Use of chromium-based stainless steel for manufacturing a domestic use and manual opening magnetic unit actuated by thermocouple or equvalent element

Description

Field of the Invention

[0001] The present invention relates to a domestic use and manual opening magnetic unit actuated by a thermocouple or equivalent element. It particularly relates to the use of a chromium-based stainless steel alloy in the production of the magnetic armature, of the magnetic core or of both elements of said magnetic unit.

Background of the Invention

[0002] The magnetic units forming part of a Magnetic Unit-Thermocouple Assembly are elements which are well known and used in the state of the art, which are disclosed, among others, in the following documents MU 200203006, MU 200502016, EP 1624247, EP 1909029 or WO03/085324. They are used as safety systems for domestic gas cookers, for domestic gas water heaters and for domestic gas water boilers. The Magnetic Unit-Thermocouple Assembly acts as a system for cutting off the gas flow to the apparatus when the flame of the burner is extinguished for some reason.

[0003] The thermocouple generates in the presence of the flame an electrical voltage which keeps the valve of the Magnetic Unit open, and allows the gas to pass. If the flame is extinguished for some reason, the Thermocouple (or equivalent element) stops generating the electrical voltage, the Magnetic Unit closes the gas valve, and thus prevents the gas from coming out in the electrical appliance, which could cause explosions or poison people.

[0004] The Magnetic Unit consists of several elements, including the magnetic core and the magnetic armature. The magnetic core is the element excited by a coil receiving the electrical voltage generated by the thermocouple, or equivalent functional element; and attracts the magnetic armature, which is solidarily joined to the gas valve. There is also the Magnetic Unit valve, a component which is located in the gas valve, responsible for opening or closing the gas passage.

[0005] In the state of the art the magnetic armature and the magnetic core of a magnetic unit actuated by a thermocouple are manufactured from a material consisting of a Fe-Ni alloy. These Fe-Ni alloys have an excellent combination of those properties which are necessary to meet the demands of magnetic units, namely, magnetism, magnetic hysteresis, residual magnetism, coercivity and resistance to corrosion. However, currently used Fe-Ni alloys are very expensive due to the fact that the minimum amount of Ni which must be present in said alloys is of the order of 48%. In this sense it is known that amounts of Ni lower than 48% provide alloys with a much lower resistance to corrosion and are therefore unacceptable.

[0006] There is therefore the need in the state of the art to provide new alternative magnetic units which are effective and at the same time cheaper.

Description of the Invention

[0007] The inventors have discovered that it is possible to manufacture the magnetic armature, the magnetic core or both elements of a domestic use and manual opening magnetic unit actuated by a thermocouple from chromium-based stainless steel alloys and obtain an efficient and totally satisfactory functionality of said magnetic core. These alloys have an excellent combination of the magnetic properties which are desirable in an armature and a magnetic core so that they efficiently carry out their function within the magnetic unit. Furthermore, these alloys confer the necessary resistance to corrosion to the armature and the magnetic core throughout their useful life.

[0008] Therefore, in one aspect the invention relates to a new domestic use and manual opening magnetic unit actuated by thermocouple or an equivalent element in which the magnetic armature, the magnetic core, or both elements are made up of a chromium-based stainless steel alloy.

[0009] In the context of the present invention the chromium-based stainless steel alloys relate to those having a Cr content between 17.25 and 18.25%.

[0010] In a preferred embodiment the magnetic armature, the magnetic core, or both elements are made up of a chromium-based stainless steel alloy having an amount of nickel less than 1%. In another preferred embodiment the alloy has an amount of niobium comprised between 0% and 0.25%.

[0011] In another preferred embodiment the alloy has the following composition:

Fe	C	Cr	Ni	Nb	P	If	Mn	S	Mo
78.67	0.01	17.5	0.2	0.25	0.02	0.9	0.4	0.3	1.75

[0012] In another preferred embodiment the alloy has the following composition:

Fe	C	Cr	Ni	P	If	Mn	S	Mo
79.9 - 79.5	0.06	17.25-18.25	0.6	0.03	1-0.5	0.8	00.2-0.4	0.5

[0013] In another aspect the invention relates to the use of a chromium-based stainless steel alloy in the production of the magnetic armature, of the magnetic core or of both elements of a domestic use and manual opening magnetic unit actuated by thermocouple or an equivalent element. Said element can be any conventional element known to a person skilled in the art.

[0014] In a preferred embodiment an alloy having an amount of nickel less than 1% is used. In another preferred embodiment the alloy has an amount of niobium comprised between 0% and 0.25%.

