US2938716A

US2938716A - Apparatus for producing copper oxide cells

Info

Publication number: US2938716A
Application number: US587540A
Authority: US
Inventors: Harold B Conant
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-05-28
Filing date: 1956-05-28
Publication date: 1960-05-31
Anticipated expiration: 1977-05-31

Description

May 31, 1960 H. B. CONANT APPARATUS FOR PRODUCING COPPER OXIDE CELLS 3 Sheets-Sheet 1 Filed May 28, 1956 l2 l3 fes l23456759|0ll Mf/ru INVENTOR. Hana/0 .5. 60/74/77 May 31, 1960 H. B. CONANT APPARATUS FOR PRODUCING COPPER OXIDE CELLS Filed May 28, 1956 s'sheets-sneet 2 INVENTOR. Hana/a 5 600.40%

.4 TTORN May 31, 1960 H. s. CONANT APPARATUS FOR PRODUCING COPPER OXIDE CELLS Filed May 28, 1956 3 Sheets-Sheet 3 INVENTOR. flaw/d 5. 60/74/22 nited States Patent APPARATUS FOR PRODUCING COPPER OXIDE CELLS Harold B. Conant, 6500 0 St, Lincoln, Nebr.

Filed May 28, 1956, Ser. No. 587,540

3 Claims. (Cl. 266--5) This invention relates to electrical cells and more particularly to a method and apparatus for regulating the surface oxidation of copper blanks when the same are heated in an oxidizing atmosphere, the copper oxide cells thus produced having improved rectifying characteristics.

It has been known for some time that when a clean copper blank of suitable shape is heated in an oxidizing atmosphere for a predetermined period, and then cooled slowly to room temperature, a relatively thin layer of cuprous oxide overlaid with a substantially thinner layer of cupric oxide forms thereon. Removal of the cupric oxide layer to expose the cuprous oxide layer results in an electrical cell that will rectify alternating current passing therethrough, this property obtaining because of the relatively low resistance when the oxide layer is positive with respect to the copper and the resistance relatively high when the polarity of the impressed voltage is reversed.

Several methods of producing more efiicient copper oxide cells have beensuggested, it being now well recognized that such efiiciency is directly dependent upon the nature of the oxide coating. Proposed methods include heating the copper blanks to various oxidizing temperatures, cooling the blanks quickly or slowly, quenching them in a variety of mediums including air blasts, oil, water and glycerine, and alloying certain metallic or nonmetallic elements with the copper. Also suggested have been methods of coating the blanks by electroplating, chemical displacement or spraying onto the surface of the blanks a suitable substance, all of these coating operations being carried out prior to heat treatment.

A serious problem encountered, however, is the fact that commercially available copper stocks which are suitable for copper cell production, even though having identical assays, will vary considerably as to the types and amounts of impurities either naturally occurring or artifically incorporated therein. These impurities have a marked influence on the oxide layer formation, widely varying rectifying characteristics resulting when the blanks are heated and cooled under identical conditions.

The principal process heretofore employed in oxidizing copper cells consisted of placing the blanks in a muffie pre-set at a suitable oxidizing temperature, subsequently transferring the oxidized blanks to a similar furnace at a lower temperature, and finally quenching them in a liquid. However, this method has been found to be unsatisfactory because of the impossibility of exactly controlling the temperature of each cell at all times during the process, such lack of control being responsible for a large percentage of rejected cells.

Therefore, the most important object of this invention is to provide a method and apparatus for oxidizing copper cells wherein the temperature of each individual blank may be controlled precisely throughout the production process.

A further important object is the provision of a method for producing copper rectifying cellswhich contemplates controlling the heating-cooling curves to such an extent 2,938,716 Patented May 31, 1960 that copper oxide cells meeting a particular specification may be reproduced irrespective of the types and amounts of impurities contained in the suitable commercial blank stocks utilized.

An object of this invention is the provision of apparatus which is capable of shaping the current-resistivity curve of copper oxide cells to suit a specific application, such curve being varied by suitably shaping the heat treating curve of the cells in the apparatus.

Also an object of this invention is to provide apparatus for continuously producing copper oxide cells by disposing the copper blanks on an endless conveyor passing through a variable zone mufiie.

A further object is to provide apparatus of the character described having a plurality of variable electric resistance heaters disposed within the muffle whereby the temperature of different regions therein may be varied as the particular heating-cooling curve being maintained dictates.

An important aim is to provide a valve controlled heat exchanger in close proximity to the advancing copper blanks for suddenly depressing the temperature of the blanks if the heating-cooling curve being used demands such.

