US1770824A - Electric heater - Google Patents

Description

C. C. ABBOTT ELECTRIC HEATER July 15, 1930.

Filed May 17, 1929 Ice Charles 0 Abbott, b WM 9 His Attorney.

Patented July 15, 1930 UNITED STATES PATENT OFFICE CHARLES C. ABBOTT, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOB TO GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK ELECTRIC HEATER Application filed Kay 11, 1929. Serial no. seam.

My invention relates to electric heaters,

section taken on the line "2-2 of Fig. 1;

more particularly to moisture-proof electric Fig. 3 is an elevation partly-in section of a heaters, and has for its object the provision of a simple, inexpensive and efiicient electric heater and method of making it.-

Although obviously my invention has other applications, it is particularly useful in connection with electric immersion heaters of the type which comprises an encased or sheathed heating unit in which the insulated resistance conductor is enclosed in an outer metallic protective casing. One immersion heater of this type is described and claimed in my Patent 1,522,992, dated January 13, 1925.

In accordance with my invention, I pro vide a metallic supporting member for the sheathed heating unit having a chamber which in the assembled unit serves to receive the end portion of the sheath casing and the electrical terminal which projectstherefrom. In order to secure the sheathed unit to its support so as' to provide a mechanically strong and leak-proof connection, I wedge a body, which preferably is formed from a relatively soft metallic material such as copper between the end portion of the sheath and the surrounding walls of the chamber.

Moreover, I fill the chamber with an electrically insulating material and cover the chamber by means of a solid insulating cloak or cover which is provided with an aperture for the electrical terminal. Preferably, the insulating material is inserted in the chamber in solid form andithereafter is heated to a plastic state so that when the cover is forced into place, the insulating material willcompletely fill the chamber and be forced through been secured over the mouth of the chamber,

the aperture provided in the cover so as to insulate the terminal.

I heat the insulating material further, wliere- .by it tends to expand so as to fill completely and densely the chamber vided in the cover.

'For a more complete understanding of my invention, reference should be had to the accompanying drawing in which Fig. 1 is an elevation partly in section of an electric and aperture proheater embodying my invention; 2 is a the end portions of the legs 10,10" re spec- 100- I modified form of my invention; and Fig. 4 is a section taken on the line 44 of Fig. 3. Referring to the drawing, I have shown my invention in one form in connection with an electrical immersion heater;of the type described and claimed in my aforementioned patent. This heater is provided with a sheathed heating unit 10 and with a metallic supporting member 11 for'the heating unit. 'Preferably, and as shown, 'theelectric heater is provided with a helical coilsheathed heating unit of the type described and claimed in my Patent No. 1,367,341, dated February 1, 1921. Briefly, this heating unit 10 comprises an outer metallic sheath 12 in which an electrical resistance conductor 13 is embedded in acompacted mass of; powdered, heat 'refractory, electrically insulating material 14. The insulatin material 14 may be compacted to a hard, ense mass having good heat conductivity in any suitable manner, as for example, by reducing the diameter of the sheath resistance conductor 13 has its end secured I to the electrical terminals15 and 15 which project fromthe ends of the sheath and are electrically insulated from the sheath.

The ends of the hairpin heating unit 10 are secured to the supporting member 11 which is shown as a metallic screw plug. It will be understood that this screw plug .Wlll

After e Cover be screwed tightly in a suitable tapped hole in the heating receptacle so as to support the heating unit in position within the receptacle. The heating unit 10 thus-will be extended within the receptacle in position to be immersed in the liquid to be heated. Moreover, the support'ing member will serve to seal theterminals against moisture.

As shown.-'( Fig.1) the plug 11 is provided with a pair of chambers 17, 17' into which tively, of the heating unit 10 are projected.

Suitable passageways 18, 18 are provided in the bottom of the plug for receiving the respective end portions of the legs l0, 10". It is to be noted that preferably two heating units 10 will be mounted upon the plug support 11. In case two units are provided, it will be understood that the plug will 'be provided with another pair of chambers 17 and 17 for receiving the respective ends of the second heating unit. Moreover, it will be understood that in case two units are used, each unit will be provided with separate terminals and connections whereby the units may be connected in series or in parallel relation in a well known manner so as to regulate the amount of heat produced.

As shown (Fig. 1), the end portions of the heating unit 10 will be inserted into the passageways 18, 18 so as to project somewhat beyond the mouths of the chambers. Preferably and as shown, the lower or bottom portion of each chamber is tapered, the larger or flared end of the tapered portion merging with a straight cylindrical portion forming the mouth of the chamber.

