US2765393A - Automatic fan heater - Google Patents

Description

Oct. 2, 1956 J. P. THEISEN 2,765,393

AUTOMATIC FAN HEATER Filed March 29, 1954 3 Sheets-Sheet 1 w NH | I I I I I .3 I 1 INVE NTOR.

3!! 70g)? YZQJSQJZ Oct. 2, 1956' p, THElSEN 2,765,393

AUTOMATIC FAN HEATER Filed March 29, 1954 Z 0Q i i- 3 Sheets-Sheet 3 J6 7:8 I 7,- 70a 70 fa United States Patent AUTOMATIC FAN HEATER John P. Theisen, Jacksonville, Ill., assignor, by mesne assignments, to New York Shipbuilding Corporation, a corporation ofNew York Application March 29, 1954, Serial No. 419,274

4 Claims. (Cl. 219-39) This invention relates generally to electric space heaters and more particularly to a heater which will serve effectively both as a source of radiant heat and a circulating means. Specifically, the invention may be termed a combination heater and fan assembly having improved fea tures of design and construction which bring about improvements in functional results and operation.

It heretofore has been a practice in the art to provide combination circulating fans and electrical heater elements in which air is circulated over electrical resistance heaters. However, by and large, all such previous combination fan and heater assemblies have utilized means for the assembly which cause axial .flow of air through the assembly, that is, from front to back through the fan and housing.

.It is one of the basic intentions of this invention to provide a new improved heater and fan combination in which the housing thereof is arranged to permit a reentrant recirculation of air through an annulus or cham ber located peripherally outward of the central heating chamber to give improved operating characteristics and efficiency to an assembly of this character. Specifically, this basic intention of .my invention is carried out by providing a double shell construction in which the shells are separated by an air space. The inner shell is open ended and the outer shell encloses the rearward portions of the housing such that re-circulation of air takes place by drawing air inwardly from the frontal portions of the housing for discharge centrally of such frontal housing portion. This particular type of air flow is thought to have special advantage in providing a central core of heated air forced outwardly from the housing by a circulating fan, which is substantially uniform in its intensity across the entire frontal area of the device. Coupled with the advantages to be found in the improved housing portion of my assembly are improved control means which provide variable fan speed and heat intensities. Thermostatic means are also coupled in the assembly to provide a new and improved safety means for controlling the operation of heater elements and which is substantially responsive to ambient temperatures of the space or room in which the heater-fan is located and operated. Further means are embodied in the assembly for providing universal tilting adjustment of the housing for the fan and heater elements such that a versatile device is produced capable of a wide variety of operatingpositions.

The main object of this invention .is to provide a new and improved combination heater and fan assembly having intake and discharge passages on the same side of its housing whereby there is a reentrant air flow through the device.

Another object of this invention is to provide a new 2,765,393 Fatented Oct. 2, 1956 and improved combination heater and fan having a novel housing construction whereby the outer wall portions thereof are effectively insulated by an air passage designed to accommodate the flow of intake air for the fan.

Still another object of this invention is to provide anew and improved combination heater and fan assembly in which a thermostatic member is employed to provide a convenient climatizing control and an improved safety mechanism for preventing overheating of the device.

The above and further objects, features and advantages of this invention will become apparent to those familiar with the art from the following detailed description and specifications therefor, and with particular regard to the illustration of a preferred embodiment of its concepts as found in the accompanying drawings hereof.

In the drawings:

Figure 1 is a front elevational view of an improved heater-fan combination embodying the concepts of this invention and illustrating the general features and structural arrangements of the improved assembly thereof;

Figure 2 is a top plan view of the device illustrated in Figure 1;

Figure 3 is a side elevational view with parts thereof broken away in cross section at substantially line 3-3 of Figure l to illustrate the arrangement of elements and working mechanisms disposed within the interior of the housing whereby I am able to carry out the intents and purposes of this invention;

Figure 4 is a schematic wiring diagram showing the electrical arrangements and systems employed in my improved combination heater-fan assembly;

Figure 5 is an enlarged side elevational view of an improved control and operating switch mechanism embodied in my device;

Figure 6 is anend elevational view of the control switch mechanism found in Figure 5;

Figure 7 is a top plan view of the control device shown in Figures 5 and 6 but enlarged thereover; such illustrating in particular the thermotatic control elements e.. bodied therewith; the view being taken substantially from vantage line 7-7 of Figure 5 and Figure 8 is a cross-sectional view of the control switch illustrated in Figure v5 taken substantially at line 8-5 of Figure 5;

Figure 9 is a partial cross sectional View of the cam actuator of the switch means shown in Figure 5, taken at line 99 of Figure 5; and

Figure 10 is a cross sectional showing, similar to Figure 9, taken at line 10-10 of Figure 5.

