US2860226A - Electric heater assembly - Google Patents

Description

Nov. 11, 1958 R. l.. WILLIAMS ETAL ELECTRIC HEATER ASSEMBLY Filed March 26, 1957 ON NN. mw

United States Patent O ELECTRIC HEATER ASSEMBLY Ronald L. Williams and Carroll E. Sinciair, Pittsburgh, and Robert E. Burkhart, Wiikiusburg, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgn, Pa., a corporation ofPennsylvania Application March 26, 1957, Serial No. 648,587

16 Claims. (Cl. 219-38) The present invention relates to a replaceable electric heater assembly and more particularly to means for sealing the same and for detachably coupling the electricalV contacts thereof.

There are many applications wherein it is necessary to provide a sealed vessel or other container with a suitable heating means in order to increase or maintain the temperature of the material contained Within the vessel. ln the case of sealed or pressurized vessels, it is frequently desirable to remove the heating elements for repair or replacement without opening the vessel. Consequently, such heating elements are frequently inserted into the interior of the vessel through suitably formed apertures in the wall of the vessel.

Prior heating elements of the character described frequently had to be sealed within the vessel by means of brazing or welding to prevent leakage and thus could not be readily removed from the vessel Wall in the event of leakage or other failure of the heating element. In the event of failure of the heating element, the material contained within the vessel frequently was contaminated with insulating material or other components associated with the heating element. The diiculty or sometimes the impossibility of removing and replacing prior heating elements of this nature from the vessel Vwall compelled their operation at a relatively low Wattage density in order to minimize burnouts or other failures in the heating elements and to furnish an acceptable heater life. These prior heating elements often suffered from the additional disadvantage that in many cases no adequate means was provided for preventing escape of pressurized and frequently hazardous fluids from the vessel by way of the heater in the event of failure thereof. Prior heating elements have not been provided with adequate means for sealing the electrical connections thereof for use in corrosive atmospheres or against the release of such pressurized fluids and at the same time for providing quick detachability of the connections. Therefore in those heaters which were adapted for removability, considerable time was expended in attaching and detaching the electrical contacts thereof with the source of electrical operating potential.

In contemplation of the foregoing discussion, it is an object of the invention to provide a novel and eicient replaceable heating element.

Other objects of the invention are to provide novel means for sealing a replaceable heating element and for preventing leakage of the vessel contents in the event of failure of the heating element.

A further object of the invention is to provide a novel arrangement for quickly and eiciently inserting and removing a heating element relative to the wall of a sealed vessel. f

lStill other objects of the invention are to, provide means for quickly coupling and decoupling the electrical contacts of said heating element relativeto a source of 2,860,226 Patented Nov. 11, 1958 ICC operating potential and for conveniently providing a fluid tight housing for said means.

A further object of the invention is to provide an efficient and readily replaceable sealed heating element in combination with means for reentrantly inserting the element through a wall of a vessel.

These and other objects, features and advantages of the invention will be elaborated upon in greater detail during the ensuing description of illustrative forms of the invention, with the description being taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a longitudinal sectional view of a replaceable heating element and coupling therefor constructed in accordance with the invention and shown in connection with reentrant means for inserting the heating element through the wall of a sealed vessel;

Fig. 2 is a cross-sectional View of the coupling means of Fig. 1, which view is taken along reference lines lle-II of Fig. l;

Fig. 3 is a cross-sectional view of the coupling means of Fig. 1, with the view being taken along reference lines Ill-III thereof;

Fig. 4 is still another cross-sectional view of the cous pling means of Fig. 1, which view is taken along reference lines IV-IV of Fig. l;

Fig. 5 is another cross-sectional view taken along lines V-V of the coupling means of Fig. l;

Fig. 6 is still another cross-sectional view ofV Fig. l taken along lines VI-VI thereof; Y

Fig. 7 is an enlarged longitudinal sectional view of one of the detachable electrical contacts of Fig. l; and

Fig. 8 is a top plan view of thedetachable electrical contact of Fig. 7 shown herein in a position prior to joining the components thereof.

