Document 4vRvNLd2V1arzD8KYDnmM98Yx

FILE NAME: McGraw-Edison (ME) DATE: 1957 Dec 23 DOC#: ME012 DOCUMENT DESCRIPTION: Patent - Dynamoelectric machine winding tool with coil sides and end turns of different flexibility [Approved - 1960 Mar 15] M arch 15, 1960 l c jo n e s 2 Q2fi o c j, DYNAMOELECTRIC MACHINE WINDING COIL WITH COIL S I D E S '^ Filed Dec. 23 1957 M EN TURNS F DIFFERENT FLEXIBILITY ' ' 2 Sheets-Sheet 1 INVENTOR. Loren C.Jones BY 'fju J fz. ATTORNEYS March 15, 1960 l. c . jo n e s 2,928,964 DYNAMOELECTRIC MACHINE WINDING COIL WITH COIL SIDES AND END TURNS OF DIFFERENT FLEXIBILITY Filed Dec. 23, 1957 2 Sheets-Sheet 2 Loren C Jones. BY ATTORNEYS Jnted States Patent Office Patented Mar2.,9152,8,1996640 1 2 2,928,964 Figure 4 is a plan view of a coil showing the applica tion of pressure pads according to the present inven tion; DYNAMOELECTRIC MACHINE WINDING COIL Figure 5 is a sectional view taken along the line 5--5 WITH COIL SIDES AND END TURNS OF DIF- _ of Figure 4; FERENT FLEXIBILITY 0 Figure 6 is a sectional view, taken along the line Loren C. Jones, Columbus, Ohio, assignor, by mesne as signments, to McGraw-Edison Company, a corpora tion of Delaware Application December 23, 1957, Serial No. 704,573 ^ 6--6 of Figure 4; and Figures 7 and 8 illustrate alternate shapes for the pres sure pads illustrated in Figure 4. Referring in detail to the drawing a coil constructed according to the present invention is indicated generally 23 Claims. (Cl. 310--208) at 20 and includes slot portions 21 and 22 and end portions 23 and 24. The slot portions and end portions each include a This invention relates to coils for rotating electrical j . plurality of separate conductors 26 forming turns of the machines and to methods for preparing insulation sys coil as is best seen in Figures 2 and tems for such coils. According to one aspect of the present invention, slot In the manufacture of electrical motors and genera portions 21 and 22 are wrapped with an insulating mate tors the insulated coils employed therein comprise slot rial comprising sheets of backing material with layers portions and end portions. When the coils are installed g0 of mica flakes disposed between said sheets. Such in in an electrical machine it is necessary to insert the slot sulating material for the slot portions may consist of a portions of such coil into radial longitudinal slots in the mica tape formed in accordance with the teachings of magnetic core of the rotor, armature, or stator of the my co-pending application Serial No. 642,752 filed Febru electrical machine. In the course of inserting such slot ary 27, 1957, now abandoned. In accordance with one portions of the coils into the radial slots, the coils must 25 aspect of the invention of said co-pending application be flexed at the end portions, particularly when so called the use of a permanent binder in the mica tape is elimi "lap coils" are installed, unless special costly and time nated and instead a temporary or fugitive binder is ap consuming techniques are employed to eliminate the plied to the mica tape, during the fabrication thereof, to necessity of flexing the end turns of said "lap coils." If maintain the mica material and backing material of the the insulation system applied to such end portions are not 30 tape in assembled relationship during manufacture and flexible, the flexing of the end portions during installa during application of the tape to the conductors. The tion will seriously damage the insulation leading to pre fugitive binder is then completely removed from the mature failure of the winding. interstices of the mica material and backing material and It is therefore an object of the present invention to the insulation subsequently impregnated with a com provide improved coil construction for electrical ma- 35 pletely reactive liquid polymerizable composition or other chines having a hybrid type insulation system whereby suitable impregnant. the coil insulation can be impregnated with a thermo As another aspect of the invention of my above men setting resin and cured and yet maintain flexibility in tioned co-pending application Serial No. 642,752 an even the end portions. Hence the coil may be wound in the more efficient temporary or fugitive binder for the com core of an electrical machine without possible damage 40 ponents of the mica tape can be formulated by a solu to the insulation system using conventional winding tech tion of a surface treating material in a volatile liquid niques. compatible with the particular surface treating material. It is another object of the present invention to pro When such surface treating fugitive binders are utilized, vide a method for insulating coils using a completely the highly volatile liquid portion of the binder is re reactive thermosetting composition to impregnate the en- 45 moved from the interstices of the insulation, but the sur tire insulation system, which may be cured without effect face treating material will remain and form a film on ing the desired flexibility of the insulation cn the end the surfaces within the interstices of the mica material portions, thus enabling the coils to be wound into the and backing. Such film