Other objects of the invention include the way in Which copper blanks to be treated are automatically fed to the endless belt; the way in which a plurality of temperature sensing devices in close proximity to the advancing blanks are employed to control the temperature of the various zones within the muflle; the way in which heater means are employed adjacent the point where the blanks emanate from the mufiie so that the same have no tendency to cool before dropping into the quenching tank; the way in which the conveyor is composed of a refractory metal belt having perforations therein; and the way in which a removable metal plate is disposed between the advancing blanks and the heaters in one zone of the muflie.

In the drawings:

Figure 1 is a schematic view of a heating-cooling curve envelope for processing copper oxide cells in which the time during which the cells are subjected to heat treatment is plotted along the ordinate and the temperature to which the cells are subjected is plotted along the abscissa;

Fig. 2 is a side elevation view of apparatus capable of carrying out the concepts of the present invention with parts broken away and in section for clarity of illustratron;

Fig. 3 is a vertical, enlarged, partial cross-sectional view taken on the line III-III of Fig. 2;

Fig. 4 is a vertical, enlarged, partial cross-sectional view taken on the line IV-IV of Fig. 2;

Fig. 5 is a vertical, enlarged, partial cross-sectional view taken on the line VV of Fig. 5; and

Fig. 6 is an essentially schematic diagram illustrating the electrical aspects of the apparatus.

When a relatively pure, clean copper blank is subjected to heat treatment by increasing the temperature of the mufiie to an oxidizing atmosphere the reactions taking place during the various ranges of the process are represented by the following formulas:

Kilocalories (a) 200-500= c.-2 Cu+O =2 CuO 34.89 (b) 5001020 C.2 Cu+2CuO=2 C11 0 5.01 (c) 1020l060 C.2 CuO=Cu O+O ..+5.01

Heat energies are given as per gram-formula weight from which it can be seen that the reaction in range (a) is decidedly endothermic requiring a much greater amount of energy to reach a temperature of 500 C.

than to increase the temperature from 500 to 1020 C. in range (b). Decomposition of CuO in the ('0) range yields 5.01 kilogram calories of heat to make the reaction slightly exothermic. and if the temperature is carried to 1065 C. the reaction becomes very exothermic with'the formation of the Oil-C11 eutectic. Furthermore, in the (0) range the layer of oxide which has formed on the copper blanks is in a semi-fluid state although the temperature involved is below the melting point of either the copper, the Cu O, or the eutectic. This observed phenomenon is believed due to solution of 0 into the body of the oxide to form a mixture of lower melting point. During the cooling of the workpieces following oxidation, the previously fused mass of oxide must crystallize. The resulting crystal structure depends upon the cooling rate and subsequent holding or soaking temperatures employedand'largely determines the electrical characteristics of the rectifier produced. a Very precise control through out the entire heating-cooling cycle is essential to optimum performance of the cells, and such precision is not possible, to achieve in the heretofore known means.

From the foregoing it is manifest that if the heat supplied to the blanks were continued at the same rate in the (c) range as in the (a) range, the temperature of the blank would rise rapidly past 1065 C., the point at which the Cu O becomes soluble in the mother copper to form. the eutectic. This action is evidencedvas an incipient fusion of the blank which is thereafter useless and must be rejected. Therefore, the temperature of the blank during oxidation must remain below 1065" C., but must be sufficiently high to provide a coating of the desired thickness on the blank. It has been found that a temperature in the range of 1040 C. to 1060 C. is essential to the formation of oxides having the desired rectifying characteristics and which strongly adhere to the copper base under all operating conditions.

' 2,988,716 v i a r 4 r 7 example, rectifiers for use with certain measuring instruments must have a low forward resistance at the very small load'currents involved and the resistance at larger load currents is'of little importance. Rectifiers which operate to supply power, forinstance, battery charging, operate at near full load rating and it is desired to achieve the lowest forward resistance at full load. These two examples require that the rectifiers be made of cells as possible. Unavoidably though, when the furnace is i with entirely dilferent currenbr'esistivity curves, the formation of such cells being for the most part impractical heretofore, since one type of'apparatus was utilized for all species of cells. There is now presented, however, unitary oxidizing means which will produce cells meeting all requirements. g a. g

