Abstract:
A railroad hopper car discharge gate is assembled from unitary stacked frames that provide unimpeded flow of lading during discharge. A low-wear glide system minimizes friction between the gate panels and other components of the apparatus, and an improved sealing system protects lading from contaminants such as rain, dust and insect infestation and provides enhanced vacuum sealing for greater efficiency during vacuum discharge.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to the field of discharge gate assemblies for railway hopper cars and, more particularly, to a discharge gate for a railway hopper car that may be assembled from stacked subunits and which provides improved sealing and glide systems.  
       BACKGROUND OF THE INVENTION  
       [0002]     Railroad hopper cars are used to transport bulk lading through railway systems. A railroad hopper car typically includes discharge gates located on the underside of the car for unloading the transported materials. Discharge gates typically include one or more sliding panels that may be selectively moved between open and closed positions to expose or cover an opening in the undercarriage of the car. Typically, an opening and closing drive mechanism shifts a panel between open and closed positions via a rack or racks fixed to the panel and an operating shaft. The operating shaft carries pinions which engage the racks. The operating shaft is rotated to move the panel in the desired direction. The car may be unloaded by sliding the panel to open the gate and allowing the lading to flow through the opening.  
         [0003]     Often the materials transported comprise granular or particulate matter such as sugar, flour, grain, plastic pellets and cement. Conventional methods used to unload hopper cars include gravity discharge, vacuum discharge and pneumatic sled discharge, depending on the nature of the material transported.  
         [0004]     During gravity discharge, lading falls from the car through a discharge opening in the gate by gravity. During vacuum discharge, lading falls from the car and through an opening in the gate into a closed vacuum chamber. Vacuum nozzles, in communication with the vacuum chamber, may project from the outer surface of the gate. A vacuum hose is connected to one or more of the vacuum nozzles and vacuum is applied to the hose. Air drawn from the car and through the gate carries lading into the vacuum chamber, through the vacuum nozzles and into the hose. During pneumatic sled discharge, a pneumatic sled is attached to the bottom of the discharge opening. The pneumatic sled includes screw type conveyors for discharging lading from the hopper car. Compressed air is blown into the discharge opening to pressurize the inside of the hopper car and separate compacted lading. The lading falls through the discharge opening and into the screw conveyors for removal.  
         [0005]     In the case of high volume unloading, gravity discharge may be readily accomplished by simply opening the hopper car discharge gate and allowing the lading to flow downward through the gate. Gravity discharge is a common method of unloading used for materials such as unprocessed grains, feed, fertilizer, sand and soda ash. In the case of fine materials such as sugar, flour or cement, difficulties may be encountered during discharge due to significant quantities of the material becoming airborne. Such difficulties can lead to product contamination. In addition, fine materials may tend to accumulate on or within the elements of the discharge gate causing reduced outward flow of the lading, clogging of the discharge opening, and/or malfunction of the gate.  
         [0006]     Unloaders may attach a boot to the bottom of a gravity discharge gate to feed lading to an enclosed screw conveyor. Attachment of a boot, however, is slow and awkward and the area of the gate where the boot attaches may not be sanitary. Therefore, many handlers of finished food products such as sugar and flour, and plastic pellet handlers, prefer vacuum unloading or discharge. Discharge of fine materials may accomplished using vacuum discharge methods which can increase material flow and reduce airborne particles in the work environment proximate to the gate. Vacuum discharge is particularly preferred where avoidance of contamination is important.  
         [0007]     Difficulties in the prior art devices, however, persist relative to the seals formed between elements within the gate assembly, particularly between outer hopper or frame elements and sliding panels. Gaps between sealed components may be present as a result of dimensional variations in conventional multi-bend fabrication. In addition, surfaces for supporting the panels are prone to fouling due to build-up of transported matter, and wear due to friction caused by repetitive sliding of the panels over the support surfaces.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0008]     Various aspects of the hopper car discharge gate of the present invention include improved sealing and glide systems that provide for unimpeded flow of lading during discharge, a simplified method of assembly using multiple stacked frames that may be independently fabricated, a low-wear glide system that avoids damage to gate panels and other components due to friction, and an improved sealing system that protects lading from contaminants such as rain, dust and insect infestation and provides enhanced vacuum sealing for greater efficiency during vacuum discharge.  
