US2112729A - Electric heater - Google Patents

Description

March 29, 1938. c, C:I ABBTT ELECTRIC HEATER Filed April y1.7.8, 1936 l nventor:

Abbott, @My JWM' His A Char|es C.

'Patented Mu. 2 9, 193s ELECTRIC HEATER Charles C. Abbott, Pittsiield, Mass., assignor to General Electric Company, a corporation of New York Application april zs, 1936, serial No. 76,781

3Claims.

This invention relates to electric heaters, more particularly to electric heaters of the sheathed type, and it' has for its object the provision of an' improved method and means for making electric 5 heaters of this character.

More specifically, this invention relates to elec? tric heaters of the sheathed type in which a relating supports are spaced at intervals along the length of the resistance conductor. These supports function to position the resistance conductor centrally of the sheath while the sheath is being loaded with the insulating material and during the initial stages of the swaging operation used to'compact the insulating material. Also, these supports are prevented from endwise movement in the sheath so as to prevent endwise 30 movement of the resistance conductor during the loading and compacting operations. l

I'he supports disclosed in the Daly patent have a solid cylindrical portion that receives the conductor and an enlarged solid flange-like head portion located at one end of the cylindrical portion and arranged to hold the cylindrical portion and hence the conductor centrally of the sheath.

It has been foundin certain'cases that these insulating supports injured the inside wall sur- 'faces of the metallic sheath during the swaglng operation. thereby causing a weakening of, the sheath with the result that the sheath at times would break, especially when the finished heating' unit m being formed into a curved or angular shape. y

It is anobjeet oi this invention to provide an improved method of making relatively long heaters wherein a supporting member for the conductor is used arranged to be readily destroyed upon the application of pressure so that during the sw'ins operation the support cannot exert enough pressure on the metallic sheath to injure it.

In accordance with this invention, the insulat- 55 ing support comprises a conductor grasping por- May 23, 1933. As described in this patent, insu Y tion to receive the conductor. This portion preferably is arranged in the form of a cylinder. In addition, the support is provided -with relatively light readily destructible anges secured to the body portion and arranged to position the body 5 portion and hence the conductor centrally in the sheath.` The supporting members are secured to the conductor at spaced intervals and are mounted with the conductor in the sheath. 'I'he flanges preferably areangularly arranged with respect to the axis of the body portion and conductor received in it Vso as to be readily destroyed by application of pressure during the swaging operation. The relatively thin .readily destructible anges are broken during the initial swagng step, wherebyA injury to the sheath is obviated while the heater is being made.

For a more complete understanding of this in vention, reference should be had to the accompanying drawing, in which Fig. l is an elevation illustrating a helical resistance element Withsupports arranged in accordance with this invention spaced at intervals thereof; Fig. 2 is an elevation of the sheath illustrating the sheath at one stage in the process of making the heating unit; Fig. u 3 is an elevation partly in section illustrating the resistance conductor together with the supports mounted within the sheath and also illustrating the sheath at amore advanced stage in the process of making the electric heater; Fig. 4 is an elevation partly in section illustrating the sheath after it has been iilled with the powdered insulating material; Fig. 5 is an elevation illustrating the electric heater after the sheath has been swaged to compact the insulating material; and Fig. 6 is a. perspective view on an enlarged scale illustrating the supports for the resistance conductor arranged in accordance with this invention.

Referring to the drawing, I have illustrated my invention in one form as applied to a relatively long heatingvunit l0 having a' helical or sinuous resistance elementV ll extending-centrally of a metallic sheath I2. The heating element All in the nished heating unit (Fig. 5) is embedded inf/4 5 a. compacted mass 'of powdered.heat-refractory electrically-insulating material I3, such as magnesium oxide (Fig. 4). Suitable vterminal members Il and l5 are secured to the ends of the resistance element l i.