In order to exactly duplicate the heating curves it is necessary to provide apparatus capable of precisely controlling the temperature of each individual blank and the period during which it is maintained at such-temperature. This, of course, is not possible in the conventional'electric furnace, although the best of such furnaces do have heaters covering all inner walls including the charging door and much care is exercised in their cons'truction to maintain the heating of all parts as equally charged with copper blanks, some of the blanks are adjacent to the heated walls whereas some are in approximately the geometrical center of the chamber, the result beingthat the centermost pieces are effectively shielded Tests have indicated that the process should be carried out within certain critical parameters of time and temperature, however, regardless of the bar stock employed. These critical limitations are shown by the envelope in Fig. 1 wherein it can be seen that the blanks must be brought to the amaximum temperature of between 1040" C. and 1060 C. during a period of from four to eight minutes and maintained at such temperature for zero to four minutes.- The blanks are then lowered to the intermediate temperature of fi'om 500 C. to 700. C;

within one to ten minutes, and maintained within the p intermediate range for zero .to seven minutes. Lastly, the blanks are quenched in a liquid at or below room temperature. It is to be understood that the blanks may be heated and subsequently cooled to an intermediate temperature prior to quenching along any graphically represented time-temperature line corresponding to the upper or lower lines of the envelope illustrated in Fig. l, or in the alternative, any plotted line therebetween.

However, as previously mentioned, the electrical characteristics of the cells will vary according to the chemical composition, and therefore it is necessary to plot aheating-cooling curve for each of the various commercial stocks employed. With the rectifying specifications which,

the cells must meet being known, a heating-cooling curve fitting within the envelope of Fig. 1 may be determined. It is manifest that an infinite number of curves will fit in the envelope, each varying according to the particular sheet stock being employed. Therefore, when a number of cells are to be processed from the same stock at a subsequent time, it is but necessary to again follow the same curve in producing cells meeting the'desired specification. a i

As copper oxide cells. are employed in devices other than rectifiers, and even rectifiers are employed in :a variety of services requiring different characteristics, the ability to shape the current-resistivity curve of the cells to aspecific application is of great value. As a specific from the source of energy. Therefore, those blanks disposed adjacent the periphery of the chamber receive heat energy at a much more rapid rate than interiorly disposed blanks, notwithstanding elaborate arrangements for rapid circulation ,of the gaseous contents of the furnace.

Under these conditions the peripherally disposed blanks will reach a temperature of 1040 C. before the remainder of the'charge reaches 1020 C. As soon as the peripheral blanks reach approximately 1040 C. the oxidation reaction becomes exothermic, while the reaction of the remainder of .the charge remains endothermic. At this point the reaction becomes critical as more heat energy than barely necessary to overcome radiation losses cannot be supplied to the furnace chamber without danger of incipient fusion of 'the peripheral blanks. The same problem is present when extremely large copper blanks are employed, because the peripheral edges will heat at a much faster rate than the center portion, and therefore, heating of the area remote from the walls must be principally by lateral conduction of heat through the body of the copper.

To overcome thesev objections there is now provided apparatus designated generally by the numeral 10 and which is adapted for the controlled production of copper oxide cells 12 by passing clean copper blanks 14 through an elongated oxidizing muflie 16 which has an elongated conveyor belt-receiving passage 18 passing therethrough, communicating with inlet 20 and outlet 22; Mufile 16 includes an oxidizing section 24 and a temperature maintaining section 26 which are suitably secured together. Section 24 is preferably formed of a metal box 28 having the end thereof engaging section 26 open, and contains insulation material 30 in surrounding relationship to passage 18. Disposed within the oxidizing portion of passage 18 is a tubular element 32 which extends from inlet 20 to the zone of juncture between sections 24 and 26. Element 32 is preferably formed of porous refractory material such as Alundum or the like and serves a purpose hereinafter set forth. Section 26 is formed of cast monolith blocks 34 and 36 of suitable insulating material,

and block 34 is provided with. hollowed out portions38 horizontal portion of which is disposed in passage 18 and which passes over a drive pulley 46 secured to an axle 48 pivotally mounted on framework designated broadly by the numeral 50 adjacent the inlet end of muffle 16. Belt 44 additionally passes over a driven pulley 52 which is suitably mounted adjacent the outlet end of mufiie 16 and over a second drive take-up pulley 54 secured to a shaft 56 which is in turn pivotally mounted in-a member 58 pivotally mounted on shaft 48. A worm gear 60 secured to shaft 48 meshes with a worm 62 on the drive shaft 64 of a variable speed gear box 66 which is operably connected to a prime mover such as an electric motor 68 by belt and pulley means 70. A sprocket wheel 72 secured to shaft 56 provides means for driving pulley 54 by virtue of a roller link chain 74 passing over wheel 72 and a similar sprocket wheel 76 secured to shaft 48. From the foregoing it can be seen that belt 44 is driven at a predeterminable constant speed by virtue of a pair of drive pulleys such as 46 and 54, the lowermost pulley 54 serving the additional function of maintaining a constant tension on belt 44. This is of importance because, as will be hereinafter set forth, one end of mufile 16 is shiftable vertically with respect to the other end. Also it is to be pointed out that pulleys 54 and 46 are considerably larger than breakover pulley 52 for the reason that, when the oxidized cells emerge from mufile 16 at outlet 22, they break over the relatively small pulley 52 and are dislodged therefrom without any tendency to stick thereto.

