CH629397A5 - Process for forming a hardened, resin-like coating on an object - Google Patents

Description

The invention relates to a method of forming a hardened, resinous coating on an article, the article preferably having insulation.

Conductors that are to be used as coils in generators and motors are isolated using the VPI (vacuum pressure impregnation) process by first holding the conductor with mica tape, then with a glass binding tape to hold the brittle mica tape in place , wrapped. The wrapped conductor is then placed in a vacuum and then under pressure in a resin. The soaked wrapped conductor is then removed and heated in an oven to cure the resin.

This system is already being used commercially, but it requires quite a lot of energy to cure in the furnace because, together with the resin, the copper in the coils must also be heated. Resin dripping may occur during curing, and expansion of the copper during curing and the subsequent contraction during cooling may cause mechanical stress in the resin.

Anaerobic resins are those that do not cure in the presence of oxygen, but cure when placed between two oxygen impermeable surfaces. These anaerobic resins are therefore generally used as adhesives.

The object of the invention is to provide a resin system that allows Isolierimg without excessive energy losses and in which mechanical stresses on the resin remain as small as possible.

The method according to the invention is defined in patent claim 1 and the object according to the invention provided with a hardened, resin-like coating is defined in patent claim 13.

It has been found that insulated conductors impregnated with anaerobic resins do not cure in a vacuum, which is an advantage in the VPI process, but that the resins can, however, be cured by contact with a gaseous atmosphere which contains pure oxygen. This means that the resins can be cured at room temperature, thereby avoiding the problems mentioned above in connection with the thermosetting resins. The electrical properties are comparable to that of thermosetting resins currently used, with the exception of high voltage applications. In contrast to resins hardened by electron beams or UV light, anaerobic resins harden under gas hardening to substantial depths, which can reach 25 cm or more.

The invention is explained in more detail below with reference to exemplary embodiments which are illustrated in the drawings.

It shows:

1 is a perspective sectional view of an insulated conductor impregnated with an anaerobic resin;

2 shows a diagram of a device for the continuous coating of a wire using the method according to the invention.

In Fig. 1, a conductor 1 is covered with numerous layers of mica tape insulation 2 and a layer of woven organic tape insulation 3, which holds the mica insulation in place. An anaerobic resin 4 impregnates the insulation and forms an outer coating.

2, a conductor 5 runs from a roll 6 into a bath 7 with an anaerobic resin 8. The wire then runs over a disk 9 into a closed tank 10. An inert gas flows from a line 11 into the tank. During the wire

2nd

s

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

629 397

runs over disks 12 arranged in the tank, it is hardened. The wire then leaves the tank and is wound on a roll 13.

An anaerobic resin is a resin that does not cure in the presence of oxygen, but cures at room temperature when placed between oxygen-impermeable surfaces. Solvent-free anaerobic resins are required for the VPI process. Most anaerobic resins are acrylic resins that polymerize through addition via a double bond. Commonly used anaerobic acrylic resins include tetraethylene glycol dimethacrylate and tetraethylene glycol diacrylate. An anaerobic acrylic resin can contain a reactive comonomer such as ethyl methacrylate, styrene or 2-ethylhexyl acrylate. An organic peroxide initiator that forms free radicals, such as cumene hydroperoxide or t-butyl perbenzoate, is often used to initiate curing. An accelerator, generally a tertiary amine such as N, N-dimethyl-p-toluidine, and a coaccelerator, usually an organic sulfimide such as benzoic acid sulfimide, may be present to reduce curing time. The free radical initiator can be stabilized with a free radical stabilizer such as hydroquinone. There are many U.S. patents dealing with anaerobic resins, and many of the anaerobic resins described therein can be used in accordance with the invention. In this connection, reference is made to US Pat. Nos. 3,616,040, 3,634,379, 3,775,385, 3,855,040, 3,880,956, 3,041,322, 3,125,480, 3,203,941, 3,300,547.3,419,512. 2 895 950, 3 043 820, 3 046 262, 3 218 305.3 435 012 and 3 720 656.

The conductor is preferably made of copper. This material is most often provided with electrical insulation, and copper is known to accelerate the hardening of anaerobic resins. However, other metals can also be used.

