CA2212342C - Tubular heating element with insulating core - Google Patents
Tubular heating element with insulating core Download PDFInfo
- Publication number
- CA2212342C CA2212342C CA002212342A CA2212342A CA2212342C CA 2212342 C CA2212342 C CA 2212342C CA 002212342 A CA002212342 A CA 002212342A CA 2212342 A CA2212342 A CA 2212342A CA 2212342 C CA2212342 C CA 2212342C
- Authority
- CA
- Canada
- Prior art keywords
- metal tube
- heating element
- tubular heating
- preformed
- tube
- 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 - Fee Related
Links
Classifications
-
- 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
- H05B3/40—Heating elements having the shape of rods or tubes
-
- 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—Heater elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heater 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
-
- 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
- H05B3/40—Heating elements having the shape of rods or tubes
- H05B3/42—Heating elements having the shape of rods or tubes non-flexible
- H05B3/48—Heating elements having the shape of rods or tubes non-flexible heating conductor embedded in insulating material
Landscapes
- Resistance Heating (AREA)
Abstract
A tubular heating element (10) having a metal tube (12) filled with a ceramic material (14). The metal tube has a near zero or slightly positive temperature coefficient of resistance. In an alternative embodiment, a wire (16) is coaxially supported within the metal tube (12) by the ceramic material (14).
This wire may be used to stiffen the tubular heating element (10) or may be used as an electrical conductor.
This wire may be used to stiffen the tubular heating element (10) or may be used as an electrical conductor.
Description
TUBULAR HEATING ELEMENT
WITH INSULATING CORE
Technical Field The invention is related to the field of electric heating elements and in particular to a tubular electric heating element with an insulating core.
Background Art Heating elements consisting of a resistive heating wire enclosed is a metal sheath are known in the art. The sheathed resistance heater taught by Naruo et al in U.S. Patent 4,506,251 is typical of such a heating element. This sheathed resistance heater consists of a heating wire coaxially supported in a metal sheath by an electrically insulating powder. Similar heating ele-ments are taught by Neemanns et al in U.S. Patent 4,080,726, Neidhardt et al in U.S. Patent 3,621,204 and Read in U.S. Patent 1,127,281.
The problem with these electric heater ele-ments is that the resistivities of the metal alloys which are resistant to oxidation and corrosion at elevated temperatures are relatively low. Therefore, to achieve the desired resistance, either the diameter of the heater wire must be relatively small or considerable lengths are required. Reducing the diameter of the heater wire makes it relatively sensitive to oxidation or corrosion and therefore subj ect to failure . Reducing the diameter of the wire heater also increases the surface loading required to achieve the desired radiated heat energy.
Alternatively, increasing the length of the wire to obtain the desired electrical resistance increases the total quantity of the heater wire required which, in turn, increases the cost of the elE~ctric heater element. Increasing the length of the wire often results in excessive bulk which may cause packaging problems.
What is needed is a heater element in which the resistivity of the metal heater is effectively increased, permitting shorter lengths and lower surface loading.
Summary of the Invention The invention is a heater element consisting of a metal tube filled with an insulating ceramic material. The diameter of the metal tube can be selected to produce the desired surface loading while the cross-sectional area of the metal tube and its length can be selected to produce a desired resistance and a desired surface load. In a second embodiment, a wire element may be coaxially supported in the metal by the ceramic powder to increase the structural rigidity of the heater element.
The invention may be summarized according to one broad aspect as a tubular heating element comprising: a preformed metal tube having a predetermined temperature coefficient of resistance for generating heat when an electrical current passes through the preformed metal tube; a ceramic material disposed in and filling said preformed tube; and a single, continuous linear -2a-metal wire coaxial:Ly supported in said metal tube along the entire length of s<~id metal tube by said ceramic material.
Accordin<~ to another broad aspect the invention provides a tubular heating element comprising: a performed metal tube having a predcstermined temperature coefficient of resistance for gencsrating heat when an electrical current passes through the preforrned metal tube; a single, continuous linear wire coaxially disposed in said preformed metal tube along the entire length of the tube; and a ceramic material filling said preformed metal tube and mechanically supporting said wire coaxially within said preformed metal tube.
