SOFT MAGNETIC LAMINATED CORE AND METHOD OF PRODUCING A LAMINATED CORE FOR A STATOR AND/OR ROTOR OF AN ELECTRIC MACHINE

Abstract

A soft magnetic laminated core is provided which comprises first laminations and second laminations arranged in a stack having a stacking direction substantially perpendicular to a major surface of the first laminations and the second laminations. The first laminations comprise a first soft magnetic alloy and the second laminations comprise a second soft magnetic alloy different from the first soft magnetic alloy. The first laminations and the second laminations are distributed in the stacking direction throughout the stack. The first laminations and/or the second laminations comprise an insulating coating that is thermally stable up to at least 850° C.

Claims

1. A soft magnetic laminated core, comprising: first laminations and second laminations arranged in a stack having a stacking direction substantially perpendicular to a major surface of the first laminations and the second laminations, wherein the first laminations comprise a first soft magnetic alloy and the second laminations comprise a second soft magnetic alloy different from the first soft magnetic alloy, wherein the first laminations and the second laminations are distributed in the stacking direction throughout the stack, and wherein the first laminations and/or the second laminations comprise an insulating coating that is thermally stable up to at least 850° C.

2. The soft magnetic laminated core according to claim 1, wherein the first laminations comprise a FeSi-based alloy and the second laminations comprise a CoFe-based alloy.

3. The soft magnetic laminated core according to claim 1, wherein the first laminations comprise a Fe—Si-based alloy comprising 2 weght % to 4.5 weght % of at least one of the group consisting of Si and Al, with remainder comprising Fe and unavoidable impurities.

4. The soft magnetic laminated core according to claim 1, wherein the second laminations comprise a CoFe-based alloy comprising 35 to 55 wt % Co, up to 2.5 wt % V, with the remainder comprising Fe and unavoidable impurities.

5. The soft magnetic laminated core according to claim 4, wherein the CoFe-based alloy comprises 45 wt %≦Co≦52 wt %, 45 wt %≦Fe≦52 wt %, 0.5 wt %≦V≦2.5 wt %, remainder Fe and unavoidable impurities.

6. The soft magnetic laminated core according to claim 4, wherein the CoFe-based alloy comprises 35 wt %≦Co≦55 wt %, 0 wt %≦Ni≦0.5 wt %, 0.5 wt %≦V≦2.5 wt %, remainder Fe and unavoidable impurities.

7. The soft magnetic laminated core according to claim 4, wherein the CoFe-based alloy comprises 35 wt %≦Co≦55 wt %, 0 wt %≦V≦2.5 wt %, 0 wt %≦(Ta+2Nb)≦1 wt %, 0 wt %≦Zr≦1.5 wt %, 0 wt %≦Ni≦5 wt %, 0 wt %≦C≦0.5 wt %, 0 wt %≦Cr≦1 wt %, 0 wt %≦Mn≦1 wt %, 0 wt %≦Si≦1 wt %, 0 wt %≦Al≦1 wt %, 0 wt %≦B≦0.01 wt %, remainder Fe and unavoidable impurities,

8. The soft magnetic laminated core according to claim 1, wherein the first laminations include a first insulating coating and the second laminations include a second insulating coating and the first insulating coating and the second insulating coating are one of the same composition or of different compositions.

9. The soft magnetic laminated core according to claim 1, wherein the first laminations and/or the second laminations comprise an inorganic coating.

10. The soft magnetic laminated core according to claim 9, wherein the first laminations comprise a FeSi-based alloy and the inorganic coating.

11. The soft magnetic laminated core according to claim 1, wherein the first laminations and/or the second laminations comprise a dielectric coating, the dielectric coating comprising Magnesium oxide or Zirconium oxide.

12. The soft magnetic laminated core according to claim 11, wherein the second laminations comprise a CoFe-based alloy and the dielectric coating comprises Magnesium oxide.

13. Method of producing a laminated core for a stator and/or rotor of an electric machine, comprising: forming a plurality of first laminations from a first foil comprising a first soft magnetic alloy; forming a plurality of second laminations from a second foil comprising a second soft magnetic alloy, covering the first laminations and/or the second laminations with an insulating material, stacking the first laminations and the second laminations to form a laminated core so that the first laminations and the second laminations are distributed throughout the laminated core, and heat treating the laminated core, wherein the heat treating the laminated core comprises heat treating at 700° C. to 1200° C. for 2 hours to 10 hours.

