US1237592A - Electrical heating unit. - Google Patents

Description

L. R. WHITE.

ELECTRICAL HEATING UNIT.

APPucATmN FILED ocT.21.191s.

1,237,592. Patented Aug. 21,1917.

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ELECTRICAL HEATING UNIT.

specication of Letters Patent. Patented Aug. 21,1917.

Application filed October 21, 1915. Serial No. 57,037.

To all 'whom it may concern:

' Be it known that I, LOUIS R. WHITE, a citizen` of Athe United States, residing at Bennington, county of Bennington, and State of Vermont, have invented a new and useful Improvement in Electrical Heating Units, of which the following is a specification.

My invention relates to a heating unit comprising an embedded electrical conductor adapted 'to be heated by the passage of electric current therethrough. Such units, of various types of construction, are known in the art and extensively used for cooking purposes in the homeI and factory, for heating rooms or other inclosures, and for various industrial purposes in the arts. My invention relates more particularly to an electrical heating unit for domestic purposes to be used in cooking, heating water and the like.

The object of my invention is to provide a heating unit of the class described which shall be capable of heating a given body of material to a given temperature more quickly and with a less expenditure of energy than has hithertol been the case.

My invention will be better understood by referring to the accompaniyng drawings in which Figure 1 represents an elevation, part section, of a unit of my invention as embodied in an ordinary hot plate for heating or cooking any material placed thereon; and Fig. 2 represents a plan view, part section, of Fig. 1.

Referring to the drawings the heatin unit proper, 1, is constituted as follows: A disk, 2, of rigid material, preferably iron, is provided with integrally attached upstanding ribs, 3, of the same material. Preferably, these ribs are very narrow as compared with their height and are given the form of a continuous ribbon arranged as a spiral, beginning near the center of the disk, 2, and ending near its periphery. A11 annular rib, 4, of the same character bounds the disk.

The spiral rib 3 is of uniform width except near the ends, which preferably taper to athinedge, and with the bounding rib, 4, act as stiening devices to maintain the disk, 2, flat when subjected to heat in th normal operation of the device.

Resistance material adapted to have anv electric current passed through it is placedbetween the spaced convolutions of the cement for this purpose is alundum, a mal terial which contains from 92% to 100% of pure aluminum oxid and which can be readily'purchased upon the open market. This material is an electrical nonconductor, both when heated and when cool and, if the wire helix is suitably proportioned, may be inserted in the spiral channel with and surrounding the wire helix so as to perfectly insulate, electrically, said helix from the rib, 3, and from the disk, 2.

The ends of the resistance helix may be joined to terminals, 6, 6, insulated from the disk, 2, but suitably attached to said disk near the ends of the helix.

As shown in the drawing, the heating unit proper, as above described, is placed (a coating of heat resistant varnish or plastic 'cement may be used to assist in holding the unit in place) in a recess formed in a plate,

7, of any suitable vrefractory ma-l terial. Preferably I prefer for this plate a material which is a good insulator, both for heat and electricity, although the charac teristic of electrical nonconductibility is of no particular importance. There are numerous compositions which satisfy my requirements and among the best, I ind, are those which are constituted substantially of asbestos fiber suitably compressed and united by a binder. cess is, preferably, such that the top ofthe ribs, 3, and, 4, lies substantially below the top of the plate; the entire unit is then covered, with the same cement asis used be-v tween the ribs, up to the level of the plate, 7.

The plate, 7 ismounted in the usual way upon a cylindrical casing 8, itself mounted upon and above a base, 9. The terminals, 6, of the resistance helix are connected by conductors, 10, 10, to a suitable plug switch element, 11, yby means of which connection can be made to any convenient source of electrical supply.

The casing, 8, is preferably filled with The depth of the reunit may be alternately raised to a high heat such as a red heat, as described, and current turned off and the unit allowed to cool to normal temperature as often as desired with impunity. The material will not crack under these circumstances, nor will the plate warp. This freedom from warpingpis probably largely due to the stiffness obtained by the use of the multiplicity of upstanding ribs.

A characteristic feature of this, my invention, is that the material of the helix is directly in contact with the body of the ce- -ment and the upper surface of the cement is directly in contact with the vessel containing the material to be heated. I have found from observation, in connection with numerous experiments, that the rate at which the temperature of the surface of a given i heat unit or a hot plate is reachedis greatly for two reasons.

affected by the number of surfaces of separation between the material which actually carries the current and the surface of the hot plate. Thus a heat unit having an insulated wire embedded in enamel with the enamel itself in contact with the lowerv surface of an iron disk whose upper surface constitutes the effective heating surface of the hot plate, other things being equal, for a given expenditure of electrical energy will develop the maximum temperature at the upper surface of the hot plate much more slowly than will be the case at the upper surface of my hot plate, as above described, where the bare wire of the resistance material is directly in contact with the cement and the surface of the cement itself is the surface of the :hot plate. This fact is 'of lgreat importance to the economical operation of the hot plate In the first place, if a given maximum temperature is arrived at at the surface of one hot plate more uickly than at the surface of another it ollows that the material heated by the first hot plate will attain its desired temperature more qlllickly than the same materialheated by t e second hot plate so that the current may be turned off more quickly in I.the one case than in the other. Furthermore, the heat lostby radiation will be very much less in the case of the first plate than in the case of the second plate,l since thefmounting of theheat unit w1ll reach a substantially lesser temperature in the case of the first unit than in the case of the second unit and, since the heat loss is proportional to the temperature gradient, it is clear that the loss of heat from the second unit will be much greater than that from the first unit.

While I have shown my improved heat unit as applied to an ordinary portable hot plate this has been done merely as a matter of convenience and it is clear that the same unit may be applied to electrical Stoves having any desired number of hot plates as Well as to electrical heating devices of various forms. Thus, -for example, the principles of my invention may be embodied in electrical heaters having the form of receptacles or having the form of rods intended to be immersed in liquids or having any other of numerous possible forms.

While I prefer a spirally disposed rib, as described, a series of concentric ribs may be used instead, the resistance helices being also disposed concentrically between the ribs and connected together in series in any convenient way; or some other disposition of the ribs might be employed.

Furthermore, I find that it is possible, in some cases, to omit the ribs 3 on Ndisk'Q and, in other cases to entirely dispense with both disk and ribs. And this of course, holds truev for equivalent stiffening means which may be used in spiral forms of hot plates, or in water heaters or other electric heating devices. Whether disk alone, or disk and ribs, or any othery stiffenin device be used will depend upon size, s ape andl other physical characteristics of the particular heating unit under consideration as well as upon the uses to which it is to be ut.

Having described my invention, I

An electric heater comprisingaJ support, a plate of insulating refractory material carried by .said support and having a circular recess, a heating unit in said recess attached to the plate, said unit comprising a metallic plate having an integral spirally disposedupstanding rib, a body of alundum filling in between the convolutions of the rib and attached to said plate and rib with resistance material disposed in the spiral channel between the rib walls and covered by and directly in contact with the alundum, the free surface of the alundum being above the ribs and flush with the surface of the outer refractory plate.

In testimony whereof I have hereunto set my hand.

p LOUIS R. WHITE. Witnesses: i

MARGm L. WHITE, .LEONI Wm'rn.

claim: f

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