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US2494333A - Concentric coil sheath heating unit - Google Patents

Concentric coil sheath heating unit Download PDF

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Publication number
US2494333A
US2494333A US3197848A US2494333A US 2494333 A US2494333 A US 2494333A US 3197848 A US3197848 A US 3197848A US 2494333 A US2494333 A US 2494333A
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Prior art keywords
sheath
terminal
resistance
concentric
outer
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Loretta M Daly
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General Electric Co
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General Electric Co
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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B3/00Ohmic-resistance heating
    • H05B3/40Heating elements having the shape of rods or tubes
    • H05B3/42Heating elements having the shape of rods or tubes non-flexible
    • H05B3/48Heating elements having the shape of rods or tubes non-flexible heating conductor embedded in insulating material

Description

Jan. l0, 1950 L. M. DALY coNcEN'rRIc con. sHEA'm HEATING UNIT Filed June 9, 1948 Inventor Loretta M. Daly,

by m 10m He* Attorney.

UNITED STATE Patented. l0, i950 2,494,333 CONCENTRIC COIL SHEATH HEATING UNIT Loretta M. Daly, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application June 9, 1948, Serial No. 31,978

9 Claims. (Cl. 201-.67)

My invention relates to electric heating units, more particularly to electric heating units of the sheath wire type, and has for its object the provision of an improved heater of this character.

More specically, my invention relates to electric heating units of the sheath wire type in which concentric coils of equal or unequal resistance enclosed by the metallic outer sheath, are embedded in a powdered heat refractory insulating material which is compacted to a hard dense mass so that it may readily conduct heat from the coils to the sheath.

Heretofore in order to secure a high temperature output from a given length of heatentwo single coil metallic sheath units were placed side by side within a third sheath of oval cross-section and the resulting unit was subjected to a swaging process to compress the unit to a circular cross-section. The coils were then connected in series. In the swaging process, the two inner sheaths were distorted within the new conilguration, becoming two lobes filling the now circular outer sheath and in contact with each other along a diametric plane of the outer sheath.

Using this method, even though the two inner units were packed and swaged before lbeing placed within the outer sheath, the swaging of the outer sheath often resulted in decreased electrical clearances Within the inner units, so that they would break down under high potential test. Such faulty units could not be repaired and their scrapping caused high manufacturing losses.

My invention is less costly since the two inner sheaths used in the former method are eliminated. Units constructed by the former method were less eiiicient in operation since after swaging the two innersheaths did not completely fill the circular area within the outer sheath. Instead, it was found that definite voids or air spaces resuited between adjacent inner surfaces. These voids caused a heat transfer loss from the single coil units tothe sheath, increasing the coil temperature required to produce a given temperature of outer sheath. Also, my invention results in increased insulative clearance since for equal cross-section, the volume of the inner metallic sheaths of the former design has been replaced by insulation material.

In my invention a plurality of coils are mounted concentric with an outer sheath and suspended between stepped concentric insulated terminals using ceramic spacers between two adjacent coils as well as between the outer coil and the sheath. By vibrating powdered insulation into the end capped outer sheath, the insulation is caused to fill completely the voids in and between the coils and between the coils and the sheath. The ends of the sheath are capped with the terminal members fastened securely to the caps and the whole unit -is subjected to a diameter reducing process such as swaging. This reducing process serves to compact the insulation about the coils even more densely to effect a maximum heat transferability as well as maximum electrical insulation.

During the reduction process, the whole unit becomes elongated as well as reduced in outside diameter, and the encompassed coils are lengthened proportionately without changing the relative position of the coils and the sheath. Since the reduction process in my invention is a uniformly undistorted reduction in diameter, the possibility in the former method of diminution of insulative or electrical clearance within the inner sheaths due to distortion during the diameter reduction process, does not exit. The heat loss in the former method caused by voids within the outer sheath due to the use of inner sheaths is eliminated since in my invention, there are no inner sheaths. The same or greater value of electricai resistance, therefore, may be included in a unit of equal length and diameter without these limitations and disadvantages of the former method.

