US3678249A

US3678249A - Heater element

Info

Publication number: US3678249A
Application number: US82654A
Authority: US
Inventors: Thomas H Lennox
Original assignee: ARC O VEC Inc
Current assignee: ARC O VEC Inc
Priority date: 1970-10-21
Filing date: 1970-10-21
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18

Abstract

An electrical resistance heater is disclosed in an elongated tubular form wherein at least one resistance heating unit is coiled within a tubular housing. The resistance heating units include a coiled metallic sheath containing an internally coiled resistance wire that is fixed in the sheath by a mass of magnesium oxide. The heating units are similarly fixed in the tubular housing. Heating units coiled with a variable pitch and plural heating units of different characteristics are disclosed to accomplish different heat zones within the apparatus.

Description

United States Patent [15] 3,678,249 Lennox 1451 July 18, 1972 HEATERELEMENT 2,725,457 11/1955 Norton ..338/240x 1 1 1mm m Zilfil 52323 $83377.:11:..............::::::5i3i [73] Assigneez Arc-O-Vec, lnc., Stanton, Calif. FOREIGNPAEMSORAPPUCAfiONS [22] Film M21397 474,783 10/1952 ltaly ..219/243 [2]] App]. No.: 82,654

52 11.5. c1. ..219/544, 219/523, 219/534, 338/239, 338/240 1 s 1 1111. c1. .110511 3/44, H05b 3/50 58 1 16111 1115mm ..-....219/523, 534, 544, 552-553; 338/2311-243, 218, 328

[56] I Relerencee Cited UNITED STATES PATENTS 3,340,382 9/1967 Lennox ..219/544 1,350,910 8/1920 Abbott.. ..338/243 2,371,696 3/1945 Levitt 219/523 x 1,451,880 4/1923 Lightfoot ..338/240 x Primary Examiner-Volodyrnyr Y. Mayewsky Attorney-Nilsson, Robbins, Wills & Berliner [57 ABSTRACT An electrical resistance heater is disclosed in an elongated tubular form wherein at least one resistance heating unit is coiled within a tubular housing. The resistance heating units include a coiled metallic sheath containing an intemally coiled resistance wire that is fixed in the sheath by a mass of magnesium oxide. The heating units are similarly fixed in the tubular housing. Heating units coiled with a variable pitch and plural heating units of diflerent characteristics are disclosed to accomplish difi'erent heat zones within the apparatus.

llClaims,3Drawingl1gures HEATER ELEMENT BACKGROUND-AND SUMMARY OF THE INVENTION In recent years a considerable demand has developed for electrical-resistance heating elements which are capable of attaining, and performing at, relatively high temperatures. One such form of a heating element is shown and described in U. S. Pat. No. 3,305,820 entitled RESISTANCE HEATING ELE- MENT, issued Feb. 21, 1967 to the present inventor.

Generally, these structures include a length of resistance heating wire variously housed in an elongate metallic tube and separated from the walls of the tube by a mass of electrically insulating material. Specifically, for example masses of magnesium oxide (MgO) have been employed. That material'is effective to solidify the heating element as awhole, and additionally serves to isolate the electrical resistance wire from oxidizing gases. Furthermore, magnesium oxide tends to absorb moisture which might otherwise reach the resistance element with detrimental effects.

- The attainment of increasingly higher temperatures by increased output from heating elements has been attained by various structural improvements as disclosed in U. 8. Pat. 3,340,382 entitled MULTl-CELL ELECTRlCAL HEATER issued Sept. 5,- 1967 to the inventor herein. Although resistance heatingelements ofthe prior art, including those disclosed in the above-referenced patents, have been manufactured and used with considerable success, a need continues to exist for heaters that are capable of attaining still-higher temperatures; Another desired characteristic for such heating elements is the capability to provide different heat zones along thelength'of a heater, in accordance with the particular design. Furthennore, improved structural forms to facilitate economical manufacture, as usual, is an important consideration with regard to heating elements of the type here being considered. 3' a 1 a in general, the present invention enables the certain improvem'en'ts considered above as a result of a structural form that includes a coiledresistance wire contained within an elongate metal sheath, which is in turn coiled within an elongated housing tube. All voids within the structure are filled with pulverized electrically-insulating mineral, e.,g., magnesium oxide, whichis compacted to provide a solid and durable heating element. J

a BRIEF DESCRIPTION or THE oaxwmos In the drawing which constitutes a part of this specification,

I an exemplary, embodiment demonstrating various objectives and features hereof is set forth as follows:

2 FlGbl. is asectioned trimetric view of a heating element constructed inaccordance with the present invention;

H0. 2 is a vertical sectional view through another form of heating element-constructed in accordance with the present invention; and

FIG. 3 is a vertical sectional view of still another form of heating element constructed in accordance withthe present invention.