Belt 44 is formed of loosely woven refractory material such as Nichrome or Chromel. A plurality of elongated slides are preferably provided in the lowermost part of passage 18 and coextensive in length therewith for slidably supporting belt 44 as the latter passes therethrough, the slides being designated by number 78.

Framework 50 includes a horizontal frame 80 which is disposed adjacent the lowermost end of mufiie 16 at the inlet end thereof and rests on floor 82, frame 80 being adapted for pivotally supporting the muflle 16 at that end thereof and thus allowing vertical reciprocation of the outlet end of the mufiie with respect to the inlet. By virtue of this construction it can be seen that passage 18 may be inclined at various angles relative to the horizontal position and in this respect, mean is provided adjacent the outlet end of mufile 16 for holding that end thereof in such inclined positions. Manifestly, any type of suitable adjustable means may be provided for holding muflie 16 in an inclined position and for this reason, adjustable means such as 84 is shown attached to a beam 86.

Mechanism is provided for automatically feeding blanks 14 to conveyor belt 44 and may conveniently take the form of an automatic magazine 88, located adjacent pulley 46 and having a reciprocable slide 90 which is driven by motor 68 through suitable cam and friction clutch means (not shown). Delivery of blanks 14 to belt 44 by horizontal reciprocation of slide 90 is variable, depending upon the particular heating curve employed for oxidizing the blanks 14.

A series of

electric resistance heaters

90, 92, 94, 96, 98 and 100 are mounted in passage 18 in parallel alignment with belt 44,

heaters

90, 92 and 94 being located adjacent the inlet end of muffle 16 and

heaters

96, 98 and 100 being disposed adjacent the outlet end thereof. Each of the

heaters

90, 92 and 94 is provided with a platinum heating element 102 which is wound around the tubular element 32 as clearly shown in Fig. 3 of the drawings. It can now be understood that the three

heaters

90, 92 and 94 each have a heating element 102 wound around tubular element 32 in such a manner that the blanks passing through section 24 on belt 44 are exposed to the heat from elements 102 in all directions. Furthermore, as will be hereinafter explained, since the heat output of each of the

heaters

90, 92 and 94 is variable, blanks 14 may be exposed to difierent temperatures within section 24.

Each of the

heaters

96,98 and 100 have platinum heating elements 102 disposed inparallel alignment with belt 44 in hollowed out portion '40 of-block 34. Suitable means such as a plurality of elongated insulating rods formed of refractory material and designated by the numeral 104 are provided within hollowed out portion 40 for supporting the platinum elements 102 of heaters 96, 98 and respectively, above the belt in heat transfer relationship thereto.

Another heater element 106 having a platinum resistance element 102 is disposed exteriorly of mufile 16 adjacent the breakover pulley for maintaining the oxidized blanks 12 at a predetermined temperature as they emerge from the outlet 22 and gravitate into an elongated upright liquid quench tank 108. A removable heavy metal equalizer plate 110 is mounted within muflie 16 in hollowed out portion 40 between

heaters

96, 98 and 100 and belt 44 passing thereunder to equalize the temperature along that section of belt 44 if desired. Plate 110 is removable either by providing an opening 112 at the outlet end of the muffle 16 or block 34' is constructed so that it is removable from block 36 and thus the plate 110 may be liftedthereoutof. Disposed in the hollowed out portion 38 of block 34 is heat exchanging structure designated broadly by the numeral 111 which includes a heat exchanger 114 which has a plurality of interconnected liquid coolant passages 116 therein and which are connected to a liquid coolant delivery conduit 118 and aliquid coolant return conduit 120. As seen in Fig. 4, a valve 122 is provided for controlling the rate of flow of liquid coolant to the exchanger 114. A liquid coolant system is provided for supplying coolant to the conduit 118. As is shown in Fig. 4 of the drawings, heat exchanger 114 and

the'associated conduits

118 and 120 are constructed so that they are shiftable vertically with respect to the belt 44.

Breakover pulley 52 contains an integral heater 121 for maintaining cells 12 at the proper temperature as they emerge from outlet 22 and drop into quench tank 108. Electrical energy is supplied to heater 121 from power lines 124 and 126 to the primary coil 128 of an adjustable transformer 130, the secondary coil 132 of which is connected to supply

lines

134 and 136 which are in turn connected to insulated graphite bearings such as 138. The platinum resistance element 140 is provided in the pulley to heat the same and has suitable electrical connection to bearings 138. An ammeter 142 is provided in line 134 and a volt meter 144 is connected to

lines

134 and 136 by virtue of

lines

146 and 148.