My invention is adapted for use as a cpmpact unit for the general purposes of sheath type heaters, or as an immersion or insertion type heater. In the general purpose heater, by using different resistances and providing a means for externally changing the connection between the coils, a selective heat feature is included in my invention allowing a choice of several overall heating values in one unit. Either immersion type or insert typeheaters are obtained by eliminating the connection at one end of the unit and, internally connecting the coils in series. Y

My invention will best be understood by reference to the accompanying drawing, in which Fig.

2 is a sectional view of a terminal filled with insulation and ready to be swaged. Fig. 1 is a sectional view of the complete heating-unit; Fig. 3 is a view of a terminal for a Iheater in'which two coils are series connected; Fig. 4 is an alternate construction of an immersion or insert type heater.

Referring to Fig. 2, one embodiment of my invention in which a sub-assembly of a terminal l member comprising two concentric terminals or conductors is shown, a metallic terminal rod I is inserted within a metallic tubular terminal 2 po- SitiQiled vertically with the inner terminal pro- 3 jecting at one end. The cup washers I and 4 position the two terminals concentrically. The voids are illled with powdered insulation material l through apertures provided in the upper cup washer 3 for this purpose. During the filling process the sub-assembly is continually vibrated to insure compact nlling of the voids between the terminals. The terminal members are cut back at both ends in stepped relation to provide connection surfaces. A second sub-assembly is formed by securing the coils 1 and 8 respectively between equal diameter surfaces of the two terminal members l. For securing such members,

welding is preferred to crimping to avoid danger of distortion of tubular terminals. Ceramic spacers (not shown) are mounted at intervals between the two coils to insure maintenance of their substantially concentric relative position during the subsequent insulation illling operation. The second sub-assembly of terminals and coils is mounted within the vertically disposed outer sheath 9 of the unit and held concentric with the sheath by means of end washers and cross pins (not shown), and ceramic spacers (not shown) suitably disposed between the outer coil and the sheath. Both sets of ceramic spacers are used to hold coils and sheath concentric while assembling in the outer sheath and during the following insulation filling operation. The spacers may break up and mingle with the insulation material during the subsequent diameter reduction proc ess. The unit is then vibratingly lled with pow dered insulation through apertures provided in the upper washer provided for the purpose and the whole unit is reduced in diameter to compact the insulation to a hard dense mass so the insulation will conduct heat readily from the resistance elements to the outer sheath. The outer sheath is cut away at each end to the desired length. The end washers used in the filling and reduction operation, are replaced by insulating washers In and terminal Wires Il are clamped tightly to the contact surfaces of the terminals by means of collars I2 with set screws I3 to tighten against the terminal sheath. Insulating washers i4 are slid over the ends of the terminal rods and suitable terminals i5 are attached to the rods.

When more than two concentric coils are desired, the voids of the concentric terminals are vibrationally filled simultaneously in a similar manner to that described above. The terminals are cut back at each end in stepped relation and the surfaces of corresponding diameter are connected respectively by the concentric resistance coils.

My invention allows several values of resistance to be obtained from the two coil units merely by changing the external connections. Either coil may be used individually or the unit may be used with the coils in series connection or in parallel connection. If two different values of coil resistance are used, the number of combinations is increased. In a three or more concentric coil unit, many values of unit resistance are available by the use of unequal individual coil resistances and shunt and series interconnections.

Fig. 3 is a view of a, one piece terminal for use where two coils are to be connected in series only.

Fig. 4 is a view of a two-coil immersion or insertion type heater with one piece terminal I6 for series connection betweenV coils. Cap I`1 completely covers the immersion end of the unit and is tightly attached to the outer sheath'around a recessed portion of the outer surface oi' the sheath to waterproof the unit.

