US2780705A - Dielectric heater - Google Patents

Description

Feb. 5, 1957 A. J. SQIEGMETH 2,78 ,7 5

DIELECTRIC HEATER Filed Nm r. 19, 1954 4 Sheets-Sheet 3 s ALFRED J.$/EGME7'H, INVENTOR.

9 HUEBNER, 555mm,

WORREL 8 HERZ/G,

, ATTORNEYS- By m ML Feb. 5, 1957 A. J. SIEGMETH DIELECTRIC HEATER 4 Sheets-Sheet 4 Filed Nov. 19, 1954 m H H mm Ewm WV V Hiam J sand I] .w mm 2 m uo w Hw A ae M United States Pa g 2,780,705 DiELECTRiC nearest Alfredv Siegmeth, Sierra Madre fca'liftg assignor to Resdel Engineering Corporation, Los Angeles, Califi, a corporation of California Ap iieaann November 19, 1954,- senar No: 469,951 16 Claims. (Ci. 2i--i0.67'j

The invention relates to electric perman nce; and in particular a heating device opefatirig on the diele ctric principle which makes use of high nqnency oscillations to generate heat in the work insuch nanner that: the work is uniformly heated throughout its mass at a rapid rate. is

Dielectric heating has; been practiced for a number of years and more recently has found considerable use in industry. One of the advantages in dielectric heating 'is that the heating operation can be accurately controlled, theworlt sought to be heated can be brought up to its desired temperature with su fii cient rapidity to be an economic advantage in the resumed; cycle, and that the heating operation can be advantageously located with respect to the production operation. There'a're, however, disadvantages" prevalent in heating devices of this kind,- chief aino'h'g them being the 'diiiicillty his tuning the device so that the radio-frequency waves made use of in the device do not interfere withotherele'c'tric'al in; stalla-tions in the vicinity; Another difficulty in ina mg use of known shielding principles is to soarratig a housing or container" wherein the high os'cil-la-ting fre quencies are generated that it can be loaded arid unloaded without impairing its eifective operation; Further, be; cause of the very high voltages encountered and thecliarf acter of the apparatus necessary to generate" dielectric heat, power tubes have been prone towear out and give out more rapidly than necessary, thereby increasing the cost of the operation, because of inability to proprly cool the power tube during certain portions of tli'op' erating cycle. I 7

It istherefore" among the objects ofthe invention to providea new and improved rapidly operating dieletrid heater wherein'objects' to be heated can be quickly'loaded into the heating apparatus, rapidly and effectively he ed to their desired temperature, and theiaftrprop'erly' un loaded for further operation.

Another object of" the invention is to provideanw'f and improved-self contained dieleetriclieater of highefii'cien'cy which is snihciently compact and" completewithin" itself that it can be located as a unitat any desired'loca'tion in a production cycle.

Still another object of theinvention is toprovide' a new and improved dielectric heating device which is ef fectivelyshielded so that the high frequency radiowaves are properly-confined within the apparatus and especially are confined against a-leak past the necessaryrdoor with" the apparatus may be equippedfor loading-and unloading the work; I t t Still another swagg r lheinVenfiOn is to provide a cabinetor housing for a dielectric heater-wherein al'single access door for loading andunlfoading the work is so constructed and msna'tedniti shields the device with an effectiveness equal to assume walled shielding-housmg.

A fui'ther 'objec't of theinvention is to p rovide a new. and ifnproveddilefcftric 'hea teiwhereinjall operative parts are contained within 'a double walled housing and where- 2 in, a teens and ventilating system is built into thewalls at the so that air is brought in initially intothe space between the double walls and thereafter forced first over the hottest portion of the operation, namely, around the power tube and thereafter in a more highly heated condition forced through that portion of the unit housing the work so as to simultaneously cool and ventilat'etthe chamber in which the work has been heated, tlere being further provided proper shielding over air passages so that the high radio frequencies do not escape the cabinet at those areas. 7 M t t Still further among the objects of the invention to provide a new and improved mounting means for the powertube and alsofor the electrodes so that th are effectively contained at a location such that the constructioii is simplified and at the same time the operation is greatly facilitated to accommodate different conditions and work of different character, the objects also including a protective feature for the electronic circuit such that in the case of an overload voltage, low voltage circu s will be shorted out, thereby avoiding damage to expensive portions of the electrical system, I

With these and other objects in view, the invention consists in the construction, arrangement and cornbina tion of the various parts of the device whereby the objects contemplated ar attained, hereinafter set forth, pointed out in the appended claims and illustrated in the accompanyingrdrawing's.

In the drawings: Figure 1' is a front perspective View of the self co'n tained unit'hous'ing'the invention. I a t V H Figure 2 is a rear view partially broken away taken on the line'l-J of Figure l. V

Figure 3 is a fragmentary perspective view of one side of the unit taken on the line 3-3 of Figure 1. t

Figure 4 is a longitudinal sectional view of the unit showing the interior arrangement.