The embodiment of this invention as illustrated in Figures 1 through 3 of the drawings includes a standard or support member 20, having two substantially U-..hapcd divergent leg portions 21, 21, each carrying rubber foot pads 22, 22 adjacent opposite ends of a lower platform portion 23 thereof. Pivot bearing housings 2d are formed at the juncture points of the two leg portions, or that is at opposite upper ends of the standard; such bearing -housings being coaXially aligned. The standard 24? connects directly to and pivotally supports a substantially frustroconical shaped outer shell member 26 of the fan housing. Shell member 26 carries on opposite sides and at positions located just slightly below its horizontal diametrical center line, a pair of trunnion ' post members 27, 27 which are pivotally housed in the two pivot housing members 24 of the bracket standard 20.

From Figure 2 in particular it will be recognized that tne outer housing shell 26 is enclosed on its rearward side by a conical shaped rearward wall portion 28, and that the front side thereof (see Figure 3) is open except at its outer periphery where the same is rolled inwardly to formulate a lip portion 29 of annular configuration.

Supported concentrically inward and coaxially of the outer shell is an inner shell member 30, formed as a substantially open-ended cylinder, which is attached to and supported by the outer shell by means of intermediate-1y extending and radially disposed Web arm members 3f, the outermost radial ends of which are conveniently riveted or fastened rigidly to the lip member 29 of the outer shell and the innermost ends of which are riveted or rigidly fastened to the exterior side walls of the inner. shell; rivet members 32 being utilized for this purpose in the particular embodiment illustrated.

With further regard to the inner shell 30, it will be noticed that the same carries a grid plate 33 transversely thereacross adjacent its forward or front end; such grid plate being formed with a plurality of air passage apertures or as a screen member. A decorative hub and supporting member 34 is disposed substantially diametrically across the forward end of the inner shell, outwardly of the screen grid 33. Since the screen grid 33 is placed slightly inwardly from the leading edge of the inner shell the latter member is rolled inwardly as at 35 to assist irl promoting the decor of the frontal aspects of the housing and to perform the function of hiding the fastening of the grid member 33 to the inner shell member, as by rivet means 36. It will further be regarded that while the nner and outer shells are aligned concentrically or coaxrally, the inner shell extends forwardly of the forward lip or edge of the outer shell so that the Web arms 31 connect to the cylindrical wall of the inner shell at positions substantially midway between its front and back edges. (See Figure 3.)

The concentric arrangement of the inner and outer shells provides or forms an inner space or chamber of annular configuration, labelled generally by number 38 located intermediate the opposed wall faces of the two described shell mcmbers, or that is, between the two shell members. As stated heretofore, the rearward wall 28 of the outer shell is substantially uninterrupted by openings. However. a slotted portion or aperture 39 is provided adjacent the unoer end thereof which permits the accessible proiection of a control knob 40 for a combination contro switch means 41 which will be described more fully hereinafter. Located immediately beneath the control knob 4th of the switch assembly is a handle member 42 joined to the re rward wall 28 of the other shell; this latter member being for the convenience of tilting the housing assembly about the pivots or trunnions formed at the junction points of the outer shell with the standard member 20.

Within the outer shell 26 and immediately behind the inner shell 3% is a switch sup orting baffle plate means 43 disposed in substantial parallelism to the rearward wall 23 of the outer shell and located generally at the upper end of the device as shown in Figure 3. Such baffle wall 43 has a lower platform portion 44 on which the switch assembly 41 is supported. A secondary bafile extension 45 is joined to the balfle wall 4-3 adjacent the latform portion 44 thereof. Located directly behind the baffie wall extension 45 is an electric indicator lamp means 46, and mounted beneath such lamp and substantially coaxially of the inner and outer shell members is an electric fan motor means 47 having the usual armature shaft for supporting a conventional fan blade means 43. Motor 47 is supported on a bracket means 49 which in turn is carried at its lower end by an annular bafile ring 50 radially surrounding the fan blade means 48 concentrically inward of the inner shell 30. A plurality of combination bracket and heating element holder means 51 serve to join the concentric baflle ring'50 coaxially of the inner shell 30 and support two substantially annular heating coils 52 and 53, best shown in Figure 4.