14. The method according to claim 13, wherein the first laminations and the second laminations are stacked in a stamping tool in a pattern by stamping a first lamination core from the first foil and by stamping a second lamination core from the second foil in the order of the pattern.

15. The method according to claim 13, further comprising joining the first laminations and the second laminations.

16. The method according to claim 15, wherein the first laminations and the second laminations are joined by welding.

17. The method according to claim 13, wherein after placing one of the first laminations or second laminations on the stack, the one of the first laminations or second laminations is joined to an underlying lamination of the stack.

18. The method according to claim 13, wherein the heat treating the lamination core takes place in one of a vacuum, a protective atmosphere, or in a hydrogen-containing reducing atmosphere.

19. The method according to claim 13, wherein the heat treating the laminated core comprises heat treating at 700° C. to 880° C. for 2 hours to 10 hours.

20. The method according to claim 13, further comprising heat treating the laminated core in an oxidizing atmosphere.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Embodiments will now be described with reference to the drawings and examples.

[0077] FIG. 1 illustrates a schematic view of a laminated core including a stack of first laminations and second laminations having a first pattern.

[0078] FIG. 2 illustrates a schematic view of a laminated core including a stack of first laminations and second laminations having a second pattern.

[0079] FIG. 3 illustrates a schematic view of a laminated core including a stack of first laminations and second laminations having different thicknesses.

[0080] FIG. 4 illustrates a graph of induction B measured at different field strengths (H) for the laminated cores and calculated values of the induction B at different field strengths (H).

[0081] FIG. 5 illustrates a graph of losses of the laminated cores measured at 1.5 T and a frequency of 50 Hz.

[0082] FIG. 6 illustrates a graph of losses of the laminated cores measured at 1.5 T and a frequency of 400 Hz.

[0083] FIG. 7 illustrates a graph of losses of the laminated cores measured at 1.7 T and a frequency of 50 Hz.

[0084] FIG. 8 illustrates a graph of losses of the laminated cores measured at 1.7 T and a frequency of 400 Hz.

[0085] FIG. 9 illustrates a graph of losses of the laminated cores measured at 2.0 T and a frequency of 50 Hz.

[0086] FIG. 10 illustrates a graph of losses of the laminated cores measured at 2.0 T and a frequency of 400 Hz.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0087] Table 1 illustrates the coercive field strength, permeability, induction and polarisation measured for laminated cores according to the invention and comparison laminated cores.

[0088] Table 2 illustrates the losses measured for the laminated cores.

[0089] FIG. 1 illustrates a schematic review of a laminated core 10 including a plurality of first laminationd 11 and a plurality of second laminations 12. The first laminations 11 include a first soft magnetic alloy of a first composition and the second laminations 12 include a second soft magnetic alloy of a second composition which is different from the first composition. In this particular embodiment, first laminationd 11 include an FeSi-based alloy and the second laminations 12 include a CoFe-based alloy. The first laminationd 11 and the second lamination 12 are arranged in a stack in an alternating pattern to form a stack 13 having a stacking direction that is substantially perpendicular to a major surface of the first laminations and of the second laminations. The stacking direction is indicated in the drawings with an arrow. The pattern can be described as ABAB.

[0090] In the laminated core 10, the thickness of the first laminationd 11 and the thickness of the second laminations 12 is substantially the same. Therefore, if the number of first laminationd 11 and the number of second laminations 12 is also the same, the laminated core 10 includes 50% of the first soft magnetic alloy forming the first laminationd 11 and 50% of the second soft magnetic alloy forming the second laminations 12.

[0091] Since the first soft magnetic alloy forming the first laminationd 11 and the second soft magnetic alloy forming the second laminations 12 have different compositions, the soft magnetic properties of the first laminationd 11 and of second laminations 12 are different. Therefore, the laminated core 10 includes properties which are an average of the properties of the first soft magnetic alloy and the second soft magnetic alloy. For example, if the first magnetic alloy has an induction B(H).sub.A and the second soft magnetic alloy an induction B(H).sub.B, the laminated core has an induction B(H).sub.core substantially corresponding to (B(H).sub.A+B(H).sub.B)/2.

