US3591771A - Electric heaters - Google Patents

Abstract

An electric heater comprising a terminal section including a terminal rod disposed in electrically insulated concentric relation within a metal tube, and a pair of concentric coiled resistors, the outer resistor having an end electrically connected to the tube and the inner resistor having an end electrically connected to the terminal rod. The terminal section, with attached resistors, are then disposed in coaxial relation within a tubular metal sheath and refractory material is inserted within the sheath for electrical insulation. The sheath is hermetically sealed at one end by a plug welded in the sheath, and at the other end by a terminal housing which is welded to the sheath. The terminal housing contains electrical connections with the terminal rod and metal tube, and such connections include looped portions to accommodate expansion and contraction.

Description

United States Patent [72] Inventor John F. Volker 2,632,834 3/1953 Huck et al. 338/261 X Pittsburgh, Pa. 3,087,l34 4/1963 McOrlly 338/273 [211 App]. No. 10,684 3,254,320 5/1966 Hill et al, 338/24] [22] Filed Jan. 22, 1970 Division of Ser. No. 755.297. Aug. 8, 1968. 52 ;,'T ',f" i z Mayewsky figxNQiQiZlJ-SZ 0mey l iams an res e [45] Patented July 6, 1971 [73] Assignee Emerson Electric Company St. Louis, Mo.

ABSTRACT: An electric heater comprising a terminal section including a terminal rod disposed in electrically insulated concentric relation within a metal tube, and a pair of concentric [541 ELECTRIC HEATERS coiled resistors, the outer resistor having an end electrically 5 Claims 10D connected to the tube and the inner resistor having an end rawlng Figs.

electrically connected to the terminal rod. The terminal sec- [52] [1.5. Cl 219/553, (ion, with attached resistors, are then disposed in coaxial rela- 338/239 tion within a tubular metal sheath and refractory material is [5 I] ll". inserted within the sheath for electrical insulation. The heath [50] Field ofSearch 219/553, is hermetically sealed at one end by a plug welded in the 523, 261, 273;29/61l, 619 sheath, and at the other end by a terminal housing which is 6 welded to the sheath. The terminal housing contains electrical [5 1 References cued connections with the terminal rod and metal tube, and such UNITED STATES PATENTS connections include looped portions to accommodate expan- 2,494,333 1/1950 Daly 338/239 sion and contraction.

a4 0/ W 7a" %%z 61 ({(C/{l/j/l/l/i/l/l/lIll/A7//I///w I M M: {e -A Qfi 101 1'"- \\\\\\\\v-m= illllll-lllll r a. maz am t at I v I, I i\\ :\\}'\\\\7\:\\\ I: m Ill; 1. j f M a! a! ts y i s a "a I I.- 'QQKQL m I A y M PATENTED JUL 6197i SHEET 2 OF 3 INVENTOR. JOHN F. VOLKER A TTOR/V/f hat/MW ELECTRIC HEATERS This application is a division of application Ser. No. 755,297, filed Aug. 8, I968, and now US. Pat. No. 3,521,352.

BACKGROUND AND SUMMARY Electric heaters of the type shown in McOrlly US. Pat. No. 3,087,134 have been found to be extremely reliable in operation in uses where durability and dependability are required. As the size and capacity of the heaters are increased in accordance demands, the construction of the patented heaters required change, and the present invention provides a heater construction which permits the incorporation of the desirable qualities of the patented heaters in larger sizes and capacities.

DESCRIPTION OF THE DRAWINGS In the drawings accompanying this description and forming a part of this specification, there is shown, for purposes of il- :lustration, an embodiment which my invention may assume,

1 the construction of FIGS. 2 through 4 within a metal sheath,

prior to a filling operation,

FIG. 6 is a broken sectional view of the parts shown in FIG. but after filling and side pressing and certain machining operations,

FIG. 7 is an enlarged, broken sectional view showing the electric heater in final assembly,

FIG. 8 is a fragmentary sectional view of a detail of the construction shown in FIG. 7, and

FIGS. 9 and 10 are perspective views of parts used in the assembly shown in FIG. 7.

DETAILED DESCRIPTION The terminal rod section 10 of the heater is formed as a separate assembly, and comprises a metal tube 11 and a terminal rod 12. The terminal rod 12 has a connector portion 14 at one end, for connection to the spline of a conventional filling machine. A mica bushing 15 is disposed in one end of tube 11 to close this end, and the tube is uprighted with the bushing 15 lowermost, and placed in the filing machine for the operation which fills the space between the terminal rod 12 and the interior of the tube lll with powdered refractory material 151 in known manner. As is well known in the art, the filling operation provides a certain degree of compactness to the refractory material.