         [0009]     In one embodiment of the discharge gate a generally horizontally disposed gate panel is provided that is movable in opposite directions between an open position and a closed position. A frame structure defines a discharge opening for flow of material from the hopper car, and has first and second spaced side members presenting first and second edges respectively at the discharge opening extending generally in the directions of movement of the panel. Flexible seal strips on the side members extend along the respective edges and project into the discharge opening. Transversely spaced support surfaces for the panel are provided which underlie the seal strips. The panel is mounted on the support surfaces for movement between its opened and closed positions in sliding contact with the seal strips to thereby seal the discharge opening when the panel is closed and, when opened, provide for discharge of material through the opening without accumulation at the edges of the side members and the support surfaces.  
         [0010]     In another embodiment a method is provided for controlling discharge of material from a hopper car, and comprises the steps of providing an upper, unitary hopper subassembly presenting an opening for downward flow of material thereinto, and a second, unitary gate subassembly beneath the upper subassembly in alignment with the opening. The second subassembly has a gate panel component movable between a closed position and an opened position permitting discharge of material therethrough. A third, unitary gate subassembly may also be utilized and is positioned beneath the second subassembly for receiving material discharged therefrom, and has a gate panel component movable between a closed position, when vacuum discharge is being utilized, and an open position permitting discharge of material by gravity flow through the open gates.  
         [0011]     Other aspects of the present invention include the utilization of elongated glide elements to present the support surfaces for gate panels, and additional sealing components, such as wiper seals, to insure that when vacuum discharge is utilized the suction provided by vacuum apparatus at the unloading facility is effectively maintained within the hopper gate.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a frontal and side perspective view of a two-door, railroad car discharge gate in accordance with an embodiment of the present invention.  
         [0013]      FIG. 2  is a side elevational view of the discharge gate of  FIG. 1 .  
         [0014]      FIG. 3  is a side perspective view of the discharge gate.  
         [0015]      FIG. 4  is a front perspective view of the discharge gate.  
         [0016]      FIG. 5  is an upper, front perspective view of the discharge gate.  
         [0017]      FIG. 6  is a plan view of the upper frame of the discharge gate.  
         [0018]      FIG. 7   a  is a partial, exploded view of the discharge gate.  
         [0019]      FIG. 7   b  is a partial, simplified, exploded view of an alternative embodiment the discharge gate.  
         [0020]      FIG. 8  is a plan view of the discharge gate, showing the upper panel partially open.  
         [0021]      FIG. 9  is a partial, transverse, enlarged sectional diagram of the discharge gate along line  9 - 9  in  FIG. 8 .  
         [0022]      FIG. 10  is a partial, longitudinal, enlarged sectional diagram of the discharge gate along line  10 - 10  in  FIG. 8 .  
         [0023]      FIG. 11  is a further enlarged, partial view of the diagram of  FIG. 9 .  
         [0024]      FIG. 12  is a further enlarged, partial view of the diagram of  FIG. 10 .  
         [0025]      FIG. 13  is a simplified rear perspective view of the discharge gate showing the upper panel in an open position and the lower panel closed.  
         [0026]      FIG. 14  is a partial sectional diagram of a railroad discharge gate in the prior art.  
         [0027]      FIG. 15  is an exploded, partial sectional diagram of a discharge gate in accordance with an aspect of the present invention.  
         [0028]      FIG. 16  is a partial, diagrammatic view showing a triangular seal in place inside a chamber created by the interface of upper and middle frame sides and an upper panel.  
         [0029]      FIG. 17  is a partial perspective view with parts broken away to show the interior of triangular chambers formed by the interface of upper and lower panels and sidewalls of the upper, middle and lower frames.  
         [0030]      FIG. 18  is a bottom perspective view of the discharge gate of  FIG. 1 .  
         [0031]      FIG. 19  is an enlarged portion of the view of  FIG. 18 .  
