US 3860738 A
In a vacuum oven for firing such ceramic materials as false teeth, a sealing plate is pneumatically reciprocable into and out of sealing engagement with a bottom opening in a vertical firing chamber of the oven, with a carrier for the ceramic material being mounted on the sealing plate and spaced therefrom to carry the material into the chamber when the sealing plate is moved vertically upwardly. A slow closing movement is made possible by providing an additional, crank driven lifting element programmed to be vertically reciprocable between a first position in detachable engagement with the sealing plate and a second position vertically removed therefrom, in which position the pneumatic downward reciprocation rapidly opens the oven for removal of the fired material.
Description (OCR text may contain errors)
United States Patent 11 1 1111 3,860,738
Hintenberger Jan. 14, 1975 1 FIRING OVEN FOR CERAMIC MATERIAL 3,641,250 2 1972 Hintenberger 13/31  Inventor: Karlmntenbergermogersm 4 3,655,941 4/1972 Schaum ..219/390 F kf t ran Ur am Mam Germany Primary Examiner-Velodymyr Y. Mayewsky 1 1 Flledi 1973 Attorney, Agent, or Firm-Kurt Kelman Appl. No.2 340,719
Related U.S. Application Data Continuation-in-part of Ser. No. 246,642, April 24, 1972, abandoned.
Foreign Application Priority Data Apr. 27, 1971 Germany 2120592 References Cited UNITED STATES PATENTS 4/1964 Hintenberger 13/31 4/1969 Eicker 13/20  ABSTRACT In a vacuum oven for firing such ceramic materials as false teeth, a sealing plate is pneumatically reciprocable into and out of sealing engagement with a bottom opening in a vertical firing chamber of the oven, with a carrier for the ceramic material being mounted on the sealing plate and spaced therefrom to carry the material into the chamber when the sealing plate is moved vertically upwardly. A slow closing movement s ma Q b x ranki anaddit on crank driven lifting element programmed to be vertically reciprocable between a first position in detachable engagement with the sealing plate and a second position vertically removed therefrom, in which position the pneumatic downward reciprocation rapidly opens the oven for removal of the fired material.
2 Claims, 1 Drawing Figure FIRING OVEN FOR CERAMIC MATERIAL This is a continuation-in-part of my copen'ding application Ser. No. 246,642, filed Apr. 24, 1972, now abandoned.
The present invention relates to an improvement in an electrically heated oven for firing ceramic material, particularly in the manufacture of false teeth, wherein the oven comprises a thermally insulated and vacuumtight shell defining a vertical firing chamber therein.
My U.S. Pat. No. 3,641,250, dated Feb. 8, 1972, describes and claims a furnace for firing a ceramic object, which comprises a shell defining a chamber therein, the shell having a closed top and a bottom opening connecting the chamber with the ambient atmosphere, a firing zone adjacent the closed top, a sealing plate mounted outside the shell in alignment with the chamber opening for pneumatically operable movement into sealing engagement with the chamber opening, a pneumatic cylinder receiving compressed air, a piston defining an axial bore affixed to the sealing plate and glidable in the cylinder, the piston being actuated under the pressure of the compressed air to move the sealing plate into the sealing engagement, evacuating means for withdrawing air from the chamber when the opening is sealed, a carrier for the object between the sealing plate and the chamber opening, a piston glidable in the sealing plate piston bore and affixed to the carrier, and a constricted orifice in the sealing plate piston for admitting a controlled amount of the compressed air into the axial bore to move the carrier piston in respect of the sealing plate piston.
In such a furnace, the firing temperature in the firing zone need not be lowered each time the firing chamber is charged since the double-acting pistons for the carrier and the sealing plate control the carrier movement so that the object dwells for a certain time in the vacuum zone before it enters the firing zone proper.
However, this arrangement has the disadvantage that the pneumatic lifts for the sealing plate and the carrier make it difficult to lift the sealing plate and the carrier with the ceramic object slowly, i.e., in about 6 minutes, through a relatively short path, and then to move them down rapidly into the cooling position after the ceramic object has been fired in the furnace. Hydraulic means could be used to achieve this but this would involve relatively complex and correspondingly expensive structures while being undesirable, due to possible leaks in the hydraulic circuit and the general instrumentation of the apparatus.
It is accordingly an object of the invention to provide an oven of the generally indicated type but which automatically assures a slow movement of the ceramic material into the firing chamber while rapidly removing the fired material therefrom, the fully automatic operation making it possible for unskilled personnel to operate the oven, the only task of the operator being the placing of the ceramic material on the carrier and the removal of the fired material therefrom.