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

1. An electric heating unit comprising a metallic sheath, a plurality of helical resistance elements of different diameters in said sheath extending lengthwise thereof in substantially concentric relation with each other, a compact mass of powdered heat conductive'electrical insulation material in said sheath embedding said resistance elements, a terminal member assembly extending into at least one end of said sheath and having its inner end embedded in said insulation material, said terminal member assembly comprising an outer tubular terminal and an inner terminal rod, electrical insulating material in said tubular terminal' securing said terminal rod in substantially concentric relation therewith, and electrical connections respectively between the inner ends of said terminals and said' resistance elements.

2. An electric heating unit comprising a metallic sheath, a plurality of substantially concentric helical resistance elements, a powdered heat conductive electrical insulation material, said resistance elements being embedded in the said insulation material within the sheath, said insulation material being compacted to a hard dense mass to insure that said mass conducts heat readily from the said resistance elements to the said sheath, and a terminal member in each end of the said sheath, each of said terminal members comprising electrically insulated substantially concentric terminals in each end of said sheath connected respectively to said concentric resistance elements, said terminalmembers protruding from each end of said sheath, and said terminals being cut back from their ends in stepped relation to form terminal surfaces for the connection of the said unit in an electric circuit.

3. An electric heating unit comprising a metallic outer sheath, a plurality of substantially concentric helical resistance elements and powdered heat conductive electrical insulation material,

said resistance elements being embedded in said insulation material, said insulation material being compacted to a hard dense mass to insure that said mass conducts heat readily from the said resistance elements to the sheath, and terminal members each comprising electrically insulated substantially concentric terminals secured respectively to the ends of said resistance elements, said terminal members projecting beyond said outer sheath to form terminals for the connection of the said unit in an electric circuit.

4. An electric heating unit comprising a metallic outer sheath, a plurality of substantially concentric helical resistance elements and powdered heat refractory insulation material, said resistance elements being embedded in the said insulation material, said insulation material being compacted to a hard dense mass within said sheath to insure that said mass conducts heat readily from the said resistance elements to the said sheath, and terminal members each comprising electrically insulated substantially concentric termlnals, said terminals being cut back yfrom each end in stepped relation to form connection contact surfaces, said terminals at their inner ends being secured respectively to ends of the said concentric resistance elements, said terminal members projecting beyond said outer 'sheath to form terminals for the connection oi.' 75 the said unit in an electric circuit.

5. An electric heating unit comprising va metallic outer sheath, two concentric helical resistance elements, powdered heat refractory electrical insulation material, said resistance elements being embedded in the said insulation material within the said sheath and said insulation material being compacted to a hard dense mass to insure that said mass conducts heat readily from the said resistance elements to the sheath, said unit having terminal members projecting beyond either end of the said outer sheath, one of said terminal members comprising a sub-assembly of electrically insulated concentric terminals, said concentric terminals being out back in stepped relation at their inner ends and respectively secured to the ends of the said concentric resistance elements, the outer ends of the said terminals` being cut back in stepped relation to form terminal contact surfaces forthe attachment of lead wires, the other of said terminal members being cylindrical and having its inner end secured to the one of said resistance elements of larger diameter, said other terminal having a cylindrical projection of smaller diameter to which is secured the other of said resistance elements, said other terminal member providing at its outer end a single terminal'for the attachment of the unit in an electric circuit.

6. An electric immersion heating unit comprising a metallic sheath, a plurality of concentric helical resistance elements, powdered heat refractory insulation material, said resistance elements being embedded in said insulation material within the said sheath, said resistance material being compacted to a hard dense mass to insure that said mass readily conducts heat from the said resistance elements to the sheath, a terminal member in one end of said sheath comprising a sub-assembly of electrically insulated concentric terminals, said terminals being out back from each end in stepped relation to form connection contact surfaces, and the said connection surfaces at the outer end of the said v terminal member forming terminals for the connection of the unit in an electric circuit, the said contact surfaces at the inner end of the said terminal member being respectively secured to the ends of the said concentric resistance elements the opposite end of the said resistance element of larger diameter being secured to a cylindrical terminal, said cylindrical terminal having a concentric cylindrical projection of smaller diameter to which is secured the inner of the said concentric resistance elements, said unit being provided with a cap completely enclosing the end of the unit and secured tightly to a recessed end portion of the outside surface of the said sheath to waterproof the unit.

