US3523040A - Method of sealing a magnetic core - Google Patents

Method of sealing a magnetic core Download PDF

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Publication number
US3523040A
US3523040A US618432A US3523040DA US3523040A US 3523040 A US3523040 A US 3523040A US 618432 A US618432 A US 618432A US 3523040D A US3523040D A US 3523040DA US 3523040 A US3523040 A US 3523040A
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US
United States
Prior art keywords
core
coating
cores
temperature
curing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US618432A
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English (en)
Inventor
John T Lee
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Spang and Co
Magnetics Inc
Original Assignee
Magnetics Inc
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Publication date
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Publication of US3523040A publication Critical patent/US3523040A/en
Assigned to SPANG & COMPANY, A CORP OF PA reassignment SPANG & COMPANY, A CORP OF PA ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: SPANG INDUSTRIES INC., A PA CORP
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/02—Casings
    • H01F27/022—Encapsulation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/005—Impregnating or encapsulating
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/4902—Electromagnet, transformer or inductor

Definitions

  • This invention is concerned with electrical insulation, magnetic cores and magnetic core manufacture.
  • Fluidized coating of boxed cores described in the patent to Goethe et a1. #3,l48,346, requires relatively high capital investment for equipment and has a number of inherent difiiculties. These include holding the core during dipping, recoating steps to cover grip points, and a requirement for heavy coating thickness in order to obtain reasonable voltage breakdown protection. Further, fiuid ized coatings produce a hard finish which does not provide the desired support for coil windings. Neither the paint methods of prior practice nor the fluidized coating method provide adequate corner protection without increasing the average coating thickness such that loss of substantial coil winding space results.
  • the electrical insulating material of the present invention provides good edge coverage without excessive build-up of coating thickness on core flat surfaces, provides desired voltage breakdown protection from minus 100 F. and below to above 450 F. without physical or electrical degradation, is impervious to common solvents, acid, and alkali solutions, and is capable of sealing a core to prevent entrance of potting compounds and varnishes during vacuum impregnation.
  • Prior art coatings have a hard, glossy finish which do not effectively hold the coil windings within desired sectors. For example, when attempting to make coil windings in a 90 arc of a toroidal core, the windings spread out easily to a greater arc because of slippage on the hard, glossy finish. Also, while coatings of the prior art are adequate for flat surfaces they do not maintain coating thickness on corners as required. Corner coverage with these coatings is usually less than 50% of the coating thickness on the fiat surfaces of the core.
  • the desired thixotropic properties are developed by a selection of a solid particulate material which is carried in colloidal suspension in the spray-on insulating material.
  • This solid particulate material in developing desired thixotropic properties, contributes to the formation of a matte-finish whch provides for non-slip Winding of coil windings.
  • corner coverage provided is at least of the average coating thickness on fiat surfaces of a product.
  • the solid particulate material referred to herein as a filler
  • a filler should be inert, electrically insulating, temperature stable to at least 500 F., and have a particle size which develops desired thixotropic properties.
  • a suitable filler is silica i.e. substantially pure silicondioxide, amorphous in structure, with a particle size less than .02 micron in diameter or cross-sectional length.
  • a solid, pulverized, inorganic pigment which is temperature stable to 500 F. or higher.
  • temperature stable here is meant that the pigment remains solid and has color retention, i.c. does not oxidize at temperatures below 500 F.
  • suitable pigments are molybdate orange and mercadmium red.
  • a suitable base for the solid filler and pigment is an important teaching of the invention.
  • the base must be a fluid and temperature stable to about 500 F.
  • Suitable synthetic resins include silicones, alkyds, epoxies, and silicone-modified alkyds and epoxies. Silicones or silicone modified high temperature resins are preferred because of the likelihood of silicone contamination of external surfaces of a boxed core. With silicones or silicone-modified resins, silicone contamination on a product does not inhibit bonding.
  • the fluid resin, pigment, and filler are mixed with a volatile liquid, such as aromatic hydrocarbons in proportions providing suitable viscosity for spraying.
  • a volatile liquid such as aromatic hydrocarbons
  • a high boiling point solvent should be included in the vehicle for carrying out the method of the invention.
  • a boiling point for the solvent between about 225 F. and about 300 F. is preferred in order to prevent drying of the material on the heated product before proper w of the coating.
  • a specific embodiment of a coating compound in accordance with the teachings of the invention includes the following percentages by weight:
  • the mixture should have a viscosity 'within the range of 200-500 centipoises when measured immediately after thorough agitation of the mixture.
  • FIG. 1 is a sectional view of a boxed core
  • FIG. 2 is an expanded sectional view of a portion of a boxed core showing the effects of gas expansion on electrical insulation applied in accordance with the prior art
  • FIG. 3 is a sectional view of a portion of a boxed core sealed in accordance with the present invention
  • FIG. 4 shows a cross-sectional view of a boxed core insulated in accordance with the present invention
  • FIG. 5 shows a cross-sectional view of an unboxed core partially sealed in accordance with the present invention
  • FIG. '6 shows sectional view of a portion of the core of FIG. 5 sealed in accordance with the teachings of the present invention.
  • the boxed core of FIG. 1 includes a trough-like, nonmagnetic, metallic container 12 which can be toroidal, rectangular, or other configuration.
  • the open end of the trough-like container 12 is covered with closure means 14 resting on shelf means 16 and 18.
  • Closure means 14 is held to the trough-like container 12, for example by deforming portions of the container 20 and 22, i.e. by folding over lip portions of the metal. Where closure means 14 meets trough-like container 12 an external juncture is formed at 24 and 26 between these two portions of the core encasement.
  • a tape-wound magnetic core 28 is supported by cushioning material 30.
  • FIG. 2 shows an expanded portion of a core, such as that shown in FIG. 1, at the juncture line 26 of that core.
  • an insulating coating 32 applied in accordance with the prior art, has been added.
  • Typical bubble or pinhole formation in the coating of prior art cores is shown at 34 above juncture 26.