Figure Skis cross-sectional view of the unit taken on the line 515 of Figure 4.

,Figure 6 is a fragmentary enlarged sectional View showing an ,.overload voltage protector taken on the line 6-6 ofFigure 5. I

Figure 7 is a' fragmentary enlarged sectionalview of one of the binding posts for the power tube taken on" the line,7- 7 of Figure 5.

Figure} is a wiring diagram of the'electro'riic circuit. As shown on the drawings the unit comprises an outer lion generally indicated by the reference character- 10 having a frontwall 11, a rear wall 12, andside walls 13 and 14. At their lower edges the side, front and rear walls join a bottom 15 and at their upper edges join a top As noted particularly inFigures 1 and 4' the trontwall ll is set well forward of a wall. section 17 to provide extra space and a sloping panel 18 provides an nesr ine location of various controls. Bosses 19 serve to support the outer boxat a location slightly above whatever surface it may be mounted upon. In practice ithas be'lenifo'und that the outer box may advantageously betc'onst'r'ucted of a material such as stainless steel.

Inside ot the, outer box issuspended an inner box indic'a id generally by the reference character 20... The inner bolt comprises a front Wall 21, a rear wall 22 side wallsand 24, and a bottom 25; The inner boxis" preferably constructed of a material such as sheetalumfi nurnwhich forms in effect a closed box on all sides exptths t p-q The inner box has a large opening 26 extending z'rlrnos t entirely over the top area but bounded around thee dges by a flangei27. The flange may be considered as comprisingan inwardly turned rim 28 formed of the material forming thefront, rear and side walls of the innerbox,

together with a separate angle element 29, having onel'eg w lying against the rim 28 and the other leg upstanding, as indicated in Figure 4. For the sake of uniformity in description the top 16 of the outer box may also be considered as a flange or rim, this being joined to the rim 28 by means of bolts 30. Mounted in this manner the inner box is suspended within the outer box and is in contact with the outer box only at the area of the rim 28. Thus suspended there is provided a space between the two boxes which may for convenience be identified as a blower space 31 at the front, and adjoining accessory space 32 between the bottoms and all comunicating with spaces 33, 34 and 35 at the sides and rear respectively. It will be appreciated, therefore, that there is a double electrical shielding efiect, one provided by the inner box, and the other provided by the outer box with a space between the boxes on all sides except the top.

The inner box has mounted therein a partition 36 of a dielectric substance, preferably sheet silicone, dividing the interior of the inner box into an upper heating chamber 37 and a lower tube chamber 38. Inasmuch as the work suggested in dotted lines by a disc 39 must be placed inside of the heating chamber and removed therefrom with considerable frequency, the provision of a large opening 26 such as has already been described at the top of the inner box is requisite. Provision of a large opening of this kind, however, necessitates that special care be given to the design and construction of a door 40. The door must have shielding characteristics comparable to the shielding characteristics of the double wall construction and also be capable of being quickly opened and closed.

To accomplish the desired result the door is constructed of a relatively thick plate 41 which spans substantially the entire open area of the opening 26. A continuous hinge 42 extends throughout the entire length of a rear edge 43 of the plate and is joined to the inner face of the upstanding portion of the flange of angle element 29 by suitable bolts. A stop 44 is provided for limiting upward tilt of the door.

On the remaining three sides of the door there is provided angle elements 45 having one leg 46 attached to the upper surface of the plate 41 and the other leg 47 extending downwardly around adjacent portions of the angle element 29 but spaced outwardly therefrom. Cousiderable overlap is provided. To insure a snug seal with an electrical contact a resilient flap 48 is secured to the angle element 45 on each of the three sides and spaced inwardly from the angle element at a suitable location by means of blocks 49. The flap is so formed that when the door is closed, there is a continuous line contact between the flap and the outer face of the upstanding leg of angle element 29 throughout the three sides in which the flap is located. Consequently there is a complete electrical contact entirely around the door when the door is closed.

When the door is to be opened, the operator can lift the door by means of handle 50 which is attached to the top of the plate 41 by a long arm 51, the handle preferably being of an insulating material. inasmuch as the door and portions of the device mounted thereon is relatively heavy, counter-balance springs 52 may be provided to hold the door in an open position. Each spring 52 has one end 53 secured to the angle element 45 at the side of the door and another end 54 secured to a suitable retainer 55 on the top 16 of the outer box. The spring may be mounted on an outwardly extending end of a hinge pin 56. Contact screws 57 are mounted on a suitable bracket 58 and these may be adjusted and suitably locked so that when the door is closed a positive electrical contact between the door and the outer box is assured thereby to improve the shielding.

