CA1069805A - Electrically insulating coatings - Google Patents
Electrically insulating coatingsInfo
- Publication number
- CA1069805A CA1069805A CA244,667A CA244667A CA1069805A CA 1069805 A CA1069805 A CA 1069805A CA 244667 A CA244667 A CA 244667A CA 1069805 A CA1069805 A CA 1069805A
- Authority
- CA
- Canada
- Prior art keywords
- alkali metal
- silicate
- sodium
- metal salt
- slurry
- 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
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02K—DYNAMO-ELECTRIC MACHINES
- H02K1/00—Details of the magnetic circuit
- H02K1/04—Details of the magnetic circuit characterised by the material used for insulating the magnetic circuit or parts thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
- H01B3/025—Other inorganic material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
- H01F1/18—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets with insulating coating
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F19/00—Fixed transformers or mutual inductances of the signal type
- H01F19/04—Transformers or mutual inductances suitable for handling frequencies considerably beyond the audio range
-
- 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
- H01F41/02—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 for manufacturing cores, coils, or magnets
- H01F41/04—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 for manufacturing cores, coils, or magnets for manufacturing coils
- H01F41/12—Insulating of windings
- H01F41/122—Insulating between turns or between winding layers
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Dispersion Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Multimedia (AREA)
- Chemical Treatment Of Metals (AREA)
- Inorganic Insulating Materials (AREA)
- Iron Core Of Rotating Electric Machines (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method for producing an electrically insulating coating upon a metal substrate comprises reacting upon the substrate a deposited mixture incorporating an aluminium silicate and at least one suitable alkali metal salt selected from the group including an alkali metal silicate, phosphate, borate, chromate and fluoride.
A method for producing an electrically insulating coating upon a metal substrate comprises reacting upon the substrate a deposited mixture incorporating an aluminium silicate and at least one suitable alkali metal salt selected from the group including an alkali metal silicate, phosphate, borate, chromate and fluoride.
Description
s This invention rel~tes to electrically lnsul~ting coatings ~nd i~ particularly concerned with such coating~ ~pplied to elec-trical steel sheet or strlp, that is to say sheet or strlp inten-ded to form a magnetic circuit in ~n electric machine.
In alternating current electric mach~nes such as transformers or motors, operating magnetic fields are generated by current flow through conductors wound around a magnetic core generally formed of stacked laminations punched or cut ~ the requ~red shap~ from electrical sheet or strip material of the required characteristics~
The operating efficiency of such a machine is dependent inter alia upon the proportion of the ~nput electrical energy which be-comes dissipated as heat within the core as a result of current arising from inter-laminar voltages which are indu~ed when the core is cyclically magnetised.
It is now accepted practice to reduce current flow arising from inter-laminar voltages, by providing at l~ast one face of each lamination in the core with an ~le~trically insulating coat-ing whlch i8 applied to the electrical steel sheet or strip before or after the laminations are st~mped~ The type of c~ating used 2Q is dependent on the end use of the sh~et or strip; thus for small motors a blue oxide film may provide sufficient insulation between the laminations of the motor core~ Larger motors or rotating machines may require coatings with better insulation properties and for low temperature operation, for ex~mple below 200C, organic varnishes are often used to provide electrical insulat~on9 For high temperature insulation or for those cases where the steel sheet ~r laminations stamped from the ~heet have to withstand stress relief annealing treatment, an inorganic coating must be used~
Inorg~nic coatings with suitable properties are known. They include sodium silicate, or mixtures of sodium silicate with ~al-clum silicate but these coatings display several disadvantages~
Both tend to cause sticking of ad~ac~nt lamin~tions during anneal-ing and the costing slurry us~d for the latter coating tends to solidiy and set during use, thus blocking pipe~ork and storage tanks used in the coati~g operation.