The electrical energy furnished to each element 102 is controlled by an adjustable transformer '150 having its primary coil 152 connected to power lines 124 and 126 and its secondary coil 154 connected to element 102 by

lead lines

156 and 158. Interposed in each line 156 is an ammeter 160, and a volt meter 162 is connected between

lines

156 and 158 by

lines

164 and 166. Motor 68 is also connected to power lines 124 and 126 by supply lines 168 and 170, and a small electric lamp 172 is connected to power lines 124 and 126 by virtue of

lead lines

174 and 176. As can be seen in Fig. 2 of the drawings, lamp 172 is disposed above mufiie 16 in alignment with an elongated slit between sections 24 and 26 which allows viewing of the blanks 14 as they pass through the mufiie on conveyor belt 44.

Temperature indicating devices

178, 180, 182, 184, 186, 188, 190, 192, 194 and 196, in the nature of thermocouples or resistance bulbs are located at various points in the apparatus and as shown in Fig. 2 of the drawings,

devices

178, and 182 are disposed adjacent the elements 102 of

heaters

90, 92 and 94 respectively,

devices

184, 186 and 188 are disposed proximate to exchanger 114,

devices

190, 192 and 194 are disposed

adjacent heaters

96, 98 and 100 respectively, and device 196 is disposed interjacent heater 106 and breakover pulley 52. Each of the temperature indicating devices is connected are then cooled to 500 C. to 700 C. by heat exchanger 114, maintained at that temperature by heaters 96,98

and. 100 in conjunction with plate 110, and finally discharged through outlet 22 and allowed to drop into tank 108 over breakover pull'ey 52.

It is now seen that means is provided for precisely controlling the oxidation of copper oxide cells 12 during all phases of theoperation'. When the proper heatingcooling curve for the particular copper stock being used is determined-such curve can be easily duplicated utilizing apparatus 10 as willhereinafter be described. As soon'as blanks 14 are conveyed into muffle 16' it is desirable to'raise their temperature rapidly. Thus element 102 of heater 90 is supplied with sufiicient power to bring blanks 14 to 1040 C. to 1060 C. quickly and, since'the reaction at this point'tends to become'exothermic, heaters 92 and'94 put out correspondingly less heat so that there is no tendency for incipient fusion to take place. However, it can be appreciated that if the particular heating-cooling curve being duplicated calls for a slow heating of blanks 14 to the maximum temperature, such may be easily accomplished by reducing the power input to element 102 of heater 90 and making corresponding increases in the power input to elements

1020f heaters

92 and 94. a p Following, coolingby heat exchanger 114,-blanks '14 enter the intermediate temperature zone of 500 C. to 700 C. which is equalized over its entire length by plate 110. In this respect it is to be noted that if the particular curve calls for a slow cooling of the blanks 14 tothe intermediate temperature, valve 122 of exchanger 114 may be closed, the plate 110 removed and power input to elements 102 of'

heaters

96, 98 and 100 varied accordingly. Also, the rate at which the blanks 14 are cooled to the intermediatetemperature can be varied considerably by merely regulating the flow of coolant to passages 116'by virtue of the valve 122. Alsoit is to be noted that the exchanger 114 can be reciprocated vertically in the hollowed outportion 38 and thus, the relative position of exchanger 114 with respect to blanks 14 on belt 44 may be changed according to the'heattransfer desired. This is a very important part of the present invention for the reason that heat flow from the blanks 14 to the cooler surface of the heat exchanger 114 is proportional to the inverse square of the spacing between them. Thus, minute changes in the amount of heat being transferred can be eflectedr g As to the liquid coolant used in the heat exchanger structure it has been found that a light viscosity-oil which permits operation of the significant lower surface of the heat exchanger at up to 380 C. without heating the coolant more than 200 C. is desirable, the difference in temperature between the coolant and the exchanger being effected because of the heat lag through the metalcomprising heat exchanger 1'14. 5 s Q The means for controlling the speed at which theblanks 14 are advanced through-mutfle 16 is also extremely important, because this controls the amount of time each blank 14 is'subjected to a. particular temperature. By utilizing a variable speed gear box '66 the speed of belt 44 may be accurately'adjusted and also the operation of slide 90 may be varied to supply blanks 14 to belt 44 in the proper time interval.