After the tube 11 has been filled with refractory material, it is removed from the filling machine and a mica plug 16 is inserted with the upper end of the tube so that the latter may be handled and worked without loss of refractory material. Instead of powdered refractory material, a series of refractory bushings may be inserted over the terminal pin to occupy the space between the pin and tube interior, and the filling machine operation may thus be eliminated.

The assembly thus produced is side pressed to further compact the refractory material. Then, the connector portion 14 is cut off, and stepdown or neck portions 17 and 18 are machined on the tube 11 and terminal rod 12, respectively.

The heating resistors comprise outer and inner coils l9 and 20, each preferably formed ofa suitable metal ribbon which is wound spirally. One end of the outer coil has an internal diameter to fit closely over the neck portion 17 of the tube 11 (see FIG. 2) and one end of the inner coil 20has in internal diameter to fit closely over the neck portion 18 of the terminal rod 12, and such end portions are welded to the neck portions, such as by a heliarc weld.

The coils I9 and 20 are preferably of constant diameters and the coil 20 is disposed concentrically within the coil 19, as shown. The opposite end (right-hand end in FIG. 2) has a conical formation 19c to fit closely over a conical metal plug 21, as best seen in FIG. 3, and is welded to the plug. The plug 21 is formed with a central longitudinal opening 22 to receive the adjoining end of the inner coil 20 so that the coils at this end are held in concentricity. The plug 21 is also formed with a peripheral undercut 23 and a transverse opening 24 is provided so that a weld 25 may be made between the plug 21 and the inner coil 20. The plug 21 is formed with a central threaded opening for a purpose later to appear.

A centering bushing 26 is disposed over the conical end of the outer coil 19, the bushing having its periphery formed with longitudinal grooves, as shown at 27, and having a center opening 28. The bushing 26 is fomied of an electric insulating material such as Alsimag 714 or equivalent, since it is required to be of a crushable nature, yet fired to produce sufficient hardness to prevent breakage from normal handling.

The assembly thus far produced is placed within an outer tubular metal sheath 29, as shown in FIG. 5. Ceramic bushings 30 are disposed over the tube 11 to fill the space between the tube 11 and sheath 29, the bushings 30 preferably ending at the neck portion 17 of the tube 11. A ceramic bushing 31 is disposed over the outer coil 19 and between this coil portion and the interior of sheath 29. A further ceramic bushing 32 is disposed between the coils l9 and 20. The bushings 31 and 32 insure that the coils are electrically insolated at this point.

The assembly is now ready for receiving powdered refractory material to fill the space within the sheath 29 and around and between the coils 19 and 20. Preparatory for the filling operation, an upper filling machine plug 35 is assembled with the right-hand end (FIG. 5) of the sheath 29. The plug includes a shank 36 which has an end threaded into the plug 21. A closure disc 37 is threaded onto the shank 36 and seats on the end of the sheath 29. The disc 37 may be rotated on the shank to establish a desirable tension on the inner and outer coils 20 and 19 and thus hold them in separated, concentric relation. The disc is apertured as at 38 to pass the refractory material, and bushing grooves 27 also accommodate this function. It will be noted that the metal tube 11 and terminal rod 12 will withstand a heavy pull on the resistor coils, and such pull in necessary due to the size of the coils.

A lower filling-machine plug 39 is connected to the lefthand end (FIG. 4) of the sheath 29, and closes the opening into the sheath. The plug 39 has a tubular portion 40 which fits into the space between the tube 11 and sheath 29 to maintain the same in concentric relation. The left end of the terminal rod 12 projects through an opening 41 in the plug and setscrews (not shown) are threaded into apertures 42 to engage the rod and hold it centered.

The foregoing assembly is then placed within a conventional filling-machine in upright position and powdered refractory material 42 is caused to flow through the openings 38 in the upper plug 35 to fill the open spaces in the sheath 29. This material will flow through the grooves 27 in the centering bushing 26 and, starting from the bushing 31 and working upwardly to the plug 35, will fill all cracks and crevices within the sheath 29, and indeed may filter downward to fill any small spaced between the ceramic bushings 30 and adjoining sheath surfaces. The filling operation is accompanied by a vibratory action to assist in compactly filling all spaces.