According to yet another aspect the invention provides a tubular heating element comprising: a preformed inner metal tube; an outer metal layer overlaying said inner metal tube along its entire length, at least one of said inner metal tube and said outer metal layer having a predetermined temperature coefficient of resistance; and a ceramic material filling said inner metal tube.
One advantage of the tubular heating element is that its diameter can be selected to produce a desired surface loading.
WITH INSULATING CORE
Technical Field The invention is related to the field of electric heating elements and in particular to a tubular electric heating element with an insulating core.
Background Art Heating elements consisting of a resistive heating wire enclosed is a metal sheath are known in the art. The sheathed resistance heater taught by Naruo et al in U.S. Patent 4,506,251 is typical of such a heating element. This sheathed resistance heater consists of a heating wire coaxially supported in a metal sheath by an electrically insulating powder. Similar heating ele-ments are taught by Neemanns et al in U.S. Patent 4,080,726, Neidhardt et al in U.S. Patent 3,621,204 and Read in U.S. Patent 1,127,281.
The problem with these electric heater ele-ments is that the resistivities of the metal alloys which are resistant to oxidation and corrosion at elevated temperatures are relatively low. Therefore, to achieve the desired resistance, either the diameter of the heater wire must be relatively small or considerable lengths are required. Reducing the diameter of the heater wire makes it relatively sensitive to oxidation or corrosion and therefore subj ect to failure . Reducing the diameter of the wire heater also increases the surface loading required to achieve the desired radiated heat energy.
Alternatively, increasing the length of the wire to obtain the desired electrical resistance increases the total quantity of the heater wire required which, in turn, increases the cost of the elE~ctric heater element. Increasing the length of the wire often results in excessive bulk which may cause packaging problems.
What is needed is a heater element in which the resistivity of the metal heater is effectively increased, permitting shorter lengths and lower surface loading.
Summary of the Invention The invention is a heater element consisting of a metal tube filled with an insulating ceramic material. The diameter of the metal tube can be selected to produce the desired surface loading while the cross-sectional area of the metal tube and its length can be selected to produce a desired resistance and a desired surface load. In a second embodiment, a wire element may be coaxially supported in the metal by the ceramic powder to increase the structural rigidity of the heater element.
The invention may be summarized according to one broad aspect as a tubular heating element comprising: a preformed metal tube having a predetermined temperature coefficient of resistance for generating heat when an electrical current passes through the preformed metal tube; a ceramic material disposed in and filling said preformed tube; and a single, continuous linear -2a-metal wire coaxial:Ly supported in said metal tube along the entire length of s<~id metal tube by said ceramic material.
Accordin<~ to another broad aspect the invention provides a tubular heating element comprising: a performed metal tube having a predcstermined temperature coefficient of resistance for gencsrating heat when an electrical current passes through the preforrned metal tube; a single, continuous linear wire coaxially disposed in said preformed metal tube along the entire length of the tube; and a ceramic material filling said preformed metal tube and mechanically supporting said wire coaxially within said preformed metal tube.
According to yet another aspect the invention provides a tubular heating element comprising: a preformed inner metal tube; an outer metal layer overlaying said inner metal tube along its entire length, at least one of said inner metal tube and said outer metal layer having a predetermined temperature coefficient of resistance; and a ceramic material filling said inner metal tube.
One advantage of the tubular heating element is that its diameter can be selected to produce a desired surface loading.
Another advantage of the tubular heater ' element is that the cross-sectional area of the metal tube may be selected to produce a desired linear resis-' tivity.
Still another advantage of the tubular heater element is that a coaxial wire may be used to improve the rigidity of the tubular heater element.
Further, another advantage of a coiled tubular heater element is that it is structurally more rigid than a coiled solid wire.
Yet another advantage is that a hardenable wire may be coaxially supported within the metal heater tube to stiffen the heater element after forming by heat treatment.
These and other advantages of the tubular heater element will become more apparent from a reading of the specification in conjunction with the drawings.
Brief Description Of 1'he Drawings FIGURE 1 is a perspective view of a first embodiment of the tubular heating element;
FIGURE 2 is a perspective view of a second embodiment of the tubular heating element;
FIGURE 3 is a perspective view of a third embodiment of the tubular heating element;
WO 96!26626 PCT/US95/01876 FIGURE 4 shows a first circuit arrangement of the tubular heating element of Figure 1 with a source of electrical power;
FIGURE 5 shows a second circuit arrangement of the tubular heating element of Figures 2 or 3 with a source of electrical power;
FIGURE 6 shows a tubular heating element wound around a ceramic tube; and FIGURE 7 shows atubular heating element in a self standing coiled configuration.