Within the heating chamber 37 are the negative elec trode 60 and the positive electrode 65.. The negative electrode is mounted so that its position can be adjusted up or down to vary the distance between itself and the positive electrode. To make the negative electrode ad justable, there is provided a negative electrode supporting column 62 which extends upwardly through the plate 41 and also through a pair of blocks 63 and 64 suitably apertured so as to slidably accommodate the column. A plate 65 is secured on top of the block 63 with a more snugly fitting aperture for the column 62. On the plate is a housing 66 likewise having therein an aperture 67 for slidably receiving the column 62, the aperture being broken away at 68 to facilitate mounting of a pinion 69 on an appropriate shaft at the outer ends of which are hand wheels 70. The pinion 69 meshes with a rack 71 at the upper end of the column and by manipulation of the hand wheels the column can be moved up and down, thereby changing the location of the negative electrode 60.

To assure a good electrical ground between the negative electrode and the cabinet, there are provided flexible strips 72 and 73, each securely fastened at one end to an outer edge of the negative electrode and securely fastened at the other end to the plate 41 of the cover 40 by suitable bolts. These strips form a positive electrical contact, which positive contact is not effectively supplied by the rather loose sliding fit of the column 62 in its support.

The positive electrode 61 as shown is mounted in a position parallel to and adjacent the partition 36, the partition 36 in turn being joined to a suitable bracket device 74 on the inner Wall of the inner box.

A four-corner support is mounted upon the bottom 25 of the inner box, this support serving a multiple purpose in that it is designed to carry a power tube 75, connecting means 76 therefor, and the positive electrode 61, and an appropriate tank coil 77.

The support comprises essentially four upright columns 78 preferably of silicone material establishing four corners of a relatively square area. The columns are mounted in sleeves 79 secured by appropriate means to the bottom 25. Intermediate the bottoms and tops of the columns 79 is a platform 80 fastened to the columns so that its position is fixed at a desired location. The platform provides a mounting for the power tube 75. Nearer the upper ends of the columns is a capacitor 81 transversely located sleeves 82 at the tops of the columns mount a plate 83 forming part of the positive electrode. A central screw 84 extending through blocks 85 held within sleeves 86 secures the upper plate of the positive electrode to the lower plate. The tank coil 77 is mounted upon and connected to the positive electrode by means of a bracket 87.

When the dielectric heater is used for the purpose of heating discs, blocks, or other pieces of work such, for example, as blocks of plastic prior to subjecting the blocks to a molding process, the block in question is placed upon the positive electrode as suggested by the position of the disc 39. The door 40 is then closed and the power turned on. Application of the power through the power tube generates a very substantial amount of heat in the block or disc and at a relatively rapid rate. The power tube warms up to a high temperature. The temperature in the heating chamber 37 also raises considerably. Moreover, moisture present in the block or disc 39 is released and accumulates in the heating chamber. When the heating has been completed, the moisture tends to remain. For proper operation it is advisable to cool the power tube and also to both cool and ventilate the heating chamber 37 prior to the deposit therein of another block or disc to be heated. For general overall efficiency it is also desirable to circulate air between the inner box and the outer box. To this end a ventilating system is provided.

The air for ventilating and cooling enters through an air inlet opening 90, passing from there into the acces sory space 32 and also circulating through the spaces 33, 34 and 35. To effect a forced circulation of air, a blower 91 is mounted in the blower space 31 in front of the front wall 21 of the inner box and behind the front wall 11 of the outer box. Any one of a number of con assays-e ventionalblowers. may be found suitable but inany event it is desirable that the blower draw air from the blower space 31 and pass: it underscme pressure-through an air passage 92 of the front wall 21 and thence through a distributor horn 93,- by means of which astream of air is directed expressly at the power tube' 75, this being the hottest portion of the-operation. By this arrangementthe: coolest air is directed toward the portion of the" apparatus most needing to be cooled. Naturally the-air willbe warmed considerablyby coming into contact with. the hot power tube. Although a small proportion of the warm air is forced outwardly through an air outlet 94 in the rear wall of the inner box, neverthe less a. substantial portion of the warm airis. forced through aventilating. passage 95, which passage has interposed therein an electrically shielding screen 96. Air forced through the ventilating passage 95 sweeps through the heating chamber and passesoutwardly at the rear through an. air outlet passage 97 carrying with it moisture released from the work togetherwith heat generated outer boxexcept for a confiningslot 101 extending around the vertical side edges and bottom; As shown in greater detail inrFigures 4-and 5, the slot 101, whether onthe verticaledges or on the bottom, comprisesan out'er flange 102 and an inner flange 103 spaced: rather close;

together to form a snug slidingfitwhere theperiphery of the frame is adapted to slide. The fit is made snug enough so that there is a positive electric contact between the frame, which may be of the same stainlesssteel material, and the material of the outer box. A

fiat portion 104-211: theupper edge of the frame is adapted tooverlie the horizontal leg of the angle element 29 in firm contact therewith, which contact may be maintained by suitable screws, not shown.