~ ' 6~ ~ S
ccording to the broadest a~pec~ of ~he pre~ent inven~ion ~n ectrlcally insulating coating upon a metal substr~te comprlses.
re~ctlng upon the substrate a deposited mixture inco~porating ~n ~; aluminlum silicate ~nd ~t least one sui~able alkali metal salt S selected from the group includlng an al~all me~al silicate, phos-phate, borate, chromate and :Eluoride.
According to a further aspe~t of ~he present invention a mix~
ture for producing an electr~cally insulating coa~ing upon a sub-strate comprises a slurry of an alumlnium ~licate with a su~table `' 10 sili~a~e, phosphate, ~or~te, chromate or fluoride of an alkali ; metal~
Preerably the Alkali meta]. is sodium, with sodi~n silicate~
i phosphate, borate, chromate or fluoride being mixed w~th the ~lu-min~um silicate to form a slurry which suitably is aqueous. The , 15 slurry which in addition to the aluminium silicate may contain more than one of the alk~l~ metal salts conveniently is produced by dispersing the aluminium silicate in water using any suitable mixlng technique and subsequently adding the salt or salts as the ~ case may be. A suitable amount of any organic or inorganic dis-,. 20 persing agent which is active in al~ali solu~lon may be added to : the slurry to improve stabllity and reduce the rate of settling ~f the suspended material. A suitable dispersing agent is Ben-tonite which con~eniently is added in concentration~ up to 1~ by weight. Optionally colloidal silica in a~ueous suspension may also be added to the slurry to improve coating characteristics r and appearanceO The colloidal silica may be added in quantlties of between 50% an~ 100% of the weight of the aluminium silicate used.
The slurry may be applied to the surface of the substrate ~` 30 by any o~ the coating methods well know~ in the art or ex~mple by spraying, roller coating or dipplng.~ In the case where the s coating is applied to metal sheet or strip by a dipping tech~i~
que, the dipped coating may be reduced to the required thickness by passing the sheet br strip through the nip between two suita-3~, ble biased rolls.
~ After coating the strip is passed through an oven or fur-$ nace m~intained at a temperature effective initially to dry out ~ the coating and subsequently to produce reaction between the i ` ~ 2 -' ' .
69l 3~5 aluminium silicate particles and the alkali metal salt,s.
Suitably the aluminium silicate is in the form of finely divided Kaolin or other aluminium silica-te rich clay m.~terial capable o~ dispersion in an aqueous mixture One other example o~ a suitable alum.inium silica-te is finely ground felspar which is a sodium or potassium aluminium silicate. A
typical slurry is for example made by dispersing between 10 to 35 parts by weight of l~ao]in or other suitable aluminium silicate in 90 parts of water and adding between 20 to 120 parts of com~ercial sodium silicate solution of specific gravity 1.38.This is equivalent to a molecular ratio of alkali metal salt to ~luminium silicate lying within -the range 0.2 to ~.3. A
molecular ratio of 0.2 is equivalent to one of the preferred limits of 35 parts of Kaolin to 20 parts by weight of sodium silicate while the mo.lecular ratio of 4.3 represents the preferred other limit of 10 parts by weight of Kaolin to 120 parts by weig~t of sodium silicate.
In a preferred embodiment, the slurry comprises 90 parts by weight of water with 15 parts o~ I~aolin or other clay and 60 parts of commercial sodium silicate solution of specific gravity 1.38 and represents a mole ratio of 1.43. Up to 1%
Bentonite is also added to the slurry before it is applied to the surface of the substrate for heating. .
In the case of coatings produced from a slurry in-corporating alkali phosphates, borates and chromates the upper molecular ratio limit conveniently is reduced to avoid the possibility of producing a coating which may be too fusible -to permi-t subsequen-t stress relief a.nnealing without s-ticking of laminations derived from the coated sheet or strip; the actual upper limit selected will vary with the actual alkali metal and salt employed.
A temperature within the range 300C to 900C is 69~S
effective to react the alum.inium silicate with sodium silicate to form a smoo-th ma-tt gray coating.
