US2527890A - Tubular heater terminal seal - Google Patents

Description

Oct. 31, 1950 J. POUCHNIK ETAL TUBULAR HEATER TERMINAL SEAL Filed March 21, 1949 )9 Y k b. w ll/47% I w w M w w W ,4

Patented Oct. 31, 1950 TUBULAR HEATER TERMINAL SEAL Lawrence J. Pouchnik, Milwaukee, andJerome B. Welch, Wauwatosa, Wis., assignorsto Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application March 21, 1949, Serial N0. 82,586

7 Claims.

' This invention relates to electric heaters and more particularly to an improved method and means for sealing the terminal ends of heaters having tubular enclosing sheaths.

- It is a primary object of the present invention toprovide for sealing the terminal ends of such heaters in a simple and expeditious manner.

Another object is to provide for sealing in such a manner that gases that may be generated within the heater during the process of sealing cannot render the resulting seals imperfect.

Another object is to provide terminal end seals which are impervious to liquids, moisture, vapors and gases.

Another object is to provide a terminal end seal which is characterized by unusual electrical resistivity, mechanical toughness and strength.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustratean embodiment of the invention which will now be described; it being understood that the embodiment is susceptible of various modifications without departing from the scope of the appended claims.

In the drawings:

Figure 1 is a view in longitudinal section of a portion of a tubular type heater prior to application of a terminal seal; the terminal lead and the resistor being. shown in elevation.

Figure 2 is similar to Fig. 1, but shows thehe'ater at one stage during the application of a terminal seal. 7

Figs. 8 and 4 show the heater at successively later stages during the application of a terminal seal, and show processing apparatus which may be employed, and

Fig. 5 is a fragmentary sectional view showing the terminal seal in a completed state; the terminal lead being shown in elevation.

Referring to Fig. 1, it shows a tubular type electric heater comprising a helical resistor 6" which is embedded in a compacted mass of refractory insulating material 1, such as magnesium oxide, and incased by a tubular sheath 8 of any preferredcross-sectional form. The resistor 6 is connected in any preferred manner to a terminal lead 9 which extends outwardly of sheath 8'. The sheath adjacent its end is unfilled and provides a recess Ill to receive the terminal seal.

The heater as shown in Fig. 1 is ready for apgreater percentage of the moisture entrained in theinsulating material 1. Further iti's assumed that in preparation for improved terminal seal the inner surface of the sheath 8 surrounding recess ID has been suitably cleaned.

. Referring to Fig. 2, a quantity of suitable vitre' ous material I l in powdered form is placed in=the recess l 0 in such amount that said recess is completely filled. It has been found that vitreous materials suitable for use with the sealing process to be hereinafter described are preferably of the pro-fused type wherein the component constituents substantially all go into solution to provide a homogeneous mixture which is amorphous'in:

character.

As the character of the resulting terminal seal depends to a great extent upon the character of the component constituents of the material ll, care should be exercised in the selection of such constituents. When such material is subsequently re-fused and solidified into a solid mass, thematerial should have a coefficient of linear thermal expansion closely approximating that of the materials of which the sheath 8 and the terminal lead 9 are formed and should retain its solidity at the temperatures attained by the terminal end portions of the heater when the latter is energized. Further, when so re-fused and solidified, such material should have relatively high electrical resistivity and be resistant to mechanical 1 breakage. There are several commercially available vitreous materials which will meet the above recited requirements and which will provide satthe application of the isfactory terminal seals when treated in accordance with themethod now to be described in detail. However, applicants havefound that a cer-' tain vitreous composition described in the appli-- cation of Fred H. Kaufmann, Serial No. 73,673,-

flled January 29, 1949, and issued as Patent No. 2,527,884 on even date herewith, is preferred as a sealing medium. The constituents of the preferred vitreous composition and percentages of each by weight based on the total weight of such composition as given in Table III of the aforementioned application are as follows:

The material ll may be placed in recess 10' in any convenient manner; an expeditious way of doing this being to force the end of the heater into a powderedmass of such material as by hand so as to cause the material to be forced into and completely fill recess I0 in a semi-compacted state.