At the lower end of the frame 100' there-is provided an opening 106 whichcommunicates with the air inlet opening 9th The opening 106 is covered with a metallicelectrically shielding mesh 107. At the upper portion of the framelllflare apertures 108 and for convenience the metallic mesh 107 may be extended over theentire area of the frame so as to cover all of the apertures 108.

So that infiowing air maybe clean, thereis provided an air filter 169 which comprises a filter frame 110 snugly fitting a confining. channel 111 attached to the frame around the opening 106. The filter frame may be so mounted that it can be removed periodically in order to'permit cleaning of an air filter membrane 112.

To properly shield the inner box 20 overthe'air outlet area 94. there is provided a frame of sheet ma-' terial, preferably aluminum under circumstances where the inner box is likewise constructed of aluminum. The frame contains apertures'121 slightly smaller-than butcoinciding with the apertures 108. To accommodatethe-frame- 12%), a flange 122' is provided extending down the side-edges. and across the bottom ofthe rear wall 22 ofthe inner box. A similar flange 123 is formed from the material of the inner box and occupies a position spaced from the flange 122 so as toprovide a narrow slot 'therebetween. The frame 120 is designed to slide snugly within the slot thus formed andwhen' in place" to form apositive electric contact around the edges of the frame; A metallic mesh 124 extends over substantiallythe 'area'of the frame oc'cupied'by the a'per t-ure's1'2t's'othat all of the openings: of the apertures are electrically shieldcd.-

overlying sheet 125 maybe provided to holdthe mesh in place. On occasions where itr is necessary to gainaccess to the interior of the innor box, the frame 120 may be slid upwardly within the confining slots. When it is slid downwardly a position closing the opening comprising the air outlet 94, the frame. is effectively secured in position after the frame 100 has been applied and secured in place in the manner previously described. By the structure thus defined it willbe apparent that although ample openings are provided for both air inlet and air outlet, the open: ings are suitably electrically shielded by a metallic mesh which on the rear; as described consists of mesh walls overportions of the area spaced one from another in much the samerelationship as the remaining imperforate walls of the inner and outer boxes. The double shieldingv mesh thereby provides aneffective electrically shielding effect.

The same elfect is also provided for vents 1'26 and 1 27 alignedadjacent'thewallsection 17 at the front of the machine.- Metallic meshes 128' at-these locations properly'shiel-d the vents which permit outflow of a--cer-' tain amount of ventilating air;

Inthe electronic circuit are sundry accessory elements, all of which compriseportionsof the circuit and are located in various portions of the unit.- A wiring diagram illustrative of the circuit is shown in Figure 8; Electric power is supplied at a-three-prong connection 131 normally locatedat the side wall 13 adjacent the bottom rear as sh'own inFigure 1. Current at the three-prong conmotion is norma'llysupplied at 220 volts A. C. Current from the connection passes through cartridge fuses 132 to a timer 13-3, there being also a direct connection to an auto transformer134 in which is a resistor 135 which" is adapted tocontrol the filamentvoltage of a filament 136 in the power tube '75. The oposite side of the auto transformer 134 is connected to the filament through feedthrough capacitors 137 and choke or filter coils 138. Bypass capacitors are indicated by the reference character 139-.-

In a portion of the circuit fed through the fuses 132 is a platetransformer 14%) capable in one embodiment of the invention ofa production of 4250 volts. The high side of the transformer 14% connects to resistors-141 and 1 i2'and an over-loadrelay 143 which are included in the same-circuit as a capacitor 144 and by-pass'capacitor'145 connected in turn to ground at 146-. In the'other branch of this circuit is a radio-frequency plate filter 147 interconnected on one point to capacitors 137, at another point to ground at 148, and at still another point to the power tube circuit through a plate choke coil 149.

Elsewhere in the circuit are located a power meter 151i associated with a bypass capacitor 151. The-blower 91' has associated with it an autotransformer 152 and a grid current meter 153 has a resistor 154 connected thereto and in turn connected to ground at 155 andto the ca pacit'ors 137. Such parts of the circuit and element's therein as have not been specifically identified aresuhstantially conventional for circuits of this character.