The above object is accomplished in accordance with this invention by providing an additional, mechanically driven element for the sealing plate, the element being arranged to be vertically reciprocable between a first or operative position in detachable supporting engagement with the sealing plate and a second or rest position vertically spaced therefrom, and programming means for reciprocating the lifting element between these positions.
In this arrangement, the mechanically driven lifting element slowly lifts the sealing plate while in supporting engagement therewith, the lifting stroke raising the object on the carrier, which moves with the sealing plate whereon it is mounted, about mm in about 6 minutes to place the object at the end of the stroke into the firing zone. After firing has been completed and the lifting element has been moved into the rest position, the pneumatically operable rod supporting the sealing plate assures a rapid downward movement thereof to avoid excessive firing of the object. The downward movement of the sealing plate is dampening when it again engages the lifting element in the second position thereof, i.e., when the sealing plate comes to rest on the lifting element while being pneumatically lowered.
In the accompanying drawing, the single FIGURE shows a schematic side view, partly in section, of the firing oven, including a diagrammatic illustration of the controls for automatically operating the oven.
The illustrated firing oven is generally conventional and comprises a shell 22 lined with thermally insulating fire bricks 23 defining a vertical firing chamber 24 which is surrounded by an electrical resistance heater 25. As shown, the shell has a closed top and a bottom opening connecting the firing chamber 24 with the atmosphere. A sealing plate 20 is mounted outside the shell in alignment with the chamber opening. Carrier 5 for ceramic materials to be fired is mounted on the sealing plate and spaced therefrom to carry the ceramic material into the firing chamber when the sealing plate is moved vertically upwardly, the carrier moving in unison with the sealing plate whereon it is mounted.
Relatively rapid vertical reciprocation of the sealing plate into and out of sealing engagement with the firing chamber opening may be effected by means of a pneumatic cylinder and piston drive, this drive comprising a cylinder 2 receiving piston 2a for glidable reciprocation therein, the piston rod 4 extending from the piston to the sealing plate which is fixed thereto to support the plate for vertical reciprocation upon supply and withdrawal of pressure fluid to and from cylinder 2.
For the slow lifting of the sealing plate into sealing engagement and the correspondingly slow movement of the carrier with the ceramic material into the firing zone, the invention provides a lifting rod 6 which is arranged to be vertically reciprocable between an operative position (shown) wherein the upper rod end 6' is in supporting engagement with the sealing plate and a rest position vertically spaced therefrom, wherein the pneumatic drive may rapidly move the sealing plate 20 and carrier 5 downwardly so as to enable an operator to remove the fired material from the carrier outside the oven. The lifting rod 6 is guided within two brackets 2, 2" affixed to cylinder 2.
The lifting rod 6 is mechanically driven, the illustrated mechanical drive being a crank drive 12 comprising a connecting rod 21 linked to the lifting rod 6 and a crank moving in a circular path 12' during reciprocation of the lifting rod.
As shown, the oven shell 22 is mounted on a control box 26 by means of steel columns 26', the abovedescribed controls and the programming means to be described hereinafter being mounted in the control box.
The oven is operated as follows:
Before a firing cycle begins and with the oven still open, inert gas is supplied to the firing chamber 24 to flood this chamber, the inert gas being fed from pressure cylinder 11 through supply conduit 11a which is connected by a suitable valve means, such as the illus trated tandem solenoid valves 17 and 16, to branch conduit 11b leading into main conduit 27 which leads into the firing chamber through the shell wall and fire brick lining of the oven. A gas pressure regulator controls the pressure of the inert gas fed into the firing chamber, and a timer or timing clock 7 is set to control the operation of solenoid valves l6, l7 electrically connected to the timer which opens the valves when it is desired to flood the firing chamber with inert gas. It should be understood that the present invention is equally useful in ovens of this type which are operated without an inert gas supply. I
