Abstract:
An automatic cleaning assembly for an analytical furnace is detachable from the filter chamber above the combustion tube. The cleaning assembly includes a rotating brush which is lowered through the filter chamber and into the combustion tube while a vacuum is drawn through the lower seal of the combustion tube. This results in a higher vacuum pressure differential and improved flow rate for removing dust from the filter of the furnace and the combustion tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) and the benefit of U.S. Provisional Application No. 61/373,014 entitled C OMBUSTION  F URNACE  A UTO  C LEANER , filed on Aug. 12, 2010, by Gordon C. Ford, et al., the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a combustion furnace for an analyzer and particularly to an automatic cleaning system. 
     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. Additionally, a filter is typically positioned adjacent the combustion tube and in the analyte gas stream to eliminate combustion debris which could degrade downstream analytical components. In one furnace system, a specimen is placed in a crucible which is positioned within the combustion tube and heated by an induction coil for the combustion of the specimen. The gases emitted therefrom are subsequently analyzed for determining one or more constituent elements of the specimen. The combustion tube so used is capable of many cycles of operation; however, after each combustion, oxides and other contaminants typically expelled during the combustion process tend to coat the interior of the tube. Thus, through the analytical process, the combustion tube and filter become coated with dust and residue debris of combustion. Removal of these combustion byproducts is essential in maintaining quality analytical results, as well as extending sample throughput. 
     The cleaning of the combustion tube and an associated filter requires moving wire brushes through the internal surfaces of the combustion tube and filter. U.S. Pat. No. 4,234,541 issued Nov. 18, 1980, discloses an early design in which a manually manipulated brush was employed to loosen debris from the filter and combustion tube, which debris is subsequently collected. 
     In current designs, dust and combustion residue is collected on a vacuum dust door enclosing the lower end of the combustion tube when the crucible pedestal and lower seal assembly are lowered. In this prior art design, a manifold communicates with the combustion tube and is coupled to a vacuum source as a non-rotating cleaning brush is linearly extended through the filter and combustion tube. The debris is then transferred to a collection box. With this design, when cleaning is complete, the vacuum dust door swings open to allow for another analysis cycle. However, too often, a combustion crucible falls into the vacuum dust door and the door becomes jammed. If this occurs, the operator must partially disassemble and repair the system prior to continuing with additional analyses. Also, with the prior art design, the vacuum dust door and/or the lower seal cup can plug due to accumulation of combustion byproducts, requiring manual cleaning. 
     Accordingly, there exists a need for an improved analytical combustion furnace in which cleaning of the filter and tube are better managed. 
     SUMMARY OF THE INVENTION 
     The system of the present invention accomplishes this goal by providing a cleaning assembly which is easily detachable from the filter chamber above the combustion tube. The automatic cleaning assembly includes a brush which rotates as it is lowered through the filter chamber and into the combustion tube while a vacuum is drawn through the lower end of the combustion tube. This results in a higher pressure differential and improved flow rate for removing dust from the filter of the furnace and the combustion tube. Additionally, the system eliminates the prior art vacuum dust door and employs the existing lower seal assembly already associated with the analytical system. This design will also dislodge crucibles sticking to the combustion tube by sequencing the brush and lower seal assembly, thereby eliminating operator intervention. This cleaning system improves analytical results and also extends analytical throughput by reducing down time due to jammed crucibles and manual cleaning. 
