Patent Publication Number: US-7896060-B2

Title: Casting furnace

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of application Ser. No. 11/399,559, filed Apr. 6, 2006, which application claims the benefit of U.S. Provisional Application No. 60/669,480 filed Apr. 8, 2005, both of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to casting furnaces wherein a mold is transported to or from a vacuum chamber, or otherwise environmentally controlled chamber, for casting with a liquid material, such as liquid metal. 
     BACKGROUND OF THE INVENTION 
     A vacuum casting furnace is used to cast a liquid material, such as a molten metal alloy, into a mold. While referred to as a “vacuum” furnace, the furnace may cast in other controlled environments, such as an argon atmosphere. Generally a metal charge is placed in a crucible located in the controlled environment melt chamber and melted into a liquid by using a suitable energy source, such as electric induction power. A mold is transported to and from the melt chamber via a chamber serving as a controlled environment lock since it is generally desirous to maintain the melt chamber at vacuum while molds transition to and from the melt chamber. 
     There are methods to raise and lower a mold through a mold lock chamber to deliver the mold to the melt chamber, and to remove a filled mold from the melt chamber, respectively, wherein components of the mold transport system are located in the mold lock chamber. However the mold lock chamber presents a severely adverse environment for components of the mold transport system. When metal is poured, molten metal splatter can fall into the mold lock chamber and damage or degrade these components. Occasionally a mold will crack while in the melt chamber, or mold lock chamber, and metal leaking out of the mold can severely damage these components. Additionally the environment of the mold lock chamber is generally hot and contains particulate, which results in decreased life and increased maintenance of the components of the mold transport system. 
     One object of the present invention is to provide a mold transport system with components that are located outside of the casting furnace. 
     Another object of the present invention is to provide a mold transport system with components that are easily accessible and maintainable, and that will have a relatively long life even if installed in the casting furnace. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, the present invention is an apparatus for, and method of, producing a casting in a casting furnace having a controlled environment melt chamber in which a liquid metal is poured into a mold that is transported to the controlled environment melt chamber via a mold lock chamber by a mold transport system. The mold transport system comprises a rotary screw drive having a rotary screw and linear motion driven shaft element attached to the rotary screw. The rotary screw drive is located external to the casting furnace and on the side of the controlled environment melt chamber in one example of the invention. A drive means is provided to rotate the rotary screw. A lift shaft is attached to a linear motion guide element. The first end of the lift shaft is attached to the linear motion driven shaft element, and a support arm is attached at its first end near to the second end of lift shaft. A mold support structure, upon which a mold can be placed, is attached to the second end of the support arm. The linear motion driven shaft element moves along the longitudinal vertical axis of the rotary screw when the screw is rotated, which also raises or lowers the mold seated on the mold support structure. The lift shaft and first end of the support arm are disposed in a lift shaft housing that is connected to the mold lock chamber. The lift shaft housing may be attached to a wall of the mold lock chamber, or to a door located in a wall of the mold lock chamber. When so located in the door, the lift shaft can be detachably connected to the external linear motion driven shaft element so that when the door is opened the lift shaft, support arm, mold support structure, and a mold seated on the mold support structure, will protrude out of the mold lock chamber. The rotary screw drive may be a planetary rotary screw drive. In other examples of the invention, the rotary screw may be replaced by a hydraulic actuator. 
     In another aspect, the present invention is an apparatus for, and method of, producing a casting in a casting furnace having a controlled environment melt chamber in which a liquid metal is poured into a mold that is transported to the controlled environment melt chamber via a mold lock chamber by a mold transport system. The mold transport system comprises a cylinder screw drive having a hollow cylindrical screw with an interior threaded surface, and an externally threaded lift screw inserted in the cylindrical screw. A drive is provided to rotate the cylindrical screw, which causes the lift screw to move along the longitudinal axis of the cylindrical screw, whereby one end of the lift screw moves further into or out of a lift screw housing attached to the mold lock chamber. 