[0092] The stacking pattern ABAB repeats throughout the height of the stack 13 so that the first laminationd 11 and second laminations 12 are distributed uniformly throughout the stack 13 in the stacking direction.

[0093] The laminated core may also have different stacking patterns. For example, the stacking pattern may include two first laminations stacked on two second laminations to give a pattern AABB, which when repeated throughout the stack in the stacking direction, results in AABBAABB.

[0094] In some embodiments, such as that illustrated in FIG. 2, the number of the first laminationd 11 and the number of the second laminations 12 within the laminated core 10′ differs. The different numbers of first laminationd 11 and second laminations 12 may be used in order to provide differing proportions of the first soft magnetic alloy and second soft magnetic alloy within the laminated core 10′. For example, if the first laminationd 11 and the second laminations 12 have the same thickness, in order to provide a core including one third of the first soft magnetic alloy and two thirds of the second magnetic alloy, a stacking order of ABBABB, as illustrated for the laminated core 10′ in FIG. 2, may be provided.

[0095] In some embodiments, such as that illustrated in FIG. 3, the first laminations 11′ and the second laminations 12′ of the lamination core 10″ have different thicknesses. The different thicknesses may also be used to vary the proportion of the first soft magnetic alloy and the second magnetic alloy within the laminated core 10″. In the embodiment illustrated in FIG. 3, the number of first laminations 11′ and the number of second laminations 12′ is the same and the thickness of the first laminations 11′ is less than the thickness of the second laminations 12′. The stacking pattern is ABAB which is the same as that illustrated in FIG. 1. However, due to the differing thicknesses, the proportion of the first soft magnetic alloy in the laminated core 10″ is less than 50% and the proportion of the second soft magnetic alloy is more than 50%. For example, to provide 60% of the second soft magnetic alloy and 40% of the first soft magnetic alloy, the second laminations 12′ may have a thickness of 0.525 mm and the first laminations 11′ may have a thickness of 0.35 mm if same number of first and second laminations 11′, 12′ is provided.

[0096] In some embodiments, the number and thickness of the first and second laminations may be selected so as to tailor a magnetic property of the laminated core according to the following equation:

Z.sub.C=Z.sub.A*(X/(X+Y))+Z.sub.B*(Y/(X+Y))

wherein Z is the magnetic property, Z.sub.C is the value of the magnetic property Z of the laminated core, Z.sub.A is the value of the magnetic property Z of the first soft magnetic alloy, Z.sub.B is the value of the magnetic property Z of the second soft magnetic alloy, X is the volume of the first magnetic alloy in the laminated core, Y is the volume of the second magnetic alloy in the laminated core and (X+Y) is the total volume of the laminated core. For example, Z may be the induction B(H).

[0097] The stack may be formed by preforming the first laminations and the second laminations, for example by cutting laminations of the desired shape from alloy foil of the two desired compositions, and then stacking the preformed first and second laminations in the desired pattern to form the laminated core. In some embodiments, the stacking is carried out in a stamping tool such that the first and second laminations are cut from the foil in the order of the pattern. For example, a lamination is stamped from a foil comprising a first soft magnetic alloy, the next lamination is stamped from a foil comprising the second soft magnetic alloy, the next lamination is stamped form a foil comprising the first soft magnetic alloy and so on in order to form a stack having a pattern ABAB within the stamping tool.

[0098] After the stack of first and second laminations has been formed, the first and second laminations may be joined to one another by welding. In some embodiments, as each lamination is added to the stack, it is welded to the underlying lamination of the stack. The first and second laminations may also be joined by gluing or interlocking.

[0099] If gluing is used, the first and/or second foil may be cut into sheets, the laminations cut from the sheet, for example by stamping or laser cutting. The first and/or second laminations may be annealed and optionally surface oxidised in air or steam and then stacked so that the first and second laminations are distributed through the stack and glued to form a laminated core in which the first and second laminations are distributed throughout the stack.

[0100] After production of the laminated core, the laminated core may be heat treated to achieve the desired magnetic properties. For a laminated core including laminations comprising a CoFe-based alloy, the heat treatment may be carried out at 700° C. to 880° C. for 2 to 10 hours for example. The heat treatment may be carried out in vacuum or under a protective gas, such as argon, or a hydrogen containing gas. The heat treatment may be carried out statically or continuously.

