US2043195A - Electric heater - Google Patents

Description

June 2, F, E, FINLAYSON 2,043,195

ELECTRIC HEATER Filed Nov. l1, 1932 Fmemk E. Fini@ s on,

HIS Attormw.

Patented June 2, 1936 UNITED STATES PATENT OFFICE ELECTRIC HEATER New York Application November 11, 1932, Serial No. 642,256

3 Claims.

My invention relates to electric heaters and the like, and has for its object the provision of an improved method and means for sealing the terminals of heaters of this type.

Although not limited thereto, my invention has particular application to electric heaters of the incased or sheathed type wherein a resistance conductor embedded in an insulating material is inclosed by an outer metallic protective casing,

In one of its aspects, myinvention contemplates the provision of improved means for sealing the terminals of electric heaters of the sheathed type whereby the heaters are rendered impervious to moisture, oil, gas and like fluids.

In accordance with my invention, I place a tubular member, which preferably Will be formed of metal, over each terminal of the heater, and provide a fluid impervious joint between the terminal and the tubular member. Surrounding the tubular member is a layer of vitreous material which is arranged to make a uid impervious joint with it. In heaters of the sheathed or incased type, it is preferable to surround the vitreous layer with a casing which may be either the sheath or a separate member. In these arrangements, the vitreous layer is arranged to make a uid impervious joint with the surrounding casing. In case a separate casing member be used a fluid impervious joint will be eiected between this member and the sheath.

For a more complete understanding of my invention, reference should be had to the accompanying drawing in which Fig. 1 is an elevation of a sheathed electric heater provided with terminal seals arranged in accordance with my invention; Fig. 2 is a fragmentary sectional view of the electric heater of Fig. 1 illustrating a terminal seal arranged in accordance with my invention and used in the heater of Fig. 1; Fig. 3 is a fragmentary sectional view of a heater embodying a modified form of my invention; and Fig. 4 is a fragmentary sectional View of an electric heater embodying still another modified form of i -my invention.

Referring to the drawing, I have shown my invention as applied to a helical coil sheathed electrical heating unit of the type described and claimed in United States Patent No. 1,367,341 to C. C. Abbott, dated February l, 1921, and particularly intended to be used as an immersion heater. 1 As shown, the heating unit comprises a helical resistance conductor Ill embedded in a compacted mass of powdered heat refractory insulating material lII, the conductor and insulating material being incased by a metallic sheath I2. The insulating material II may be any suitable substance, but preferably will be formed of powdered magnesium oxide. This material may be compacted to a hard dense mass having a good heat conductivity in any suitable manner, such as by reducing the diameter of the sheath after the unit has been assembled and the sheath has been loaded with the magnesium oxide. The sheath may be reduced by swaging or rolling.

The resistance conductor I extends through a considerable portion of the length of the sheath I2 and has its two ends connected'tc terminal members I3 which project from the ends of the sheath. While the conductor may be connected to its terminals I3 in any suitable manner, I prefer to connect them in the fashion described and claimed in United States Patent No. 1,494,938 to C. C. Abbott, dated May 20, 1924. As there described, the terminal members I3 have their inner ends threaded and are electrically and mechanically connected with the resistance conductor by screwing a number of the end turns of the conductor onto the threaded ends of the terminals. In this arrangement the terminals may have a diameter slightly larger than the diameter of the helix of the conductor IIJ.

As vshown (Figs. 1 and 2), each terminal I3 projects somewhat from its end of the sheath and is supported at its inner end by the compacted insulating material II.

Heating units of this type can be bent easily into any desired shape. In the immersion heater shown, the heating element is bent substantially in the form of a hairpin. The adjacent ends of the heating element are received by a suitable supporting member I4 which may be in the form of a plate, or which may be in the form of a threaded plug (as shown) arranged to be received in a threaded aperture provided for it in a wall or supporting plate 0f a receptacle or other device.

A pair of spaced apertures I5 are provided in the supporting member I4 for receiving the two ends of the heating element. As shown (Fig. 2) the ends of the heating element are inserted within the passageways I5 so as to project somewhat beyond the plate on the opposite side thereof.

Suitable uid impervious joints are eiected between the heating element and its supporting plug I4. As shown, at the points where the ends of the heater enter and emerge from the plug I4, fluid tight seals are provided which may be formed by brazed joints I6 between the sheath and the plug. For this purpose. the apertures or holes I5 in the plug I4 are provided at their ends with recesses I'I, as clearly shown in Fig. 2, these recesses serving to receive the brazing material I6 providing the huid-tight joints between the sheath ends and the plug.

In order to render the terminals absolutely impervious to the leakage of uids into the sheath and to facilitate the construction of the unit, I surround each terminal I3 Awith a tubular member 2| which has an internal diameter slightly larger than the diameter of the terminal so as to leave a relatively small annular space between these members. Surrounding this tubular member 2| is a substantially homogeneous mass of vitreous material 22, such as a high temperature glass, arranged to adhere both to the tubular member and to the inner walls of the sheath so as to form fluid impervious joints with these members.

