The present invention relates to a method for manufacturing a magnetic part of a
high-sensitivity differential relay.
It in particular applies to the manufacture of differential protection switches or
circuit breakers.
Such differential switches or circui 5 t breakers are designed to provide for the safety
of people by quickly cutting a primary electric circuit when a fault appears on that circuit.
In particular, differential circuit breakers of the "inherent current" type are made up of a
fault current detector, a high-sensitivity differential relay, and a mechanism for opening the
primary electric circuit.
10 The differential relay comprises a magnetic circuit comprising two magnetic parts,
which are a moving vane and a stationary armature.
When a fault appears on the primary electric circuit, the fault current detector is
able to send an electric signal to the differential relay. In response to the electric signal,
the differential relay opens, by pivoting the vane relative to the armature, which sets the
15 opening mechanism of the primary electric circuit in motion.
The magnetic parts of the differential relay are made up of a soft magnetic alloy,
characterized by a high saturation induction, a low coercive field strength and a relatively
high electric resistivity. Such features ensure a proper operation of the differential relay.
In order to meet the desired magnetic characteristic conditions, it is known to
20 manufacture the magnetic parts of the magnetic circuit from a magnetic alloy such as iron
and nickel, for example an alloy comprising 46 wt% to 49 wt% of nickel, in particular 48
wt%, the rest being iron and impurities resulting from development. This alloy has the
advantage of having a saturation induction Bs of 1.5 Tesla and a coercive field strength
Hc of 4 A/m.
25 The magnetic parts thus manufactured may nevertheless be subject to moist
atmospheric conditions, which causes a risk of corrosion between the iron and the nickel
of the alloy forming the iron oxides and hydroxides leading either to untimely triggering of
the differential relay, or on the contrary to sticking of the vane on the armature.
Furthermore, the successive contacts between the vane and the armature may
30 lead to local wear and deformation of those parts, causing incorrect operation of the
differential relay.
Generally, the nickel-based magnetic alloys used have a low hardness
(approximately 120 HV) and a low wear resistance. Furthermore, these nickel alloys are
not stainless, and their corrosion resistance under usage conditions of the relay is
35 insufficient.
3
It has therefore been proposed to improve the hardness and wear resistance of the
contact surfaces of the magnetic parts of relays by producing metal coatings on those
surfaces that also increase the corrosion resistance of the contact surfaces. These metal
coatings are for example deposits of gold, chromium or diamond carbon.
5 Nevertheless, this technique is very expensive.
It has also been proposed to package the differential relays in impermeable plastic
housings, able to protect the magnetic circuit from corrosion. However, this technique
does not make it possible to resolve the problems related to the wear of the magnetic
circuit.
10 One aim of the invention is to resolve these drawbacks and provide a method for
manufacturing magnetic parts of a differential relay with good wear resistance, and that is
less expensive to implement than the methods according to the state of the art.
To that end, the invention relates to a method of the aforementioned type, said
manufacturing method comprising a surface treatment step by shot-peening at least one
15 portion of a surface of said magnetic part, said shot-peening surface treatment step
comprising a projection of pressurized microbeads on said surface portion.
According to other aspects of the invention, the manufacturing method comprises
one or more of the following features:
- said magnetic part is an armature or a vane of a magnetic circuit;
20 - said part is made from a Fe-Ni alloy comprising from 46 wt% to 49 wt% of nickel,
the rest being iron and impurities resulting from the development;
- said microbeads are glass, ceramic or steel microbeads;
- said microbeads are projected on said surface portion at a pressure comprised
between 1 and 5 bars;
25 - the manufacturing method further comprises an intermediate surfacing step for
said magnetic part, carried out before the shot-peening surface treatment step;
- the manufacturing method further comprises a final surfacing step for said
magnetic part, carried out after the shot-peening surface treatment step.
The invention also relates to a method for manufacturing a magnetic circuit of a
30 high-sensitivity differential relay, said magnetic circuit comprising two magnetic parts
forming an armature and a vane, said method comprising:
- manufacturing said magnetic parts, and
- assembling said magnetic parts to form said magnetic circuit,
wherein the manufacture of at least one of said magnetic parts is done using a method for
35 manufacturing a magnetic part according to the invention.
4
The invention also relates to a magnetic part of a magnetic circuit of a highsensitivity
differential relay, characterized in that it is obtained through a method for
manufacturing a magnetic part according to the invention.
