US3813771A

US3813771A - Method of producing electrical resistance heaters, and the improved heater products

Info

Publication number: US3813771A
Application number: US00376103A
Authority: US
Inventors: T Skogland
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-07-02
Filing date: 1973-07-02
Publication date: 1974-06-04
Anticipated expiration: 1991-06-04
Also published as: CA1020732A

Abstract

This disclosure relates to a method of making an electrical heating unit comprising a concentric assembly of a helical wire electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath. The method comprises means for controlling the longitudinal expansion of the helix of the wire heating element and the uniformity of the helical pattern of the wire extending along the length of the heating unit. The disclosure also includes the improved products of the method which have more uniform heating capacities. This disclosure is especially advantageous and effective in continuous manufacturing systems for the formation and assembly of electrical heating units in extended uninterrupted lengths.

Description

it 11 1 [11] 3,813,771 Sltoglantl June 4, 1974 [54} METHOD or PRODUCING ELECTRICAL RESISTANCE HEATERS, AND THE IMPROVED HEATER PRODUCTS Inventor: Tholrbjorn Skogland, Shelbyville,

Assignee: General Electric Company,

Indianapolis, 1nd.

Filed: v July 2, 1973 Appl. No.: 376,103

US. Cl 29/615, 29/423, 29/611, 338/238, 338/267 llnt. Cl H0lc 15/04, H01c 17/00 Field of Search 29/615, 614, 613, 611, 29/423; 338/203, 238, 267, 299

References Cited UNITED STATES PATENTS Desloge et al. 29/615 FOREIGN PATENTS OR APPLICATIONS 652,051 11/1962 Canada 29/614 Primary Examiner-Charles W. Lanham Assistant ExaminerV. A. DiPalma [57] ABSTRACT This disclosure relates to a method of making an electrical heating unit comprising a concentric assembly of a helical wire electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath. The method comprises means for controlling the longitudinal expansion of the helix of the wire heating element and the uniformity of the helical pattern of the wire extending along the length of the heating unit. The disclosure also includes the improved products of the method which have more uniform heating capacities. This disclosure is especially advantageous and effective in continuous manufacturing systems for the formation and assembly of electrical heating units in extended uninterrupted lengths.

15 Claims, 4 Drawing Figures METHOD OF PRODUCKNG ELECTRllCAL RESISTANCE HEATERS, AND THE IMPROVED HEATER PRODUCTS BACKGROUND OF THE INVENTION The handling of typical helical or other sinuous shaped electrical resistance wire heating elements, and in particular their assembly within enclosed heater units, can be especially troublesome because of the typ ically very low resistance to longitudinal expansion and lack of resiliency of the helical or sinuous configurations of high resistance materials for such heating elements. This shortcoming of the heating element configuration and compositions is particularly evident when installing a helical or sinuous resistance heating element within a tube-like enclosing sheath, and also upon filling the interior of the enclosing sheath about the heating element with a particulate insulating material in the assembly of heater units. Moreover the very low resistance to uncontrollable distension of the heating element configuration renders it difficult to produce typical heating units with the helical heating element contained within an elongated sheath and extended therein the length of the unit in a substantially uniform pattern or concentration, and in turn of uniform heat distribution capabilities.

Prior efforts to overcome the difficulties of installing helical or sinuous electrical resistance wire heating elements in the manufacture'of typical heating units have resulted in complex and costly means and procedures,

for instance the use of periodic heater element supports in cooperation with reduced portions in the sheath size such as advocated in US. Pat. No. 1,9l 1,063.

Moreover, the prior remedies such as proposed by US. Pat. No. 1,911,063, are not suitable or practical for use in continuous production systems in the uninterrupted formation and assembly of typical heater units in continuous lengths.

SUMMARY OF THE INVENTION This invention comprises a new method of manufacturing electrical heating units comprising a concentric assembly of an electrical conducting resistance heating element or wire in the form ofa helix or other sinuous configuration, embedded in particulate insulating material and enclosed within an elongated sheath, wherein the longitudinal expansion of the helix or other sinuous configuration, and also the uniformity of extension of the helix or other sinuous pattern of the heating element within the heater product is controlled. The invention also includes the improved products of the method.