The glass 22, the tubular member 2| and casing I2 will have such coeiiicients of expansion that the glass will have :duid impervious joints with the tubular member and casing. I have found that a tubular member 2| made of a nickel-iron alloy consisting of approximately 64% iron and 36% nickel and known as Invar, is satisfactory, and that satisfactory results are obtained if the casing is formed of steel.

Between the end of each terminal and its surrounding tubular member 2| is a suitable fluidimpervious joint 23. f

Interposed between the glass seal 22 and the inner end of the tube 2| and the insulating material II is an insulating washer 24 formed of any suitable electrically insulating material, such as mica. This material increases the insulation between the terminals I3 and sleeves 2| and the sheath I2. Preferably, the centrally arranged apertures in the washers 24 will have diameters substantially equal to the diameters of the terminals I3.

' It will be understood that in making the heating unit, the terminals I3 will be attached to the conductor IU and then the conductor with the terminals attached will be assembled with the sheath I2. The sheath will then be loaded with the magnesium oxide I I, which will be compacted by subsequently rolling or swaging the sheath. The terminal ends of the sheath will then be squared oil'. After this, the heating element is bent in the form of a hairpin and is assembledY with the plug I4 as above described.

In making my terminal seal, I remove the insulating material II from each terminal end of the sheath for a short distance, as shown in Fig. 2. This may be done either before or after the unit is bent and assembled with the plate |4. The inner exposed walls of the sheath and terminals are then cleansed in a suitable manner, and then, if necessary, these walls of the sheath may be sized to accommodate the seals. As shown, these ends of the sheath have been bored out somewhat so as to enlarge their 'internal diameter, and to further cleanse the inner wall of the sheath.

After the magnesium oxide has thus been removed and the sheath and terminals have been cleaned, the insulating discs or washers 24 are threaded over the terminals so as to seat in the bottom of the recesses provided by the removal of the magnesium oxide.

Then I place over each terminal, its tubular member 2| which, as previously pointed out, prefl erably will have an internal diameter slightly larger than the diameter of the terminal, and

' which preferably will be formed of metal.

Then I thread each tubular terminal member 2| with a tube (not shown) formed of the glass 22, referred to above, after which the terminal assembly is heated to a temperature at which the glass tube becomes plastic. These tubes generally will become suiliciently plastic when heated to a temperature of 1700o to 1750D F.

After the glass has been heated to the plastic state, it is subjected to pressure so as to completely ll the available space and to insure a firm adherence of the glass to the tubular members 2| and the inner walls of the casing I2.

This pressure may be applied by any suitable means, such as by tubular pressure members (not shown) arranged to be threaded over the tubular members 2| so as to contact with the exposed surfaces of the glass surrounding these members.

'I'he external surfaces of the tubular members 2| and the inner surfaces of the sheath I2 in contact with the glass 22, should be thoroughly cleansed before the glass is applied so that these surfaces will be wetted by the glass when it is rendered plastic and pressure is applied, whereby when the glass hardens upon subsequent cooling fluid impervious joints will be effected or produced between the glass and the members 2| and the casing I2. These surfaces may be cleansed by machining operations or by sand blasting or by any other suitable cleansing process. I have found that the Invar of which the sleeves 2| are made has the characteristic of making very good joints with the glass seals.

After the glass 22 has thus been applied and the terminal ends of the heater have been allowed to joints 23 between these members. As shown, the l outer ends of the tubes 2| are countersunk so as to provide a well or cup 25 in which the solder or brazing or like material is received.

After the tubular members 2| have been brazed to the terminals, suitable terminal connector members 26 may be attached to the sleeves 2| which are of such a length that they project outwardly somewhat beyond the glass 22, as shown. These connectors may be secured to the sleeves in any suitable manner.

It is to be understood that it is not necessary to use glass for the sealing material 22, but that any other suitable material, such as vitreous enamel may be used. It is important, however, that the glass or other sealing material have a high electrical resistance at the operating temperatures of the terminals.

'I'he tubular terminal members 2| in addition to their functions previously pointed out have the important function to provide for the release of air from the sheath I 2 during the sealing process. It will be understood that the granular insulating material contains more or less air which, when the sheath is heated while being sealed, expands and tends to escape from the ends of the sheath. The tubular members cooperating 'with the terminals provide paths through which this air can escape. This permits the glass 22 to be pressed into position without danger of air bubbling up through the glass and forming bubbles in it. Bubbles weaken the seal and often cause leaks. Hence, it is always advisable to eliminate the possibility of their formation'.

In Fig. 3 I havev shown a modied form of my invention wherein the seal between the tubes provided for the terminals. and the vitreous sealing material is effected before these members are assembled with the heating unit.

In making the terminal seal of the heater of Fig. 3, each terminal sleeve or tubular member 30 is arranged in substantially concentric relation with a casing 3|. 'I'he terminal sleeve 30 is assembled with the tubular member 3| and with a tube (not shown) formed of the glass sealing material 32 in substantially the same positions relative to each other that they will occupy in the nished heater. In other words, they will be assembled in positions relative to each other substantially the same as those shown in the finished heater of Fig. 3.

