US1751416A - Electric heating unit - Google Patents

Description

March 18, 1930. C us ov 1,751,416

ELECTRIC HEATING UNIT Filed March 4, 1926 lnventor-z John C. Musg-rove,

his Agborheg.

.45 ment 11 is Patented Mar. 18, 1930 UNITED STATES PATENT JOHN G. MUSGROVE, LANESBORO, MASSACHUSETTS, ASSIGNOR TO GENERAL ELEG- TRIC COMPANY, A CORPORATION OF NEW YORK ELECTRIC HEATING UNIT Application filed March 4, 1926. Serial No. 92,280.

My invention relates to electric heating units and has for its object the provision of a simple, reliable and efiicient device of this character.

5 More specifically my invention relates to electric heating units of the type provided with a protective sheath, although it has obvious application to various other types of electric heating units. In one form of 1 sheathed heating unit the resistance conductor is embedded in electrically insulating heat refractory material inside a metallic sheath. In one construction, the resistance conductor is given a sinuous form, such as the form of a helix, as described and claimed in Patent N 0. 1,367,341 to Abbott dated February 1, 1921. his resistance conductor extends substantially throughout the full length of the sheath and has its ends secured to metallic terminal members which project from the sheath.

In one of its aspects my invention relates to the provision of a resistance element having relatively low resistance but made of relatively small wire, and to that end I provide in 26 one form of my invention a plurality of helical resistance conductors having a substantially common axis and arranged with their turns alternating.

For a more complete understanding of my an invention reference should be had to the accompanying drawing in which Fig. 1 is a fragmentary view of a partially constructed electric heating unit,embodying my invention; Fig. 2 is a sectional View along the line 2-2 of Fig. 1 looking in the direction of the arrows; Fig. 3 is a fragmentary view partially in section of an electric heating unit embodying my invention; while Figs. 1, 5 and. 6 are views showing details of construction.

Referring to the drawing, embodying my invention form cylindrical, in which a resistance heating eleembedded in powdered heat refractory insulating materialf'1'2, such as magnesium oxide. The resistance element 11 is a heating unit comprises in one Wound helicallyand extends substantially.

throughout the length of the sheath. It is electrically connec ed at its ends with metallic an outer metallic sheath 10, preferably Th terminal members 13 and 14: which project from the ends of the sheath. Preferably, the insulating material 12 is compacted by reducing the diameter of the sheath 10, for example, by swaging.

Any suitable connection may be used between the terminal members 13 and 14 and the resistance element whereby good electrical and mechanical connections are assured. Preferably, however, the terminal members, as indicated at Fig. 4, are cylindrical in form and of such size at their inner ends that these inner ends can be inserted easily in the ends of the helix of the resistance element, i. e., inserted in a plurality of turns of the helix at each end. After being thus inserted in the helix each terminal is secured in a suitable manner. As shown, the turns of the resistance conductor surrounding the inner end of each terminal are secured thereto by compressing these turns, for example, by swaging, as described and claimed in a copending application of Charles C. Abbott and George D. Milnes, Serial N o. 7 9,878, filed January 7, 1926. This swaging has the effect of forcing the end turns of the resistance element into the metal of the terminal and a good mechanical as Well. as electrical connection is thus formed. The partial embedding of the turns of the resistance element is clearly shown in Fig. l in which the bare inner end of the terminal 13 is shown after the compressing or swaging operation. Preferably pressure to secure the end turns to the terminal is applied at a number of spaced points around the circumference of the turns, for example,- at diametrically opposite points along two diameters at right angles to each other, as indicated in the drawing. This makes four zones of pressure around the circumference of the turns, each zone extending longitudinally with respect to the terminal. is compressing operation may be carried out by means of tv vo pairs of swaging jaws. If desired, however, the connections between the terminal members and the resistance conductor may be made by threading the inner ends of the terminals and then screwing the endvturns of the resistance element on to these threaded portions of the terminals, as described and claimed in Fatent No. 1,494,938 to Abbott, dated May 20,1924. I

When the terminals are inserted in the ends of the resistance element helix as previously described, there is a tendency, when a resistance conductor of large diameter is'used in If such resistance conductors of large diameters are used therefore, it is desirable to provide a sheath 10 of relatively large diameter in order that itinay not be unduly weakened duringthe swa-ging operation. The use of a relatively large sheath, however,-is an obvious disadvantage since the unit then occupies more space and cannot be as conveniently applied to the parts to be heated, nor as easily bent into various shapes. Another disadvantage of using 'a resistance conductor of largev diameter, is that the resulting stiifnessof such a unit makes ithard to assemble. I

In accordance with my invention I provide a heating element comprising a plurality of helical resistance conductors, each being connected at its ends to the terminal members. As shown in the drawing, two helically 1 wound resistance conductors 11 and 11 are provided, although obviously any suitable number may be used. The turns of the two helixes are placed between each other as in-- dicated clearly in Fig. 5," and wheremore than two helixes are used the turns will be arranged consecutivelyin a similar manner. Preferably the heating element is formed by winding the plurality of resistance conductors together on a single arbor or mandrel, the two or more resistance conductors being placed sideeby side and wound on the arbor I m the manner of a single. conductor. As wound the turns of the resistanceconductor are arranged tightly together inengagement with each other and the end turns as shown are secured in this relation on the terminal members. Subsequently, when the resistance conductor is placed in the sheath, it is stretched to .separate the intermediate turns between the 'terminal members as will be hereafter. pointed out.

