Abstract:
A combustion tube mounting system releasably mounts a combustion tube to an aperture in the floor of a furnace housing. The combustion tube has a base assembly with a cam and can be manually or automatically unlocked by cam pins in the floor for selectively engaging the cam for lowering the combustion tube from the floor of the furnace. When a new combustion tube is placed on the lower seal assembly and raised, it automatically aligns and engages the upper furnace seal and engages cams on the floor of the furnace housing which lock the combustion tube in place as it is introduced into the furnace.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/889,628, filed Sep. 24, 2010, entitled E ASILY  R EMOVABLE  C OMBUSTION TUBE , which claimed priority under 35 U.S.C. §119(e), and the benefit of U.S. Provisional Application No. 61/245,732 entitled E ASY  R EMOVABLE  C OMBUSTION TUBE , filed on Sep. 25, 2009, by Gordon C. Ford, et al., the entire disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a combustion furnace for an analyzer and particularly to the removable mounting of a combustion tube therein. 
         [0003]    The combustion of inorganic solid samples using an induction furnace requires a pressurized oxygen-rich environment. A quartz combustion tube is typically used to maintain this pressurized environment but becomes coated with byproducts of combustion during the combustion process. The quartz tube must be cleaned and eventually replaced to maintain the accuracy of sample results. The mounting of a combustion tube in existing furnaces equipped with an auto cleaner is both time consuming and cumbersome, requiring that fluid fittings and electrical connections be removed and the auto-cleaner device removed from the combustion tube area of the furnace. The combustion tube is removed from the front of the furnace housing once the disassembly has been completed. Once a new combustion tube has been installed, the furnace has to be reassembled, frequently including the connection of fluid couplings which can lead to leaks in the system if not properly accomplished. Thus, the maintenance, removal and replacement of combustion tubes in existing furnaces is difficult, time consuming, and leads to downtime for the operation of an analyzer. 
         [0004]    Accordingly, there exists a need for an improved analytical combustion furnace in which a combustion tube can be readily accessed without disconnecting fluid fittings, auto-cleaners, or the like from the furnace assembly. 
       SUMMARY OF THE INVENTION 
       [0005]    The system of the present invention accomplishes this goal by providing a combustion tube mounting system in which the combustion tube is removably installed through an aperture in the floor of the furnace housing. The combustion tube can be manually or automatically unlocked from the floor of the furnace housing by a cam-locking mechanism for positioning the combustion tube in an open area of the furnace below the furnace housing for easy removal and replacement. 
         [0006]    In a preferred embodiment, a combustion tube includes a base seal assembly which is placed on the lower seal assembly and raised to automatically align with the upper furnace seal. Cams in the floor of the furnace housing engage a cam associated with the base seal assembly to lock the combustion tube in place as it is raised into the furnace housing. As a result of this downwardly removable combustion tube, the steps of disassembling the furnace components, including the self-cleaning mechanism located above the combustion tube, is eliminated as is the necessity for skilled technicians to replace the combustion tube. An operator can easily unlock the combustion tube from the furnace and lower it for access and replacement. 
         [0007]    These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a front perspective view of a furnace embodying the present invention; 
           [0009]      FIG. 2  is an enlarged front perspective view of the furnace housing with the cover removed showing the combustion tube locking mechanism in an unlocked position; 
           [0010]      FIG. 3  is a perspective view of the combustion tube with its base seal assembly; 
           [0011]      FIG. 4  is an exploded perspective view of the base seal assembly; 
           [0012]      FIG. 5  is a cross-sectional view of the assembled base seal assembly; 
           [0013]      FIG. 6  is a front perspective view of the furnace shown with the locking mechanism in an unlocked position; 
           [0014]      FIG. 7  is a partial front perspective view of the furnace shown in  FIG. 6 , shown with the cover removed; 
           [0015]      FIG. 8  is a front perspective view of the furnace shown in  FIG. 7 , showing the lowering and raising of the combustion tube through an aperture in the furnace housing floor; 
           [0016]      FIG. 9  is a front perspective view of the furnace shown in  FIG. 8 , showing the combustion tube lowered from the furnace housing in a position for removal/replacement; 
           [0017]      FIG. 10  is a bottom perspective view of the furnace housing; 
           [0018]      FIG. 11  is a left front exploded perspective view of the furnace housing and locking mechanism for the combustion tube; 
           [0019]      FIG. 12  is a right front perspective view of the assembled furnace housing; 
           [0020]      FIG. 13  is a fragmentary vertical cross-sectional view of the cam locking mechanism for the combustion tube; 
           [0021]      FIG. 14  is a fragmentary vertical cross-sectional view of a combustion tube shown in a locked position within the floor of the furnace housing; and 