According to the invention, a hermetically sealed heating element is adapted for insertion into a hermetically sealed reentrant thimble, therefor and means are provided for sealing the thimble to the wall of a sealed vessel and for detachably sealing the thimble to the hermetically sealed casing of the replaceable heating element. Additional means are provided for imparting a quick-detachable feature to a means for electrically coupling thev heating element to a source of operating potential therefor and for detachbly sealing a housing surrounding the electrical coupling to the casing of the hermetically sealed heating element. With this arrangement of the invention the electrical contacts of the heating element are positively coupled to the source of operating potential but nevertheless are readily detachable to permit removal or replacement of the hermetically sealed heating element. When in its operating position, the replaceable heating element, the aforesaid reentrant thimble, and the sealed detachable electrical coupling are completely sealed to form an integral enclosure comprising these components so that in the event of a leak or failure in the reentrant thimble or of a double leak or failure in the reentrant thimble and in the hermetically sealed heating element inserted therein, escape of lluid, through the heating element or the reentrant thimble from a pressurized vessel in which the replaceable heating elementsk are employed is prevented.

Referring now more particularly to the drawings, the exemplary form of the invention illustrated therein comprises a hermetically sealed replaceable heating element 2t) including an end sealing arrangement 25, a reentrant thimble`22, and a sealed casing 24 for enclosing a detachable electrical coupling. The reentrant thimble 22 extends through a channel 26l formed in the wall 28 of a sealed vessel and extends through suitable thermal sulation 30, if such material is employed. Thereentr thimble is secured against longitudinal movement in channel 26 and is rigidly secured to the wall 28 ant the the vessel by means of an annular sealing weld 29. Adjacent the outward end of the reentrant thimble 22, a cup-shaped sealing cap 32 is inserted thereoverand is secured to the exterior surface of the reentrant thimble by an annular sealing weld 34. To the outer end of the sealing cap 32 an outwardly extending tubular projection 36 is secured or is formed integrally therewith. The projection 36 is threaded exteriorly and is provided with an interiorly disposed conical surface 38 for purposes presently to be explained. A cup-shaped sealing member 40 is threadedly engaged with the tubular extension 36 of the sealing cap 32 and suitable sealing means is inserted between the member 40 and the projection 36 for sealing l the outward end of the reentrant thimble 22 and associated components thereof to the hermetically sealed replaceable heating element 20. One form of such sealing means includes a pair of wedge-shaped annular sealing rings 42 whose surfaces adjacent the tapered portions thereof tightly engage the heating element in a known manner upon tightening down the cup-shaped member 40. The sealing rings 42 are preferably fabricated from a metal such as stainless steel in order to provide a rigid metal-to-metal uid tight seal between the reentrant thimble assembly 22 and the heating element 20.

The replaceable heating element20 is adapted for insertion into the central channel 44 of the reentrant thimble assembly 22 and therefore the heating element comprises an elongated cylindrical casing member 46 extending substantially along the interior length of the reentrant thimble assembly 22 and protruding a short distance outwardly therefrom. Positioned within the casing member 46 in order to lie interiorly of the wall 28 of the vessel is a heating coil 48 coupled by means of conductors 50 and S2 to the sealed casing arrangement 24, which is presently to be described in greater detail. The heating coil 48 and the conductors 50 and 52 are embedded in suitable electrically insulating material 54 which, when used in conjunction with a high temperature sealed vessel, is formed from a ceramic material such as magnesium oxide or aluminum oxide. The insulating material 54 extends along substantially the entire interior length of the casing 46.

The outward end of the casing 46 is provided with means sealed thereto for enclosing and hermetically sealing the conductors 50 and 52 at points adjacent to their emergence from the casing member 46. In this example of the invention the hermetically sealing means comprises a relatively short annular sleeve member 56, a relatively thinner connecting sleeve 58 and the coupling member 60. The annular member, the connecting sleeve and the coupling member are in turn inserted and hermetically sealed one toranother, and the annular member is hermetically sealed to the sealed casing 46 of the heating element 20, as by the annular sealing welds 62, 64, and 66 respectively. The coupling member 60 is provided with a radially projecting portion 68, the outward surface of which isA threaded for the purpose of engaging the sealed casing structure 24, presently to be described. The radial projection 68 Afurther is provided with a groove 70 formed on the end surface of the radial projection for receiving a resilient O-ring 72 to aid in sealing the casing 24 in a manner to be elaborated upon in greater detail.

