Title:
Encased resistor unit
United States Patent 2360263


Abstract:
My invention relates to encased or sheathed electric resistor or heating units and among the objects of my invention are the following: To provide a relatively simple electric resistor or heating unit having a minimum number of parts and therefore relatively inexpensive and easy to assemble;...



Inventors:
Osterheld, Clark M.
Application Number:
US46420542A
Publication Date:
10/10/1944
Filing Date:
11/02/1942
Assignee:
MCGRAW ELECTRIC CO
Primary Class:
Other Classes:
338/234, 338/262, 338/293, 338/294, 338/333
International Classes:
H05B3/42
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Description:

My invention relates to encased or sheathed electric resistor or heating units and among the objects of my invention are the following: To provide a relatively simple electric resistor or heating unit having a minimum number of parts and therefore relatively inexpensive and easy to assemble; to provide an electric resistor and particularly a heating unit having an integral electric-insulating coating of a particular kind between the resistor conductor and the outer casing; to provide an electric heating unit or resistor unit in which the layer of electric-insulating material may exist on only one of the parts thereof or on two engaging parts thereof and which, while of very small and even microscopic thickness, is high temperature-resisting and heatconducting as well as able to withstand relatively high break-down voltages.

Other objects of my invention will either be apparent from a description of several modifications embodying my invention or will be pointed out hereinafter in the course of such description and more particularly set forth in the appended claims.

In the drawings, Figure 1 is a fragmentary perspective view of an outer tubular heat-conducting casing, Pig. 2 is a view, in side elevation, of a resistance conductor ready for insertion into the member shown in Fig. 1, Fig. 3 is an end view thereof, Fig. 4 is a.fragmentary perspective view of an assembled resistor or heating unit, Fig. 5 is an end view of a slightly modified form of resistance conductor, Fig. 6 is a view in side elevation thereof, Fig. 7 is an end view of a still further modification of a resistor embodying my invention, Fig. 8 is a view in side elevation thereof, Fig. 9 is an end view of a still further modification of resistance conductor, Fig. 10 is a view in side elevation thereof, Fig. 11 is a view of a still further modification of a resistance conductor shown in an intermediate stage of its manufacture, Fig. 12 is a perspective view of the resistance conductor shown in Fig. 11 as substantially ready for insertion into an outer casing, Fig. 13 is a fragmentary view in perspective of an assembled resistor or heating unit embodying the resistance conductor shown in Fig. 12, Fig. 14 is a view in perspective of a resistor strip, Fig. 15 is a view of the resistor strip shown in Fig. 14 and in an intermediate step of its manufacture, Fig. 16 is a fragmentary view in perspective showing the resistor conductor of Fig. 15 as assembled in an outer casing, Fig. 17 is a view in perspective of a still further form of resistance conductor shown in an intermediate stage of manufacture, and, Fig. 18 is a fragmentary view in perspective showing a resistor or heating unit embodying the resistor conductor of Fig. 17.

Referring now to Figs. 1 to 4 inclusive, I have shown in Fig. 1 a tubular outer casing 21 of metal, preferably of aluminum or of an aluminum alloy.

The inner surface of the tubular casing 21 is provided with an integral, inorganic, coherent, heat-conducting, high temperature-resisting and electric-insulating coating which coating may be produced thereon, for instance, by use of the method disclosed in Patent No. 1,526,127, and usually called "anodic" coatings. The method there disclosed is that an aluminum article, which may for example be the casing 21, is made the anode in an electrolyte containing certain solutions such as ammonia and ammonium sulfide. An electric current is passed through this electrolyte with the aluminum article as the anode and, under the proper operating conditions, within a certain length of time there will be produced an electric-insulating coating on that surface of the aluminum article through which the current passed from the electrolyte to the article itself, which coating is very thin, such as on the order of .001" or even .0004". This coating may be produced in other ways now well known in the art to make a dense, hard, corrosion-resistant coating having the above mentioned characteristics which will permit of changing the initial shape of the article thus coated. It is to be understood that this inorganic coating is different from that used in dry rectifiers in that it prevents the passage of any electric current in either direction.

While my invention concerns itself more particularly with aluminum articles and surfaces provided with these so-called anodic coatings, I 4u do not desire to be limited thereto since it is possible to produce similar coatings on other types of metals.

I desire also to point out that while I have referred to an early patent showing the use of an electrolytic method, the production of an anodic coating is not dependent upon this but may also be produced by immersion of an aluminum or other metallic article in the proper solution, all as now well known in the art.

In Figs. 2 and 3 of the drawings I have shown a helically coiled resistor strand 23 which, in these figures, is seen to be a strip which is bent into helical shape flatwise of the strip. It is also to be noted that the work of coiling this strip has been done in such manner that there is a slight clearance between adjacent turns of the helically wound resistor strand and this is necessary if an uncoated resistor member is used, such as the resistance material Nichrome now used for the making of heating units.