7. A method of forming a concentric coil electric heating unit comprising a metallic outer sheath, a sub-assembly of concentric helical resistance elements and terminal members and compacted powdered heat refractory insulation, said resistance elements being embedded in the said powdered insulation material within the said sheath, said terminal members protruding from each end of the said sheath to provide terminals for connection of the said heating unit in an electric circuit, said method comprising forming a secondsub-assembly of each of said terminal members by vibratingly lling the voids between concentric terminals withthe said powdered refractory insulation material to insure that the relative positions of the said terminals be maintained during subsequent operations, cutting back tion to provide connection contact surfaces forming the said sub-assembly by suspending the said.-

concentric coils between the said terminal members and securing the ends of the coils respectively to the said concentric connection surfaces at the inner ends of the said terminal members, mounting the said sub-assembly concentrically within a metallic outer sheath with the terminal members projecting substantially equally at both ends of the said outer sheath, vibratingly filling the voids within the said outer sheath with said powdered refractory insulation material and, by means of a diameter reducing process applied to the said outer sheath, compressing the insulation to a hard compact mass so that the said mass may readily conduct heat from the said resistance elements to the said sheath.

8. A method of forming a concentric coil electric heating unit comprising a sub-assembly of two concentric helical resistance elements attached to terminal members, compacted powdered heat refractory insulation, and a metallic outer sheath, said resistance elements being embedded in said compacted powdered insulation within the said outer sheath, said terminal members protruding from each end of the said sheath to provide terminals for connection of the said heating unit in an electric circuit, said method comprising forming a second subassembly of one of the said terminal members by vibratingly filling the voids in and between concentric terminals with a powdered refractory insulation material to insure that the relative positions of said terminals be maintained during subsequent operations, cutting back both ends of the said terminals in stepped relation to form connection contact surfaces at one end for connection of the said unit in an electric circuit and at the other end for attachment to the concentric helical resistance elements, the other of said terminal members comprising a cylindrical bar with a concentric cylindrical projection, the diameters of said bar and said projection being equal to the diameters of the terminals of the said second sub-assembly, forming the said sub-assembly by suspending the said helical concentric resistance elements respectively between the said equal diameter surfaces of theA two said terminal members and securing the ends of the saidhelical elements to the said surfaces, mounting the whole concentrically within a metallic outer sheath with the terminal members projecting substantially equally at both ends of the said outer sheath, vibratingly filling the voids within the said outer sheath with the said powdered refractory insulation material and by means of a diameter reducing process applied to the said outer sheath, compressing the insulation to a hard compact mass so that the said mass may readily conduct heat from the resistance elements to the sheath.

