US2166807A - Electric heater - Google Patents

Description

July 18, 1939. F. J. EWALD. JR 2,166,807

ELECTRIC HEATER Filed April 26, 1938 I Inventor: a Fred J. Ewal dJn,

w b Maw Adm 3 His Attorneg.

Patented July 18, 1939 UNITED STATES,

PATENT OFFICE ELECTRIC HEATER Application April 26, 1938, Serial No. 204,331

7 Claims.

This invention relates to electricheaters and the like, and it has for its object the provision of improved terminal structure in heaters of this type having means for sealing and protecting the terminals of the heater.

This invention is particularly applicable to electric heaters of the sheathed type wherein a resistance conductor is enclosed by an outer metallic protective casing and is embedded in a heat-conducting, electrically-insulating material which supports the conductor in spaced relation with reference to the casing. And it contemplates the provision of improved 'means for sealing the terminals of electric heaters of this type whereby the heaters are rendered impervious to moisture,

oil, gas, and like fluids.

In accordance with this invention in one form thereof, each terminal of the heater is surrounded with a sleeve-like body formed of some suitable electrically-insulating material, such as lava or porcelain. This body is arranged in spaced relation both with the terminal of the heater and with the sheath. And interposed within the spaces between the sleeve and the terminal, and

25, the sleeve and the sheath is a vitreous mass of sealing material adhering to the surfaces of the terminal, the sleeve and the sheath with fluidtight joints. A cup-like protective shield, preferably formed of a non-corrosive metal, such as stainless steel, is provided around the insulating sleeve and terminal; this member has a relatively small section inserted in the space between the insulating sleeve and the sheath, and this section is embedded in the vitreous sealing mass, which functions to secure the cup to the heatenand also to separate the small section both from the insulating sleeve and the sheath. Here again, the sealing mass adheres to the surfaces of the cup to have fluid-tight joints with it. In addition, the cup has a relatively large outer section flaring outwardly from the sheath and defining a protective casing both for the outer surfaces of the insulating sleeve, and also for the terminal section that emerges from the sleeve. For a more complete understanding of this invention, reference should be had to the accompanying drawing in which Fig. 1 is a fragmentary elevation, partly in section, of an electric heater arranged in accordance with this invention Fig. 2 is an enlarged sectional view taken through one terminal end of the electric heater of Fig. 1; and Fig. 3 is a fragmentary elevation in section illustrating my invention as applied to a hotplate of an electric range, the figure being drawn to a reduced scale.-

Referring to the drawing this invention has been shown in one form as applied to a helicalcoil sheathed electric heating unit of the type described and claimed in the United States patent to c' 0. Abbott, No. 1,367,3 dat d F uary 5 1921. As shown, the heating unit comprises ahelical resistance conductor I0 embedded in a compacted mass of powdered heat-refractory, electrically-insulating material I l which supports the conductor in spaced relation with reference to 10 an outer metallic protective sheath l2. The insulating material ll may be any suitable substance, but preferably will be formed of powdered magnesium oxide. The resistance conductor ID has its two ends secured to terminals l3 and I3a 15 projezting from the opposite ends of the sheath, as shown.

In order to render the terminals absolutely impervious to the leakage of fluids into the sheath, each terminal is surrounded with a body It (only 20 that for the left-hand terminal i3 being shown in Fig. 2) formed of some suitable fluid-impervious electrically-insulating material, such as lava or porcelain. Each insulating body is provided with a centrally arranged aperture Liv so that it may be threaded over its terminal, and each is provided with a relatively small section I6 that is introduced into the associated end of the sheath, as shown in Fig. 2. Moreover, it is provided with an enlarged outer flange-like head section ll which overhangs the end of the sheath, as shown. The two sections l6 and I1 preferably will be and as shown are formed integrally with each other.

The centrally arranged aperture I5 is somewhat larger than is the outside diameter of the terminal (3, and the outside dimensions of the inner extension iii are somewhat smaller than the inside dimensions of the sheath so that spaces are provided between the insulating member I l and the terminal, and between this member and the 40 sheath.