After the filling operation, the top closure 35 is removed and a plastic bushing (not shown) is rammed in place to close the end of sheath 29. The assembly is then turned end for end and the bottom closure 39 is removed and a plastic bushing (not shown) is rammed in place to close this end of the assembly. The assembly is then subjected to a side pressing operation to compact the powdered refractory material 42 to a rocklike density. The sidepressing operation also crushes the bushings 26, 30, 3] and 32 to powdered but rocklike density, and by reducing the transverse size of the assembly, insures that all cracks and crevices are filled with insulating material. it should be noted that the conical plug 21 holds against any reduction of the dielectric spacing between the inside diameter of the sheath 29 and the outside diameter of the outer coil 19. After the side pressing operation, the ends of the assembly are machined, as shown in FIG. 6, to remove the portions indicated in dotted lines and to bevel the left-hand ends of the tube 11 and sheath 29, as shown respectively at 44, 45. Refractory material from the right-hand end (FIG. 6) of the sheath 29 is removed and mica discs 46 and a metal plug 47 are inserted with the plug peripherally welded to the sheath as shown at 48 to form a hermetic seal.

The heating unit is now ready for final assembly operations. Referring to FIG. 6, the refractory material is removed from the left end of the tube 11 and sheath 29 and ceramic bushings 50, 51 are cemented in the spaces thus provided.

An electrical connector 52 has a semicircular hub 53 (see FIGS. 7 and 9) which is welded to the tube 11 and 54. The hub is semicircular to enable its installation behind the enlarged head of the bushing 50, since this bushing is already cemented in place. An expansion loop 55 is integral with the hub and extends therefrom and terminates in a flat tail 56. An electrical connector 57 has a portion 58 which is apertured as at 60, to pass the end of the terminal rod 12, the portion 58 being connected to the rod by a weld 61. An expansion loop 62 is integral with and extends from the portion 58 and terminates in a flat tail 63.

Either before or after welding of the connectors 52 and 57 to the tube 11 and terminal rod 12, respectively, terminals 64, 65 are brazed to respective tails 56 63. The terminals are similar and only the terminal 64 is shown in detail in FIG. 8. This terminal extends through and is hermetically sealed to an elongated dielectric sleeve 66 which may be formed of ceramic or other rigid, temperature resistant, insulating material. An apertured cup-shaped metal member 67 is suitably bonded to the exterior of one end of the sleeve and is circumferentially brazed or otherwise suitably secured at 68 to the portion of the wall 69 of a coupling 70. A cup-shaped metal member 71 is bonded to and over the other end of the sleeve 66.

Since the coupling 70 is already in assembled relation, a large metal sleeve 72 is inserted over the right-hand end (FIG. 7) of the heater assembly and moved along the sheath to the left until it meets the coupling 70, and is joined to the latter by the mutual engaging screwthreads 73. The two parts 70, 72 are threaded to completely seat the threads home, and then unthreaded about one turn to allow for expansion. The parts 70, 72 are then welded together by the peripheral weld 74 to hermetically seal their interconnection. The nose end 75 of the sleeve 72 is then welded to the sheath 29 by a peripheral weld 76, to hermetically seal their interconnection. ln forming the welds 74, 76 considerable heat is generated causing considerable longitudinal expansion of the parts. Since the conductors 64, 65 are brazed to the coupling 70 and respective connectors 52, 57, the terminal assembly is submitted to iongitudinal stress during the welding operations. However, since the connectors 52, 57 have expansion loops therein, no harm is done to any critical connection since the expansion loops absorb expansion and contraction forces.

The sleeve 72 is formed with an opening 77 and powdered refractory material 78 is introduced, under pressure, through this opening to completely fill the space within the sleeve 72 and coupling 70. The opening is then hermetically sealed with a plug weld 79. A dielectric bushing 80 is then disposed over the projecting prongs 81 of the conductors 64, 65 to electrically insulate the same from the coupling 70, and terminal clips 82 are brazed at 83, to the prongs to hold the bushing in place. A rubber boot 84 is disposed around the bushing 80 and surrounds the clips 82 to protect the electrical connections against grounding.

lclaim:

1. An electric heater, comprising a metal conductor rod disposed concentrically within a metal conductor tube, compacted refractory insulation between the outer surface of said rod and the inner wall of said tube, an end of said rod extending outwardly from an adjoining end of said tube and both ends having an undercut portion, a pair of concentrically arranged resistors having common ends closely disposed around and mechanically and electrically connected to respective undercut portions of said rod and tube, said resistors extending longitudinally from said rod and tube, means electrically interconnecting those common ends of said resistors which are opposite the first-mentioned common ends, a metal sheath concentrically surrounding said conductor tube and said resistors with peripheral space therebetween, said sheath being closed at the end adjacent to said electrical interconnection, refractory material filing said peripheral space to electrically insulate said tube and said resistors from said sheath, and a pair of electrical conductors extending outwardly of the opposite end of said sheath, one conductor being electrically connected to the opposite end of said rod and the other being electrically connected to the adjoining end of said tube opposite ends of said metal sheath being hermetically sealed.

