US3366913A - Heater construction - Google Patents

Description

Jan. 30, 1968 B, DMS ETAL 3,366,913

HEATER CONSTRUCTION Filed March l0, 1965 ff/a far?

United States Patent O 3,366,913 HEATER CNSTRUCTIN Bayard C. Davis, Lombard, Alvin Singer, Glencoe, and

Milford T. hapman, Jr., Addison, Ill., assignors, by

direct and mesme assignments, to Continental Sensing,

Inc., Melrose Parli, Ill., a corporation of Illinois Filed Mar. 10, 1965, Ser. No. 438,488 11 Claims. (Cl. 33E-322) ABSTRACT GF THE DISCLOSURE A heater structure and a method for making it. A resistive heating element is butt-welded to a pair of terminal segments. The weld junctions 'are enclosed by tubular terminal elements which encompass the terminal segments and a portion of the heating element at each end. The terminal elements are slightly chamfered to mate with peripheral grooves in the heating element, and are subjected to suitable swaging and/ or drawing operations. The terminal elements and segments and the heating element are surrounded by a layer of heat conductive, electrically insulating material, and the entire structure is enclosed in a metallic sheath.

This invention relates to heater constructions and more particularly to an improved method of fabricating resistive heating elements.

It is an object of the present invention to provide an improved heater construction.

Still another object of the present invention is to provide a heater construction wherein the high resistance heating element employed therein is bonded to the terminals of the heater by structurally reinforced junctions.

An 'additional object of the present invention is to provide an improved method of fabricating resistive heating elements so that the resulting heater construction is characterized by relatively long lived operation, an absence of hot spots and an ability to withstand normal handling without having the continuity thereof disturbed.

Other objects and advantages of the present invention will become apparent from the following detailed description of one preferred embodiment thereof particularly when considered in conjunction with the accompanying drawing wherein:

FIGURE 1 is a perspective View of a portion of a resistive heater constructed in accordance with the present invention; and

FIGURE 2 is an enlarged cross sectional view with portions broken away to further illustrate the preferred fabrication technique of the present invention.

In general, the present invention is directed to an improved technique for fabricating heaters whereby the resistive heating element is joined to low resistance terminals by structurally stable and reinforced welded junctions. As a result, the operational life of the heater isA increased, the possibility of hot spot formations is minimized, and the heater can be normally handled without disturbing the continuity thereof.

Referring to the drawing, there is shown a preferred embodiment of a resistive heater fabricated in accordance with the method of the present invention. The particular embodiment illustrated is -a heater wherein a resistive heating element 11 and terminal conductors 12 and 13 that are associated therewith are surrounded by a densely compacted, heat conductive insulating material 14 and confined within a suitable external sheathing 1S. However, it should be understood that the fabrication technique as hereinafter described in det-ail can be applied to all forms of heaters whether or not such heaters employ the additional protective sheathing (c g. stainless steel) and surrounding conductive insulating material (e.g. MgO).

Referring more particularly to FIGURE 2, the method of the present invention contemplates the joining of the resistive heating element 11 to each of the terminal conductors 12 and 13 by means of reinforced welded junctions 12a and 13a respectively. In this connection, the fabrication of the heater 1t) is initiated by selecting a suitable high resistance material (e.g. Kanthal) having a preselected diameter and length. This member serves as the heating element 11, and the dimensions and thermal energy producing characteristics thereof are, in a well known manner, dictated by the particular application to which the heater is to be put.

After the selection of the appropriate heating element 11, a pair of low resistance terminal segments 17 and 18 (eg. formed of nickel) are selected and joined to the oppositely disposed ends of the heating element. These segments constitute an integral portion of the terminal conductors 12 and 13. Preferably, the terminal segments 17 and 18 are butt-welded to the ends of the heating element 11 and, accordingly, these segments preferably have cross-sectional dimensions corresponding to those of the heating element 11 to insure that these welding operations are effected in the most simple, reliable, and efficient manner. After the welding of these segments has been completed, the reinforcement of the welded junctions is effected by the insertion of the partially fabricated heater into tubular terminal elements 19 and 20 that form the remaining portion of the terminal conductors 12 and 13. The terminal segments 17 and 18 in certain applications (eg. when using extremely long tubular terminal elements 19 and 20) will extend the entire length of these tubular terminal elements as depicted in FIG. l. In other constructions, the terminal segments 17 and 18 yare relatively short elements which do not extend along the entire length of the terminal elements.

The tubular elements 19 and 20 are formed with inside diameters that complement the outside diameters of the joined terminal sections 17 and 18 and heating element 11. The complementary dimensions of these Subcomponents of the heater 10 are such that the joined terminal sections and heating element `are somewhat force fitted into the free ends of the tubular elements. In this connection, these components are joined so that a major portion of the resistive heating element 11 extends beyond and between the tubular elements 19 and 20 while at the same time insuring that the welded junctions are fully encompassed by the tubes.