A ceramic insulating member 74, in this example fabri cated from aluminum oxide, is partially inserted into the intermediate sleeve S8 and positioned thereat by means of an annular shoulder 76 formed on the outer periphery of the insulating member 74. The insulating member is hermetlcally sealed to the sleeve 58 and a pair of apertures 78 `are formed in the insulating member 74, through which apertures the conductors 50and 52 extend respectively. Each of the apertures 78 is provided with an intermediately disposed widened portion 80 into which portions the insulating member 74 by means of portions 84 of silver brazing material fused into the recesses 86 provided in the ceramic insulating member 74 and individually surrounding the metallic sleeves 82 when inserted in the aforesaid apertures 78. The metallic sleeves 82 preferably are hermetically sealed to the ceramic insulating member prior to assembly thereof to the heating element 22 with the result thatupon inserting the insulating member into the inner sleeve 58 and the conductors 50 and 52 through the apertures of the insulating member, the latter can be conveniently and hermetically sealed to the conductors 50 and 52 simply by brazing or soldering the nickel sleeves 82 to the conductors 50 and 52, respectively.

The sealed casing 24, which is presently to be described and which encloses a pair of detachable electrical contacts indicated generally by the reference characters 88 and 90, is sealed to the radially extending portion 68 of the coupling member 60 by means of a coupling nut 92 threadedly engaged therewith. The coupling nut 92 is provided with an inwardly extending ange 94 which engages a complementary, outwardly extending ange 96 of an outer cylindrical casing section or housing 98 of the sealed casing 24. The end surface 100 of the housing ange 96 is machined for sealing engagement thereof with the sealing O-ring 72. Adjacent the other end of the housing 98 the interior portion thereof is threaded for engagement with an exteriorly threaded cable sealing nut 102. The latter part is' provided with a tubular extension 104 having a central opening of suicient diameter to permit the passage of a shoulder 106, which in this case is formed on the outer surface of a desirably resilient, impervious, electric cable sheath 108, for purposes presently to be exemplified.

Mounted coaxially within the housing section 98 is a generally cylindrical sealing member which is'provided with a reduced tubular extension 112. Inserted into the tubular extension 112 is a resilient sealing ring 114 arranged to iit relatively closely with the interior of the tubular extension 112 and with the exterior surface of a reduced portion 116 formed upon the cable sheath 108. An annular compressional member 118 is positioned between the sealing ring 114 andthe inward extremity of the tubular extension 104 of the cable sealing nut 102 and is further arranged tot relatively `closely within the tubular extension 112 of the sealing member 110. Accordingly, upon tightening the cable sealing nut 102 the abutting engagement thereof with the compressive ring 118 compresses the sealing ring 114 to form a seal between the impervious cable sheath 108 and the inner sealing member 110', in order to seal the housing 24 and associated components thereof to the electric cable.

The sealing member 110 is in turn sealed to the housing 98 through the intervention of a sealing O-ring 120 disposed in an annular groove 122 formed in the inner surface of the housing 98. When positioned in this manner the O-ring is adapted for sealing engagement with a thickened portion 124 of the wall of the sealing member 110. The aforesaid wall is necked down gradually, as indicated by the reference character 126, to form an inclined or camming surface thereof in order to facilitate engagement of the thickened wall portion 124 with the sealing O-ring 120. Engagement of the aforesaid thickened Wall portion is affected by threading the sealing member 110 into the housing 98. In furtherance of this purpose the sealing member 110 is further provided with an annular shoulder 128, the radial, outward periphery of which is threaded for engagement with the interior threaded portion of the housing 98. Moreover, the tubular extension 112 of the sealing member 110 is provided with an outward hexagonal configuration 113, as better shown in Fig. 2 of the drawings, or some other wrenching surface, for use in conjunction with a suitable asm-aas toolfor threading an'dadjusting the sealing-member 110 relative to the housing 98.