The main insulation is preferably mica, especially for high voltage applications because mica has excellent electrical properties. Glass, asbestos, Nomex (a polyamide sold by Dupont and likely composed of meta-phenylenediamine and isophthalyl chloride) and other types of insulation could be used in the same way, either alone or mixed or mixed with mica. The mica insulation is usually made with a polyester backing to hold the mica material together. The insulation may be in the form of a tape wrapped around the conductor, the amount of insulation depending on the voltage drop across the insulation. Mica-5 isolation is preferably impregnated with about 3 to 30% (a weight range of about 5 to about 12 based on mica weight is particularly favorable) of a polymer that reacts with the anaerobic resin for better Ensure bond. Polyesters, acrylics, io polybutadienes or other unsaturated monomers can also be used as co-reactive resins.

The VPI process is the preferred method of isolating a conductor because this process leaves very few air gaps in the insulation, but other methods can also be used. The wrapped conductor is placed in a tank, which is then evacuated. The anaerobic resin is supplied under pressure, usually under a pressure of at least about 3.23 kg / cm 2, although pressures from about 6.3 to about 7.0 kg / cm 2 are preferred. The resin should saturate the insulation. Typically, the isolation will contain from about 5 to about 35% (weight percent based on the weight of the isolation) of anaerobic resin, although from about 20 to about 30% is preferred. The resin is allowed to drain from the wrapped conductor and then cured by contacting it with a gas that does not contain any significant amounts of oxygen. This can be done in the same tank, but the wrapped conductor can be cured in another tank. Nitrogen, carbon dioxide, 30 or mixtures of these two gases are particularly preferred because they are cheap, safe and easy to handle, but other inert gases (except oxygen) can also be used. It has been found that when nitrogen is used to cure an acrylic resin, the 35 curing rates are optimal with a nitrogen flow rate of about 6 to 201 / min.

The invention will now be explained in more detail using the following examples:

40

Example I

The following table lists various compositions for anaerobic resins that were prepared and then tested for their gel time and storage stability.

Resin-

Difunctional

Vinyl-

Catalyst,

Accelerator,

Co-accelerator,

No.

Acrylic monomer monomeric

Cumene hydro

N, N-dimethyl

Benzoic acid

(75 pieces)

(25 pieces)

peroxide p-toluidine sulfimide

(Parts)

(Parts)

(Parts)

1

T etraethylene glycol

Styrene

2.0

0.4

0.30

dimethacrylate

2nd

dto.

Styrene

2.0

0.4

1.0

3rd

dto.

Styrene

2.0

0.4

3.0

4th

dto.

Styrene

2.0

1.0

0.30

5

Tetraethylene glycol

Styrene

2.0

0.4

0.30

diacrylate

2-ethylhexyl acrylate

6

dto.

2.0

0.4

0.30

7

dto.

0.4

0.30

8th

dto.

Ethyl methacrylate

2.0

0.4

0.30

9

dto.

Styrene

2.0

0.4

0.30

10th

dto.

Ethyl methacrylate

2.0

0.4

0.30

11

dto.

Ethyl methacrylate

2.0

0.4

0.30

629397

4th

Resin no.

Inhibitor,

Hydroquinone (parts)

Viscosity at 25 ° C (cps)

Gel time in N2 at 25 JC (hours)

Storage stability in air at 25 ° C (days)

1

0.04

3.0

8-16

> 100

2nd

0.04

3.0

5-6

48

3rd

0.04

3.0

3-4

> 100

4th

0.04

3.0

8-16

56

5

0.04

3.0

2-3

15

6

0.04

0.5

3-4

> 100

7

0.04

0.5

4- 5

> 100

8th

0.04

0.5

<1.0

> 100

9

0.08

3.0

4- 5

> 100

10th

0.08

0.5

<1.0

> 100

11

0.16

0.5

1-2

> 100

Samples of the above resins were limited to approximately 50 g due to the high exothermic heat generated during curing. The storage stability tests, which determine the storage time until visible gelation occurs, were carried out on samples consisting of approximately 50 g of the resin, which were stored in glass or polyethylene containers with a content of 0.121. Because of the uncertain effects of fluorescent lighting in the laboratory on resin stabilities, the samples were stored in the dark. The gel times (under N2 gas flow) on the samples were determined at periodic intervals in order to check the remaining hardening reactivity during storage.