           [0022]      FIG. 15  is a fragmentary vertical cross-sectional view showing the combustion tube in an unlocked position for removal. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    Referring initially to  FIG. 1 , there is shown an analyzer  10  which includes an induction furnace assembly  20 , including the auto cleaning mechanism  30  described in detail in U.S. Provisional Patent Application Ser. No. 61/373,014, filed Aug. 12, 2010, entitled C OMBUSTION  F URNACE  A UTO  C LEANER , the disclosure of which is incorporated herein by reference. The analyzer components themselves can be similar to those employed in a carbon sulfur analyzer, Model No. CS600, available from Leco Corporation of St. Joseph, Mich. The analyzer  10  is shown in  FIG. 1  with the cover shrouds removed to expose the components of the induction furnace, which are also shown in  FIGS. 2-5 . The detachable auto cleaner assembly  30  is removably mounted by a bayonet connection to a heated filter assembly  40 , which is sealably secured at  65  to the top wall  51  of combustion housing  50 . Housing  50  additionally includes side walls  53  and  55 , an interface back wall  57 , and floor  58 , as best seen in  FIGS. 7-12 . The housing  50  is mounted to structural base  17  of the analyzer  10 , which includes housing  50 . The front of furnace housing  50  is enclosed by a quickly removable door  52 , which, when removed as seen in  FIG. 2 , exposes an induction coil  61  which surrounds a combustion tube  60  ( FIG. 7 ) in a conventional manner to heat an analytical specimen held in a ceramic crucible  14  ( FIG. 1 ) when introduced into the hot zone of combustion tube  60  by vertically movable pedestal  12 . Tube  60  is sealably coupled to the lower end of filter assembly  40  by an upper seal assembly  65  in a conventional manner. The pedestal  12  ( FIG. 1 ) for holding a sample-holding crucible  14  is positioned on a cup-shaped lower seal assembly  16  and is raised and lowered into combustion tube  60  by means of a pneumatic cylinder  18  and cylinder rod  22  ( FIG. 7 ) coupled to assembly  16 . In the position shown in  FIG. 1 , the cylinder rod  22  is in a lowered retracted position within cylinder  18 . 
         [0024]    A combustion tube base assembly  80  ( FIGS. 3-5 ) sealably couples the lower end of tube  60  to lower seal assembly  16  such that, during combustion of a sample, oxygen flows upwardly through a gas inlet in assembly  16  to sweep byproducts of combustion into gas outlet  13  ( FIG. 1 ) for analysis. Oxygen is also supplied to the upper end of combustion tube  60  by an oxygen inlet  15  and suitable passageways to an inlet lance to direct oxygen into crucible  14  during combustion. Housing  50  includes cam-actuated locking assembly  100  which cooperates with base assembly  80  to allow the combustion tube  60  to be easily withdrawn from underneath the floor of combustion housing  50 , as described later. 
         [0025]    Combustion tube  60  can be a conventional quartz combustion tube available from Leco Corporation, Part No. 619-590-775 or its equivalent. The combustion tube, as seen in  FIGS. 3-5 , includes a base assembly  80  having a generally cylindrical collar  82  with a central aperture  81  therein for receiving the combustion tube  60 , as seen in  FIG. 3 . Near the upper edge of collar  82  is an annular recess  83  for receiving an O-ring seal  84 . A locking cap  85  is threaded onto collar  82  and compresses the O-ring seal once the combustion tube has been inserted therein for sealably holding the combustion tube within the collar  82 . Collar  82  includes a lower cylindrical sleeve  86  having internal annular recess  87  for receiving a second O-ring  88  for sealing the base assembly  80  onto the lower seal assembly  16 . Further, the assembly  80  includes a metal RFI shield  89  and a third sealing O-ring  78  ( FIGS. 14 and 15 ) positioned within an annular recess  91  of collar  82 . 
         [0026]    Collar  82  includes a cam  90  which has an outer annular vertical surface  92 , an upper chamfered surface  94  chamfered upwardly and inwardly at an angle of about 45° from the vertically extending annular surface  92  and a lowered chamfered surface  96  inwardly and downwardly beveled at an angle of about 45° from surface  92 . The two surfaces thus form an angle of about 90° between them to fit (as described below with respect to  FIG. 14 ) within a 90° slot  107 . Collar  82  also includes an annular flange  93  having a diameter greater than aperture  59  in furnace housing floor  58  to engage the undersurface of floor  58  when the combustion tube is in an installed locked position as seen in  FIG. 14 . The cam  90  so-defined interengages with the cam pins  106  and  108  of cam-actuated assembly  100  for locking and unlocking the combined combustion tube  60  and base assembly  80  (shown in  FIG. 3 ) as now described. 
         [0027]      FIGS. 7-15  illustrate the removal of the combustion tube  60  from the furnace housing  50  and, for purposes of clarity, the induction coils and other parts unnecessary to the description of the cam-actuated combustion tube mounting arrangement have been deleted from these figures. Also, in  FIGS. 7-10 , the pneumatic actuators for automatically operating the cam-actuated assembly  100  are not shown as these figures are primarily for the purpose of illustrating the motion of the combustion tube during its removal and replacement.  FIGS. 7-9  illustrate the motion of the combustion tube when cylinder  18  is moved to a retracted position once the cam-actuated assembly  100  has been moved to an unlocked position allowing, as seen in  FIG. 8 , the combustion tube to be lowered through the circular aperture  59  ( FIG. 10 ) in the floor  58  of furnace housing  50 . When lowered to a position as seen in  FIG. 9 , the combustion tube  60  and base assembly  80  can be lifted from the lower seal assembly  16  and combustion tube  60  replaced with a new combustion tube by loosening locking ring  85 , allowing the tube to be removed from the base assembly  80 . The cam-actuated assembly  100  cooperates with the cam  90  of the combustion tube base assembly  80  to form a releasable locking mechanism to lockably hold and alternately release the combustion tube  60  from below the furnace housing  50 . 
