Metal treatment – Stock – Magnetic
Reexamination Certificate
1998-07-02
2001-02-20
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C148S310000, C148S311000, C148S312000, C148S120000, C148S121000, C420S446000, C420S451000, C420S452000, C420S583000
Reexamination Certificate
active
06190465
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a soft magnetic alloy having good magnetic properties and, at the same time a good hardness and good corrosion resistance. This alloy is useful generally, and is particularly suitable for the manufacture of the magnetic circuit of a relay of an own-current residual current device.
DISCUSSION OF THE BACKGROUND
Residual current devices are intended to ensure the safety of individuals by rapidly cutting off a main electrical circuit when a fault appears in the circuit. Several types of residual current devices exist, especially residual current devices of the so-called “own current” type. Own-current residual current devices consist of a current fault detector, a high-sensitivity relay, a trip and a mechanism for opening the main electrical circuit. When a fault appears in the main electrical circuit, the fault detector sends an electrical pulse to the high-sensitivity relay, which opens and actuates the trip, thereby setting into motion the mechanism for opening the main electrical circuit.
The high-sensitivity relay consists of a magnetic circuit, having a moving contact and a fixed U-shaped armature, of a return spring, of a permanent magnet and of a coil. The permanent magnet is placed beneath the lower bar of the U-shaped fixed armature and the coil surrounds one arm of the U. The moving contact lies on both ends of the arms of the U, and one of its ends is fixed to the return spring. When the relay is at rest, i.e. ready to be actuated, no current flows through the coil, the permanent magnet causes a continuous magnetic flux to circulate in the magnetic circuit, creating an attraction force which holds the moving contact against the fixed armature, and the return spring is under tension. When an alternating fault appears in the main electrical circuit, the fault detector sends an electric current into the coil of the relay. This current generates a magnetic field which demagnetizes the fixed armature, thereby decreasing the magnetic attraction force holding the moving contact against the fixed armature and causing the moving contact to tilt due to the effect of the tension in the return spring. By tilting, the moving contact actuates the trip.
In order for such a relay to operate properly, the magnetic circuit must be made of a soft magnetic alloy characterized by as high as possible a saturation induction, as low as possible a coercive field and a relatively high electrical resistivity. However, in order for the relay to operate reliably over a long period, it is also desirable, on the one hand, for the soft magnetic alloy to have good resistance to wet atmospheric corrosion in order to prevent the formation of oxides in the contact area between the moving contact and the fixed armature, and, on the other hand, for the hardness to be high enough to prevent local wear and deformation of the components which successive operations could cause.
In order to meet the desired magnetic-property conditions, the magnetic circuit is manufactured from a soft magnetic alloy of the iron-nickel type containing 48% nickel by weight, the balance being iron and impurities resulting from the smelting process. This alloy has the advantage of having a saturation induction Bs of 1.5 tesla and a coercive field Hc of 4 A/m, which corresponds to the best characteristics that can be obtained. However, this alloy has the drawback of having quite a low hardness (about 100 HV) and of having too low a corrosion resistance. In order to compensate for these insufficiencies, the magnetic circuit, or at least the moving contact, is protected by an anticorrosion coating (for example, by depositing gold) or by a hardening and corrosion-resistant coating, for example by depositing chromium. However, this technique has the drawback of being expensive and of creating, in the contact area between the moving contact and the armature, an additional thickness which detracts from the magnetic behavior of the magnetic circuit taken in its entirety because of an air-gap effect and of residual stresses.
In order to remedy the hardness problem, it has been proposed, especially in European Patent Application EP 0 740, 313, to use, for this purpose, a soft magnetic alloy of the iron-nickel-titanium type containing, by weight, 46 to 46.5% nickel, approximately 1.8% titanium, from 0% to 1% niobium, from 0.45% to 0.5% manganese and from 0.25% to 0.45% silicon, the balance being iron and impurities resulting from the smelting process. This alloy has the advantage of having a saturation induction of 1.35 tesla and a hardness greater 220 HV. However, it has the drawback of having a coercive field Hc of 10 A/m, which is relatively high, and in addition, it has a somewhat insufficient corrosion resistance.