In order to secure the heating unit to the plug so as to provide a leak-proof connection, I provide abushing 20 for each chamber and force the bushing, which preferably is made of a suitable metallic material such as soft copper, into the tapered chamber between the end portion of the metallic sheath and the surrounding walls of the chamber. It will be understood that the copper bushing may be applied to the sheath and plug in any suitable manner. Thus the bushing may be hammered into position. Preferably the straight cylindrical mouth portion of each chamber will have a length about equal to the length of the bushing and moreover, will have a diameter of such proportions that an annular space will be formed about the projecting sheath of a size just sufficient to receive the copper bushing. It is impossible therefore for the end of the bushing to lower as it 1s being driven into the tapered portion. Thus a very tight joint is insured. As an added proof against leaks, I further secure the heating unit to the plug by brazed or soldered joints 21 and 21. It will be understood that if the sheath be brazed to the plug, it is desirable that the passages 18, 18*" be slightly larger at their outer ends that the respective sheath portions pass therethro'ugh. Thus the brazing material will be allowed to enter the enlarged portion so as to provide a more perfect brazed connection.

After the heating unit has thus been secured to the pliig, I fill the chambers 17, 17 with an electrically insulating scaling ma terial 22, this sealing material being placed in the chambers while heated to a semi-plastic state. Moreover, the insulting material will be placed over and about the projecting end portions of the metallic sheath so as to embed the outer ends of the heating unit and its terminals, thoroughly sealing the ends of the heating unit. Any suitable sealing material such as bakelite may be used.

After the receptacles have been filled with the sealing material and this material has been positioned around the projecting ends of the sheath, the chambers will be closed with a solid electrically insulating cover 23 made from a suitable material, such as porcelain. As shown, this cover is sufficiently large to cover the mouths of both of the chambers and rests upon the edge of the plug surrounding the chambers. The cover 28 is hollowed so that achamber 23 is provided in the cover, this chamber together with the chamber 17, 17 in the assembled terminal serving to form'one large chamber 2A into which the ends of all of the heating units project. The cover is provided with a plurality of apertures 25 for receiving the projecting terminals 15, 15 of the heating units. Thus if two heating units 10 be used, the cover will be provided with four apertures, two for each heating unit. Preferably and as shown these apertures will be tapered with their larger or flared ends opening into the chamber.

It will be understood that this-insulating material 22 will be provided in sufficient quantity so that when the cover is assembled with the unit, the chamber will be entirely filled with the insulating material. It will be observed that the tapered apertures 25 are slightly larger even at their smaller ends than the terminals which they serve to receive; By reason of this construction the plastic insulating material will be forced upwardly through these apertures about the terminals when the cover is positioned over the chambers.

After the insulating cover 23 has been assembled, suitable terminal or lead connectors 26 will be secured to the terminals 15, 15 which, of course, will be projected from the cover so that the terminals may be received Preferably the connectors will be of the tubular type and will be compressed upon the terminals in any suitable manner as by swaging. It will be observed that each connector at its cover end is provided with a knife-like edge 26 so that in the assembled unit these terminals not only serve as lead connectors but also'serve t'o tightly close the apertures provided in the cover 23. It will be .impos-. sible therefore for the bakelite to escape through these apertures. Moreover, these knife edges perform a very important function in the connector assembly operation. It will be understood that whenthe connector is swaged on its terminal, it has a tendency to elongate in the die and thus during the pressing opertion a heavy pressure is likely to develop between the connector and the porcelain cover. The knife edge serves to abmaterial.

be deep as compared with the chambers prosorb any shock or blow which otherwise might be transferred to the porcelain.

After the cover and connectors have been assembled, the insulating material 22 is treated by baking at a suitable temperature, such as approximately 150 C. This heat treatment tends to swell or expand the insulating It will be observed, therefore, that as a result of this curing operation, the large chamber 24 and the tapered apertures 25 provided in the cover will be filled completely and densely with the insulating material, so densely that it will be impossible for water or moisture to come in contact with the terminals or ends of the heating unit. It will be understood of course that the porcelaincover 23 will have sufiicient mechanical strength to withstand the pressure of the in sulating material.

Each connector 26 is provided with a suitable clamping member 27 which is secured to the connector by means of a screw 28. Preferably a lock washer 29 will be interposed between the clamping member 27 and the head of the screw.

A suitable cap or cover 30 is provided, which is secured to the plug by means of screws 31 and 32, and encloses the connectors and clamping members. An insulatin bushing 33 is provided in the cap or cover through which conductors may be led to the connectors in order to connect the heater to a suit-' able source of electrical supply.