The appearance of the coating can be modified without detriment to the other properties by including in the slurry, sodium, : - 3a -6~1B~5 _aborate or tetr~borate ln a~ounts correRponding to be~ween 5%
and 25~ of the weight of Kaolin used~ The co~ting change~ from a matt to a glossy appearance as the proportion of sodium, me~-borate, or tetraborate lncreases. More glossy coat~ng may ~180 be obtained by replacing a part of the sodium Rilic~te in ~he slurry with tribasic sodium phosphate op~ionally in conjunction : with sodium, metaborate or tetraborate.
I As one example of the invention applied to the provlsion of : an electrically in~ulating coatlng on grain ~rlen~e~ sili~on ~teel : 10 strip, a mixture is formed comprising Rn aqueous slurry including 90 parts by wei~ht of w~er, 15 parts by weight of Kaolin and 60 parts by wei~h~ of commerclal sodium s~ te solutlon of speclfic gr~vity 1.380 The slurry is applied a~ a controlled rate to ~he upper surface of the moving strip immediately up-s~ream of the :. 15 nip between a pair of grooved "doctor" rolls through which the strip passes and which are biased to redu¢e ~he appli~d coating to the required thicknessO The stri~ is coated on it~ underside by contact with the lower grooved doctor roll which ls parti~
immersed in a bath of the slurry~ Slurry applied di~ectly to the upper surface of the strip and to the bath is derived by way o a branched feed pipe from a storage chamber which is continMally stirred to prevent settlement of solids~
After coating the strlp is passed in conventional ma~ner in-to a furnace in which its.~temperature is r~6ed to 830C which is 2i maint~ined for ~b~ut 30 seconds, After leaving the furnace the strip is allowed to cool and is wound into a coil by any of the methods well known in the art.
` It has been found that an electrically in~ulating coating produced according to the lnvention is strongly adherent to the 31` metal strip surface, is insoluble ln water and forms a barrier effective to protect the u~derlying steel surface against cor~
rosion~ In contrast to some,previously used inorganic coatings for silicon steels the coating of the invention is capable of being annealed at temperatures of ab~ut 800C without deteriora-~5 tion of the coatings or sticking of the laminations producedfrom the coated strip.
`~:
`:
.
~a~g~os : Franklin coatin~ reslstance te~ts on ~he co~ted mate~ial y gave results whlch were ~ubstantlally in excess o~ 10~ ohm cm20 Subsequent stress relief annealing of l~minAti~n~ cut from thc ~` co~ted strlp carried out in an atmo~phere of ~ir or ni~rogen S containing up to 3% of hydrogen did not affect the resistance or inte~rity of the coating.
It will be appreciated that while th~s example h~s been described with reference to the use of sodium silicate, compara-ble coatings may be produced by reacting aluminium silica~e j 10 with the silicates, pho~phates, borates, chroma~e~ or fluorides of other alkali metals~
In a second example of the invention an electric~lly insu-lating coating is similarly produced by the depositlon of the slurry including ~0 parts by weight of wa~er, lS parts by weig~t of Kaolin, and 7,5 parts by weight of sodium tetrabora~e,repre-senting a mole ratio of 0.34.
Ater depositing the slurry layer by way of a process as described with reference to the foreg~ing cxample, the strip is heated at a selected temperature within the range 300C to 9DO~C.
While any temperature within this range will in ~eneral be suita- !
ble to produce reaction between the aluminium silicate of the Kaolin and the alkali salt or salts, the actual temperature selec-ted will depend upon ~he characteri~tics of the urnace employed, the dwell time of the strip within the furnace and the ancillary heat treatment of the steel strip which is produced~
In a third example, a satisfactory coating is produced by depos~tion of a slurry contai~ing 9D.parts by weight of water, 15 p~rts by weight of Kaolin and 7~5 parts by weight of sodium perchromate representin8 a mole ratio of 0~43.
