|Publication number||US2529914 A|
|Publication date||Nov 14, 1950|
|Filing date||Jun 22, 1950|
|Priority date||Jun 22, 1950|
|Publication number||US 2529914 A, US 2529914A, US-A-2529914, US2529914 A, US2529914A|
|Inventors||Ansel P Challenner|
|Original Assignee||Denison Mattress Factory|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (30), Classifications (17)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Nov. 14, 1950 A. P. CHALLENNER ELECTRICAL HEATING ELEMENT 2 Sheets-Sheet 1 Filed June 22, 1950 grwvm/fm finse/ Cha//enn Nov. 14, 1950 A- P. CHALLENNER 2,529,914
ELECTRICAL HEATING ELEMENT Filed June 22, 1950 2 Sheets-Sheet 2 Ansel I? Ch al/enner Patented Nov. 14, 1950 ELECTRICAL HEATING ELEMENT Ansel P. Challenner, Norman, Oklm, minor to Denison Mattress Factory, Denison, Tex a partnership Application June 22, 1950, Serial No. 169,623
relatively small size so that the elements may be 1 flexed or bent to a considerable degree without damage, and also whereby electrical connections need be made to one end only of said element.
A particular object of the invention is to provide an improved heating element including a pair of concentric conductors adapted to be connected to opposite poles or terminals of an electrical circuit, said conductors being enclosed in an insulating shield whereby any short circuits or breaks which may occur in the circuit will result in an are within said insulating shield rather than exposing surrounding material to the influence and danger of such an arc.
Another object of the invention is to provide an improved heating element of the character described wherein the concentric conductors are separated by an insulating material, said insulating material functioning to insulate the conductors one from another, to conduct heat outwardly from the central conductor, and to generate a certain degree of heat by reason of its dielectric loss.
Yet another object of the invention is to provide an improved heating element having a central conductor surrounded by an outer tubular conductor spaced therefrom by insulating material, the composite conductors being surrounded by an insulating shield whereby the possibility of electrical shock is minimized since the differences of electrical potential are confined to the interior of the composite conductor.
An important object of the invention is to provide an improved electrical heating element employing electric power of high frequency in coaxial conductors whereby heating may be effected through dielectric loss within the element.
A particular object of the invention is to pro- -vide an improved electrical heating element permitting the passing of a high frequency alternating electrical current through a pair of concentric conductors separated by an insulating material having a high dielectric loss whereby heat is generated by the leakage of electrical current through the insulating material.
An important object the invention is to provide an improved electrical heating element having a pair of concentric conductors connected at one end to a suitable source of power supply and having their opposite ends shorted together wherein the voltage drop in the outer conductor is relatively small so that a greater degree of safety is insured.
A construction designed to carry out the invention will be hereinafter described together with other features of the invention.
The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings, wherein examples of the invention are shown, and wherein:
Fig. l is a view in elevation of a portion of a heating element constructed in accordance with this invention with various of the layers and conductors being broken away to illustrate the structure thereof.
Fig. 2 is a view similar to Figure 1 and illustrating a modified form of the invention.
Fig. 3 is a view similar to Fig. 1 and illustrating a still further modification of the invention,
Fig. 4 is a cross-sectional view taken on the line 4-4 of Fig. 1,
Fig. 5 is a cross-sectional view taken on the line 5-5 of Fig. 2,
Fig. 6 is a cross-sectional view taken on the line G6 of Fig. 3,
Fig. '7 is a schematic view of the heating element arranged in a blanket and coupled to a high frequency source of energy,
Fig. 8 is an enlarged schematic view of the coupling arrangement,
Fig. 9 is an enlarged view of the remote end of the heating element, and
Fig. 10 is a schematic view of the heating element arranged in a blanket and connected to a low frequency source of energy.
This application is a continuation-in-part of my copending application, Serial No. 61,488, filed November 22, 1948, which, in turn, was a continuation-in-part of my application, Serial No. 787,781, filed November 24, 1947, both abandoned.
