DE1947677B2 - Mica insulation made from large scales - Google Patents

Description

The invention relates to mica insulation. In particular, it relates to mica insulation sheets and -strips with improved physical properties, particularly resistance to break-through and severe mechanical abuse.

Breakdown of electrical insulation occurs when during application or use a sharp edge or corner of an isolated part forces its breakthrough and physically the Isolation separates, causing electrical failure. A special !!, acute breakthrough problem consists of high-voltage turbine generators with rectangular copper conductors separated from each other and need to be isolated from the earth. The insulation used must be unusual electrical and mechanical Have properties, particularly against breakthrough and heavy mechanical Abuse, and must withstand when twisted around small-angled bends and in narrow gaps ω is forced without cracking, splintering, or developing voids, resulting in electrical failure would cause. It has been found that the strength against this type of failure from the Results of a laboratory test can be predicted '> "> that measures the force required to break a sharp edge through electrical insulation Mica has excellent electrical, mechanical, and thermal properties but is in its own right naturally occurring state thick and inflexible. Lamellar mica crystals are manually closed Non-contiguous flakes have been stripped, by hand or by machine in overlapping Patterns laid and bonded with resinous material to form an insulating sheet that is suitable for for most purposes adequate strength against mechanical abuse and breakthrough owns. However, machine-laid sheets are thick, often discontinuous, tend to flake, are not uniform and must be used in thick layers in order to have adequate electrical properties achieve. Hand-laid insulation sheets are expensive, difficult to manufacture and also tend to Flaking.

U.S. Patents 24 05 576, 25 49 880 and 26 14 055 describe mica insulating sheets made from naturally occurring mica which are made into thin, continuous flakes in the absence of an inactivating atmosphere, compressing the flakes and drying under heat and pressure. U.S. Patent 3,131,114 describes the wide range of flake sizes from about 5.66 mm to 0.038 mm for use in mica flake insulating sheets with glass flake entrapped therein. Mica insulating sheets produced in this way have good electrical properties and are considerably more flexible and uniform than sheets made from mica flakes, but they are opaque and depend on an impregnating resin for resistance to breakage. When impregnated with soft resin, the sheets lack resistance to physical abuse and deformation, while sheets impregnated with hard resin will crack and splinter during use, resulting in deterioration in electrical insulating property.

Defies the long-recognized usefulness of mica sheet or strip insulation with both Resistance to breakthrough and physical abuse of mica flakes, and the electrical superiority, uniformity, poor strength, and flexibility of newly made mica is such a product has not previously been available.

This invention relates to mica insulating sheets and strips which have excellent strength against Breakthrough and physical abuse with electrical superiority, uniformity, minor Combine the thickness and flexibility of mica.

Insulating sheets and strips made in accordance with this invention have excellent electrical properties Physical Properties. They are pliable, dense, uniform, continuous, translucent, non-flaky and retain their electrical properties, such as arc resistance and corona resistance, dielectric strength and low electrical Heavy duty power factor at. Furthermore, these bows are ideally suited for insulating bows, - Wraps and strips with significantly improved resistance to break-through and mechanical Abuse During Application and Use. The insulating sheets of this invention are excellent suitable for technical use in the insulation of direct current traction motors, alternating current motors, and transformers and are particularly well suited for insulating the rectangular conductors of

High voltage turbine generators. These mica insulating sheets can around the sharp angled bends including the right angle bends on the Edges of right-angled conductors are bent and pushed into narrow cracks without the There is a risk of electrical failure.

It has surprisingly been discovered that a mica insulating sheet is made up of large mica flakes can be made to then have a strength in the unimpregnated state against breakthrough that are more than 200% larger than the wide range of scale sizes of known newly made Is mica arcs and yet has the beneficial uniformity, flexibility and electrical properties maintains. The mica flakes used to make these arches are considerably larger than the average size of mica flake used to make known arches. The mica insulating sheet from an overlapping arrangement of non-impregnated mica flakes is according to the invention characterized in that at least 40% by weight of the flakes are larger than 1.41 mm, at least 70% are larger than 0.50 mm and at least 90% larger than 0.249 mm.

