Patent Publication Number: US-2012031891-A1

Title: Furnace

Description:
The present invention relates to a furnace for the firing of dental prostheses or partial dental prostheses. 
     Such furnaces as a rule have a firing chamber, a heating device for the heating of the firing chamber and a firing tray arranged within the firing chamber during firing. In conventional furnaces, a lifting mechanism can be provided, for example, which serves for raising and lowering the firing tray to move it between a loading position and a firing position. 
     An important property of furnaces of the initially named kind is a simple and safe operability in order, on the one hand, to allow an economically efficient operation of the device and, on the other hand, to ensure the safety of the operator. In addition, it is of great importance that a homogeneous temperature distribution is present at least in a region in which the dental prosthesis or partial dental prosthesis to be fired is located in the firing process. 
     It is therefore an object of the present invention to provide a furnace which is easy and safe to operate and which simultaneously provides reliably good firing results. 
     This object is satisfied by a furnace having the features of claim  1 . 
     The furnace in accordance with the invention of the initially named kind additionally has, beside the lifting mechanism, a moving mechanism by which the firing tray is movable with an open firing chamber between a lifting position and a loading position laterally offset thereto. 
     In other words, the mechanism provided for the loading of the furnace includes components which allow a lateral movement of the firing tray in a horizontal plane and a vertical movement perpendicular thereto. A loading of the firing tray is simplified by the lateral movement since said firing tray—unlike loading mechanisms which only comprise a lifting mechanism—is also easily accessible from above, for example. After the loading of the firing tray in the loading position, it is moved into a lifting position. The firing chamber is open during this process. Subsequently, a vertical movement—raising or lowering—of the firing tray is initiated to move the firing tray into the firing chamber until the firing material is located in a predefined position in the interior of the firing chamber. The firing chamber is preferably closed by the vertical movement. 
     It is efficiently prevented by the vertical and lateral offset between the loading position/unloading position of the firing tray and the firing chamber that the operator comes too close to the firing chamber, which may in particular still be very hot after a firing process under certain circumstances. The embodiment of the furnace in accordance with the invention described above can moreover be implemented in a very compact configuration from a construction aspect. 
     In accordance with an embodiment of the furnace, the firing tray is arranged on a platform, with the platform in particular having at least one thermally insulating component which at least functionally forms a section of the firing chamber or a closure of a loading opening of the firing chamber. For example, the platform is a base or a top of the firing chamber and essentially has the same insulation as the rest of the firing chamber. Provision can, however, also be made that the firing chamber is provided with a loading opening which does not include the whole base region of the firing chamber and which can be closed by a platform acting as a kind of stopper. It is generally also possible that the platform includes a section of the firing chamber, for example, a lower half of the firing chamber, so that the platform not only includes a base of the firing chamber, but also a part of the side walls of the firing chamber. The firing chamber is thereby divided into two, with one part of the firing chamber being able to be raised or lowered with respect to the other part to open the firing chamber. The construction height of the furnace can thereby be reduced. The thermally insulating component can in another respect be made up of a plurality of individual parts to be able to provide the desired insulating properties. 
     The firing tray can be a table-like structure, for example, which includes a table top and a frame, in particular of ring shape, on which the table top is arranged. The ring-shaped frame can have cut-outs in order also to allow a radiation connection at the lower side of the table top of the firing tray, whereby an improved temperature distribution is achieved in the region of the firing material to be fired. 
     The platform is in particular releasably connectable to the lifting unit and/or to the moving mechanism. It lies, for example, only on the named components. It is thus possible also to load the platform separately from the furnace or to wait and only to bring it into connection with the lifting unit and/or the moving mechanism when the furnace is in use. The lifting unit and the moving mechanism are in particular designed such that the platform is transferred from the moving mechanism to the lifting unit, or vice versa, during the feeding process. 
     The thermally insulating component of the platform can have sealing segments which are associated with sealing segments of an insulation of the firing chamber which are complementary thereto. They can, for example, be provided by a suitable embodiment of the section of the insulating component and of the corresponding regions of the insulation of the firing chamber which are in contact with the insulating component with a closed firing chamber. The insulating components can, for example, have a step which cooperates in an exactly fitting manner with a step of complementary design at the insulation of the firing chamber to close it and to prevent the arising of cold bridges as much as possible. 