The invention comprises the application of a filament or thread-like stop member to regulate and restrain the lengthwise expansion of the helix or sinuous configuration of the heating element during manufacture of the heating unit assembly. The restraining stop member is therafter destroyed or effectively eliminated by the conventional swaging operation which permit the helical or sinuous pattern of the element to extend itself substantially uniformly and approximately commenserate in degree with the elongation of the enclosing sheath or overall assembly of the heating unit due to the swaging.

In the practice of this invention the filament-like stop member is secured to at least the leading end of the helical heating element which is to be first introduced and passed into an enclosing sheath during assembly. Thus, when moving the heating element within the confines of the sheath, the longitudinal expansion of its configuration can then be controlled by restraining its extension to a substantially uniform expansion of any predetermined or desired length by means of the stop member.

Preferably the stop member is secured at several predetermined intervals along a considerable length of helical heating element with each location of attachment defining a section of predetermined length. Alternatively, several individual stop members in sequence can be secured in series along the length of the helical heating element with each individual member spanning a section of predetermined length.

Also predetermined lengths of individual sections of the helical heating element can be connected in continuous series through intermediate terminals, with the stop member or members spanning the length of each section of the heating element and secured to the intermediate terminals which join each section of the heating element.

The conventional swaging operation which is employed in the manufacture of this type of electrical heating unit to consolidate the granular insulating material and product a reduction in the units cross-section with a corresponding extension of its length, causes multiple breaks along the length of the filamentary stop member. The breaking of the stop member releases the restraint upon the helical heating wire and permits it to extend itself substantially uniformly and in an amount approximately commensurate with the elongation of the enclosing sheath. The fractured remainants of the stop memberare not detrimental to the product in that they cause no discernable short circuiting or other degrading effects.

OBJECTS OF THE INVENTION A primary object of this invention is to provide an effective method of controlling the degree and uniformity of the longitudinal'expansion of a helical or other sinuous electrical resistance heating element or wire in the manufacture of electrical heating units comprising a concentric assembly of a helical or sinuous electrical heating element embedded in particulate insulating material and enclosed within an elongated sheath.

Another object of this invention is to provide means for regulating the longitudinal expansion of an electrical resistance heating element having a helical or other sinuous configuration, and for regulating the uniformity of its extension throughout the performance of continuous manufacturing processes for the production of extended uninterrupted lengths of electrical heating units comprising a concentric assembly of an electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath.

A further object of this invention is to produce improved electrical heating units having a heating elementor resistance wire therein of helical or other sinuous configuration which is extended in a substantially uniform pattern and thereby provides uniform heating along its length.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of a section of a consecutive series of helical electrical resistance heating elements or wires joined together with intermediate connecting terminal members;

FIG. 2 is a partially sectionalized view of the section of the heating element ofFIG. 1, showing a preferred arrangement of the filamentary stop member which is suitable for use in a continuous manufacturing systems, and the introduction of a leading end portion of the heating element into an enclosing sheath;

FIG. 3 is also a partially sectionalized view of the section and arrangement as in FIG. 2, showing the series of heating element and the intermediate connecting terminals members positioned generally concentrically within an enclosing sheath and embedded within particulate insulating material; and,

FIG. 4 shows a similar partially sectionalized view of the assembled product of FIG. 3 undergoing swaging whereby its cross-sectional diameter is reduced and its length extended, thereby causing multiple breakes in the filamentary stop member.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawing which illustratesa preferred embodiment of this invention, FIG. 1 shows a portion of a series of sinuous electrical resistance heating elements for the manufacture of electrical heating units, composed of alternating units ofa helical heating wire 12, 12', et seq., of any given length joined together in series through intermediate sleeve-like terminal members 14, 14', et seq.

As shown in FIG. 2, one or more

filamentary stop members

16, 16, et seq., and are affixed at 18, 18, et seq., such as by brazing or soldering, to the interior of each intermediate terminal member I4, l4 et seq.