Preferably at least 50% of the flakes are larger than 1.41 mm, at least 80% larger than 0.50 mm and at least 95% larger than 0.249 mm. Known established glinimer isolation sheets use a broad one Scale size distribution from about 5.66 mm to 0.038 mm, mainly from about 0.50 mm to 0.038 mm. It is believed that the large surface area of the individual flakes is a large one Overlap area, which increases the cohesion between the flakes, allows internal voids in the sheet eliminated so that the specific weight increases and creates a continuous arc. It will too believed that the large surface area of the large scales contributed to the excellent strength contributes to breakthrough and physical abuse. 4c

The strength and the resistance to abuse of the mica insulating sheets are illustrated by the tensile strength (ASTM test D-828). A known insulating sheet made from a wide range of sizes (commercially available from Integrated Mica Corporation under the trade designation "Aoim") has an average tensile strength of about 28 to 35 kg / cm ² , while sheets made according to this invention have an average tensile strength of about 245 up to 350 kg / cm ² .

The freedom from internal voids that characterizes the arc of this invention is characterized by this specific gravity of about 1.6 to 2.5 illustrated, which is about 2.7 to 2.8 times the specific gravity of corresponds to solid muscovite. A mica insulating sheet has a specific gravity of about 0.9 to 1.5 what clearly shows that it contains a large number of voids. The specific weight of Mica insulating sheet is easily determined by the Mercury Intrusion method, which is in Bulletin bo 2405-A from American Instrument Company.

Muscovite and phlogopite mica that is larger than about 6.3 mm can be used to make these large ones Mica flakes can be used. After a preliminary <■ >> see with water to remove dust and small fragments are the Glimnner blocks by means of Jets of water falling onto the mica blocks practically parallel to the cleavage plane, like the one in the U.S. Patent No. 24 05 576 is split. The scales are coated with the appropriate U.S. Standard screen classified and made into a mica insulating sheet using standard paper manufacturing techniques, which has an overlapping arrangement of large mica, the surfaces of which are in abutting Relationship. Scales splintered in this way are very thin and have compared to their thickness a large surface area. When reassembled, the individual mica flakes adhere by natural cohesive forces in contrast to mica flakes, which are bonded with resin need to be connected.

After the mica insulating sheet is manufactured, the sheet may be coated with inorganic resin such as boron phosphate or potassium borates or organic resin, such as shellac, epoxy, alkyd, polyester or silicone resin etc., whereby the choice of resin depends on the cost balance, temperature resistance, depends on the flexibility and the required electrical strength. Inorganic or organic Binders, fibers, and threads can optionally be incorporated into the sheet. For certain industrial ones For applications it is appropriate to use the impregnated insulating sheets made from large flakes a tape, such as a polymeric film, or woven or nonwoven products, either using the impregnating resin as an adhesive, or by applying a separate one Adhesive between the tape and the insulating sheet. The improved breakdown strength of great The mica insulation sheet created by dandruff does not depend on the saturating resin or the substrate (backing Web), which allows the use of numerous soft resins that reduce the flexibility of the insulating sheet maintained.

Resistance to breakthrough is provided by installing a 1.25 χ 1.25 χ 7.5 cm Mild steel rod with a 0.0008mm thick finishing on all sides in each clamp of a one Pressure cell containing tensile tester determined. Both rods are at right angles on the edge used to each other so that only one point of contact occurs when the rods touch. The selected Sample is brought between the rods and the machine clamps at one speed closed at 1.25 cm / minute. The right-angled edges are forced through the mica arch until they touch each other and thereby close an electrical circuit that a lamp is used to Illuminates, indicating that the breakthrough is complete. The tensile tester recorder gives a accurate reading of the force required to force the sharp edges through the mica sheet.

The following examples, in which all parts are parts by weight unless otherwise specified, illustrate the manufacture of the insulating sheets and strips of this invention without limiting the scope thereof.