The invention also relates to a magnetic circuit of a high-sensitivity differential
relay, 5 said magnetic circuit comprising two magnetic parts forming an armature and a
vane, characterized in that at least one of said magnetic parts is a magnetic part
according to the invention.
The invention will be better understood upon reading the following description,
provided solely as an example and done in reference to the appended figures, in which:
10 - figure 1 is a diagrammatic view of a circuit breaker comprising a high-sensitivity
differential relay according to the invention,
- figure 2 is a diagrammatic view of a device for carrying out the method according
to one embodiment of the invention,
- figure 3 is a diagram of an electrical assembly for determining the impedance of
15 magnetic circuits according to the invention.
Figure 1 shows a circuit breaker 1 interposed on a primary electric power circuit of
an electrical apparatus 2, to detect a leak current in that primary electric circuit.
The circuit breaker 1 comprises a magnetic toroid 3, a high-sensitivity differential
relay 5, and a mechanism 7 for opening the primary electric circuit.
20 The magnetic toroid 3 is able to detect a current fault on the primary circuit.
The differential relay 5 comprises a magnetic circuit 9, a permanent magnet 11
and a return spring 13.
The magnetic circuit 9 comprises two magnetic relay parts, which are a moving
vane 15 and a U-shaped stationary armature 17.
25 The armature 17 comprises a base 18, and first and second branches 19 and 20,
the branches 19 and 20 each ending with a planar polar surface 19a, 20a.
The vane 15 is mounted across from the polar surfaces 19a, 20a of the armature
17. The vane 15 comprises a substantially planar polar surface 15a, able to come into
contact with the polar surfaces 19a and 20a of the armature 17.
30 The vane 15 is mounted pivoting around an axis corresponding to an edge 21 of
the first branch 19 of the armature 17, between an idle position, shown in figure 1, in
which the polar surface 15a of the vane 15 is in contact against the polar surfaces 19a,
20a of the armature 17, and a pivoted position, in which the vane 15, having pivoted
around the edge 21, is no longer in contact with the polar surface 20a of the second
35 branch 20.
5
The polar branch 15a of the vane 15 and the polar surfaces 19a and 20a of the
armature17 are contact zones designed to come into contact with one another.
The vane 15 and the armature are made from a Fe-Ni alloy. The Fe-Ni alloy is for
example an alloy comprising from 46 wt% to 49 wt% of nickel, the rest being iron and
impurities resulting 5 from the development. This is for example an alloy of the Supra50®
type.
The permanent magnet 11 is in the form of a parallelepiped bar. The permanent
magnet 11 is placed between the branches 19 and 20 of the armature 17, one of the poles
of the magnet 11 being alongside the base 18 of the armature 17, and the other pole
10 being placed across from the vane 15.
The permanent magnet 11 is able to exert a magnetic force on the vane 15 to keep
it in the idle position.
Furthermore, the return spring 13 is able to exert a force on the vane 15,
antagonistic to the force exerted by the permanent magnet 11, to drive it toward the
15 pivoted position.
A control coil 23 is wound on the second branch 20 of the armature 17. The control
coil 23 is supplied with electrical current by means of the magnetic toroid 3. The control
coil 23 is able to create a magnetic flux opposite the flux of the permanent magnet 11 in
the branch 20 when the control coil 13 is traveled by an excitation current.
20 When a current fault is detected by the toroid 3, an excitation current is generated
in the control coil 23, which creates a magnetic flux in the magnetic circuit 9 opposite the
flux of the permanent magnet 11, and causes a reduction or cancellation of the
maintaining force exerted on the vane 15. The force exerted by the return string 13
exceeds the maintaining force exerted on the vane 15, which drives a pivoting of the vane
25 15 toward its pivoted position.
As an example, the spring is tared so that a fault current greater than or equal to
30 mA causes the vane 15 to pivot toward its pivoted position.
The movement of the vane 15 from its idle position to the pivoted position makes it
possible to actuate the mechanism 7 for opening the primary electric circuit, and therefore
30 to cut the electric power supply of the apparatus 2.
The manufacture of the magnetic circuit 9 comprises manufacturing the two
magnetic parts of that circuit, i.e., the vane 15 and the armature 17, and assembling those
two parts to form the circuit.
The manufacture of each of the magnetic parts comprises the manufacture of a
35 preformed part.
6
Each preformed part is manufactured in a strip of Fe-Ni alloy, followed by shaping
by bending, so as to give each of the parts the desired geometry, the cutting being
followed by heat treatment at a high temperature (greater than 1000°C) designed to give
the strip the desired mechanical and magnetic properties, in particular a very low coercive
5 field strength, for example less than or equal to 15 A/m.
