GB1564476A - Electric furances - Google Patents
Electric furances Download PDFInfo
- Publication number
- GB1564476A GB1564476A GB5157577A GB5157577A GB1564476A GB 1564476 A GB1564476 A GB 1564476A GB 5157577 A GB5157577 A GB 5157577A GB 5157577 A GB5157577 A GB 5157577A GB 1564476 A GB1564476 A GB 1564476A
- Authority
- GB
- United Kingdom
- Prior art keywords
- furnace
- cavity
- resistance
- furnace according
- ring
- 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
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 21
- 229910002804 graphite Inorganic materials 0.000 claims description 21
- 239000010439 graphite Substances 0.000 claims description 21
- 238000010438 heat treatment Methods 0.000 claims description 16
- 239000011819 refractory material Substances 0.000 claims description 12
- 238000007789 sealing Methods 0.000 claims description 12
- 239000000463 material Substances 0.000 claims description 9
- 239000007787 solid Substances 0.000 claims description 9
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 7
- 230000000737 periodic effect Effects 0.000 claims description 6
- 239000004020 conductor Substances 0.000 claims description 5
- 238000009529 body temperature measurement Methods 0.000 claims description 2
- 238000009826 distribution Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 230000020169 heat generation Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000009987 spinning Methods 0.000 description 2
- 238000004857 zone melting Methods 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 229910052702 rhenium Inorganic materials 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
- C03B37/025—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor from reheated softened tubes, rods, fibres or filaments, e.g. drawing fibres from preforms
- C03B37/029—Furnaces therefor
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
- H05B3/145—Carbon only, e.g. carbon black, graphite
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/62—Heating elements specially adapted for furnaces
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2205/00—Fibre drawing or extruding details
- C03B2205/60—Optical fibre draw furnaces
- C03B2205/62—Heating means for drawing
- C03B2205/63—Ohmic resistance heaters, e.g. carbon or graphite resistance heaters
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Resistance Heating (AREA)
- Furnace Details (AREA)
Description
(54) IMPROVEMENTS IN OR RELATING TO ELECTRIC FURNACES
(71) We, CSELT--CENTRO STUDI E
LABORATORI TELECOMUNICAZIONI, S.p.A., of
Via Guglielmo Reiss Romoli, 274, 10148
Torino, Italy, a joint stock company organized under the laws of Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to electric furnaces for attaining medium-high temperatures, and more particularly it refers to a resistance muffle furnace, in which the heating element is formed of powdered graphite.
Resistance heated electric furnaces having a solid-graphite or metallic resistance element have previously been proposed in order to attain medium-high temperatures, that is temperatures in the range from lOOO0C to 2000 C. Yet both these kinds of furnaces present a number of disadvantages.
In particular, in solid graphite furnaces, the heating element must be suitably shaped in order to obtain an electric resistance as high as possible, so that high powers may be reached by means of electric currents as low as possible.
For this purpose the useful surface of the heating element is necessarily increased and this gives rise to a number of disadvantages which make this kind of furnace inadequate for certain special applications recently introduced, such as the spinning of vitreous fibres, zone melting and the production of wintered materials.
Among these disadvantages, structural brittleness is worth mentioning, which causes a corresponding unreliability of operation and a rather high thermal capacity which does not give the furnace the speed of response required by fine temperature servocontrols.
Moreover, even by suitably shaping the heating element, it is not possible to increase the electric resistance beyond a given limit, which is why rather high currents are required. This makes it necessary, in turn, to employ large-sized supply conductors with subsequent increased size of the furnace, and difficult operation when the furnace is intended for uses at different locations.
Metallic resistance element furnaces present disadvantages similar to and even more serious than solid graphite furnaces, owing to the lower resistivity of the material employed (generally Nb, Re, Mo, W). Moreover, they are very expensive, owing to the high cost of the materials employed, so that it is necessary to recover damaged resistance elements and utilize them again after their reconstruction.
Furnaces having a solid graphite resistance element as well as those having a metallic resistance element also have the disadvantage of requiring, according to the temperature, a reducing or inert atmosphere, in order to avoid oxidation of the heating element, and of having a temperature gradient along the furnace axis which is very difficult to modify, so they are scarcely versatile.
An object of the present invention is to obviate or mitigate the aforesaid disadvantages.