contains a reactive organic group electrical machine without damaging the insulation. that not only can combine with the subsequently applied It is another object of the present invention to provide 50 completely reactive polymerizable impregnating composi a method for insulating a coil whereby an impervious tion but also improves the wetting characteristics of the film is utilized in a novel manner to prevent excessive impregnant. Hence when such surface treating fugitive run-out of the impregnant during the curing process. binders are employed an extremely strong bonding bridge It is another object of the present invention to provide is obtained between the impregnating composition and a method for insulating a coil whereby pressure pads 55 the surfaces within the interstices of the mica tape. are utilized in a novel manner to consolidate the end turn Moreover, the interstices are completely filled with the insulation during the curing process. impregnating composition whereby the insulation is free Other objects and advantages of the present invention of voids which, if present, would be detrimental to the will be apparent from the following description, reference electrical and structural characteristics of the insulation. being made to the accompanying drawings wherein pre- 60 _An alternative type of wrapping material for slot por ferred forms of embodiments of the invention are clearly tions 21 and 22 may consist of mica tape composed of shown. sheets of backing material between which are sandwiched In the drawing: mica flakes or mica paper united with a resinous binder Figure 1 is a perspective view of a coil that has been gg that compatibly mixes with a subsequently applied im constructed according to the present invention; pregnant. Various suitable mica tapes incorporating Figure 2 is a sectional view of a slot portion of the liquid resinous bnders are described in detail in United coil of Figure 1 with the section being taken along the States Letters Patent No. 2,656,290 to Berberich. line 2--2 of Figure 1; The end portions 23 and 24 are wrapped with a differ Figure 3 is a sectional view taken through an end - n ent type of insulating material from that applied to the turn portion of the coil of Figure 1 with the section being 1 slot portions 21 and 22 as described above. Prior to taken along the line 3--3 of Figure 1; wrapping the end portions 23 and 24, however, it isdesir- 3 ,8 2 8 ,9 8 4 3 able to treat the surfaces of the individual conductors 26 occur between the conductors when the coils are being of the end portions, Figure 3, with a coating of a mate flexed during installation in an electrical machine. rial that permits filling of all voids between the conduc The slot portions 21 and 22 are next wrapped with tors but prevents bonding of the conductors by the im a mica wrapping material 29, Figure 6, containing the prgnant that is subsequently applied to the coil during 6 previously described fugitive binder that serves to unite the impregnating cycle. Suitable materials for this ap the mica flakes and backing material during the wrap plication consist of the various mould release agents ping operation. specifically made to prevent polymerizable liquid resins The end portions 23 and 24 are then wrapped with from bonding to jigs or moulds after curing. Examples one of the previously described mica wrapping materials of commercial release agents for this application are 10 28, Figure 5, that are incompatible with the imprgnant Dow-Corning's DC-20, Axel Plastics "Mold Wiz," and to be subsequently applied. Ram's 225 release agent. Other suitable materials for The entire coil 20 is then covered with a wrapping treating surfaces of the individual conductors 26 consist material 30, Figures 5 and 6, of glass, cotton, asbestos, of silicone pastes and greases. Examples of commercial or Dacron which acts as a protective covering. materials in this category are Dow-Corning's 2007 and 15 The entire insulated coil 20 is next temporarily covered 2049, which are silicone pastes, and DC 3 and DC 7 with an impervious film 32, Figures 5 and 6, usually 1 to which are silicone greases. These materials are inert to 2 mils thick. The impervious film 32 may be formed by the subsequently applied imprgnant and exhibit little or no physical change with temperature extremes encoun wrapping of polyvinyl, polytetrafluoroethylene or poly ethylene terephthalate. tered in service. 