Such a coercive field makes it possible to obtain a high-sensitivity of the relay, for
example an electric triggering power of less than 250 μVA and preferably comprised
between 50 and 150 μVA.
In a known manner, the strip of alloy is obtained from an ingot by hot rolling,
10 followed by cold rolling.
Each preformed part then undergoes a surface treatment step by shot-peening, in
which microbeads are projected on at least one portion of the surface of each preformed
part. For each of the magnetic parts, the surface portion of which the microbeads are
projected comprises at least the contact zones of that part, i.e., the zones of that part
15 designed to come into contact with the other part.
According to one embodiment, the microbeads are projected on the sides of the
magnetic parts comprising the contact zones of those parts, i.e., the zones of those parts
designed to come into contact with one another.
Treatment by shot-peening results in producing a surface strain hardening
20 penetrating several hundredths of millimeters, in particular from 0.03 mm to 0.05 mm, over
a treated surface portion, and thus increasing the hardness of the part of a surface
portion. As an example, the shot-peening treatment makes it possible to increase the
Vickers hardness on the surface of the part by more than 50 HV, the hardness for
example going from 120 HV to more than 170 HV.
25 A depth of at least several hundredths of millimeters, in particular approximately
0.03 mm, is sufficient to retain the possibility of performing, surfacing operations with
slight material removal after the shot-peening treatment, while retaining an increased
hardness on the surface of the part of at least 170 HV. Furthermore, a depth of at most
several hundredths of millimeters, in particular at most 0.05 mm, makes it possible to
30 preserve the magnetic properties of the part.
At the end of the shot-peening treatment, each of the parts undergoes a finishing
treatment designed to give the part the desired appearance, roughness and flatness for
the application.
In particular, obtaining a roughness Ra at least equal to 0.03 m and less than 0.5
35 m makes it possible to ensure good contact quality between the contact surfaces of the
two parts.
7
The vane 15 and the armature 17 thus manufactured are then assembled to form
the magnetic circuit 9.
Alternatively, an intermediate finishing treatment step may be done on the
preformed parts, before the shot-peening treatment step.
The sh 5 ot-peening treatment step will now be described in more detail in reference
to figure 2, which diagrammatically shows a device 50 for carrying out that step.
The device 50 comprises an enclosure 52 comprising an opening 54 for inserting
preformed parts, able to be sealed to close the enclosure 52 tightly.
The device 50 further comprises support means 56 for preformed magnetic parts,
10 and means 58 for projecting a stream of microbeads conveyed in a fluid onto the parts
held by the support means 56.
The microbead projection means 58 comprise a nozzle 60 for projecting a stream
of microbeads conveyed in a fluid, and means for supplying the nozzle 60 with a
pressurized fluid conveying microbeads.
15 The beads are micrometric glass, ceramic or steel beads. For example, the
microbeads have a diameter comprised between 20 m and 200 m.
As an example, the microbeads are of the SS19 type marketed by Rössler France.
These microbeads are made from sodiocalcic glass with a mean diameter substantially
equal to 40 m.
20 The fluid in which the microbeads are conveyed is for example water or air.
For example, the fluid used is water, in which the microbeads are mixed, the
mixture comprising 25 vol% of microbeads.
The nozzle 60 comprises an opening 62 through which the pressurized fluid, mixed
with the microbeads, is projected. The shape and size of the opening 62 are adjustable
25 based on the span of the surface to be treated and the homogeneity of the desired
projection. The opening 62 is for example a circular opening, with a diameter comprised
between 5 and 12 mm, in particular equal to 10 mm.
The pressure of the fluid mixed with the microbeads at the outlet of the nozzle 60
is for example comprised between 1 and 5 bars.
30 The support means 56 are able to keep a magnetic part in a predetermined
position across from the opening 62 of the nozzle 60 during the projection of the
microbeads on that part. The support means 56 are also able to modify the position of the
magnetic part relative to the projection means 58, in particular the distance d between the
part and the opening 62 and the orientation of the part relative to the jet coming from the
35 opening 62, hereinafter referred to as the angle of attack .
The distance d is for example comprised between 100 mm and 200 mm.
8
The angle of attack is for example equal to 90°, i.e., the jet coming from the nozzle
has an incidence angle on the part substantially equal to 90°. The angle of attack may
also be chosen to be less than 90°, for example equal to 75°.
The adjustment of the distance d and the angle  make it possible to control the
5 strain hardening obtained on the treated part.