     
    
     DETAILED DESCRIPTION  
       [0032]     Referring now to the drawings, and initially in particular to  FIGS. 1-8 , wherein like reference numerals indicate like parts throughout the several views, a railroad hopper car discharge gate  100  is illustrated and includes a generally rectangular upper frame or hopper  102  surrounding a generally rectangular discharge opening  104  (see  FIG. 6 ). The upper frame  102  includes four upper sidewalls  106 ,  108 ,  110  and  112 . Each of the sidewalls  106 ,  108 ,  110 , and  112  has an inner edge  106   a,    108   a,    110   a,    112   a  that, in combination, define the discharge opening  104 . The discharge gate  100  may be provided with an upper door panel  114  and a lower door panel  116  that slide between open and closed positions within respective middle  118  and lower  120  frames. A pair of opposed vacuum nozzles  122  and  124  are mounted on the frames  118 ,  120  so as to open into a chamber below the discharge opening  104 . Transversely extending upper drive shafts  126  and  128  and lower drive shafts  130  and  132  engage the upper door panel  114  and lower door panel  116  respectively, so as to move the door panels  114  and  116  between open and closed positions when the shafts  126 ,  128 ,  130  and  132  are rotated in the appropriate direction. Gears (not shown) driven by the drive shafts engage racks  184  attached to the panels to provide a rack and pinion drive system.  
         [0033]     The upper frame sidewalls  106 ,  108 ,  110  and  112  have diverging angular sides  106   b,    108   b,    110   b,    112   b  that extend upwardly from the inner edges  106   a,    108   a,    110   a,    112   a  toward the upper portion of the frame. Typically, the upper portion of the frame is defined by a relatively flat, horizontal lip  106   c,    108   c,    110   c  and  112   c  extending from each sidewall. Each lip  106   c,    108   c,    110   c  and  112   c  may include a plurality of mounting holes  154  spaced along its perimeter. While the discharge gate  100  may be mounted directly to the undercarriage of the railroad car via these mounting holes  154 , typically a separate interface (not shown) is used to allow for differences between the hole patterns in the discharge gate  100  and the various mounting structures that may be encountered on the car.  
         [0034]      FIG. 7   a  is an exploded view of the gate  100  of  FIGS. 1 through 6  with major components of the gate separated from one another for clarity.  FIG. 7   b  is a simplified, exploded view of the gate  100  including illustrations of some of the major components of the gate including the upper frame  102 , middle frame  118 , upper panel  114  (in phantom lines), lower frame  120  and lower panel  116 . The middle frame  118  is secured to the underside of the upper frame  102  and comprises sidewalls  134 ,  136 , and  138 . The upper panel  114  slides within the middle frame  118  and is typically supported principally by sidewalls  136  and  138  or by support components associated with sidewalls  136  and  138 . The walls of the middle frame define a lower discharge opening  140 .  
         [0035]     The lower frame is  120  is secured to the underside of the middle frame  118  and comprises sidewalls  142 ,  144 , and  146 . The lower panel  116  slides within the lower frame  120  and is typically supported principally by sidewalls  144  and  146  or by components associated with sidewalls  144  and  146 . The lower discharge opening  140  may be sealed shut by positioning lower panel  116  in a closed position as shown in  FIGS. 8 and 13 .  
         [0036]     When the lower panel  116  is in the closed position a sealed primary vacuum chamber  148  is formed ( FIGS. 9 and 10 ). The primary vacuum chamber  148  is defined by lower panel  116 , the sidewalls  142 ,  144  and  146 , and a plenum  150  that forms a secondary vacuum chamber for receiving discharged material flowing from the primary vacuum chamber  148 . Material then flows from the plenum  150  to the vacuum nozzles  122  and  124  ( FIG. 8 ).  
         [0037]      FIG. 8  is a plan view of a discharge gate  100  showing features illustrated in  FIGS. 1 through 7   b  including the upper panel  114  in a partially open position to reveal the lower panel  116  below in a closed position.  FIGS. 9 and 10  illustrate the relative positioning of gate elements in the stacked frame assembly of the discharge gate  100 . In  FIG. 10  the upper panel  114  is shown in the closed position.  
         [0038]     As illustrated in  FIG. 9 , the upper frame sidewalls  106  and  108  have sloping sides  106   b  and  108   b  that extend upwardly from the sidewall edges  106   a  and  108   a  toward upper lips  106   c  and  108   c.  In  FIG. 10 , upper frame sidewalls  110  and  112  define the back and front of the hopper formed by the upper frame  102  and also have sloping sides  110   b  and  112   b  that extend upwardly from edges  110   a  and  112   a  to upper lips  110   c  and  112   c.    