Furthermore, the exact temperature of each individual blank 14 maybe eflfectively controlled impeach zone of muffle 16 by virtue'of temperature indicating devices 178, 1-80, 182, 184, 186, 188, 190,192,194, and 196. Each of the

deViceS1

78, 180, 182, 190,'192:a11d194 316 dis posedwithin a fraction of an inch above the surface of to the intermediateor soaking furnace.

each blank '14 and a very accurate temperature of the surface of the blank is obtained. Also, device 184 is located proximate to the blanks 14 while device 186 is located-on theexternal surface of heat exchanger 114, thereby giving the temperature difierential between blanks 14 and exchanger 114. At the same time a device 188 is disposed within a passage 116 of exchanger 114', thereby giving 'a temperature differential reading between the external surface of exchanger 114 and the coolant passing therethrough. H v 3 7 It is to be noted that blanks 14 are disposed on belt 44 in slightly spaced relationship to prevent transfer of heat directly between the individual blanks by contact conduction. Thus each individual blank 14 is conveyed through precisely the same sequence of heating and cooling zones and must, therefore, receive identically the same heat treatment. Bycomparing the temperature-resistivity coefficient of platinum heaters 102 with the readings of .meters 200 it is possible-to very accurately control the exact temperature of each blank 14. The coeificient of the platinum elements 102 provides an indication of the average temperature of the sections of muffle 16 served .by the

respective heaters

90, 92, 94, 96, 98 and 100,

while the

devices

178, 180, 182, 184, 190, 192 and 194 provide temperature indications for a plurality of points along the length of passage 18.

V Blanks 14 are disposed on belt 44 with the side which is to be oxidized face up. .The opposite side of blank 14 from which the oxide will be subsequently removed, rests in contact with belt 44but, by virtue of the open weave thereof, oxide forms on both sides to an equal thickness.

It is also to be pointed out that the shape of the curve produced by a metal plate of a given size is greatly influenced by the thermal conductivity of the metal employed to fabricate such plate. Therefore, if the plate is made of, for example, nickel with'a thermal conductivity of 0.088 at 600 C., the curve will show an almost linear slope between 800 C. and 600 C. over that portion of the curve corresponding to the length of the plate. On the other hand, if the plate is made of silver, whose thermal conductivity is at least ten times as great, the curve will fall more quickly to 600 C. and be substantially flat over most of that portion represented by the length ofthe plate.

In passing through the plurality of zones within tnuflie 16, heat energy is addedto and/ or removed frorriblanks 14 by the mechanism of spherical radiation from a hotter to a cooler region. The quantity of heat transferred or removed in a given time is proportional to the temperature gradient, thus the process is influenced principally by the temperature gradients between the heated mufiie walls of passage 18, the cooled heat exchanger -114'and the blanks 14 as they are conveyed through the plurality of temperature zones in mufiie 16, and to a negligible degree by the low velocity air streams which are preferably directed through passage 18,in order to insure an adequate supply of oxygen. Since the elements 102 of proximity to the surface of blanks 14, spherical radiation.

to the blanks occurs with good efliciency and great uniformity, with little or no disturbance from unrelated causes which are present in the heating furnaces heretofore. employed and particularly present .whenlcopper oxide cells 12 are transferred from the oxidation furnace The provision of means for inclining the f Co with respect to the horizontal is of great significance because such inclination promotes the axial flow of the gaseous contents of the muflle by normal convection, and the introduction into the muflle of gaseous reagents other than atmospheric air or solid reagents, volatile at furnace'teniperatures, when desired to effect changesin-the electrical characteristics of the finished cells 12. As'shown itt Fig.

2 of the drawings, the proper air flow is in the direction of belt travel and the entire muflie 16 is usually inclined to place the discharge opening 22 in a slightly higher plane than the inlet opening 20, thus promoting convective movement of the gaseous contents of the muflie. The discharge opening 22 may be partially boxed in if desired, to avoid premature chilling of the workpieces by convective air currents.

The cooling rate of blanks 14 is readily controlled because of the position of heat exchanger 114 relative to the blanks on belt 44, the rate of removal of heat energy from blanks 14 being easily controlled by maintaining a given temperature gradient between heat exchanger 114 and the blanks 14. This gradient is readily established since the temperature of blanks 14 as they leave the maximum temperature zone and that of heat exchanger 1-14 are indicated by the

devices

184, 186 and 188.

It is now apparent that apparatus is provided for producing copper oxide cells 12 as long as copper blanks 14 are supplied to the apparatus, Since belt 44 moves at a constant speed, processed cells 12 are discharged from mufiie 16 at the same rate as copper blanks 14 are deposited on belt 44 by magazine 88. The capacity of a given apparatus can be increased by either a wider belt 44 or increasing the overall length of muffle 16 coupled with a corresponding increase in electric resistance heaters and heat exchangers. Although the mutfie structure shown in the drawings is adapted for heat transfer between plane surfaces that are substantially parallel, it is manifest that other types of mufiies may be constructed which are adapted for oxidizing any type of cell having varying surface characteristics but still utilizing the principles of the instant invention. For example, if large blanks 14, with preformed connecting lugs on both sides of which the oxide is formed, are to be oxidized, means would have to be provided to suspend the blanks from thee conveyor belt and transport them through a muffle design to transfer heat to or from such blanks.