The other end of the cylindrical sealing member 110 is beveled inwardly for engagement with a complementarily disposed beveled portion 130 formed upon an electrical insulator 132, through suitable apertures 131 of which the elongated detachable electrical contacts 88 and 90 extend. The contacts are slidably mounted relative to the aforesaid aperture for purposes hereinafter explained more fully. The insulator 132 is slidably mounted relative to the interior surface of the housing 98 but is positioned longitudinally thereof by engagement with the beveled end of the sealing member 110 and with an inwardly extending annular shoulder 134 disposed on the inward surface of the housing 98 adjacent the anged end thereof. The beveled end portion of the sealing member 110y serves the additional function of preventing distortion thereof upon engagement of the thickened wall portion 124 of the sealing member 110 with the sealing 0-ring 120.

The detachable electrical contacts 88 and 90, for purposes of the invention, can each be provided in form of a severable pair of electrical contacting members which are maintained in alignment and consequently in electrical contact therebetween by insertion of each pair of contacting members, when engaged, through an associated one of the aforesaid apertures 131 in the insulator 132. When thus positioned, suitable means are provided for securing the components of each of the electrical contacts 88 and 90, which means can be provided in the form of that presently to be described or in the form of any known means adaptable for this purpose. The insulator 132 and the associated housing 98 are then moved to a position relative to the contacts 88 and 90 Whereat the aforesaid joining means is enclosed within the apertures 131 of the insulator in order to positively prevent disengagement of the electrical contacts 88 and 90 during operation of the heating element.

When it is desired to disengage the electrical contacts 88 and 90 and to disengage the casing structure 24 from the hermetically sealed casing 25 associated with the end ofthe heating element casing 46, in a manner presently to be described, means are provided for exactly positioning the insulator 132 at a position indicated by the dashed lines 136 whereat the means coupling .each of the detachable electrical contacts 88 and 90 is exposed for convenient removal thereof. At this position of the insulatora portion of each of the electrical contacts is still inserted within the respective apertures 131 of the insulator in order that convenient reassembly of the casing 24, the hermetic sealing arrangement 25 and the electrical contacts 88 and 90 conveniently can be made. The partial insertion of each of the contacts, of course, serves as a means for guiding the contacts through the apertures 131 during movement of the insulator 132 and the casing 24 relativeto the detachable contacts 88 and 90.

One arrangement for so positioning the insulator 132 relative to the electrical contacts includes the employment of the aforesaid cable casing shoulder 106 to limit the outward or leftward movement of the casing 24 relative to an electrical cable 138, which is secured to the electrical contacts 88 and 90 in a manner presently to be described. In furtherance of this purpose, a channel 140 extending coaxially through the tubular extension 104 of the cable sealing nut 102 and through the compressional ring 118 is provided for suicient diameter to permit passage of the aforesaid cable casing shoulder 106. Therefore, upon loosening the cable sealing nut 102 and disengaging the coupling nut 92, and release of the compressive stress imparted to the resilient sealing ring 114, the sealing ring is then free to move along the reduced portion 116 of the cable casing 108 until the outward side of the sealing ring engages the cable casing shoulder 106. At this latter position of engagement, the

insulator 132 has been moved relative to the contacts 88 andto theposition indicated by the dashed lines 13 6 by engagement of the housing ribs 134 therewith and by unitary movement of the casing 24 to the left as aforesaid. When the sealed casing 24 is withdrawn in this fashion, the mechanical connection of the cable conductors 142 and 144 with the heater conductors 50 and 52, respectively, by means of the as yet undetached electrical contacts 88 and 90 maintains the latter of course in the same position relative to the heating element 20 and the electric cable 138.

Upon recoupling the housing 98 to the coupling member 60, a coaxially extending, tubular projection 146 secured to the flanged end of the housing 98 serves as a guide for coaxially aligning the housing 98 with the coupling member 60 secured to the hermetic heater sealing arrangement 25 in order to reassemble the coupling nut 92 thereto. The tubular housing extension 146 is provided with a slot 148 which functions in conjunction with a pin 150 mounted on the inward surface of the coupling member 60 for preventing rotation of the housing 98 relative to the coupling member 60 and consequent distortion or twisting of the contacts 88 and 90 and the conductors 142, 144 and 50, 52.

