US2577080A - Electric heater - Google Patents

Description

Patented Bec. 4, 1951 UNETED STATES PATENT OFFICE ELECTRIC HEATER Irving G. Glenn, New York, N. Y.

Application May 31, 1049, Serial No. dllil 3 Claims. (Cl. 20L-87) This invention relates to electric heaters and more particularly to certain improved struc tural features by which production is greatly facilitated and expedited and the heater produced is freed of g objectionable defects of present-day heaters and possesses important points of superiority over the same.

The lengthy operation, under present practice, of entering and packing granular insulating material in and around the helically-wound resistor element and in the annular' space be tween it and the surrounding tubular metal jacket, is largely avoided in carrying the inverotion into effect. l'lhis is accomplished by the use oi a preformed tube of challry porcelain or other suitable material, proportioned to snugly receive the resistor element in the bore thereof and hill the greater portion of the space between it and the inner surface of the enclosing metal jacket. This insulating tube is preferably given a ribbed formation externally, the ribs extendlng lengthwise thereof and radially outward to meet the inner wall of the jacket. Thus constructed and arranged, the tube serves to hold the resistor element accurately and firmly centered in the jacket and against displacement and tsulting hot spots and burn-outs. The remain ing unoccupied space within the jacket is thus reduced to the bore of the resistor winding and the channels between the ribs of the insulating tube, the lllling of which, in the usual manner, with powdered inagnesite or like material, is efiected in a comparatively short time. The iinal step of contracting the metal jacket by machine swagine crushes the ribs of the insulating tube and compresses and compacts the body thereof and the filling material solidly in and about the resistor.

A second feature of improvement consists in utilizing integral extensions of the resistor winding as the terminals thereof, to avoid vwelded or pressed joints or other special construction required for attaching terminals to the same. This is made practically possible by reinforcing the extensions with a winding of Nichrome or nickel wire, which strengthens and renders them durable for all purposes. The extensions are brought out of the jacket through plugs or washers of mica. or other material, sealed in the jacket with silicon, closing the ends thereof.

Other features of the invention not specially mentioned above will be brought to attention in the detailed description that follows.

The accompanying drawing will serve to illustrate a construction suitable for carrying the invention into effect, but it is to be understood that no limitations are intended by this showing other than are imposed by the appended claims.

In the drawings- Fig. l. is a view in elevation on an enlarged scale, oi' the heater with parts broken away show the internal construction.

Fig. 2 is a detail perspective View, on a greatly enlarged scale, with proportions exaggerated for clearness or illustration, showing the several elements that make up the heater.

Fig. 3 is a cross sectional view on the line s3s3 of Fig. l, and

Fig. e is a detail View showing 'the integral terminal extensions oi the resistor and their reinforcement.

Referring now to the drawings, l indicates the resistor element of the heater, which may be of any suitable or well known form but is preferably a helical winding of Nichroine wire, the end portions oi which are drawn out and straightcned to serve as terminals 2, l?, as hereinafter described.

The resistor element is jacketed by an outer metal tube il, of suitable diameter to provide an annular space il between the inner surface there of and the resistor winding for the reception ci refractory insulating material, by which the winding is spaced apart from the jacket wall and held in centered relation therein. 'lhe jacket is of greater length than the resistor winding to provide clearance for closing and sealing the open ends thereof, as hereinafter described.

As a ller for the annular space 4, between the jacket and the resistor winding, a preformed tube 5 of suitable refractory insulating material is provided, which is proportioned to receive the winding in snug relation in the bore 6 thereof by being slipped over the same and has an external formation of radially disposed ribs l, that` extend to the inner wall of the jacket and may be slidingly entered therein. While the tube may be made of any of the various well known refractory materials suitable for insulating the winding and serving other necessary purposes, chalky porcelain is preferred, owing to its ready and uniform compressibilty under machine swaging to which the assembly is subjected as the nal step in the completion of the heater.