     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 
         FIG. 1  is a right-side elevational view of an induction furnace embodying the auto cleaner of the present invention, partly shown in block form; 
         FIG. 2  is an enlarged detail drawing in vertical cross section of the auto cleaner positioned above the induction furnace; 
         FIG. 3  is a vertical cross-sectional view of the induction furnace, combustion tube mounting system, and crucible pedestal located below the cleaning system shown in  FIG. 2 ; 
         FIG. 4  is a vertical cross-sectional view of the auto cleaner mechanism and combustion furnace with the auto cleaner shown in a raised position; 
         FIG. 5  is a vertical cross-sectional view of the structure of  FIG. 4  with the auto cleaner shown in a lowered use position; 
         FIG. 6  is a flow diagram of the programming of the auto cleaner control for automatic operation; 
         FIG. 7  is a perspective view of the bayonet mount between the auto cleaner housing and the filter assembly; 
         FIG. 7A  is an exploded fragmentary perspective view of the locking ring and its relationship to cleaner assembly  30 ; 
         FIG. 8  is a perspective view of the cup-shaped lower seal body assembly, showing the vacuum aperture for removing debris; and 
         FIG. 9  is an exploded perspective view of the combustion tube base assembly and combustion tube. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to  FIG. 1 , there is shown an induction furnace assembly  20 , including the auto cleaning mechanism of the present invention. The furnace  20  can be used with an analyzer similar to a carbon sulfur analyzer, Model No. CS600, available from Leco Corporation of St. Joseph, Mich. The induction furnace  20  includes a detachable auto cleaner assembly  30 , which is removably mounted by a bayonet connection  95  ( FIGS. 1 and 7 ) to a heated filter assembly  40 , which is sealably secured to the combustion housing  50  by mounting flange  49 . It is important that the bayonet mount  95  with mating flanges  96  and grooves  98  is proximate and above gas inlet  14  ( FIG. 1 ) and outlet  42  and other connections related to the lower dust filter  40 . Locating these connections on the lower side of the bayonet mount  95  significantly reduces the likelihood of leaks when the system is disassembled on a daily basis for maintenance. In order to lock the bayonet mount  95  in place during rotation of the cleaning brushes as described below, a keyed axially slideable torque locking ring  61  ( FIGS. 2, 4, 5, 7, and 7A ) is employed. As best illustrated in the fragmentary exploded view of  FIG. 7A , ring  61  is captively and rotatably indexably held to the outer cylindrical wall  32 ′ of the auto cleaner housing  30  by means of radially inwardly extending tabs  71  on ring  61 , which slideably cooperate with grooves  73  in wall  32 ′. Grooves  73  terminate in a ledge  75  such that ring  61  can be raised above the intersection of housing  30  and filter assembly  40  at the bayonet mount but is captively held to housing  30 , as seen in  FIG. 7 . When the cleaner assembly housing  30  is secured to the filter assembly housing  41  by the bayonet mount, ring  61  is lowered such that radially inwardly projecting tabs  63  in ring  61  slide through grooves  79  in wall  32 ′ to engage grooves  65  in the outer cylindrical wall  41 ′ of filter housing  41  ( FIG. 7 ). This interlocks housings  30  and  40  to prevent the bayonet mount from inadvertently loosening during the cleaning process. 
     Housing  50  includes a quickly removable door  52 , which, when removed, exposes a combustion tube  54  surrounded by an induction coil  56  ( FIG. 3 ). Tube  54  is sealably coupled to the lower end of filter assembly  40  by an upper seal assembly  58  ( FIG. 4 ) in a conventional manner. A pedestal  60  ( FIG. 3 ) holding a sample-holding crucible  62  is raised and lowered into combustion tube  54  through a cup-shaped assembly  70  by means of a pneumatic cylinder  72  having a rod  74  ( FIGS. 1 and 3 ) coupled to assembly  70 . In the position shown in  FIG. 3 , the cylinder rod  74  is in a raised position placing crucible  62  within the combustion tubes  54  for combustion of a sample therein by induction heating through RF coil  56 . 
     A combustion tube base assembly  80  ( FIGS. 3 and 9 ) includes an O-ring  81  which sealably couples the lower end of tube  54  to assembly  70  such that, during combustion of a sample, oxygen flows upwardly through a gas inlet  76  ( FIG. 8 ) in assembly  70  to sweep byproducts of combustion into gas outlet  42  ( FIG. 1 ) for analysis. Oxygen is also supplied to the central aperture  44  in spiral retainer  45  above combustion tube  54  ( FIG. 2 ) by an oxygen inlet  14  ( FIG. 1 ) and suitable sealed passageways  86  in inlet lance  82  and shaft extension  47  communicating with the aperture  44 . During cleaning, dust and debris flow in a stream of air, as shown by arrow A in  FIGS. 1 and 3 , into assembly  70  and particularly through opening  76  ( FIGS. 3 and 8 ), which leads to a vacuum hose  77  and a pneumatically actuated pinch valve  78  ( FIG. 1 ) used in connection with a dust trap  102  coupled by hose  101  to a vacuum cleaner  100  for the vacuum removal of combustion debris in association with auto cleaner  30 . 
     Housing  50  includes an easily removable combustion tube assembly  90  ( FIG. 1 ) which cooperates with base assembly  80  and allows the combustion tube  54  to be easily withdrawn from the lower end of combustion housing  50 , as described in detail in U.S. patent application Ser. No. 12/889,628, filed Sep. 24, 2010, and entitled E ASILY  R EMOVABLE  C OMBUSTION  T UBE , the disclosure of which is incorporated herein by reference. 