2. The construction according to claim 1 wherein said electrical interconnection comprises a metal conductor plug having an opening to closely receive the adjoining end of the inner resistor and further having an outer peripheral surface closely received within the outer resistor.

3. The construction according to claim 2 wherein said plug has a threaded opening adapted to receive the threaded end of rod utilized during'assembly operations to maintain the resistors against sagging.

4. The construction according to claim 1 wherein said electrical conductors include expansion joints.

5. An electric heater, comprising a terminal assembly in cluding a metal conductor rod concentrically disposed within a metal conductor tube, compacted refractory insulation between the outer surface of said rod and the inner surface of said tube, a pair of concentrically arranged resistor coils having common ends closely fitting over respective first adjoining ends of said rod and tube and mechanically and electrically secured to the same, said coils extending in an axial direction from said rod and tube and the latter forming elongated terminals for the former, means mechanically and electrically interconnecting those common ends of said resistors which are opposite said first mentioned common ends, a metal sheath surrounding said tube and resistors with a peripheral space therebetween, said first adjoining ends of said rod and tube being disposed at one end of said sheath and said electrical interconnecting means being disposed at the other end of said sheath, refractory insulating material within said peripheral space to electrically insulate said tube, resistors and electrical interconnecting means from said sheath, means hermetically sealing said other sheath end, a pair of thermal expansion but electrically conducting members respectively electrically connected to said first adjoining ends of said rod and tube, a metal sleeve hermetically sealed to said one sheath end and having a transverse closure wall spaced from the latter, a pair of terminal conductors electrically connected to respective thermal expansion members and extending through said closure wall in electrically insulated hermetically sealed manner, and refractory material within said sleeve and surrounding said thermal expansion members and the portions of said terminal conductors within said sleeve, said terminal conductors being adapted for connection to a power source.

Claims (5)

1. An electric heater, comprising a metal conductor rod disposed concentrically within a metal conductor tube, compacted refractory insulation between the outer surface of said rod and the inner wall of said tube, an end of said rod extending outwardly from an adjoining end of said tube and both ends having an undercut portion, a pair of concentrically arranged resistors having common ends closely disposed around and mechanically and electrically connected to respective undercut portions of said rod and tube, said resistors extending longitudinally from said rod and tube, means electrically interconnecting those common ends of said resistors which are opposite the first-mentioned common ends, a metal sheath concentrically surrounding said conductor tube and said resistors with peripheral space therebetween, said sheath being closed at the end adjacent to said electrical interconnection, refractory material filing said peripheral space to electrically insulate said tube and said resistors from said sheath, and a pair of electrical conductors extending outwardly of the opposite end of said sheath, one conductor being electrically connected to the opposite end of said rod and the other being electrically connected to the adjoining end of said tube opposite ends of said metal sheath being hermetically sealed.

2. The construction according to claim 1 wherein said electrical interconnection comprises a metal conductor plug having an opening to closely receive the adjoining end of the inner resistor and further having an outer peripheral surface closely received within the outer resistor.

3. The construction according to claim 2 wherein said plug has a threaded opening adapted to receive the threaded end of rod utilized during assembly operations to maintain the resistors against sagging.

4. The construction according to claim 1 wherein said electrical conductors include expansion joints.

5. An electric heater, comprising a terminal assembly including a metal conductor rod concentrically disposed within a metal conductor tube, compacted refractory insulation between the outer surface of said rod and the inner surface of said tube, a pair of concentrically arranged resistor coils having common ends Closely fitting over respective first adjoining ends of said rod and tube and mechanically and electrically secured to the same, said coils extending in an axial direction from said rod and tube and the latter forming elongated terminals for the former, means mechanically and electrically interconnecting those common ends of said resistors which are opposite said first mentioned common ends, a metal sheath surrounding said tube and resistors with a peripheral space therebetween, said first adjoining ends of said rod and tube being disposed at one end of said sheath and said electrical interconnecting means being disposed at the other end of said sheath, refractory insulating material within said peripheral space to electrically insulate said tube, resistors and electrical interconnecting means from said sheath, means hermetically sealing said other sheath end, a pair of thermal expansion but electrically conducting members respectively electrically connected to said first adjoining ends of said rod and tube, a metal sleeve hermetically sealed to said one sheath end and having a transverse closure wall spaced from the latter, a pair of terminal conductors electrically connected to respective thermal expansion members and extending through said closure wall in electrically insulated hermetically sealed manner, and refractory material within said sleeve and surrounding said thermal expansion members and the portions of said terminal conductors within said sleeve, said terminal conductors being adapted for connection to a power source.

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