     A safety device can be provided for the avoidance of incorrect operations of the furnace, said safety device being configured such that the lifting unit can only be activated when the moving mechanism is in a predefined position. Alternatively or additionally, the safety device can be configured such that the moving mechanism can only be activated when the lifting unit is in a predefined position. The safety device can, for example, have mechanical guide elements which serve for the aforesaid purpose. IT is also additionally or alternatively possible to provide sensors which detect the position of the lifting unit or of the moving mechanism and forward it to a control unit to be able to control the moving mechanism or the lifting unit accordingly. 
     A locking device can furthermore be provided which is configured such that the moving mechanism can be locked in at least one predetermined position and/or such that the lifting unit can be locked in at least one predetermined position. The locking device can have a pivotable blocking element which is pivotable into or out of a blocking position by a vertical movement of the firing tray and/or of the platform to secure or release the moving mechanism. 
     The lifting unit preferably includes a scissor lifting mechanism which can in particular be driven by a spindle drive. Such a mechanism or drive is compact and reliable. 
     The furnace in particular has a housing which surrounds the firing chamber, the firing tray and—at least in the closed state of the furnace—the lifting unit and the moving mechanism, with the housing preferably having a housing section separated at least partly from the remainder of the housing by a partition wall. The housing section is arranged laterally offset to the firing chamber so as to be influenced less pronouncedly by heat escaping from the firing chamber on an opening thereof. The housing section also accepts means for the actuation and/or control of the lifting unit and/or of the moving mechanism. 
     A handle can be provided for the actuation of the moving mechanism which is coupled with the platform and which is movable, in particular pivotable, in dependence on the lifting position between an engagement position and a rest position. The position of the handle thus indicates the position in which the platform is located. The handle preferably has an operational surface which is biased against an actuation section of the platform and which is configured such that the handle is automatically pivotable at least partly into an interior of a housing of the furnace by a movement of the platform in the direction of the firing chamber. The operator is in particular reliably prevented from opening the furnace when the handle is pivoted so far into the housing from a predefined lifting position of the platform onward that its actuation is no longer easily possible. 
     The operational surface can have a latch section which is in contact with the actuation section of the platform in a lower end lifting position of the firing tray to secure the position of the handle with respect to the housing of the furnace. 
     The invention further relates to a furnace for the firing of dental prostheses or partial dental prostheses having a firing chamber, a heating device for the heating of the firing chamber and a firing tray arranged within the firing chamber during firing, in particular in accordance with at least one of the embodiments described above. 
     In accordance with the invention, the heating device includes one or more heating elements, with all the heating elements of the heating device—that is the one heating element or all of the plurality of heating elements—being arranged, in the position of use of the furnace, above a plane which is called the firing material plane and in which firing material to be fired is arranged in a loaded state of the furnace. 
     This means that all the heating elements are located above the dental prostheses or partial dental prostheses to be fired with a closed heating chamber—relative to a position of use of the furnace. A comparatively large region can thereby be provided in an efficient manner in which the temperature distribution is homogenous and corresponds to the respectively applicable process instructions. In addition, the firing chamber can be given a compact design in such an arrangement of the heating elements, in particular when all the heating elements are arranged in an upper third of the firing chamber, preferably in each case in direct proximity to an inner side wall and/or a top of the firing chamber. A further advantage is that a feeding of the firing chamber can easily be realized from below in this type of construction. 
     The heating device can include at least two heating elements which are arranged in a substantially horizontal plane to achieve a homogeneous temperature distribution. 
     The heating elements can be made elongate, in ring-shape or helical to be able to produce a desired temperature distribution in the firing chamber. Combinations of differently designed heating elements are also conceivable to provide a heating device suitable for the respective firing chamber. 
     The heating element or—if a plurality of heating elements are provided—the heating elements can be arranged at least partly laterally offset to the firing tray with respect to a vertical projection of the firing tray to prevent material falling from the heating element(s) from falling directly onto the firing material and contaminating it. 
     To utilize the heat output of the heating elements as efficiently as possible and simultaneously to keep the firing chamber small and therefore able to be heated homogeneously more easily, an inner side wall of the firing chamber which extends parallel to the at least one, preferably elongate, heating element can have a slanted extent at least sectionwise with respect to a vertical. 
     Further features of the invention are set forth in the description, in the claims and in the drawings. 
    
