taking either the initial readings or the readings after 2 minutes) for the ordered, the curve obtained would be close to a hyperbola.

In other experiments, other classes of insulating varnish are applied to a 25.4 mm coil to study the action of microwaves. In all cases, the applied liquid varnish changes to a cooked or partially cooked state after 4 minutes at a power of 40% (0.35 kWh). The final room temperature exceeds 149 C, which indicates s
1) that all of the solvent has been removed, thus allowing
at room temperature to exceed 1260C,
2) that the room temperature is well within
temperatures of
the cooking / cooking interval, traditionally established.

The specific results are given below.

Varnish used Classification Temperature State of
cooking ISOLITE% 991 Polyester 1490C cooked (not catalyzed) unsaturated
ISOLITE R2 991 Polyester 1490C baked catalyzed with unsaturated
1% TBP ISONEL 32E50 Polyester 1490C baked
Edited by
phenol
ISOPOXY R 433-50A Modified epoxy 149 C cooked
by phenol
Dow DC-997 Sticky 930C Silicone
In the case of DC-997, this tackiness is not unexpected, since normally silicones require 4 times more time to cure than a phenol modified polyester.

 Isolite 2991 is an unsaturated polyester-reactive unsaturated monomer composition obtained from a polyester made from dimerized fatty acids (Empol 1018), propylene glycol and maleic anhydride, and vinyl toluene as the unsaturated monomer. . Glyceryl tris (12-hydroxy stearate) is added to it as a thixotropic agent and Resimene X-745. Isolite 2991 contains approximately 60% of solid product in vinyl toluene used as a solvent. Also present are small amounts of hydroquinone and tertbutyl catechol, acting as polymerization inhibitors.

 It is quite surprising that this resin composition hardens without a catalyst.

 Isolite 2991, catalyzed with 1% tert-butyl peroxide (TBP), is identical to the previous Isolite 2991, except that 1% of TBP has been added thereto based on the weight of the resin solution before its application. on the wire.

 Isonel 32E50 is a phenol-modified polyester insulating varnish, comprising a polyester obtained from tall oil fatty acid, trimethylol ethane, isophthalic acid, soybean oil and glycerin, and a phenolic resin obtained from bisphenol A, p-alkylphenol and formaldehyde, dissolved in a mixture of xylene and mineral spirits, so as to form a product containing about 5046 solids; the viscosity at 77% solid matter, in this solvent, is 190-245 centipoise.

 Isopoxy 433-50A is an insulating varnish, particularly suitable for seals, obtained from a phenolic resin and Epon 1007 (bisphenol A-epihln-rhydrine), dissolved in a mixture n-butanol, of monomethyl ether of propylene glycol, and xylene, having a solids content of the order of 50%, with a viscosity of 560-880 centipoise.

 Dow DC-997 is a silicone resin containing an insulating varnish.

 In another embodiment of the present invention, binder wire can be prepared; it is a wire, for example made of copper, coated with an enamel, such as polyvinyl formal (Formvar), or with a polyester-imidepolyamide, itself covered with polyvinyl butyral (Butvar) or any other thermoplastic polymer, for example a linear polyester such as polyethylene terephthalate (Dacron). This binder wire is preformed into a winding, then is exposed to microwaves so that the heat causes the thermoplastic / overcoat to flow, resulting in an assembly of the layers adjacent to the winding.

 In a particular example, a copper binder wire is used, that is to say covered with Formvar, with a layer of Butvar modified with phenol (polyvinyl butyral modified by p-phenylphenol-formaldehyde) on top of it. being wound on a plastic reel; it is placed in a microwave oven giving 0.268 kWh. After one minute, in this oven, the winding temperature reaches 1570C; after 2 minutes the cover will soften and the fibers will be connected to each other.

Claims (7)

RSVEND ICATIONS  1. A method of baking a curable synthetic resin, deposited on a metal part in the form of a winding or laminate, with a dielectric substance incorporated between the layers, characterized in that one uses, as a source of energy microwaves, preferably between 900 and 950 megahertz, or between 2400 and 2500 megahertz, or better still of the order of 2450 megahertz.  2. Method according to claim 1, characterized in that the synthetic resin is a polyester obtained from a diol, in particular ethylene glycol, a triol like glycerine or tris isocyanurate (2-hydroxyethyl), and a dicarboxylic acid, in particular iso- or terephthalic acid.  3. Method according to one of claims 1 or 2, characterized in that the polyester is not modified by oil.  4. Method according to one of claims 1 to 3, characterized in that the polyester is ethylenically unsaturated and is optionally dissolved in an ethylenically unsaturated monomer, in particular styrene, butyl styrene, methyl methacrylate, vinyl toluene or diallyl phthalate.  5. Method according to one of claims 1 to 4, characterized in that the polyester is modified with an oil, preferably with soybean oil or tall oil acid.  6. Method according to one of claims 1 to 5, characterized in that the metal part covered with synthetic resin is a winding, preferably in cui vre. 7. Method according to one of the preceding claims, characterized in that the wire is made of copper covered with an enamel, with a surface coating of thermoplastic polymer.