US707194A - Electric rheostat or heater. - Google Patents

Description

No. 707,|94. Patented Aug. l9, I902.

H. P. BALL.-

ELECTRIC BHEOSTAT 0R HEATER.

(Application filed Nov. 2, 1896.)

(No Model.)

M/ VE/VTOI? A ITO/MUS- UNITED STATES PATENT OFFICE.

HENRY PRICE BALL, OF BROOKLYN, NEIV YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO II. IVARD LEONARD, OF BRONXVILLE, NEl/V YORK.

ELECTRIC RHEOSTAT OR HEATER.

SPECIFICATION forming part of Letters Patent No. 707,194, dated August 19, 1902.

Application filed November 2, 1896. Serial No. 610,795. (No model.)

To all whom it may 0012007 12,;

Be it known that I, HENRY PRICE BALL, a citizen of the United States, residing inthe city of Brooklyn, in the county of Kings and State of New York, have invented certain new and useful Improvements in Electric Rheostats or Heaters, of which the following is a specification, reference being had to the accompanying drawings, forming a part hereof. My invention relates to devices in which electric energy is converted into heat. Such a device, whether a rheostat or an electric heater, should be so constructed that there shall be a maximum conductor-surface in order that it may have the greatest amount of surface for radiating heat or imparting heat to the radiating part of the device. The conductor should also be of as high specific resistance as obtainable, the other properties of the conductor being equally good, such as its non-oxidation at any but a high temperature, if at all. Furthermore, the conductor, particularly if small and of little mechanical strength, should be supported or held so that it cannot shake or vibrate or sag out of position. The supporting-body for the conductor acts as the radiating part of the device, and it will be seen then that the heat generated in the conductor must pass first from the conductor to the insulation between the conductor and the support and then through the support to the radiating-surface, so that it is very necessary to have the thickness of insulation between the conductor and the support a minimum and the thickness of the support also a minimum, while the radiating surface is a maximum, and the extent of contact between the conductor and the insulation and between the insulation and the support is a maximum. The entire device, outside of the conductor, should be as good a conductor of heat as practicable in order that the heat may be quickly conducted from the conductor or heat-generator to the dissipating or radiating surface, and it is desirable to so construct the device that when it is unequally loadedthat is to say, when one part of the device is generating more heat than anotherthe supporting part shall equalize or distribute the heat over the entire or greater part of the radiating-surface, thereby reducing the temperature of the device and permitting the device to be made smaller than otherwise would be possible. I attain all of these advantages by my invention, which is fully described hereinafter and is illustrated in the accompanying drawings, in which-'- Figure 1 is a side view of a rheostat or heater constructed in accordance with my invention. Fig. 2 is an edgewise view of the same looking at Fig. 1 from the right, partly in vertical section. Fig. 3 is a horizontal section of the same. Fig. 4 is a view similar to Fig. 3, but showing a slightly-different form of the support. Fig. 5 is a partial View, in vertical section, showing another form of the support, which may be employed where radiation from one side only is desired. Fig. 6 is a partial horizontal section similar to Figs. 3 and at, showing still another form of the support.- Fig. 7 is a transverse sectional view illustrating a different embodiment of a feature of the invention.

In the constructions shown in Figs. 1, 2, 3, and i the support for the conductor or resistance 3 is represented as composed of two parts 1 and 2, which are formed of reflexed or corrugated sheet-iron or copper or other suitable material, the corrugations being such that when the parts are laid together and secured face to face by rivets 4 or otherwise the oppositely-concave portions of the sheet or support form a number of parallel receptacles .or spaces, substantially tubular, into which the parallel conductors or resistances 3 can be placed and by, which they are supported. As an insulating material between the conductor 3 and the supporting shells or plates 1 and 2 I use enamel or mica or any material that can be used in a thin layer, enamel having the advantage that it can be placed all over the supporting shells or plates, both inside and out, as indicated at 5 and 6, thereby reducing the liability of a ground from any connecting-wire accidentally touching the outside of the supporting-plates.

It will be seen that by the use of corrugated sheet metal, which conforms substantially to the general shape of the resistances, I have the same distance at all places for the heat to travel from the conductor to the radiating surface, while at the same time the radiatingsurface is greatly increased by the use of the corrugated surface. The corrugations therefore serve a double purpose, that of holding.

the resistance on one side of the sheet and that of radiating or dissipating the heat on the other, while at the same time there is a minimum of material, and therefore the least possible difference of temperature between the conductor and the radiating surface. The conductor 3 may be inserted into the holder or receptacle in a contracted state and then allowed to revolve and expand into the spaces provided. This brings the conductor into touch with the insulation between it and the support, and the heat is rapidly drawn off. As shown in Fig. 4, the radiatingsurface may be further increased by crimping the material of the support, as represented at 7.