9. A method of forming a concentric coil immersion or insert type electric heating unit comprising a sub-assembly of concentric helical resistance elements and terminal members, powdered insulation material, an outer metallic sheath, and a waterproof end cap, said resistance elements being embedded in the said insulation material within the said sheath, said material being compacted to a hard dense mass so that said mass may readily conduct heat from the said elements to the said sheath, one of the said terminal members protruding from the said outer sheath to provide terminals for connection of the anima od comprising forming the said sub-assembly by vibratingly filling the voids of the said one terminal member with the said powdered refractory insulation material to insure that the relative positions of the said terminals be maintained during subsequent operations, cutting back the said terminals from each end in stepped relation to form yconcentric contact surfaces, the other of the said terminals comprises a cylindrical rod with a. concentric cylindrical projection at one end the diameters of the surfaces of said rod and said projection being substantially equal to the diameters of the terminals of the said one terminal member, suspending the said helical elements respectively between the said equal surfaces and securing the ends of the said helical elements to the said surfaces, mounting the whole concentrically with the said outer sheath with the terminal members projecting at both ends of the said outer sheath, vibratingly filling the voids within the said outer sheath with said powdered refractory insulation material and Aby means of a diameter reducing process applied to the said s heating unit, compressing the insulation to a hard dense mass so that the said mass may readily conduct heat from the said resistance elements to l the said sheath, fitting the said end cap over a recessed portion of the said outer sheath and securing the said cap to the said recessed portion to make the unit waterproof.

LORET'I'A M. DALY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

US2494333A 1948-06-09 1948-06-09 Concentric coil sheath heating unit Expired - Lifetime US2494333A (en)

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2632834A (en) * 1950-06-17 1953-03-24 Knapp Monarch Co Multiple heating element
US2632833A (en) * 1950-06-03 1953-03-24 Knapp Monarch Co Heating element with internal return lead
US2858401A (en) * 1956-02-27 1958-10-28 Gen Electric Electric heating units and methods of making the same
US3521352A (en) * 1968-08-26 1970-07-21 Emerson Electric Co Electric heaters
US3591765A (en) * 1968-06-17 1971-07-06 Dreamland Electrical Appliance Electric blankets
US3591771A (en) * 1970-01-22 1971-07-06 Emerson Electric Co Electric heaters
US4010350A (en) * 1976-06-16 1977-03-01 Emerson Electric Co. Electric heating elements
US4046989A (en) * 1976-06-21 1977-09-06 Parise & Sons, Inc. Hot water extraction unit having electrical immersion heater
US4210799A (en) * 1978-10-04 1980-07-01 Emerson Electric Co. Electric heating units
FR2579854A1 (en) * 1985-03-29 1986-10-03 Etirex Shielded electrical resistor with coaxial windings

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1119336A (en) * 1914-08-26 1914-12-01 Frank Wylde Ball Electrical heating unit.
US1718676A (en) * 1926-01-07 1929-06-25 Gen Electric Electric heating unit
US2455186A (en) * 1946-11-02 1948-11-30 Gen Motors Corp Domestic electric heater

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1119336A (en) * 1914-08-26 1914-12-01 Frank Wylde Ball Electrical heating unit.
US1718676A (en) * 1926-01-07 1929-06-25 Gen Electric Electric heating unit
US2455186A (en) * 1946-11-02 1948-11-30 Gen Motors Corp Domestic electric heater

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2632833A (en) * 1950-06-03 1953-03-24 Knapp Monarch Co Heating element with internal return lead
US2632834A (en) * 1950-06-17 1953-03-24 Knapp Monarch Co Multiple heating element
US2858401A (en) * 1956-02-27 1958-10-28 Gen Electric Electric heating units and methods of making the same
US3591765A (en) * 1968-06-17 1971-07-06 Dreamland Electrical Appliance Electric blankets
US3521352A (en) * 1968-08-26 1970-07-21 Emerson Electric Co Electric heaters
US3591771A (en) * 1970-01-22 1971-07-06 Emerson Electric Co Electric heaters
US4010350A (en) * 1976-06-16 1977-03-01 Emerson Electric Co. Electric heating elements
FR2355425A1 (en) * 1976-06-16 1978-01-13 Emerson Electric Co An electrical heating element
US4046989A (en) * 1976-06-21 1977-09-06 Parise & Sons, Inc. Hot water extraction unit having electrical immersion heater
US4210799A (en) * 1978-10-04 1980-07-01 Emerson Electric Co. Electric heating units
FR2579854A1 (en) * 1985-03-29 1986-10-03 Etirex Shielded electrical resistor with coaxial windings

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