     A support arm is attached at its first end to the end of the lift screw in the lift screw housing. A mold support structure, upon which a mold can be placed, is attached to the second end of the support arm. The lift screw moves linearly along the longitudinal axis of the cylindrical screw when the cylindrical screw is rotated, which also raises or lowers the mold seated on the mold support structure. The lift screw housing may be attached to a wall of the mold lock chamber or a door located in a wall of the mold lock chamber. When so located in the door, when the door is opened the support arm, mold support structure, and a mold seated on the mold support structure, will protrude out of the mold lock chamber. 
     In another aspect, the present invention is an apparatus for, and method of, producing a casting in a casting furnace having a controlled environment melt chamber in which a liquid metal is poured into a mold that is transported to the controlled environment melt chamber via a mold lock chamber by a mold transport system. The mold transport system comprises a rack and worm screw drive wherein the teeth of the worm screw engage the teeth of the rack so that the worm screw travels linearly along the length of the rack when the worm screw is rotated. The worm screw is suitably attached to the first end of a support arm. A mold support structure, upon which a mold can be placed, is attached to the second end of the support arm so that the support arm, mold support structure, and mold seated on the mold support structure travel linearly along the length of the rack along with the worm screw. The rack and worm screw drive may be contained in a drive housing attached to a wall of the mold lock chamber, or to a door located in a wall of the mold lock chamber. When so located in the door, when the door is opened, the support arm, mold support structure, and a mold seated on the mold support structure, will protrude out of the mold lock chamber. 
     These and other aspects of the invention are set forth in this specification and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustrating the invention, there is shown in the drawings a form that is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. 
         FIG. 1(   a ) is a cross sectional side elevational view of one example of the casting furnace of the present invention. 
         FIG. 1(   b ) is a front elevational view with partial cross section of the example of the casting furnace in  FIG. 1(   a ). 
         FIG. 1(   c ) is a cross sectional view of the example of the induction casting furnace in  FIG. 1(   a ) through line A-A with additional illustration of furnace doors in the opened position. 
         FIG. 1(   d ) is a detail of one means of connection between the linear lift drive element and lift shaft used in the casting furnace shown in  FIG. 1(   a ) through  FIG. 1(   c ). 
         FIG. 2(   a ) is a side elevational view with partial cross section of another example of the casting furnace of the present invention. 
         FIG. 2(   b ) is a front elevational view with partial cross section of the example of the casting furnace in  FIG. 2(   a ). 
         FIG. 2(   c ) is a cross sectional view of the example of the induction casting furnace in  FIG. 2(   a ) through line B-B with additional illustration of doors in the opened positions. 
         FIG. 3(   a ) is a cross sectional side elevational view of another example of the casting furnace of the present invention. 
         FIG. 3(   b ) is a cross sectional view of the example of the induction casting furnace in  FIG. 3(   a ) through line C-C with additional illustration of doors in the opened positions. 
         FIG. 4(   a ) is a cross sectional side elevational view of another example of the casting furnace of the present invention. 
         FIG. 4(   b ) is an elevational view of the rack and worm screw drive used with the example of the casting furnace in  FIG. 4(   a ). 
         FIG. 4(   c ) is a cross sectional view of the example of the casting furnace in  FIG. 4(   a ) through line D-D with additional illustration of a mold lock chamber door in the opened position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like numerals indicate like elements, there is shown in  FIG. 1(   a ) through  FIG. 1(   d ) one example of the casting furnace  10  of the present invention. A controlled environment melt chamber, also referred to as melt chamber  12 , contains crucible  14  (shown in solid lines in upright position and dashed lines in pouring position) for holding a liquid metal. The controlled environment may be a contained atmosphere, such as an argon atmosphere pumped into the chamber, or a vacuum. For convenience the controlled environment melt chamber is further referred to as a melt chamber and the process as a vacuum pour. Metal may be melted in crucible  14  by electric induction or other suitable heating means, or liquid metal may be poured into the crucible from an external source before the chamber is sealed for a pour. Mold  90  is inserted into melt chamber  12  by vertically lifting the mold through the mold lock chamber, which is positioned below the melt chamber. In  FIG. 1(   a ) mold  90  is shown in solid lines in the melt chamber and dashed lines in a second position in mold lock chamber  16 . 
