+

US1367341A - Electric heating unit - Google Patents

Electric heating unit Download PDF

Info

Publication number
US1367341A
US1367341A US262722A US26272218A US1367341A US 1367341 A US1367341 A US 1367341A US 262722 A US262722 A US 262722A US 26272218 A US26272218 A US 26272218A US 1367341 A US1367341 A US 1367341A
Authority
US
United States
Prior art keywords
sheath
resistance
tube
electric heating
helix
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US262722A
Inventor
Charles C Abbott
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
Original Assignee
General Electric Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Family has litigation
Priority to NL9276D priority Critical patent/NL9276C/xx
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=22998739&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=US1367341(A) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by General Electric Co filed Critical General Electric Co
Priority to US262722A priority patent/US1367341A/en
Priority to DEI20568D priority patent/DE383355C/en
Application granted granted Critical
Publication of US1367341A publication Critical patent/US1367341A/en
Priority to FR535632D priority patent/FR535632A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/16—Rigid-tube cables
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49082—Resistor making
    • Y10T29/49087—Resistor making with envelope or housing
    • Y10T29/49089—Filling with powdered insulation
    • Y10T29/49091—Filling with powdered insulation with direct compression of powdered insulation

Definitions

  • My invention relates to-elctric heating elements of the type in which a resistance conductor is inclosed' in a metallic sheath ducing such a resistance element is to locate a straight resistance conductor. which may be called the core wire. centrally of a metallic tube which is to form the sheath and fill the tube with an insulating powder. such as magnesia. so as to completely embed and properly center the core wire. The ends of the tube are then plugged, suitable provision being made for the ends of the core wire which extend beyond the tube. and the 'tube is subjected to a reducing process. The result of this operation is the reduction of both the sheath and the core wire, with the consequent compacting of the insulating material.
  • the arrangement is such that when the core wire is reduced to its desired size.
  • the insulating material is so thoroughly compacted that it becomes practically a unit with the core wire and may be drawn or rolled like a solid metal.
  • This element being supplied with the proper terminals, constitutcs an cilicient heating unit since it is exceedingly rugged and requires no insulat ing support, the core wire being well insulated and protected from mechanical injury.
  • Such a resistance element naturally has its limitations. since the space available for the heating element is not always suflicient to contain the length of conductor necessary to produ e the required resistance; This is particularly true where the element is to be used on a circuit of 220 v. or higher.
  • sheath wire having a helical or slllllOlls conductor instead of a straight core wire may be produced having all the advantages of the above described .straight conductor sheath wire in addition to advantages of its own.
  • the principal advantage of this form of unit liesin the fact that a much greater length of core wire may be contained 111 a given. space so that the unit is much more compact and self contained and is readily adapted to *the higher voltages. without occupying increased space.
  • advantages however, both from the standpoint of the manufacture and of the utility of the unit itself which are important.
  • One ofthese advantages arises from the fact that the core wire is not reduced in diameter by the reduction of the sheath.
  • the core wire Since the core wire is not drawn down, a of wire which is difficult to draw. but whlch may be more suitable, may be used. A greaterthickness' of insulating material which will give greater margin of safety to the electrical insulation may also be used since the core wire is not reduced, whereas in reducing straight core wire, it the thickness of the insulating material is above a certain maximum. the core wire ⁇ vill'not be drawn down properly. Furthermore the core wire retains its surface left by the drawing dies. and a smaller wire may be used than would be safe where it is drawn down in the tube. There are also certain other advantages. such as simplified terminal connections, greater latitude in thegrade and character of the metals used for the sheath.
