US3512114A

US3512114A - Electric resistance heater

Info

Publication number: US3512114A
Application number: US701157A
Authority: US
Inventors: Walter J Dzaack
Original assignee: Edwin L Wiegand Co
Current assignee: Edwin L Wiegand Co
Priority date: 1968-01-29
Filing date: 1968-01-29
Publication date: 1970-05-12
Anticipated expiration: 1987-05-12

Description

WLJ. DZAACK ELECTRIC RESISTANCE HEATER May 12, 1970 2 Sheets-Sheet; 1

Filed Jan. 29, 1968 INVENTOR. WALTER J Dz AACK A TTORNE 6 BY% I May 12, 1970 w. ,1. DZAACK ELECTRIC RESISTANCE HEATER 2 Sheets-Sheet 2 Filed Jan. 29, 1968 mA m WA m mm M mm m United States Patent 3,512,114 ELECTRIC RESISTANCE HEATER Walter J. Dzaack, Glenshaw, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa. Filed Jan. 29, 1968, Ser. No. 701,157 Int. Cl. H01c 1/02, 1/14; Hb 3/10 US. Cl. 338-241 3 Claims ABSTRACT OF THE DISCLOSURE An electric resistance heater and method of making the same in which an elongated resistor wire is disposed within a metallic sheath and has terminal conductor portions at respective ends thereof for protrusion beyond one sheath end for connection to a source of electrical energy. The resistor wire is supported by an elongated dielectric core having end portions closely fitting within the sheath and a separate, relatively small in cross-section intermediate portion maintaining the core end portions in spaced relation. The core end portions have circumferentially spaced, longitudinally extending rectilinear slots for receiving the heating wire and the latter is anchored to respective core end portions and is tensioned therebctween to maintain them assembled with the core intermediate portion.

Preamble Electric resistance heating elements of the so-called cartridge type wherein a resistor conductor is supported on a preformed, rigid, dielectric core and disposed within a metallic sheath filled with highly compacted, electricinsulating, heat-conductive material have long been used.

It has been common knowledge that if the dielectric core could be omitted and the entire space within the sheath filled with the granular material, a more etficient heater would result. However, the disposition of the resistor conductor in cartridge heaters is such that a preformed, rigid core must be used to support the conductor during its assembly with the sheath and during filling of the latter with the granular material.

While the present invention does not omit the core in cartridge heaters, it does permit a drastic reduction in mass thereof and this not only reduces core costs, it also improves heater efliciency since more of ther mass within the sheath consists of granular material and less of such mass consist of the preformed core.

These and other advantages of the present invention will readily become apparent from a study of the following description and from the appended drawings.

Description of drawings In the drawings accompanying this specification and forming a part of this application there is shown, for

purpose of illustration, an embodiment which the invention may assume, and in these drawings:

FIG. 1 is a side elevational view of an electric resistance heater embodying the present invention,

FIG. 2 is an enlarged sectional view generally corresponding to the line 2-2 of FIG. 1,

FIG. 3 is an enlarged fragmentary elevational view of an end of the resistor conductor along with its terminal conductor pin,

FIG. 4 is an enlarged elevational view of a resistor conductor assembled with its core prior to disposition of the assembly within its tubular sheath.

FIGS. 5 and 6 are respective end elevational views of the subassembly seen in FIG. 4,

FIG. 7 is an exploded perspective view of the core seen in FIG. 4, and

3,512,114 Patented May 12, 1970 Detailed description With reference to FIGS. 1 and 2 wherein a completed electric resistance heater is shown, such heater comprises a tubular metallic sheath 10 in which a resistor conductor 11 is disposed. The resistor conductor has terminal conductor portions 12 which extend in spaced, side-byside relation outwardly of one sheath end for connection to a source of electrical energy.

The resistor conductor is supported within the sheath 10 by a preformed, rigid dielectric core 13 and such sheath is filled with highly compacted electric-insulating, heatconductive refractory material such as powdered magnesium oxide 14. Although not shown, the sheath end adjacent the terminal conductors 12 may be closed by a suitable plug through which the terminal conductors pass while the opposite end of the sheath may be closed by a suitable plug such as a metal wall which could be welded to the sheath, crimped therein, or even formed integrally therewith.

As viewed in FIG. 3, the fragmentarily shown resistor conductor is of the usual type in which a ressitor wire is in the form of a helical coil. Welded or otherwise mechanically and electrically secured to the ends of the resistor wire coil are respective terminal conductor pins 12 previously mentioned. Although only one end of the coiled resistor 11 is shown in FIG. 3, it is to be understood that its oppoiste end is preferably identical to that illustrated. Each terminal conductor pin 12 is preferably provided with an annular enlargement, or shoulder 12.1 intermediate its ends for a purpose later to appear.