     Suitable heating means may optionally be provided to keep the mold at a desired temperature during the pouring process and/or the withdrawal of the mold from the melt chamber. For example electric induction power may be used by surrounding mold  90  with susceptor material  18  while it is in the melt chamber. Induction coil  92  surrounds the susceptor material and an ac current flowing through the coil inductively heats the susceptor material. The induction coil is shown in cross section  FIG. 1(   a ) as a series of vertical circles on either side of the susceptor material. Heat generated in the susceptor heats the mold by convection. When inserted into the melt chamber for a pour, the opening in sprue  90   a  of the mold aligns with the opening in cover  18   a  that is placed over the mold so that liquid metal can be poured into the mold from the crucible. Means can be provided for rotation and translation, if necessary, of the crucible during a pour. 
     In other examples of the invention the mold heating means may not be required. In this case the mold will be lifted to enable a pour of liquid metal into the mold. In this case the mold may not necessarily be raised completely out of the mold lock chamber into the melt chamber, but sufficiently raised to allow pouring in the mold. Further in other examples of the invention the mold heating means may be provided near the top of the mold lock chamber so that only the sprue of the mold protrudes into the melt chamber. 
     In one non-limiting example of the invention, metal charge is placed in crucible  14 . A vacuum is drawn in melt chamber  12 . Sealable opening  22  provides a means for entry and exit of a mold into the melt chamber. Hatch or valve  23 , shown in the position when sealable opening  22  is opened, pivots and raises to seal around the perimeter of opening  22  when a mold is not in the melt chamber. A suitable power drive can be provided to operate valve  23 , such as hydraulic drive  20  (illustrated in  FIG. 2(   a )), which can be mounted on the outer surface of a wall of the mold lock chamber. 
     Mold lock chamber  16  can also be maintained at vacuum when opening  22  is opened. Door  25  (best seen in  FIG. 1(   c )) in one wall of the mold lock chamber pivots open to allow entry or removal of a mold from the mold lock chamber as further described below and is sealed closed when the mold lock chamber is at vacuum. 
     Referring to  FIG. 1(   a ) a rotary screw drive is located in drive housing  42 . The drive housing is located external to the casting furnace, and in this example of the invention, on the side of the melt chamber, which is above the mold lock chamber. Locating the drive in this position physically isolates it from the environment of the mold lock chamber and allows convenient access to the drive, for example, for maintenance. In this non-limiting example of the invention the drive housing is attached to the side of the melt chamber. Connecting means are provided to connect roller  44 , which serves as a linear motion driven shaft element, to the top of lift shaft  46 . Lift shaft  46  moves vertically in and out of lift housing  48  through sealing element  49 . In this non-limiting example of the invention, the lift housing is attached to the exterior of door  25 . The bottom of lift shaft  46  is suitably attached to one end of structural support arm  41  upon which mold support structure  24  is mounted. Rotary drive means, such as electric motor  50 , is used to rotate threaded rotary screw  40 , which, in turn, causes roller  44  to raise or lower around screw  40 , depending upon the rotational direction of the screw, since the roller is threadably connected to screw  40 . Other suitable drive means, such as a hydraulic motor, may be used. Rotary screw  40  is only shown partially threaded along its axial length for convenience in  FIG. 1(   a ). Generally rotary screw  40  is threaded substantially along its entire axial length. Since roller  44  is attached to the lift shaft, raising or lowering of the roller will also raise or lower lift shaft  46 , support arm  41 , mold support structure  24  and mold  90  sitting on the mold support structure. As most clearly illustrated in  FIG. 1(   b ) drive housing  42  and enclosed rotary screw drive components are vertically offset from lift housing  48  and enclosed components (shown partially in solid lines in the closed door position and in dashed lines in the door opened position). 