The oscillator 75 is a high-frequency changer, one-satisfactorymodel of which is RCA No. 5786 as currently identified. The oscillator is one capable of increasing the frequency to something in the nature of 90 megacycle-s. Associated with the power tube is a coupling capacitor 15d located immediately adjacent the positive electrode or anode 61 and its corresponding negative electrode 60, these in the form of the invention selected for the purpose of illustration being plates held inparallel relationship to each other. The tank coil 77 is shown interconnectedwith the positive electrode.

in'the filament circuit there is located an overload-voltage protector 160, this being shown also in detail in Figure 6. The overload voltage protector consists of a plate 161 secured to a dielectric sheet 162 by means of a bolt 163;, the bolt being'one extending into engagementwith the bottom25 of the inner box to establish a ground can'- nectionr Also mounted upon the dielectric sheet 162 is an angle element 164 which employs a bolt 165 serving as a binding post to secure the angle element to the sheet and also to provide a connection for a wire 166 joining the filament circuit. Mounted in the angle element is an adjusting screw 167 having a screw head 168 by means of which it may be manipulated, and a lock nut 169 to securely lock it in adjusted position. A tapered point 170 on the screw lies immediately adjacent the plate 161 so that the screw can be adjusted to vary the length of an air gap 171. It has been found in practice that a grid voltage of three to four hundred volts serves as a workable voltage for certain operating conditions. When this is the selected voltage, it is desirable to short the circuit in the event that the voltage should rise inadvertently to about double the figure, namely, about six to eight hundred volts. To set the overload voltage protector to operate at this voltage a suitable instrument can be connested in circuit with it and the adjusting screw moved to set the length of the air gap 171 so that the air between the tapered point 170 and plate 161 will break down and ionize at the selected voltage, thereby grounding the filament circuit and protecting the other elements of the circuit from damage which might result should the voltage exceed the figure for which the overload voltage protector is set.

When the device is to be operated, the door 40 is lifted by manipulation of the handle 50. This lifts the negative electrode 60 out of the way and the work can be placed directly upon and supported by the positive electrode 61. Thereafter the door 40 is closed snugly to the position illustrated in Figure 4. The negative electrode 60 should preferably not come into direct contact with the work but should lie adjacent thereto, in which position it can be set by manipulation of the hand wheels 70. Let it be assumed meanwhile that the current has been turned on in the filament circuit by use of the filament toggle switch 172. The timer 133 is then set for the proper heating cycle, to 30 seconds frequently being sufiicient. A start button 173 is then pressed starting the timing cycle and current will flow to the power tube generating the oscillating waves for the length of time set, the action of which will raise the work to the desired temperature. After the timer has stopped the operation, the door 40 is lifted and the work removed. The unit then is ready for heating the next work piece.

From the foregoing description it will appear that the unit described is compactly housed within the inner and outer boxes wherein all electrical elements are contained together with the mechanically functioning portions of the device. By providing a wide-open top, ready access can be had to the heating chamber so that work pieces up to the maximum size permissible due to the interior dimensions of the heating chamber can be conveniently inserted and removed. The door is so constructed that it can be lifted and lowered with a minimum of effort and will hold its position either open or closed. The shielding character of the door is comparable to the shielding character of the double walled box construction. All parts are readily accessible from the rear by removal of the frames 100 and 120 when servicing is necessary. It is further possible, should occasion require, to disconnect the inner box from the outer box and to lift the inner box from the outer box to give access to the interior of the outer box. Constructed as shown the unit can be mounted as such at any desired location in a production line or production operation to afford maximum elficiency where the heating of small objects in a production opera tion is necessary.

' While I have herein shown and described my invention in what I have conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of my invention, which is not to be limited to the details disclosed herein 8 but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices. Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An electron cabinet heater comprising an inner box of electrical shielding material having a bottom, front and rear walls, side walls and an open top, an insulated tube support mounted in the box, a partition of insulating material separating the box into an upper heating chamber and a lower tube chamber, an outer box of electrical shielding material surrounding and spaced from all sides and bottom of the inner box and having an open top, a flanged junction between the top of the inner box and the top of the outer box thereby to support said inner box, a loading door hinged to the boxes at said junction, said door having a downwardly extending resilient rim adapted when closed to surround and press against the flanged junction, a positive electrode plate supported in the heating chamber above the partition, a negative electrode mounted in said heating chamber in spaced parallel relation to the positive electrode when the door is closed, means forming an electrical shielded air inlet passage to said chambers, and means in the wall of said inner box and in an adjacent wall of the outer box forming an electrical shielded air vent from said chambers to the atmosphere.