3 Then the portion of sheath 8 coextensive with recess I is subjected to localized heating to effect fusion and/or liquefaction of the material i I. Such heating may be done in any preferred way, for example, by subjecting such portion of sheath 8 to the heat of a plurality of gas fiames.

When the material II has become re-fused and has attained a homogeneous liquid or plastic conan intermediate member I4, a shaft I 5, and coolsistency, heating of the sheath 8 is terminated and a pressure plunger or punch I2, shown in Figs. 3 and 4, is fitted over the terminal lead 9 and moved downwardly and inwardly of the recess I0 so as to exert pressure on the fused but unsolidified matreial which in Fig. 4 is designated I l instead of II in view of its altered state. The pressure applied by the punch I2 on the material II should be on the order of 2100 pounds per square inch and the duration of such pressure need not exceed two or three seconds. Punch I2 during such operation should be maintained at ordinary room temperature, and preferably lower, to insure that the material II will not stick or adhere to the punch.

Application of the aforementioned amount of pressure on the fused but unsolidified material I I in the manner aforedescribed elfects a reduction in the volume of such material to substantially one-half its original volume, thus densifying the same to a large degree. Such densification of the material I l eliminates any voids or pockets which may form as an incident to re-fusion the material. Further, the relatively cool pressure applying punch tends to effect rapid solidification of the material II into a solid body designated II While some gases may be generated in the insulating material I as a result of the heating of the sheath 8 as aforedescribed and would have a tendency to form bubbles or pin holes in the material II during solidification, the counteracting pressure and rapid solidifying action imparted by the punch I2 prevents this from occurring.

After completion of the aforementioned pressure applyin operation on the material II and after the latter has solidified, the solid fused Vitreous body II results in the recess II] of the heater, the punch I2 preferably being shaped to afford the body II the form shown in Fig. 5. The body II thus formed strongly adheres in a bonded relation to the inner surface of sheath 8 and to the terminal lead 9 and provides a sealed barrier against the ingress or egress of moisture, vapors or gases into or from the insulating material I. Assuming that the composition of the material I I initially used in the sealing operation meets the requirements aforementioned, the resulting seals will retain their bond and solidity at the temperatures attained by the terminal end portions of the heaters when the latter are energized. The preferred vitreous composition aforementioned, if used as the sealing medium in connection with the sealing process hereinbefore described, results in terminal seals which meet all of the aforementioned requirements and in addition have unusually high electrical resistivity, on

the order of 61 megohms at 760 F., and unusual mechanical toughness, being able to withstand mechanical shocks on the order of 2000 footfound to be highly satisfactory in applyingthe,

ant conducting conduits I6 and IT. The punch I2 is preferably made of hardened steel. Block I3 is made of a high heat conducting metal such as copper. With the punch I2, block I3, member I4, and conduits I6 and Il formed and assembled as shown, a chamber I8 is provided in which a cooling medium such as water may be circulated by virtue of the conduits I6 and IT. Continuously subjecting the punch l2 to influence of circulating water at ordinarysupply temperatures will insure that in repeated pressure applying operations the material II will not stick or adhere to the punch and rapid solidification of such material will be facilitated.

We claim:

1. The method of sealing the terminal end of an electric heater wherein a resistor enclosed in an open end tubular sheath is embedded in insulation terminating at a distance from the end of the sheath to leave the sheath with an open end recess, and wherein the resistor has a terminal portion projecting through said recess to a point beyond the sheath, which comprises filling the end recess with a vitreous material in powdered form, heating locally the end of the sheath to fuse said material, and subjecting said material in fused but unsolidified state to pressure on the a point beyond the sheath, which comprises filling the end recess with a vitreous material in powdered form, heating locally the end of the sheath to fuse said material, and subjecting said material in fused but unsolidified state to pressure on the order of 2,100 pounds per square inch at least briefly while permitting said material to cool, maintaining in a relatively cool state the pressure applying means.