According to the present invention, there is provided an electrical resistance heated furnace comprising a pair of tubular coaxial elements made of refractory material defining an annular cavity therebetween, a resistance heating element of compacted powdered graphite in said cavity; electrically conductive sealing means closing the ends of the cavity and contacting the heating element so as to be capable of transmitting electric current to the resistance heating element; metallized zones on said sealing means welded to metallized zones on the adjacent walls of said refractory elements in such a manner as to render said cavity water-proof; and conductor means for connecting the metallized zones of the tubular elements to a supply of electric current.
An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing in which: Fig. 1 is an axial section of a furnace according to the invention;
Fig. 2 is a section along the line II--II of
Fig. 1.
In Fig. 1, two tubular elements 1 and 2 made of refractory material, for instance two hollow and coaxial cylinders form respectively the outer element and the internal element of a muffle furnace. Cylinder 1 has no end wall and cylinder 2 is deprived at least of one and possibly of both end walls, if required by the applications of the furnace. In the embodiment of the invention the cylinder 2 has no end walls.
Metallized rings la, 2a and ib, 2b on said cylinders allow the furnace to be connected, for instance thrcugh members 3 which are connected to but project from the rings in, ib to a source of electrical supply (not shown in the drawing).
Between the two cylinders 1 and 2 there is defined an annular cavity 4 which houses a resistance heating element 5 of compacted powdered graphite.
Compacted powdered graphite has an electric resistivity of some orders of magnitude higher than that of solid graphite (about 1000 times higher). It is therefore clear that by low currents, high powers and consequently a considerable heat-generation can be obtained.
Thus the above-mentioned disadvantages arising from the use of high currents are avoided.
Two solid graphite rings 6 which act as end seals for the cavity 4, each comprise a body 6a of a thickness basically identical to the width of cavity 4, and an extension 6b of reduced thickness. The rings 6 also act as electrical conductors between the members 3 and the body of powdered graphite 5.
To this end, the side walls of each body 6a are metallized, as at 7, so as to provide for electrical contact with the metallized rings la, 2a; lb, 2b of cylinders 1, 2, the metallized zones 7 being soldered to said rings by means of braze welding through a binder melting at low temperature (alloy of Sn or
Ag) so as to make cavity 4, containing the powdered graphite, water-proof.
Extensions 6b, can be shaped either as shown in Fig. 1 of the drawing, or they can be of triangular cross-section with the base of the triangle integral with body 6a of the rings. The extensions 6b provide an increase in the contact surface between rings 6 and the resistance element 5 to assist current flow.
A ring 8 of refractory material, formed of the same material as cylinders 1 and 2 is located in the cavity, when it is necessary to obtain particular temperature distributions inside the furnace. To this end, ring 8 can have a uniform thickness or present one or more zones having a greater thickness; for instance it can have the shape illustrated in Fig. 1 of the drawing. Ring 8 can be kept in its place by the powdered graphite resistance element 5, or it can be secured to the external cylinder 1.
Materials particularly suitable for use as refractory materials for ring 8 and cylinders 1 and 2, are oxides of elements in Group
III of the Periodic Table and more particularly Al2Oa, or oxides of elements of Group
IV of the Periodic table as for instance
ZrO2 duly stabilized by Mg or Ca.
The method of operation of the electric furnace according to the invention is identical to that of conventional resistance heated electric furnaces i.e. the electric current flowing through resistance element 4, heats it proportionally to the square of its intensity, until it reaches incandescence.
In the absence of refractory ring 8, the resistance element will have a uniform thickness substantially over the whole length of the furnace, except adjacent the extensions 6b of rings 6, and therefore a uniform temperature distribution will be present over substantially the whole length of the furnace.
If, on the contrary, a higher temperature is required in some zones of the furnace, it is enough to equip the same with a ring 8.
In this case the resistance element will present at least a zone Sn of a thickness reduced by the thickness of the ring itself, where higher resistance and thus a greater heat generation will be obtained.
By suitably choosing the shape of section of ring 8, particular temperature distributions along the furnace axis can be obtained as may be necessary for special uses of the furnace.
Owing to the simplicity of the heating element, it is clear that the furnace is easy to construct and maintain where an entire or partial replacement of the powdered graphite electrode is necessary. Also the securing of the refractory ring 8, if present does not present any difficulty.