  • a sinuous or helical resistance element is centrally located in a metallic sheath.
  • FIG. 1 is a sectional view of the resistance conductor mounted in a tube ready for filling
  • Fig. 2 is an end view of the same
  • Fig. 3 is aview of the filled tube partially broken away to show the terminals
  • F 1g. 4 is a view showin the unit re **d
  • Fig. 5 is a detail 0 the terminal-
  • I form a sinuous resistance element which is preferably in the form of a helix, the material being a high resistance material such as nickelchromium allo
  • This conductor is supported centrally of the tube 11 which may be of any desired metal capable of being drawn or swaged down.
  • the helix when wound may be a closed helix but, when it is supported in the tube, it is stretched so as to separate the turns and at the same. time the tension will tend to keep the helix in a central position.
  • the two ends of the helix are thus provided with terminal sup rts which are passed through holes in tin caps 15 and 16 which are fitted over the ends of the tube, the terminals being secured to the caps by set screws 17 and 18.
  • the wire is preferably under tension, as above inted out, and is supported so that the he ix will be kept in its proper central position.
  • the cap 15 is provided with a funnel 19 havin rforations 20 throu h which the insu ating material is pou into the tube.
  • the insulating material employed is one which has the quality of compacting into a solid mass and at the same time has high electrical insulatirig properties and high heat conductivity. agneslum oxid is a suitable material for this purpose.
  • the helix is not materially extended by drawing it out so asv to se pressing the helix. without-substantial movement of the helix with ref'eiehc'e to the surrounding insulation.
  • the insulating material is thus very thoroughly'compacted all around the helix. It is, therefore, ssible to determine very accurately just w at the resistance of the helix will be upon a given reduction, or to put it in another way, it is possible to determine just when a certain resistance is reached by measuring the length of the tube. When the tube is properly reduced, the sheath and insulating material are cut away so as to expose the terminal for some length, as shown in Fig. 4, and the unit is then ready for use.
  • Ain electric heating unit comprising a the-sheath to compact the insulating mate- 60 powdered heat refractory dense mass within saidsheathfand a helix resistance element embedded in said mass so as ,to readily conduct heat from the resistance element to the sheath.
  • An electric heating unit comprising a metallic sheath
  • An electric heating unit comprising a -metallic. sheath, powdered heat refractory -5. .An electric heating unit comprising a metallic sheath,
  • electric heating unit comprising a metallic sheatlf, Wdered heat refractory insulating" material compacted to a' hard dense mass within said sheath, a helical resistance element embedded in said mass so as to readily conduct heat from the resistance element to the sheath and terminal members secured to ,the ends of the element and pro- -jecting'from the sheath, said members havmg enlarged ends upon which the element is mo ted.
  • the method of forming a resistance unit' which. consists in mounting a sinuous resistance elementin a metallic sheath, fillingntihe space around the element with a heat re ctosy insulatingmaterial and reducing the-sheath sufficiently to thoroughly compact the insulating material around the resistance element.
  • an electric heating unit which consists in fitting terminal members intothe end of a helical resistance conductor and mounting the .same in a metallic sheath, filling the space around the element with a heat refractory insulating material and then compacting the material around the .element and terminal to fix them against displacement.
  • An electric heating unit comprising a metallic sheath, powdered heat refractory insulating, material compacted to a hard dense mass within said sheath, a helical resistance element embedded in said mass so as to. readily conduct heat from the resistance element to the sheath and terminal members inserted in the element and projecting from the sheath.

Landscapes

  • Resistance Heating (AREA)