To insure the proper positioning of the joined terminal sections and heating element and to facilitate the positive reinforced mounting of these joined elements, peripheral portions of the heating element 11 adjacent the oppositely disposed ends thereof are formed with slight grooves 11a and 11b. The partially joined assembly formed by the heating element 11 and terminal sections 17 and 18 is inserted into the tubular elements 19 and 2li to a point whereat the ends of the tubular elements, which are preferably slightly chamfered, are aligned with the grooves 11a and 11b. To complete the assembly pursuant to the present invention, this fabricated structure is then subjected to suitable swaging and/or drawing operations such that the free ends of the tubular elements 19 and 2li are intimately formed about the welded junctions with the extreme chamfered ends thereof being forced into the grooves 11a and 11b. This final forming of these overlapping sleeve type tubular elements 19 and 2t) is effected so that the possibility of any void spots is eliminated.

t will be appreciated from the foregoing that the method of the present invention provides for the ready fabrication of structurally stable heater constructions. That is, any structural weakness in the heater as a result of the welding operations (eg. crystallization) is effectively compensated for by utilizing the overlapping sleeve type tubular elements 19 and 20 and forming (eg. by drawing and/or swaging) the ends of the elements into intimate overlapping and 4reinforcing contact with the joined subassembly. Additional structural stability of the overall heater construction stems from forcing the slightly chamfered ends of the tubular elements into mating engagement with the peripheral grooves fia and lib. The fabrication method as described herein also results in the elimi nation of any void spots adjacent the junction of the high and low resistive components of the heater so that hot spot formations are precluded.

When a heater constructed in accordance with the aforedescribed method is designed to be confined within a densely compacted heat conductive insulating material and surrounded by suitable moisture impervious metallic sheathing as shown in the accompanying drawing, addi tional fabrication steps are necessary to complete the entire assembly. In this connection, after the heater has been fabricated, a plurality of suitably apertured, structurally stable ceramic insulator strips (not shown) are strung onto the heater, including the terminal conductors, along substantially the entire length thereof. This partially assembled unit is then inserted into surgically clean metallic tubing. Thereafter, this assembled unit is subjected to suitable successive drawing and/ or swaging operations to insure that the insulator strips are densely compacted about the heater and that the sheathing is drawn into intimate contact with the materials confined therein. Upon completion of this unit, suitable terminal elements (not shown) can be secured to the free ends of the terminal conductors thereby completing the confined assembly for operation.

lt will be appreciated from the foregoing that the present invention provides an improved technique for effecting tho fabrication of heaters independent of the size or nature of the various components employed therein. The method allows such heaters to be constructed in a reliable and efficient manner and calls for a minimum number of operational steps absent any critical drilling and/ or multiple welding operations. Obviously, various modifications of the fabrication technique of the present invention might be devised by one skilled in the art without departing from the invention, various features of which are set forth in the accompanying claims.

What is claimed is:

ll. A method of fabricating resistive heaters which comprises joining each oppositely disposed end of a high resistance heating element to a low resistance terminal segment and thereby providing a heater subassembly, inserting the joined terminal segments and heating element into the free ends of a pair of tubular terminal elements so that the free ends of said terminal elements encompass the junctions of said subassembiy and so that a substantial portion of said heating element extends between the free ends of said tubular terminal elements, and drawing said tubular elements about the junctions of said terminal segments with said heating element so that said junctions are positively confined within the terminal elements and void spaces between the conned portions of said subassemblies and said confining portions of said tubular terminal elements are eliminated.

Z. A method of fabricating resistive heaters which comprises welding each oppositely disposed end of a high resistance heating element having a preselected cross sectional configuration and dimensions to a low resistance terminal segment having a corresponding configuration and dimensions to thereby provide a heater subassembly, inserting the joined terminal segments and heating element into the free ends of a pair of tubular terminal elements so that the free ends of said terminal elements encompass the welded junctions of said subassembly and so that a substantial portion of said heating element extends between the free ends of said tubular terminal elements, and drawing said tubular elements about the welded junctions of said terminal segments with said heating element so that said junctions are positively confined within the terminal elements and void spaces between the confined portions of said subassemblies and said confining portions of said tubular terminal elements are eliminated.

3. A method of fabricating resistive heating structures which comprises welding each oppositely disposed end of an elongated high resistance heating element to a low resistance terminal segment and thereby providing a heater subassembly; inserting the joined terminal segments and heating element into the -free ends of a pair of tubular terminal elements so that the free ends of said terminal elements encompasses the junctions of said subassembly and so that a substantial portion of said heating element extends between the free ends of said tubular terminal elements; drawing said tubular elements about the welded junctions of said terminal segments with said heating element so that said welded junctions are positively confined within the terminal elements and void spaces between the confined portions of said subassemblies and said confining portions of said tubular terminal elements are eliminated; and enclosing said joined heating element, terminal segments and tubular terminal elements with a densely compacted layer of a heat conductive insulating material surrounded by a confining moisture impervious tubular metallic sheath.