3~ In yet a further example a satisf~ctory coatin~ is produced by deposition of a slurry containing 90 parts by weight of water, 15 parts by weight of Kaolin and 7.5 parts by weight of tribasic sodium phosphate representing a mole ratio of 0.34.
Each of the coatings produced by the slurries described by 3S way of example may be modified by the addition to the slurry of up to 25 parts by weight of commereial colloidal sllica in order to improve the coating characteristics and coating appearanceO
:`
6~
The coating slurri~6 descrlbed in the above examples have been used for coat~ng b~th oriented ~nd ~on~oriented grades of silicon steel., In the ca6e of orlented steel~ as well as the desirable properties of good insulation resistance, good adhe sion to the steel base and aT)ili~y to withstand annealing, it is also desirable that the coating should hold the underlying steel in tension9 Ihis has the effect of improving the 8pecific total loss at high magnetic inductions and reducing magnetostrlction parti-cularly in cases where the steel is compressed along the plane of the strip, as can happen when laminations are built into tr~nsormer cores. Magnetostriction is evident as a cyclic change in length tha~ ocaurs during cyclic magnetisation and which contributes to transformer noise~
It has been found that the addition of fluorides, such as alk~li or alkaline earth metal fluorides or aluminium fluoride alone or in combination in amounts up to 20% by weight of the aluminium sillcate present can produce a coating which reduces mugne~ostriction.
In one example, a slurry containing 4D parts by weight of water, 15 parts by weight of Kaolln, 60 parts by weight of com~
merclal sodium silicate solution of æpecific gravlty 1.38 and 0.3 parts by weight of sodium flu~ride was used to coat oriented steel strip which was subsequently heated to 83~C to cure the 2S coatlng. Samples of the coated strip were then stress relief annealed at 800C before measuring the cyclic han~e in length durlng cyclic magnetisation at 1.5 te~la and 50Hz3 ~hlle the ¦ sample was held in compression along the direction of rolling., The m~gnitude of the relative change in length wa~ reduced by a factor of three when compared with similar mat~rial coated ~` without the addition of fluoride to the coating slurry. S~mll~r results are obtained when other fluorides are used as additives.
It will be appreciated that while the examples have been described with reference to coatings produced from slurrles cono ` 35 taining 80dium salts, comparable coating~ may be made with slur ! ries contsining the ~licates3 phosphate~, borates, chromates or fluorides of other alk~li metals such a~ potas~ium~ lith~um or , - caesium3
In alternating current electric mach~nes such as transformers or motors, operating magnetic fields are generated by current flow through conductors wound around a magnetic core generally formed of stacked laminations punched or cut ~ the requ~red shap~ from electrical sheet or strip material of the required characteristics~
The operating efficiency of such a machine is dependent inter alia upon the proportion of the ~nput electrical energy which be-comes dissipated as heat within the core as a result of current arising from inter-laminar voltages which are indu~ed when the core is cyclically magnetised.
It is now accepted practice to reduce current flow arising from inter-laminar voltages, by providing at l~ast one face of each lamination in the core with an ~le~trically insulating coat-ing whlch i8 applied to the electrical steel sheet or strip before or after the laminations are st~mped~ The type of c~ating used 2Q is dependent on the end use of the sh~et or strip; thus for small motors a blue oxide film may provide sufficient insulation between the laminations of the motor core~ Larger motors or rotating machines may require coatings with better insulation properties and for low temperature operation, for ex~mple below 200C, organic varnishes are often used to provide electrical insulat~on9 For high temperature insulation or for those cases where the steel sheet ~r laminations stamped from the ~heet have to withstand stress relief annealing treatment, an inorganic coating must be used~
Inorg~nic coatings with suitable properties are known. They include sodium silicate, or mixtures of sodium silicate with ~al-clum silicate but these coatings display several disadvantages~
Both tend to cause sticking of ad~ac~nt lamin~tions during anneal-ing and the costing slurry us~d for the latter coating tends to solidiy and set during use, thus blocking pipe~ork and storage tanks used in the coati~g operation.