The gel time measurements (this is the time required for visible gelation to occur) were made on 10 g samples in 5 cm diameter aluminum plates. It was found that the usual laboratory vacuum was not sufficient to gel the samples within a reasonable time. However, rapid gelation was achieved by placing the samples in a dryer and passing nitrogen through the dryer. The following table shows the results of testing resin No. 10.

Curing condition

Gel time at 25 "C

air

N2 flow (131 / min) vacuum

48 hours 30-60 min 24 hours

At the end of the 24 hours, very little gelation (approximately 7% of the resin) was observed at the bottom of the aluminum plate on the sample, which was placed in a vacuum.

The following table shows the results of similar tests performed on Resin No. 9.

Curing condition

Gel time at 25 ° C

C02 (131 / min) N2 (3.5 kg / cm2, static) air (131 / min) Oz (131 / min)

20 min 7-8 hours> 2 days> 2 days

Carbon dioxide occurs at atmospheric pressure, but requires less gas.

Using similar procedures, the effect 20 of nitrogen flow rate on resin # 9 was found. The following table shows the results.

Pressurized C02 with 3.5 kg / cm2 also produced quick curing. Static nitrogen or carbon dioxide under pressure led to slower curing than under a nitrogen flow or during

Flow rate (1 / min = lpm)

Gel time (hours)

25th

1.62 3.25 6.50 13.0 30 20.0 26.0

7.5 4.0 2.0 1.5 3.0 4.0

The table above shows that a flow rate of about 35 to about 20 lpm is a critical value in order to obtain rapid curing at a pressure of about one atmosphere.

Example II

40 power factor data were obtained for mica compositions impregnated with the most promising anaerobic resins, namely Resin Nos. 8 and 9. Two types of compositions were made, one (Sample A) was made by adding a 45 anaerobic resin in one piece "Raw" mica paper ("Co-gemica", sold by Cogebi Co.) was brushed, which had a size of about 20 x 20 cm and a thickness of 0.5 mm, while the other sample (sample B) was produced thereby that the anaerobic resins were brushed onto a polyester-50 impregnated mica tape, which was wound six layers thick (ie three semi-overlapping wraps) on copper pipes (20 cm long, 1.3 cm outer diameter). Because of the very fluid nature (<3.0 cps) of these anaerobic resins, rapid and complete penetration of these gum products was observed.

The samples were gelled under N2 flow (13.01 / min) at room temperature and it was noted that the copper tube samples showed rapid gelation under these circumstances (i.e. <30 min). In order to determine the extent of curing of the anaerobic resins in these compositions and the existing or nonexistent need for post heat treatment of these materials, it was decided to cure a set of these samples for four hours 65 hours at a temperature of 135 ° C after the initial curing had taken place at room temperature. It was assumed that a comparison of the electrical data obtained from these two sets of samples

would determine whether additional heat treatment is necessary to fully cure these anaerobic materials.

Power factor measurements were performed at 25 and 150 ° C. The copper pipe samples were also examined at 1, 1.5 and 2 kV at both temperatures, around the Ein5 629 397

flows of voltage to determine the power factor values of these mica compositions.

The power factor data obtained from copper pipes wrapped 5 with sample B mica tape and impregnated with two of the anaerobic resins are shown in the following table.

Resin temperature heat curing? % Power factor (100 x tan y)

(C) (4 hours at 135 C) applied voltage

1.0

1.5

2.0

9 25

No

2.10

2.16

2.71

Yes

2.3

2.32

2.59

150

No

31.4

32.4

35.8

Yes

28.3

28.9

31.9

8 25

No

2.32

2.32

2.5

Yes

2.48

2.49

2.52

150

No

27.9

28.9

31.1

Yes

34.2

35.7

37.7

The results with Resin No. 9 at 150 ° C show that the sample that was not subjected to any heat treatment after the initial curing had slightly higher power factor values than the sample that had been subjected to heat treatment. However, both samples showed similar power factor values at 25 ° C.