20 Pads 34 or 34-A, cut from felt sheet material, are next After the confronting surfaces of the individual conduc taped to the end portions 23 and 24 by a second serving tors 26 of end portions 23 and 24 have been treated in of the impervious film as is illustrated in Figure 5. Fig the manner just described, the end portions 23 and 24 are ure 4 shows tile position and location of pads 34 or 34-A, wrapped with a sheet insulating material to form an in it being understood that the pad type 34, Figure 7, in sulation sheath containing voids between the layers of 25 cludes a U-shaped portion 36 which covers a side of the wrapping material and interstices in the material itself. knuckle portion 37 as shown in Figure 4. Tire pad type The characteristics of this end turn insulation sheath are 34-A, Figure 8, differs from pad type 34, Figure 7, in such that the voids and interstices are filled by the im that it does not include the U-shaped portion 36 for cov prgnant subsequentsy applied to the coil to form a void- ering the sides of the knuckle portion 34. free insulation system. This end turn insulation system, 30 The coil is then subjected to a vacuum cycle to remove however, differs from that applied to the slot portions 21 all volatile matter and impregnated in a liquid resinous and 22 in that the wrapping material and cured imprg composition of the type described in detail in my co nant do not form a homogeneous insulation system. The periding application Serial No. 462,752 filed February system is non-homogeneous in the sense that the resinous 27, 1957. tape binder and subsequently applied imprgnant do not 35 The slot portions 21 and 22 are next cured in conven form a compatible mixture. This results in a boundary tional heated hot press dies conforming to the required condition between the binder and imprgnant that pro finish dimensions. This operation does not heat the end vides flexibility in the end turn insulation. portions 2.3 and 24 sufficiently to cure the imprgnant As one aspect of the present invention the end portions which is subsequently accomplished by placing the coil 23 and 24 may be wrapped with a wrapping material com 40 in a heated oven. prising sheets of backing material between which are After curing in the oven, the temporary impervious films sandwiched a layer of mica flakes or mica material with 32 and 32-A and the felt pads 34 or 34-A are removed a resinous binder being utilized to unite mica and back resulting in a finished coil ready for installation in an ing. In such instances, however, the resinous binder is electrical machine. non-reactive with the subsequently applied imprgnant. It should be pointed out that the above mentioned ap The binder in this type of wrapping material for the end 45 plication of the impervious film 32 provides a covering portions is preferably in a semi-cured form. The binder having tape laps that permit the escape of volatiles and may be any one of the common varnish type resins such air in the insulation outwardly between the laps. Fur as plasticized natural resins, oil-modified alkyds, silicone thermore, the imprgnant can pass inwardly between the base resins, oil-modified phenolics, thermosetting varnish tape laps to completely impregnate the insulation. Once of the oil-modified phenolics, or oleo-resinous types. Ex 50 the imprgnant has entered the interstices of the insula amples of suitable resinous liquid binders for the wrap tion, the impervious film 32 serves to prevent escape of ping material are known to the trade as follows: the imp-esnant during subsequent handling of the coil. Silicone base resins-- Dow-Corning's DC 997 or DC 935 Union Carbide R-61 Oieo-Resinous Resins-- Acme Wire Co.'s 501 As additional advantages of the impervious film 32, when the coil 20 is removed from the impregnating tank 55 all excess imprgnant drains rapidly from the outside of the film leaving relatively tack-free surfaces for con venience in handling in the shop. Moreover, the im pervious film prevents evaporation of the imprgnant and porAtisonasno2t3hearndasp2e4ctmoafy thbee wprreaspepnetdinwviethntirounbbtehre teynpde 80 ctoonctaumrininga. tioEnqoufatlhlye oimutpeorrstaunrfta, ciems poefrtvhieouisnsfuillamtio3n2ppriroer wrapping material such as glass reinforced or unrein vents air inhibitation of the impregnating resin during forced silicone rubber tape. The subsequently applied im the curing process and also acts as a natural mold re prgnant will fill the voids in the wrappings but does not lease material between the hot press die and the slot bond them together. 65 portion insulation. Reference is next made to Figures 4 through 8 for pur The impervious film 32 and 32-A is preferably formed poses of describing the preparation of a coil according to of a heat shrinkable material, such as polyethelene the methods of the present invention. First, only the terephthalate; so that upon the application of the heat, end portions 23 and 24 of the individual conductor 26 required to cure the imprgnant, the film 32 and 32-A are treated with one of the previously described coating 70 shrinks and thereby applies pressure that further con materials which prevents the subsequently applied imprg solidates the insulation system. nant from bonding said conductors together. Such treat The felt pads 34 or 34-A are used to achieve uniform ing of the surfaces allows the imprgnant to fill all voids application of pressure over the entire side surfaces of the between conductors but prevents them from being bonded end portions 23 and 24 upon heat induced contraction of together and hence allows some relative movement to 75 impervious film 32. This is particularly advantageous since conforming dies cannot be economically applied to which are compatible with said subsequently appiie the end turn portions 23 and 24. imprgnant; wrapping said end portion with a second It might further be mentioned that because the im sheet insulating material, formed of rubber or the