The unit is assembled insubstantially the manner described in the aforesaid Patent No. 1,494,938. The terminals 13 and 1.4 are first attached to the resistance conductor and then the resistance conductor with the terminals is inserted in the sheath. A spacing block 15 made of a suitable refractory insulating material, such as lava, is provided on each cated by the reference terminal, this block being square and of such size that its corners engage with the inner surface of the sheath (Fig. 2), thus holding the inner end ofthe terminal in a central position. As shown in Fig. 4 the outer end of the terminal is somewhat larger than the inner end portion, which is of such size as to beinserted easily in the resistance conductor, so that a shoulder 16 is formed. The small inner end of the terminal is inserted in the he 'jcal resistance conductor until the end of the resistance conductor rests against the shoulder '16, and then these two parts are secured together by swaging as previously described. Thereafter the spacing block 15 is slipped over the larger outer end of the terminal and seated against the inner end of the resistance conductor, the outside diameter of the resistance conductor helix being somewhat greater than the diameter of the outer end of the terminal. The block 15 is secured in this position by forcing cars 15 out of-the sides of the terminal." The outer end of the terminal is also cut away at opposite sides to form a flat portion which is provided with an aperture 17 Continuing with the assembly of the unit,

one end of the sheath is closed by 'means of a washer 18 which is seated against a shoulder formed by countersinking the end of the sheath, and the terminal at that end, indinumber 13, is secured against longitudinal movement inward by inserting a pin 19 through-its aperture 17. The other terminal 14 is secured by passing a pin .20 similar to pin 19 in an aperture in its outer end, this pin resting at its ends on a shoulder formed by countersinking the end of the sheath. The helix is of such length that when the terminals are secured in the sheath as previously described, the resistance conductor is stretched whereby its turns are separated, as shown in the drawing.

The unit as thus far.assembled is next placed in a suitable vibrating machine, the end closed by the washer 18 being at the bottom, and powdered insulating material poured in at the upper end past the sides of the pin 20. After the sheath has been filled with the insulating material it is closed by means of a washer 21, the end being crimped over at 22 to secure the washer in place, and the opposite end may be likewise criniped as indicated by reference numeral 23 to prevent the terminals 13 from being accidentally forced outward. In the next step the unit, assembled as shown in Fig. 1, is passed through a suitable swaging or rolling machine whereby the insulating material is compacted. Preferably the insulating ma-' terial is compacted to a hard dense mass which is a good electrical insulator, and also a good'conductor of heat. This swaging operation reduces the diameter of the unit and also increases its length somewhat.

It will thus be observed that in the specific embodiment of my invention disclosed the helical resistance conductors, having equal diameters, are arranged in the sheath with the turns of each helix spaced apart and spaced from the turns of the other helix while the insulating material is compacted in the sheath around the turns of each helix and between theturns of the helixes.

The pins 19 and 20 are off-set at the center as indicated in Fig. 6 so as to form a central recess 24 on one side and a corresponding extension 25 on the opposite side. This construction provides for centering the outer end of the terminal 14 While the sheath is being filled with insulating material since the fiat outer end of the terminal seats itself in the recess 24, as shown. Another object of this irregular construction of the pins is to permit them to collapse readily during the swaging operation when the sheath is, being'reduced in diameter.

After the swaging operation the unit-is cut otf ateach end to remove the washers and the flattened ends of the terminals, and the sheath cut back at each end to expose short lengths of the terminals after which terminal lugs 26 and 27 are secured in the manner disclosed in the aforesaid patent to Abbott No. 1,494,938. Briefly, this operation consists in providing nicks 28 on opposite sides of the terminals and compressing the terminal lugs into these nicks so as to secure them, each end of the unit being closed by an insulating washer 29 against which the terminal lug is seated.

lVhile I have described my invention as embodied in concrete from and as operating in a specific manner 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 from the spirit of my invention, the scope of which is set forth in the annexed claims.

lVhat 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, compacted powdered insulating material in said sheath, a pair of metallic terminal members projecting from-said sheath, anda plurality of sinuous resistance conductors embedded in said insulating material, each of said resistance conductors having a plurality of turns at each end surrounding said terminal members respectively and secured thereto.

2. An electric heating unit comprising a metallic sheath, compacted powdered insulating material in said sheath, a pair of metallic terminal members projecting respectively from the ends of said sheath, and a.- plurality of helical resistance conductors of equal diameters embedded in said insulating material, said resistance conductors being arranged so that their axes are substantially coincident with their turns side by side in spaced relation, each of said resistance conductors having a plurality of turns at each end surrounding and secured to said termina s.

3. An electric heating unit comprising a metallic sheath, a plurality of helical resistance conductors arranged in said sheath with their axes substantially coincident and with the turns of each helix spaced apart and spaced from the turns of the other helix, said helixes having equal diameters, and powdered insulating material in said sheath compacted around the turns of each of said helixes and between the turns of said helixes, metallic terminal members extending into said sheath, and connections between the ends of said resistance conductors and said terminals.

In witness whereof, I have hereunto set my hand this first day of March, 1926.

JGHN C. MUSGROVE.

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