With regard to the heater elements and combination holding means 51 therefor, it will be recognized that the same are located intermediate the annular baffle ring member and the inside wall of the inner shell 30, that is, within a second annular space formed by the concentric interpositioning of such housing portions.

The above described elements and arrangement comprise the major mechanisms and portions which, when assembled in the manner illustrated, go to make up the improved combination heater and fan assembly of this invention. However, particular advantage and merit is to be found in the new and improved combination control switch means or assembly 41 which will now be described in greater detail and which is illustrated specifically in Figures 5 through 10 of the drawings.

The switch assembly 41 comprises a switch block 54 of Bakelite or other suitable insulating material which is shaped substantially as a horseshoe or that is, U-shaped. for the rotatable reception or mounting of a barrel switch cam member 55 mounted on a rotatable thermostat and switch actuating shaft member 56. The assembly also includes a thermostatic means, indicated generally by numeral 57 and a plurality of leaf spring switch-arms or blades 58, 59 and 60.

Specifically the switch block 54 carries the switch arms 586ll along one side thereof, so that the same bridge or extend across the central opening of the block in which the rotatable cam member 55 is housed. Such switch arms or blades, are rigidly held at one end as by screw means 61 to one upright arm portion of the U-shaped switch block leaving the other end thereof free for flexing movement toward and away from contact members 62, 62a and 62]) carried on the other arm of block 54, such as contact 62 illustrated in Figure 8 in particular. It will be noted that each of such contact members is associated with a terminal connector 63 of electrical conductive material. Further, each of the switch blades is adapted at one end adjacent the connective screws 61, for connection with electrical supply conductors and the like. such adaptation taking the form of terminal connectors 64.

The combination thermostat and switch actuating shaft 56 is rotatably supported on a lower wall portion 65 of the switch block and a bracket means 66 is utilized directly beneath the operating knob 40 for supporting the shaft. The cam member 55, as will be recognized presently from Figures 8, 9 and 10, is supported on shaft 56 for rotation therewith, and such comprises an insulating member having three cam lobes or portions which are staggered in arcuate disposition as at 68, 69, and 7 9. Lobe is common to all three of the cam lobe portions and extends the full vertical height of the cam member. Portion 68 is located adjacent the upper end of the cam member and portion 69 is located at a level lower or beneath the level of cam portion 68. Such two cam portions 68 and 69 are so related to one another in vertical dis osition that the same individually actuate switch blades 58 and 59 respectively, While cam portion 70 initiates all three of the switch blades simultaneously. Cam portion 68 comprises substantially a full annular surface with the exception of a cut-out portion 71 which lies over cam por tion 69 and extends to cam portion 70. When the barrel cam member is rotated such as to bring the peripheral or outside edge of cam portion 68 into engagement with the leaf switch blade 58, the latter is biased outwardly from its corresponding contact 62 which is carried on the switch block. This serves to open circuit between a contact 73 carried by switch blade 58 and opposed contact 62 on the switch block. Likewise, when cam portion 69 is brought into position so that it contacts the intermediate switch plate 59, circuit is broken between the latter member and its corresponding contact 62a carried by the switch block. When cam portion 70 is brought rotatably to an operating position or is in contact with all three of the switch blades, the latter are simultaneously biased outwardly from their corresponding contacts on the switch block to interrupt all circuits relatedthereto.

It will benoted additionally, that cam portions 69 and 70 each bear a detent projection 69a and 70a respectively, which are designed to engage with detent depressions 72 formedin the switch blades 58-60. Such detent arrangement serves to'lock removably the rotatable cam member in designed positions of operation for certain purposes. In greater particular when cam portion 70 engages all three of the switch blades all circuits through the switch assembly are broken and the detent means 70a removably holds this condition by engaging depressions 72 of the switch blades. Also while the cam surface 68 engages switch blade 58, the remaining two switch blades 59 and 60 will be in circuit closing contact with their contacts 62a and 62b on the switch block, while blade 58 will be biased to a position as illustrated in Figure 8, whereat circuit therethrough is interrupted. When cam ortion 69 is in operating engagement with switch blade 59, circuit therethrough is open and circuits through blades 58 and 60 closed. Other combinations and arrangements of the switch cam means .may be readily adapted for the purposes illustrated, but for present purposes the arrangement shown and described hereinabove, willmeet the conditions and requirements of the several circuits and controls necessary to carry out the intents and purposes of my invention. Of further consequence 'in the operation of the switch cam, is the space or gap left intermediate cam detent portions 6% and the leading edge or corner 74 of the cam surface 68. When the .gap portion of the cam is opposite the switch blades 58, 59 and 60, all three of the latter have their respective contacts 73, 73a and 73b in engaging position with the respectively associated contacts 62, 62a and 62b so that all circuits through the switch means are energized.