The length ofa filamentary stop member 16, or a section thereof, is predetermined in relation to the designed length for a section of the helical configuration of the heating element 12. Thus the stop member will restrain or control the amount of longitudinal extension and the uniformity of the helix during the assembly of the heater unit which includes passing the helical heating wire into the elongated sheath 20, and the filling of the enclosing sheath with particulate insulating material about helix of the heating element contained therein. The subsequent swaging of the assembled unit breakes the stop member and releases its restraining effect upon the helix thereby permitting the helix to uniformly extend itself commensurate with the elongation of the assembled unit.

FIG. 2 shows a leading end portion 22 of electrical heating element 10 being introduced and passed into a typical sheath member 20 in assemblying the unit. Introduction of a leading end portion and extension of the electrical heating element 10 within the sheath member 20 may be effected by conventional means including pulling devices or supporting frames (not shown). FIG. 3 shows the heating element 10 positioned within the sheath 20 and the generally concentric arrangement of the assembly.

Particulate electrical insulating material 24 such as granular or powdered metal oxides, for example magnesium oxide or aluminum oxide, or silica, is introduced to substantially fill the space within sheath 20 and about the helical wire 12, as shown in FIG. 3. The filling of the sheath and embedding of the electrical heating element with the insulating granules serves to support and fix the position of the wire helix in relation to the assembly as well as electrically insulate the electrically conductive heating wire 12 from the surrounding sheath 20.

Following completion of the assembly, including introducing the helical heating wire 12 into the enclosing sheath 20 and filling the sheath and embedding the helical wire in particulate insulating material, all while rcstraining the longitudinal expansion of the wire helix with the stop member to any predetermined degree of extension and preserving the uniformity of its helical pattern, the assembly is subjected to a swaging operaton. Swaging is commonly achieved by passing the elongated sheath and its assembled contents of resistance wire and particulate insulation through two or more

size reducing rolls

26, 26 which progressively reduces the cross-sectional dimension of the assembly while extending its length, thereby consolidating and compressing the particulate insulating filler about the heating wire helix. The swaging of the assembly and its reduction in section and extension in length is illustrated in FIG. 4. The progression of the elongation or stretching along the length of the assembly due to the swaging produces a progressive multiple breaking of the filamentary stop member along its length such as shown in FIG. 4. This progressive sequential breaking of the stop member 16 releases its restraining effects in response to the elongation of the assemblage, and thereby enables the helical configuration of the heating wire to be extended substantially uniformly in length commensurate with the elongation of the enclosing sheath and its contents.

According to one embodiment ofthis invention, after completion of the steps of assembly, a continuous unit or long section thereof can be divided into several discrete units by cutting and separating the assembly at the predetermined locations of the intermediate terminal members 14, such as at broken lines CC in FIG. 4

This invention is especially useful in the manufacture of electrical heating units by means of continuous forming procedures wherein the enclosing sheath of the unit is progressively shaped from a strip of metal and the electrical resistance heating element and particulate insulating material are continuously introduced into the formed sheath. Such continuous manufacturing procedures for the production of electrical heating units in continuous sections of very long lengths are known in the prior art, such as shown in U.S. Pat. Nos. 1,127,281; 1,192,457; 2,808,492; and French Pat. No. 902,739.

It should be appreciated that the advantages provided by this invention can also be beneficial in the manufacture of conventional heating units in individual sections of relatively short length, such as of only a few feet. For instance the steps of this invention apply and are effective in substantially all systems of manufacture comprising passing a sinuous heating element into an enclosing sheath or tube and embedding it within particulate insulating material wherein any pulling or dragging force upon the sinuous member may tend to over extend or nonuniformly expand it.

Moreover, it should be understood that in its broader aspects this invention includes affixing the filamentary stop member to a portion of the leading end of a length of sinuous heating element to be first introduced into a sheath, and restraining the elongation of the sinuous configuration of the element with the stop member to whatever degree or relative rate of its extension is desired during its introduction into a sheath, the thereafter filling of the sheath with insulating material and compacting the same.