Preferably, the end section in of the sheath that receives the portion l6 of the insulating sleeve will taper or flare outwardly as shown, and the inner section I6 of the sleeve I4 will have a complementary taper.

A relatively large cup-shaped protective shield i8 is provided to protect the insulating sleeve l4 and also the terminal I3, this member having a relatively large semicircular section l9 whose side Walls flare outwardly from the end of the sheath, and a relatively small inner tapered section 20 interposed between the tapered section iii of the sleeve I4 and the tapered end wall section l2a of the sheath. The section 20 of the shield I8 is sealing glass 2!.

spaced both from the section l6 of the sleeve and the tapered wall section I2a.

The inner section N of the insulating sleeve 14, and the inner section 20 of the cup l8. are embedded in a sealing mass 2l of a suitable vitreous material, such as a suitable lead glass. As shown, the vitreous mass 2| completely fills the annular space between the sleeve l4 and the terminal, the space between the section iii of the sleeve and the section 20 of the cup, and also the spacebetween the section 20 of the cup and the sheath. Preferably, the sealing material also will be interposed between the overhanging flange .H of the member I4 and that section of the cup immediately next to it, as indicated by the numeral 22.

The mass of glass 2|, 22 forms fluid impervious joints with the surfaces that it engages of the terminal l3, the insulating sleeve M, the section 20 of the cup, and the sheath. The glass preferably will have a relatively high electrical resist ance at the operating temperatures of the heating unit; and preferably, it will have substantially the same thermal coefficient of expansion as the terminal, the cup and the sheath, as well as of the insulating sleeve M.

In making the terminal sealing structure, it will be understood that after the resistance conductor l0 and its terminal have been mounted within the sheath. l2 and insulated therefrom by the compacted layer H, a small section of the insulating material II will be removed from the terminal end of the sheath to provide space for the insulating sleeve M, the cup section 20 and the Then the cup l8 and sleeve M will be threaded on the terminal, and then the space which has been provided by the removal of the insulating material II will be filled with the vitreous sealing material, preferably in powdered form. The assembly, including the sheath and powered vitreous glass, is 'then heated until the glass is molten. The sleeve l4 and the cup I8 are then pushed down on the terminal into the glass to force the glass up around the terminal and around and about the section l6 of the sleeve [4 and the section 20 of the cup, as shown in Fig. 2. When the glass cools, a seal is produced wh ch is substantially water and air-tight.

The terminal structure of this invention, while it has. more general application. is particularly applicable to hotplates for electric ranges and the like wherein the terminal sections of the heater are directed downwardly from the cook ng surface. One hotplate of this type is described and claimed in the copending application of.J. C. Sharp, Serial No. 187,416 filed January 28. 1938, and assigned to the same assignee as this invention. This hotplate is shown in Fig. 3, and

as there shown, itis provided with the terminal structure of this invention. As shown, the terminal ends of the sheath are directed downwardly from the heating surface 23. Thedownturned terminals l3 are received in a terminal housing 24 which has apertures 25 receiving the terminals (only one aperture shown). The outer end of the shield l8 preferably will be provided with a flange 26 that rests against the upper surface of the housing 24, and as shown, the housing preferably will be provided with a protuberance 21 around. its aperture 25 that extends up into the cup is. The housing 24 and its protuberance 21 preferably will be formed integrally with each other and preferably will be formed of a suitable electrically insulating material, such as a phenol condensation product. The cup l8 prevents the entrance into the terminal of grease, drippage 'and the like falling from the hotplate.

that I do not wish to be limited thereto since,

many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

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

1. An electric heater comprising a resistance conductor, a terminal secured to said resistance conductor, a metallic sheath encasing said resistance conductor and terminal, the end of said terminal projecting from the end of said sheath, an electrically insulating sleeve within said sheath surrounding said terminal in spaced relation with said terminal and said sheath, a protective cup having a section received in the space between said sleeve and sheath and an enlarged section flaring outwardly from the sheath and insulating sleeve, and vitreous sealing material within said sheath filling the space between the terminal and insulating sleeve, and also adhering bothwith the sheath and the section of said cup that is received therein so as to secure the insulating sleeve and cup to the sheath.