As better shown in Figs. 7 and 8 of the drawings, one form of detachable electrical contact 88 or 90 arranged according to the invention and alluded to generally heretofore includes a pair of contact coupling members 1.60 and 162 of complementary configuration. The coupling member is provided with a necked-down portion or reduced extension 164 thereof having a central recess 166 disposed substantially along the length of the extension 164. The cable conductor 142 is inserted into the recess 166, with a portion of the insulation 168 thereof being removed for this purpose. The extension 164 is then crimped or pressed about the end of the conductor 142 when inserted therein, in order to cause the extension 164 to frictionally engage the conductor.

The other coupling member 162 is provided with a conductor receiving recess 170 extending a short distance into the outward end of the coupling member 162. The end of the heating element conductor 50 is inserted into the recess 170 and the latter conductor is secured to the coupling member 162, and electrical Contact therewith is ensured, by soldering or brazing the conductor S0 to the coupling member as indicated by the annularly disposed, fused material 172. Obviously, the contact 88 or 90 can be made up of identical coupling members which both can take the form of coupling members 168 or 162.

Each of the coupling members 160 and 162 is formed with a slot 174 and an elongated electrical contacting surface 176 and with a tab member 178 desirably adjoining the contacting surface 176 and adapted for insertion into the slot 174 of the complementary coupling member. The coupling member 160 is provided further with an upstanding pin disposed substantially centrally of the contacting surface 176 and rigidly secured to the coupling member 160. For engaging the pin 180, the coupling member 162 is formed with an aperture 182 likewise centrally disposed relative to its aforesaid contacting surface and extending through the coupling member desirably at right angles to the contacting surface. As better shown in Fig. 8 of the drawings, the coupling member 162 is assembled relative to the coupling member 169 by disaligning the coupling member 162 relative to the member 160 and inserting the pin 180 of the coupling member 160 into the afor-esaid aperture 182 of the coupling member 162. The coupling members 160 and 162 are then pressed into engagement at their contacting surfaces 176, respectively, and the coupling member 162 is rotated into longitudinal alignment with the coupling member 160' by pivoting the coupling member 162-about the pin 180 and thereby inserting the tab members 178 of the coupling members' 160 and 162 respectively into the associated slots 174 of the coulpling members.

Y To aid this insertion the lateral edges of the tabs 178 desirably are beveled or rounded-oft" slightly as shown in Fig. 4. In this manner a secure electrical joint is formed between the coupling members 160 and 162 by insertion and engagement of the associated tabs 178 thereof in the slots 174 of the cornplementary coupling member. Since a frictional engagement between the tabs 178 and the slots 174 is uniform Cross-sectional configuration along substantially the entire length thereof such that the insulator 133 can be moved along the length of the contacts 8S and 90 during the operations of coupling and decoupling the sealed casing 24 relative to the hermetically sealing arrangement 25 which is secured to the heating element 20. When the sealedcasing 24 is coupled thus to the replaceable heating element 20 and its associated components as illustrated in Fig. l of the drawings, the insulator 132 substantially surrounds the contacting surfaces 176of the couplingmembers 166 and 162 of each of the contacts 3S and 99 in order thereby to maintain longitudinal alignment of the coupling members and to prevent positively the Severability thereof during operation of the heating element.

From the foregoing it will be apparent that a novel and encient replaceable heating element .has been disclosed herein. The heating element and its associated components, including the detachable electrical contacting means therefor, are all adapted for convenient sealing or pressurizing. At the same time the heating element is adapted for ready insertion or removal relative to a sealed or pressurized vessel, or the like, for replacement or repair of the element. Although the replaceable heating element can be quickly detached from its source of electrical operating potential, the element can be quickly and eifectively sealed, including the electrical contacting means therefor, against the escape of pressurized, high temperature or other hazardous materials being processed within the vessel.

it will be appreciated that the embodiments of the invention exemplied in the foregoing description are -presented for the purpose of illustrating the invention and therefore are not limitative in nature. Accordingly, numerous modincations of the invention will occur to those skilled in the art without departing from the spirit and scope of the invention. Moreover, it is to be understood that certain features of the invention can be utilized without a corresponding use of other features.

We claim as our invention:

l. A replaceable heating element assembly comprising a reentrant thimble extending through a vessel wall and rigidly secured and sealed thereto, an electric heating element inserted into said thimble, an impervious casing surrounding said heating element, means for detachably sealing said reentrant thimble to said casing, means for detachably and electrically connecting said heating element to a source of electric potential, and a detachable sealed housing enclosing said electrical connecting means and sealed to said casing.