The support means 56 for example comprise a magnet able to exert a magnetic
force on a magnetic part to keep it in position, the magnet being able to be rotated relative
to the nozzle 60 to rotate the magnetic part relative to the nozzle 60.
The support means 56 thus make it possible to perform sweeping of one or several
10 part(s) by the jet coming from the nozzle 60.
As an example, strips were manufactured from a Fe-Ni alloy, comprising 48% of
Ni, the rest being iron and impurities resulting from the development, from ingots, by hot
rolling, followed by cold rolling.
Preformed vanes and armatures were next manufactured by cutting the strips,
15 followed by shaping by bending, and a thermal treatment designed to give the strip the
desired mechanical and magnetic properties.
An intermediate finishing operation was then performed on a first series of
preformed armatures, followed by a shot-peening treatment using the device described in
reference to figure 2. At the end of the shot-peening treatment, a finishing treatment was
20 applied again to the armatures to obtain finished armatures
A shot-peening treatment was also done on a second series of preformed
armatures, without intermediate finishing treatment, using the device described in
reference to figure 2. At the end of the shot-peening treatment, a finishing treatment was
applied to the armatures to obtain finished armatures.
25 A shot-peening treatment was also done on a series of preformed vanes, without
intermediate finishing treatment, using the device described in reference to figure 2. At the
end of the shot-peening treatment, a finishing treatment was applied to the vanes to
obtain finished vanes.
All of the shot-peening treatments were done using microbeads of type SS19
30 described above, conveyed in water, the water-microbead mixture comprising 25 vol% of
microbeads.
The nozzle used is a nozzle having a circular opening 62 with a diameter equal to
10 mm. Furthermore, the distance between the opening 62 of the nozzle 60 and the vanes
and armatures was set at 150 mm.
9
Each series of armatures and vanes was divided into nine groups, and each
armature or vane of each group was treated by shot-peening using the angle of attack ,
pressure P and exposure time T parameters appearing in table 1 below.
Series Group
No. (°) P (bars) T (s)
First series
of
armatures
1 90 1 7
2 90 1 14
3 90 1.5 7
4 90 1.5 14
5 90 2 7
6 90 2 14
7 75 2 7
8 90 2.5 7
9 90 2.5 14
Second
series of
armatures
1 90 1 7
2 90 1 14
3 90 1.5 7
4 90 1.5 14
5 90 2 7
6 90 2 14
7 75 2 7
8 90 2.5 7
9 90 2.5 14
Series of
vanes
1 90 1 7
2 90 1 14
3 90 1.5 7
4 90 1.5 14
5 90 2 7
6 90 2 14
7 75 2 7
8 90 2.5 7
9 90 2.5 14
5 Table 1: shot-peening treatment parameters applied to each group
The influence of the shot-peening treatment on the hardness of the surface of the
vanes and armatures was next measured.
To that end, the Vickers hardness HV 0.025 and HV 0.01 of the vanes or
10 armatures of each of the groups was measured.
The roughness coefficient Ra of the armatures and vanes of each of the groups
was also measured.
The obtained measurements, resulting within each of the groups from a mean of
the roughness, fall and Vickers hardness values measured on five vanes or armatures
15 from that group, are provided in table 2.
10
Furthermore, the influence of the shot-peening treatment on the electrical
properties of the magnetic circuit formed with the treated vanes and armatures was
determined. In particular, the impedance of a magnetic circuit according to the state of the
art, formed by assembling a vane and an armature that has been coated but not shotpeened,
is typically 5 comprised between 1.10 and 1.75 . Magnetic circuits were thus
formed from the vanes and armatures of each of the groups, and the impedance of the
magnetic circuits thus formed was measured, i.e., the resistance of the circuits to the
passage of a magnetic flux.
The impedance measurement of each circuit was done based on the assembly
10 described in reference to Figure 3.
As illustrated in Figure 3, a force F was applied on the vane 15 using a weight.
That force is designed to simulate the force exerted by the permanent magnet 11 when
the differential relay 5 is in operation.
A first coil 70, comprising N1 turns, was wound around one of the branches 19 of
15 armatures 17, and a second coil 72, comprising N2 turns, was wound around the other
branch 20 of the armatures 17.
The first coil 70 is connected to an AC current generator 74, and the second coil is
connected to a voltmeter 76.
An AC current I was generated by the generator 74 in the first coil 70, the value of
20 the current being controlled using an ammeter 78.
The voltage V across the terminals of the second coil 74 was measured.