vIn making the electric Yheater in accordance `with^this invention, insulating supports I6 are threaded .on the resistance element Il, The insulating supports i6 are provided with a grasping portion ll arranged, as shown, in the form 55 of a cylinder. The grasping portion I1 is arranged to receive the resistance conductor II, as shown in Figs. 1, 3, 4, 5 and 6, and it has a diameter slightly larger than the diameter of the helical coil so that it may be readily threaded over the coil. 'I'he support I6 is provided at each end with a pair of flanges I8. The two flanges I8 at each -end are positioned on opposite sides of a central plane or on opposite sides of the central axis of the cylinder .I1 and flare outwardly at an angle to the cylindrical body portion, as clearly shown in the drawing. I have found that very satisfactory results are obtained when the flanges are arranged at an angle of substantially 45 to the central axis of the body portion Il.

'I'he anges I8 preferably are given a curved form, as clearly shown in Fig. 6, the outer edges of the flanges having a curve substantially concentric with the walls of the cylindrical portion I1.

It is alsopreferable that the curved edges of the flanges I8 lie in a circle, which is slightly smaller in diameter than the internal diameter of the sheath I2 before it is swaged so that when the conductor Il and supports I6 are mounted in the sheath the flanges serve to position the conductor substantially centrally of the sheath.

Moreover, it is preferable to provide the outer edges of the flanges with relatively narrow supporting ledges I9 which are arranged to lie concentric With the inner walls of the sheath when the supports are placed within it. It is further desirable that the extreme outer edges of the flanges be fiat, as indicated by the numeral 20, and arranged substantially at right angles to ledges I9.

The insulating supports I6, it will be observed, are formed of very thin walls. The walls of the cylindrical portion Il have a very small thickness and so also have the flanges I 8 secured to it. While the insulators I6 may be made of any suitable electrically insulating material that is readily destructible when subjected to pressure, I prefer to form the insulators of lava.

The insulating supports I6 that are threaded on the resistance conductor are spaced at intervais thereon and are secured against endwise movement relative to the conductor in any suitable znanner, as by flattening a few adjacent turns lIa,.and IIb on opposite sides of each insulator.

After this has been done, the terminals I and l5 are secured to the resistance conductor. If desired, before the terminals are applied, suitable insulating supports IGa may be mounted on the terminals, as clearly shown in the drawing. These supports are similar to the supports I6, but have supporting flanges at one end only, as clearly shown in the drawing.

The outer end of the terminal Il is provided with a solid loading washer 2I, while the outer end of the terminal I5 is provided with a loading pin 22, which is freely directed through an eye 23 provided for it in the terminal.

After the terminals have been secured to the conductor II, the conductor with the terminals and insulating supports IG and I6a mounted thereon is threaded through the sheath I2; and the exterior walls of the sheath are provided with suitable indications or markings on the sides of the .insulators toward the terminals Il. For this purpose, suitable chalk marks 24 may be provided on the exterior walls, as described in the above mentioned Daly patent.

It will be understood that the left-hand end of sheath I2 will be provided with a suitable counterbore 25 which receives the solid loading washer 2 I while the right-hand end of the sheath will be provided with a similar counterbore 25a which receives the loading pin 22. After assembly, the left-hand end of the sheath is peened over to secure the solid loading washer 2|; and narrow sections of the sheath at the chalk marks 24 are reduced to define restrictions 26 which function to prevent movement of the insulators, and hence, of the conductor toward the left-hand end of the sheath while the insulating material I3 is loaded in the sheath.

The electric heater is now in the condition shown in Fig. 3 and is ready for the loading operation. The sheath is loaded with the insulating material through its right-hand end. To accomplish this, the sheath is held in an upright position with the right-hand end uppermost. The insulating material can freely flow from the upper to the lower end of the sheath through the cylindrical portions of the supports I6 and through the secant shaped spaces between the sides of. the supports IB and IGa and the sheath. The solid washer 2I holds the material in the sheath.

After the sheath has been loaded, as shown in Fig. 4, a solid washer 21 is placed in the counterbore 25a over the pin 22 and this end of the sheath is peened over to secure the solid washer.