         [0039]     The middle frame  118  is positioned below, and is attached to, the upper frame  102 . The middle frame  118  includes two transversely spaced, parallel sidewalls  136  and  138  that define a space below the discharge opening  104 . In  FIG. 9 , the middle frame sidewalls  136  and  138  extend downward from the upper frame sloping sides  106   b  and  108   b.  Ledges  136   c  and  138   c  project from the inner surfaces of the support walls  136  and  138  to present an L-shaped configuration as viewed in  FIG. 9 . The ledges  136   c  and  138   c  include upper glide elements  160   a  and  160   b  such as flat strips or bars of bronze or ultra high molecular weight (UHMW) plastic. The upper panel  114  is supported within the middle frame  118  upon these glide surfaces  160   a  and  160   b  so that the upper panel  114  may slide across the upper discharge opening  104  between open and closed positions. Additional support for the upper panel  114  may provided by a center rail  152  (see  FIGS. 1, 7   a,    7   b,    8 ,  9 , and  13 ). Typically, the rail  152  is in the form of a cylinder or rectangular bar. Preferably, the rail  152  is formed of bronze, steel capped with bronze, or steel capped with UHMW plastic.  
         [0040]     The sidewalls  136  and  138  of the middle frame  118  include integral lower sidewalls  136   b  and  138   b  that extend inwardly at an angle from the ledges  136   c  and  138   c.  The lower sidewalls  136   b  and  138   b  terminate at inner edges  136   a  and  138   a.  In  FIG. 10  the front sidewall  134  of the middle frame  118  extends downward from sloping side  110   b  of the upper frame  102  and includes surface  134   b  that slopes inwardly to edge  134   a.  Edges  134   a,    136   a  and  138   a  partially define the borders of the lower discharge opening  140 .  
         [0041]     A lower frame  120  may be positioned below and attached to the middle frame  118  in order to assemble a discharge gate  100  suitable for vacuum discharge. As illustrated in  FIGS. 9 and 10 , the lower frame  120  includes two elongated, spaced, parallel sidewalls  144  and  146  that extend downward from the middle frame sloping sides  136   b  and  138   b.  Sidewall  142  extends downward from sloping side  134   b.  Ledges  142   a,    144   a  and  146   a  project inward from sidewalls  142 ,  144  and  146  to support a lower door panel  116  which may slide across the lower discharge opening  140  between a closed position shown in  FIG. 10  and an open position (not shown) displaced to the right as viewed in  FIG. 10 . The ledges  144   a,    146   a  and  142   a  are provided with glide elements  162   a,    162   b  and  162   c,  respectively, to provide low friction surfaces.  
         [0042]     The lower door panel  116  is positioned below the edges  136   a  and  138   a  and rests on support structures provided by the lower frame  120  that may comprise ledges  144   a  and  146   a  formed from, or projecting from, the lower frame sidewalls  144  and  146 . Since the lower door panel  116  is not typically subject to weight exerted by lading during transport, as is upper door panel  114  which is used to close the opening in the railroad car, additional support for the lower door panel  116  is typically not required but may provided by a center rail (not shown).  
         [0043]     From the forgoing, it may be appreciated that the sloping surfaces thereby provided by upper frame  102  and middle frame  118  allow material discharged from a railroad car to readily flow down the surfaces of the walls and through the upper and lower discharge openings  104  and  140 .  
         [0044]     As illustrated in  FIGS. 7   a,    7   b  and  10 , discharge gate  100  is adapted for vacuum discharge and includes plenum  150  for receiving discharged lading and directing the lading to vacuum nozzles  122  and  124  (see  FIGS. 1-8 ). The plenum  150  may be attached to, or integral with, the middle frame  118 . As shown in  FIG. 10 , the forward wall  150   a  of the plenum  150  forms the rear wall of the primary vacuum chamber, and the front wall of the secondary vacuum chamber.  FIG. 13  is a front perspective view of a discharge gate  100  in which the upper panel  114  is in an open position and the lower panel  116  is in a closed position. Lading passing through the upper frame  102  falls through the upper discharge opening  104  onto lower panel  116 . Vacuum applied to vacuum nozzle  122  and/or  124  draws the lading through a space or spaces provided between the lower panel  116  and the forward wall  150   a  of the plenum  150 .  