In some instances it might be advisable to cause the wire to adhere at all points along its length to the support. In such cases I cover the conductor with a layer of enamel, which being fused to the enamel that is under the conductor envelops or embeds the conductor in a body of insulating material, as indicated at 8 in Fig. 7 and in the left-hand portion of Fig. 3.

It will be observed that the two sheets or plates 1 and 2 are precisely alike and are laid upon and secured to one another in such a manner that the edge of each plate projects beyond the corresponding edge of the other, thus allowing ready access to the ends of the resistance-coils for the purpose of connecting them to or disconnecting them from the hinding-screws 9, which pass through porcelain insulators 10, although, if desired, the hinding-screws may be dispensed with and the resistance passeddirectly from one chamber into the next.

It is obvious that the supporting shell or plate may be made in one continuous piece, as shown at 11 in Fig. 6, instead of being made in two separate pieces, as above described. It is also obvious that when radiation is desired from one side only a plate 12, of insulating or other material, such as slate, may be employed with a single corrugated sheet 13 to hold the resistances 3 in the corrugations thereof.

I am aware that conductors have been enameled to plates of cast-iron; but the impracticability of this lies in the fact that castiron cannot be enameled on its surface with a thoroughly-vitrified enamel, whereas sheetiron or copper can. Enamel on the surface of cast-iron is porous and can and does absorb moisture. It is of the nature in that respect of a brick, and as any glassy enamel placed upon the first coat becomes in practice full of minute fissures or cracks the dampness or moisture finds a very ready path to the absorbing coat of enamel and destroys the insulation between the conductor and support. It is therefore seen that sheet metal such as I use possesses advantages peculiar to itself and not attained in the use of cast metals. It is also to be observed that there is a distinct difference between enameling or embedding in enamel a conductor on the inside of a cylindrical support 14, as shown in Fig. '7, over enameling one on the outside from the fact that enamel beinga very brittle material will fly away from the metallic surface the moment any strain is brought to bear upon it in the right direction to tear it therefrom, as in the case of a conductor being enameled on the outside of, a cylinder. Here the moment the wire expands through the heat developed by a current passing through it a strain is placed upon the enamel, tending to rupture it from the cylindrical body. In the event, however, ofa wire being enameled on the inside of a tube, as shown in Fig. 7, for example, all the strain placed upon the enamel is backed up by the tube and there is no tendency for the enamel to break away.

In practice it is generally necessary to construct rheostats with steps of different resistances, and in this case the last step thrown into circuit beginningat low-resistance steps) is the one that generates the most heat. This is the case in a field-rheostat. In the case of a motor-starting rheostat or a theater-dimmer or a motor-regulator only part of the resistance is generally in circuit at one time. If each step in the resistance were entirelyseparate, different parts of the rheostat would have different temperatures, and some would have the atmospheric temperature. Now I make use of all of the radiating-surface at all times by using supporting-shells for all or a number of the steps, which are in thermic contact from one end of the device, thereby distributing the heat evenly, and I preferably use copper sheets, which will conduct the heat rapidly from the hot parts of the device to cold parts, quickly equalizing the temperature over the radiating-surface.

Iclaim as myinvention and desire to secure by Letters Patent- 1. In an electric rheostat or heater, the combination of a metallic support comprising two plates having irregular outer surfaces and grooved inner surfaces, a layer of insulating material in said grooves, and a separate resistance-step in each groove, and an edge of one plate projecting beyond the other to expose the ends of the resistances.

2. In an electric rheostat or heater, the combination of a metallic support comprising two plates having irregular outer surfaces and grooved inner surfaces, a layer of insulating material in said grooves, a separate resistance-step in each groove, and an edge of one plate projecting beyond the other to expose the ends of the resistances, and a series of binding-posts mounted on the projecting edge and to which the resistance-steps are secured.

8. A rheostat or electric heater having a se ries of resistances, two similar, thin sheets of metal to inclose the resistances in close proximity thereto, thin insulating material applied to the opposing faces of said sheets, and means to secure said sheets together face to face with the edge of each projecting beyond the edge of the other to expose the ends of the resistances.

4. In an electric rheostat or heater, the combination of two metallic plates having a series of grooves or corrugations, a layer of insulating material on the inner sides thereof, a separate resistance-step in each groove, said plates having the ends projecting beyond each other so as to expose the ends of the resistances, and binding-posts for said resistances at the projecting ends of the plates.

Images