In the preferred form of my invention, shown in Figs. 3 and 4, I provide the heating unit 40 with a supporting member 41 shown as a metallic screw plug. The supporting plug 41 will be provided with a plurality of chambers 42, two of which will be provided for each heating unit 40. Thus if the electrical heater be provided with two heating units 40, the metallic plug 41 will be provided with four chambers, two. for each heating unit. As shown, each chamber 42 is provided with a passageway 42 for receiving the end portion of the sheath. These chambers 42 will vided in the plug 11 of Fig. 1. Thus it will be observed by reference to Fig. 3 that in the assembled heater the end portions of the sheathed heating unit 40 will be projected into these chambers but will not extend completely through the chambers so as to project beyond their mouths, as shown in Fig. 1. The electrical terminals 43, however, which projectfrom the ends of the sheath will bev of such length that they will project considerably beyond the mouths of the chambers 42.

In Fig. 3 therefore eachend of each heating unit will be provided with an individual chamber. Preferably and as shown the low port. into place, the second bushing 45 will be' drical portion forming the mouth of the chamber.

- The heating unit 40 will be secured to the plug 41 in a manner similar to the method disclosed in Fig. 1. However, in this case,

two bushings '44 and 45 will be provided for each chamber 42. Thus into each chamber a soft metallic bushing 44 will be driven about the projecting end portion of the heating unit between the outer walls of this unit and the walls of the surrounding chamber so as to I provide a mechanically strong and leakproof joint. As with the chambers 17, 17' of Fig.

1, the straight cylindrical mouth portion of each chamber 42 will have a length about equal to the length of the bushing and moreover. will have a diameter of such proporti ons that the annular space formed about the sheath will be of a size just sufficient to receive the copper bushing. This construction, as has been explained, insures a very tight joint between the heating unit and its sup- After this bushing 44 has been forced forced over the first bushing between the extreme outer end portion of the sheath and the surrounding walls of the tapered chamber. The heating unit 40 will be further secured to'the plug 41 by means of the brazed or soldered joints 46 and 46*.

Each'chamber 42 will then be provided with suitable electrically insulating material 47, such as bakelite. However, instead of fillin the chamber with the insulating materia while it is heated to a plastic state, as was the case with the method described in the assembly of the heatershown in Fig. 1, the insulating material will be placed in the chamber while in a solid condition} Thus this material will be preformed somewhat like a washer so that it will, when placed in the chamber, embrace the terminal 43 projecting from the heating unit.

After the insulating material has been placed within the chambers, the unit will be warmed slightly so as to heat the material to a plastic state. Each chamber 42 is then closed by means of a solidelectrically insulating block 48 formed from a suitable insulating material, such as porcelain. As shown,-the insulating cover 48 1S provlded with an aperture 49 for the terminal 43. This cover 48 is slightlylarger than the mouth of the chamber which it serves to close and rests on the ledge surrounding the mouth of the chamber so as to close the chamber completely. Preferably a recess 50'will be provided j in the plug about the mouth of each chamber to receive the cover 48 provided for the chamber. The solid cover is provided with an extension 48 on its inner side which projects downwardly into the sealing material 42. It will be understood, of course, that this cover 48 will be put in place while the sealing material is in its semi-plastic stateso that the material is free to flow around the extension 48 and secure the cover upon hardening. Preferably the aperture 49 will be tapered with its larger or flared end opening into the chamber and will be larger even at its smaller end than the terminal which it serves to receive. It will be understood therefore that when the cover is forced into the soft insulating material that the material will flow upwardly through the tapered aperture about the-terminal.

A connector 51 will then be secured to the end of each terminal. Preferably these connectors will be of the tubular type and will be compressed about the projecting ends of the terminals in some suitable manner as by swaging. It will be observed that each connector is provided with a knife edge 51 at its cover end so as to close etfectively the open end of the aperture provided in the cover, and to prevent injury to the cover during the assembly of the connector. Each connector. will be provided with a clamping member 52 secured to the connector by means of a screw 53.

As before, the heater will then be baked at a suitable temperature, such as 150 C., in order to cure the insulatin compound. As described, this process tends to expand the insulating compound so as to fill completely and densely the chambers 42 and the tapered apertures provided in the cover members 48. In order to insure that there will be no leakage of bakelite during the heating or baking operation, I provide a suitable washer 54 for each cover -18. Preferably a dish-shaped copper washer will be provided. In the assembly of the heater, the washer will be inserted under the head of the porcelain insulating cover with its small diameter against the head of the cover. It will be observed therefore that when the cover is forced into position over the chamber, the washer will be flattened out so that its outer or larger diameter will be forced against the walls of the recess while its smaller diameter will be forced against the relativel irregular surface of the porcelain cover. reason of this construction a very tight joint is-efiected.