Although the invention has been described with reference to a preferred embodiment thereof, numerous modifications are possible and it is desired to cover all modifications falling within the spirit and scope of the invention.

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

l. A method of making an electrical heating unit comprising a concentric assembly of a sinuous wire electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath, comprising the steps of:

a. affixing a filamentary stop member to one end of a length of heating element having a sinuous configuration;

b. introducing the end of the heating element with the affixed stop member into an elongated sheath and extending the heating element with the stop member within the sheath while restraining the longitudinal expansion of the sinuous configuration of the element with the stop member;

c. substantially filling the elongated sheath with particulate insulating material and embedding said sinuous heating element therein while restaining the longitudinal expansion of the sinuous configuration of the element with the stop member; and,

d. swaging the resultant assembly of sinuous heating element embedded in the particulate insulating material and enclosed within the elongated sheath whereby the cross-section of the assembly is reduced and its length is extended, and thereby breaking the filamentary stop member and permitting thesubstantially uniform extension of the sinuous configuration of the heating element by an amount approximately commensurate with the elongation of the enclosing sheath.

2. A method of making an electrical heating unit comprising a concentric assembly ofa helical wire electrical resistance heating element embedded in particu late insulating material and enclosed within an elongated sheath, comprising the steps of:

a. affixing each end of a predetermined length of a filament stop member to corresponding ends of a predetermined length of a helical heating element.

. swaging the resultant assembly of helical heating element embedded in the particulate insulating material and enclosed within the elongated sheath whereby the cross-section of the assembly is reduced and its length is extended. and thereby breaking the filamentary stop member and permit- 6 ting the substantially uniform extension of the helical heating element approximately commensurate with the elongation of the enclosing sheath.

3. The method of making an electrical heating unit of claim 2, wherein the filamentary stop member is affixed to the helical heating element at multiple intervals of predetermined length.

4. The method of making an electrical heating unit of claim 3, wherein the helical heating element comprises a series of discrete sections of predetermined length consecutively joined together by intermediate terminal members.

5. The method of making an electrical heating unit of claim 4, wherein the filamentary stop member is affixed to the intermediate terminal members connecting the predetermined lengths of the helical heating element.

6. The method of making an electrical unit of claim 2, wherein a series of discrete filamentary stop members in predetermined lengths are consecutively affixed at their ends to the helical heating element at intervals of predetermined length.

7. The method making an electrical heating unit of claim 6, wherein the helical heating element comprises a series of discrete sections of predetermined length consecutively joined together by intermediate terminal members.

8. The method of making an electrical heating unit of claim 7, wherein the ends of the discrete filamentary stop membersare affixed to the intermediate terminal members connecting the predetermined lengths of the helical heating element.

9. The method of making an electrical heating unit of claim 8, wherein the elongated sheath iscontinuously formed by progressive shaping from a strip of metal, and the helical heating element with affixed stop member and the particulate insulating material are continuously applied into the continuously formed sheath.

10. A method of making an electrical heating unit comprising a concentric assembly of a helical wire electrical resistance heating element embedded in particulate insulating material and enclosed within elongated sheath, comprising the steps of:

a. continuously forming an elongated sheath;

b. affixing the ends ofa predetermined, length ofa filamentary stop member to a helical heating wire at locations thereon defining a predetermined length;

c. continuously passing the helical heating wire with the affixed stop member into the elongated sheath and substantially filling the elongated sheath with particulate insulating material and embedding said helical heating wire enclosed therein while restaining longitudinal expansion of the helix of the wire with the stop member; and,

d. continuously swaging the resulting assembly of helical heating wire embedded in the particulate insulating material and enclosed within the elongated sheath whereby the cross-section of the assembly is reduced and its length is extended, and thereby breaking the filamentary stop member and permitting the substantially uniform extension of the helix of the wire by an amount approximately commensurate with the elongation of the enclosing sheath.