4. A method of fabricating resistive heaters which comprises joining each oppositely disposed end of a high resistance heating element to a low resistance terminal segment and thereby providing a heater subassembly; forming slight peripheral grooves in said heating element adjacent each of said ends thereof and in preselected spaced relation to said junctions; inserting the joined terminal segments and heating elements into a pair of tubular terminal elements having slightly charnfered end portions so that the said tubular terminal elements encompass the junctions of said subassembly in a sleevelike configuration and so that a substantial portion of said heating element extends between the slightly chamfered ends of said tubular terminal elements; and drawing said tubular elements about the junctions of said terminal segments with said heating element so that said chamfered end portions are urged into mating relationship with said peripheral grooves, said junctions are positively confined within the terminal elements and void spaces between the confined portions of said subassemblies and said confining portions of said tubular terminal elements are eliminated.

5. A method of fabricating resistive heaters which comprises welding each oppositely disposed end of a high resistance heating element having a preselected cross sectional configuration and dimensions to a low resistance terminal segment having a corresponding configuration and dimensions to thereby provide a heater subassembly; forming slight peripheral grooves in said heating element adjacent each of said ends thereof and in preselected spaced relation to said junctions; inserting the joined terminal segments and heating element into the ends of a pair of tubular terminal elements having slightly chamfered end portions so that the free ends of said terminal elements encompass the welded junctions of said subassembly and so that a substantial portion of said heating element extends between the free ends of said tubular terminal elements; and drawing said tubular elements about the welded junctions of said terminal segments with said heating element so that said chamfered end portions are urged into mating relationship with said peripheral grooves, said junctions are positively confined within the terminal elements and void spaces between the confined portions of said subasseinblies and said conining portions of said tubular terminal elements are eliminated.

6. A method of fabricating resistive heating structures which comprises welding each oppositely disposed end of an elongated high resistance heating element to a low resistance terminal segment and thereby providing a heater subassembly; forming slight peripheral grooves in said heating element adjacent each of said ends thereof and in preselected spaced relation to said junctions; insetting the joined terminal segments and heating element into the free ends of a pair of tubutar terminal elements having slightly chamfered end portions so that the free ends of said terminal elements encompass the junctions of said subassernbly and so that a substantial portion of said heating element extends between the free ends of said tubular terminal elements; drawing said tubular elements about the welded junctions of said terminal segments with said heating elements so that said chamfered end portions are urged into mating relationship with said peripheral grooves, said welded junctions are positively confined within the terminal elements and void spaces between the confined portions of said subassemblies and said conning portions of said tubular terminal elements are eliminated; and enclosing said joined heating element, terminal segments and tubular terminal elements with a densely compacted layer of a heat conductive insulating material surrounded by a confining moisture impervious tubular metallic sheath.

7. A terminal construction comprising a conductive element having a peripheral groove formed therein adjacent an end thereof; a terminal segment having a crosssectional configuration corresponding to that of said conductive element, said segment being electrically and mechanically connected to said end of said conductive element; and a tubular terminal element having one end portion thereof slightly chamfered, said terminal element being drawn into direct forced contact with and about a portion of said conductive element, the junction between said conductive element and said terminal segment, and at least a portion of said terminal segment so that said chamfered end portion mates with said peripheral groove.

8. A conductor structure comprising an elongated conductive element; a pair of terminal segments each having a cross-sectional configuration corresponding to that of said conductive element, one of said terminal segments being Welded to each end of said conductive element to form a junction therebetween; a pair of tubular terminal elements, one each of said terminal elements being drawn into direct forced contact with and about one of said terminal segments, said junction and a portion of said conductive element; a densely compacted mass of heat conductive insulating material surrounding said conductive element, said terminal segments and sai-d terminal elements; and a confining moisture impervious tubular metallic sheath surrounding said mass of material.

9. A conductor structure as deued in claim 8, wherein said conductive element has a peripheral groove formed adjacent each of said junctions, and each of said terminal elements has a slightly chamfered end portion, said terminal elements being formed about said conduck tive element so that said chamfered end portions mate with said grooves.

10. A heater structure comprising a high resistance heating element having a peripheral groove formed therein adjacent at least one end thereof; a terminal segment having a cross-sectional configuration corresponding to that of said heating element, said segment being joined to said one end of said heating element; and a tubular terminal element having one end portion thereof slightly chamfered, said terminal element being drawn into direct forced contact with and about a portion of said heating element, the junction between said heating element and said terminal segment, and said terminal Segment, so that said chamfered end portion mates with said peripheral groove.

11. A heater structure as dened in claim 10, wherein said heating element, said terminal segment and said terminal element are surrounded by a densely compacted mass of heat conductive insulating material, and said mass of material is surrounded by a confining moisture impervious tubular metallic sheath.

References Cited UNITED STATES PATENTS 3,320,659 5/1967 Jerome 174-94 X 3,138,656 6/1964 Merrell 174-90 FOREIGN PATENTS 60,105 10/1947 Netherlands.

843,825 4/1939 France.

RICHARD M. WOOD, Primary Examiner. J. G. SMITH, Assistant Examiner.

Images