2. An electron cabinet heater comprising an inner box of electrical shielding material having a bottom, front and rear walls, side walls and an open top, a tube support of insulating material mounted on the bottom of the inner box, a partition of insulating material in a transversely extending position separating the box into an upper heating chamber and a lower tube chamber, an outer box of electrical shielding material surrounding and spaced from all sides and bottom of the inner box and having an open top, a flanged junction between the top of the outer box and the top of the inner box thereby to support said inner box, a loading door hinged at one edge to the flanged junction, said door having a downwardly extending re silient rim adapted when closed to surround and press against the box flanged junction, a positive electrode plate supported in the heating chamber, a negative electrode supported in said heating chamber on said door in spaced parallel relation to the positive electrode when the door is closed, means forming an electrical shielded air inlet to space between said inner and outer boxes, means in the wall of the inner box forming an air passage between said space and said tube chamber, means in said partition forming a ventilating passage from said tube chamber to said heating chamber, means in the wall of said inner box forming electrical shielded air outlets from said chambers and means in an adjacent wall of the outer box forming an electrical shielded air vent from said outlets to the atmosphere.

3. An electron cabinet heater comprising an inner box of electrical shielding material having a bottom, front and rear walls, side walls and an inner box flange around the top of the walls forming an open top, a tube support comprising columns of insulating material mounted on the bottom of the box, a partition of insulating material carried by the tube support in a transversely extending position separating the box into an upper heating chamber and a lower tube chamber, an outer box of electrical shielding material surrounding and spaced from all sides and bottom of the inner box and having an outer box flange at the top joined to the inner box flange thereby to support said inner box, a loading door hinged at one edge to the inner box flange, said door having a downwardly extending rim adapted to encompass said flanges when in closed position and having a resilient inner flap on the rim adapted when closed to surround and press against the inner box flange, a positive electrode plate supported in the heating chamber by the tube support, a negative electrode adapted to be suspended in said heating chamber on said door in spaced parallel relation to the positive electrode when the door is closed, means forming an electrical shielded air inlet to space-between said. inner and outer boxes, means in thewall of the inner boxfor-ming; an. air passage between said space and-said tube chamher and a blower in said passage, means in said partition forming. a ventilating passage from said tube chamber to said heating chamber, means in the Wall of said inner box forming electrical shielded air outlets from said chambers and means in an adjacent wall of the outer box forming an electrical shielded air vent from said outlets to the atmosphere.

4-. An electron cabinet heater comprising an outer box, an inner box in the outer box and havingwalls and a bottom spaced from theouter box, said boxes each having top openings coincident one with another, an upstanding flange common to both the inner box and the outer box, said inner box having aheating chamber at the upper end beneath the opening, a positive and negative electrode plate in the heating chamber, a door of electrical shieldinglmaterial having a thickness greater than the thickness of the flange and having a hinge joined to the boxes, a rigid downwardly extending rim on said door adapted in closed position of the door to occupy a position laterally spaced from and enclosing said upstanding flange, a resilient flap on the door at the inside-of the rim and spaced therefrom and adapted to resiliently engage the upstanding flange with a line contact throughout the perimeter.

5'. An electron cabinet heater comprising an outer box, aninner box in the outer box and having walls and a bottom spaced from the outer box, said boxes each. having top openings coincident one with another, and an upstanding flange common to both the inner box and the outer box, said inner box having a heating chamber at the upper end beneath the opening, a positive elect-rodeplate atone-side of the heating chamber, a substantially flatdoor of electrical shielding-material having ahinge joined to'the boxes, a rigid downwardly extending rim on said door adapted in closed position of the door to enclose. said upstanding flange, a resilient flap on the door at the inside of the rim and spaced therefrom and adapted to-engage the upstanding flange with a line contact throughout the perimeter, a negative electrode plate support extending through the door and adjusta'bly mounted therein, and a negative electrode plate on said negative electrode support havingaposition when the door is closed Within the inner box parallel to and spaced from the positive electron plate.

6-. An electron cabinet heater comprising an outer box, an inner box in the outer box and having walls and a bottom spaced from the outer box, said boxes each. having top openings coincident one with another and an upstanding flange at the top of the inner box surrounding the opening and joined throughout its entire perimeter to the outer box with a metal to 'met-ai seal, said inner box having a heating chamber at the upper end beneath the opening and a separate tube chamber at the lower end, a positive "electrode plate at the bottom of the heating chamber, a door of electricalshielding material having a hingeat one edge joined to the flange on one side of the inner box, a rigid downwardly extending rim on said door adapted in closed position of the door to enclose said upstanding flange, a continuous resilient flap on the door at the inside of the rim and spaced therefrom and adapted to resiliently engage the upstanding flange with a line contact throughout the perimeter, a negative electron plate support extending through the door and adjustably mounted therein, a negative elect-rode plate on said negative electrode support extending beyond the open edge of the door and having when the door is closed a position within the inner box and parallel to and spaced from the positive electrode plate, resilient strips between the edges of said negative electron plate and said door, and counter-balance springs at said hinge between the door and said flange.