OBJECTS OF THE INVENTION
None of the known alloys is therefore completely satisfactory, and therefore one object of the present invention is to remedy this drawback by providing a soft magnetic alloy which is well suited to the manufacture of the magnetic circuit of a high-sensitivity relay, having a saturation induction BS of greater than 0.9 tesla, a coercive field HC of substantially less than 10 A/m, an electrical resistivity p of greater than 60 &mgr;&OHgr;.cm, a hardness of greater than 200 HV, and good resistance to atmospheric corrosion.
SUMMARY OF THE INVENTION
For this purpose, the subject of the invention is a soft magnetic alloy of the iron-nickel type, whose chemical composition comprises, by weight based on total weight:
40%≦Ni+Co≦65%
0%≦Co≦7%
2%≦Cr≦5%
1%≦Ti≦3%
0%≦Al≦0.5%
0% Mn≦2%
0%≦Si≦1%
optionally, up to 3% Mo, up to 2% W, up to 2% V, up to 1.5% Nb, up to 1% Ta and up to 3% Cu, the sum of the Cr, Mo, W, V, Nb, Ta and Cu contents being less than 7% and the sum of the Mo, W, V, Nb, Ta and Cu contents being less than 4%, the balance comprising or being iron and impurities, such as carbon, sulfur and phosphorus, resulting from the smelting process, the chemical composition furthermore satisfying the relationships:
Cr<5−0.015×(Ni+Co−52.5)
2
if: Ni+Co≦52.5
Cr<5−0.040×(Ni+Co−52.5)
2
if: Ni+Co≧52.5
the alloy having a saturation induction Bs of greater than 0.9 tesla, a coercive field of less than 10 A/m, an electrical resistivity p of greater than 60 &mgr;&OHgr;.cm and a hardness of greater than 200 HV.
Preferably, the chemical composition of the alloy is such that:
48%≦Ni+Co≦55%
0%≦Co≦3%
2%≦Cr≦4%
0%≦Mo+W+V+Nb+Ta+Cu≦1%
1.3%≦Ti≦1.7%
0.05%≦Al≦0.25%
0.1%≦Mn≦0.3%
0%≦Si≦0.1%.
And it is preferable for the impurities resulting from the smelting process to be such that:
C<0.01%
S<0.001%
P<0.01%.
Better still, the chemical composition of the alloy should be such that:
50%≦Ni+Co≦52%
0%≦Co≦3%
3%≦Cr≦4%
0%≦Mo+W+V+Nb+Ta+Cu≦0.5%
1.3%≦Ti≦1.7%
0.05%≦Al≦0.25%
0.1%≦Mn≦0.3%
0%≦Si≦0.1%.
In order to manufacture a strip or a component made of soft magnetic alloy according to the invention, it is preferable to anneal the strip, or the component, at high temperature, namely between 1000° C. and 1175° C., for 2 to 6 hours and for it to be tempered at a temperature of between 650° C. and 750° C. for 1 to 5 hours.
The invention also relates to a high-sensitivity relay, and especially a relay for an own-current residual current device, of the type comprising a magnetic circuit consisting of a moving contact and a fixed armature, in which the moving contact or the fixed armature, or both of them, are made of a soft magnetic alloy according to the invention.
The soft magnetic alloy may also be advantageously used for the manufacture of certain types of small electric motors or generators, such as a motor for an electric watch with hands. This is because, in this application, the desired magnetic properties are very comparable and the problem of corrosion resistance arises in a similar fashion.
More g
Chaput Laurent
Coutu Lucien
Waeckerle Thierry
Imphy Ugine Precision
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sheehan John
LandOfFree
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