    
     
       An embodiment of the present invention will be described in the following purely by way of example with reference to the enclosed drawings. There are shown: 
         FIGS. 1 to 5  sectional drawings through an embodiment of the furnace in accordance with the invention in respective different respective states. 
     
    
    
       FIG. 1  shows a furnace  10  with a firing chamber  12  which can be heated with the help of two elongate heating elements  14  arranged parallel and perpendicular to the plane of the drawing. A sensor  16  is provided to monitor the temperature in the firing chamber  12  and is connected to control electronics  18  which in turn control the heating elements  14  in dependence on the signals of the sensor  16  and on a DESIRED temperature value preset by a firing program. 
     The firing chamber  12  is surrounded by an insulation layer  20 . The insulation layer  20  is—as can be seen in FIG.  1 —composed of a plurality of different components to screen the environment from the high temperatures in the interior of the firing chamber which occur in a firing process of dental ceramics. 
     In the condition shown, the firing chamber  12  is open at the bottom to enable a feeding of the fuel chamber  12  from this side. The feeding of the firing chamber  12  takes place by a moving mechanism  22  and a lifting mechanism  24 . The moving mechanism  22  is made in the manner of a drawer. In the condition shown, a base section of the firing chamber  12  serving as a closure and having a firing tray arranged thereon is not yet arranged on the moving mechanism  22 . A locking device  26  is provided to secure the moving mechanism  22  in the position shown and to enable a loading thereof. The locking device  26  includes a left-hand and a right-hand two-armed pivot lever  28  and  28 ′ respectively which were pivoted into the position shown due to gravity alone in the situation shown. A right hand arm  28   a  of the pivot lever  28 ′ cooperates with an abutment  30  to prevent the moving mechanism  22  from being able to be moved into a housing  32  of the furnace  10 . 
     A housing door  34  at which a grip  36  is pivotably supported is arranged at the moving mechanism  22 . The grip  36  is automatically pivoted inwardly by the effect of a biasing device (not shown). 
       FIG. 2  shows the furnace  10  still in an open state. However, unlike the situation in  FIG. 1 , a base section  38  is now arranged on the moving mechanism  22  and serves for the closing of the firing chamber  12  at the base side. The base section  38  is made in table top form and includes a recess in which a firing tray  40  is arranged on which a firing material (not shown) to be fired can be arranged. The firing tray  40  includes a table top  42  and a crown-shaped frame  44  which is essentially formed by a ring which has U-shaped cut-outs  44 ′ at its upper side. The cut-outs  44 ′ make it possible that heat radiation can also impact the table top  42  obliquely from below, whereby a more uniform heating of the firing material arranged thereon is produced in the firing process. 
     The base section  38  has an insulation layer  20 ′ which is made in a comparable manner to the insulation layer  20  of the upper part of the firing chamber  12 . The insulation layer  20 ′ has a step  46  which ensures, together with a step of the insulation layer  20  (not shown) made in a complementary manner, a good thermal insulation of the firing chamber  12  in the closed state. 
     The right-hand pivot lever  28 ′ was pivoted by the placing of the base section  38  onto the moving mechanism  22  so that the pivot lever arm  28   a  is no longer in contact with the abutment  30  and the moving mechanism  22  can thus be pushed into the housing  32  of the furnace  10  in a similar manner to a drawer. 
     The grip  36  was moreover outwardly pivoted when the base section  38  was placed on to indicate that the moving mechanism  22  is now loaded and to give an operator the opportunity also to be able to operate it comfortably. The pivoting of the grip  36  is produced by a cooperation of an actuation section  48   m  which is made from Teflon, for example, and which is arranged at the base section  38  with an operational surface  50  formed at the grip  36 . As can be seen in  FIG. 1 , a lower section of the operational surface  50  has a latch section  52  which ensures that the base section  38  is not tilted on a pushing movement of the moving mechanism  22  by means of the grip  36 , which would be the case if the actuation section  48  were in contact with the operational surface  50 . The latch section  52  is, for example, a surface which is vertical—with respect to the position of the handle  36  shown in FIG.  2 —or a surface which extends slightly obliquely to the vertical from the bottom left to the top right. 
       FIG. 3  shows the furnace  10  in a condition in which the moving mechanism  22  has reached an end abutment with respect to a horizontal movement. The base section  38  is now located beneath the firing chamber  12  and has to be raised to close it at the base side and to bring the firing tray  40  into the suitable position for the firing of the firing material. A securing device can be provided which ensures that a lifting movement of the base section  38  can only be initiated when the end abutment is reached. 
       FIG. 4  shows the furnace  10  in a snapshot during the lifting movement of the base section  38 . The base section  38  which previously lies on the moving mechanism  22  now lies on a lifting plate  54  which is raised by a scissor lifting mechanism  56  of the lifting mechanism  24  which is in turn actuated by a spindle drive  60  driven by a motor  58 . It was made possible by the raising of the base section  38  for the pivot levers  28 ,  28 ′ to pivot, with the left hand pivot lever  28  now preventing, in cooperation with the abutment  30 , an inadvertent actuation of the moving mechanism  22 . 