     In  FIG. 1(   a ) mold  90  and lift elements, such as mold support structure  24 , support arm  41 , lift shaft  46 , roller  44 , and linear slide bearings  54  are shown in dashed lines when the mold support structure is in its lowest position in the mold lock chamber, and in solid lines when the mold support structure is in its highest position with mold  90  seated on the support structure and in position for a pour. Linear slide rail  52  is attached to the back interior wall of lift housing  48 . One or more linear slide bearings  54 , which are attached to the lift shaft, are slidably attached to the linear slide rail. This connection provides one non-limiting means for keeping vertical movement (raising and lowering) of the mold in alignment relative to the melt and mold lock chambers. Bellows boot  56  may be optionally provided around the lift shaft. 
     Optional openings for access to various components of the furnace may be disposed around the sides of the furnace. Referring to  FIG. 1(   c ), as previously mentioned, door  25  is provided in a first wall of the mold lock chamber to provide a means for insertion or removal of a mold from the chamber. Melt chamber hatch or door  60  provides closure for an opening located in a wall of the melt chamber that is above a second wall of the mold lock chamber. Optionally crucible  14  may be attached to door  60  so that the crucible protrudes from the melt chamber when the door is opened. Rear access hatch or door  62  provides closure for an opening located in a third wall of the mold lock chamber, which is the side of the mold lock chamber opposite door  25 . In  FIG. 1(   c ) the doors and associated components are shown in solid lines in the closed position and in dashed lines in the opened position. 
       FIG. 1(   d ) illustrates the details of one non-limiting example of providing the connecting means between roller  44  and lift shaft  46  wherein the connection automatically uncouples when door  25  pivots to the opened position. Angle element  72  is attached to gusset backing plate  74 . The angle element and backing plate are attached directly or indirectly to plate  76  sitting on top of roller  44  and around rotary screw  40  so that when the roller is raised or lowered, as described above, the angle element and backing plate will also be raised or lower. An opening or slot in the horizontal region of angle element  72  provides an opening for insertion of rod or ball  78 , which is attached directly or indirectly to the top of lift shaft  46 . With this arrangement, when door  25  is in the closed position, ball  78  is retained in the slot in the angle element causing the lift shaft to raise and lower with movement of roller  44 . When door  25  is swung open, ball  78  exits the slot in the angle element to disconnect the lift shaft from the roller disposed in the drive housing mounted external to the mold lock chamber. Consequently the lift shaft, support arm  41 , mold support structure  24  and mold  90  seated on the support structure (if any) swing out and away from the furnace when door  25  is opened. This facilitates maintenance and replacement of these items that are directly or indirectly mounted to door  25 , and also facilitates placing a mold on the support structure, or taking a mold off of the support structure. 
     A chill plate may be provided as an interface between the bottom of the mold and mold support structure  24  upon which the mold sits. The chill plate is typically used to keep the bottom of the mold at a relatively low temperature to assist in solidification of a liquid metal poured into the mold. Optionally, for example, tubing  94  and  96  for supply and return of a cooling or heating medium, such as water, from the exterior of the furnace to internal passages in the chill plate may be routed through a vacuum seal at the top of the lift shaft and through the interior of the lift shaft when the lift shaft has a hollow interior. Other components, such as thermocouples, that require tubing or wiring from the exterior of the furnace to components on the mold support structure may also be made through the interior of the lift shaft. 
     There is shown in  FIG. 2(   a ),  FIG. 2(   b ) and  FIG. 2(   c ) another example of the casting furnace of the present invention. This example is generally similar to the example illustrated in  FIG. 1(   a ) through  FIG. 1(   d ) except that lift shaft  46 , support arm  41 , mold support structure  24  and associated components are in lift housing  48  that is attached to wall  16   a  of the mold lock chamber and not to a door as in the example above. Molds are loaded onto, or taken off of, the mold support structure through an opening in another wall of the mold lock chamber, such as wall  16   b  ( FIG. 2(   c )). Door  25   a  provides a means for closing the opening to seal the mold lock chamber. 
     By way of example and not limitation, the rotary screw drive used with the embodiments of the invention illustrated in  FIG. 1(   a ) through  FIG. 1(   d ), and  FIG. 2(   a ) through  FIG. 2(   c ) may be a planetary roller screw, such as but not limited to, PRS Series Planetary Roller Screws available from Exlar, Corp., Chanhassen, Minn. In these embodiments, a plurality of roller screws are provided between one or more rollers  44  (or nuts) and rotary screw  40 . The one or more rollers are suitably connected to the top of lift shaft  46 . 