Then the assembly is heated to a temperature at which the glass becomes soft. 'Ihe glass is then compressed until it completely fills the space between the tubular members 3|) and 3| so that upon subsequent cooling it will adhere to these members to make fluid impervious joints with them. Preferably, the tubular members 30 and 3| will be cleansed before the glass 32 is applied.

The unitary structure comprising the tubular members 30 and 3| and the glass 32 adhering to them is then assembled with the heater so that the terminal 33 of the heater is received in the tubular member 30 and so that the tubular member 3| embraces the terminal end of the sheath. The outside diameter of that portion of the sheath which is received by the member 3| may be reduced somewhat, as indicated in Fig. 3, the internal diameter of the member 3| being substantially the same as the diameter of the sheath portion to which it is fitted. The tubular member 3| is sealed to the sheath I2 by means of a brazed, soldered or welded fluid impervious joint 3|a. The end of the tubular member 30 is brazed or otherwise connected with the end of the terminal 33 so as to be joined therewith by a fluidtight joint 34.

If desired, and it is usually preferable to do so, a washer 35 formed of an insulating material, such as mica,-wi1l be threaded over the terminal before the seal is assembled with the heater so as to increase the electrical insulation between the terminals and the sheath.

Instead of being sealed to the sheath by brazing, soldering, ete., the tubular member surrounding the glass may have a threaded connection with the sheath so as to provide a huid-tight joint, as shown in Fig. 4. In this arrangement, the terminal sleeve 40, the surrounding tubular member 4| and glass seal 42 between these members are arranged in substantially the same fashion as are the corresponding elements 30, 3| and 32 of Fig. 3. In Fig. 4, however, the tubular member 4| is provided with an internal threaded portion 43 arranged to be screwed on a corre--l sponding threaded portion 44 provided on the terminal end of the sheath. A suitable sealing compound may be placed on the cooperating threads between the casing 4| and the sheath.

It will be understood that here again the terminal sleeve will be connected or joined with the terminal by means of a brazed joint 46.

And here also it is preferable to thread a mica washer 41 over the terminal before the seal is assembled with the heater.

It will be observed that I have provided a terminal seal which comprises a tubular member 2 I, 30, 4|) surrounding the terminal of the heater, this member in turn being surrounded by a substantially homogeneous layer 22, 32, 42 of glass which makes fluid impervious joints both with this tubular member and with the surrounding casing. This casing, as previously pointed out, may be either the walls of the sheath of the heater (Figs. 1 and 2), or it may be a separate member 3l, 4| (Figs. 3 and 4) which is attached to the sheath with a fluid impervious joint. The tubular member 2|, 30, 40 surrounding the terminal is joined with it by means of a iluid impervious joint 23, 34, 46.

The provision of the tubular members 2|, 30, 40 surrounding the terminals provides for expansion and contraction of the glass seals independently of expansion and contraction of the sheath or the terminal. This obviously is of advantage in that it is quite unlikely that the seal will be broken by reason of expansion and contraction of the vitreous sealing material.

The terminal seals of my invention effectively prevent the admission of uids into the sheath. It ls to be understood, however, that they may be used just as effectively to retain a selected atmosphere in the sheath, such as an atmosphere for preserving the life of the resistance heating element. Thus, for example, the seals may be used to retain a non-oxidizing or reducing atmosphere in the sheath to protect the heating element.

While I have shown several particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

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

1. The method of sealing the terminal end of an electric heater provided with a resistance conductor, a terminal and a metallic sheath incasing said conductor which comprises placing a tubular member over said terminal, said tubular member having a diameter somewhat larger than that of said terminal so that a relatively small passageway is provided between these members, interposing between said tubular member and said sheath a mass of vitreous material, heating to soften said material while said tubular member is opened so as to allow the escape of gas from said sheath, then allowing said vitreous material to cool so that said vitreous material adheres to said tubular member and said sheath and then sealing said tubular member to said terminal.

2. The method of sealing the termin-al end of an electric heater provided with a resistance conductor, a terminal and a metallic sheath incasing said conductor which comprises placing a metallic tubular member over said terminal, said tubular member having a diameter somewhat larger than the diameter of said terminal so that a relatively small passageway is provided between said members, surrounding said tubular member with glass, heating said glass to a plastic condition while said tubular member is open to allow the escape of gas from said sheath and applying pressure to said glass so as to cause this glass to adhere to said tubular member and said sheath with fluid impervious joints and placing a sealing material between said terminal and said tubular member so as to form a fluid impervious joint between these members.

3. I-Ihe method of sealing the terminal end of an electric heater provided with a resistance conductor, a terminal and a metallic sheath incasing said conductor which comprises placing a metallic tubular member around said terminal,

said tubular member having a diameter somewhat larger than the diameter of said terminal so that a relatively small passageway is provided between said members, surrounding said tubular member with glass, heating said glass to a. plastic condition While said tubular member is open to allow the escape of gas from said sheath'and applying pressure to said glass so as to cause said glass to adhere to said tubular member and said sheath with uid impervious joints and then brazing the end of said terminal to said metallic tubular member so as to form a uid impervious 5 joint between these members.

FRANK E. FINLAYSON.

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