         [0045]     The stacked assembly method of construction whereby separate unitary bodies comprising the upper frame  102 , middle frame  118  and lower frame  120  are assembled to construct a discharge gate, provides significant advantages both in the construction and in the operation and use of the assembled device. In the prior art, a discharge gate  200 , as illustrated in diagrammatical form in  FIG. 14 , is typically formed in the shape of a hopper having inwardly sloping sidewalls  190  and  192  that define one or more discharge openings. Ledges  190   a  and  192   a  or similar structures for supporting panels or doors  194  and  196  are typically formed by creating a series of bends in each wall. When assembling the gate  200  several important dimensional criteria are considered. First, if the gate is to be mounted to the underside of a railroad hopper car by using holes provided in the upper lip of the sidewalls  190  and  192 , then it is important that the holes align with matching attachment structures on the railroad car. For example the distance between points  2   a  and  2   b  as indicated by arrow  2  in  FIG. 14  should be maintained during assembly of the discharge gate  200 . In addition, the distance between points  4   a  and  4   b,  as indicated by arrow  4 , should be maintained so that upper panel  194  may slide freely upon ledges  190   a  and  192   a  and between walls  190  and  192 , while minimizing the gap between walls  190  and  192  and the proximate edges of the panels  194  and  196 . In addition, the distance between points  6   a  and  6   b,  as indicated by arrow  6 , should also be maintained so that the lower panel  196  may slide freely upon ledges  190   b  and  192   b  and between walls  190  and  192 . Ledges  190   a  and  192   a,  and  190   b  and  192   b,  along with respective tranverse panel support members (not shown) should also be assembled so as to present support surfaces in a common plane. Otherwise an associated panel will not be evenly supported. Although other criteria may also apply, achieving close tolerances may present a considerable difficulty in the prior art due to the number of sequential bends required in each section of sidewall.  
         [0046]     The discharge gate  100  is formed by stacking previously assembled gate components comprising the upper frame  102 , middle frame  118  and lower frame  120 . Each component, therefore, may be constructed with only one of the above criteria being critical to the final component dimensions. For example, when constructing the upper frame  102  the required distance between points  8   a  and  8   b,  as represented by arrow  8 , may be maintained without the need for considering, or making adjustments based on, the distance between middle or lower frame ledges. As shown in  FIG. 15  the upper frame  102 , middle frame  118 , and lower frame  120  may each be constructed independently in a manner that maximizes precision and accuracy of distances  8 ,  10 , and  12 . Because the mating surfaces of the upper, middle and lower frames are angled and nest one inside the other, they tend to be self centering and therefore slight deviations from the norm in one frame will tend not to affect the critical dimensions of the other frames.  
         [0047]     To maximize the efficiency of vacuum discharge, the discharge gate  100  may be provided with a system of seals to close gaps within the gate assembly, particularly gaps between stationary frame elements and moveable elements such as the upper and lower panels  114  and  116 .  FIGS. 9 and 10  disclose a system of seals attached to the side edges of the upper and middle frame  102  and  118  sidewalls. For clarity,  FIG. 11  is provided as an enlarged partial view of  FIG. 9 , illustrating seals associated with sidewalls  136  and  144 .  FIG. 12  is provided as an enlarged partial view of  FIG. 10 .  
         [0048]     Flexible seal strips (see  FIGS. 11 and 12 ), preferably formed from a resilient material such as ultra high molecular weight (UHMW) polyethylene, are attached to the underside of the upper frame  102  sidewalls  106 ,  108 ,  110  and  112 , for sealing against upper door panel  114 . Similar seal strips are attached to the underside of the middle frame  118  sidewalls  134 ,  136  and  138  and plenum rearward wall  150   b  for sealing against lower door panel  116 .  
         [0049]     In particular, as illustrated in  FIG. 11 , seal strip  170   a  is attached to the underside of sidewall edge  106   a  so as to contact the upper surface of upper panel  114 . Seal strip  172   a  is attached to the underside of sidewall edge  136   a  so as to contact the upper surface of lower panel  116 . Similarly, seal strip  170   c  is attached to the underside of sidewall edge  110   a  and seal strip  172   c  is attached to the underside of sidewall edge  134   a  to contact the surface of upper panel  114  and lower panel  116 , respectively. To minimize wear and/or failure of seal strips  170   c  and  172  due to repetitive contact with the leading edges of panels  114  and  116 , seal strips  170   c  and  172  may be bent to face in a forward direction as shown in  FIGS. 12 and 10 .  