[0015] In another preferred embodiment the alloy called Alloy 1 is used, the composition of which is the following:

Fe	C	Cr	Ni	Nb	P	If	Mn	S	Mo
78.67	0.01	17.5	0.2	0.25	0.02	0.9	0.4	0.3	1.75

[0016] In another preferred embodiment an alloy (Alloy 2) having the following composition is used:

Fe	C	Cr	Ni	P	If	Mn	S	Mo
79.9 - 79.5	0.06	17.25-18.25	0.6	0.03	1-0.5	0.8	00.2-0.4	0.5

[0017] These alloys have the properties which are indicated in the following Table:

	Permeability	Coercivity A/m	Saturation, Gauss
Alloy 1	1,500	200	15,000
Alloy 2	2,500	130	2,500 a 8,000

[0018] Alloy 1 is stabilized with a niobium content of 0.25%, which provides it with a greater resistance against oxidation. Its permeability is lower than that of Alloy 2, and its coercivity is somewhat higher. Its saturation is also higher, and this parameter is very suitable for its use according to the present invention.

[0019] Alloy 2 has a lower resistance against oxidation than Alloy 1, which is something to be considered when selecting it for its use according to the present invention. The use of one alloy or another can depend considerably on the characteristics of the gas which is going to be used in the electrical appliance in which the Magnetic Unit is placed. Both are commercially available.

[0020] Alloy 1 shows a better resistance against corrosion and has magnetic characteristics similar to Alloy 2, it is therefore the preferred alloy for its use in corrosive media. Its resistance against the corrosion has been analyzed with standard moisture and salt spray tests in environments with increasing temperatures and in much severer conditions than those that the domestic use magnetic groups of the invention must withstand; both tests shows the same conclusions.

[0021] On the other hand, the use of intense magnetic fields in the manufacturing process, both for handling the materials and in their inspection, or in the elimination of voltages, can leave a permanent magnetism therein which is not suitable for the function to be performed, it is for this reason that the use thereof has to be limited as much as possible. The presence of a residual magnetism can furthermore attract small metal particles which could affect the good performance of the assembly.

[0022] Working in cold conditions makes the coercivity of the materials rise.

[0023] It is therefore advisable to thermally treat the materials, apply a treatment eliminating voltages and preventing the possible presence of magnetism therein, demagnetizing them. The temperature to be applied to the chromium-based alloys is about 850ºC. Highly pure and well annealed alloys are the ones having an optimal magnetic performance.

[0024] The better resistance against corrosion is obtained without passivation, when the surface of the parts are free of chips or other foreign particles; if steel tools are used in the core and/or armature manufacturing processes, the application of a final passivation process eliminating the contaminating particles coming from the manufacturing process is recommended.

Claims

1. Use of a chromium-based stainless steel alloy as a raw material for manufacturing the magnetic core, the magnetic armature or both of a domestic use and manual opening magnetic unit actuated by thermocouple or an equivalent element.

2. Use according to claim 1, wherein the chromium-based stainless steel alloy has an amount of nickel less than 1%.

3. Use according to claim 1 or 2, wherein the chromium-based stainless steel alloy has an amount of niobium comprised between 0% and 0.25%.

4. Use according to claim 1 or 2, wherein the alloy has the following composition:

Fe	C	Cr	Ni	Nb	P	If	Mn	S	Mo
78.67	0.01	17.5	0.2	0.25	0.02	0.9	0.4	0.3	1.75

5. Use according to claim 1 or 2, wherein the alloy has the following composition:

Fe	C	Cr	Ni	P	If	Mn	S	Mo
79.9 - 79.5	0.06	17.25 - 18.25	0.6	0.03	1-0.5	0.8	00.2- 0.4	0.5

6. Domestic use and manual opening magnetic unit actuated by thermocouple or an equivalent element wherein the magnetic armature, the magnetic core, or both elements are made up of a chromium-based stainless steel alloy.

7. Magnetic unit according to claim 6, wherein the chromium-based stainless steel alloy has an amount of nickel less than 1%.

8. Magnetic unit according to claim 6 or 7, wherein the alloy has an amount of niobium comprised between 0% and 0.25%.

9. Magnetic unit according to claim 6, wherein the alloy has the following composition:

Fe	C	Cr	Ni	Nb	P	If	Mn	S	Mo
78.67	0.01	17.5	0.2	0.25	0.02	0.9	0.4	0.3	1.75

10. Magnetic unit according to claim 6, wherein the alloy has the following composition:

Fe	C	Cr	Ni	P	If	Mn	S	Mo
79.9 - 79.5	0.06	17.25-18.25	0.6	0.03	1-0.5	0.8	00.2-0.4	0.5