2. A replaceable heating element assembly comprising a reentrant thimble extending through a vessel Wall and rigidly secured and sealed thereto, an electric heating element inserted into said thimble, an impervious casing member surrounding said heating element, a pair of detachable electrical contacts for coupling said heating element to a source of electric potential, a hermetically sealed enclosure joined to said casing and to the conductors of said element, a sealed housing enclosing said contacts, and means for detachably joining and sealing said housing to said enclosure.

3. A replaceable heating element assembly comprising an electric heating element, an elongated, open-ended impervious casing member surrounding said heating element,` a pair of 'elongated detachable electrical contacts for coupling said heating element to a source ofoperating potential, means joined to the open end of said casing and to the conductors of said element for sealing said casing and said conductors, a sealed housing enclosing said contacts and detachably joined and sealed to said sealing means, an electrical insulator having apertures through which said contacts are inserted, respectively, said insulator being arranged for sliding movement thereof relative to said contacts, and means for mounting said insulating member interiorly of said housing.

A replaceable heating element assembly comprising a heating element, an impervious casing surrounding said heating'element, a pair of elongated detachable electrical contacts for coupling said heating element to a source of operating potential, said contacts each being formed from complementary coupling members, means for detachably joining said coupling members, a housing enclosing said contacts and detachably joined to said casing, an electrical insulator having apertures through which said contacts respectively are inserted, said insulator being arranged for sliding movement thereof rela- -tive to said contacts, and means for mounting said insulator interiorly of said housing at a position Whereat said insulator at least partially surrounds said coupling member joining means when said housing is joined to said casing.

5. A replaceable heating element assembly comprising a heating element, an impervious casing surrounding said heating element, a pair of elongated detachable electrical contacts for coupling said heating element to a F source of operating potential, said contacts each being formed from complementary coupling members, means for detachably joining said coupling members, a movable housing enclosing said contacts and detachably joined to said casing, an electrical insulator having apertures through which said contacts respectively are inserted, said insulator being arranged for sliding movement thereof relative to said contacts, means for mounting said insulator interiorly of said housing at a position whereat said insulator at least partially surrounds said coupling member joining means when said housing is joined to said casing, and means for limiting the movement of said housing and said insulator to prevent removal of said contacts from said insulator apertures when said housing is detached from said casing.

6. A detachable electric coupling arranged for electrically connecting a means for utilizing electric current to a source of potential, said coupling comprising alignable electric contacting means arranged to connect conductors of said source and said utilizing means, said contacting means being disengageable only when disposed out of alignment; a housing for enclosing said contacting means and detachably secured to said current utilizing means; an insulating member having at least one aperture extending therethrough, said contacting means being insertable in said aperture, said housing being arranged for longitudinal movement relative to said contacting means to a position Whereat said insulating member maintains alignment of said contacting means by insertion thereof intc said aperture; and means for mounting said insulating member interiorly of said housing.

7. In combination with an electric cable and means for utilizing electric current, at least one detachable, elongated, electrical contact arranged electrically to connect conductors of said cable and said utilizing means respectively; a housing for enclosing said Contact; means for detachably securing said housing to said cable and to sai utilizing means, said housing being arranged for longitudinal movement relative to said contact when detache from one of said utilizing means and said cable; an insulating member having an aperture extending therethrough, said contact being inserted loosely through said aperture and being supported therein by said insulating member; means for mounting said insulating member interiorly of said housing for movement of said insulating member with said housing; a sheath surrounding said cable, said sheath having a reduced portion adjacent the end of said cable, said reduced portion forming a shoulder on the outer surface of said cable at a position such that said shoulder limits the longitudinal movement of said housing and said insulating member to maintain at least partial insertion of said contact in said aperture.