For Resin No. 8, the sample with the additional heat treatment showed slightly higher power factor values at 150 ° C than the sample that did not have this additional curing. However, the room temperature values remained the same for both samples. Based on this data, it is difficult to determine whether additional heat treatment for these anaerobic materials is necessary in order to achieve full curing. However, it may be significant that all four samples showed very similar room temperature power factor values.

Although no attempt was made to determine the optimal mica tape for these anaerobic impregnants, the power factor values for these compositions using the Sample B mica tape were not considered to be excessively high. Although the 25 values (i.e. 32 to 37% at 150 ° C and 2 kV) would be unacceptably high for high voltage applications, they would be suitable for the insulation of low voltage systems (e.g. <13.8 kV).

Dielectric strength measurements were made for 30 mica compositions made with Sample A and impregnated with Resin No. 8. The samples were tested under an aliphatic hydrocarbon transformer oil manufactured by Westing-house Electric Corp. is sold under the trade name «WEMCO 35 C». The tests were carried out at room temperature using a voltage rise of 1 kV / s. Power factor and dielectric constant data were obtained for compositions of Sample A using Resin No. 10 and are summarized in the following 40 table.

Test temperature curing conditions (° C)

25 16 hours at 25 ° C under N2

dto. + 4 hours at 135 ° C in air 150 16 hours at 25 ° C under N2

dto. + 4 hours at 135 ° C in air

Again, there appears to be an interesting difference between the sample that received the additional heat treatment and that without the additional heat treatment. The performance factor of the sample cured at room temperature, measured at 150 ° C, was much lower than that of the other sample. The reasons for these differences are currently not quite clear yet. However, both samples have a sufficiently low power factor and acceptable dielectric constant values for insulation up to voltages of approximately 13.8 kV.

Capacity power factor% dielectric

(pF) (100 x tan y) constant (E ')

36.3 0.89 3.4

58.4 1.6 5.2 138.6 4.8 12.9

94.2 23.0 8.4

The following table shows the dielectric strength for the two samples used in the table above. The measurements were carried out at an N2 flow rate of 13.0 lpm under «WEMCO C» oil at 25 ° C using a voltage increase of 1 kV / s. Both composition samples were used for the above power factor measurements and were believed to be at 150 ° C for one hour before being tested for dielectric strength.

Curing condition Thickness of breakdown dielectric

Composition tension strength O / iooo)

(kV, RMS value) (V / Viooo ")

overnight (16 hours) at 25 = C in N2 flow 21 16.0 765

dto. + 4 hours at 135CC in air 20 16.5 830

dto. 4-4 hours at 135 ° C in air 20 18.5 935

629397

The sample that had the additional curing at elevated temperature appears to have somewhat higher dielectric strength than the sample cured at room temperature. However, both compositions appear to have higher dielectric strengths than epoxy resin impregnated mica compositions of similar thickness. Typically, epoxy mica compositions show values of 400 to 600 V per viooo "compared to 700 to 900 V per viooo" for anaerobic resin samples.

Example III

The importance of curing these resins under ei6

To illustrate a N2 flow, the following experiment was carried out. Four copper tubes were wrapped with Sample B mica tape as described above. One set (two) of these samples was impregnated with resin # 5 and # 5 and the other set with resin # 8. One tube from each set was allowed to cure in an N2 flow (flow rate 13 lpm) for 32 hours. Thereafter, both sets were left in the air for two weeks. The curing conditions and resin retention for each of these samples are shown in the following table.

Rehearse-

Resin-

copper

Weight of

Curing

Weight

resin

No.

No.

tube wrapped conditions after retention

Weight

Copper pipe

impregnation

(G)

(G)

(G)

B1

5

58.97

69.38

air

70.25

0.87

B2

5

56.56

67.13

n2

68.18

1.05

B3

8th

57.79

67.93

n2

69.06

1.13

B4

8th

56.90

67.23

air

68.36

1.13

% Resin retention on mica

8.35 10.00 11.15 10.92

The resins had been stored in polyethylene bottles at room temperature for two months before being used. The "runoff" of the resin from the samples that were cured under N2 was found to be negligible.