Description

C. C. ABBOTT.
ELECTRIC HEATING UNIT,
APPLICATION FILED NOV. 15. 1918.
Patented Feb. 1, 1921,
Inventor: Charfles QfibbOtt, 9 WM His aqttorneg.
UNITED STATES- PATENT OFFICE.
CHARLES C. OF PITTSFIELD. MASSACHUSETTSaA'SSIGNOB TO GHIRRAL ELECTRIC COMPANY. A CORPORATION OF NEW YORK.
ELECTRIC HEATING- UNIT.
i Specification of Lettcrs latent.
Patented Feb. 1. 1921.
Application tiled November is, 1918. Serial No. 262.722.
7 '0 all whom it may concern:
Be itknown that I, CHARLES C. Anno'r'r. a citizen of thel nited States, residing at Pittsfield, county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Electric Heating Units. of which the following is a specification.
My invention relates to-elctric heating elements of the type in which a resistance conductor is inclosed' in a metallic sheath ducing such a resistance element is to locate a straight resistance conductor. which may be called the core wire. centrally of a metallic tube which is to form the sheath and fill the tube with an insulating powder. such as magnesia. so as to completely embed and properly center the core wire. The ends of the tube are then plugged, suitable provision being made for the ends of the core wire which extend beyond the tube. and the 'tube is subjected to a reducing process. The result of this operation is the reduction of both the sheath and the core wire, with the consequent compacting of the insulating material. The arrangement is such that when the core wire is reduced to its desired size. the insulating material is so thoroughly compacted that it becomes practically a unit with the core wire and may be drawn or rolled like a solid metal. This element, being supplied with the proper terminals, constitutcs an cilicient heating unit since it is exceedingly rugged and requires no insulat ing support, the core wire being well insulated and protected from mechanical injury. Such a resistance elementnaturally has its limitations. since the space available for the heating element is not always suflicient to contain the length of conductor necessary to produ e the required resistance; This is particularly true where the element is to be used on a circuit of 220 v. or higher.
I have found that sheath wire having a helical or slllllOlls conductor instead of a straight core wire may be produced having all the advantages of the above described .straight conductor sheath wire in addition to advantages of its own. The principal advantage of this form of unit liesin the fact that a much greater length of core wire may be contained 111 a given. space so that the unit is much more compact and self contained and is readily adapted to *the higher voltages. without occupying increased space. There are other advantages, however, both from the standpoint of the manufacture and of the utility of the unit itself which are important. One ofthese advantages arises from the fact that the core wire is not reduced in diameter by the reduction of the sheath. Since the core wire is not drawn down, a of wire which is difficult to draw. but whlch may be more suitable, may be used. A greaterthickness' of insulating material which will give greater margin of safety to the electrical insulation may also be used since the core wire is not reduced, whereas in reducing straight core wire, it the thickness of the insulating material is above a certain maximum. the core wire \vill'not be drawn down properly. Furthermore the core wire retains its surface left by the drawing dies. and a smaller wire may be used than would be safe where it is drawn down in the tube. There are also certain other advantages. such as simplified terminal connections, greater latitude in thegrade and character of the metals used for the sheath.
In accordance with my invention, therefore, a sinuous or helical resistance elementis centrally located in a metallic sheath.
filled with powdered insulating material which is compacted to a high degree so as ,to form a very dense insulating body having relatively high heat conducting properties, so that the heat will be transmitted to the sheath at the greatest possible rate consistent with good electrical insulation, there-- by producing a mechanically rugged resistance element capable of embodying a high resistance in a relatively small space.
My invention will best be understood by reference to the. accompanying drawings in which-Figure 1 is a sectional view of the resistance conductor mounted in a tube ready for filling; Fig. 2 is an end view of the same; Fig. 3 is aview of the filled tube partially broken away to show the terminals; F 1g. 4 is a view showin the unit re duced; and Fig. 5 is a detail 0 the terminal- In the manufacture of sheath wire in accordance with my invention I form a sinuous resistance element which is preferably in the form of a helix, the material being a high resistance material such as nickelchromium allo This conductor is supported centrally of the tube 11 which may be of any desired metal capable of being drawn or swaged down. The helix when wound may be a closed helix but, when it is supported in the tube, it is stretched so as to separate the turns and at the same. time the tension will tend to keep the helix in a central position. In order to form enlarged tar minals, upon the helix and at the same time furnish a suitable support for the helix for 12; as shown in:=detail in Fig; 5.
the filling'and subsequent drawing opera-- tion, I mount each end of the helix on a rod This rod,
which is preferably of the same material as the core wire, soas to prevent any-galvanic action between the core and the terminals, is
provided with an enlarged upon which the helix fits. wire-is then wound onto the inclined surfacev ofthe head and on to the rod for a plointed head 13 short distance, theend being finally inserted 5 in a slot Min-the rod. The edges of the slot are then swaged over the end of the wire so as to make a good electrical contact and securely fix the end of the wire to'the terminal. The two ends of the helix are thus provided with terminal sup rts which are passed through holes in tin caps 15 and 16 which are fitted over the ends of the tube, the terminals being secured to the caps by set screws 17 and 18. The wire is preferably under tension, as above inted out, and is supported so that the he ix will be kept in its proper central position. The cap 15 is provided with a funnel 19 havin rforations 20 throu h which the insu ating material is pou into the tube. The insulating material employed is one which has the quality of compacting into a solid mass and at the same time has high electrical insulatirig properties and high heat conductivity. agneslum oxid is a suitable material for this purpose. When the tube is filled and the material somewhat compacted by some means, as for instance, by jarring or vibrating the sheath tube, the caps 15 and 16 are removed and the ends of the tube permanently closed. As shown, this is accomplished by means of metallic disks 21 and 22 over which the metal is bent, the ends of the terminals assin through the disk and being form into heads 23 and 24. The tube is'now in the condition shown in Fig. 3. The tube is now subjected to a reducing process which consists in passin it through a swaging or IOlllng machine. he amount heend ofthe.
'from the spirit of my invention,
of reduction necessary is not great since its purpose is largely to compact the powdered material around the helix, Ordinarily a reduction in diameter and consequent 13f"!- ening of the tube, such as is represen by the relative dimensions of the parts shown in Figs. and 3, will accomplish this purpose. I have found, for instance, that a tube having an outside diameter of g" and an internal diameter of when properly reduced will have an outside diameter of and an elongation of about 15%.
Que of the results obtained by such a reducing process is that the electrical resistance of the resistance conductor decreases to a certain extent and this was found to found that there is a direct relation between the decreased reslstance and the increase in the length of the tube, that is, the-ratio between the resistance of the helix before swagmg and after swagingis equal to the ratio between the length of the tube after swaging and before swa 'ng. The reason i for this seems to be that since the number of turns of the helix remains the same, while the diameter of the helix is decreased, the
length of each turn is also decreased. The helix is not materially extended by drawing it out so asv to se pressing the helix. without-substantial movement of the helix with ref'eiehc'e to the surrounding insulation. The insulating material is thus very thoroughly'compacted all around the helix. It is, therefore, ssible to determine very accurately just w at the resistance of the helix will be upon a given reduction, or to put it in another way, it is possible to determine just when a certain resistance is reached by measuring the length of the tube. When the tube is properly reduced, the sheath and insulating material are cut away so as to expose the terminal for some length, as shown in Fig. 4, and the unit is then ready for use.
While I have described my invention as embodied in concrete form in accordance with the provisions of the patent statutes, it should be understood that I do not limit my Invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing the scope of which is set forth in the annexed claims.
What I claim as new and desire to separate the turns but by comeuro by Letters Patent of the United States,
metallic sheath,
insulating material compacted to a hard 2. Ain electric heating unit comprising a the-sheath to compact the insulating mate- 60 powdered heat refractory dense mass within saidsheathfand a helix resistance element embedded in said mass so as ,to readily conduct heat from the resistance element to the sheath.
'3. An electric heating unit comprising a metallic sheath,
dense mass within said sheath, a sinuous resistance element embedded insaid mass so as to readily conduct heat from. the resist-' ance element to the sheath and terminal members secured to the'element and projecting from. the sheath.
4. An electric heating unit comprising a -metallic. sheath, powdered heat refractory -5. .An electric heating unit comprising a metallic sheath,
powdered heat refractory insulating matenalcompacted to a hard dense mass within said sheath, a sinuous resistance element embedded in said mass so as to readily conduct heat from'the res1st-- ance'element to the sheath and terminal members inserted in and secured to the ele ment and having reduced end portions profrom the sheath. electric heating unit comprising a metallic sheatlf, Wdered heat refractory insulating" material compacted to a' hard dense mass within said sheath, a helical resistance element embedded in said mass so as to readily conduct heat from the resistance element to the sheath and terminal members secured to ,the ends of the element and pro- -jecting'from the sheath, said members havmg enlarged ends upon which the element is mo ted. a L
7. The method of forming a resistance unit'which. consists in mounting a sinuous resistance elementin a metallic sheath, fillingntihe space around the element with a heat re ctosy insulatingmaterial and reducing the-sheath sufficiently to thoroughly compact the insulating material around the resistance element.
8. The method of forming a resistance unit which consists in mounting a helical resistance elementin a metallic sheath, filling the'space around the element with a heat refractory-insulating material and reducing powdered heat refractoryinsulating'material compacted to a hard" rial and compress the element without substantially separating its turns.
9. The method'of forming a resistance unit which consists'in securing enlar terminals to. a helical resistance e ement,
"; mounting said element and terminals in a metallic sheath with ends projecting therefrom and the element under tension filling the space around the element with a heat refractory insulating material and reducing the sheath sufiiciently to thoroughly compact the insulating material around the element and the terminals.
10. The method of'forming an electric heating unit which consists of mounting a helical resistance element a in a metallic sheath, filling the space around the element witha heat refractory insulating material and then compactingl'the materiaLui-ound the element.
11. The method of forming anv electric heating unit which consists of mounti a helical resistance element in a-v meta lic compacting the material around the element and finally compacting the material still further by reducing the sheath.
12. The method of forming -.an electric heating unit which consists of mounting a helical resistance element in a metallic sheath, filling the space around the element with a heat refractory insulating material,
' compact ing the material around the element by a vibrating or jarring action upon. the material and finally compacting the material still. further by reducing the sheath.
13. The method of forming an electric heating unit which consists in fitting terminal members intothe end of a helical resistance conductor and mounting the .same in a metallic sheath, filling the space around the element with a heat refractory insulating material and then compacting the material around the .element and terminal to fix them against displacement. 14. An electric heating unit comprising a metallic sheath, powdered heat refractory insulating, material compacted to a hard dense mass within said sheath, a helical resistance element embedded in said mass so as to. readily conduct heat from the resistance element to the sheath and terminal members inserted in the element and projecting from the sheath.
In witness whereof, I have, hereunto set my hand this 13th day of Nov. 1918.
, CHARLES ABBOTT.
It is hereby certified that in Letters Patent No. 1,367 ,341, granted February 1,
1921, upon the application of Charles C. Abbott, of Pittsfield, Massachusetts, for
an improvement in Electric Heating Units, an error appears in the printed specification requiring correction as follows: Page 2, line 76, after the word .of
insert a; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofliee.
Signed and sealed this 15th day of March, A. D., 1921.
[sun] M. H. couns'ron,
Commissioner qfPatmle. Cl. 219-67.
US262722A 1918-11-15 1918-11-15 Electric heating unit Expired - Lifetime US1367341A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
NL9276D NL9276C (en) 1918-11-15
US262722A US1367341A (en) 1918-11-15 1918-11-15 Electric heating unit
DEI20568D DE383355C (en) 1918-11-15 1920-07-11 A method of manufacturing an electric heating unit of the sheathed wire type
FR535632D FR535632A (en) 1918-11-15 1921-05-18 Improvements in electrical heating elements and their manufacturing processes

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US262722A US1367341A (en) 1918-11-15 1918-11-15 Electric heating unit

Publications (1)

Publication Number Publication Date
US1367341A true US1367341A (en) 1921-02-01

Family

ID=22998739

Family Applications (1)

Application Number Title Priority Date Filing Date
US262722A Expired - Lifetime US1367341A (en) 1918-11-15 1918-11-15 Electric heating unit

Country Status (4)

Country Link
US (1) US1367341A (en)
DE (1) DE383355C (en)
FR (1) FR535632A (en)
NL (1) NL9276C (en)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2456343A (en) * 1944-12-06 1948-12-14 Tuttle & Kift Inc Electric heater and method of making same
US2637755A (en) * 1950-02-16 1953-05-05 Harold N Ipsen Electric heating apparatus
US2809223A (en) * 1955-09-26 1957-10-08 Lindberg Eng Co Terminal for heating furnaces
US2816200A (en) * 1954-12-15 1957-12-10 Int Nickel Co Electrical heating unit
US2854556A (en) * 1954-07-26 1958-09-30 Wiegand Co Edwin L Sheathed electric heater and method of making the same
US2927299A (en) * 1954-05-20 1960-03-01 Fredrick L Lefebvre Heater tube mounting
US2995646A (en) * 1959-02-26 1961-08-08 Arthur W Kawalle Removable type electric heating element
US3263275A (en) * 1963-07-22 1966-08-02 Thiokol Chemical Corp Apparatus for casting small solid propellant rocket motors for testing purposes
DE1291427B (en) * 1963-09-09 1969-03-27 Proctor Silex Corp Electric iron
US5644835A (en) * 1996-08-20 1997-07-08 Mold-Masters Limited Heating element method

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE942884C (en) * 1944-04-21 1956-05-09 Siemens Ag A method of manufacturing an electric heating unit of the sheathed wire type
DE949071C (en) * 1950-10-19 1956-09-13 British Insulated Callenders Insulated electrical conductors

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2456343A (en) * 1944-12-06 1948-12-14 Tuttle & Kift Inc Electric heater and method of making same
US2637755A (en) * 1950-02-16 1953-05-05 Harold N Ipsen Electric heating apparatus
US2927299A (en) * 1954-05-20 1960-03-01 Fredrick L Lefebvre Heater tube mounting
US2854556A (en) * 1954-07-26 1958-09-30 Wiegand Co Edwin L Sheathed electric heater and method of making the same
US2816200A (en) * 1954-12-15 1957-12-10 Int Nickel Co Electrical heating unit
US2809223A (en) * 1955-09-26 1957-10-08 Lindberg Eng Co Terminal for heating furnaces
US2995646A (en) * 1959-02-26 1961-08-08 Arthur W Kawalle Removable type electric heating element
US3263275A (en) * 1963-07-22 1966-08-02 Thiokol Chemical Corp Apparatus for casting small solid propellant rocket motors for testing purposes
DE1291427B (en) * 1963-09-09 1969-03-27 Proctor Silex Corp Electric iron
US5644835A (en) * 1996-08-20 1997-07-08 Mold-Masters Limited Heating element method

Also Published As

Publication number Publication date
NL9276C (en)
DE383355C (en) 1923-10-12
FR535632A (en) 1922-04-19

Similar Documents

Publication Publication Date Title
US1367341A (en) Electric heating unit
US3678249A (en) Heater element
US5481150A (en) Brush and commutator motor having brush device using the same
US3382387A (en) Electrical current collection and delivery method and apparatus
US2130715A (en) Electric heating element
US3290472A (en) Electric current collecting element
US5670926A (en) High-voltage fuse having a core of bound silica sand about which fusible elements are wound
US2046102A (en) Electric terminal connection
US2552193A (en) Heating device
US2494333A (en) Concentric coil sheath heating unit
US2009980A (en) Electric heating unit
US3374330A (en) Current limiting fuse
US2063642A (en) Electric heating unit
US1475162A (en) Electric heater
US1463005A (en) Heating unit
US1735831A (en) Electric heater and method of making the same
US2515781A (en) Electric heating unit
US2858401A (en) Electric heating units and methods of making the same
US1718676A (en) Electric heating unit
US3234633A (en) Method of making a sheathed electric heating unit
US1698289A (en) Heating unit and method of making it
US1494938A (en) Electric heating unit
US3217280A (en) Heating element
US1708995A (en) Electric soldering iron
US1869140A (en) Electric heater
点击 这是indexloc提供的php浏览器服务，不要输入任何密码和下载