Detailed Description of the Invention The details of a first embodiment of the tubular heating element are shown in Figure 1. The tubular heating element 10 has a metal tube 12 filled with an insulating mineral powder 14 such as magnesium oxide. Alternatively, the metal tube 12 may be filled with a PTC (positive temperature coefficient) conductive ceramic powder in place of the insulating mineral powder. The metal tube 12 is made from a metal alloy such as Chrome!-C or any other alloy having a near zero or a slightly positive temperature coefficient of resis-tance. Constantan and various nickel-chromium alloys meet these criteria. The outside diameter (OD) and inside diameter (ID) of the metal tube 12 are selected to produce desired linear electrical resistivity. The heating element may be made using any conventional method used to fabricate metal tubes. In the preferred embodiment, the metal tube 12 is a ceramic filled welded seam tube fabricated using known welded seam tube WO 96/26626 PCTlUS95l01876 manufacturing techniques such as taught by Lewis in U. S .
Patent 4,269,639. After fabrication, the heating element is drawn to the desired outside diameter. The insulating material 14 is used to prevent the metal tube 12 from collapsing while it is being drawn down to the desired diameter.
The advantages of the tubular heating element may best be described by way of an example of a commercial application such as a heating element for an 10 electric clothes dryer. Conventionally, this heating element consists of a solid 16-gauge (.0508 inch dia-meter) Chromel-C solid wire having a 10 ohm cold resis-tance and an 11 ohm resistance at its operating tempera-ture. The cold linear resistance of the Chromel-C wire is approximately 0.26 ohms per ft. , therefore a Chromel-C wire approximately 38.5 feet long is required to produce the desired resistance. This solid wire heating element has a weight of approximately 0.28 pounds. In operation, approximately 240 volts are applied across the solid wire heating element, producing 5,200 watts of . heat energy. The surface loading, i.e., heat radiated per square inch of surface area, of this solid wire heating element is 70.5 watts/inch2.
This same surface loading may be achieved with a tubular heating element 10 having a Chromel-C metal tube whose cross-sectional area is approximately 220 of the total cross-sectional area of metal tube 12. The metal tube 12 for example may have 0.084 inch O.D. and a 0.074 inch I.D. The linear resistivity of this metal tube is approximately 0.427 ohms per foot; therefore only 23.5 feet are required to produce the desired 10 ohm total resistance. The weight of this tubular heating element a.s approximately 0.1 pounds which represents a 64 o reduction in the amount of the metal required to make the tubular heating element.
In a second example, the cross-sectional area of the metal tube sheath is 40% of the total cross-sectional area of the tubular heating element. For example, the metal tube 12 may have a 0.067 inch OD and a 0.052 inch ID. The linear resistance of this metal tube is approximately 0.378 ohms and requires a length of 27 feet to produce the desired 10 ohm resistance.
The weight of this tubular heating element is approxi-mately 0.14 pounds, which is approximately one-half (1/2) the weight of the equivalent heating element made from the 16-gauge solid wire.
Both embodiments of the tubular heating element described above would operate at the same temperature as the solid wire_ heating element, but because of their larger diameter would last longer.
In an alternate example of the advantages of the tubular heating element 10, consider a tubular heating element 10 whose metal tube 12 has the same linear resistance as the solid wire heating element described above, has the same length, and has a cross-sectional area which is 22 0 of the total cross-sectional area of the tubular heating element 10. In this embodi-ment, the metal tube 12 would have a 0.109 inch OD and a 0.096 inch ID. The weight of the metal tube is the same as the weight of the solid Chromel-C wire, however, its surface load would be reduced to approximately 33 watts/inch2. This lower surface load would significantly _7_ reduce the surface temperature of the tubular heating element 10 and substantially increase its life.