~ ' 6~ ~ S
ccording to the broadest a~pec~ of ~he pre~ent inven~ion ~n ectrlcally insulating coating upon a metal substr~te comprlses.
re~ctlng upon the substrate a deposited mixture inco~porating ~n ~; aluminlum silicate ~nd ~t least one sui~able alkali metal salt S selected from the group includlng an al~all me~al silicate, phos-phate, borate, chromate and :Eluoride.
According to a further aspe~t of ~he present invention a mix~
ture for producing an electr~cally insulating coa~ing upon a sub-strate comprises a slurry of an alumlnium ~licate with a su~table `' 10 sili~a~e, phosphate, ~or~te, chromate or fluoride of an alkali ; metal~
Preerably the Alkali meta]. is sodium, with sodi~n silicate~
i phosphate, borate, chromate or fluoride being mixed w~th the ~lu-min~um silicate to form a slurry which suitably is aqueous. The , 15 slurry which in addition to the aluminium silicate may contain more than one of the alk~l~ metal salts conveniently is produced by dispersing the aluminium silicate in water using any suitable mixlng technique and subsequently adding the salt or salts as the ~ case may be. A suitable amount of any organic or inorganic dis-,. 20 persing agent which is active in al~ali solu~lon may be added to : the slurry to improve stabllity and reduce the rate of settling ~f the suspended material. A suitable dispersing agent is Ben-tonite which con~eniently is added in concentration~ up to 1~ by weight. Optionally colloidal silica in a~ueous suspension may also be added to the slurry to improve coating characteristics r and appearanceO The colloidal silica may be added in quantlties of between 50% an~ 100% of the weight of the aluminium silicate used.
The slurry may be applied to the surface of the substrate ~` 30 by any o~ the coating methods well know~ in the art or ex~mple by spraying, roller coating or dipplng.~ In the case where the s coating is applied to metal sheet or strip by a dipping tech~i~
que, the dipped coating may be reduced to the required thickness by passing the sheet br strip through the nip between two suita-3~, ble biased rolls.
~ After coating the strip is passed through an oven or fur-$ nace m~intained at a temperature effective initially to dry out ~ the coating and subsequently to produce reaction between the i ` ~ 2 -' ' .
69l 3~5 aluminium silicate particles and the alkali metal salt,s.
Suitably the aluminium silicate is in the form of finely divided Kaolin or other aluminium silica-te rich clay m.~terial capable o~ dispersion in an aqueous mixture One other example o~ a suitable alum.inium silica-te is finely ground felspar which is a sodium or potassium aluminium silicate. A
typical slurry is for example made by dispersing between 10 to 35 parts by weight of l~ao]in or other suitable aluminium silicate in 90 parts of water and adding between 20 to 120 parts of com~ercial sodium silicate solution of specific gravity 1.38.This is equivalent to a molecular ratio of alkali metal salt to ~luminium silicate lying within -the range 0.2 to ~.3. A
molecular ratio of 0.2 is equivalent to one of the preferred limits of 35 parts of Kaolin to 20 parts by weight of sodium silicate while the mo.lecular ratio of 4.3 represents the preferred other limit of 10 parts by weight of Kaolin to 120 parts by weig~t of sodium silicate.
In a preferred embodiment, the slurry comprises 90 parts by weight of water with 15 parts o~ I~aolin or other clay and 60 parts of commercial sodium silicate solution of specific gravity 1.38 and represents a mole ratio of 1.43. Up to 1%
Bentonite is also added to the slurry before it is applied to the surface of the substrate for heating. .
In the case of coatings produced from a slurry in-corporating alkali phosphates, borates and chromates the upper molecular ratio limit conveniently is reduced to avoid the possibility of producing a coating which may be too fusible -to permi-t subsequen-t stress relief a.nnealing without s-ticking of laminations derived from the coated sheet or strip; the actual upper limit selected will vary with the actual alkali metal and salt employed.