7. -An electron'cabinet heater comprising an outer box having side walls, a bottom, and atop having an opening therein, an inner box having a flange at the top secured to the top of the outer box whereby the inner box is suspendedin the outer box spaced from the walls thereof and providing communicating, spaces adjacent the walls adjacent the bottom, means on a wall of the inner box forming an air passage from said spaces to the interior of said inner box, means forming an air outlet on another Wall of the inner box, a frame of electrical shielding sheet material received in electrical shielding engagement with said other wall around the opening therein, said frame having apertures therethrough and electrical shielding pervious material in said apertures, means forming an opening in a wall of the outer box adjacent said other wall of the inner box and a frame of electrical shielding sheet material received in electrical shielding engage meat with said last wall of the outer box, and having apertures therein coinciding with apertures in the frame for said inner box and electrical shielding pervious material in said last apertures, means in the frame of said outer box forming an air inlet opening communicating with said spaces, a filter frame over said air inlet opening and a. perv-ions electrical shielding material over said inlet opening in said frame.

8'. An electron cabinet heater comprising an outer box having side walls, a bot-tom, and a top having an opening therein, an inner box having a flange at the top so cured to the top of the outer box whereby the inner box is suspended in the outer box spaced from the Walls thereof and providing a space therearound, a partition having an opening theret-hrough forming upper and lower chambers in said inner box, means on one wall of the inner box forming an air passage from said space to the lower chamber of said inner box, means forming an outlet in. another wall of the inner box, a frame of electrical shielding sheet material removably received in electrical shielding engagement with said other wall of the inner box around the opening and having apertures therethrough and electrical shielding pervious material in said apertures, means forming an opening in a wall of the outer box adjacent said other wall of the inner box, and a. frame of electrical shielding sheet material removably received on said wall of the outer box and having apertures therein coinciding with-apertures in the frame for said inner box and electrical shielding pervious material in said last apertures, means in the frame of said outer box forming an air inlet opening communicating with said. space, and a filter frame covering said last identified opening. and. having a pervious electrically shielding material thereover, said frame being removably secured in-electrically shielding engagement with the frame in the outer box.

9. An electron cabinet heater comprising an outer box having sidewalls, a bottom, and a top having an opening therein, an inner box having. a flange at the top secured to the top of the outer box whereby the inner box is suspended in the outer box "spaced from the walls and bottom thereof and providing a blower space adjacent the .front wall and an accessory space adjacent the bottom communicating with the blower space, means on an adjacent wall of the inner box forming an air passage from said blower space to the interior of said. inner box, electrical shielding slot elements on the side edges and bottom of the rear wall of the inner box and means forming an air outlet surrounded by said slot elements, a frame of electrical. shielding sheet material slidably received in said slot elements and having apertures therethrough and electrical shielding pervious material in said apertures, means forming an opening in the. rear wall of the outer box, electrical shielding slot elements at the side edges and bottom of the rear wall of the outer box surrounding said opening-and a frame of electrical shielding sheet material slidably received in said slot elements and having apertures therein coinciding with apertures in the frame for said inner box and electrical shielding pervious material in said last apertures, means in they frame of said 11 outer box forming an air inlet opening opposite said accessory space, an electrical shielding channel surrounding said opening, a filter frame in said channel and a pervious electrical shielding material in said frame and an electrical shielding grill covering said last identified opening at the inner side of said filter frame.

10. A cabinet electron heater comprising an outer box, an inner box suspended at upper ends of said boxes in the outer box and in spaced relation thereto, said boxes having coinciding loading openings at the tops thereof, an electron tube support mounted on the bottom of the inner box and comprising a series of columns of insulating material, a tube base mounted intermediate upper and lower ends of the columns, a partition of insulating material mounted in the inner box above the columns and dividing the interior of said inner box into a lower tube chamber and an upper heating chamber, an electrode support carried by said columns and extending through said partition, a positive electrode plate on said electrode support and in said heating chamber, and a negative electrode plate carried by said niner box in a position spaced from and parallel to said positive electrode plate when in operating position.

11. A cabinet electron heater comprising an outer box, an inner box suspended at upper ends of said boxes in the outer box and in spaced relation thereto, said boxes having coinciding loading openings at the tops thereof, an electrode tube support mounted on the bottom of the inner box and comprising a series of four silicone corner columns, a tube base mounted intermediate upper and lower ends of the columns, a platform at upper ends of the columns, and a partition of silicone material secured to walls of the inner box dividing the interior of said inner box into a lower tube chamber and an upper heating chamber, an electrode support on said platform extending through said partition, a positive electrode plate carried on said electrode support and in said heating chamber, and a negative electrode plate carried by said inner box in a position spaced from and parallel to said positive electrode plate when in operating position.