A second embodiment of the tubular heating element 10 is shown in Figure 2. In this embodiment, a wire 16 is coaxially supported within the metal tube 12 and is electrically insulated therefrom by the ceramic powder 14. The wire 16 may be a single solid wire, a plurality of wires, or a braided wire. This wire 16 may perform a variety of functions as discussed below. The wire 16 may be used to provide rigidity to the tubular heating element 10 during the forming process. The wire 16 may provide rigidity to the tubular heating element 10 at room and elevated temperatures. The wire 16 also may be made from an hardenable metal and used to stiffen the finished tubular heating element 10, after being formed, by heat treating. Also, the wire 16 may be made from a metal such as copper or any other metal or alloy having a low electrical resistivity or be made from a material used to provide a temperature control to avoid catastrophic overheating as shall be explained relative to Figure 5.
As shown in Figure 3, the metal tube 12 may be overlayed with one or more layers of different metals or alloys to provide a performance superior to the perfor mance attainable from any single alloy alone. In the embodiment shown in Figure 3, the metal tube 12 consists of an inner tube 18 having an outer layer 20 disposed thereon. It is recognized that additional layers may be used as desired.
In a first example, an alloy having good hot strength may be selected for the inner tube 18 and an WO 96/26626 PCT/US95l01876 _g_ alloy having good oxidation or corrosion resistance may be selected for the outer layer 20. The outer layer 20 will protect the inner tube 18 from oxidation and corrosion. Alternately, the outer layer 20 may be made from a premium heat resistant alloy and the inner tube may be made from a less expensive alloy.
The tubular heating element shown in Figure 3 may have a solid coaxial wire 16 as shown and described relative to Figure 2 or the solid coaxial wire may be omitted, as shown in Figure 1.
Referring now to Figure 4, a source of elec-trical power, illustrated as battery 22, may be electri-cally connected to the opposite ends of the metal tube 12 of the tubular heating element 10. It is recognized that although the source of electrical power 22 is illustrated as a battery, the source of electrical power may be an alternating current generator or electrical power received from conventional commercial or household alternating current electrical power outlets.
In Figure 5, one output terminal of an alter-nating source of electrical power 24 is electrically connected to one end of the metal tube 12 and the other terminal of the source of electrical power 24 is con-nected to one end of the coaxial wire 16. The opposite end of the coaxial wire 16 is connected to the opposite end of the metal tube 12 completing the circuit between the terminals of the source of electrical power 24.
With this arrangement, the coaxial wire 16 may be made from an alloy which will melt when the current through the metal tube approaches a value preselected to prevent a catastrophic failure of the tubular metal heater 10.
Alternatively, the wire 15 may be made from an alloy having a positive temperature coefficient of resistance such that when the current through the metal tube 12 exceeds a predetermined value, the resistivity of the wire 16 rapidly increases, thereby maintaining the current flow through the metal tube 12 at a value less than a current sufficient to produce catastrophic failure of the tubular heating element 10.
The tubular heating element 10 may be used in the same manner as a conventional solid wire heating element. As shown in Figure 6, the tubular heating element may be wound around a ceramic cylinder 26, or may be coiled or may be spiral wound as shown in Figure 7 to form a free standing heater.
The disclosed tubular heating element has many operational and economic advantages over solid wire heating elements:
~ The tubular heating element can have a higher linear resistance than comparable solid wire heating elements having approximately the same diameter.
~ The tubular heating element can reduce the quantity of a premium resistive alloy required to make a heating element having the desired resistance and surface load.
~ The tubular heating element can reduce surface loading on the heater element having the desired resistance.
~ The tubular heating element can operate at lower surface temperatures, thereby increasing its life.
It is recognized that while various embodi-ments of the invention have been shown in the drawings ' and discussed in the specification, those skilled in the art may make changes and/or improvements to the tubular heating element as set forth in the appended claims.
Still another advantage of the tubular heater element is that a coaxial wire may be used to improve the rigidity of the tubular heater element.
Further, another advantage of a coiled tubular heater element is that it is structurally more rigid than a coiled solid wire.
Yet another advantage is that a hardenable wire may be coaxially supported within the metal heater tube to stiffen the heater element after forming by heat treatment.
These and other advantages of the tubular heater element will become more apparent from a reading of the specification in conjunction with the drawings.
Brief Description Of 1'he Drawings FIGURE 1 is a perspective view of a first embodiment of the tubular heating element;
FIGURE 2 is a perspective view of a second embodiment of the tubular heating element;
FIGURE 3 is a perspective view of a third embodiment of the tubular heating element;
WO 96!26626 PCT/US95/01876 FIGURE 4 shows a first circuit arrangement of the tubular heating element of Figure 1 with a source of electrical power;
FIGURE 5 shows a second circuit arrangement of the tubular heating element of Figures 2 or 3 with a source of electrical power;
FIGURE 6 shows a tubular heating element wound around a ceramic tube; and FIGURE 7 shows atubular heating element in a self standing coiled configuration.