In winding this resistance conductor 23 into helical shape on a rod or mandrel, the diameter of this rod or mandrel is such that the outer diameter of the individual turns is substantially that of the internal diemeter of the casing 21.

I so practice the initial steps in the manufacture of this coiled resistor conductor that it retains or has an inherent springiness. This will permit the helically coiled resistor strip 23 when the starting end has been held in a suitable manner at the beginning of the operation of winding the coil and after the release of the final end of the coil, to slightly spring outwardly whereby it can easily and quickly be removed from the rod or mandrel upon which it was wound.

In order to insert this resistor conductor in the substantially circular outer casing 21, it is only necessary to provide proper means to wind up the coil of the resistor conductor 23 to such a degree that its external diameter will be slightly less than that of the internal diameter of the member 21, whereupon it is easy to insert the temporarily stressed helical coil into the member 21 after which the stress can be released, whereupon the resistor member 23 will be in substantially continuous peripheral engagement with the inner surface of the member 21 which surface has, as hereinbefore pointed out, an electricinsulating coating thereon which is relatively very thin, integral with the casing 21, is heatconducting and is high temperature-resisting.

Referring to Figs. 5 and 6, I have there shown a resistance conductor 25 which is of substantially the same shape in lateral section as resistor member 23 but in case this resistance conductor is made of aluminum, as I may desire to do, and is coated as was hereinbefore described for member 21 I can provide a greater number of turns longitudinally of the heating unit since the entire surface of the strand 25 is coated also so that adjacent turns of the coil can engage each other.

It may be noted here that the break-down voltage between the conductor 25 and the outer casing 21 will be on the order of twice as great as if only the inner coating on member 21 had been provided.

Referring now to Figs. 7 and 8, I have there illustrated a resistance conductor 21 which is of wire and the same comments as made hereinbefore in regard to conductor 23 shown in Figs. 2 and 3 will apply.

Referring to Figs. 9 and 10, I have there shown a resistance conductor 29 of wire shape which is wound helically so closely that the adjacent turns engage each other and it is, of course, to be understood that the conductor 29 is provided with an anodic coating thereon to permit of electric-insulating engagement of the adjacent turns of the conductor.

Referring now to Figs. 11, 12 and 13, I have there shown another form of resistance conductor. A conductor 31, which may be of strand, strip or wire form, is first convoluted to include a ulurality of substantially straight portions extending laterally of the longitudinal length of the resistance conductor and substantially parallel to each other. As a next step in the manufacture of the resistance conductor it is bent around a rod or mandrel to the shape shown in Fig. 12 of the drawings. I provide an outer casing 21 and in order to introduce the circularly shaped convolutions of the resistor member 31 into this casing, any suitable or desired compressing means may be embodied, say located on the inside of the curved resistor member 31 effective to reduce the outer diameter to a dimension below that of the inner diameter of the member 21.

Upon removal of this clamping or compressing member the resistor conductor 31 will open or spring outwardly because of inherent springiness or resiliency so that the outermost peripheral surface of each of the convolutions will be in close operation and heat-conducting engagement with the coated inner surface of member 21.

Referring now to Figs. 14 to 16 inclusive, I have there shown another form of resistance conductor 33 embodying thin initially imperforate, elongated bar or strip of resistance material which may, as has hereinbefore been mentioned, be of Nichrome or even of aluminum or of an aluminum alloy and which has been provided with lateral slits alternately extending to the two edges thereof. This resistance conductor 33 is then shaped in substantially the same manner as hereinbefore set forth for conductor 31 in Fig. 12 to substantially circular shape and the same method of inserting the shaped conductor 33 into an outer casing 21 having a coating on its inner surface may be used and the conductor 33 in its substantially circularly curved form will, because of its inherent springiness, hold itself in proper operative position in the outer casing.

Referring now to Figs. 17 and 18, I have there shown a still further modification of a resistance conductor here designated by the numeral 35 and it is to be noted that the initial shape of conductor 35 shown in the full lines in Fig. 17, is somewhat like that of resistance conductor 31, as shown in Fig. 11 of the drawings. It is to be noted that the laterally extending straight convolutions of resistor member 35 are not parallel but extend slightly angularly relatively to each other and, to locate the resistance conductor 35 in substantially its initially shaped position as shown in Fig. 17, it is only necessary that a slight tension be applied to the two opposite ends of the conductor 35 to cause the adjacent return-bent portions at one side of the resistor member to move slightly farther apart so that the overall lateral dimension of the resistor member is less than before, whereupon it is easy to insert the resistor in a casing 21 having an anodic electricinsulating coating on its inner surface. Release of the tension applied to the two ends of the resistor will then permit return of the convoluted resistor to its initial shape and particularly its initial lateral dimension so that the return-bent portions of the convolutions will be in close operative engagement with the anodic coating on the inner surface of the tubular casing.