  • Such bubbles or pinholes are formed during curing of the prior art cores, when the cores are subjected to a higher curing temperature than that existing at the time of coating the cores. They are caused primarily by expanding gas escaping along a juncture line between the closure means of the metallic container. Similar defects occur due to expanding gas from interstitial portions of unboxed cores. The result of such defects is a non-sealed or poorly sealed core for vacuum impregnation purposes and also a likely shorting path for voltage breakdown between coil windings and the magnetic core or its metallic enclosure.
  • FIG. 3 is a sectional view of a portion of a core in a rigid container.
  • Core 34 is formed by placing electrically insulated magnetic sheet material in overlapping contact.
  • the core is placed within non-magnetic metallic container 36 and is supported by cushioning material 38.
  • Closure means 40 covers the open end of container 36 to provide a rigid encasement for core 34.
  • the encased core is heated above about 225 F. but not higher than about 425 F.
  • the core is heated to a temperature such that a temperature of 275, plus or minus 5, is maintained at the time of subsequent coating and curing. Heating of the uncoated boxed core expands gases within the core box permitting escape of gases before the first seal coating has begun to solidify.
  • closure means 40 and metallic container 36 on the exterior of the encasement are coated by spraying on electrical insulating material.
  • the electrical insulating material is sprayed on in a batch operation providing high volume production.
  • the cores are positioned closure end up on spraying trays and the upper surface of the core is sprayed with electrical insulating material 42. While in this position inner and outer diameters of the metallic container can also be sprayed. Normally the upper corners, and the inner and outer diameters are coated as shown in FIG. 3.
  • the cores After spraying the cores are returned to an oven for partial curing, i.e. solidfication of the spray coating 42 at a temperature above about 225 F. but not significantly higher than the temperature of the core when sprayed.
  • solidification of the sprayed-on coating seals the cores and the sealed cores are held in the above temperature range for approximately one-half hour after which the sealer coat will have cured suiiiciently to prevent escape of any expandable gases within the container.
  • the core is then raised to a temperature of about 300 F. to insure that the sealer coat is properly cured to withstand subsequent heating and cooling cycles.
  • the cores are turned after removal from a 300 F. oven and the remainder of the boxed core is sprayed with coating 44, as shown in FIG. 4. This coating is solidified as described above. Plural coating can be applied with intermediate partial curing of previous coatings.
  • the cores are returned to an oven between 425 F. and 500 F. for about one-half hour. This is the final hardening cure which bonds all coats together and prevents softening of the coatings if the part is heated to elevated temperatures during use.
  • the coating of unboxed cores is similar to the coating of boxed cores except that sealing on a plurality of surfaces is required.
  • Coating 50 applied to unboxed core 52 seals the interstitial openings at the upper end of the core between edge portions of the magnetic material and covers corner surfaces at the upper end of the core.
  • coating 50 can be extended to inner diameter 54 and outer diameter 56.
  • coating 50 is applied in a plurality of layers with intermediate partial curing of each layer as previously described. After partial curing of coating 50 the cores are turned. The cores are heated to a temperature above about 225 F. but less than about 425 F. This expands any gases between the insulated magnetic material and permits these gases to escape.
  • the core While in this heated condition the core is sprayed with coating layer 58 and cured at a temperature of the core when applying layer 58. Additional coats may also be applied by separate sprayings with intermediate curing, depending on the desired final coating thickness. The coating is cured at a final curing temperature between 425 F. and 500 F. for the purposes previously mentioned.
  • the present invention provides voltage breakdown protection in excess of 1000 volt potential with a coating thickness no greater than .007 to .010 inch.
  • the tape of the core should be wound tightly with a quality weld holding the inner and outer lap to the remainder of the core.
  • a single coating layer of the above-described insulation material of an average thickness of .004 inch will provide voltage breakdown protection of at least 500 volts.
  • the teachings of the invention are also applicable to applying voltage breakdown protection to other than tape wound cores such as powder metal cores.
  • the procedures for preheating of the core and curing of the coatings described above are followed in coating such cores so that expandable gases from interstitial portions of the core do not impair the properties of the finish.
  • silicone resins or other high temperature silicone-modified resins in the electrical insulating material described above provides better adherence to external surfaces of the core box materials which are ordinarily contaminated with silicone prior to the time of coating.
  • the fluid resin, pulverized pigment and sub-micron size filler are mixed with a vehicle, typically an aromatic hydrocarbon.
  • a vehicle typically an aromatic hydrocarbon.
  • a high boiling point solvent is included in the vehicle for spraying heated products in order to avoid drying of the spray-on material before proper coverage is obtained.
  • the thixotropic properties provided by the filler maintain corner coverage without the running of the coating prior to curing experienced with prior art coatings.
  • the material can have, by weight, about 8% filler, about 35-40% pigment, and the balance resin.
  • Method for sealing a magnetic core prior to winding coil windings on the core comprising the steps of heating the magnetic core above about 225 F. but not higher than about 425 F. to cause expansion and escape of interstitial core gases, then spraying an electrical insulating material in liquid form on the magnetic core while the magnetic core is above 225 F. but not higher than about 425 F., and
  • the electrical insulating material is prepared in liquid form by mixing a fluid resin, which is temperature stable to 500 F. and a solid, particulate, inorganic filler, which remains solid at about 500 F., with a volatile liquid vehicle.
  • filler comprising essentially silicon dioxide with a cross-sectional particle size of about .02 micron
  • the balance volatile liquid carrier including a solvent having a boiling point above about 200 F. but not higher than about 300 F.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Manufacturing Cores, Coils, And Magnets (AREA)
  • Insulating Of Coils (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
US618432A 1967-02-24 1967-02-24 Method of sealing a magnetic core Expired - Lifetime US3523040A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US61843267A 1967-02-24 1967-02-24