With reference to FIG. 4, resistor 11 is adapted to be supported by the core 13 which is herein shown formed of an end portion 15, an oppoosite end portion 16, and an intermediate spacer portion 17. Each of the

core portions

15, 16 and 17 is formed of a rigid, dielectric, heat-resistant material such as, for example, powdered magnesium oxide mixed with a suitable binder and cured to a solid mass. The

core end portions

15, 16 are preferably of a transverse size to closely fit within the sheath 10 while the transverse size of the core intermediate portion is much smaller, and indeed, need only be large enough to possess the necessary strength to withstand normal handling during the assembly operation.

As herein shown, and as best seen in FIG. 7, the core intermediate portion may be square in cross-section and the adjoining faces of the

core end portions

15, 16 may be provided with respective centrally located square recesses 1 8 for closely receiving respective end of the core intermediate portion. For a reason to appear, the end of the core intermediate portion adjacent the core end portion 16 will be transversely slotted at 19.

As best seen in FIG. 7, core end portion vided with axially extending,

peripheral grooves

20, 21, 22 and 23 which are evenly spaced circumferentially of the core portion. Thus, grooves 20, 22 are in opposed relation with each other as are the

grooves

21, 23. At the end of core portion spaced from the core intermediate portion, arcuate of

grooves

21, 22 and 20, 23 respectively. Each of the grooves through 25 are of a width to receive the coiled resistor 11 therein and each is of such depth that the coiled resistor will be disposed well beneath the outer surface of the core end portion when the resistor is fully seated in respective grooves. Intermediate the grooves 20 through 23, relatively wide but shallow peripheral grooves 26 are provided for a purpose to appear.

15 is

progrooves

24, 25 connect the pairs Still referring to FIG. 7, the core portion 16 is prefera'bly provided with peripheral grooves similar to grooves 20 through 23 of core portion. Accordingly, the peripheral grooves of core portion 16 are identified with the same reference characters as before but with the sutfix a. Also in a manner similar to core portion 15, core portion 16 is provided with intermediate shallow grooves identified with the same reference character as before but with the sutfix a added.

It is important to note that with the

core portions

15, 16 assembled with the core intermediate portion 17, the peripheral grooves of the

core portions

15, 16 are in axial alignment with each other and such alignment is assured by the fit of the square core intermediate portion in the square recesses of the core end portions.

While the grooves 20 through 23 of core portion are of a width to receive the coiled resistor 11, the corresponding grooves a through 23a of core portion 16 are of a width to receive the terminal conductor pins 12. Accordingly, grooves 20a through 23a may, depending upon the transverse size of such pins, be of a somewhat different Width. Additionally, and although not shown, the face of core portion 16 remote from the core intermediate portion may be provided with shallow recesses centered at the base of the grooves 20 a through 23a for receiving the previously mentioned terminal conductor pin shoulders 12.1.

To assemble the resistor conductor 11 with the core 13, the resistor conductor with it attached terminal pins will be doubled back on itself to form a pair of legs 27, 28 connected by a bight portion 29 (see FIG. 8). The bight portion 29 will then be disposed in the core intermediate portion slot 19 with the legs 27, 28 extending along the core intermediate portion on opposite sides thereof. The core end portion 15 may now be assembled with the core intermediate portion and the resistor legs 27, 28 extended through respective slots 20, 22.

The resistor leg 27 may now be stretched longitudinally to place it under slight tension and then doubled over to form a leg 30 joined to the leg 27 by a bight portion 31. Such bight portion will be disposed in the arcuate slot of the core portion 15 and the leg then extended under slight tension to dispose its conductor pin in the slot 23a of the core portion 16, the latter having been previously assembled with the core intermediate portion 17, with the pin shoulder 12.1 abutting the adjoining end of the core portion 16 to retain the pin in the slot.

Similarly, the resistor leg 28 will be stretched longitudinally to place it under slight tension and then doubled over to form a leg .32 joined to the leg 28 by a bight portion 33. Bight portion 33 will be disposed in the core portion arcuate slot 24- and the leg 32 extended under slight tension to dispose its conductor pin in the slot 21a of the core portion 16 with its shoulder 12.1 abutting the end of the latter.

With the parts thus assembled as seen in FIG. 4, such assembly will 'be disposed in the sheath 10 with the terminal conductor pins 12 projecting from one sheath end. The sheath 10 may now be filled with the powdered magnesium oxide material from its terminal conductor end, such material readily gravitating past the

core portions

15, 16 via the

grooves

26, 26a respectively, to fill all voids within the sheath.