11. The continuous method of making an electrical heating unit of claim 10, wherein the filamentary stop member is affixed to the helical heating wire at a plurality of intervals of predetermined length.

member comprises a series of discrete filamentary stop members in predetermined lengths with each consecutively affixed at its ends to a intermediate terminal member connecting the predetermined lengths of the helical heating wire.

15. An electrical heating unit comprising a concentric assembly of a sinuous wire electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath, consisting of the product of claim 1.

Claims

1. A method of making an electrical heating unit comprising a concentric assembly of a sinuous wire electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath, comprising the steps of: a. affixing a filamentary stop member to one end of a length of heating element having a sinuous configuration; b. introducing the end of the heating element with the affixed stop member into an elongated sheath and extending the heating element with the stop member within the sheath while restraining the longitudinal expansion of the sinuous configuration of the element with the stop member; c. substantially filling the elongated sheath with particulate insulating material and embedding said sinuous heating element therein while restaining the longitudinal expansion of the sinuOus configuration of the element with the stop member; and, d. swaging the resultant assembly of sinuous heating element embedded in the particulate insulating material and enclosed within the elongated sheath whereby the cross-section of the assembly is reduced and its length is extended, and thereby breaking the filamentary stop member and permitting the substantially uniform extension of the sinuous configuration of the heating element by an amount approximately commensurate with the elongation of the enclosing sheath.

2. A method of making an electrical heating unit comprising a concentric assembly of a helical wire electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath, comprising the steps of: a. affixing each end of a predetermined length of a filament stop member to corresponding ends of a predetermined length of a helical heating element. b. passing the predetermined length of the helical heating element with the affixed stop member into an elongated sheath, and substantially filling the elongated sheath with particulate insulating material and embedding the said helical wire therein while restraining the longitudinal expansion of the helical heating element with the stop member; and, c. swaging the resultant assembly of helical heating element embedded in the particulate insulating material and enclosed within the elongated sheath whereby the cross-section of the assembly is reduced and its length is extended, and thereby breaking the filamentary stop member and permitting the substantially uniform extension of the helical heating element approximately commensurate with the elongation of the enclosing sheath.

8. The method of making an electrical heating unit of claim 7, wherein the ends of the discrete filamentary stop members are affixed to the intermediate terminal members connecting the predetermined lengths of the helical heating element.

9. The method of making an electrical heating unit of claim 8, wherein the elongated sheath is continuously formed by progressive shaping from a strip of metal, and the helical heating element with affixed stop member and the particulate insulating material are continuously applied into the continuously formed sheath.

10. A method of making an electrical heating unit comprising a concentric assembly of a helical wire electrical resistance heating element embedded in particulate insulating material and enclosed within elongated sheath, comprising the steps of: a. continuously forming an elongated sheath; b. affixing the ends of a predetermined length of a filamentary stop member to a helical heating wire at locations thereon defining a predetermined length; c. continuously passing the helical heating wire with the affixed stop member into the elongated sheath and substantially filling the elongated sheath with particulate insulatiNg material and embedding said helical heating wire enclosed therein while restaining longitudinal expansion of the helix of the wire with the stop member; and, d. continuously swaging the resulting assembly of helical heating wire embedded in the particulate insulating material and enclosed within the elongated sheath whereby the cross-section of the assembly is reduced and its length is extended, and thereby breaking the filamentary stop member and permitting the substantially uniform extension of the helix of the wire by an amount approximately commensurate with the elongation of the enclosing sheath.

12. The continuous method of making an electrical heating unit of claim 11, wherein the helical heating wire comprises a series of discrete sections of predetermined length consecutively joined together by intermediate terminal members.

13. The continuous method of making an electrical heating unit of claim 12, wherein the filamentary stop member is affixed to the intermediate terminal members connecting the predetermined lengths of the helical wire.

14. The continuous method of making an electrical heating unit of claim 13, wherein the filamentary stop member comprises a series of discrete filamentary stop members in predetermined lengths with each consecutively affixed at its ends to a intermediate terminal member connecting the predetermined lengths of the helical heating wire.