A temperature within the range 300C to 900C is 69~S
effective to react the alum.inium silicate with sodium silicate to form a smoo-th ma-tt gray coating.
The appearance of the coating can be modified without detriment to the other properties by including in the slurry, sodium, : - 3a -6~1B~5 _aborate or tetr~borate ln a~ounts correRponding to be~ween 5%
and 25~ of the weight of Kaolin used~ The co~ting change~ from a matt to a glossy appearance as the proportion of sodium, me~-borate, or tetraborate lncreases. More glossy coat~ng may ~180 be obtained by replacing a part of the sodium Rilic~te in ~he slurry with tribasic sodium phosphate op~ionally in conjunction : with sodium, metaborate or tetraborate.
I As one example of the invention applied to the provlsion of : an electrically in~ulating coatlng on grain ~rlen~e~ sili~on ~teel : 10 strip, a mixture is formed comprising Rn aqueous slurry including 90 parts by wei~ht of w~er, 15 parts by weight of Kaolin and 60 parts by wei~h~ of commerclal sodium s~ te solutlon of speclfic gr~vity 1.380 The slurry is applied a~ a controlled rate to ~he upper surface of the moving strip immediately up-s~ream of the :. 15 nip between a pair of grooved "doctor" rolls through which the strip passes and which are biased to redu¢e ~he appli~d coating to the required thicknessO The stri~ is coated on it~ underside by contact with the lower grooved doctor roll which ls parti~
immersed in a bath of the slurry~ Slurry applied di~ectly to the upper surface of the strip and to the bath is derived by way o a branched feed pipe from a storage chamber which is continMally stirred to prevent settlement of solids~
After coating the strlp is passed in conventional ma~ner in-to a furnace in which its.~temperature is r~6ed to 830C which is 2i maint~ined for ~b~ut 30 seconds, After leaving the furnace the strip is allowed to cool and is wound into a coil by any of the methods well known in the art.
` It has been found that an electrically in~ulating coating produced according to the lnvention is strongly adherent to the 31` metal strip surface, is insoluble ln water and forms a barrier effective to protect the u~derlying steel surface against cor~
rosion~ In contrast to some,previously used inorganic coatings for silicon steels the coating of the invention is capable of being annealed at temperatures of ab~ut 800C without deteriora-~5 tion of the coatings or sticking of the laminations producedfrom the coated strip.
`~:
`:
.
~a~g~os : Franklin coatin~ reslstance te~ts on ~he co~ted mate~ial y gave results whlch were ~ubstantlally in excess o~ 10~ ohm cm20 Subsequent stress relief annealing of l~minAti~n~ cut from thc ~` co~ted strlp carried out in an atmo~phere of ~ir or ni~rogen S containing up to 3% of hydrogen did not affect the resistance or inte~rity of the coating.
It will be appreciated that while th~s example h~s been described with reference to the use of sodium silicate, compara-ble coatings may be produced by reacting aluminium silica~e j 10 with the silicates, pho~phates, borates, chroma~e~ or fluorides of other alkali metals~
In a second example of the invention an electric~lly insu-lating coating is similarly produced by the depositlon of the slurry including ~0 parts by weight of wa~er, lS parts by weig~t of Kaolin, and 7,5 parts by weight of sodium tetrabora~e,repre-senting a mole ratio of 0.34.
Ater depositing the slurry layer by way of a process as described with reference to the foreg~ing cxample, the strip is heated at a selected temperature within the range 300C to 9DO~C.