Publications (1)

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US3523040A true US3523040A (en) 1970-08-04

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US618432A Expired - Lifetime US3523040A (en) 1967-02-24 1967-02-24 Method of sealing a magnetic core

Country Status (3)

Country Link
US (1) US3523040A (enrdf_load_stackoverflow)
DE (1) DE1639330A1 (enrdf_load_stackoverflow)
GB (1) GB1226351A (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3713886A (en) * 1971-01-15 1973-01-30 Rca Corp Encapsulated magnetic memory element
US4728919A (en) * 1985-11-25 1988-03-01 Siemens Aktiengesellschaft Moisture-tight wound ferrite toroidal core with resin envelope
DE10141985A1 (de) * 2001-08-28 2003-04-03 Daimler Chrysler Ag Verfahren zur Herstellung von Elektromagneten
US20060012128A1 (en) * 2000-12-20 2006-01-19 Dominique Lutaud Lip sealing ring
CN107533908A (zh) * 2015-04-28 2018-01-02 信越化学工业株式会社 稀土类磁铁的制造方法和稀土类化合物的涂布装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB842134A (en) * 1957-12-04 1960-07-20 Submarine Cables Ltd Method of bonding thermoplastic materials to metals
US2972553A (en) * 1957-04-01 1961-02-21 Gen Plastics Corp Nylon coating method
US2997776A (en) * 1958-05-26 1961-08-29 Gen Motors Corp Electrical apparatus and method of making same

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2972553A (en) * 1957-04-01 1961-02-21 Gen Plastics Corp Nylon coating method
GB842134A (en) * 1957-12-04 1960-07-20 Submarine Cables Ltd Method of bonding thermoplastic materials to metals
US2997776A (en) * 1958-05-26 1961-08-29 Gen Motors Corp Electrical apparatus and method of making same

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3713886A (en) * 1971-01-15 1973-01-30 Rca Corp Encapsulated magnetic memory element
US4728919A (en) * 1985-11-25 1988-03-01 Siemens Aktiengesellschaft Moisture-tight wound ferrite toroidal core with resin envelope
US20060012128A1 (en) * 2000-12-20 2006-01-19 Dominique Lutaud Lip sealing ring
DE10141985A1 (de) * 2001-08-28 2003-04-03 Daimler Chrysler Ag Verfahren zur Herstellung von Elektromagneten
CN107533908A (zh) * 2015-04-28 2018-01-02 信越化学工业株式会社 稀土类磁铁的制造方法和稀土类化合物的涂布装置
CN107533908B (zh) * 2015-04-28 2021-03-12 信越化学工业株式会社 稀土类磁铁的制造方法和稀土类化合物的涂布装置
US11224890B2 (en) 2015-04-28 2022-01-18 Shin-Etsu Chemical Co., Ltd. Method for producing rare-earth magnets, and rare-earth-compound application device

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Publication number Publication date
GB1226351A (enrdf_load_stackoverflow) 1971-03-24
DE1639330A1 (de) 1970-06-04

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Legal Events

Date Code Title Description
AS Assignment

Owner name: SPANG & COMPANY, P.O. BOX 751, BUTLER, PA 16003-07

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:SPANG INDUSTRIES INC., A PA CORP;REEL/FRAME:004368/0644

Effective date: 19850131