Another feature of apparatus is that in processing cells 12 of the usual form, that is, fiat copper disks or annular rings, no supporting racks or fixtures are needed, this fact being of importance because in conventional furnaces where such supporting structure is employed, the racks and copper cells thereon are all quenched in the liquid tank, thereby causing contamination of the racks with mineral salts contained in the quench bath and necessitating cleansing of the racks prior to each use.

By provision of the elongated slot 206 between sections 24 and 26, visual inspection of blanks 14 on belt 44 is possible because of the reflected light of lamp 172 and serves as a double check on indications of the pyrometers, since the appearance of the formed oxide indicates the progress of the process up to this inspection point.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

1. In apparatus for producing a copper oxide cell having electrical rectifying characteristics by oxidation of substantially pure copper blanks, an elongated, refractory muflle having an inlet at one end thereof and an outlet at the opposite end thereof; a conveyor system for continuously advancing a plurality of blanks through the mufiie including a driving pulley mounted exteriorly of the muffle adjacent said inlet and a driven pulley mounted exteriorly of the mufile adjacent said outlet, an endless belt of refractory material passing over the pulleys and having aportion thereof passing through the muffle from the inlet to the outlet, said driving pulley being operably connected to a variable speed gear box, and a prime mover connected to said gear box for driving the belt at a predetermined speed; a pair of series of aligned heaters disposed parallel to said belt, each of the heaters including an electrical resistance element within the mufiie proximate to said belt, each of said elements being in circuit with an adjustable transformer for varying the supply of current thereto, and means for measuring the .10 supply of current from the transformer to the element, one of-said series being located adjacent said inlet for heating the blanks to an oxidizing temperature, and the other series being located adjacent the outlet for maintaining the blanks at a predetermined intermediate temperature; power means for supplying current to said transformer; structure for lowering the oxidized blanks to said intermediate temperature, said structure including a heat exchanger shiftably mounted within the mufiie proximate to said belt, and disposed interjacent the series of heaters, and conduit means adapted for delivering liquid coolant from a coolant system to said exchanger,

there being provided valve structure in said conduit means for regulating the delivery of coolant to the exchanger; a metal equalizer plate removably mounted in the muffie between the belts and said other series of heaters for uniformly distributing heat to the blanks disposed thereunder; and temperature sensing means for each heater respectively including a bulb disposed between the belt and a respective element, each of said bulbs being connected to a corresponding temperature measuring device whereby the temperature of a plurality of points within the muffle is accurately determined.

2. In apparatus for producing a copper oxide cell having electrical rectifying characteristics by oxidation of substantially pure copper blanks, an elongated muflie having an inlet and an outlet; endless conveyor mechanism for continuously advancing a plurality of blanks along a predetermined path of travel within the muflie from the inlet to the outlet, said conveyor mechanism including an endless belt of refractory material passing over a driving pulley and a driven pulley, each of the pulleys being disposed exteriorly of said muifle, the driven pulley being located adjacent the outlet opening and including an integral heater therein for maintaining the oxidized blanks at a predetermined temperature as they emerge from the rnufile, and said driving pulley being located adjacent the inlet opening and operably connected to a variable speed gear box, said gear box being joined to a prime mover whereby the speed of said belt may be controlled; a series of individually adjustable heaters within said muffle above the portion of the belt within said muflle, for heating the blanks to an oxidizing temperature; heat exchanging structure located along said path interjacent said series of heaters and the outlet for subsequently cooling said blanks to an intermediate temperature, said heat exchanging structure being shiftable substantially perpendicularly to said path of travel to predetermined positions above the belt; a series of individually adjustable heaters disposed along said path between the structure and the outlet for maintaining the blanks at said intermediate temperature, each of the heaters including an electrical resistance element disposed adjacent the mechanism and connected to an adjustable transformer for varying the supply of current to a respective element; temperature sensing means for each heater respectively and each including a heat sensing component disposed between the belt and a respective heater and a temperature indicating device connected to each of said components; and removable means mounted between the mechanism and said last mentioned series of heaters for uniformly distributing heat to blanks on said belt.

3. Apparatus as set forth in claim 2 wherein is provided a temperature sensing element adjacent said driven pulley whereby said integral heater may be regulated to maintain said driven pulley at a predetermined temperature.