2. An electric heater comprising a sheath, a resistance conductor within said sheath having a terminal projecting fromthe sheath, insulating material within the sheath between the walls of the sheath and said resistance conductor and that part of the terminal within the sheath, a mass of sealing glass within said sheath between the terminal and walls of the sheath, an electrically insulating sleeve threaded on said terminal and a protective cup for the sleeve surrounding the sleeve, and both the sleeve and cup having sections extending into the sheath and embedded in said mass of glass so that the glass separates the sleeve both from the terminal and the cup and also separates the cup from the sheath.

3. 'An electric heatencomprising a resistance conductor, a metallic sheath encasing said conductor, a terminal for said conductor and means sealing said terminal comprising a substantially homogeneous layer of electrically insulating material between said terminal and said sheath substantially filling the space between these members but spaced from each of them, a relatively large protective cup flaring outwardly from the sheath and having a relatively small section extending into the sheath but spaced from the sheath and said layer of electrically-insulating material, and substantially homogeneous layers of glass having relatively high electrical resistivity at the operating temperatures of the heater arranged in the spacesbetween said terminal and insulating material and between the said small section of said cup and said insulating material and sheath.

4. The combination with an electric heater provided with a resistance conductor embedded in an insulating material enclosed by a metallic sheath and a terminal secured to said conductor and projecting from said sheath of an electrically insulating body in said sheath surrounding said terminal insubstantially concentric relation therewith and with said sheath and in spaced relation with these members, said body projecting from said sheath and having a flange exteriorly of said sheath and overlapping the adjacent end of said sheath, a metallic cup having a relatively small section extending into said sheath and an aieaao r enlarged section outside of the sheath flaring outwardlyiromsaidsmallsectionandthesmallsection spaced both from the part 0! said insulating body in said sheath and from the sheath, and a massoi'sealingglaasflllmgthespacesbetween the insulating body and terminal and said small cup section, .and between said section and said sheath, and also between said flange and the enlarged section of said cupand adhering to all of these members so as to have fluid-tight joints with them.

5. An electric heating imit comprising a sheath, a heating element in said sheath, a terminal iorsaid heating element projecting from said sheath, an insulating block having an openhis in which the end oi. said terminal is received, and also a portion extending into said sheath, a cup-shaped shield around said terminal having a part inserted in the end of said sheath in the space between the sheath and the portion of the insulating block that is in the sheath, and sealing material within said sheath between that part of the shield that is in the sheath and the inner walls of the sheath and said insulating block.

6. An electric heating unit comprising a sheathed heating element having a terminal end, a terminal projecting from said end, a cup-shaped shield around said terminal having a part-inserted in the end 01' said sheath, an insulating block having an opening in which the end of said terminal is received, and also having a flangelike protuberance around said opening and received in said cup-shaped shield, and sealing material interposed between said flange-like protuberance and said shield and also embedding the parts of said shield and insulating block that are within said sheath.

7. An electric heater comprising a resistance conductor, a terminal secured to said resistance conductor, a metallic sheath encasing said resistance conductor and terminal, the end of said terminal projecting from the end of said sheath, an electrically insulating sleeve within said sheathsurrounding said terminal in spaced relation with said terminal and said sheath, the section of said sheath around said sleeve flaring outwardly toward the end of the sheath, a protective cup having an enlarged part flaring outwardly from the sheath and a relatively small part inserted in said sheath, tapered to the flare of the sheath, and spacedboth from the sheath and the sleeve, and a substantially homogeneous mass of glass filling the spaces between the sleeve and terminal and tapered section of said cup, and also the space between said tapered section and said sheath.

FRED J. EWALD. JR.

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