In addition to the several switching means hereinabove described, the switch assembly 41 includes the thermostatic assembly 57 which will .now be described. It will be understood from an examination of Figures 5, 6 and 7, in particular, that the switch block 54 has a fixed ear bracket portion 75 carrying a laterally extending bi-metal arm member 76 supporting an adjustment collar and screw means 77 at its outermost end. Such screw means is adapted to bear against a resilient leaf 78 carrying a contact member 79 and which in turn is mounted in cantilever fashion on an insulating block assembly 80. Block 80 also includes a terminal connector means 81 which is connected with the resilient switch blade 78. The block assembly 84) includes additionally, a secondary switch arm 82 carrying a contact member-83, the latter of which is disposed opposite contact 79 of theresilient blade 78.

The entire block assembly is supported on a bracket means 84 which is pivotally connected 'by pin '85 to the switch block bracket 75. Bracket 84 is formed with a vertical or upright wall portion 86 which serves to act as a bearing surface for an eccentric 87 carried for rotation with shaft means 56. A leaf spring 88 is joined to the block assembly 88 and wall portion '86, as by bolt or screw means 89; such leaf spring bearing against the shaft means 56, but on the opposite side thereof from wall portion 86 of the bracket means 84. As the shaft 56 is rotated, the eccentric 87 causes the entire switch assembly including bracket 84, secondary contact arm 82 and resilient blade 78 to pivot about the axis defined by pivot means 85. Thus, simple variations in the tension or bias of the switch blade 78 relative to contact 83 of the secondary switch arm 82 are accomplished by pivotally moving the switch assembly relative to the end of adjustment screw means 77. Stated in other words, the normal bias or operating characteristic of the switch blade 78 is set at initial installation by adjusting the axial extent of the screw means 77 beyond bi-metal arm 76, thereby to tension the blade 78 and regulate its action toward and away from the secondary switch arm '82 under certain thermal conditions. Thus as the eccentric 87 is rotated with shaft 56, the switch assembly (i. e., resilient blade '78 and arm 82) is gradually moved away from the adjusting screw 77. This makes 'it necessary for the bi-metal blade 76 to travel further in order to have screw 77 bear against resilient blade 78 to thereby separate the contact 79 from the contact 83.

Return movement of the thermostatic assembly to the position illustrated in Figure 7 is accomplished by and large through the medium of the spring means 88 which engages the shaft 56 in a manner to urge the switch assembly to follow the eccentric during rotational motion of shaft 56 and control knob 40.

Relating the thermostatic system to the control knob and the several leaf spring switching elements controlled by cam means 55, it will be understood from Figure 8 that the eccentric 87 and the operation of the thermostat takes place by and large during the operation of cam surface 68, or that is, throughout the arcuate extent of this cam portion. This in effect, permits variable control of the circuit being energized when cam surface 68 is in operating relation with its adjacent contact arm 58 as will now be explained.

Referring now to Figure 4 of the drawings, wherein I have set forth a schematic layout of a typical circuit and electrical control system for the operation of my present device, it will be recognized that the several switch arms 58, 59 and 60, are represented therein, in conjunction with associated contacts 62, 62a and 62b, respectively, carried by the switch block 54 as heretofore described. Switch blades 58 and '59 are connected in circuit with line or supply conductor 90 by intermediate conductors 91 and 92 respectively. Switch blade 58 cooperates with the contact 62 which is in circuit with conductor 93 leading to the motor 47, a conductor 94 connects the motor 47 to a conductor 95 which is in circuit with contact 62b, switch arm 60 and a return line conductor 96. Conductor 95 also is coupled to the thermostatic assembly comprising contacts 79 and 83, and the resilient switch arm 78. A conductor 97 couples the resilient blade 78 to the indicator light 46 and conductor 98 couples light 46 to contact 62a which cooperates with the switch blade 59. A first heater element 53 is connected across the light 46 and joined to conductors 97 and 98. A second heater element 52 is arranged in series with conductor '53. This arrangement gives a complete circuit with the exception of a resistance 99 coupled between conductors 93 and 98, between the motor 47 and contacts 62 and 62a.