It will be seen that the insulator tube forms a complete filler for the main portion of the jacket and leaves only the bore of the resistor winding and the channels between the ribbed formation of the tube to be filled with granular insulating material, which is done. with powdered magnesite, as indicated at 8, in the con.

ventional manner and in a comparatively short period of time.

The relative proportions oi' the ribs and channels may obviously be such that under machine swaging, the crushed ribs will provide suiflcient material to fill the channels and avoid the ne' cessity of entering granular material therein as a ller. I

Closures are provided for the open ends of the jacketl in the form of tightly fitting mica plugs or washers, indicated at 9, which are sealed with silicon against displacement or leakage.

The end closures of the jacket are centrally bored for the passage through the same ofv the integral extensions of the resistor winding, which, as above stated, serve as the terminals thereof and, in order to give the terminals the required strength to withstand careless or rough handling, they are reinforced with a winding of Nichrome or nickel wire, as indicated at I0. This reinforcement may extend from a point at each end within the jacket and on through the end closures or may be limited to that portion of the terminals that projects beyond the closures, whichever is preferred.

Assembled as above described, the heater is machine-swaged, the effect of which is to reduce the diameter of the enclosing jacket and thereby compress and compact the insulation into a solid body in and around the resistor winding, which secures the same permanently in centered relation in the jacket and against possible displacement.

Prominent-among the important advantages of the invention may be mentioned the following:

The instant lling of the greater portion of the heater jacket by the use of a preformed insulator tube, which effects a great saving in time over the conventional method of entering and packing a filler of granular insulating material therein.

The definite and positive centering of the resistor permanently in the jacket and against possible displacement likely to result in hot spots, burn-outs or other shorts.

The use of a preformed insulator tube of chalky porcelain, owing to its ready and uniform compressibility to solid and compact form under machine swaging.

The reduction to a minimum of the jacket space to be filled by the conventional slow method of entering and packing granular insulating material therein.

The closure of the jacket ends air and watertight by the use of sealed mica plugs.

The avoidance of welded, pressed or other joints or connections, by the use of integral extensions 1. The method of making metal sheathed electric heating units comprising inserting a helically-wound. open core electric heating element into a tubular liner of a frangible insulating material with the opposite end portions of the heating element extending substantially axially from opposite end portions of said liner, inserting the assembled liner and heating element axially into a tubular metal sheath with the axially disposed terminal portion of the electric heating element projecting beyond the ends of the sheath, filling substantially all of the unoccupied space within the tubular metal sheath with powdered insulating material, swaging the metal sheath sufliciently to contract the same radially'and crush the frangible tubular liner and compact the same with the powdered insulation material to fix the electric heating element substantially centrally of the metal sheath, and insulatingly sealing the ends of the metal sheath about the projecting ends of the electric heating element.

2. The method of claim 1 wherein the heater element is inserted within a continuous one piece tubular liner of frangible insulating material which liner supports and encloses all of the heater element except the projecting ends thereof.

3. The method of claim l wherein the heater element is inserted within a continuous one piece tubuler liner of frangible insulating material having longitudinally extending, radially projecting ribs externally dimensioned to snugly engage the inner surface of the metal sheath when the assembled liner and heater are inserted in said sheath, to thereby center the liner and heater within the sheath.

' IRVING G. GLENN.

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

UNITED STATES PATENTS Number Name Date 1,227,346 Trood et al May 22, 1917 1,359,400 Lightfoot Nov. 16. 1920 1,394,518 Abbott -Oct. 25. 1921 1,507,901 Wells Sept. 9. 1924 1,783,554 Backer Dec. 2, 1930 1,910,041 Noguchi lMay 23, 1933 1,927,035 Hicks Sept. 19, 1933 1,982,885 Stupako Dec. 4, 1934 FOREIGN PATENTS Number Country Date 1,922 Great Britain Jan. 26, 1909 109,500 Australia Jan. 18, 1940 OTHER REFERENCES Bass, Silicones, Proceedings I. R. E., July 1945, pages 441-447.

Croft, American Electricians Handbook, 1913, page 91, Fig. 98.

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