The impedance Z was then determined as the ratio of the voltage V to the current
I.
In particular, armatures from each of the groups of the first series were assembled
25 with vanes not coated and not shot-peened, with vanes coated with a chromium coating
and not shot-peened, and lastly with vanes obtained using the method according to the
invention, therefore not coated but shot-peened, from the corresponding group of the
series of vanes.
Armatures from each of the groups of the second series were also assembled with
30 vanes not coated and not shot-peened, with vanes coated with a chromium coating and
not shot-peened, and lastly with vanes obtained using the method according to the
invention, therefore not coated but shot-peened, from the corresponding group of the
series of vanes.
Measurements were next done of the electric impedance, denoted Z pal. prod, of
35 the magnetic circuits formed by the armatures from each of the groups and the vanes not
coated and not shot-peened; the electrical impedance, denoted Z pal Cr, of the magnetic
11
circuits formed by the armatures of each of the groups and the vanes coated with
chromium and not shot-peened; and the electrical impedance, denoted Z pal bill, of the
magnetic circuits formed by the armatures of each of the groups and the vanes according
to the invention from the corresponding group.
5 The measured impedances are provided in table 2.
Likewise, vanes were assembled from each of the groups of the series of vanes
with armatures not coated and not shot-peened, with armatures coated with a chromium
coating and not shot-peened, and with armatures obtained using the method according to
the invention, therefore not coated but shot-peened, with the corresponding group of the
10 first series of armatures.
Measurements were next done of the electrical impedance, denoted Z arm. prod,
of the magnetic circuits formed by the vanes of each of the groups and armatures not
coated and not shot-peened; the electric impedance, denoted Z arm Cr, of the magnetic
circuits formed by the vanes of each of the groups and armatures coated with chromium
15 and not shot-peened; and the electric impedance, denoted Z arm bill, of the magnetic
circuits formed by the vanes from each of the groups and armatures according to the
invention with the corresponding group of the first series of armatures.
The measured impedances, expressed in ohms, are provided in table 2.
It should be noted that the electric impedance Z arm bill of the magnetic circuit
20 formed by a vane from one group and an armature according to the invention from the
corresponding group of the first series of armatures is necessarily identical to the electric
impedance Z pal bill of a magnetic circuit formed by an armature of the first series of that
group and a vane according to the invention of the corresponding group, as shown in
table 2.
25
12
Series Group
No.
Z pal.
prod
Z pal.
revê
Z pal.
μbill
HV
0.025
HV
0.01
Ra
(m)
First series
of
armatures
1 1.732 1.248 1.424 269 253 0.0764
2 1.614 1.252 1.458 289 290 0.0406
3 1.452 1.16 1.322 273 259 0.0358
4 1.6 1.202 1.378 276 298 0.0392
5 1.658 1.19 1.292 274 229 0.0388
6 1.476 1.174 1.294 297 317 0.0382
7 1.572 1.166 1.378 287 234 0.0384
8 1.484 1.174 1.36 275 275 0.052
9 1.454 1.246 1.32 275 251 0.0356
Second
series of
armatures
1 1.74 1.35 1.482 297 255 0.0372
2 1.644 1.284 1.32 305 285 0.0412
3 1.574 1.276 1.304 271 295 0.0366
4 1.62 1.246 1.372 294 276 0.041
5 1.532 1.242 1.414 257 287 0.0418
6 1.532 1.216 1.32 289 300 0.0394
7 1.542 1.282 1.382 281 255 0.0384
8 1.462 1.112 1.322 242 270 0.0384
9 1.458 1.07 1.226 312 311 0.0456
Series Group
No.
Z arm.
prod
Z arm.
revê
Z arm.
μbill
HV
0.025
HV
0.01
Ra
(m)
Series of
vanes
1 1.74 1.218 1.424 240 231 0.0678
2 1.498 1.232 1.458 215 213 0.066
3 1.274 1.016 1.322 246 238 0.0586
4 1.454 1.052 1.378 260 224 0.058
5 1.536 1.06 1.292 251 249 0.056
6 1.422 1.068 1.294 265 257 0.062
7 1.482 1.114 1.378 256 232 0.064
8 1.448 1.102 1.36 253 263 0.056
9 1.492 1.07 1.32 261 245 0.06
Table 2: Impedance, hardness and roughness measurements
The results provided in table 2 show that the manufacturing method for the vanes
and armatures according to the invention, in particular the step for shot-peening those
vanes and armatures, make it 5 possible to increase the surface hardness of those parts in
a very satisfactory manner. In fact, whether the angle of attack is equal to 90° or 75°, and
irrespective of the pressure of the stream projected at the outlet of the nozzle, between 1
bar and 2.5 bar, the Vickers hardnesses HV 0.025 and HV 0.01 are clearly higher than the
initial hardness of the parts (120 HV), and also clearly higher than hardnesses generally
10 obtained using coating methods (170 HV).