Detailed Description of the Invention The details of a first embodiment of the tubular heating element are shown in Figure 1. The tubular heating element 10 has a metal tube 12 filled with an insulating mineral powder 14 such as magnesium oxide. Alternatively, the metal tube 12 may be filled with a PTC (positive temperature coefficient) conductive ceramic powder in place of the insulating mineral powder. The metal tube 12 is made from a metal alloy such as Chrome!-C or any other alloy having a near zero or a slightly positive temperature coefficient of resis-tance. Constantan and various nickel-chromium alloys meet these criteria. The outside diameter (OD) and inside diameter (ID) of the metal tube 12 are selected to produce desired linear electrical resistivity. The heating element may be made using any conventional method used to fabricate metal tubes. In the preferred embodiment, the metal tube 12 is a ceramic filled welded seam tube fabricated using known welded seam tube WO 96/26626 PCTlUS95l01876 manufacturing techniques such as taught by Lewis in U. S .
Patent 4,269,639. After fabrication, the heating element is drawn to the desired outside diameter. The insulating material 14 is used to prevent the metal tube 12 from collapsing while it is being drawn down to the desired diameter.
The advantages of the tubular heating element may best be described by way of an example of a commercial application such as a heating element for an 10 electric clothes dryer. Conventionally, this heating element consists of a solid 16-gauge (.0508 inch dia-meter) Chromel-C solid wire having a 10 ohm cold resis-tance and an 11 ohm resistance at its operating tempera-ture. The cold linear resistance of the Chromel-C wire is approximately 0.26 ohms per ft. , therefore a Chromel-C wire approximately 38.5 feet long is required to produce the desired resistance. This solid wire heating element has a weight of approximately 0.28 pounds. In operation, approximately 240 volts are applied across the solid wire heating element, producing 5,200 watts of . heat energy. The surface loading, i.e., heat radiated per square inch of surface area, of this solid wire heating element is 70.5 watts/inch2.
This same surface loading may be achieved with a tubular heating element 10 having a Chromel-C metal tube whose cross-sectional area is approximately 220 of the total cross-sectional area of metal tube 12. The metal tube 12 for example may have 0.084 inch O.D. and a 0.074 inch I.D. The linear resistivity of this metal tube is approximately 0.427 ohms per foot; therefore only 23.5 feet are required to produce the desired 10 ohm total resistance. The weight of this tubular heating element a.s approximately 0.1 pounds which represents a 64 o reduction in the amount of the metal required to make the tubular heating element.
In a second example, the cross-sectional area of the metal tube sheath is 40% of the total cross-sectional area of the tubular heating element. For example, the metal tube 12 may have a 0.067 inch OD and a 0.052 inch ID. The linear resistance of this metal tube is approximately 0.378 ohms and requires a length of 27 feet to produce the desired 10 ohm resistance.
The weight of this tubular heating element is approxi-mately 0.14 pounds, which is approximately one-half (1/2) the weight of the equivalent heating element made from the 16-gauge solid wire.
Both embodiments of the tubular heating element described above would operate at the same temperature as the solid wire_ heating element, but because of their larger diameter would last longer.
In an alternate example of the advantages of the tubular heating element 10, consider a tubular heating element 10 whose metal tube 12 has the same linear resistance as the solid wire heating element described above, has the same length, and has a cross-sectional area which is 22 0 of the total cross-sectional area of the tubular heating element 10. In this embodi-ment, the metal tube 12 would have a 0.109 inch OD and a 0.096 inch ID. The weight of the metal tube is the same as the weight of the solid Chromel-C wire, however, its surface load would be reduced to approximately 33 watts/inch2. This lower surface load would significantly _7_ reduce the surface temperature of the tubular heating element 10 and substantially increase its life.