     It can furthermore be recognized that the grip  36  folds into the housing interior due to the bias acting on the grip  36  and to the cooperation of the actuation section  48  with the operational surface  50  to indicate that the base section  38  is in a lifting movement. The moving mechanism  22  is admittedly—as described—secured by the left hand pivot lever  28  and the abutment  30  against an inadvertent actuation; however, the safety of the furnace  10  is additionally improved by this visual indication of the position of the base section  38 . 
       FIG. 5  shows the furnace  10  with a closed firing chamber  12 . The base section  38  now closes the firing chamber  12  and the firing tray  40  is located in a position in which the firing material (not shown) lying on the table top  42  is located in a region which has a homogeneous temperature distribution in the firing process. 
     The heating elements  14  are arranged outwardly offset somewhat with respect to a vertical projection of the table top  12  to prevent material which may release from the heating elements  14  under certain circumstances from falling onto the firing material. Due to the lateral offset of the heating elements  14 , which are essentially arranged in a plane directly beneath the top of the firing chamber  12 , the firing chamber  12  is wider in the region of the heating elements  14  than in the region of the table top  42 . The side walls of the firing chamber  12  associated with the heating elements  14  therefore have side wall sections  62  inclined with respect to a vertical. 
     A compact construction of the furnace  10  can be realized by the feeding of the firing chamber  12  from below. In the embodiment shown, the base section  38  is a closure of the firing chamber  12  over its total base region. An advantage of this construction is that the furnace  10  can be given a comparatively compact design in the vertical direction. The minimal stroke of the base section  38 , which has to be covered on the opening of the firing chamber  12  so that the firing material can be safely removed therefrom, is namely only defined by the spacing between the upper edge of the firing material on the firing tray  40  and the lower edge of the insulation layer  20 . It is, however, understood that the firing chamber  12  can also have an opening at the base side which does not include the total base region of the firing chamber  12  so that parts of the base of the firing chamber  12  are connected together with a corresponding insulation at least partly fixedly to the side walls of the firing chamber  12 . It is alternatively also possible to provide a partition of the firing chamber  12  in which an upper part remains fixedly in the housing, while a lower part, which includes sections of the side walls and the total base of the firing chamber  12 , is moved on the opening of the firing chamber  12 . This construction is characterized by a particularly small minimal stroke, in particular when the sections of the side walls associated with the lower part project beyond the upper edge of the firing material in the vertical direction. 
     It can furthermore be seen from  FIG. 5  that the grip  36  was now completely pivoted into the housing  32  to indicate clearly, also visually, the present operating state. 
     An opening of the firing chamber  12  after a firing of the firing material has taken place substantially includes an actuation of the described component in reverse order. The motor  58  provides, via the spindle drive  60 , that the scissor lifting mechanism  56  moves the lifting plate  54 , and thus the base section  38 , downwardly until it is again seated on the moving mechanism  22 . The grip  36  is in this respect gradually pivoted outwardly. As soon as the base section  38  is again seated on the moving mechanism  22 , the left hand pivot lever  28  again releases it so that the drawer-like moving mechanism  22  can be pulled out of the housing  32  with the help of the grip  36 . 
     The electronics  18  required for the operation of the furnace  10  are arranged in a housing section  64  which is separated by a partition wall  66  from a part of the housing receiving the firing chamber  12 , the moving mechanism  22  and the lifting mechanism  24 . The motor  58  is also arranged in the housing section  64 . The housing section  64  is arranged laterally offset with respect to the firing chamber  12  so that it is not impinged directly by a heat current which escapes from the firing chamber  12  on an opening thereof after a firing process. The partition wall  66  provides a sufficient thermal decoupling even if it does not thermally separate the housing section  64  from the remainder of the housing  32 . The volume of the housing  32  is sufficiently large to receive the heat escaping on the opening of the firing chamber  12  so that the furnace  10  overall does not heat up excessively. 
     REFERENCE NUMERAL LIST 
     
         
           10  furnace 
           12  firing chamber 
           14  heating element 
           16  sensor 
           18  control electronics 
           20 ,  20 ′ insulation layer 
           22  moving mechanism 
           24  lifting mechanism 
           26  locking device 
           28 ,  28 ′ pivot lever 
           28   a  pivot lever arm 
           30  abutment 
           32  housing 
           34  housing door 
           36  grip 
           38  base section 
           40  firing tray 
           42  table top 
           44  frame 
           44  cut-out 
           46  step 
           48  actuation section 
           50  operational surface 
           52  latch section 
           54  lifting plate 
           56  scissor lifting mechanism 
           58  motor 
           60  spindle drive 
           62  side wall section 
           64  housing section 
           66  partition wall