It will be recognized that as the cam member 55 is rotated clockwise from its off position whereat detent portion 78a is in engagement with the detent recesses 72 of the several switch blades, cam portion 69 effectively biases blade 59 outwardly from contact 620, which condition may be maintained by locking detent portion 6911 with recess 72 of blade 59, if desired. Thus circuits through blades 58 and 68 are energized, resulting in a direct energization of the motor 47 through conductors 98, 91, 93, 94, 9'5, switch blade 60 and return line concluctor 96. The low energization of the heating coil circuit also takes place via conductors 9'0, 91, 93, blade 58, resistor 99, conductor 98, heating coils 52 and 53, conductor 97, thermoplastic switch 57, conductor 95 and the closed switch blade 68 and return line conductor 96. Due to the resistance 99, the energization of the heating coils 52 and 53 in this particular operating condition is only slight, so that for all practical purposes the fan is on at full speed with very little or no heat being emitted by the energization of the heater coils. This operating condition is best suited for and designed to accomplish circulation of air, as for instance in the summer time.

When the cam 55 is rotated to bring the gap between corner 74 of the cam surface 68 and the detent portion 69a of cam portion 69 opposite the blades 58, 59 and 60, then all three of the circuits are energized, that is all three of the switch blades 58, 59 and 60 are closed with their associated contacts 62, 62a and 6217, respectively, resulting in a high motor speed and a high heat output.

Continued clockwise rotation of the cam member 55, however, brings the cam surface 68 thereof into engagement with switch blade 58 to bias the latter outwardly or to break circuit therethrough. In this operating condition switch blades 59 and 60 will be closed so that the circuit through the motor 47 will include conductors 90, 92, blade 59, conductor 98, resistance 99, conductors 95 and switch blade 6t and return line conductor 96. Since the motor is energized over resistance 99 its speed is correspondingly reduced. Energization of the heating coils 52 and 53 will take place directly however, with the circuit thcrethrough including conductors 99, 92, switch blade 5% conductor 93, coils 52 and 53, conductor 97, the switch means 57, conductor Q5, closed switch blade 69 and return line conductor 96. In this condition, the thermostatic means, will continue to maintain the circuit to the heating elements closed, so long as the ambient heat generated by the heating elements is not sufficient to cause an automatic opening of the thermostatically controlled switch. Since the switch blade 78 is automatically returned to its operating condition upon cooling of the bimetal blade 76 in this condition of operation, the thermostat controls intermittent energization and deenergization of the heating elements depending on the operating characteristics of the thermostat eccentric. It will be recognized also, as related to the eccentric means 87, that as continued rotational adjustment of the cam 55 takes place, throughout the length of cam portion 63, decreasing tension is placed on the resilient blade 7 8 as the eccentric 87 moves the switch assembly away from the adjustment screw 77. Thus toward the end of the cam surface 67, or that is, in that portion adjacent gap portion 71, the

eceentrics bias of switch means 57 is greatest and a maxi mum amount of heat will be needed to cause opening operation of the thermostatic control. Thus throughout the length of cam surface 68, there is provided a means for gradually varying the heat output of the heating coils by adjusting the operating characteristic of the thermostatic control. Of course, as stated heretofore, when cam portion 70 is brought opposite the detent portions 72 of the several switch blades 58, 59 and 60, all three of the switch blades are held away from their respective contacts 62, 62a and 62b, thus, deenergizing the entire device.

With respect to the thermostatic control means, herein shown and described, it is also of importance to note, that in addition to the automatic energization and deenergization of the heating coil elements as caused by current surges and ambient temperatures of the return air in chamber 38 especially, the thermostat also provides a unique safety shut-off for the device. For example, if for any reason the air discharge passageway becomes blocked over, as by the device tipping over on its face, rapid increase in the ambient temperature surrounding the thermostat will result, causing a disruption of the circuit to the heating elements etc.

It is also of importance to note that in addition to the particular position of the heater housing illustrated, the same may be tilted universally about its pivotal axis as provided by its connection with the standard means 20. Thus, great convenience and the versatility of operation is afforded the user.