References Cited in the file of this patent UNITED STATES PATENTS (Other references on following page) 11 UNITED STATES PATENTS Moore et a1. Dec. 27, 1932 Machlet Jan. 3, 1939 Conrad et a1 Mar. '17, 1942 Terry et a1 Sept. 21, 1943 Hein et a1. May 16, 1950 Briggs July 24, 1951 12 Taylor et a1 Oct. 14, 1952 'Skivesen' Oct. 6, 1953 Holcroft' Feb. 16, 1954 Ne Sbitt Oct. 12, 1954 -Coni1ey May 22, :1956 Besselm-gn et a1.'l June26, 1956 Stenzy June 26, 1956

Claims

1. IN APPARATUS FOR PRODUCING A COPPER OXIDE CELL HAVING ELECTRICAL RECTIFYING CHARACTERISTICS BY OXIDATION OF SUBSTANTIALLY PURE COPPER BLANKS, AN ELONGATED, REFRACTORY MUFFLE HAVING AN INLET AT ONE END THEREOF AND AN OUTLET AT THE OPPOSITE END THEREOF, A CONVEYOR SYSTEM FOR CONTINUOUSLY ADVANCING A PLURALITY OF BLANKS THROUGH THE MUFFLE INCLUDING A DRIVING PULLEY MOUNTED EXTERIORLY OF THE MUFFLEADJACENT SAID INLET AND A DRIVEN PULLEY MOUNTED EXTERIORLY OF THE MUFFLE ADJACENT SAID OUTLET, AN ENDLESS BELT OF REFRACTORY MATERIAL PASSING OVER THE PULLEYS AND HAVING A PORTION THEREOF PASSING THROUGH THE MUFFLE FROM THE INLET TO THE OUTLET, SAID DRIVING PULLEY BEING OPERABLY CONNECTED TO A VARIABLE SPEED GEAR BOX, AND A PRIME MOVER CONNECTED TO SAID GEAR BOX FOR DRIVING THE BELT AT A PREDETERMINED SPEED, A PAIR OF SERIES OF ALIGNED HEATERS DISPOSED PARALLEL TO SAID BELT, EACH OF THE HEATERS INCLUDING AN ELECTRICAL RESISTANCE ELEMENT WITHIN THE MUFFLE PROXIMATE TO SAID BELT, EACH OF SAID ELEMENTS BEING IN CIRCUIT WIUTH AN ADJUSTABLE TRANSFORMER FOR VARYING THE SUPPLY OF CURRENT THERETO, AND MEANS FOR MEASURING THE SUPPLY OF CURRENT FROM THE TRANSFORMER TO THE ELEMENT, OF ONE OF SAID SERIES BEING LOCATED ADJACENT SAID INELT FOR HEATING THE BLANKS TO-AN OXIDIZING TEMPERATURE, AND THE OTHER SERIES BEING LOCATED ADJACENT THE OUTLET FOR MAINTAINING THE BLANKS AT A PREDETERMINED INTERMEDIATE TEMPERATURE, POWER MEANS FOR SUPPLYING CURRENT TO SAID TRANSFORMER, STRUCTURE FOR LOWERING THE OXIDIZED BLANKS TO SAID INTERMEDIATE TEMPERATURE, SAID STRUCTURE INCLUDING A HEAT EXCHANGER SHIFTABLY MOUNTED WITHIN THE MUFFLE PROXIMATE TO SAID BELT, AND DISPOSED INTERJACENT THE SERIES OF HEATERS, AND CONDUIT MEANS ADAPTED FOR DELIVERING LIQUID COOLANT FROM A COOLANT SYSTEM TO SAID EXCHANGER, THERE BEING PROVIDED VALVE STRUCTURE IN SAID CONDUIT MEANS FOR REGULATING THE DELIVERY OF COOLANT TO THE EXCHANGER, A METAL EQUALIZER PLATE REMOVABLY MOUNTED IN THE MUFFLE BETWEEN THE BELTS AND SAID OTHER SERIES OF HEATERS FOR UNIFORMLY DISTRIBUTING HEAT TO THE BLANKS DISPOSED THEREUNDER, AND TEMPERATURE SENSING MEANS FOR EACH HEATER RESPECTIVELY INCLUDING A BULB DISPOSED BETWEEN THE BELT AND A RESPECTIVE ELEMENT, EACH OF SAID BULBS BEING CONNECTED TO A CORRESPONDING TEMPERATURE MEASURING DEVICE WHEREBY THE TEMPERATURE OF A PLURALITY OF POINTS WHITHIN THE MUFFLE IS ACCURATELY DETERMINED.