As has already been set forth hereinbefore, the manufacture of the resistance conductor is so conducted that when it is of convoluted shape, which is to be understood as including any of the forms shown in the drawings, it will have an outwardly effective springiness so that when the same has been properly initially located in the tubular casing, the resistance conductor will hold itself in proper operative position in the tubular casing.

I desire to point out that where I use the word "convoluted" in the claims, I desire it to be understood that not only the forms shown in the various figures of the drawings but also any other which is effective to hold itself in proper operative position within the casing and independently of the casing by inherent outwardly effective spring action, are included.

It is, of course, evident that the area of the heat flow path between the conductor 35 and the casing 21 is not as large as in the case of the resistance conductors 33, 23 or 25 but the same comments will apply to all of these forms, which are in general that the extreme thinness of the electric-insulating, high-temperature resisting, inorganic coating having high heat-conductivity will have the effect of providing good heat-transmission between the resistor and the outer surface of the outer tubular casing.

While I have shown a substantially circular lateral section of tubular casing, I do not desire to be limited thereto but any shape of tubular casing having, for instance, a flattened portion is included so long as it is covered by any one or more of the appended claims.

One of the results of a heating unit structure of the kind herein disclosed is that the temperature of the resistor conductor itself is only on the order of say 2000 F. or 300* F. above that which is desired by me in the operations in which electric heating units are required, such as cooking or the heating of water.

It is to be further understood that while no specific terminal means are shown or referred to, this is for the reason that such members do not constitute any part of the present invention which relates more specifically to the use of members of relatively small heat storage mass having an inorganic integral, anodic coating, as hereinbefore described, to separate or space apart the resistance conductor and its outer casing.

Various modifications may be made in the system embodying my invention as herein shown and described and all such modifications clearly coming within the scope of the appended claims are to be considered as being covered thereby.

I claim as my invention: 1. An encased resistor unit comprising an outer tubular metallic casing member and an inherently resilient convoluted resistor member within the casing member held in operative heat-transmitting engagement therein by inherent radiallyacting spring effect of the convoluted resistor member, the surface of one of said members operatively engaged by the other member having thereon an integral, inorganic, heat-transmitting, high temperature-resisting, electric-insulating coating to electrically insulate said two members from each other.

2. An encased resistor unit comprising an outer metallic tubular casing having an integral, inorganic, electric-insulating, heat-conducting, high temperature-resisting coating on its inner surface and an inherently resilient convoluted resistor conductor in the casing held therein by its Inherent radially-acting spring effect.

3. An encased resistor unit comprising an outer metallic tubular casing, an inherently resilient convoluted resistor conductor in the casing held therein by outwardly-acting spring effect of the convoluted resistor conductor, said conductor having an integral electric-insulating, heat-conducting, high temperature-resisting coating on the casing-engaging outer surface of the resistor conductor.

4. An encased resistor unit comprising an outer tubular metallic casing having an integral, inorganic, electric-insulating, heat-conducting, high temperature-resisting coating on its inner surface and an inherently resilient convoluted resistor conductor within the casing, said conductor having an integral, inorganic, electric-insulating, high temperature-resisting coating on its outer casing-engaging surface.

5. An encased resistor unit comprising an outer tubular metallic casing and an inherently resilient helically-wound resistor conductor within the casing having an integral external heat-conducting, electric-insulating high temperature-resisting coating thereon and being held in proper operative position in the casing by inherent radially-outwardly acting spring effect causing operative engagement of the outer peripheral surface of the resistor conductor with the inner surface of the casing.

6. A resistor unit as set forth in claim 5 in which the adjacent turns of the helically-wound resistor members are in operative engagement with each other.

7. An enclosed electric heating unit comprising an outer tubular metal casing having on its surface an integral, inorganic, heat-conducting, high temperature resisting and electric-insulating coating, the thickness of this coating being not to exceed .001" and a convoluted resistor strand within the casing having an inherent outwardlyacting spring effect to hold itself in good operative engagement with the casing, the thermal reluctance of the coating and of the casing being such that the excess of temperature of the resistor over that of the outside of the casing will be on the order of not to exceed 300° F.

8. An enclosed electric heating unit comprising an outer tubular aluminum casing and a convoluted resistor conductor of aluminum within the conductor having an inherently outwardlyacting spring effect to hold itself in good heatconducting engagement with the casing, the interior surface of the casing and the entire outer surface of said conductor having thereon an integral, inorganic, heat-conducting, high temperature resisting and electric-insulating coating, the thermal reluctance of the casing and of the 5s coatings being such that the excess of temperature of the conductor over the outside of the casing will not exceed 3000 F.

CLARK M. OSTERHELD.