     The operation of cylinder  72  raises rod  74  which, in turn, raises a crucible  62  into the combustion tube  54  and seals the lower end of the tube by the sealed interface between assemblies  70  and  80  for the combustion of a sample and the subsequent analysis by the analyzer as well as during a cleaning sequence. The induction heater  56  heats a combustion sample to from about 1000° C. to about 1500° C. for the combustion of a sample under the influence of oxygen injected through the oxygen lance aperture  44  ( FIGS. 2, 4, and 5 ) centered above the crucible during combustion. 
     The mechanism for extending the coaxially aligned spiral retainer  45 , a first brush  46 , a shaft extension  47 , and a second brush  48  into the combustion tube  54  is now discussed in connection with  FIGS. 2-6 . The auto clean assembly  30  includes a cylinder  37  having a wall  32  housing a piston  34  coupled to a piston rod  36 . The rod surrounds a stationary cylindrical guide sleeve  38  which captively holds a threaded drive nut  39  in fixed relationship to sleeve  38 . Pneumatic pressure is applied to either the upper surface of piston  34  by supply conduit  31  ( FIG. 1 ) which receives air pressure from a suitable source of air pressure to lower piston  34  or through conduit  37  to apply pressure to the lower surface of piston  34  for raising piston  34 . Suitable pneumatic valves  35  and  35 ″ are coupled to conduits  31  and  37  and are sequentially actuated by controller  92  programmed as shown, in part, by the flow diagram of  FIG. 6  to operate the components of the system including cylinder  72 , valve  78 , cleaner  100 , and valves supplying air or oxygen to passageways  86 . 
     The raising and lowering of piston  34  is translated to rotary movement of the brushes  46 ,  48  and spiral retainer  45  by a threaded lead screw  64  which is coupled to piston rod  36  by inlet lance  82  ( FIG. 2 ). Thus, movement of piston  34  causes lead screw  64  to move up and down through the fixed drive nut  39  threadably coupled to lead screw  64  such that the lead screw also rotates and is supported by a thrust bearing  68  below retainer  66 . A wiper seal  67  extends between the retainer  60  and thrust bearing  68 . The lower end of lead screw  64  is coupled by a somewhat flexible pin coupling  69  ( FIG. 2 ) to inlet lance  82  which includes O-ring seals  83  which sealably engage the cylindrical opening  84  at the upper end of filter assembly  40 . When in a raised position, inlet lance  82  blocks the flow of air from passageways  85  ( FIG. 4 ) in mounting and air inlet flange  88  coupling auto cleaning assembly  30  to filter assembly  40 . When the cleaning brushes are lowered, the three 120° spaced passageways  85  in flange  88  are open to the atmosphere, allowing air to be drawn therein while a vacuum is applied to the chamber during cleaning through a vacuum source, such as a vacuum cleaner  100 , coupled to a dust collection box  102  by conduit  101  ( FIG. 1 ). The input through dust collection box  102  is coupled to vacuum hose  77  and pinch valve  78  coupled to the cup-shaped assembly  70  to draw a vacuum through aperture  76  ( FIG. 8 ) which is sealably coupled by combustion tube base assembly  80  ( FIG. 9 ) to the lower end of combustion tube  54 . The pinch valve  78  on compressible conduit  77  allows a vacuum provided by cleaner  100  to provide a significant pressure differential between the atmosphere at the upper end of combustion tube  54  and filter assembly  40  and conduit  77 . When pinch valve  78  is opened, a rush of cleaning air, aided by pulsed oxygen, through lance  82  dislodges debris, which is captured in vacuum cleaner  100 . The flow path for the dust and debris collecting flow of air is shown by arrow A in  FIGS. 1 and 3 . 
     Thus, the actuation of piston  34  not only rotates and advances the cleaning brushes but also opens to the atmosphere through passageways  85  and the movement of inlet lance  82  a flow of air which transfers dust and debris from the induction furnace during the movement of the brushes downwardly and rotatably through the combustion tube  54 . During the initiation of the cleaning cycle, the output tube  42  of the filter chamber, which typically carries byproducts of combustion to the analyzer, is momentarily reversed with a pulse of oxygen to assist in cleaning the dust filter  110  ( FIG. 2 ) concentrically mounted within the cylindrical housing  41  of filter assembly  40 . The dust filter is heated to approximately 120° C. by a surrounding coil heater  112  to remove moisture from material collected on the filter during the combustion process. The programming of the controller  92  ( FIG. 1 ) to provide the sequence of operation of the various valves accomplishing the cleaning process as described above is shown in connection with the self-explanatory labeled flow diagram of  FIG. 6 . 
     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.