         [0028]    Assembly  100  is used for either manually or automatically unlocking the combustion tube  60  (and attached base assembly  80 ) from the combustion housing  50  as best seen in  FIGS. 11-15 . Floor  58  of combustion housing  50  includes a pair of blind cylindrical apertures  102  and  104 , which rotatably receive cam pins  106  and  108  of mechanism  100 . Apertures  102  and  104  are formed and sized to intersect opposite edges of aperture  59  in floor  58  and are positioned such that generally V-shaped 90° slots  107  on the inner-facing edges of pins  106  and  108  are exposed through openings  111  in the so truncated cylindrical side wall of aperture  59 . Springs  110  and  112  engage the inner ends of pins  106  and  108 , which are retained within the apertures  102  and  104  by a mounting plate  114  secured to the front face  116  of floor  58  by fasteners  118  extending through apertures  120  in mounting plate  114 . A pair of manually actuated handles  122  and  124  are pinned to apertures  123  and  125 , respectively, near the ends of cam pins  106 ,  108 , such that pins  106  and  108  can be manually rotated by the manipulation of the operator of handles  122  and  124  rotating them inwardly, as seen, for example, in  FIGS. 7-10 , to an unlocking position. Springs  110 ,  112  urge handles  122 ,  124  into concave recesses  113 ,  115  on the inner facing surface of plate  114  urging them into a releasable locked position (FIGS.  1  and  12 - 14 ). In the unlocked position illustrated in  FIG. 15 , the handles are rotated out of recesses  113 ,  115  rotating the 90° slots  107  of pins  106  and  108  to a position in which surfaces  105  and  109  of slots  107 , which normally engage the chamfers  94  and  96  on cam  90  of assembly  80 , respectively, release cam  90  allowing, as seen in  FIG. 15 , the combustion tube  60  and base assembly  80  to be lowered downwardly in the direction indicated by arrow A for removal when in the position shown in  FIG. 9 . Surfaces  105  and their tip junction with cylindrical pins  106  and  108  also urge against chamfer  94  of cam  90  to assist in freeing base assembly  80  and combustion tube  60  downwardly from floor  50 . 
         [0029]    The cam-actuated combustion tube releasing assembly  100  can either be manually actuated by an operator squeezing the handles  122 ,  124  toward one another to rotate pins  106 ,  108  and release the combustion tube  60  or the operation can be automated. For such purpose, floor  58  includes a pair of arcuate recesses  130  and  132  forwardly of aperture  59  in floor  58  and which communicate with apertures  102  and  104  to expose apertures  127  and  129  ( FIG. 11 ) on pins  106  and  108 , which receive actuator pins  131  and  133 . Pins  131 ,  133  extend upwardly from floor  58  and can be engaged, as best seen in  FIGS. 12 and 13 , by actuator rods  140  and  142  of pneumatic cylinders  141  and  143 , respectively. Cylinders  141  and  143  are secured within recesses  150  in the side walls  53  and  55  of the housing  50  by fasteners  145  in a conventional manner. Thus, the cam-actuated assembly  100  can either be manually entered by the operator engaging handles  122  or  124  or electrically by the actuation of cylinders  141  and  143  to rotate the pins  106  and  108  from a locking position, shown in  FIG. 14 , to an unlocked position, shown in  FIG. 15 . When in the unlocked position, the combustion tube and its seal assembly can be dropped downwardly utilizing cylinder  18  to lower the combustion tube  60  into the position shown in  FIG. 9  where it can be removed from the furnace housing and replaced. 
         [0030]    Once the combustion tube has been replaced with a new tube and mounted to the base assembly  80 , the cylinder  18  can then be actuated, reversing the process by raising the combustion tube in an upwardly direction, as seen in  FIG. 8 , to a locked position shown in  FIG. 1 . As the combustion tube is raised through aperture  59 , the surface  94  of cam  90  engages the camming surface  105  on pins  106  and  108  rotating them when combustion tube  60  is moved in the direction opposite arrow A in  FIG. 15 , to again move the locking pins  106 ,  108  to the locked position illustrated in  FIG. 14 . In this position, surfaces  105 ,  109  on pins  106 ,  108  engage the chamfered surfaces  94 ,  96 , respectively, of cam  90  and securely hold the combustion tube  60  in place with the flange  93  of the base assembly engaging the lower surface of floor  58  of the furnace housing  50 . As seen in  FIG. 15 , the pins  106  and  108  extend sufficiently outwardly through slots  111  in the cylindrical side wall of aperture  59  so as to engage cam  90 . 
         [0031]    It will become apparent to those skilled in the art that various modifications to the preferred embodiment of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.