12. In an electron heater a box having side walls and a bottom, a plurality of silicone columns mounted in the box, a tube base mounted on said columns intermediate upper and lower ends, a platform on the upper ends of the columns, a sheet of silicone material on said platform, an electrode support on said platform extending through said sheet, an electrode carried on said support above the sheet and an opposite electrode carried on said box in a position spaced from the first electrode.

13. An electron heater device comprising a positive electrode element and a negative electrode element spaced one from another and adapted to receive between them an object to be heated, an oscillator power tube having elements comprising a filament, a grid and an anode, a source of electric power having respective positive and negative terminals, and an electronic circuit interconnecting said source of electric power and said tube elements, and a composite boosting and heating circuit comprising a boosting sub-circuit and a parallel resonant sub-circuit, said first identified sub-circuit comprising said anode, a coupling capacitor element, said positive electrode, a resonant coil, said grid, said filament, and a negative terminal of said power source, said capacitor element and said positive electrode having an air gap therebetween, a high frequency filter system connected between said filament and said source of electric power, said parallel resonant sub-circuit comprising said resonant coil, said positive electrode and said negative electrode, and a high voltage hot circuit between the anode and a positive terminal of the power source.

l4. An electron heater device comprising a cabinet housing a heating chamber, a positive electrode element and a negative electrode element spaced one from another in said chamber and adapted to receive between them an object to be heated, an oscillator power tube in said cabinet having elements comprising a filament, a grid and an anode, a source of high and low voltage of electric power having respective positive and negative terminals, and an electronic circuit interconnecting said source of electric power and said tube elements, and a composite boosting and heating circuit comprising a boosting sub-circuit and a parallel resonant sub-circuit, said first sub-circuit comprising said anode, a coupling capacitor element, said positive electrode, a resonant coil, said grid, said filament, and a negative terminal of said power source, said capacitor element and said positive electrode having comparable areas and an air gap therebetween, a high frequency filter system connected between said grid, said filament and terminals of said power source, said parallel resonant sub-circuit comprising said resonant coil, said positive electrode and said negative electrode, and a high voltage hot circuit between the anode and a positive terminal of the power source.

15. An electron heater device comprising a cabinet housing a heating chamber, a positive electrode element and a negative electrode element spaced one from another in said chamber and adapted to receive between them an object to be heated, an oscillator power tube in said cabinet outside said heating chamber and having elements comprising a filament, a grid and an anode, a source of high and low voltage of electric power having respective positive and negative terminals, and an electronic circuit interconnecting said source of electric power and said tube elements, and a composite boosting and heating circuit comprising a boosting sub-circuit and a parallel resonant sub-circuit, said first sub-circuit comprising said anode, a coupling capacitor element, said positive electrode, a resonant coil, said grid, said filament, and a negative terminal of said power source, said capacitor element and said positive electrode having comparable areas and an air gap therebetween, a high frequency filter system comprising in series a pair of choke coils and capacitors connected to opposite terminals of the low voltage source of power, a plurality of high frequency capacitors connected to said filament and a center tap thereof, a by-pass capacitor in series with said first capacitors and said grid, said parallel resonant subcircuit comprising said resonant coil, said positive electrode and said negative electrode, and a high frequency choke between the anode and a positive terminal of the high voltage power source.

16. An electron heater device comprising a cabinet housing a heating chamber, a positive electrode plate and a negative electrode plate spaced one from another in said chamber and adapted to receive between them an object to be heated, an oscillator power tube in a portion of said cabinet outside said heating chamber and having elements comprising a filament, a grid and an anode plate, a source of high and low voltage of electric power having respective positive and negative terminals and an electronic circuit interconnecting said source of electric power and said tube elements, and a composite boosting and heating circuit comprising a boosting subcircuit and a parallel resonant sub-circuit, said boosting sub-circuit comprising said anode plate, a coupling capacitor plate, said positive electrode, a resonant coil, said grid, said filament, and a negative terminal of said high voltage source connected in series, said capacitor plate and said positive electrode having comparable areas and a fixed air gap therebetween, a high frequency filter system comprising in series a pair of choke coils and capacitors connected to opposite terminals of the low voltage source of power, a pair of high frequency capacitors connected to said filament and to a center tap of said tube, a bypass capacitor in series with said first capacitors and said grid, said parallel resonant sub-circuit comprising said resonant coil, said positive electrode and said negative electrode, and a high frequency choke between the anode plate and a positive terminal of the high voltage power source and means adjustably mounting one of said plates whereby to vary the space therebetween and the frequency of said resonant sub-circuit for the heating of said object.

References Cited in the file of this patent 5 UNITED STATES PATENTS 14 Bandino Feb. 2, 1943 Stodola Mar. 26, 1946 Albin June 1, 1948 Anderson et a1 Dec. 30, 1952 Revercomb Mar. 17, 1953 FOREIGN PATENTS Great Britain Nov. 25, 1948 Germany May 11, 1929

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