         [0050]     The seal strips extend along the associated sidewall edges and project partially into the proximate discharge openings  104  or  140  ( FIG. 7   b ). As shown in  FIGS. 11 and 12 , seal strips, for example  170   a,    172   a,    170   c  and  172   c,  may be held by compression in a sandwiched configuration between the underside of sloping sides  106   b,    136   b,    110   b  and  134   b  and backing strips or blocks  180   a,    182   a,    180   c  and  182   c.  Preferably the panels are disposed so that the seal strips are forced to deflect and press against the surface of the panels thereby enhancing the seal created between a given seal strip and the associated panel.  
         [0051]     The bottom wall of the plenum  150  is formed by the lower panel  116 . Therefore, when the lower panel  116  is fully opened the plenum  150  is open on the bottom for ready access for cleaning. In addition, when the lower panel  116  is fully opened a sanitary sealing surface is exposed (see seals  172   a,    172   b,    172   c  and  172   d ) for sealing a boot to the bottom of the gate  100 .  
         [0052]     As can be seen in  FIGS. 9 and 11 , a chamber, generally triangular in cross-section, is formed by the sloping side  106   b,  panel  114  and sidewall  136 . Similar chambers are formed where panel  114  meets sidewall  138  and  108   b,  and where panel  116  meets sidewall  136  and  144 , and  138  and  146 . When the upper panel  114  is in a partially open to fully open position the associated triangular chambers present potential air paths from the primary vacuum chamber  148  to the exterior of the discharge gate  100 . To block this route for loss of vacuum during vacuum discharge, triangular seals adapted to fit the interior contours of the triangular chambers are positioned at the forward end of panel  114 . As can be seen in  FIGS. 7   a  and  7   b,  triangular seals  156  and  158  are affixed to the forward end of panel  114  (drawn in phantom lines in  FIG. 7   b ) and are positioned to project perpendicularly upward from the upper surface of the panel  114 . Triangular seals  166  and  168  ( FIG. 7   b ) may be affixed to the forward end of lower panel  116  in a similar manner if the device  100  is to be unloaded using a vacuum sled or bottom boot instead of the vacuum outlets  122 ,  124 .  FIG. 16  is a cross-sectional diagram showing a triangular seal  156  in place inside a triangular chamber created by the interface of side  106   b,    136  and upper panel  114 . A complementary triangular backing block  156   a  is used to compress the seal  156  against an attachment block or flange  159  ( FIGS. 7   a,    7   b  and  17 ) projecting from the upper panel  114 . Triangular seals may be sandwiched between two triangular backing blocks. As the upper panel  114  is moved between open and closed positions, the triangular seal  156  wipes the interior of the chamber and acts as a barrier between the area of the chamber forward of the seal  156  and the exterior of the gate  100 .  FIG. 17  is a partial cut-away showing the interior of such a triangular chamber formed by the interface of panel  114 , sloping side  108   b  and sidewall  108 . As illustrated, the upper panel  114  is in the closed position.  
         [0053]     Additional vacuum air leakage can occur between the bottom surface of the upper door panel  114  and the top of the rear cross member. To seal this zone a seal  172   f  is affixed to the forward wall  150   a  of the rear cross member  150  so as to wipe against the bottom surface of the upper door panel  114  (see  FIG. 10 ). Rear seals  170   d  and  172   d  provide the primary sanitary seal to the top of their respective door plates, and additional seals  170   e  and  172   e  are mounted at a reverse incline to scrape heavy road debris from the top surfaces of the door panels  114  and  116  and to provide a secondary seal against dirt and moisture, including rain.  
         [0054]      FIG. 18  is a bottom perspective view of the discharge gate  100  of  FIG. 1 .  FIG. 19  is an enlarged portion of the view of  FIG. 18  showing a portion of the bottom surface of the hopper  102  and seals  170   b,    172   b,    170   c  and  172   c.    
         [0055]     It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto except insofar as such limitations are included in the following claims and allowable equivalents thereof.