The uses of the described furnaces are many. The following are examples: - high temperature spinning of silica glass fibres (for instance optical fibres) as well as of low-melting glasses;
- zone melting for crystal purification, a typical operation of semiconductor manufacture;
- production of special metals ("hard metals", sintered metals, and the like); annealing operations;
- attainment of medium-high temperatures, with possible sudden variations for laboratory reasons;
- generation of gauged thermal shocks for tests on given materials or for the tempering of special materials, at given temperatures and with given temperature gradients;
- utilization as a "black body" for irradiation and temperature measurements.
The furnace of the present invention makes use of a resistance element of powdered graphite which has an electrical resistivity about one thousand times higher than solid graphite and therefore allows high electrical resistances to be achieved without the use of complicated shapes of resistance element. Consequently, the furnace is easy to construct, inexpensive and robust. The temperature gradient along the length of the furnace is easily modified and finally it does not require an inert atmosphere.
WHAT WE CLAIM IS:- I. An electric resistance heated furnace comprising a pair of tubular coaxial elements made of refractory material defining an annular cavity therebetween, a resistance heating element of compacted powdered graphite in said cavity; electrically conductive sealing means closing the ends of the cavity and contacting the heating element so as to be capable of transmitting electric current to the resistance heating element; metallized zones on said sealing means welded to metallized zones on the adjacent walls of said refractory elements in such a manner as to render said cavity water-proof; and conductor means for connecting the metallized zones of the tubular elements to a supply of electric current.
2. A furnace according to claim 1, in which the sealing means comprises a pair of sealing rings, each having a body of a thickness substantially corresponding to the width of the cavity, and an extension of reduced thickness which is housed in the resistance element in contact therewith.
3. A furnace according to claim 1 or 2, in which the sealing means is of solid graphite.
4. A furnace according to any of claims 1 to 3, in which said cavity houses a ring made of refractory material, to define at least a zone of reduced width inside the cavity, whereby one zone at least of the resistance element has a reduced thickness, and therefore higher electrical resistance.
5. A furnace according to claim 4, in which said refractory ring is made of the same material as the tubular elements.
6. A furnace according to any of claims ] to 5, in which the refractory material from which said tubular elements and/or said ring are formed is an oxide of a metal of
Group III of the Periodic Table.
7. A furnace according to any of claims 1 to 5 in which the refractory material from which said tubular elements and/ or said ring are formed is an oxide of a metal of Group IV of the Periodic Table.
8. An electric resistance furnace, substantially as hereinbefore described with reference to the accompanying drawing.
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (8)
- **WARNING** start of CLMS field may overlap end of DESC **.- utilization as a "black body" for irradiation and temperature measurements.The furnace of the present invention makes use of a resistance element of powdered graphite which has an electrical resistivity about one thousand times higher than solid graphite and therefore allows high electrical resistances to be achieved without the use of complicated shapes of resistance element. Consequently, the furnace is easy to construct, inexpensive and robust. The temperature gradient along the length of the furnace is easily modified and finally it does not require an inert atmosphere.WHAT WE CLAIM IS:- I. An electric resistance heated furnace comprising a pair of tubular coaxial elements made of refractory material defining an annular cavity therebetween, a resistance heating element of compacted powdered graphite in said cavity; electrically conductive sealing means closing the ends of the cavity and contacting the heating element so as to be capable of transmitting electric current to the resistance heating element; metallized zones on said sealing means welded to metallized zones on the adjacent walls of said refractory elements in such a manner as to render said cavity water-proof; and conductor means for connecting the metallized zones of the tubular elements to a supply of electric current.
- 2. A furnace according to claim 1, in which the sealing means comprises a pair of sealing rings, each having a body of a thickness substantially corresponding to the width of the cavity, and an extension of reduced thickness which is housed in the resistance element in contact therewith.
- 3. A furnace according to claim 1 or 2, in which the sealing means is of solid graphite.
- 4. A furnace according to any of claims 1 to 3, in which said cavity houses a ring made of refractory material, to define at least a zone of reduced width inside the cavity, whereby one zone at least of the resistance element has a reduced thickness, and therefore higher electrical resistance.
- 5. A furnace according to claim 4, in which said refractory ring is made of the same material as the tubular elements.
- 6. A furnace according to any of claims ] to 5, in which the refractory material from which said tubular elements and/or said ring are formed is an oxide of a metal of Group III of the Periodic Table.
- 7. A furnace according to any of claims 1 to 5 in which the refractory material from which said tubular elements and/ or said ring are formed is an oxide of a metal of Group IV of the Periodic Table.