Furthermore, the reference coefficients of the vanes and armatures are also
satisfactory, in particular greater than 0.03 m. Thus, these results show that the surface
strain hardening of the surface of the parts makes it possible to perform satisfactory
13
finishing of the parts with removal of material, while keeping a surface with a high
hardness.
One can also see that the electric impedances of magnetic circuits formed by a
vane and an armature manufactured using the method according to the invention have a
5 satisfactory electric impedance, comprised between 1.10  and 1.75 . These
satisfactory values are also observed for electric circuits whereof only one of the
mechanical parts is manufactured using the method according to the invention.
These results thus show that the shot-peening treatment step makes it possible to
increase the hardness of the surface of these magnetic parts without negatively affecting
10 other properties, in particular the impedance of the magnetic circuit or the ability of those
parts to undergo an effective finishing treatment.
The contact surfaces of the magnetic parts according the invention consequently
have a very satisfactory wear resistance, substantially greater than the wear resistance of
relays comprising metal coatings of a known type.
15 It must, however, be understood that the example embodiment described above is
not limiting.
In particular, according to one alternative, only one vane or only one armature may
be manufactured using a method according to the invention.

I/We Claim:
1.- A method for manufacturing a magnetic part (15, 17) of a high-sensitivity
5 differential relay (5), said manufacturing method comprising a surface treatment step by
shot-peening at least one portion of a surface of said magnetic part (15, 17), said shotpeening
surface treatment step comprising a projection of pressurized microbeads on said
surface portion.
2.- The method for manufacturing a magnetic part (15, 17) according to claim 1,
10 wherein said magnetic part is an armature (17) or a vane (15) of a magnetic circuit (9).
3.- The method for manufacturing a magnetic part (15, 17) according to any one of
claims 1 or 2, wherein said part is made from a Fe-Ni alloy comprising from 46 wt% to 49
wt% of nickel, the rest being iron and impurities resulting from the development.
4.- The method for manufacturing a magnetic part (15, 17) according to any one of
15 claims 1 to 3, wherein said microbeads are glass, ceramic or steel microbeads.
5.- The method for manufacturing a magnetic part (15, 17) according to any one of
claims 1 to 4, wherein said microbeads are projected on said surface portion at a pressure
comprised between 1 and 5 bars.
6.- The method for manufacturing a magnetic part (15, 17) according to any one of
20 claims 1 to 5, further comprising an intermediate surfacing step for said magnetic part (15,
17), carried out before the shot-peening surface treatment step.
7.- The method for manufacturing a magnetic part (15, 17) according to any one of
claims 1 to 6, further comprising a final surfacing step for said magnetic part (15, 17),
carried out after the shot-peening surface treatment step.
25 8.- The manufacturing method according to any one of claims 1 to 7, characterized
in that it comprises, before said surface treatment step, a step for manufacturing a
preformed magnetic part, comprising a phase for cutting a strip obtained by hot rolling
followed by cold rolling, said surface treatment step being carried out on said preformed
magnetic part.
30 9.- The method according to claim 8, characterized in that said step for
manufacturing the preformed magnetic part further comprises, after the cutting phase, a
phase for shaping the cut strip by bending.
10.- A method for manufacturing a magnetic circuit (9) of a high-sensitivity
differential relay (5), said magnetic circuit (9) comprising two magnetic parts (15, 17)
35 forming an armature (17) and a vane (15), said method comprising:
- manufacturing said magnetic parts (15, 17), and
15
- assembling said magnetic parts (15, 17) to form said magnetic circuit (9),
wherein the manufacture of at least one of said magnetic parts (15, 17) is done using a
method for manufacturing a magnetic part according to any one of claims 1 to 9.
11.- A magnetic part (15, 17) of a magnetic circuit (9) of a high-sensitivity
5 differential relay (5), characterized in that it is obtained through a manufacturing method
according to any one of claims 1 to 9.
12.- A magnetic circuit (9) of a high-sensitivity differential relay (5), said magnetic
circuit (9) comprising two magnetic parts (15, 17) forming an armature (17) and a vane
(15), characterized in that at least one of said magnetic parts is a magnetic part according