A second embodiment of the tubular heating element 10 is shown in Figure 2. In this embodiment, a wire 16 is coaxially supported within the metal tube 12 and is electrically insulated therefrom by the ceramic powder 14. The wire 16 may be a single solid wire, a plurality of wires, or a braided wire. This wire 16 may perform a variety of functions as discussed below. The wire 16 may be used to provide rigidity to the tubular heating element 10 during the forming process. The wire 16 may provide rigidity to the tubular heating element 10 at room and elevated temperatures. The wire 16 also may be made from an hardenable metal and used to stiffen the finished tubular heating element 10, after being formed, by heat treating. Also, the wire 16 may be made from a metal such as copper or any other metal or alloy having a low electrical resistivity or be made from a material used to provide a temperature control to avoid catastrophic overheating as shall be explained relative to Figure 5.
As shown in Figure 3, the metal tube 12 may be overlayed with one or more layers of different metals or alloys to provide a performance superior to the perfor mance attainable from any single alloy alone. In the embodiment shown in Figure 3, the metal tube 12 consists of an inner tube 18 having an outer layer 20 disposed thereon. It is recognized that additional layers may be used as desired.
In a first example, an alloy having good hot strength may be selected for the inner tube 18 and an WO 96/26626 PCT/US95l01876 _g_ alloy having good oxidation or corrosion resistance may be selected for the outer layer 20. The outer layer 20 will protect the inner tube 18 from oxidation and corrosion. Alternately, the outer layer 20 may be made from a premium heat resistant alloy and the inner tube may be made from a less expensive alloy.
The tubular heating element shown in Figure 3 may have a solid coaxial wire 16 as shown and described relative to Figure 2 or the solid coaxial wire may be omitted, as shown in Figure 1.
Referring now to Figure 4, a source of elec-trical power, illustrated as battery 22, may be electri-cally connected to the opposite ends of the metal tube 12 of the tubular heating element 10. It is recognized that although the source of electrical power 22 is illustrated as a battery, the source of electrical power may be an alternating current generator or electrical power received from conventional commercial or household alternating current electrical power outlets.
In Figure 5, one output terminal of an alter-nating source of electrical power 24 is electrically connected to one end of the metal tube 12 and the other terminal of the source of electrical power 24 is con-nected to one end of the coaxial wire 16. The opposite end of the coaxial wire 16 is connected to the opposite end of the metal tube 12 completing the circuit between the terminals of the source of electrical power 24.
With this arrangement, the coaxial wire 16 may be made from an alloy which will melt when the current through the metal tube approaches a value preselected to prevent a catastrophic failure of the tubular metal heater 10.
Alternatively, the wire 15 may be made from an alloy having a positive temperature coefficient of resistance such that when the current through the metal tube 12 exceeds a predetermined value, the resistivity of the wire 16 rapidly increases, thereby maintaining the current flow through the metal tube 12 at a value less than a current sufficient to produce catastrophic failure of the tubular heating element 10.
The tubular heating element 10 may be used in the same manner as a conventional solid wire heating element. As shown in Figure 6, the tubular heating element may be wound around a ceramic cylinder 26, or may be coiled or may be spiral wound as shown in Figure 7 to form a free standing heater.
The disclosed tubular heating element has many operational and economic advantages over solid wire heating elements:
~ The tubular heating element can have a higher linear resistance than comparable solid wire heating elements having approximately the same diameter.
~ The tubular heating element can reduce the quantity of a premium resistive alloy required to make a heating element having the desired resistance and surface load.
~ The tubular heating element can reduce surface loading on the heater element having the desired resistance.
~ The tubular heating element can operate at lower surface temperatures, thereby increasing its life.
It is recognized that while various embodi-ments of the invention have been shown in the drawings ' and discussed in the specification, those skilled in the art may make changes and/or improvements to the tubular heating element as set forth in the appended claims.
Claims (24)
1. A tubular heating element comprising:
a preformed metal tube having a predetermined temperature coefficient of resistance for generating heat when an electrical current passes through the preformed metal tube;
a ceramic material disposed in and filling said preformed tube; and a single, continuous linear metal wire coaxially supported in said metal tube along the entire length of said metal tube by said ceramic material.
a preformed metal tube having a predetermined temperature coefficient of resistance for generating heat when an electrical current passes through the preformed metal tube;
a ceramic material disposed in and filling said preformed tube; and a single, continuous linear metal wire coaxially supported in said metal tube along the entire length of said metal tube by said ceramic material.
2. The tubular heating element of claim 1 wherein said wire has a mechanical strength greater than said metal tube to provide rigidity to said tubular heating element.