[0101] In the examples, seven laminated cores are produced. In each case, the thickness of the laminations is 0.35 mm and measurements are carried out for ring shaped laminations having an outer diameter of 28.5 mm and an inner diameter of 20.0 mm. The first laminations are formed from a FeSi-based alloy including 3% silicon, The second laminations are formed from a CoFe-based alloy, in particular VACODUR® 49. A reference laminated core, example 7, includes laminations of a CoFe-based alloy including 17% Co, in particular VACOFLUX® 17.

[0102] The laminated core of example 1 is a comparison example and includes only laminations of the FeSi-based alloy and can be considered to have a pattern AAAA.

[0103] The laminated core of example 6 is a comparison example and includes only laminations of the CoFe-based alloy and can be considered to have a pattern BBBB.

[0104] The laminated core of example 2 includes two-thirds FeSi laminations and one-third CoFe laminations and has a stacking pattern AABAAB.

[0105] The laminated core of example 3 includes 50% FeSi laminations and 50% CoFe laminations and includes a stacking pattern ABABAB.

[0106] The laminated core of example 4 also includes 50% FeSi laminations and 50% CoFe laminations and has different stacking pattern of AAABBB.

[0107] The laminated core of example 5 includes one third FeSi and two third CoFe and includes a stacking pattern ABBABB.

TABLE-US-00001 TABLE 1 B B B B B J (300 (1000 (2500 (5000 (10000 (10000 Stacking Hc A/m) A/m) A/m) A/m) A/m) A/m) # Materials sequence in A/m μmax in T in T in T in T in T in T 1 only 3% SiFe AAAAAA . . . 32.0 14643 1.390 1.467 1.537 1.617 1.730 1.717 2 ⅔ SiFe AABAAB . . . 38.1 14893 1.603 1.717 1.784 1.843 1.923 1.911 ⅓ CoFe 3 ½ SiFe ABABAB . . . 41.2 15732 1.719 1.840 1.904 1.953 2.017 2.004 ½ CoFe 4 ½ SiFe AAA . . . BBB 41.0 15772 1.718 1.777 1.900 1.948 2.009 1.996 ½ CoFe 5 ⅓ SiFe ABBABB . . . 43.4 16579 1.831 1.964 2.023 2.061 2.107 2.094 ⅔ CoFe 6 only 50% CoFe BBBBBB . . . 46.8 18335 2.047 2.200 2.250 2.270 2.283 2.270 7 Reference: CCCCCC . . . 82.5 4172 1.228 1.527 1.655 1.763 1.908 1.895 17% CoFe

[0108] The coercive field strength, permeability and induction polarisation measured for examples 1 to 7 are summarised in table 1 and illustrated in the graph of FIG. 4. The laminated cores of examples 2 to 5 include both FeSi-based laminations and CoFe-based laminations and have an induction B measured at 300 A/m, 1000 A/m, 2500 A/m, 5000 A/m and 10000 A/m which is greater than that measured for the laminated core of example 1 which includes only FeSi laminations. For example, examples 2 to 5 include an induction of greater than 1.6 T for B measured at 300 A/m, which is higher than the value of 1.39 T measured for example 1. The values of B(H) measured for example laminated cores 2 , 3 and 5 correspond to the values of B(H) which are predicted by calculation, as is illustrated in FIG. 4.

TABLE-US-00002 TABLE 2 P P P P P P (1.5 T; (1.5 T; (1.7 T; (1.7 T; (2.0 T; (2.0 T; Stacking 50 Hz) 400 Hz) 50 Hz) 400 Hz) 50 Hz) 400 Hz) # Materials sequence in W/kg in W/kg in W/kg in W/kg in W/kg in W/kg 1 only 3% SiFe AAAAAA . . . 2.45 44.1 3.11 56.6 — — 2 ⅔ SiFe AABAAB . . . 2.11 40.2 2.73 54.4 3.97 77.4 ⅓ CoFe 3 ½ SiFe ABABAB . . . 1.94 37.7 2.52 51.8 3.40 73.6 ½ CoFe 4 ½ SiFe AAA . . . BBB 1.96 37.6 2.52 51.7 3.58 74.8 ½ CoFe 5 ⅓ SiFe ABBABB . . . 1.87 35.6 2.39 48.5 3.46 68.2 ⅔ CoFe 6 only 50% CoFe BBBBBB . . . 1.79 32.6 2.23 44.5 2.99 63.7 7 Reference: CCCCCC . . . 3.8 54.1 4.8 69.1 7.0 88.0 17% CoFe