While any temperature within this range will in ~eneral be suita- !
ble to produce reaction between the aluminium silicate of the Kaolin and the alkali salt or salts, the actual temperature selec-ted will depend upon ~he characteri~tics of the urnace employed, the dwell time of the strip within the furnace and the ancillary heat treatment of the steel strip which is produced~
In a third example, a satisfactory coating is produced by depos~tion of a slurry contai~ing 9D.parts by weight of water, 15 p~rts by weight of Kaolin and 7~5 parts by weight of sodium perchromate representin8 a mole ratio of 0~43.
3~ In yet a further example a satisf~ctory coatin~ is produced by deposition of a slurry containing 90 parts by weight of water, 15 parts by weight of Kaolin and 7.5 parts by weight of tribasic sodium phosphate representing a mole ratio of 0.34.
Each of the coatings produced by the slurries described by 3S way of example may be modified by the addition to the slurry of up to 25 parts by weight of commereial colloidal sllica in order to improve the coating characteristics and coating appearanceO
:`
6~
The coating slurri~6 descrlbed in the above examples have been used for coat~ng b~th oriented ~nd ~on~oriented grades of silicon steel., In the ca6e of orlented steel~ as well as the desirable properties of good insulation resistance, good adhe sion to the steel base and aT)ili~y to withstand annealing, it is also desirable that the coating should hold the underlying steel in tension9 Ihis has the effect of improving the 8pecific total loss at high magnetic inductions and reducing magnetostrlction parti-cularly in cases where the steel is compressed along the plane of the strip, as can happen when laminations are built into tr~nsormer cores. Magnetostriction is evident as a cyclic change in length tha~ ocaurs during cyclic magnetisation and which contributes to transformer noise~
It has been found that the addition of fluorides, such as alk~li or alkaline earth metal fluorides or aluminium fluoride alone or in combination in amounts up to 20% by weight of the aluminium sillcate present can produce a coating which reduces mugne~ostriction.
In one example, a slurry containing 4D parts by weight of water, 15 parts by weight of Kaolln, 60 parts by weight of com~
merclal sodium silicate solution of æpecific gravlty 1.38 and 0.3 parts by weight of sodium flu~ride was used to coat oriented steel strip which was subsequently heated to 83~C to cure the 2S coatlng. Samples of the coated strip were then stress relief annealed at 800C before measuring the cyclic han~e in length durlng cyclic magnetisation at 1.5 te~la and 50Hz3 ~hlle the ¦ sample was held in compression along the direction of rolling., The m~gnitude of the relative change in length wa~ reduced by a factor of three when compared with similar mat~rial coated ~` without the addition of fluoride to the coating slurry. S~mll~r results are obtained when other fluorides are used as additives.
It will be appreciated that while the examples have been described with reference to coatings produced from slurrles cono ` 35 taining 80dium salts, comparable coating~ may be made with slur ! ries contsining the ~licates3 phosphate~, borates, chromates or fluorides of other alk~li metals such a~ potas~ium~ lith~um or , - caesium3
Claims (16)
1. A method for producing an electrically insulating coating upon a metal substrate, which comprises reacting upon the substrate a deposited mixture incorporating an aluminium silicate and at least one suitable alkali metal salt selected from the group consisting of an alkali metal silicate, phosphate, borate, chromate and fluoride.
2. A method as claimed in claim 1, wherein the mixture is deposited in the form of a slurry.
3. A method as claimed in claim 2, wherein the slurry is aqueous.
4. A method as claimed in claims 1, 2 or 3, wherein the molecular ratio of alkali metal salt to aluminium metal silicate lies within the range 0.2 to 4.3.
5. A method as claimed in claim 1, wherein the alkali metal salt is sodium silicate.
6. A method as claimed in claim 5, wherein the molecular ratio of sodium silicate to aluminium silicate is 1.43.
7. A method as claimed in claim 1, wherein the alkali metal salt is selected from the group consisting of an alkali metal phosphate, borate and chromate.
8. A method as claimed in claim 7, wherein the alkali metal salt is sodium tetraborate, sodium perchromate or sodium phosphate.
9. A method as claimed in claim 1, wherein the molecular ratio of alkali metal salt to aluminium silicate lies within the range 0.35 to 0.43.