DESCRIPTION OF THE lLLUSTRATlV E EMBODIMENT Referring initially to FIG; 1, an embodiment of the present invention is disclosed in the conventional elongated tubular form and provided with cold terminal conductors emerging from the ends for connection to a source of electrical energy.

(not shown). I I

The element is housed in an elongated metallic tube 10 which may-for example comprise stainless steel, and in-some forms, a dual-wall structure may be employed as disclosed in the above-referenced U.S. Pat. No. 3,305,820. The ends of the tube 10 are closed by flat circular disks l2 and 14, which may be welded or otherwise affixed to the tube 10. Extending between the disks l2 and 14, within the tube 10, is a coiled heating unit 16, the ends 17 of which are straight and extend concentrically throughcentral bores 18 in the end disks l2 and I4.

Theheating unit 16 includes a finely coiled length of resistance wire 20 which is contained within an elongated sheath 22 that is in turn coiled within the cylindrical tube). The sheath 22 may be of stainless steel or nickel alloy. The resistance wire 20 (of various alloys) in its coiled configuration is fixed in spaced relationship within the sheath 22 by a mass 24 of compacted magnesium oxide.

The doubly-coiled resistance wire 20 extends through the coiled sheath 22 to a location contiguous the

disks

12 and 14, at which the resistance wire 20 is connected to

lead wires

26 and 28 to provide low-resistance cold terminal couplings. These may be welded connections. The heating unit 16 is held in position within the tube 10 by a mass 30 of heat-transmissive electrically-insulating inorganic material, e.g., fine particle mineral, as magnesium oxide. Thus a solid compact structure is accomplished. a

In the manufacture of an element as shown in FIG. 1, the heating unit may be manufactured as a separate sub-assembly. Specifically, for example, the coiled resistance wire 20 may be fixed centrally within a straight length of the sheath 22 with the

lead wires

26 and 28 connected and extending from the sheath 22. With the wire 20 held spaced apart from the interior walls of the straight sheath, the sheath may then be filled with magnesium oxide in a powdered form. The insulating powder may then be somewhat compacted by agitation. Next, the elongated straight sheath containing the coiled wire, may be coiled, as on a mandrel, which process may include swaging to reduce the diameter of the sheath 22 slightly, thereby further compacting the magnesium oxide powder.

In a final assembly the somewhat cylindrical coil of the heating unit 16 may be concentrically aligned within the tube 10 which is then filled with magnesium oxide powder to be subsequently compacted into the mass 24. Finally, the

disks

12 and 14 areaffixed to the tube 10, as bewelding, to complete the element. Generally,.electrical contact is provided between the

disks

12 and 14 and the sheath 22 for grounding the sheath.

In using the element hereof, as shown in FIG. 1,-any of a variety of circuits and connective configurationsmay be utilized, some of which are disclosed in the above-referenced U.S. Pat. No. 3,340,382. With a source of electrical energy providing current through the resistance wire 20, an incandescent state is attained by wire 20 providing a substantial quantity of heat at the external surface of the tube 10. The coiled configuration of the heating unit 16 affords a heating element which is economical to manufacture, enables effective zone-heating, provides good heat-transfer characteristics, and leaves the central core space of the heating element available for connections and sensors as described'below. lt is to be noted that although the heating unit 16 is shown coiled into a helical form, the coil may take various physical configurations including lapped loops and reversing turns. in that regard, the specific form of the heating unit 10 is dictated to some extent by the application of the heating element.

Referring now to FIG. 2, another embodiment of the present invention is disclosed incorporating some of the additional structural features as suggested above. Generally, the structure of FIG. 2 includes a junction box 32 which is integral with an elongated tubular heating section 34. The tubular section 34 contains a bifiler resistance heating unit 36. Somewhat similar to the structure of the heating unit 16 (FIG. 1) as previously described. The unit 36 includes a doubly coiled resistance wire 38 that is supported within a coiled, elongated sheath 40 by a mass 42 of compacted magnesium oxide. The bifiler coil form of the unit 36 provides both ends 44 and 46 of the resistance unit 36 at the end of the section 34 that is adjacent to the junction box 32. That is, the resistance unit 36 is a single length, formed with its

ends

44 and 46 adjacent and extending in alternate interleaved loops of helical turns, to a lower end 47 (as shown).

sistance wire 38 terminates at connection points with

lead conductors

48 and 50, which are in turn affixed to terminals 52 which define threaded bores for receiving screws 54 for mechanical connection to power leads 56. Metallic connections, as by welding may be provided between the wire 38, the

lead conductors

48 and 50, and the terminals 52.