like, pervious films 32 and 32-A are removed from the coil, incompatible with said subsequent applied imprgnant; all surplus cured resin on the outer surfaces of the coil, S impregnating said wrapped coil with said imprgnant particularly the contained resin at the corners along the comprising a liquid resinous composition; and thereafter slot portions, is removed along with the removal of film 32. curing said imprgnant to form homogeneous insulation for said slot portions the components of which are bonded In summary, it will be understood that the resinous together and to form non-homogeneous relatively flexible composition applied to the slot portions will completely 10 insulation for said end portion. fill the interstices of the mica wrap material to form a 4. The steps in the method of insulating a coil having bonded homogeneous insulation system. The imprg slot portions, a connecting end portion, and a plurality nant will also fill all voids between the conductors and of turns having confronting surfaces, for use in a rotating bond to the conductor surfaces. In the case of the end electrical machine, which method comprises wrapping the portions, however, the surface treatment of the individual 15 slot portions with a first insulating material comprising turns and the previously described wrapping material a sheet backing and mica flakes disposed on said backing, applied to the end portions allows the impregnating ma said first sheet material being impregnatable by a sub terial to fill all interstices of the conductors and wrapping sequently applied imprgnant, said backing and flakes material, but prevents a rigid bond between the confront forming interstices the surfaces of which are compatible ing surfaces of the individual turns and the layers of 20 with said subsequently applied imprgnant; applying to wrapping material. Hence, it will be understood that said surfaces of the turns of said end portion a coating the ultimate in insulating properties is achieved in the of material incompatible with said subsequently applied slot portions and, at the same time, the end turn insula imprgnant; wrapping said end portion with a second tion is modified slightly to achieve sufficient flexibility to insulating material containing a binder not compatible permit installation in the slots of an electrical machine. 25 with a subsequently applied imprgnant; impregnating While the forms of embodiments of the present inven said wrapped coil with said imprgnant comprising a tion as herein disclosed constitute preferred forms, it is liquid resinous composition; and thereafter curing said to be understood that other forms might be adopted, all imprgnant to form homogeneous insulation for said slot coming within the scope of the claims which follow. portions the components of which are bonded together, I claim: 30 and to form non-homogeneous relatively flexible insula 1. The steps in the method of insulating a coil having tion for said end portion. slot portions and a connecting end portion, for use in a 5. The steps in the method of insulating a coil having rotating electrical machine, which method comprises slot portions and a connecting portion, for use in a ro wrapping the slot portions with a first insulating material tating electrical machine, which method comprises wrap comprising a sheet backing and mica flakes disposed on 35 ping the slot portions with a first insulating material said backing, said first insulating material being impreg- comprising a sheet backing and mica flakes disposed on natable by a subsequently applied imprgnant, said back said backing, said first insulating material being im ing and flakes forming interstices the surfaces of which pregnatable by a subsequently applied imprgnant, said are compatible with said subsequently applied imprg backing and flakes forming interstices the surfaces of nant; wrapping said end portion with a second insulating 40 which are compatible with said subsequently applied im material containing a binder not compatible with said prgnant; applying to the surfaces of said conductors of subsequently applied imprgnant; impregnating said said end portion a coating of material incompatible with wrapped coil with said imprgnant comprising a liquid said subsequently applied imprgnant; wrapping said end resinous composition; and thereafter curing said imprg portion with a second insulating material comprising a nant to form homogeneous insulation for said slot por sheet backing and mica flakes disposed on the backing and tions the components of which are bonded together, and 45 a polymerized resinous binder uniting the mica flakes to form non-homogeneous relatively flexible insulation for said end portion. 