8. A detachable electric coupling arranged for electrically connecting a means for utilizing electric current to a source of potential, said coupling comprising at least one detachable, elongated, electrical contact arranged electrically to connect conductors of said source and said utilizing means, respectively, said detachable contact including a pair of alignable complementary, pivoted coupling members and means for securing electrical contact therebetween only when pivoted to an aligned position; a housing for enclosing said contact; means for detachably securing said housing to said current utilizing means, said housing being arranged for longitudinal movement relative to said contact when detached from said utilizing means; an insulating member having an aperture extending therethrough, said contact being slidably mounted in said aperture; and means for mounting said insulating member interiorly of said housing, said housing and said insulating member being movable to a position whereat insertion of said coupling member securing means within the aperture of said insulating member prevents pivoting of said coupling members from said aligned position.

9. A detachable electric connector comprising a pair of complementary coupling members, a pivot pin secured to one of said members and inserted into a hole in the other of said members, and means for pressing said coupling members laterally into engagement when said other member is pivoted about said pin to the coupling position relative to said one member.

10. A replaceable heater assembly comprising, a pressure vessel having an opening in one Wall, an elongated tubular pressure thimble inserted in said opening and having a closed inner end and an open outer end located outside said vessel, said thimble being rigidly secured and sealed to said vessel at said opening, an elongated electric heating element having an impervious tubular sheath receiving an elongated resistance heater and adapted to be received in said thimble, said resistance heater being rigidly secured in said sheath and having terminal ends projecting outwardly of the outer open ends of said sheath and said thimble, the inner end of said sheath being closed, releasable means located outside the vessel for sealing said sheath to said thimble, and means for permanently sealing the terminal ends of said resistance heater to said sheath.

l1. A replaceable heating element assembly comprising a reentrant thimble extending through a vessel wall and rigidly secured and sealed thereto, an electric heating element inserted into said thimble, an impervious casing surrounding said heating element, means for detachably sealing said reentrant thimble to said casing, means for detachably and electrically connecting said heating element to a source of electric potential, a detachable sealed housing enclosing said electrical connecting means and sealed to said casing, and additional means for detachably joining and sealing said housing to a source y cable.

12. A replaceable heating element assembly comprising a reentrant thimble extending through a vessel wall and rigidly secured and sealed thereto, an electric heating element inserted into said thimble, an impervious casing member surrounding said heating element, a pair of detachable electrical contacts for coupling said heating element to a source of electric potential, a hermetically sealed enclosure joined to said casing and to the conductors of said element, a sealed housing enclosing said contacts, means for detachably joining and sealing said housing to said enclosure, and additional means for detachably joining and sealing said housing to a source cable.

13. A detachable electric coupling arranged for electrically connecting a means for utilizing electric current to a source of potential; said coupling comprising at least one detachable, elongated, electrical contact arranged to connect conductors of said source and said utilizing means respectively, said contact including a pair of complementary pivoted coupling members; means for securing electrical contact therebetween when coupled; an insulating member having an aperture extending therethrough, said contact being slidably mounted in said aperture; means for movably mounting said insulating member; and said insulating member being movable to a position whereat said insulating member surrounds both said coupling members to prevent pivoting thereof when electrical contact is secured between said coupling members.

14. A detachable electric connector comprising a pair of complementary coupling members, a pivot pin secured to one of said coupling members and inserted into a hole in the other of said members, at least one of said members terminating in a tab extending transversely of said pivot pin and insertable into a complementary slot formed in the other member and likewise disposed transversely of said pin.

15. A detachable electric connector comprising a pair of complementary coupling members, a pivot pin secured to one of said coupling members and inserted into a hole in the other of said members, at least one of said members terminating in a tab extending transversely of said pivot pin and insertable into a complementary slot formed in the other member and likewise disposed transversely of said pin, the opposing sides of said slot in the plane of said tab being open to permit pivotal movement of said tab and coupling member in either direction from said slot.

16. A detachable electric connector comprising a pair of alignable complementary coupling members, a pivot pin secured to one of said members and inserted into a hole in the other of said members, means for pressing said .coupling members laterally into engagement when said other member is pivoted about said pin to an aligned coupling position relative to said one member, and means for maintaining said coupling members in said aligned coupling position.

References Cited in the le of this patent UNITED STATES PATENTS 1,731,119 Abbott et al. Oct. 8, 1929 1,829,785 Christian Nov. 3, 1931 1,916,861 Hynes et al. July 4, 1933 2,626,168 Macy Jan. 20, 1953 2,740,098 Phillips Mar. 27, 1956

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