The junction box 32 may contain a solidified mass 58 of any of a variety of non-conductive materials including various heat-durable ceramics and cementitious compounds. The

- mass 58 abuts another mass 60 which fills the void in the tubular section 34 that is not occupied by the heating unit 36 and a pair of

sensors

62 and 64. Leads 66 and 68 extend from the

sensors

66 and 68 to the junction box 32 and terminals 63.

The end of the heating element that is remote from the junction box 32, includes an end cap 70 which may be welded or otherwise affixed to close the tubular section 34. It is to be noted that the metallic sheath 40 firmly contacts the cap 70 so as to provide a grounding connection between the sheath 40 and the external housing.

In the structure hereof as shown in FIG. 2, different heatproducing zones are provided by varying the taper of the heating unit 36. Specifically, in a central zone, generally indicated at 72, the heat-producing capacity is somewhat less than the capacity of

adjacent zones

74 and 76. This heat zone relationship is established by changed pitch or spacing relationship between the individual turns in the coiled configuration of the heating unit 36. While-the individual turns are contiguous in

zones

74 and 76, the pitch of the unit through the zone 72 provides the turns spaced apart. That is, approximately one-half as much resistance wire is provided (per unit of length) in zone 72 as exists in

zones

74 and 76. Consequently, the heat produced from the zone 72 is a fraction of that produced from the

zones

74 and 76. Thus, in accordance herewith, effective zone control may be economically provided simply by varying the taper or pitch of the turns, i.e., helical spacing, in the coiled heating unit 36.

Another feature of the present invention as illustrated in the structure of FIG. 2 resides in the provision of the

sensors

62 and 64 within the central core of the heating unit 36. The

sensors

62 and 64 may take the form of thermocouples or any of a variety of other well known sensors. However, the significant consideration lies in the fact that an effective space for such sensors is simply and easily provided by the structure of the present invention.

In the manufacture of the embodiment hereof as shown in FIG. 2, the primary housing including the junction box 32 and the tubular section 34 may be formed of stainless steel or other corrosion-resistant metals or alloys by using any of a variety of well known metal-shaping processes. Again, the resistance unit 36 may be formed as a sub-assembly by initially loading a linear section of tubular sheath with the resistance wire 38 and the pulverized inorganic electrically insulating material, then subsequently developing the coil while reducing the diameter of the sheath to compact the pulverized material, e.g., MgO. The variable pitch of the unit 36 may be accomplished during the formative process or subsequently in accordance with well known coil-winding techniques.

Upon completion of the heating element 36, the junction connections may be affixed and the sub-assembly placed in the integral heater section 34 along with the

sensors

62 and 64. With the cap 70 welded in place, the masses 58 and 60 may be formed and compacted to provide a solid, safe and economical electrical element.

Considering still another embodiment of the present invention which may be utilized for the development of different heating zones, reference will now be had to FIG. 3. An elongate metallic outer tube is again provided as a major housing structure. As indicated with reference to previously described embodiment, the tube 80 may comprise stainless steel or other corrosion-resistant material which has good heat transmissivity. The tube 80 is closed at its lower end by a cap 82 (of similar material) which may be welded or otherwise affixed in position. The interior of the tube 80 is solid, being filled by three linearly aligned

heating units

84, 86 and 88 and an enclosing mass 90 of heat-transmissive electrically-insulating material. As previously explained, the insulating mass may well take the form of an inorganic powder, e.g., magnesium oxide.

At the upper end of the tube 80 a header 92 is provided affording connections from the

heating units

84, 86 and 88 to plug pins 94. Specifically, the terminations of each of the heating units are similar and include cold connection leads 96 extending from the six ends 96 of the resistance wires, through a potted header 100 to define a set of connection pins 94. The header 100 may be cement or ceramic as well known.

The lower heating unit 88 in the combination of FIG. 3 includes a bifiler-wound portion 102 and

straight lengths

104 and 106. The

lengths

104 and 106 extend from the coiled portion 102 through the interior of

heating units

84 and 86 to the header structure 92. Somewhat similarly, the heating unit 86 includes a coil section 108 and

lengths

110 and 112 which extend through the heating unit 84 to the header structure 92. The upper heating unit 84 is primarily a bifilar coil form.