Power factor measurements at 1 kV were then performed on these four samples at 25 ° C. The results are shown in the table below.

Sample power factor (100 x tan y) at 60 Hz

No. at 25 ° C at 150 ° C at 25 ° C after after 3 days 3 days at 150 ° C

B1 B2 B3 B4

25.6 3.5 4.5 32.8

30.2 23.1

25.8

23.9

1.4 1.2 1.8 1.8

Samples B2 and B3, which were allowed to cure in a stream of N2, showed much lower power factor values than the samples left in air. This is not so surprising since the last two samples were still very sticky, even after two weeks. The other samples were firm and tack-free after a few hours in N2.

In order to explain the lack of curing of samples B1 and B4, all four samples were post-cured for three days at 150 ° C 30 and the power factor values measured again at 25 ° C and also at 150 ° C. This data is also shown in the table above. At room temperature, all four samples gave similar values (between 1.2 and 1.8%), as did at 150 ° C (23.1 to 30.2%).

35 It can thus be seen that the samples which were exposed to the N2 flow were more fully cured than the two samples which were left in air. Additional heat treatment of the material did not appear to be necessary for a typical Class F motor because full curing could be achieved after the coils were wrapped in a stator because the operating temperature of the motor is high enough to allow full curing.

Winding only partially cured coils (provided that the resin no longer sticks) could also be advantageous, since the mica insulation would still retain a certain degree of favorable flexibility. Conventionally manufactured coils are sometimes a bit stiff and therefore difficult to wind up without breaking the insulation.

s

1 sheet of drawings

Claims (19)

629397 PATENT CLAIMS 1. A method of forming a hardened, resinous coating on an article, characterized in that a resin which does not cure in the presence of oxygen is applied to the article in the presence of oxygen and the article in a gaseous atmosphere which contains no oxygen , brings. 2. The method according to claim I, characterized in that the gaseous atmosphere consists of nitrogen and / or carbon dioxide. 3. The method according to claim 1 or 2, characterized in that an acrylic resin is used as the resin. 4. The method according to claim 1, 2 or 3, characterized in that the object used is a conductor covered with insulation. 5. The method according to claim 4, characterized in that the insulation consists of mica and the conductor consists of copper. 6. The method according to claim 4 or 5, characterized in that the insulated conductor is brought into a vacuum and the insulation is then impregnated with the resin under pressure. 7. The method according to claim 6, characterized in that the pressure is 3.2 to 7.0 kg / cm2. 8. The method according to claim 1, 2 or 3, characterized in that the object used is a wire which is passed continuously through the resin and from there through the gaseous atmosphere which contains no oxygen. 9. The method according to any one of claims 1 to 7, characterized in that a motor or generator coil is used as the object. 10. The method according to any one of claims 1 to 9, characterized in that the resin is solvent-free. 11. The method according to any one of claims 1 to 10, characterized in that the resin contains an accelerator. 12. The method according to claim 11, characterized in that benzoic acid sulfimide is used as the accelerator. 13. A article provided with a hardened, resin-like coating, produced by the method of claim 1, characterized in that it has a conductor covered with insulation, the insulation being impregnated with the hardened resin. 14. Article according to claim 13, characterized in that the insulation consists of mica, glass, asbestos and / or organic resins. 15. An article according to claim 14, characterized in that the mica-containing insulation contains 3 to 30% by weight, based on the weight of the insulation, of an organic resin which is co-active with the resin which does not harden in the presence of oxygen . 16. Article according to claim 13, 14 or 15, characterized in that the resin which does not cure in the presence of oxygen is an acrylic resin. 17. The article according to claim 16, characterized in that the acrylic resin is modified with styrene. 18. Article according to one of claims 13 to 17, characterized in that the amount of resin which does not cure in the presence of oxygen is 5 to 35 wt .-%, based on the weight of the insulation. 19. Object according to one of claims 13 to 18, characterized in that the conductor consists of copper.