US2874256A - Heating element - Google Patents

Description

G. H. CALVERT HEAT Feb. 17, 1959 NG ELEMENT Filed July 21, 1955 [N VEN TOR. 6255M 64 (44 V5277 HEATING ELEMENT Gresham H. =Calvert, Santa Cruz, Calif.

Application July 21, 1955, Serial No. 523,535

1 Claim. (Cl. 201-66) This invention relates to and in general has for its object the provision of an infrared or black body radiating heating element for therapeutic heaters and which constitutes an improvement in and to the heating element described and claimed in my Patent No. 2,596,837 of May 13, 1952 and in my Patent No. 2,690,491 of September 28, 1954.

The heating elements disclosed in these patents include a coiled Nichrome wire resistance element coaxially suspended within a glass tube. Although the continued use of such an element does not appear to impair its electrical characteristics, it does result in a decrease in its resiliency, for when operated in a vertical position it sags to an extent such that its lower convolutions contact each other. This in effect shorts out these convolutions and decreases the total resistance in the circuit. This holds true even though the resistance element is originally coated with a dielectric material, for in time the dielectric material tends to scale from the resistance wire.

More specifically, the primary object of this invention is the provision of a heating element of the character above described wherein the glass tube is partially filled with a solid dielectric fluid, such as aluminum oxide crystals, serving to positively hold the convolutions of the coiled wire resistance element in spaced relation relative to each other regardless of the position in which the heating element is operated.

The invention possesses other advantageous features, some of which, with the foregoing will be set forth at length in the following description where that form of the invention which has been selected for illustration in the drawings accompanying and forming a part of the present specification, is outlined in full. In said drawings, one form of the invention is shown, but it is not limited to such form, since the invention as set forth in the claim may be embodied in other forms.

Referring to the drawings:

Fig. 1 is a perspective view of a heating element embodying the objects of my invention.

Fig. 2 is a side view of the heating element illustrated in Fig. l with portions thereof broken away to better illustrate its construction.

Fig. 3 is a transverse section of the device taken on the section line 3-3 of Fig. 2.

Fig. 4 is an enlarged fragmentary section of the aluminum oxide coated resistance element of the unit.

As illustrated in these various figures, the objects of my invention have been embodied in a heating element comprising an outer section of glass tubing 1 and an inner coaxial section of glass tubing 2, together defining an intermediate annular chamber 3 filled with an annular body of an inorganic granular material 4, such as silica carbide, galena, pitchbleude, powdered garnet and powdered topaz and other industrial gems and/or crystals, preferably ground to from to 250 mesh.

Disposed between the ends of tubing sections 1 and 2 is an asbestos spacing ring 5. Fitted within the end of the outer tubing section 1 is an annular asbestos gasket 2,874,256 Patented Feb. 17, 1959 6 provided at its outer end with an outwardly extending flange 7 overhanging the end of the outer tubing section 1. Closing the outer end of the gasket 6 and extending thereinto is a porcelain plug or cap 8 provided with a flange 9 overlying the gasket flange 7 and formed at its outer end with a terminal recess 11 and with radially aligned screwdriver kerfs 12. Since both ends of the heating element or unit are identical, this description of course applies equally to both of said ends. Inserted coaxially of the plug 8 is a screw 13 threaded into a nut 14 countersunk in the inner end of the plug.

Coaxially suspended within the inner tube section 2 and positively spaced therefrom is a coiled Nichrome wire resistance element 15 coated with a layer 16 of aluminum oxide and connected at each of its ends to one of the screws 13. As best shown in the left-hand end of Fig. 2, each of the free ends of the element 15 is sheathed in a small hole 16 formed longitudinally in each cap 8. Also as shown in this figure, the screws 13 serve as connectors for connecting the unit through leads 17 with a conventional plug or source of 110 volt A. C. house current.

Partially filling the inner tube 2 and surrounding the coiled wire resistance element 15 is a body 18 of granules or crystals of a dielectric material such as aluminum oxide. It is essential that this material only partially fill the tube 2 so as to permit it to expand in response to increases in temperature without at the same time breaking the tube or disengaging the porcelain plugs 8. Since the aluminum oxide is fluid, it will of course always seek its own level and therefore support the lowermost of the resistance element against sagging regardless of the position in which the heating element is being operated. For

this purpose then, the function of the aluminum oxide is purely physical or mechanical, and as a consequence, any other dielectric solid fluid material capable of withstanding the temperatures developed by the heating element, and inert at such temperatures with respect to the tubing and the resistance element, can be substituted for the aluminum oxide. Although the degree to which the tube is filled with the granular material is not critical, a

percent fill has proved satisfactory.

Also, it should be observed that although the heating element above described involves the use of two radially spaced concentric tubes, the present invention is equally applicable to a heating element involving only one tube such as described and claimed in my said Patent No. 2,596,837.

Although not shown, the unit above described is designed to be mounted within a reflector supported by a table type or floor type pedestal.

From the above description it will be seen that I have provided a heating element of the character described in my issued patents but which constitutes an improvement thereto in that the resistance element is restrained against sagging and therefore shorting out by a solid fluid material.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

A heating element comprising a tubular member, plugs positioned in the ends of said tubular member, a coiled wire resistance element positioned in said tubular member, the diameter of the convolutions of said coiled resistance element approaching the inside diameter of said tubular element, said coiled resistance element having a coating of refractory material adhering to the convolutions thereof, said resistance element being substantially surrounded by a fluid granular electrically insulating material for engaging said coating of refractory material and for supporting said resistance element to prevent said resistance element from sagging, said coating engaging said fluid granular material to prevent said granular material from contacting the heated coiled resistance element and being caked, said granular material being sufliciently loose in said tubular member to permit expansion eonvolutions of said coiled resistance element when the orientation of the heating element is altered whereby said res'istance'elment' is silpported away from the inner sur face of said tubular member.

References Cited in the file of this patent UNITED STATES PATENTS Whittingham Mar. 23, 1897 Leonard Oct. 24, 1899 Monnot Apr. 8, 1913 Cook Mar. 7, 1916 Shriner Aug. 28, 1928 Wiegand Feb. 10, 1942 Calvert May 13, 1952 Calvert -i Sept. 28, 1954

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