- A suitable cap or cover 55 is provided which is secured to the plug by means of screws 56 and 57, and encloses theconnectors-and clamping members. This cover is provided with an insulating bushing 58 through which conductors may bepassed tothe connectors in order to connect the heater to a suitable source of electrical supply.

-What I claim as new and. desire to secure by Letters Patent of the United States, is:

1. An electric heater comprising a metallic sheath from which an electrical terminal projects, a support for said metallic sheath,

said support being provided with a chamber into which the end portion of said sheath is projected, means for securing said sheath to said support comprising a metallic member wedged about the projecting end portion of said sheath between said portion and the surrounding walls of said chamber, and insulating sealing means in said chamber about the end of said sheath and said projecting terminal.

2. An electric heater comprising a metallic sheath from which an electrical terminal projects, a support for said sheath, said support being provided with a chamber and a passageway through which the end portion of said sheath is extended so as to project into said chamber, means for securing said sheath to said receptacle comprising a metallic member surrounding the projecting end portion of said sheath and wedged tight- 1y between said projecting end portion and the adjacent walls of said chamber, an insulating sealing material in said chamber embedding the projecting end portion of said sheath and said terminal and a block of insulating material closing said chamber providedwitli an aperture for said terminal.

3.- An electric immersion heater comprising a metallic sheath from which an electric'al terminal projects, a support for said sheath, said support being provided with a chamber and a passageway through which the end portion of said sheath is extended so as to project into said chamber, means for securing said sheath to said receptacle so as to form a water-tight connection therewith comprising a metallic: member surrounding v the projecting end portion of said sheath and wedged tightly between said projecting end portion and the her, an insulating sealing material in said chamber embedding the projecting end portion of said sheath and said terminal, a block of insulating material closing said chamber provided with an aperture for said terminal, a resistance conductor in said sheath electrically connected with said terminal and powdered heat refractory insulating material compacted in said sheath around said resistance conductor so as to conduct heat freely from said resistance conductor to said sheath.

4. An electric heater comprising a metallic sheath from which an electrical terminal pro- 'ects, a support for said sheath, said support ing provided with a chamber and a passageway through which the end portion of' said sheath is extended so as to project into said chamber, means for securing said sheath 1'.)

to said support comprisinga metallic memadjacent walls of said chamber surrounding the projecting end portion r of said sheath and wedged tightly between said projecting end portion and the adjacent walls of'said chamber, an insulating sealing in material in said chamber embedding the projecting-endsportion of said sheath and said terminal, a block of insulating material covering said. chamber and projecting into said insulating material, said block having an aperture for said terminal, and a lead connector secured to the end of said terminal so as to secure said cover and close the aperture extending therethrough.

5. An electric immersion heater comprising a metallic sheath having its ends adjacent each other and from which electrical terminals project, a support for said sheath pro- ,vided with a pair of chambers into which the respective end portions of said sheath are projected, means for securing said sheath to said support comprising a pair of metallic bushings, one for each chamber, each metallic bushing surrounding the end portion of the sheath projecting into its chamber and being wedged tightly between the sheath and the surrounding walls of the chamber, an insulating sealing material in each chamber embedding the end of the sheath within the chamber and the terminal projecting from said sheath, a pair of insulating covers, one for each chamber, each cover projecting into the insulating material within its chamber and provided with an aperture for the terminal, and a pair of connectors,one for each terminal, said connectors serving both to secure said covers and to close the apertures extending therethrough.

6. The method of making a moisture-proof electric heater having a metallic sheath, an

electrical terminal projecting from said sheath and a support for said sheath which comprises forming a chamber in said support and a passageway for the chamber leading from the chamber to the exterior of said support, inserting the end of said sheath through said passageway so that the end portion thereof projects into said chamber, securing said sheath to said support, inserting aebody of solid insulating material within said chamber, warming said insulating material to a plastic state, providing a cover for said chamber formed with an aperture therethrough for receiving said projecting terminal, securing said cover over the mouth of said chamber and then heating said unit whereby the insulating material tends to expand so as to fill completely and densely the" chamber and aperture extending through said cover.

7. The method of making an electric immersion heater provided with a metallic sheath having its ends adjacent eachother, an electrical terminal projecting from each end of said sheath and a metallic support for said chambers, respectively, wedgmg a metallie bushing between each projectm end por-- tion of the sheath andthe surroundingwalls tapered aperture, compressing a tubular lead connector member about each terminal so as to secure the covers and close their apertures and then heating said unit whereby the insulating material tends to expand so as to fill completely and densely the chambers and aperture provided in their covers.

In witness whereof I have hereunto set my hand this 14th day of May, 1929.

-- CHARLES C. ABBOTT.

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