The entire unit is now passed through a swaging or rolling machine for the purpose of compacting the insulating material I3 within the sheath toa hard dense mass, the swaging operation reducing the diameter and increasing the length of the unit.

If desired, the insulating material I3 may be compacted between the reduced sections 26 beforethe swaging operation, as pointed out in detail in the above-mentioned Daly patent.

The sheath is reduced to a diameter equal to or less than the diameter of the reduced portions 26. It usually is desirable to pass the unit through the swaging machine a number of times so as to reduce the diameter gradually. It has been found that the readily destructible fragile flanges I8 of the insulating supports I6 break oif and are destroyed during the initial swaging steps so that they exert very little pressure on the inner walls of the sheath I2 during the reducing and elongating operation. Because of this, the strength of the sheath is not reduced at the sections where the insulators are located, as has been the case in certain instances heretofore. As pointed out previously, the flanges Il are arranged at a substantial angle to the axis of the cylindrical portion I1; in the particular support illustrated this angle is 45". This is desirable because it causes the forces applied by the sheath to the ends of the flanges during the swaging operations to be applied on a relatively large leverage. This, of course, permits a relatively small applied force to break the flanges. It is to be understood of course that the angle of the flanges may vary widely and may be greater or less than 45.

Apparently, the flanges that are broken off in the initial stages of the swaging operation float along with the insulating material as the material is moved in the sheath by the swaging. The

flanges at no time are forced outwardly or bear on the sheath with sufl'icient force to cause any damage or injury to the sheath.

I have found that very long heating units having lengths of 25' or 30' or more can be made successfully by this invention, and that after they have been made they may be given various suitable non-rectilinear forms without danger of failure of the sheath at any point throughout heating units by otherV methods. Thus, the insulator 'oi this invention may be used to advantage in any sheathed electric heater where it is desired to hold theresistance conductor centrally of the sheathduring the loading and swaging operations.

While I have shown a particular embodiment of my invention, it will be understood, of course,

that I do not wish to-be limited thereto since many modications may be made and I, there- -fore, 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:

a 1.` A support for the resistance conductor of a sheathed heater which is reduced in diameter to compact its insulation comprising a body portion arranged to coact with the conductor to prevent substantial relative movement between the body portion and conductor, and relatively thin readily destructible anges extending outwardly from said body portion at its ends and at an angle to the body portion such that they will readily break from said body portion upon application of transverse pressure to them by said sheath when its diameter' is reduced to thereby obviate injury to the sheath, and said ilanges being adapted to position said body portion and conductor in predetermined spaced relation with the sheath until said anges have been broken from the body portion.

2. An electrically insulating support for the resistance conductor oi' a .tubular sheathed heater, the support being formed of a material readily destructible when subjected to pressure comprising a cylindrical body portion arranged to receive the conductor to prevent substantial relative movement between the body portion and conductor,l and a pair of iianges at each end of said body portion on opposite sides of its axis having curved sections substantially concentric with said cylindrical body portionand arranged at an angle of substantially45" to said axis, said flanges being adapted to position said body portion and conductor in the sheath of said heater and by reason of said angle being readily destructible and separable from the body portion when the sheath of the heater is compressed to thereby obviate injury to the sheath.

3. A support for the resistance conductor of a sheathed heater whose sheath is reduced in diameter to compress the insulation of the heater comprising a cylindrical body portion arranged to receive and coact with the conductor to pre-v vent substantial relative movement between the body portion and conductor, a plurality of relatively thin readily destructible flanges extending outwardly at an angle from the. body portion adapted to position the body portion and conductor in the sheath of the heater, and the angle being such that the iangsvreadily break from the body portion by application of transverse pressure from the sheath -when its diameter is reduced to thereby obviate injury to the sheath, and the outer edges of the ianges being provided with relatively narrow ledges defining small areas that obviate the application of concentrated pressure to the sheath as its diameter is reduced.

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