2. The steps in the method of insulating a coil having and the backing, said binder being incompatible with said subsequently applied imprgnant; impregnating said wrapped coil with said imprgnant comprising a liquid slot portions and a connecting end portion, for use in a resinous composition; and thereafter curing said imprg rotating electrical machine, which method comprises 50 nant to form homogeneous insulation for said slot por wrapping the slot portions with a first insulating material tions the components of which are bonded together and comprising a sheet backing and mica flakes disposed on said backing, said first insulating material being impreg- to form non-homogeneous relatively flexible insulation for said end portion. natable by a subsequently applied imprgnant, said back 6. The steps in the method of insulating a coil having ing and flakes forming interstices the surfaces of which 55 slot portions and a connecting end portion, for use in a ro are compatible with said subsequently applied imprgnant; tating electrical machine, which method comprises wrap wrapping said end portion with a second insulating mate ping the slot portions with a first insulating material com rial comprising a sheet backing and mica flakes disposed prising a sheet backing and mica flakes disposed on said on the backing and a polymerized resinous binder uniting backing, said first insulating material being impregnatable the mica flakes and the backing, said binder being in 60 by a subsequently applied imprgnant, said backing and compatible with said subsequently applied imprgnant; flakes forming interstices the surfaces of which are com impregnating said wrapped coil with said imprgnant patible with said subsequently applied imprgnant; ap comprising a liquid resinous composition; and thereafter plying to the surfaces of said conductors of said end curing said imprgnant to form homogeneous insulation portion a coating of material incompatible with said for said slot portions the components of which are bonded 65 subsequently applied imprgnant; wrapping said end por together and to form non-homogeneous relatively flexible tion with a second sheet insulating material, formed insulation for said end portion. of rubber or the like, incompatible with said subsequently 3. The steps in the method of insulating a coil having applied imprgnant; impregnating said wrapped coil with slot portions and a connecting end portion, for use in a said imprgnant comprising a liquid resinous composi rotating electrical machine, which method comprises 70 tion; and thereafter curing said imprgnant to form wrapping the slot portions with a first insulating mate homogeneous insulation for said slot portions the com rial comprising a sheet backing and mica flakes disposed ponents of which are bonded together and to form non on said backing, said first insulating material being im- homogeneous relatively flexible insulation for said end pregnatable by a subsequently applied imprgnant, said portion. backing and flakes forming interstices the surfaces of 75 7. The steps in the method of insulating a coil having 2 , 928,984 7 . . slot portions and a connecting end portion, for use in a prising a liquid resinous composition; and thereafter cur rotating electrical machine, which method comprises ing said imprgnant to form homogeneous insulation for wrapping the slot portions with a first insulating mate said slot portions the components of which are bonded rial comprising a sheet backing and mica flakes disposed together, and to form non-homogeneous relatively flexible on said backing, said first insulating material being im- 5 insulation for said end portion. pregnatable by a subsequently applied imprgnant, said 11. The steps in the method of insulating a coil having backing and flakes forming interstices the surfaces of slot portions, a connecting end portion and a plurality which are compatible with said subsequently applied of turns having confronting surfaces, for use in a rotating imprgnant; wrapping said end portion with a second electrical machine, which method comprises wrapping the insulating material comprising a sheet backing and mica 10 slot portions with a first sheet insulating material com flakes disposed on the backing and a varnish type resin prising a sheet backing and mica flakes disposed on said uniting the mica flakes and the backing, said varnish type backing, said first insulating material being impregnatable resin being incompatible with said subsequently applied by a subsequently applied imprgnant, said backing and imprgnant; impregnating said wrapped coil with said flakes forming interstices the surfaces of which are com imprgnant comprising a liquid polymerizable resinous 15 patible with said subsequently applied imprgnant; apply composition; and thereafter curing said imprgnant to ing to said surfaces of the turns of said end portion a form homogeneous insulation for said slot portions the coating of silicone rubber paste incompatible with said components of which are bonded together and to form subsequently applied imprgnant; wrapping said end por non-homogeneous relatively flexible insulation for said tion with a second insulating material containing a binder end portion. _ 20 not compatible with said subsequently applied imprg 8. The steps in the method of insulating a coil having nant; impregnating said wrapped coil with said imprg slot portions and a connecting end portion, for use in a nant comprising a liquid resinous composition; and there rotating electrical machine, which method comprises after curing said imprgnant to form homogeneous in wrapping the slot portions with a first insulating material sulation for said