3. The tubular heating element of claim 1 wherein said wire has a low electrical resistivity.
4. The tubular heating element of claim 1 wherein said wire has a temperature coefficient of resistance more positive than the temperature coefficient of resistance of said metal tube.
5. The tubular heating element of claim 1 wherein said wire is an age hardenable material.
6. A tubular heating element of claim 1 wherein said preformed metal tube comprises at least an inner tube of a first alloy and an outer layer of a second alloy, said outer layer extending along the length of said inner tube.
7. The tubular heating element of claim 6 wherein said inner tube is made from an alloy having good hot strength and said outer layer is made from an alloy having good oxidation resistance.
8. The tubular heating element of claim 6 wherein said inner tube is made from an alloy having good hot strength and said outer layer is made from an alloy having good corrosion resistance.
9. The tubular heating element of claim 6 wherein said outer layer is made from a premium heat resistance alloy and said inner tube is made from an alloy having good working and drawing properties.
10. The tubular heating element of claim 1 wherein said ceramic material comprises magnesium oxide.
11. A tubular heating element comprising:
a performed metal tube having a predetermined temperature coefficient of resistance for generating heat when an electrical current passes through the preformed metal tube;
a single, continuous linear wire coaxially disposed in said preformed metal tube along the entire length of the tube; and a ceramic material filling said preformed metal tube and mechanically supporting said wire coaxially within said preformed metal tube.
a performed metal tube having a predetermined temperature coefficient of resistance for generating heat when an electrical current passes through the preformed metal tube;
a single, continuous linear wire coaxially disposed in said preformed metal tube along the entire length of the tube; and a ceramic material filling said preformed metal tube and mechanically supporting said wire coaxially within said preformed metal tube.
12. The tubular heating element of claim 11 wherein said predetermined temperature coefficient of resistance is a positive temperature coefficient of resistance.
13. The tubular heating element of claim 11 wherein said metal tube comprises at least an inner metal tube and an outer metal layer disposed on said inner metal tube, said outer metal layer extending the entire length of said inner metal tube.
14. The tubular heating element of claim 12 wherein said wire has a mechanical stiffness greater than said metal tube.
15. A tubular heating element comprising:
a preformed inner metal tube;
an outer metal layer overlaying said inner metal tube along its entire length, at least one of said inner metal tube and said outer metal layer having a predetermined temperature coefficient of resistance; and a ceramic material filling said inner metal tube.
a preformed inner metal tube;
an outer metal layer overlaying said inner metal tube along its entire length, at least one of said inner metal tube and said outer metal layer having a predetermined temperature coefficient of resistance; and a ceramic material filling said inner metal tube.
16. The tubular heating element of claim 15 further comprising a wire coaxially supported in said inner metal tube along the entire length of said metal tube by said ceramic material.
17. The tubular heating element of claim 15 wherein said inner metal tube has good hot strength and said outer metal layer has good corrosion resistance.
18. The tubular heating element of claim 15 wherein said inner metal tube has good hot strength and said outer metal layer has good oxidation resistance.
19. The tubular heating element of claim 1 wherein the cross-sectional area of the metal portion of said preformed metal tube is greater than 20% of the total cross-sectional area of the preformed metal tube.
20. The tubular heating element of claim 19 wherein said cross-sectional area of the metal portion of said preformed metal tube is in the range from 20 % to 40% of the total cross-sectional area of the preformed metal tube.
21. The tubular heating element of claim 11 wherein the cross-sectional area of the metal portion of said preformed metal tube is greater than 20% of the total cross-sectional area of the preformed metal tube.
22. The tubular heating element of claim 21 wherein the cross-sectional area of said metal portion is in the range from 20% to 40% of the total cross-sectional area of said preformed metal tube.
23. The tubular heating element of claim 15 wherein the cross-sectional area of the metal portion of said preformed inner metal tube is greater than 20% of the total cross-sectional area of said preformed inner metal tube.