     In the above examples of the invention, drive housing  42  is attached to a wall of the melt chamber. In other examples of the invention the drive housing may be attached directly to the top of lift housing  48  or structural elements separate from the casting furnace. Alternatively, in other examples of the invention, the lift drive housing  42  and associated components may be inverted from the position shown in  FIG. 1(   a ) and mounted on the mold lock door. In this arrangement, the top of lift shaft  46  would be suitably attached to rollers  44  (or nuts) on the inverted rotary screw  40  so that when the rotary drive means rotates screw  40 , which, in turn, causes roller  44  to raise or lower around the screw, and the lift shaft, support arm, mold support structure, and mold sitting on the mold support structure will also be raised or lowered in similar fashion as that in the above examples of the invention. 
     While the above examples of the invention illustrate one rotary screw drive, two or more rotary screw drives and lift shafts may be used in the invention. For example, a pair of drives and lift shafts may be located on opposing sides of the furnace to lift both ends of the support arm. 
     In the above examples of the invention, the rotary screw drive may be replaced by a linear hydraulic actuator. The output rod or shaft of the hydraulic actuator would be attached to the first end of the lift shaft, in place of the linear motion shaft driven element used in the rotary screw drive. In this arrangement, the linear hydraulic actuator is located external to the casting furnace. Motion of the output shaft causes a mold seated on the mold support structure in the mold lock chamber to be raised or lowered since, similar to the arrangements with the rotary screw drive, the output shaft is attached to the lift shaft, which in turn, is attached to the support arm, mold support structure. 
     There is shown in  FIG. 3(   a ) and  FIG. 3(   b ) another example of the casting furnace of the present invention. In this arrangement cylinder screw drive housing  42   a  is provided external to the casting furnace. Generally the cylinder screw drive comprises a hollow cylindrical element, wherein the interior surface of the hollow cylindrical element is threaded, and an externally threaded screw. The externally threaded screw is threadably connected to the interior threaded surface of the cylindrical element, either directly or indirectly, for example, via worm screws as described above. Rotating the cylindrical element will cause the threaded screw to either protrude from or recede into the hollow cylindrical element. The cylindrical element is housed in drive housing  42   a  in  FIG. 3(   a ). Suitable drive means, such as electric motor  50   a  is used to rotate the cylindrical element. Depending upon the direction of rotation externally threaded screw  43  either moves in or out of the cylindrical element in the drive housing and, correspondingly, out or in of lift screw housing  48   a . Externally threaded screw  43  is only shown partially threaded along its axial length for convenience in the figures. Generally the externally threaded screw is threaded substantially along its entire axial length. Drive housing  42   a  and/or threaded screw  43  penetrate the lift screw housing through suitable seal  49 . One end of threaded screw  43  is suitably connected to an end of structural support arm  41  upon which mold support structure  24  is mounted. Consequently rotating the cylindrical element of the cylinder screw drive will result in the support arm, mold support structure, and mold  90  seated on the mold support structure to raise or lower within the mold lock chamber. 
     Features of the inventions illustrated in  FIG. 1(   a ) through  FIG. 1(   c ) and described above, may be used in other examples of the invention wherein the rotary screw drive is replaced with the cylinder screw drive. In the cylinder screw drive embodiments, the end of the threaded screw is connected directly to the support arm. Consequently there is no need for connecting means illustrated by example in  FIG. 1(   d ) for the rotary screw drive. In  FIG. 3(   a ) and  FIG. 3(   b ) cylinder screw drive housing  42   a  is mounted directly to the top of lift screw drive housing  48   a  and the lift screw drive housing is attached to door  25   b . In other arrangements of the invention the lift screw drive housing and enclosed components may be attached to a sidewall of the mold lock chamber. 
     Further while the examples of the invention illustrated in  FIG. 3(   a ) and  FIG. 3(   b ) illustrate one cylinder screw drive, two or more cylinder screw drives may be used in the invention. For example, a pair of cylinder screw drives may be located on opposing sides of the furnace to lift both ends of the support arm. 