With the sheath filled, it may be swagged or otherwise transversely reduced to size to compact the powdered magnesium oxide to a rock-like hardness, with the core assembly, the resistor conductor and the adjoining terminal conductor pins embedded therein.

It will have been noted that while core portion 16 is provided with the four peripheral grooves 20a through 23a, only

grooves

21a and 23a have respective terminal pins 12 disposed therein while

grooves

20a, 22a are unused. Nevertheless, it is preferable to provide all four of such grooves in core portion 10, even though only two will be used, since by providing all four grooves, it is unnecessary to orient core portion 16 in any particular way with the core intermediate portion 17 other than to seat the end of the core intermediate portion in the core end portion recess 18.

In view of the foregoing it will be apparent to those skilled in the art that I have accomplished at least the principal object of my invention and it will also be apparent to those skilled in the art that the embodiment herein described may be variously changed and modified, without departing from the spirit of the invention, and that the invention is capable of uses and has advantages not herein specifically described; hence it will be appreciated that the herein disclosed embodiment is illustrative only, and that my invention is not limited thereto.

I claim:

1. A cartridge heater wherein an electric resistance wire is disposed in a metallic sheath and wherein such wire has terminal conductor portions at respective ends thereof for protrusion beyond an end of said sheath for connection to a source of electrical energy, the improvement comprising:

an elongated dielectric core disposed within and extending longitudinally of said sheath and having end portions proportioned to closely fit therewithin and an intermediate portion maintaining said end portions in spaced-apart relation, said end portions and said intermediate portion being separate pieces with the latter smaller in transverse size than the former and with facing sides of said core end portions being recessed to closely receive respective ends of said intermediate portion, said end portions being spanned by said heating wire and each core end portion having circumferentially spaced, longitudinally extending rectilinear slots for receiving said wire, said slots being of such depth that the wire portions are spaced radially inwardly of the peripheries of respective core end portions an amount to insure adequate dielectric clearance between such wire portions and the inner wall of said sheath, said heating wire having a first pair of legs extending from one core end portion to the other and disposed on diametrically sides of said intermediate portion, and a second pair of legs extending from said core other end portion to said core one end portion and disposed on opposite sides of said core intermediate portion between the legs of said first pair of legs, said heating wire legs being joined by bight portions for electrical continuity, the bight portion joining a pair of legs being anchored within a slot in said intermediate core portion adjacent said one core end portion, said heating wire being tensioned to retain core end portions and the core intermediate portion assembled, and compacted electric-insulating, heat-conducting refractory material within said sheath for insulating the heating wire and terminals from said metallic sheath. 2. A cartridge heater wherein a helically coiled resistance wire of U formation is disposed within a circular metallic sheath and wherein said wire has terminal conductor portions at its ends which extend outwardly of said sheath for connection to a source of electrical energy, the sheath containing compacted refractory material for electrically insulating said wire from said sheath and for conducting heat from said Wire to said sheath, the improvement comprising:

an elongated dielectric core within and extending longitudinally of said sheath and having end portions circular in transverse section and proportioned to closely fit therewithin and an intermediate portion maintaining said end portions in spaced relation, said end portions and said intermediate portion being separate pieces with the latter rectangular in crosssection and smaller in transverse size than the former, each of said end portions having a rectangular recess in a face thereof to closely and complementarily receive a respective end of said intermediate portion, an end of said intermediate portion having an inwardly extending groove to receive the bight of said U formed resistance wire prior to such end being inserted into the rectangular recess in the face of one of said end portions, the peripheral faces of each end portion having a plurality of longitudinal slots to pass lengths of the legs of said resistance wire, the legs lying along said intermediate portion and being stretched between said end portions, the resiliency of the coiled wire pressing the opposite ends of said intermediate portion into the rectangular recesses in said end portions. 3. The construction of claim 2 wherein each leg of said resistance Wire is stretched and passed through slots in and looped over the other end portion, then passed through other slots in said other end portion and doubled back and passed through other slots in and looped over said one end portion and disposed in respective grooves in that face thereof opposite the rectangularly recessed face, and then returned through other slots in said one end portion and overlying said intermediate portion, all out of electrical interengagement with adjacent parts of said resistance wire, said terminal conductor portions passing through other slots in said other end portion and being connected to the latter.

References Cited UNITED STATES PATENTS FOREIGN PATENTS Switzerland. Great Britain.

VOLODYMYR Y. MAYEWSKY, Primary Examiner U.S. Cl. X.R.