3. The method of sealing the terminal end of an electric heater wherein a resistor enclosed in an open end tubular sheath is embedded in insulation terminating at a distance from the end of the sheath to leave the sheath with an open end recess, and wherein the resistor has a terminal portion projecting through said recess to a point beyond the sheath, which comprises forcing the end portion of the heater into a powdered mass of vitreous material to effect filling of the end recess with said material in a semi-compacted state, heating locally the end of the sheath to fuse said material, and subjecting said material infused but unsolidified state to pressure on the order of 2,100 pounds per square inch at least briefly while permitting said fused material to cool, maintaining in a relatively cool state the pressure applying means.

4. The method of sealing the terminal end of an electric heater wherein a resistor enclosed in an open end tubular sheath is embedded in insulation terminating at a distance from the end of the sheath to leave the sheath with an open end recess, and wherein the resistor has a terminal portion projecting through said recess to a point beyond the sheath, which comprises filling the end recess with a vitreous composition in powdered form, said composition having as its constituents by weight based on the total weight.

of such composition, 27.68% silica, 7.33% boric oxide, 18.76% fluorspar, 37.69% barium oxide, 5.63% zinc oxide, 1.92% alumina and 0.99% cobalt oxide, heating locall the end of the sheath to fuse said powdered composition, and subjecting said composition in fused but unsolidified state to pressure on the order of 2,100 pounds per square inch at least briefly while permitting said composition to cool, maintaining in a relatively 0001 state the pressure applying means.

5. The combination with a tubular heater comprising a resistor having a terminal portion, an open end tubular sheath surrounding said resistor and also its terminal portion in part, and insulation in said sheath retaining said resistor in spaced relation to said sheath, said insulation terminating at a distance from the end of said sheath leaving said sheath with an open end recess through which said terminal portion projects, of a seal for the terminal end of said heater comprising a solidified body of vitreous material occupying at least a portion of the recess in said sheath and adhering in bonded relation with said sheath and said terminal portion, said vitreous material consisting of a fused mixture of 27.68% silica, 7.33% boric oxide, 18.76% fluorspar, 37.69% barium oxide, 5.63% zinc oxide, 1.92% alumina and 0.99% cobalt oxide.

6. The method of sealing the terminal end of an electric heater wherein a resistor enclosed in an open end tubular sheath is embedded in insulation terminating at a distance from the end of the sheath to leave the sheath with an open end recess, and wherein the resistor has a terminal projecting through said recess to a point beyond the sheath, which comprises filling the end of the sheath with a vitreous material in powdered form, heating said vitreous material in situ to fuse the same, and subjecting said material in fu ed but unsolidified state to mechanical pressure on the order of 2,100 pounds per square inch at least briefly while permitting the material to cool. 1

7. The combination with a, tubular heater comprising a resistor having a terminal portion, an open end tubular sheath surrounding said resistor and also its terminal portion in part, and insulation in said sheath retaining said resistor in spaced relation to said sheath, said insulation terminating at a distance from the end of said sheath leaving said sheath with an open end recess through which said terminal portion projects, of a seal for the terminal end of said heater occupying at least a, portion of the recess and adhering in bonded relation to said sheath and said terminal portion, said seal consisting of a homogeneous mass of solidified vitreous material formed in situ of a vitreous composition Of the pre-fused type by re-fusion and application of a relatively high degree of mechanical pressure thereto at least briefly during solidification.

LAWRENCE J. POUCHNIK. JEROME B. WELCH.

REFERENCES CITED The following ref rences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,043,196 Finlayson June 2, 1936 FOREIGN PATENTS Number Country Date 577,748 Great Britain May 30, 1946

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