     There is shown in  FIG. 4(   a ) through  FIG. 4(   c ) another example of the casting furnace of the present invention. In  FIG. 4(   a ) selected components are shown in two positions, namely, the position wherein mold  90  is supplied to melt chamber  12 , and the position wherein mold  90  is at its lowest position in the mold lock chamber. Components in the latter position are illustrated in dashed lines. In this arrangement a rack and worm screw drive is used to raise or lower mold  90  in mold lock chamber  16 . The drive can be located in drive housing  48   c , which is connected to the mold lock chamber. The teeth of worm screw  31  mesh with the teeth of rack  33 . The worm screw is suitably attached to shaft  35  so that when the shaft rotates the worm screw moves up or down on the shaft depending upon the direction of rotation. Drive  50   b  provides suitable drive means for rotating shaft  35 . One end of support arm  41   a  is attached to the worm screw so that it is raised or lowered as the worm screw moves up or down on the shaft. Since the support arm is attached to mold lift support structure  24  and mold  90  seated on the mold support structure, the motion of the worm screw will cause a mold to be lifted through the mold lock chamber for pour of a liquid metal into the mold from crucible  14  in the melt chamber and lowered through the mold lock chamber after the pour has been completed. 
     In one non-limiting example of the invention a rotary ball spline, type LTR, available from THK America, Inc., Schaumburg, Ill., is used for shaft  35 . The type LTR rotary ball spline comprises a spline shaft and nut  37 . The nut has inner and outer cylindrical components. The inner cylindrical component is attached to the spline shaft so that it rotates with rotation of the spline shaft and is free to move along the axial length of the shaft. The outer cylindrical component is attached to the inner cylindrical component by ball bearings so that the outer cylindrical component will move along the axial length of the shaft with the inner component, but without rotating about the shaft. In the present example of the invention the worm screw is attached to the inner cylindrical component and the end of support arm  41   a  is connected to the outer cylindrical component. 
     Means can be provided to keep the support arm, mold support structure and any mold sitting on the support structure in alignment as these components are raised and lowered through the mold lock chamber. One example of such means is best illustrated in  FIG. 4(   c ). Linear slide rails  52   a  and  52   b  are suitably attached to opposing sides of drive housing  48   c . One or more linear slide bearings  54   a  and  54   b  are attached to opposing sides of support arm  41   a  and slidably attached to the linear slide rails. 
     Optionally conduit  51  may be provided to contain tubing  94  and  96  and other components as previously described above for other examples of the invention. One end of the conduit terminates at support arm  41   a  while the other end terminates outside of the furnace. The conduit penetrates the top of the drive housing through suitable seal  49   a  and protrudes from, or recedes into the mold lock chamber as the support arm is raised or lowered, respectively. 
     Drive housing  48   c  may be connected directly to a sidewall of the mold lock chamber or to a door provided over an opening in a sidewall.  FIG. 4(   c ) illustrates an arrangement wherein the drive housing is connected to door  25   c . In  FIG. 4(   c ) the door, with associated drive housing, is shown in solid lines in the closed position and in dashed lines in the opened position. Optional melt chamber hatch or door  60  provides closure for an opening located in a wall of the melt chamber. 
     Further while the examples of the invention illustrated in  FIG. 4(   a ) through  FIG. 4(   c ) illustrate one rack and worm screw drive, two or more rack and worm screw drives may be used in the invention. For example, a pair of drives may be located on opposing sides of the furnace to lift both ends of the support arm. 
     In any examples of the invention the controlled environment melt chamber and mold lock chamber may be of modular design so that a mold lock chamber may be used with more than one controlled environment melt chamber by providing suitable interface connecting means between the controlled environment melt chamber and the mold lock chamber. For example the mold lock chamber may be provided with wheels as a means for moving the mold lock chamber between controlled environment melt chambers. 
     The above examples of the invention have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the invention has been described with reference to various embodiments, the words used herein are words of description and illustration, rather than words of limitations. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may effect numerous modifications thereto, and changes may be made without departing from the scope and spirit of the invention in its aspects.