10. A method as claimed in claim 1, wherein colloidal silica is corporated in the mixture.
11. A method as claimed in claim 10, wherein the silica is incorporated in quantities of between 50% and 100% by weight of aluminium silicate.
12. A method as claimed in claim 3, wherein a dispersing agent which is reactive in alkali solution is added to the slurry.
13. A method as claimed in claim 1, wherein the mixture incorporates sodium metaborate or sodium tetraborate.
14. A method as claimed in claim l, wherein the aluminium silicate and alkali metal salt are reacted at a temperature within the range 300°C and 900°C.
15. A metal substrate provided with an electrically insulating coating, comprising the reaction product of an aluminium silicate and at least one suitable alkali metal salt selected from the group consisting of an alkali metal silicate, phosphate, borate, chromate and fluoride.
16. A metal substrate as claimed in claim 15, wherein the alkali metal salt is sodium silicate.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4113/75A GB1537824A (en) | 1975-01-30 | 1975-01-30 | Electrically insulating coatings |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1069805A true CA1069805A (en) | 1980-01-15 |
Family
ID=9771024
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA244,667A Expired CA1069805A (en) | 1975-01-30 | 1976-01-26 | Electrically insulating coatings |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS51101899A (en) |
| AU (1) | AU504118B2 (en) |
| BE (1) | BE838007A (en) |
| CA (1) | CA1069805A (en) |
| DE (1) | DE2603179A1 (en) |
| FR (1) | FR2299708A1 (en) |
| GB (1) | GB1537824A (en) |
| IT (1) | IT1057100B (en) |
| SE (1) | SE7600934L (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5422937B2 (en) * | 2008-08-05 | 2014-02-19 | 新日鐵住金株式会社 | Insulating film coating solution and method for forming insulating film for grain-oriented electrical steel sheet |
| JP5320898B2 (en) * | 2008-08-08 | 2013-10-23 | 新日鐵住金株式会社 | Insulating film coating solution and method for forming insulating film for grain-oriented electrical steel sheet |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB300911A (en) * | 1927-11-19 | 1930-01-30 | Ass Elect Ind | Improvements relating to the manufacture of insulated plates of magnetic material for electrical purposes |
| US2785091A (en) * | 1953-10-23 | 1957-03-12 | Jack F Govan | Method of protecting metal surfaces, composition therefor, and article resulting therefrom |
| DE1906912A1 (en) * | 1969-02-12 | 1970-09-03 | Mineralchemie Werner & Co | Protecting metal surface coatings against - oxidation and scale formation |
-
1975
- 1975-01-30 GB GB4113/75A patent/GB1537824A/en not_active Expired
-
1976
- 1976-01-22 AU AU10489/76A patent/AU504118B2/en not_active Expired
- 1976-01-26 CA CA244,667A patent/CA1069805A/en not_active Expired
- 1976-01-28 BE BE163882A patent/BE838007A/en unknown
- 1976-01-28 DE DE19762603179 patent/DE2603179A1/en not_active Withdrawn
- 1976-01-29 SE SE7600934A patent/SE7600934L/en unknown
- 1976-01-29 FR FR7602428A patent/FR2299708A1/en not_active Withdrawn
- 1976-01-30 JP JP51008550A patent/JPS51101899A/ja active Pending
- 1976-01-30 IT IT67218/76A patent/IT1057100B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| DE2603179A1 (en) | 1976-08-05 |
| JPS51101899A (en) | 1976-09-08 |
| GB1537824A (en) | 1979-01-10 |
| IT1057100B (en) | 1982-03-10 |
| AU1048976A (en) | 1977-07-28 |
| AU504118B2 (en) | 1979-10-04 |
| BE838007A (en) | 1976-05-14 |
| SE7600934L (en) | 1976-08-02 |
| FR2299708A1 (en) | 1976-08-27 |
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