US2735922A

US2735922A - johnson

Info

Publication number: US2735922A
Authority: US
Publication date: 1956-02-21
Anticipated expiration: 1973-02-21

Description

Feb. 21, 1956 H. R. JQHNSON 2,735,922

HEATING ELEMENT FOR COFFEE MAKERS, ETC

Filed Feb. 2, 1955 FIG. I

INVENTOR HOWARD R. JOHNSON ATT Y United States Patent HEATING ELEMENT FOR COFFEE MAKERS, ETC.

Howard R. Johnson, Collingswood, N. J. Application February 2, 1955, Serial No. 485,678

1 Claim. (Cl. 219-19) This invention relates to electrical elements for use with vessels in which a liquid is heated, a preferred application being the heating element for a coffee-maker, such as a percolator.

The principal object of the invention is to provide a simple and eflicient heating element of this type in which there is excellent transfer of heat from the resistance wire to the liquid being heated and at the same time a very low transfer of heat to the atmosphere typified by the air below the bottom of the coffee making vessel.

A further object of the invention is to provide a competitive price assembly which will permit the use of a quite thin casing beneath or within the cofiee pot or other holding vessel. While these casings would preferably be made of aluminum this metal is not suitable in reasonably thin section for holding the usual heat transfer powder which must be put in under heavy pressures which normal thicknesses of aluminum will not stand. By substituting a lead filling which can readily be poured in, excellent heat transfer to a thin walled casing may be obtained,

Figure l is a cross-section through a preferred form of heating element which embodies the invention.

Figure 2 is a modification.

In the drawings represents a coil of Nichrome wire would on a ceramic core 11 which may be in spool shape if so desired but is illustrated as a core having only one head. Following usual practice, the wire is insulated and the coil is covered with a ceramic coating 12 coaxial with and well spaced from the casing 14 which may be of copper or other metal suitable for the purpose, my preference being for aluminum. Between the sheet metal casing 14 and the ceramic insulating covering 12 of the coil I completely fill the space with a metal 15 having a low fusing point such as white metal but is preferably lead.

The open end 16 of the metal casing 14 is closed by a circular base 20 which is of a high electrically insulating material with low heat conducting properties. A very convenient material to use for this purpose is a glass filled mica compound which molds easily and may be attached to the metal casing by a suitable sealing compound 21, a preferred material being an epoxy resin. I prefer to leave an air space 22 between the bottom of the core or spool 11 and the depressed portion 23 of the base and also prefer that the metal filling 15 shall engage the base as at 24 touching the annular portion 25 completely around.

While contact pins can readily be molded in place through any portion of the base 20, I prefer that these leads 26 and 27 extend through a central stem 30 integral with the base and forming a screw so that the heating element may be secured to a wall such as 32 of the cofiee-pot or other liquid heating vessel by a nut such as 33, the usual gasket 34 being interposed.

In making the device the Nichrome wire is wound on the core in helical fashion suitably insulated and when the coil is formed it is completely covered by an insulating ceramic coating. With the core centered in the aluminum casing 14, the space between the coil and the casing is filled with molten lead, the ends of wire from the coil having been fastened to the embedded

leads

26 and 27 in the stem. The base is now inserted in the open end of the casing and is secured to the casing by means of the epoxy resin or other sealing compound. The heating element is now ready for installation in any desired heating vessel.

In the modified form illustrated in Fig. 2, the heating element is shown as applied to the bottom 32 of the vessel holding the liquid. The coil 10a is here of torus shape, wound on an annular core 11a, the coil being coated with an electrically insulating covering material 12a which is spaced from the circular tray type casing 14a all around. The base 20a in this type element is likewise dish shaped and may or may not directly engage the bot tom of the coffee pot at its periphery 36 but preferably does, as shown. The heat conducting, low melting point metal or alloy 15 completely fills the casing 14a and hence directly engages the bottom metal wall 32. As in the preferred form, the core 11a or ceramic spool has a spiral groove or cut 37 which anchors the wire and holds it in place when it is mounted and baked, this grooving of the core being quite helpful.

What I claim is:

A heating element for liquids comprising a resistance wire wound on a ceramic spool, an insulating ceramic coating surrounding the coil so formed, a metal casing having an open end, surrounding the coating and spaced therefrom, a heat conductor completely filling such space and comprising a low-fusing metal, and a base secured to the casing by an epoxy resin sealing compound, said base being formed of a material of low heat conducting and high electrical insulating properties, and closing the open end of the casing.

References Cited in the file of this patent UNITED STATES PATENTS 1,848,449 Wiegand Mar. 8, 1932 1,897,197 Jolas Feb. 14, 1933 2,179,934 Jones Nov. 14, 1935