[0109] The losses (P) measured for the laminated cores of examples 1 to 7 are summarised in table 2 and illustrated in the graphs of FIGS. 5 to 10. The values of the losses measured at 50 Hz and 400 Hz at 1.5 T and 1.7 T are lower for the laminated cores examples 2 to 5 compared to that of the laminated core of comparison example 1. Furthermore, whereas the losses of the lamination core of example 1 measured at 2.0 T are so high as to be impractical for use as a laminated core, the laminated cores of examples 2 to 5 have losses ranging from 3.97 to 3.40 W/kg (at 50 Hz and 2.0 T). The losses of the laminated cores of examples 2 to 5 are less than that measured for reference laminated core 7 including FeCo alloy including 17% cobalt.

[0110] Whilst in the embodiments and examples, the laminated core includes laminations comprising two differing soft magnetic alloys, the laminated core is not limited to two differing soft magnetic alloys and may also include laminations of three or more differing magnetic alloys having differing compositions and properties.

[0111] According to the invention, at least one of the laminations includes an insulating coating that this thermally stable at temperatures of at least 850° C., in particular is thermally stable after a heat treatment at temperatures of at least 850° C. in a hydrogen-containing atmosphere.

[0112] The suitability of a coating can be determined by visual inspection of the coating after the heat treatment to determine if the coating is continuous. After the heat treatment, the coating may have a thickness of greater than 0.1 μm in order to provide a suitable insulation effect between neighbouring laminations of the stack. The presence of a very thin coating may be discernable visually and may be determined using optical interference methods.

[0113] “Thermally stable” denotes an insulating coating which adheres sufficiently to the lamination according to the norm DIN EN ISO 2409:2013-06. This norm defines a test in which an adhesive tape is applied to a coating and removed. If the coating has poor adhesion to the underlying substrate, such as the lamination, portions of the coating adhere to the adhesive surface of the removed adhesive tape.

[0114] The suitability of various materials as insulation coatings in laminated cores including laminations fabricated from various alloys was investigated,

EXAMPLE 1

[0115] In example 1, a laminated core including CoFe-based alloy laminations and NiFe-based alloy laminations is fabricated.

[0116] A 50%-CoFe alloy tape (VACODUR® 49) was coated with a magnesium-containing coating, in particular DL1, which after heat treatment includes magnesium oxide. DL1 denotes a coating which is applied to a surface in the form of a Mg-methylate solution which during drying is converted into magnesium hydroxide and then magnesium oxide. After the heat treatment, the coating includes magnesium oxide only.

[0117] 50%-CoFe laminations may be heat treated at 880° C. for 6 hours in a hydrogen containing atmosphere to adjust the magnetic properties. Therefore, the insulating coating was subjected to this heat treatment to determine its suitability for use in the lamination stack. After the heat treatment, visual inspection confirmed that a continuous coating was present on the 50%-CoFe tape.

[0118] A 50%-NiFe alloy (PERMENORM® 5000 V5) was coated with a zirconium-containing coating, in particular HITCOAT, which after heat treatment includes zirconium oxide. HITCOAT denotes a coating which is applied to a surface in the form of a Zr-propylate solution which during drying is converted into zirconium oxide after the heat treatment. The 50%-NiFe tape with the zirconium-containing coating was subjected to a heat treatment at 880° C. for 6 hours in a hydrogen containing atmosphere to determine its suitability for use in the lamination stack. After the heat treatment, visual inspection confirmed that a continuous coating was present on the 50%-NiFe tape.

[0119] Therefore, a laminated core including alternate laminations including 50%-CoFe and 50%-NiFe may be fabricated using insulating coatings fabricated using DL1 and HITCOAT as both coatings are thermally stable at temperatures up to at least 850° C., in particular after a heat treatment at temperatures above 850° C. in a hydrogen-containing atmosphere.