The structure of FIG. 3 enables a variety of characteristics or energizing patterns for the

independent heating units

84, 86 and 88 whereby to accomplish

distinct heating zones

114, 116 and 118. For example, by utilizing different types of wire as the

resistance wires

120, 122 and 124 in the

heating units

84, 86 and 88 respectively, distinctly different characteristics for the

heating zones

114, 116 and 118 may be accomplished. Of course, other structural parameters may also be varied, or different energization may be used to accomplish distinct heat zones.

In the production of the embodiment as shown in FIG. 3, the

individual heating units

84, 86 and 88 may be independently produced as separate sub-assemblies as described above. Again, as with the heating units of other embodiments herein, the

heating units

84, 86 and 88 include a coiled length of resistance wire contained within a coiled length of sheath and spaced therefrom by a mass of compacted electrically-insulating mineral. However, the

lower units

86 and 88 also include substantial lengths, e.g., length 104, to pass through another unit. The completed subassemblies constituting the

heating units

84, 86 and 88 may thus be inter-related and placed within the tube 80 which may then be filled with insulating powder, e.g. magnesium oxide. The powder is then compacted after which the header structure 92 may be completed.

It is to be noted that the basic configuration in accordance with the present invention facilitates the passage of lengths of the heating unit, e.g., lengths 110, through the interior of other heating units to a terminal header. Furthennore, as exemplified herein, instrumentation may also be provided within heating units hereof without difficulties of alignment or positioning. Thus, the structure may be economically manufactured while obtaining various advantages as considered above. Of course, various departures from the embodiment disclosed herein will be readily apparent to those skilled in the art and accordingly, the scope hereof is provided by the claims as set forth below.

What is claimed is:

1. An electric heater, comprising:

an elongated metallic outer housing tube means having one end closed;

a plurality of resistance heating units helically coiled in axial alignment within said outer tube means and each including an elongated coiled metallic sheath means, a resistance wire coiled within said sheath means, and a first non-conductive inorganic mass disposed within said sheath means to support said resistance wire within said metallic sheath means, the resistor wire of each of said heating units having terminals extending through the open end of the housing tube means for connecting to appropriate sources of electrical energy; and

a second non-conductive inorganic mass disposed within said outer tube means to support said resistance heating unit coiled within said outer tube means.

2. An electric heater according to Claim 1 wherein said resistance heating units are coiled to define differently spaced helical forms to provide a variation in heat along the length of said heater.

3; An electric heater according to Claim 1 wherein said resistance heating unit comprises a bifiler helical configuration.

4. An electric heater according to Claim 1 wherein said inorganic masses comprise mineral in fine particle form.

5. An electric heater according to Claim 1 wherein said inorganic masses comprise compacted particles of magnesium oxide.

6. An electrical heater according to claim 1 further including sensor means fixed within at least one of said resistance heating units.

7. An electric heater accordingto claim 1 wherein at least one of said resistance heating units comprises a bifilar helical configurationcoiled within said outer tube means.

8. An electric heater according to claim 1 wherein at least one of said resistance heating units further includes linear lengths extending through another of said resistance heating units.

9. An electric heater according to claim 1 wherein said inorganic masses each comprise particles of magnesium oxide compacted into a mass.

10. An electric heater according to claim 1 wherein said terminals comprise cold connection leads extending through a non-conductive mass contiguous said open end of the housing tube.

11. An electric heater according to claim 1 wherein said sheath means comprises material selected from the metals stainless steel and nickel alloys.

l t t I! I

Claims

1. An electric heater, comprising: an elongated metallic outer housing tube means having one end closed; a plurality of resistance heating units helically coiled in axial alignment within said outer tube means and each including an elongated coiled metallic sheath means, a resistance wire coiled within said sheath means, and a first non-conductive inorganic mass disposed within said sheath means to support said resistance wire within said metallic sheath means, the resistor wire of each of said heating units having terminals extending through the open end of the housing tube means for connecting to appropriate sources of electrical energy; and a second non-conductive inorganic mass disposed within said outer tube means to support said resistance heating unit coiled within said outer tube means.

3. An electric heater according to Claim 1 wherein said resistance heating unit comprises a bifiler helical configuration.

7. An electric heater according to claim 1 wherein at least one of said resistance heating units comprises a bifilar helical configuration coiled within said outer tube means.