24. The tubular heating element of claim 23 wherein the cross-sectional area of the metal portion of said preformed inner metal tube is in the range from 20%
to 40% of the total cross-sectional area of said preformed inner tube.
to 40% of the total cross-sectional area of said preformed inner tube.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US1995/001876 WO1996026626A1 (en) | 1995-02-21 | 1995-02-21 | Tubular heating element with insulating core |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2212342A1 CA2212342A1 (en) | 1996-08-29 |
| CA2212342C true CA2212342C (en) | 2000-05-16 |
Family
ID=22248668
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002212342A Expired - Fee Related CA2212342C (en) | 1995-02-21 | 1995-02-21 | Tubular heating element with insulating core |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0811303A4 (en) |
| JP (1) | JP3042893B2 (en) |
| AU (1) | AU1965995A (en) |
| CA (1) | CA2212342C (en) |
| WO (1) | WO1996026626A1 (en) |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2472930A (en) * | 1945-08-23 | 1949-06-14 | Western Electric Co | Electrical heating unit |
| US2866062A (en) * | 1956-03-05 | 1958-12-23 | Trent Inc | Electrical heating elements |
| DE1515017A1 (en) * | 1964-09-22 | 1969-11-13 | Licentia Gmbh | Process for the production of thin-walled metallic hollow bodies |
| NL153755C (en) * | 1966-10-20 | 1977-11-15 | Stichting Reactor Centrum | METHOD FOR MANUFACTURING AN ELECTRIC HEATING ELEMENT, AS WELL AS HEATING ELEMENT MANUFACTURED USING THIS METHOD. |
| US5066852A (en) * | 1990-09-17 | 1991-11-19 | Teledyne Ind. Inc. | Thermoplastic end seal for electric heating elements |
| JPH04272685A (en) * | 1991-02-26 | 1992-09-29 | Sakaguchi Dennetsu Kk | Sheath heater |
-
1995
- 1995-02-21 WO PCT/US1995/001876 patent/WO1996026626A1/en not_active Application Discontinuation
- 1995-02-21 JP JP08525628A patent/JP3042893B2/en not_active Expired - Lifetime
- 1995-02-21 CA CA002212342A patent/CA2212342C/en not_active Expired - Fee Related
- 1995-02-21 EP EP95912552A patent/EP0811303A4/en not_active Ceased
- 1995-02-21 AU AU19659/95A patent/AU1965995A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10508424A (en) | 1998-08-18 |
| EP0811303A1 (en) | 1997-12-10 |
| EP0811303A4 (en) | 1998-09-02 |
| JP3042893B2 (en) | 2000-05-22 |
| AU1965995A (en) | 1996-09-11 |
| CA2212342A1 (en) | 1996-08-29 |
| WO1996026626A1 (en) | 1996-08-29 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5453599A (en) | Tubular heating element with insulating core | |
| US4112410A (en) | Heater and method of making same | |
| CA1228653A (en) | Electrical heating apparatus protected against an overheating condition and a temperature sensitive electrical sensor for use therewith | |
| US5081341A (en) | Electrical heating element for use in a personal comfort device | |
| EP0125913B1 (en) | Flexible heating wire | |
| CA1301229C (en) | Flexible, elongated positive temperature coefficient heating assembly and method | |
| US5206485A (en) | Low electromagnetic and electrostatic field radiating heater cable | |
| US7566849B2 (en) | Self-regulating electrical heating cable | |
| CN1878434B (en) | Electric blanket heating apparatus without electromagnetic wave radiation and influence electricity | |
| WO1991014352A1 (en) | Electrical heating element for use in a personal comfort device | |
| EP1537761B1 (en) | Electrical heating cable | |
| US6002117A (en) | Electric heating cord with non-heating core-conducting element and reduced EMF emissions | |
| US4308448A (en) | Heating cable with a specific heating capacity | |
| CA2212342C (en) | Tubular heating element with insulating core | |
| EP0160100B1 (en) | Ptc heating wire | |
| EP0287898B1 (en) | Flexible, elongated thermistor heating cable | |
| CA1230634A (en) | Process for uniting sleeve members by brazing | |
| US5083012A (en) | Resistance wire heating element | |
| KR200186614Y1 (en) | Electric wave removal apparatus for electric heating mattress | |
| KR200317436Y1 (en) | heat cable for an electric heater | |
| EP1558926A1 (en) | Chromatography column assembly | |
| JP2958702B2 (en) | Heating element | |
| KR19980019345U (en) | Electromagnetic Removable Bedding | |
| WO1997028670A1 (en) | Electrical heating element | |
| KR20040080267A (en) | heat cable and manufacturing method for an electric heater |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |