US2824199A

US2824199A - Electrical heating element

Info

Publication number: US2824199A
Application number: US498934A
Authority: US
Inventors: Donald W Browne
Original assignee: Acra Electric Corp
Current assignee: Acra Electric Corp
Priority date: 1955-04-04
Filing date: 1955-04-04
Publication date: 1958-02-18
Anticipated expiration: 1975-02-18

Description

Feb. 18, 1958 D. w. BROWNE ELECTRICAL HEATING'ELEMENT Filed April 4, 1955 United States Patent 3 ELECTRICAL HEATING ELEMENT Donald W. Browne, Des Plaines, IlL, assignor to Acra Electric Corporation, a corporation of Illinois Application April 4, 1955, Serial No. 498,934

1 Claim. (Cl. 201-67) This invention relates to an electrical heating element and more particularly to a cartridge type heating element having an internal, electrical resistance heater.

Cartridge type electrical heating elements are known in the art-a common form being that wherein a block of heat resistant ceramic is provided with a bore through which an electrical heating resistor is inserted or threaded. Where the electrical connections are desirable at one end of the unit the core must be provided with two such bores and the resistance unit folded back on itself and threaded through each of the bores so that its connecting ends are available adjacent each other. Such construction is costly in manufacture and it is difficult and timeconsuming to thread the resistance unit.

Where the resistors are mounted externally on the core, the generally linear arrangement thereof requires a considerable tensional force on the ends of the resistor to prevent lateral movement. As the resistors are commonly formed of relatively small diameter wire, the strain produced tends to curtail the useful life of the heating element by increasing the possibility of a break in the coil.

The principal feature of this invention is the provision of a new and improved electrical heating element.

A further feature is the provision of an electrical heating element having a cylindrical core of heat resistant, electrically insulating material having helical grooves in the periphery and extending longitudinally of the core for the reception of the electrical resistance units.

A still further feature is that the electrical resistance units are helical coils of high resistance wire adapted to conform yieldingly to the helical configuration of the core grooves.

A still further feature is that one end of the core may be provided with a transverse groove communicating with at least two longitudinal grooves and a resistance unit extends from one end along the core, through the transverse groove, and back to the original end, being fully received Within grooves in the exterior of the core.

Another feature of the invention is that the resistor receiving longitudinal grooves are entirely outwardly opening along their length so that the resistance element may be inserted laterally thereinto, with such grooves being generally helical so as to allow a small amount of end tension to cause the resistance element to be retained within the grooves.

Other features and advantages of this invention will be apparent from the following description taken in con nection with the accompanying drawings wherein:

Fig. 1 is an elevational view of an electrical heating element involving the invention;

Fig. 2 is an enlarged view thereof partially broken away;

Fig. 3 is a sectional view taken approximately along the line 3 3 of Figure 2;

Fig. 4 is a sectional view taken approximately along the line 44 of Figure 2; and

Fig. 5 is a sectional view taken approximately along the line 5-5 of Figure 2.

2,824,199 Patented Feb. 18, 1958 Referring now to the drawings, an electrical heater embodying the invention may be seen to comprise a cylindrical core 10, carrying an electrical resistor 11 within a tubular jacket 12. Adjacent one end of the core 10 and within an open end of jacket 12 is disposed a cap 13 through which external connecting leads 14 extend. Bendable metal clips 15 are provided for securing the ends of the connecting leads 14 to ends of the electrical resistor 11 so that they may have electrical conductive relationship and are positioned within cap 13 when the heater is assembled. When a suitable source of elec trical potential is impressed across leads 14 current will fiow through the electrical resistor 11 thereby heating it and the surrounding elements so that heat may be transmitted outwardly from the assembly.

Jacket 12 comprises a tubular element having a closed end 12a, and an open end 12b, through which extends the core 10 and resistor 11. Adjacent the outer edge 12c, the internal diameter of jacket 12 is enlarged to form a cap receiving portion 12d, and the inner end of the enlarged portion forms a shoulder 12c against which cap 13 abuts limiting its inner movement.

The resistor supporting core 16 is provided with a plurality of exterior, helical grooves 10a. In the embodiment shown, four longitudinally extending, equally spaced, parallel grooves are provided resulting in a cruciform cross section as best seen in Figs. 3, 4 and 5; the number of grooves and their spacing, however, may be varied Without departing from the scope of the invention. The depth of the grooves is preferably such that the resistor 11 may be fully received therewithin and spaced from the jacket 12. As shown in Figures 2, 3 and 5, the outer portion of the helical grooves 10 is filled, after assembly, with a granular insulator, such as coarse magnesium oxide or zirconium oxide, which may be compacted by vibrating or swaging to fill completely this space. The outer portion 10b of the land between the grooves may be rounded, the extreme diametrical dimensioning, however, is preferably made comparable to the interior diameter of the jacket 12 to minimize lateral play between the core and the jacket. To accommodate lateral extending resistor portions one end of core 10 is provided with laterally extending slots each communicating with a different pair of grooves Illa, and the other end is provided with a single lateral slot 10d connecting with one pair of grooves.

I have found that an excellent support of resistor 11 is provided by core 10 when grooves 10a have a curvature of approximately one turn over a longitudinal length of the core ten times the maximum diameter of the core. A typical core of such construction is that wherein the diameter is .425 inch and the groove curvature is onequarter turn per inch of length of the core.

Electrical resistor 11 preferably comprises a helical coil of relatively small diameter, high electrical resistance wire formed of a heat resistant material. In the embodiment shown, resistor 11 is shown as comprising four equal coil lengths separated by three generally linear portions 11a. Resistor 11 may be formed originally with portions 11a or they may be formed during the assembly of the heating element by exertion of a slight tension on the coils at the proper points along the resistor length, thereby straightening the helix loops.

Resistor 11 is positioned in the helical groove 10a so that end portions 11b are each disposed at an end of the core 10. This arrangement is effected by placing the first section of the resistor in one of the grooves with an end 11b extending from an end of said groove, extending the linear straight portion 11a (between the first and second resistor portions) laterally through a first slot 10c, extending the second resistor portion in a second one of the helical grooves 10a, extending the linear straight portion 11a (between-the second and third resistor portions) laterally through slot 10d, extending the third resistor portion in a third groove 10a, extending the linear straight portion 11a (between the third and fourth resistor sections) laterally through a second slotdtic," and ex'tehd for fixedly securing the resistor, by placing a portion of the ends 111) in notches 10c in the erid -ofthe core 10' containing the slot 10d and retaining ends 11b therei n by suitablemeans such' as zirconium'adhes ye cement: Because of the curvature of the helical grooves 10a, the

retention of the free ends 11b m me slots liifand the" retention of the straight portions" ll zrin the slots "10c and 10d, the electrical resistor 11 isheld-in juxtaposed relationship to the bottom of the grooves rea; effectively preventing the lateral swaying or 'disp lace r'rient' common to that type of assembly wherein the resistance'coil ex tends in- 'a generally straight rathenthanku'rved line. Where granular insulation 16 is utilized *to fiIlthe'spa ce surrounding resistor 11 in the grooves ldm' ment allows for more simple m'a nufacturirrg rbca'du s,

obviating extra ps to prevent the 'ma te rial16 'fronf' being disposed between the bottom of the"grooves arid the resistor sufficiently to cause the'resisto r' tocontact"the outer jacket 12. Where insulation 16* is 'no t 11565111118 arrangement provides 'a secure mountin bfthe resistor on the core preventing the resistor froni co'ntacting the jacket 12.

Bendable clips' may be of any suitableftyp f r ing" necting electrical wires under hightemperaturefco tions. I have found that nickel-silver squeeze clipsfun tion extremely satisfactorily for thi-spurpo se. As shown? the clips may comprise a small flat' sheet of nickel silver: rolled into two separate looped "or-curled portions, witlr each portion arranged to receive one" of the wires 'to be;

connected. When the wires are inserted thereintheiclipf is' squeezed as with pliers to cause a tight mechanical binding therebetween. g V V g Cap 13 in 'which the spring clips are disposed com pris'es' a cylindrical' plug havii ig an external diameter comparable to the 'interiial diameter"ofIportiotidZd of' jacket 12. Theinner endof caplfa abuts'sh'o'ulder 12 a and the cap is retained thuslyarrahged by radially in wardlyconstricting the' outer edge-12c of'the jacket to engage" a frusto-conical outer surface "132; of the cap.

Extending longitudinally through the cap are a pair of spaced holes 13b, each of which holes terminates inwardly in a recess 13b adapted to receive the spring clips 15. Connecting leads 14 extend through the bores 13b from the spring clips 15 outwardly so that they may be connected to a source of electrical potential.

The core 10 and cap 13 are preferably formed of a vitreous ceramic material such as steatite, or similar material having high electrical resistance at elevated temperatures andwh ich may be provided with the grooves and openings by simple means such as extrusion or molding. The jacket 12 is preferably formed of a heat transmittingmaterial such as brass or copper to allow good heat transferring efficiency.

The electrical heatingelement disclosed is of simple and inexpensive manufacture; the components may be readily assembled with cast while maintaining their positional relationship. 7

While I have shown and described certain embodiments of my invention, itis tobe understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as defined in the appended claim.

I claimi An' electrical heating element of the character described, comprising: a tubular jacket; a heating coil in said jacket and com prising at least two longitudinally extending electrical coihportio-ns; and an elongated in sulating'core for carrying the heating coil in the jacket and having an axial mid-portion anclperiphe ral, longitudinally extending lands defining at least-two grooves and extending laterally outwardly to engage the jacket and divideth'e interior of isaid' jacket into a plurality of insulatedlyseparate', longitudinally extending compartments, one coil portion being received infeach compartment, said heating coil having a connecting "portion extending transversely betweentwo compartments at one end thereof whereby said "coil" is Wound around the core lengthwise thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,008,370 Robillot Nov. 14,1911 1,785,403 Babb Dec. 16, 1930 1,974,448 Crowley Sept. 25, 1934 2,062,163 Conrad Nov. 24, 1936 2,088,586 Cole et a1. Aug. 3, 1937 2,287,402 Wood June 23,1942 2,369,045 Hampton et al. Feb. 6, 1945 2,371,696 Levitt a Mar; 20, 1945 2,639,359 Glenn May 19, 1953