In the drawings in Fig. l, the numeral ll designates a central electrical conductor or wire which may be formed of copper or any other similar, low-resistance conducting material or metallic alloy. The drawing is greatly magnified to illustrate clearly the structure of the heating element contemplated by this invention. In actual practice, the conductor 10 would be of the magnitude of several thousandths of an inch in diameter, such slenderness of the conductor permitting it to bend upon a very small radius and allowing it to undergo repeated flexing and bending without undue hardening or fracture.
The conductor III is covered with a covering or casing ll of insulating material. The casing ii may be composed of glass fibers woven or formed into suitable strands or cords and arranged around the conductor It in the manner of loom, or in a basket-weave arrangement. The casin Ii snugly engages the outer periphery of the conductor it and may have a diameter of several one-hundredths of an inch, thereby being of a sizeable diameter in proportion to the diameter of said conductor and afiording adequate insulation therefor.
The material from which the casing ii is formed is important in that it must have fair insulating properties insofar as electricity is con.- cerned, but must be capable of transmitting in an efllcient fashion considerable quantities of heat while retaining a high degree of flexibility. It is not necessary that the casing be an extremely good insulator as any losses that occur within it will add to the total heat output. Its principal requirement is that it be undamaged by heat and perform the nominal function of an insulator as indicated. Due to its relatively small diameter, the casing is adapted to undergo flexing and bending about a small radius without undue distortion or separation. Also, since an appreciable portion of the heat generated by this heating element arises from the conductor it, the casing ii must be capable of transmitting this heat to the desired locality without being affected in any un-.
desirable fashion by such heat or by the high temperatures which may be attained.
Glass fiber has been found particularly advantageous for use in forming the insulating casing II. The glass fiber may be formed into strands or cords and arranged about the conductor in in a basketweave much in the nature of electrical insulating loom. An insulating casing so formed is quite flexible and may undergo repeated bending and flexing without injury. At the same time, the glass fiber offers a reasonable degree of electrical insulation while acting in an efiicient fashion to transmit heat generated in the conductor 10. Other materials, such as the halogenated vinyl resins, are also suitable for forming this insulating casing.
In addition to its electrical insulating and heat transmitting function, the casing il contributes to a marked extent to the heat output of the heating element. As appears hereinafter, the casing separates two conductors and has the nature of a dielectric. Hence, dielectric losses occur in said sleeve. The occurrence of these losses results in the generation of heat, and this heat is transmitted outwardly from the casing.
The casing is enclosed within a continuous, tubular conductor l2 formed of metal or some other conducting material which may be similar or dissimilar to the material of the conductor Ill. The insulating casing has a snug fit within the bore l3 of the tubular conductor I2 so as to space the inner wall of said conductor radially outwardly a uniform distance from the conductor l and to fill substantially the entire space between the conductors in and I2. An outer insulating casing or sleeve H has a snug fit upon the outer periphery of the conductor l2, thereby enclosing the entire assembly and the composite conductor within an insulating case. The outer insulator i4 is formed similarly to the inner insulating casing ll, being illustrated in Fig. 1 as formed with a basketweave composed of individual strands or cords of glass fiber brother suitable material such as certain of the temperature-resistant plastics.
In this manner, a unitary heating element is provided, said element including a central conductor surrounded by, or disposed concentrically of, a tubular conductor, said conductors being spaced one from the other by an insulating casing and completely encased in an outer insulating sleeve or casing which encloses the entire assembly. Although Fig. 1 illustrates this heat-1118 element in a greatly magnified or enlarged fashion, it is to be kept in mind that the outside diameter of the complete element is relatively small, possiblyin the neighborhood of 1*; of an inch, so that a high degree or flexibility is retained by the element. Due to the small crosssectional area, of the conductors ill and ii, the same will possess a marked degree of resistancev to an electrical current flowing therethrough. For this reason, several yards of this heating element will possess a quite considerable degree of resistance, and when incorporated into an electrical blanket or heating-pad, will be capable of dissipating sumcient electrical energy in the form of heat as to provide an eflicient and desirable heating structure. As before pointed out, an appreciable portion of this heating is accomplished by means of the inner conductor it which preterably is the smaller in cross-sectional area and oflers the greater resistance. This purely resistance heat of the inner conductor will be supplemented by the purely resistance heat contributed by the outer conductor i2. To this will be added the heat arising from the dielectric loss occur--v ring within the confines of the inner insulator sleeve II. The total heat output thus achieved reaches quite sizeable proportions in relation to the length of the element involved and its diameter. Ii the heating element is supplied with a high frequency alternating current, the apparent resistance of the conductors are increased due to skin effect.
In practice, the heating element is arranged in any desired configuration within the area or surface to be heated, and one of two alternative connecting arrangements employed. It the heating element is of sufilcient length and the frequency of the electric supply is high enough, it may not be necessary to connect electrically the outer ends of the conductors i0 and i2 since the entire quantity of electrical energy put into said conductors may be dissipated with the entire element acting as an open clrcuited transmission line having high losses. However, for shorter lengths of the heating element it may be desirable to connect the outer ends of the two conductors by fusing the two together within the outer conductor sleeve H. The two conductors, when so connected, represent a continuous resistance element extending from one end of the heating element to the other, and return. With either arrangement, the two terminals or poles of the electrical system which supplies electrical energy .to the heating element, may both be connected gle point at which they may be connected to said source of electrical energy.
Obviously, many additional advantages result from this structure. One important advantage is the substantial elimination of the danger of open arcs or sparks resulting from a breaking or short-circuting of this element. If, for any reason, the insulating sleeve II should be rupturedso as to permit arcing between the two conductors, such arcing would be confined within the outer insulator sleeve ll so that there would be no open are or flash which might result in burns or confiagration. This advantage is to be contrasted with the situation that obtains when using an ordinary resistance-type element. Such elements are normally encased by a single layer of insulation, and when such insulation is separated for any reason, the conductor normally arcs to any other part of the circuit with which it comes in contact, which, in many cases, includes any grounded metallic object, thereby resulting in an open flash or arc with the obvious consequent danger.
Another advantage which flows from this structure is the protection of persons adjacent to the heating element from shock by the electrical current flowing therethrough. Manifestly, to cause an electrical current to flow, the conductors I0 and I: must be at different electrical potentials. However, this difference of electrical potential is confined within the outer insulator l4 thereby 'minimizing the possibility of a person's being shocked by coming in contact with the two conductors. By connecting the outer conductor I! to the ground side of the source of electrical energy supplying this heating element and connecting the inner conductor ID to the "live or hot side of this source, the possibility of a person's being shocked may be further minimized or decreased.
In this connection, it is to be noted that the major portion of the potential drop across the heating element occurs in the inner conductor l0, and that the potential gradient along the outer conductor I2 is relatively low. This means that a person coming in contact with two exposed portions of the outer conductor is less likely to be shocked and is subjected to such small voltage differences that harm is unlikely. The larger voltage differentials are confined to the inner conductor Ill which is doubly shielded and insulated.
Still another advantage of this structure is that, when supplied with high frequency alternating current, so called standing waves occur which cause the heating to be distributed unevenly throughout the length of the heater. This uneven distribution of heat may be utilized to concentrate the heat at desired places. If on the other hand, uniform heatingis desired throughout the structure, a proper termination may be designed at the distant end which will permit this.
A valuable electrical heating system is provided when the described heating element is supplied with a high frequency electrical current. In this system, the dielectric loss between the concentric conductors and through the insulator I I becomes of considerable magnitude and results in the generation of a large proportion of the total heat output. In normal concentric or coaxial cables, the effort is to prevent or minimize such heat losses and dissipation of energy. In the present system however, this heat loss may be eflectively employed by selecting for the insulator I I a material having only fair electrical insulating properties but having good or excellent resistance to high temperatures and good heat transfer characteristics. It is also desirable that the material have a high dielectric loss, that is, the property of polyvinyl chloride.
converting the electrical energy of current passing therethrough into heat energy. The sensible heat thus provided is rapidly passed from the eleinent by reason of its high heat transmissive naure.
Glass fiber is an insulating material having these desired properties, as are the halogenated vinyl resins. Thus when these materials are used in the fabricating of the heating element set out herein, a structure is provided which implements the heating system forming a part of the present invention. Whereas, in the past, an effort has been made to eliminate dielectric loss through the conductor, this loss is now capitalized upon and used as a means for conversion of electrical energy into sensible heat energy. This is made possible by increasing the frequency of alternation of the electrical current, resulting in an increase in the heat created by dielectric loss. The
applicable range of frequencies appear, at the present, to be limited on a practical basis to the band from kilocycles to 40 megacycles, it being observed that within this range the dielectric loss becomes appreciable and may be employed as a means of heat generation. The upper limit of the band is set by the presently-existing practical boundaries upon sources of electrical power, but, on a theoretical basis, there is no upper limit for the range of frequencies which may be used. Below 100 kilocycles, the dielectric loss effect is of minor importance andthe major portion of the heating is accomplished by ordinary resistance means.
In Fig. 2 of the drawing is illustrated a modiflcation of this invention. In this modification, the same conductors I0 and I! are employed, but the insulating casing and sleeve, II and H, are replaced by different types of sleeves, i5 and I respectively. The sleeves l5 and ii are similar to one another and differ from the sleeves H and II in that the insulating material is arranged in a serving or helical winding about the outer periphery of th conductors in and II respectively. The same advantageous results are achieved by this structure and it represents merely a modification of form of the first example of the invention described. If desired, the insulating sleeves may be formed of double helices extending in opposite directions.
In Fig. 3 is shown an application of plastic insulation to this heating element. The insulation sleeves illustrated in Figs. 1 and 2 may be formed of any desirable or suitable type of plastic material, such as the sllicones, polyethylene or In addition, such plastic material may be formed into an integral sleeve having an axial bore through which the conductor or conductors extend. Thus, in Fig. 3,, the central or inner conductor I0 passes through the central opening ll of a one-piece, moulded insulator sleeve I8. The insulating sleeve II in turn passes through the axial opening or bore I. of a tubular sleeve-like conductor 20, and a tubular insulating sleeve or casing 2|, cast or extruded from plastic material, has a snug fit over the outer periphery of the conductor 20. The insulators l8 and 2| function in the same fashion as the insulators H and I4 and represent merely .a. modification of the latter. As illustrated in Fig. 3, the outer, sleeve-like or tubular conductor 20 may b in th form of a metallic loom or shield having a basketweave similar to shielding employed in various radio and communication equipment. Indeed, the outer conductor may as- 76 sum: this form in the modifications shown in P188- 1and2sinceallthatisnecessaryistonrovide a tubular conductor with respect to which the inner conductor can be concentrically disposed.
All of the forms achieve the same beneficial results, and being very small in diameter may be subjected to extensive and repeated flexing and bending. In particular, in the case of an electrically-heated blanket, this heating element may be incorporated into the weave of the blanket in place of certain of the threads thereof. In this fashion, an integral or built-in heating element may be provided in the blanket which isnot subiect to misplacement or malfunctioning.
' The utilization of the heating element in a blanket is shown in Figs. 7 through 10. In Fig. 7, a blanket 22 has the heating element 23 disposed therein in a modified spiral outline. The inner and outer conductors of the heating element, it and it, are coupled through an inductive linkage 24 with a suitable oscillator 25 which supplies electrical energy at high frequency. In this high frequency application, the remote end 28 (Fig. 9) of the heating element may or may not include a shorting together of the heating element conas ductors. in F18. 8.
An alternative and less expensive application of the heating element is shown in Fig. 10. In some ways, this form is preferred because of its simplicity and direct use of commercial 60 cycle electric current. This application connects the conductors m and I2 of the heating element directly to the power supply, and employs the shorted remote end 26 shown in Fig. 9. As pointed out hercinbefore, the major portion of the voltage drop across the heating element occurs in the inner conductor it) which is completely shielded and doubly insulated. The outer conductor, which a person is much more likely to come in contact with, has a very low potential gradient because of its larger size, and it is therefore improbable that a serious electrical shock could be received therefrom.
The foregoing description of the invention is explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made, within the scope of the appended claims, without departing from the spirit of the invention.
What I claim, and desire to secure by Letters Patent is:
1. An electric heating element comprising an elongate inner conductor surrounded with electrical insulating material; an outer elongated cylindrical conductor closely surrounding said insulating material, said inner and outer conductors having means to electrically connect at one end of the element in series with a pair of terminals of a source of electrical energy, said inner and outer conductors at the other end of the element being electrically connected together, said inner conductor having substantially higher electrical resistance than said outer conductor whereby substantially all of the potential drop of the heating element is confined to said inner conductor.
The details of the coupling are shown 2. An electric heating element comprising an 70 said insulating material, said inner and outer elongate inner conductor surrounded with electrical insulating material, said insulating material being characterized by high heat resistance high rate of heat transfer and high dielectric loss, an outer elongated cylindrical conductor closely surrounding said insulating material. said inner and outer conductors havins means to electrically connect atone end of the element in series with a pair of terminals 01 a sourceoi electrical energy. said inner and outer conductors at s the other end of the element being electrically 10 fined to said inner conductor.
3. An electric heating element comprising an elongate inner conductor surrounded with electrical insulating material, said insulating material being characterized by high heat resistance 15 high rate of heat transfer and high dielectric loss, an outer elongated cylindrical conductor closely surrounding said insulating material. said inner and outer conductors having means to electrically connect at one end of the element in W series with a pair of terminals of a source of alternating current, said inner and outer conductors at the other end of the element being electrically connected together, said inner con.- ductor having substantially higher electrical resistance than said outer conductor whereby substantially all of the potential drop of the heating -element is confined to said inner conductor.
l. An electric heating element comprising an elongate inner conductor surrounded with electrical insulating material, an outer elongated cylindrical conductor formed of similar conductive material to said inner conductor and closely surrounding said insulating material, said inner and outer conductors having means to electrically connect at one end of the element in series with a pair of terminals oi a source of electrical energy, said inner and outer conductors at the other end of the element being electrically connected together, the cross-sectional dimensions of said inner conductor being substantially less than the cross-sectional dimensions of said outer conductor to increase the resistance of said inner conductor relative to said outer conductor whereby 35 substantially all of the potential drop of the heating element is confined to said inner conductor.
5. An electric heating element comprising an elongate inner conductor surrounded with electrical insulating material, an outer elongated cylindrical conductor formed of similar conductive material to said inner conductor and closely surrounding said insulating material, said inner and outer conductors having means to electrically connect at one end of the element in series with a pair of terminals of a source of altematlng current, said inner and outer conductors at the' other end of the element being electrically connected together, the cross-sectional dimensions of said inner conductor being substantially less than the cross-sectional dimensions of said outer conductor to increase the resistance of said inner conductor relative to said outer conductor whereby substantially all of the potential drop of the heating element i confined to said inner conduc- 6. An electric heating element comprising an elongate inner copper conductor surrounded with electrical insulating material, an outer elongated cylindrical copper conductor closely surrounding conductors having means to electrically connect at one end of the element in series with a pair of terminals of a source of electrical energy said inner and outer conductors at the other end of 76 the element being electricall connected together.