Description of the preferred embodiment
example 1

This example describes how to break up mica blocks into flakes and make one newly created mica insulation sheet from large scales. Indian muscovite scrap is made into thin scales split open by exposure to jets of water,

as described in U.S. Patent No. 2,455,576. The wet mica flake slurry was classified by washing the flakes using a number of USA standard sieves ^; ficated, discarding all flakes below 0.104 mm particle size. The classified flakes are reunited in a 1 percent mica slurry in water such that 52% by weight of the flakes in the whole slurry are greater than 1.41 mm, 85% greater than 0.50 mm, and 93% greater than 0.249 mm.

The sheet was then made using technical paper mill equipment which - in combination - comprised a stirrer, a storage box and a cylinder paper machine with an endless moist press drive belt which conveyed the moist mica flake from the cylinder screen to a damp steel press roll, the speed of the cylinder screen 8 cm / second. An endless woven full construction belt transferred the damp paper tape to a dry part! the machine where the paper was dried by passing it through a series of steel cylinders heated ^{to about 60 to 80 ° C.} The speed of delivery of the mica flake slurry to the paper machine determines the thickness of the insulating sheet obtained. The sheet thickness can vary from about 0.0127 to about 0.75 mm. If thicker sheets are desired, the sheets can be stacked or sandwiched together. Mica insulating sheets made in this manner have an unusually high degree of scale uniformity as evidenced by the uniform transparency observed when a sheet is held against a light source.

An insulating sheet made as described above has an average thickness of 0.063 mm when tested according to ASTM Test D-374, Method C, a tensile strength of about 280 kg / cm ² when tested according to ASTM Test D -828 had a dielectric strength of about 643 volts per 0.0254 mm when tested according to ASTM Test D-149, a breakdown strength of about 3 kg, a specific gravity of about 1.7 and made a useful insulating sheet without impregnation. This mica sheet was impregnated, layered, wound and slit as described in Examples 2-5.

An insulating sheet using the wide 5.66 mm to 0.038 mm flake size distribution of the prior art as disclosed in U.S. Patent 3,131,114 was prepared and tested in the same manner. It had an average thickness of 0.072 mm, a tensile strength of about 14 kg / cm ² , a dielectric strength of about 350 volts per 0.025 mm, a breakdown strength of about 0.9 kg and a specific gravity of about 1.2.

Example 2

This example describes the impregnation of a portion of the newly made mica insulating sheet of Example 1 from large flakes with a polyester / epoxy resin. A mixture of 100 parts of polyester epoxy resin and one part of tertiary amine [tris (2,4,6-dimethy! Aminomethyl) phenol] was prepared according to Example 2 of US Pat. No. 3,027,279. The impregnating resin was diluted to 25% solids with methyl ethyl ketone and applied to the mica sheet using a conventional dipping and flowing process. The impregnated paper was then dried and then cured for about 15 minutes at 65 ° C for 10 minutes at 200 ⁰ C. The finished insulating sheet was tough, pliable, and fully cured. The resin content of the impregnated sheet was determined by weighing both before and after coating and found to be about 20% by weight.

If the impregnated sheet: n that in example 1 was examined manner described, resulted in a

ίο average thickness of 0.112mm. a tensile strength of about 700 kg / cm ² , a dielectric strength of 690 volts per 0.0254 mm, and your breakdown strength of about 3.5 kg.

The impregnation of a Glirnmer insulating sheet under Using the wide 5.66 mm to 0.038 mm flake size distribution known in the art in of the same kind with the same resin gave a sheet that was 0.119 mm thick, contained 20% resin and one Had breakthrough resistance of 1.5 kg.

Example 3

A portion of the large scale mica insulation sheet of Example 1 was used in the in Example 2 described manner with an isooctyiacrylate / acrylic acid / epoxy terpolymer resin and 0.45% uranyl nitrate hexahydrate impregnated as a catalyst.

The copolymer resin was prepared by first mixing 900 kg of isooctyl acrylate, 13 kg of acrylic acid, and 8 kg of tertiary dodecyl mercaptan in a stainless steel tank. A charge of 1250 kg of toluene was then placed in a 5500 liter glass-lined kettle, followed by 65 kg of the mixture in the tank. The kettle was flushed with nitrogen and ^{heated to 80 °} C. with constant stirring, while a gentle stream of nitrogen was constantly maintained through the kettle. Then 3 separate 10 kg batches of azobisisobutyronitrile dissolved in toluene were added at equal intervals over a period of approximately 50 minutes; each feed having 22% solids. During this period the mixture from the tank was continuously added at a rate of about 17 kg per minute. After a further 50 minutes, 9 kg of 20% strength azobisisobutyronitrile in toluene were added, and the temperature was ^{kept at 80 °} C. for a further 2½ hours. Then 55 kg of 3,4-epoxycyclohexylmethyl-S ^ -epoxy-cyclohexanecarooxylate having an average molecular weight of about 260 and a viscosity of about 500 centipoise at 24 ° C (Union Carbide ERL-4221) was added and mixed in thoroughly. The mica sheet was then impregnated as in Example 2 and, after drying for 10 minutes at 100 ° C. and curing for 10 minutes at 200 ° C., the resin content was determined to be 20% connected by means of coating rollers.

wi is the breakdown strength of this insulating arc much larger than that of a known mica insulating sheet, as described in Example 1, at Similar impregnation and coating.

Example 1 4

This example illustrates the impregnation of part of the mica insulating sheet of Example 1 with soft pliable silicone resin by coating

a woven glass cloth impregnated with resin and then layered on a polyethylene terephthalate film.

Polysiloxane resin (commercially available from General Electric Company under the tradename SR-32) was diluted to 35% solids in toluene. A woven glass cloth 0.05 mm thick was made impregnated with this resin by the usual immersion and flow process and applied to part of the The mica sheet of Example 1 is stacked by means of a layer roller; the layer structure was 4 minutes dried at 200 ° C. The insulating sheet contained 10% resin, was 0.2 mm thick and had a break through resistance, that of a known, as described in Example 1, similarly saturated and layered mica insulating sheet was superior.

The uncoated exposed mica surface was then coated with the silicone resin saturant described above coated according to the roller coating technique running in the same direction and for 4 minutes Dried at 120 ° C. The sticky mica surface was then rolled up with the aid of lay-up rollers coated in a jumbo roller on 0.006 mm thick biaxially oriented polyethylene terephthalate film, and then divided into 2 cm wide strip rolls. The resin content of the layer structure was 15%, and the breakdown resistance was that of one as described in Example 1 impregnated in a similar manner and coated known mica insulating sheet.

Example 5

This example illustrates the lay-up of a polyester film tape on the impregnated newly created from large scales mica sheet of Example 2. After the impregnation and the subsequent 15-minute drying at 65 ^C C the impregnated mica sheet was cooled and rotating by means of pressure rolls to 0.012 mm thick biaxially oriented Polyäthylenphthalatfilm piled up. The breakdown strength was superior to that of a known, as described in Example 1, similarly impregnated and coated mica insulating sheet.

Claims (6)

Patent claims: 1. Mica insulating sheet after an overlapping arrangement of non-impregnated mica flakes, ■> characterized in that at least 40 wt .-% of the individual flakes greater than 1.41 mm, at least 70% by weight of the individual flakes larger than 0.50 mm, and at least 90 % By weight of the individual flakes are greater than 0.249 mm. 2. insulating sheet according to claim 1, further characterized in that it is coated with an epoxy, polyester, Silicone, alkyd or acrylic resin is impregnated. 3. insulating sheet according to any one of the preceding claims, further characterized in that it coated on a fibrous tape or polymeric film. 4. insulating sheet according to claim 3, further characterized in that the tape of fibers Polyethylene terephthalate, and the polymeric film consists of biaxially oriented polyethylene terephthalate. 5. insulating sheet according to any one of the preceding claims, further characterized in that it is wound around itself in roll form and that it can be derived from it without delamination or Removal can be handled. 6. A method for producing the insulating sheet according to claim 1, characterized in that naturally occurring mica in the absence of a non-activating atmosphere in flakes When the mica flakes are split up, they are classified to a class of large flakes to obtain, in which at least 40 wt .-% of the flakes are larger than 1.41 mm, and in the In the previous step, scales of the class of large scales obtained anew into a mica insulating sheet be put together. 40