slot portions the components of which comprising a sheet backing and mica flakes disposed on 25 are bonded together, and to form non-homogeneous rela said backing, said first insulating material being impreg- tively flexible insulation for said end portion. natable by a subsequently applied imprgnant, said back 12. A coil for an electrical machine comprising a slot ing and flakes forming interstices the surfaces of which portion the adjacent turns of which are bonded together, are compatible with said subsequently applied imprg and an end portion the adjacent turns of which are move nant; wrapping said end portion with a second insulating 30 able relative to one another, said slot portion being material comprising a sheet backing and mica flakes dis wrapped with a first sheet insulating material comprising posed on the backing and a varnish type resinous binder backing material and mica flakes forming interstices, said including a plasticizer uniting the mica flakes and the end portion being wrapped with a second sheet insulating backing, said binder being incompatible with said sub material; and a cured imprgnant in said sheet insulating sequently applied imprgnant; impregnating said wrapped 35 materials and compatible with surfaces of said interstices coil with said imprgnant comprising a liquid resinous for bonding together only the components of said first composition; and thereafter curing said imprgnant to sheet insulating material on said slot portion. form homogeneous insulation for said slot portions the 13. A coil for an electrical machine comprising a slot components of which are bonded together and to form portion the adjacent turns of which are bonded together, non-homogeneous relatively flexible insulation for said 40 and an end portion the adjacent turns of which are not end portion. bonded to one another, said slot portion being wrapped 9. The steps in the method of insulating a coil having with a sheet insulating material forming interstices and slot portions and a connecting end portion, for use in a containing a cured imprgnant compatible with the sur rotating electrical machine, which method comprises faces in said interstices, and said adjacent turns of said wrappings the slot portions with a first insulating material 45 end portion being coated with a material not compatible comprising a sheet backing and mica flakes disposed on with said imprgnant. said backing, said first insulating material being impreg- 14. A coil for an electrical machine comprising a slot natable by a subsequently applied imprgnant, said back portion the adjacent turns of which are bonded together, -ing and flakes forming interstices the surfaces of which and an end portion the adjacent turns of which are not are compatible with said subsequently applied imprgnant; gg bonded to one another, said slot portion being wrapped wrapping said end portion with a second insulating ma with a sheet insulating material forming interstices and terial, formed of silicone rubber incompatible with said containing a cured imprgnant compatible with the sur subsequently applied imprgnant; impregnating said faces in said interstices, and said adjacent turns of said wrapped coil with said imprgnant comprising a liquid end portion being coated with a mould release not com resinous composition; and thereafter curing said impreg- gg patible with said imprgnant. nant to form homogeneous insulation for said slot por 15. A coil for an electrical machine comprising a slot tions the components of which are bonded together and portion the adjacent turns of which are bonded together, to form non-homogeneous relatively flexible insulation for and an end portion the adjacent turns of which are not said end portion. bonded to one another, said slot portion being wrapped 10. The steps in the method of insulating a coil having 60 with a sheet insulating material forming interstices and slot portions, a connecting end portion, and a plurality containing a cured imprgnant compatible with the sur of turns having confronting surfaces for use in a rotating faces in said interstices, and said adjacent turns of said electricai machine, which method comprises wrapping the end portion being coated with a silicone rubber paste not slot portions with a first insulating material comprising compatible with said imprgnant. a sheet backing and mica flakes disposed on said backing, gg 16. A coil for an electrical machine comprising a slot said first insulating material being impregnatable by a portion wrapped with a mica material containing a cured subsequently applied imprgnant, said backing and flakes imprgnant, said mica material and wrapping material forming interstices the surfaces of which are compatible forming interstices the surfaces in which are compatible with said subsequently applied imprgnant; applying to with said cured imprgnant to provide a homogeneous said surfaces of the turns of said end portion a coating 70 insulation system; and an end portion wrapped with a of mould release incompatible with said subsequently ap mica material containing a cured binder and said cured plied imprgnant; wrapping said end portion with a sec imprgnant, said binder and imprgnant being incom ond insulating material containing a binder not com patible and forming a non-homogeneous insulation system. patible with said subsequently applied imprgnant; im 17. A coil for an electrical machine comprising a slot pregnating said wrapped coil with said imprgnant com- 75 portion wrapped with a mica material containing a cured  ,9 8 s94 . ._ 9 _ 10 imprgnant, said mica material and wrapping material wrapping the slot portions with a first insulating material forming interstices the surfaces in which are compatible comprising a sheet backing and mica flakes disposed on with said cured imprgnant to provide a homogeneous said backing, said first insulating material being impreg- insulation system; and an end portion wrapped with a natable by a subsequently applied imprgnant, said back mica material containing a cured varnish type resin binder 5 ing and flakes forming interstices the surfaces of which and said cured imprgnant, said binder and imprgnant are compatible with said subsequently applied imprg being incompatible and forming a non-homogeneous in nant; wrapping said end portion with a second insulat sulation system. ing material containing a binder not compatible with a 18. A coil for an electrical machine comprising a slot subsequently applied imprgnant; applying a protective portion wrapped with a mica material containing a cured 10 wrapping to the entire coil; applying a temporary wrap imprgnant, said mica material and wrapping material ping of an impervious film to the entire coil; impregnat forming interstices the surfaces in which are compatible ing said wrapped coil with said imprgnant comprising a with said cured imprgnant to provide a homogeneous liquid resinous composition; thereafter curing said im insulation system; and an end portion wrapped with a prgnant to form homogeneous insulation for said slot mica material containing a varnish type binder including 15 portions the components of which are bonded together, a plasticizer and said cured imprgnant, said binder and and to form non-homogeneous relatively flexible insula imprgnant being incompatible and forming a non-homo tion for said end portion; and removing said temporary geneous insulation system. impervious film. 19. A coil for an electrical machine comprising a slot 23. The steps in the method of insulating a coil hav portion wrapped with a mica material containing a cured 20 ing slot portions and a connecting end portion, for use in imprgnant, said mica material and wrapping material a rotating electrical machine, which method comprises forming interstices the surfaces in which are compatible wrapping the slot portions with a first insulating material with said cured imprgnant to provide a homogeneous comprising a sheet backing and mica flakes disposed on insulation system; and an end portion wrapped with a said backing, said first insulating material being impreg- sheet material formed of rubber or the like and said 25 natable by a subsequently applied imprgnant, said back cured imprgnant said sheet material and said cured im ing and flakes forming interstices the surfaces of which prgnant being incompatible. are compatible with said subsequently applied imprg 20. A coil for an electrical machine comprising a slot portion wrapped with a mica material forming interstices nant; wrapping said end portion with a second insulating material containing a binder not compatible with a sub and impregnated with a cured imprgnant compatible 30 sequently applied imprgnant; applying a protective with the surfaces in said interstices and an end portion wrapping to the entire coil; applying a temporary wrap wrapped with a silicone rubber sheet material and coated ping of an impervious film to the entire coil; applying with said cured imprgnant said sheet material and said pads to the sides of said end turn with a temporary cured imprgnant being incompatible. wrapping of said impervious film; impregnating said 21. A coil for an electrical machine comprising a slot 35 wrapped coil with said imprgnant comprising a liquid portion wrapped with mica material and backing forming resinous composition; thereafter curing said imprgnant interstices and impregnated with a polymerized thermo to form homogeneous insulation for said slot portions setting composition compatible with the surfaces in said the components of which are bonded together, and to interstices to form a void-free insulation system on said form non-homogeneous relatively flexible insulation for slot portion; and an end portion wrapped with mica 40 said end portion; and removing said temporary impervious material and backing containing a cured resinous binder film and pads. and said thermosetting composition, said binder and com position maintaining their respective identities in the end turn insulation system. References Cited in the file of this patent UNITED STATES PATENTS 22. The steps in the method of insulating a coil having slot portions and a connecting end portion, for use in a rotating electrical machine, which method comprises 2,443,663 2,479,357 2,601,243 R id er----- --- :-------------June 22, 1948 H ill--------------------------- Aug. 16, 1949 B o tts--------------------- ---- June 24, 1952