A second timer or timing clock 3 is provided for control of the evacuation and sealing of the firing chamber. The timer has two operating switches 3a and 3b for controlling the chamber evacuation and sealing. Switch 3a is electrically connected to the control circuit for pump 1 and switch 3b is electrically connected to the control circuit for the operation of crank drive 12. Timer 3 controls evacuation of the firing chamber and slow sealing thereof by operation of the crank drive. Actuation of push button switch 3b starts operation of the crank drive to lift the sealing plate 20 slowly into sealing engagement with the oven opening, the sealing plate being pushed up by lifting rod 6, the crank reaching and actuating limit switch 8 when the sealing plate engages the oven opening in the highest position of rod Switch 3b is connected electrically to a servomotor (not shown) for driving the crank, the connecting rod 21 slowly lifting the rod 6 to push the sealing plate 20 from its lowermost position, when the sealing plate rests on'top, or close to the top, of control box 26, to the illustrated sealing engagement with the firing chamher opening of the oven. As the crank moves in its circular path, it reaches limit switch 8 coincident with the sealing engagement of plate 20 with the oven'operat- As shown, the input of vacuum pump 1 is'connected to evacuating conduit la which is connected to main conduit 27 through solenoid valve '19. Operation of switch 8 connected to timers 3 and 7, which are respectively connected electrically to valve 19 and valves 16, 17, opens valve 19 after valves l6, 17 have been closed so that the pump begins evacuation of firing chamber 24 through conduit 27. Simultaneously, the evacuated gaseous fluid is pumped through output conduit 1b which delivers pneumatic pressure fluid into cylinder 2, throttling valves 18 and 14 in conduit 1b controlling the flow of the fluid to determine the amount of fluid supplied to the cylinder. In this manner, the piston 2a is pressed upwardly and keeps plate 20 in sealing engagement with the oven opening while the crank continues its movement from switch 8 to limit switch 9 during which stage the lifting rod is lowered by the crank drive out of engagement with the sealing plate. Check valve 15 in conduit lb maintains the fluid pressure in the cylinder 2 during this stage of operation, i.e., the firing period.
Timers 3 and 7 are set so that, about 1 minute before the end of the firing period, valve 19 is closed and valves l6, 17 are opened so that evacuation of the firing chamber stops and inert gas is again supplied thereto. Finally, at the end of the firing period, the timers will operate limit switch 9 to stop operation of pump 1 and close the inert gas supply valves 16, 17. Pressure fluid will slowly bleed out of cylinder 2 through throttle valve 14, fluid return through conduit lb being prevented by check valve 15, and the sealing plate 20 with the fired object on carrier 5 will descend to begin the cooling period. Meanwhile, the crank continues moving in its circular path from limit switch 9 to limit switch 13, supporting the sealing plate during its descent when the plate has been lowered pneumatically into supporting engagement with end 6' of lifting rod 6. Thus, a relatively slow descent of the sealing plate during the cooling period is assured. When the crank reaches switch 13, the servomotor for the crank drive is stopped and the firing cycle is ended. Actuation of push button switch 3b initiates a new cycle.
When it is desired to close the oven rapidly to avoid heat losses, push button switch 3a is actuated while switch 3b remains open and the crank drive accordingly remains inoperative. A relay (not shown) is interposed in the electrical connection of switch 30 to pump 1 to start the pump and thus deliver pneumatic fluid to cylinder 2 to move the sealing plate relatively rapidly into closing engagement with the oven opening while the oven chamber is partially evacuated. When the vacuum in the chamber has reached a set degree, it will operate another relay in the control circuit for pump 1 so that valve 19 will be closed and the pump operation terminated. Thus, the oven will remain closed with a partial vacuum therein during intervals in the firing operation and undue heat losses from the oven will be avoided.
When it is desired rapidly to open the oven chamber, timer 7 closes valve 16, the partial vacuum in the oven chamber is reduced and the sealing plate descends, the rapidity of the lowering being controlledby throttle valvel4.
lclaimz y 1. In an oven for firing ceramic mate,rial', which' comprises an electrical circuit operable with a pneumatic circuit,.a thermally insulated and vacuum-tight electrically heated shell defining ,a vertical firing chamber therein, the shell having a closed top and a bottom opening connecting the chamber with the ambient atmosphere, a'se'aling plate mountedoutside the. shell in alignment with the chamber opening, a pneumatically operable lifting rod supporting the sealing plate and vertically reciprocable to move the sealing plate into and out of sealing engagement with the chamber opening, evacuating means for withdrawing air from the firing chamber when the chamber opening has been sealed, and a carrier for the ceramic material mounted on the sealing plate and spaced therefrom to carry the ceramic material into the chamber when the sealing plate is vertically upwardly moved, the improvement of an additional, mechanically driven lifting element for the sealing plate, the additional mechanically driven lifting elementbeing arranged to be vertically reciprocable between a first position in detachable engagement with the sealing plate and a second position vertically removed therefrom, and programming means for reciprocating the additional mechanically driven lifting element between said positions, said programming means having a crank drive linked to the additional mechanically driven lifting element.
2. In the oven of claim 1, the crank driven including a crank passing through a circular path during reciprocation of the lifting element, and limit switches mounted in said circular path.
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