EXAMPLE 2

[0120] In example 2, a laminated core including CoFe-based alloy laminations and FeSi-based alloy laminations is to be fabricated.

[0121] A FeSi alloy (M400-65A) was coated with STABOLIT® 20 and subjected to a heat treatment at 900° C. for 6 hours in a hydrogen containing atmosphere to determine its suitability for use in the lamination stack. After the heat treatment, the coating was subjected to the adhesive tape test and it was determined that only a few isolated particles were removed from the coating and adhered to the adhesive tape. For the CoFe-based alloy laminations, as coating fabricated using DL, as in example 1, may be used.

[0122] Therefore, a laminated core including alternate laminations including this FeSi alloy and 50%-CoFe may be fabricated using insulating coatings fabricated using STABOLIT® 20 and DL1, respectively, as both coatings are thermally stable at temperatures of at least 850° C., in particular in a hydrogen-containing atmosphere.

EXAMPLE 3

[0123] In example 3, a laminated core including FeSi-based alloy laminations and NiFe-based alloy laminations is to be fabricated.

[0124] To fabricate a core including laminations including 50% NiFe alloy (PERMENORM® 5000 V5), it is desirable to heat treat the core at 1150° C. for 5 hours in a hydrogen-containing atmosphere in order to adjust the magnetic properties of the 50%-NiFe alloy. The laminations including the 50% NiFe alloy were coated with HITCOAT, the laminations including FeSi were not coated with an insulating layer. The laminations of differing composition were alternately stacked so that a layer of HITCOAT is positioned between adjacent 50%-NiFe and FeSi laminations in the stack.

[0125] After a heat treatment at 1150° C. for 5 hours in a hydrogen-containing atmosphere, an iridescent effect was discernable on the coated surfaces thus confirming the presence of the coating after the heat treatment.

COMPARISON EXAMPLE 1

[0126] In comparison example 1, an FeSi alloy (N020) tape was coated with a resin which hardens upon application of heat, for example at temperatures of around 200° C. These resins may be used to adhere the laminations to one another to from the stack and form the insulating coating between neighbouring laminations. STABOLIT® 70, which is sold by thyssenkrupp Steel Europe AG of Bochum, Germany, is an example of such a resin. The tape and coating was heat treated at 500° C. for 1 hour in a hydrogen-containing atmosphere. After this heat treatment, visual inspection of the tape did not reveal the presence of a coating. Therefore, such a resin-based coating is not thermally stable at temperatures of at least 850° C.

COMPARISON EXAMPLE 2

[0127] In a comparison example 2, a tape including a FeSi alloy, in particular M400-65A, was coated with STABOLIT® 20 and heat treated at 1000° C. in a hydrogen-containing atmosphere to determine its suitability for a core including laminations including a FeSi alloy and a 50%-NiFe alloy (PERMENORM® 5000 V5). The 50%-NiFe alloy is to be heated treated at 1150° C. for 5 hours in a hydrogen-containing atmosphere in order to adjust the magnetic properties. After a heat treatment at 1000° C. in a hydrogen-containing atmosphere, the coating was subjected to the adhesive tape test according to DIN EN ISO 2409:2013-06. A continuous layer was found to be present on the removed adhesive surface indicating that a coating fabricated using STABOLIT® 20 is unsuitable for cores heat treated at temperatures of 1000° C. and above.

[0128] However, coatings fabricated using STABOLIT® 20 were found to be thermally stable at 900° C. in a hydrogen-containing atmosphere and, therefore, at temperatures up to at least 850° C.

COMPARISON EXAMPLE 3

[0129] In comparison example 3, laminations comprising a 50%-CoFe alloy (VACODUR® 49) and laminations comprising a FeSi alloy (NO10) were alternately stacked to form a core. Both compositions of the laminations were uncoated. The stack was subjected to a heat treatment at 880° C. for 6 hours in a hydrogen-containing atmosphere to adjust the magnetic properties of the 50%-CoFe alloy. After the heat treatment, at least some of the laminations of the stack were found to be welded to one another. Further contact points may occur as the result of pressure applied to the core during use. Higher eddy current losses were found to result. These higher eddy current losses are believed to result at least in part from the lack of electrical insulation between the laminations of the core.