While I have herein shown and described the elements and operating features and provisions of my invention as related to one particular form of combined heater and fan unit, it will be understood that numerous modifications, changes and substitutions of equivalents may be entered into therein without necessarily departing from the spirit and scope of its inventive concepts. Therefore, it is not my intention to herein be limited to the particular form of my device shown and described, except as may appear in the following appended claims.

I claim:

1. In a space heater, a rotatable fan means, motorized means for rotating said fan means, an outer housing shell encasing said fan and motorized means radially thereabout and to the rear thereof, said outer shell being open at one end only forwardly of said fan means, an annular baffle wall mounted concentrically of said Outer shell and radially about said fan means, said bafile wall lying wholly within the axial limits of said outer shell, an inner shell mounted concentrically between said outer shell and said battle wall to provide first and second annular spaces or chambers, said inner shell extending axially forwardly of the axial limits of said outer shell and wall, annular resistance heater means, mounted in said first chamber between said inner shell and said bafile wall, and a combined thermostatic control switch means mounted adjacent said second chamber for controlling the energization of said fan and regulating the thermal output of said heater elements in response to ambient temperatures; the path of air circulation of the heater being such that the intake air passes through the frontal wall of said heater via said second chamber across said thermostatic means to the rear of said fan and outwardly through the interior of said baflle wall and inner shell means.

2. In a space heater, a rotatable fan means, motorized means for rotating said fan means, a pair of concentrically related shell members, the outermost one of which encloses the rearward portions of said fan and motorized means, an annular bafiie wall positioned concentrically inward of the innermost of said two shell members, the concentric relationship of said shell members and wall member forming a pairof annular chambers, resistance heater coil means mounted in the radially innermost of said two chambers, and a combined thermostatic control means and plural circuit switch means located within said outermost shell and in communication with the air passageway formulated intermediate the said two shell members, the arrangement of said elements being such that the fan means serves to disperse air over said heater coils and through the interior of said bafile and innermost shell members with intake air being circulated through the annular chamber formed between said two shell members and over the thermostatic means, the latter of which controls the operation of said heater coils.

3. In a space heater of the class described, a rotatable fan means, motorized means for rotating said fan, a pair of concentrically related shell members surrounding said fan means, the outermost one of which encases said fan means to the rear thereof and formulates an enclosing rear wall for the heater, an annular baffle wall located concentrically inward of the innermost of said two shell means and surrounding said fan means, said innermost shell and baffie wall member being open ended with the concentric relation of said two shell members and bafile wall serving to formulate a pair of annular spaces or chambers, a resistance heater coil means disposed within the radially innermost one of said two chambers, and said second chamber serving as an annular air passageway for intake air; the circulation of air by the space heater being such that both intake and discharge air openings are located in one wall thereof and a combined thermostatic control means mounted adjacent in the rearmost chamber for controlling the thermal delivery of the heater coil proportional to the ambient intake air requirement.

4. In a space heater, a rotatable fan means, motorized means for rotating said fan means, an outer housing shell encasing said fan and motorized means radially thereabout and to the rear thereof, said outer shell being open at one end only forwardly of said fan means, an annular baffle wall mounted concentrically of said outer shell and radially about said fan means, said baffle wall lying wholly within the axial limits of said outer shell, an inner shell mounted concentrically between said outer shell and said baflie wall to provide first and second annular spaces or chambers, said inner shell extending axially forwardly of the axial limits of said outer shell and wall, annular resistance heater means, mounted in said first chamber between said inner shell and said bafile wall, and a combined adjustable thermostatic control switch means mounted adjacent said second chamber for controlling the energization of said fan and regulating the thermal output of said heater elements in response to ambient temperatures; the path of air circulation of the heater being such that the intake air passes through the frontal wall of said heater via said second chamber across said thermostatic means to the rear of said fan 1'0 and outwardly through the interior of said baffle wall and inner shell means and over said heater means.

References Cited in the file of this patent UNITED STATES PATENTS 1,926,537 Hoffman Sept. 12, 1933 1,954,872 Gilbert et al. Apr. 17, 1934 2,118,759 Dillman May 24, 1938 2,120,937 Kronmiller June 14, 1938 2,158,602 Calhoun May 16, 1939 2,583,754 Theisen Jan. 29, 1952 2,619,578 Jepson et a1 Nov. 25, 1952

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