- 8. An electric resistance furnace, substantially as hereinbefore described with reference to the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT7000676A IT1072241B (en) | 1976-12-17 | 1976-12-17 | ITFORNACE ELECTRIC MOLD RESISTANT LA WITH POWDER GRAPHITE RESISTIVE ELEMENT |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1564476A true GB1564476A (en) | 1980-04-10 |
Family
ID=11313282
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB5157577A Expired GB1564476A (en) | 1976-12-17 | 1977-12-12 | Electric furances |
Country Status (3)
| Country | Link |
|---|---|
| FR (1) | FR2374813A1 (en) |
| GB (1) | GB1564476A (en) |
| IT (1) | IT1072241B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2214768A (en) * | 1988-01-27 | 1989-09-06 | Miroslav Pesta | Heating device for generating very high temperatures |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2910151A1 (en) * | 1979-03-15 | 1980-10-02 | Didier Werke Ag | ELECTRIC HEATING CONDUCTOR, YOUR PREPARATION, YOUR USE IN A HEATABLE WEARING PART AND A METHOD FOR PRODUCING SUCH WEARING PARTS WITH THE HEATING CONDUCTOR |
| US9345573B2 (en) | 2012-05-30 | 2016-05-24 | Neovasc Tiara Inc. | Methods and apparatus for loading a prosthesis onto a delivery system |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR326357A (en) * | 1902-11-15 | 1903-05-23 | Rivers Edward George | Improvements to electric heaters or radiators |
| FR343094A (en) * | 1904-05-13 | 1904-09-24 | August Voelker | Electric oven device |
| US1499317A (en) * | 1921-01-17 | 1924-06-24 | Beyer Robert | Electric furnace |
| DE388877C (en) * | 1922-02-17 | 1924-01-22 | Seibert Heinrich | Electric annealing furnace with grainy resistance mass |
| CH128314A (en) * | 1927-05-01 | 1928-10-16 | Truempler Dr Gottfried | Electric resistance furnace. |
| FR871769A (en) * | 1940-12-28 | 1942-05-09 | M E C L Materiel Electr De Con | Resistance for electric heating |
-
1976
- 1976-12-17 IT IT7000676A patent/IT1072241B/en active
-
1977
- 1977-12-12 GB GB5157577A patent/GB1564476A/en not_active Expired
- 1977-12-14 FR FR7737620A patent/FR2374813A1/en active Granted
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2214768A (en) * | 1988-01-27 | 1989-09-06 | Miroslav Pesta | Heating device for generating very high temperatures |
| GB2214768B (en) * | 1988-01-27 | 1991-11-27 | Miroslav Pesta | Heating device for generating very high temperatures |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2374813A1 (en) | 1978-07-13 |
| FR2374813B1 (en) | 1980-08-22 |
| IT1072241B (en) | 1985-04-10 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3395241A (en) | Graphite heating element for electric resistance furnace | |
| KR910000069B1 (en) | Electrically conductive sintered ceramics and ceramic heaters | |
| US2215587A (en) | Rodlike heating element | |
| GB1561794A (en) | Refractory electrical resistance and terminal | |
| GB595060A (en) | Improvements in electrical heating elements | |
| JPS5920605B2 (en) | hearth electrode assembly | |
| US3984615A (en) | Electrical resistance furnace heater | |
| GB1564476A (en) | Electric furances | |
| US3336431A (en) | Electric furnace | |
| US4080510A (en) | Silicon carbide heater | |
| US3984616A (en) | High temperature furnace heater | |
| US3368019A (en) | Non-consumable electrode | |
| Davenport et al. | Design and performance of electric furnaces with oxide resistors | |
| US3373240A (en) | Method of operating an electric arc furnace | |
| US2397445A (en) | Electric resistance element and method of operating the same | |
| US2140228A (en) | Electrically heated furnace | |
| US3371142A (en) | Resistance melting furnace | |
| US3764718A (en) | Vacuum furnace with an electric heater assembly | |
| US3735008A (en) | Electric furnace | |
| US4672627A (en) | Electrode heater | |
| US3530223A (en) | Electrode apparatus for use in an arc electrode furnace and magnetic field coils for moving and focusing the arcs therefrom | |
| DE625847C (en) | Electric heating resistor for high temperatures | |
| JP4563022B2 (en) | Thin high-temperature electric heating furnace composed of plate-like heating elements | |
| US1467044A (en) | Electric furnace | |
| SU873304A1 (en) | Unsoldering furnace |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |