US2053933A - Electric heater - Google Patents

Description

Sept. 8, 1936. c, c. ABBOTT .2,053,933

ELECTRIC HEATER Filed Aug. 12, i955 Invent ow:

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Patented Sept. 8, 1936 UNITED STATES ELECTRIC HEATER Charles C. Abbott, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application August 12, 1933, Serial No. 684,832

4 Claims.

My invention relates to electric heaters, and it has for its object the provision of a simple, efiicient and inexpensive heater of this type and method of making it.

Although not limited thereto, my invention is particularly useful in connection with relatively low temperature electric heaters of the sheathed type wherein a resistance conductor is enclosed by a metallic sheath.

In carrying out my invention in one form thereof, a resistance conductor is wound upon an electrically insulating core, which preferably will be formed of a yielding fibrous insulating material, such as asbestos. This core is reinforced by means of a metallic wire or thread arranged centrally of the core. The core may be made by covering the wire with asbestos, roving in any suitable manner.

The resistance Conductor and core are enclosed by an elongated metallic sheath, and preferably will be arranged substantially centrally of the sheath. Interposed between the resistance conductor and the sheath is a highly compacted layer of yielding, fibrous, electrically insulating material, such as asbestos. Suitable terminals are electrically connected with the ends of the resistance conductor and in one form of my invention, these terminals project from the sheath. In another form of my invention, the terminals are enclosed by the sheath and suitable external leads enter the ends of the sheath where they are electrically connected with the terminals. In this form, it is preferable to reduce the sheath materially at the ends so that the sheath fits tightly about the leads. The leads in this case are permanently attached to the terminals.

In making an electric heater in accordance with my invention, a suitable resistance conductor is wound upon a core formed as described above, and then suitable terminals are connected to the ends of the resistance conductor. This may be accomplished by compressing metallic tubular terminal members upon the end portions of the core in electrical Contact with the end turns of the resistance conductor. These terminals may be compressed by swaging them upon the ocre.

Then suitable leads may be attached to the terminals, if it is desired to use permanently attached leads, and after this the resistance conductor and the core and also the terminals are covered with a `layer of asbestos which may be in the form of a roving. Then the assembly is inserted in a metallic sheath which is subsequently reduced in diameter so as to highly compact the asbestos insulating material. The sheath may be reduced by swaging or rolling.

For a more complete understanding of my invention, reference should be had to the accompanying drawing in which Fig. 1 is a fragmentary view in elevation illustrating a resistance conductor wound upon a flexible supporting core arranged in accordance with my invention, and also showing a terminal connector member used with my electric heater, portions of the core and terminal being shown in section so as to illustrate Certain structural details; Fig. 2 is a fragmentary View, partly in section, illustrating the manner in which the terminals are connected to the resistance conductor and also the manner in which leads are connected to the terminals, all arranged in accordance with my invention; Fig. 3 is a fragmentary view, mainly in section and taken on an enlarged scale, of a finished electric heater made in accordance with my invention; Fig. 4 is a complete elevation on a reduced scale of the finished electric heater of Fig. 3; and Fig. 5 is an elevation, partly in section, illustrating a nished electric heater embodying a modified form of my invention.

Referring to Figs. 1-4 inclusive, I have shown my invention in Connection with an electric heater comprising a conductor I0 mounted upon a suitable supporting core II. The resistance conductor Il) may be made of any suitable material, but preferably will be made of a nickel-chromium alloy. Preferably, the supporting core I I will be made of a suitable electrically insulating, exible and slightly yielding material, such as asbestos. And preferably, the asbestos will be reinforced by a ne metallic wire or thread I2 arranged centrally of thecore. The core I I may be conveniently formed by applying asbestos roving to the wire I2 so asvto cover the wire with a substantially uniform layer of the asbestos. The thread I2, as shown, preferably will be formed by twisting together a plurality of relatively ne wires.

When a very large number of heating elements are to be made, it is convenient to wind the resistance conductor III continuously upon a relatively long length of the asbestos core I I, after which the core and the conductor wound upon it may be cut into portions of the required length vfor the various heating units.

The provision of the heat resistant, flexible core II is an important feature of my invention. It will be appreciated that in an electric heater adapted for low temperature work, it is desirable to use a very fine resistance conductor in order to secure the required resistance. In order to use satisfactorily a very ne resistance conductor, I have provided the conductor with the flexible heat resistant core I I which serves both to support the turns of the resistance conductor and to retain the various turns in their proper spaced relation when wound. It will be observed that since the conductor is provided with a support which is slightly yielding, the conductor as it 1s being wound will slightly depress the outer surface of 2 aotaaaa the support so that each turn of the conductor will form its own recess or groove. By reason of this construction any displacement of the turns is prevented. It will be understood, however, that the asbestos supporting member II is sufficiently hard to provide a comparatively strong and firm support for the conductor I0, it being yielding merely to the extent of permitting the resistance conductor to slightly depress the outer surface. In other words, the supporting member II will be one possessing substantial mechanical strength. v

After the conductor has been wound upon its core, suitable terminals I3 are connected to the end portions of the resistance conductor. The terminals I3 are connected to the resistance conductor by means of suitable terminal connector members I Il. 'Ihe connector members Id are of tubular form and, as shown, are provided with a stepped bore; this bore has a relatively large portion Ia which serves to receive the end portion of the core with the resistance conductor wound upon it and a portion Ib of somewhat smaller diameter which receives the end of the terminal I 3.

In assembling each terminal I3 with the heater, the end portion of the core with the resistance element wound upon it that is to be attached to the terminal is inserted in the bore Ilia, in a connector member I6. Then the connector member is reduced in diameter so that the conductor will be pressed into good mechanical and electrical contact with the end turns of the coiled resistance unit. This reducing step may be accomplished by rolling or swaging the connector. Preferably, before the core is attached to the terminal,

the end of the conductor will be wound back in the opposite direction to form three or four turns Ia upon the end turns already Wound, as shown in Fig. 1. It has been found that this insures a very good electrical contact between the resistance conductor and the connector after the connector has been applied, and furthermore, that this arrangement obviates danger of the connector pulling away from the core. It is also preferable to swage the end portion of the core somewhat before it is applied to the connector so as to size it to fit the bore portion Ma, it being understood that the portion Ia before it is swaged has a diameter somewhat smaller than the diameter of the core.

After this, the terminal I3 is inserted in the bore Mb provided for it in the connector, and this portion of the connector is swaged by means of square dies so as to firmly connect the terminal to the connector. It will be understood that when the portion Ida was reduced upon the core, the diameter of the bore Ib will have been reduced somewhat at the same time. Because of this, the original diameter of the bore portion Ib will be chosen so that after the connector is applied to the core, the bore Ib will have a diameter approximately equal to the diameter of the terminal I3. Then the terminal may be inserted in the portion I 4b which will be swaged upon the terminal, as described.

It will be understood, of course, that terminals I3 will be connected to both ends of the resistance heating element by connectors Ill in the manner just described.

It will be observed that when the connector III is reduced upon its end of the core I l, the asbestos forming the end portion of the core will be squeezed into the smaller bore Ilb as clearly shown in Fig. 2. This is important because this squeezed portion completely and effectively eleotrically insulates the connector Il and terminal I3 from the metallic wire IZ.

Suitable leads I5 are then connected to the free ends of the terminals I3. For this purpose, lead connector members I are provided. The connector members I6 are similar to the connector members III. Thus, each member I6 is provided with a bore Ia of relatively small diameter and with a second bore IBI) of relatively large diameter aligned with it. The diameters of these two bores before the connector is applied to the terminal and the lead are substantially uniform throughout their lengths, as are the bores IIIa and Ibof the connector III. The connector IS is applied to the lead I5 by baring an end portion of the lead of its insulation, as clearly shown in Fig. 2, and then inserting the bared conductor Ia into the bore ISb. The connector is then reduced in diameter by swaging or rolling so as to compress it tightly upon the bared conductor. The eifect of this operation is to leave a head Ib on the end of the conductor, as clearly shown in Fig. 2. During this reducing operation, the bore Ia is reduced somewhat, but its original diameter is chosen so that after the reducing process it will be approximately the same size as the terminal I3. The terminal I3 is then inserted in the bore Ita which is swaged by means of square dies so as to reduce its diameter sufciently to eiect a very good mechanical and electrical connection between the terminal and the connector.

It will be understood that the leads I5 for both ends of the heater will be connected in this same manner.

The resistance element I0 and the core Il on which it is mounted are completely covered throughout their entire length by a layer of insulating material Il which is preferably formed of a fibrous yieldable substance, such as asbestos. This asbestos may be conveniently applied in the form of a roving. It is also preferable to cover the terminal connectors Id and the terminals I3 throughout substantially their entire lengths by means of the asbestos roving I1. The lead connectors I6 and the adjacent end portions of the leads are covered by an insulating layer I8, which may be formed of any suitable substance, but which preferably will be made of asbestos tape impregnated with a suitable electrically iri-1 sulating compound, such as a resin of the alkyd type.

When a large number of heating elements are to be made, the resistance conductor and the terminals I3 may be conveniently covered with the insulating layer I'I in the following manner. After the resistance conductor I0 has been wound continuously upon a relatively long core II and has been cut apart to the desired lengths, as previously described, the separate resistance sections are connected together by means of ter minal conductors having double the length of the terminals I3. These conductors will be secured to the ends of the resistance sections by means of the connectors I, and are subsequently used to form the terminals I3. The desired number of the resistance sections are secured together in this manner so as to form a relatively long chain which may be Wound upon a suitable collecting reel. It will be understood that the terminal conductors connecting the resistance sections are sufficiently ilexible to permit the chain to be wound upon the reel. The resistance elements thus connected together may be run through a suitable insulating machine (not shown) for applying the asbestos roving l1 to the chain so as to completely cover the resistance sections, the connectors and the terminal conductor lengths between the sections. 'Ihe resistance sections are then separated by cutting through the terminal conductors midway between the connectors. This operation, of course, divides the chain into a number of separate resistance sections, to the ends of which are'secured theseveral half sections of the terminal conductors that,-

previously connected the sections together. These half sections form the terminals I3. After this, the insulation I1 on the free ends of the terminals I3 is stripped back to provide for connection of the terminals with the leads I5 by means of the connectors I6. After the leads have been attached, the insulating layers I8 will be applied to the connectors I6 and to the adjacent ends of the leads.

The entire assembly including the core II, the resistance conductor I0, the terminals I3, the leads I5 and the insulating layers I1 and I8, is then threaded through a suitable metallic sheath 2D. The sheath will have such a diameter that the assembly will have a sliding t with the sheath.

Then the sheath 20 is reduced in diameter so as to highly compact the insulating layers I'I and I8 about the resistance element, its supporting core, the terminals and the connectors I4 and I6.

The sheath may be reduced in diameter by swaging or rolling. The end portions 20a. of the sheath are reduced to a smaller diameter than the intermediate portions of the sheath so that these end portions t tightly on the leads. This arrangement prevents the entrance of moisture and like uids into the sheath. The asbestos tape I8 impregnated with the alkyd resin assists greatly in rendering the heater moisture proof,

The sheath will be reduced considerably in diameter so as to thoroughly compact the insulating layers I1 and I8. Thus, for example, the sheath, if it had a diameter of It will also be observed that the turns of theconductor cannot become displaced and short circuit each other so that the finished heating element can be bentinto suitable desired shapes.

In Fig. 5, an electric heater embodying a modied form of my invention is shown. In this heater, the resistance conductor 30 is wound upon a core 3I which is arranged substantially as is the core II of Figs. 1-4 inclusive. Thus, the core 3l is formed of asbestos reenforced by a metallic twisted wire or thread (not shown). The resistance conductor 30 is electrically connected at its ends with terminals 33 through the medium of connector members 34, and` arranged as are the corresponding elements of Figs. 1 to 4.

The resistance conductor and the attached terminals are`then completely covered with a suitable layer 35 of insulating material, which will be similar to the insulating material Il, that is, it will Vbe formed of asbestos roving. Theassembly is inserted in a metallic sheath 35, which will have a diameter substantially equal to the diameter of the assembly and a length such that the ends of the terminals project from the sheath. Then the diameter of the sheath is reduced as by rolling or swaging so as to compress the asbestos insulation tightly about the resistance element, core and terminals.

While I have shown particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modications may be made, and I, therefore, contemplate by the appended claims to cover any such modications as fall within the true spirit and scope of my invention.

What I claim asnew and desire to secure by Letters Patent of the United States, is:

1. An electric heater comprising a core formed of a yieldingelectrically insulating material, a resistance conductor wound upon said core, the ends of said conductor being wound back in a reverse direction on the end turns of the conductor on said core, and tubular terminal members compressed on said end turns and on said re-l Vversely wound ends so as to provide a good electrical and mechanical connection between said terminal members and said resistance conductor.

2. An electric heater comprising a metallic thread, a layer of fibrous yielding electrically insulating material covering said metallic thread, a resistance conductor wound upon said layer of insulating material, tubular terminals embracing the end turns of said resistance conductor, and compressing said electrically insulating material about the ends of lsaid metallic thread so as to insulate said thread from said terminals, a second layer of brous yielding electrically insulating material covering said resistance conductor and a metallic sheath encasing said second layer of insulating material and compressed thereon so as to highly compact said layers of insulating maerial.

3. An electric heater comprising a yielding flexible core formed of electrically insulating material reenforced by a metallic thread arranged substantially centrally thereof, a resistance conductor wound upon said core, and tubular ter-- minal members compressed upon the ends of said core in electrical contact with the end turns of said resistance conductor arranged to compress the ends of said insulating material of said core over and about the ends of said metallic thread.

4. -The method of making an electric heater which comprises forming a core of flexible yielding electrically insulating material by covering a metallic thread with a layer of said material, winding a resistance conductor upon said core, compressing tubular terminal members on the end portions of said core so as to mechanically and electrically connect said members with said resistance conductor and to compress the end portions of said insulating material within said tubular members over the ends of said metallic thread to thereby electrically insulate said thread from said terminals, covering said resistance conductor and core with a layer of flexible yielding electrically insulating material, inserting said core with said layer of insulating material thereon into a metallic sheath and elongating and reducing said sheath so as to compact said layer and core of insulating material. i

' CHARLES C. ABBO'IT.

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