9 i the cross-sectional dimensions of said inner con- REFERENCES CITED ductor being substantially less than the cross- The following references are of record in the sectional dimensions of said outer conductor to m of this patent: increase the resistance of said inner conductor relative to said outer conductor whereby substan- 5 UNITED STATES PATENTS I tially all of the potential dropof the heating ele- Number Name Date ment is confined to said inner conduct 4 1,432,064 Hadaway Oct. 17, 1922 2,387,829 Burnham et a1. Oct. 30, 1945 ANSEL CHALLENNER- 2,436,421 Cork Fe 4,1
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US1432064 *||Jun 27, 1917||Oct 17, 1922||Hadaway Jr William S||Electric heater element|
|US2387829 *||Dec 29, 1942||Oct 30, 1945||Sprague Electric Co||Electrical apparatus|
|US2436421 *||May 12, 1943||Feb 24, 1948||Emi Ltd||Flexible wave guide for ultra high frequency energy|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US2717949 *||Sep 28, 1950||Sep 13, 1955||Denison Mattress Factory||Heating means|
|US2744996 *||Jan 22, 1953||May 8, 1956||Safeway Heat Elements Inc||Heating element|
|US2758194 *||Apr 27, 1954||Aug 7, 1956||Andrew G Heron||Flexible hoses|
|US2822460 *||May 2, 1955||Feb 4, 1958||Goldstaub Henry Herbert||Electrical heating devices|
|US2933710 *||May 13, 1957||Apr 19, 1960||Union Carbide Corp||Continuously gas plated wires for potentiometers|
|US2989613 *||Jan 29, 1960||Jun 20, 1961||Linton Summit Coal Company Inc||Wrap-around heater|
|US3010007 *||May 25, 1959||Nov 21, 1961||Electric Parts Corp||Flexible radiant heating panel|
|US3029360 *||Apr 29, 1958||Apr 10, 1962||Rca Corp||Heater wire coating process|
|US3051821 *||Oct 28, 1958||Aug 28, 1962||Noid Corp||Apparatus for protecting concrete and other masonry materials|
|US3153140 *||Sep 12, 1961||Oct 13, 1964||Electric Parts Corp||Radiant heating panel|
|US3191005 *||Oct 1, 1962||Jun 22, 1965||John L Cox||Electric circuit arrangement|
|US3209128 *||Nov 20, 1962||Sep 28, 1965||Smith Gates Corp||Heating mat|
|US3356835 *||Oct 8, 1964||Dec 5, 1967||Singer Co||Heating structure|
|US3454747 *||Mar 27, 1967||Jul 8, 1969||Hart Oliver M||Flexible electric heating cable|
|US3521030 *||Feb 25, 1966||Jul 21, 1970||Maahs Jerry D||Mobile oven unit|
|US3657520 *||Aug 20, 1970||Apr 18, 1972||Ragault Michel A||Heating cable with cold outlets|
|US3774013 *||Nov 13, 1972||Nov 20, 1973||Keep H||Heat treating appliance for stress-relieving steel piping and like structures|
|US3859506 *||Jun 15, 1973||Jan 7, 1975||Sola Basic Ind Inc||Constant wattage heating element|
|US3996402 *||Mar 17, 1975||Dec 7, 1976||The Boeing Company||Fastening device for use with induction heater apparatus and system for holding together two nonmetal surfaces|
|US4163145 *||Jul 19, 1978||Jul 31, 1979||Neff Paul C||Aquarium heater|
|US4240445 *||Oct 23, 1978||Dec 23, 1980||University Of Utah||Electromagnetic energy coupler/receiver apparatus and method|
|US4242573 *||Jan 24, 1979||Dec 30, 1980||Raychem Corporation||Water immersible heater|
|US4719335 *||May 19, 1987||Jan 12, 1988||Raychem Corporation||Devices comprising conductive polymer compositions|
|US4761541 *||May 19, 1987||Aug 2, 1988||Raychem Corporation||Devices comprising conductive polymer compositions|
|US4777351 *||May 20, 1987||Oct 11, 1988||Raychem Corporation||Devices comprising conductive polymer compositions|
|US5558794 *||Oct 6, 1994||Sep 24, 1996||Jansens; Peter J.||Coaxial heating cable with ground shield|
|US5596309 *||Jul 22, 1994||Jan 21, 1997||Sony/Tektronix Corporation||Reduced inductance coaxial resistor|
|US5883364 *||Aug 26, 1996||Mar 16, 1999||Frei; Rob A.||Clean room heating jacket and grounded heating element therefor|
|US6965081 *||May 24, 2002||Nov 15, 2005||Koninklijke Philips Electronics, N.V.||Cable|
|WO1991014352A1 *||Mar 5, 1990||Sep 19, 1991||Specialty Cable Corp||Electrical heating element for use in a personal comfort device|
|U.S. Classification||338/214, 219/528, 338/256, 219/675, 338/208, 338/259, 174/105.00R, 338/260|
|International Classification||H05B3/56, H05B3/34|
|Cooperative Classification||H05B2203/002, H05B3/56, H05B2203/017, H05B3/342, H05B2203/016|
|European Classification||H05B3/56, H05B3/34B|