Abstract:
A dryer for removing surface moisture from a pelletized product and more specifically a dryer which is constructed with dimensions enabling it to effectively centrifugally remove surface moisture from pellets of resin material received from an underwater pelletizer. The dryer is capable of operating at very low rates and easily cleaned with its overall size enabling it to be effectively used for small operations, especially laboratory applications.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a centrifugal dryer for removing surface moisture from pellets of resin material having a diameter generally ranging between approximately 0.015 to approximately 0.25 inches received from an underwater pelletizer. More specifically, the present invention relates to a dryer which is constructed with smaller dimensions enabling it to effectively operate at low volume rates and be easily assembled and disassembled to facilitate cleaning and replacement or interchange of components with its overall size enabling it to be effectively used in small applications, especially laboratory applications. 
     2. Description of the Prior Art 
     Centrifugal pellet dryers are well known and have been successfully used for many years to separate water from a water and pellet slurry and remove surface moisture from the pellets in order to provide relatively dry surfaces on the pellets for subsequent use. Previously known centrifugal pellet dryers are used for the purpose of removing surface moisture from pelletized products and are usually a relatively large machine for producing a large volume of dried pellets. The following U.S. patents relate to centrifugal pellet dryers: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 4,476,019 
                 5,187,880 
                 5,611,150 
               
               
                 4,570,359 
                 5,505,537 
               
               
                   
               
             
          
         
       
     
     The centrifugal pellet dryers disclosed in the above prior patents are primarily used in high volume production of dried pellets and are not practical for operation at low rates of production and are not sized to use in a laboratory application or other small operations. 
     Accordingly, the present invention seeks to overcome this deficiency in the prior centrifugal pellet drying constructions by incorporating unique features not shown in the prior art. For example, the pellet dryers of the prior art do not have a sectional housing with the sections being connected together by bolted external flanges for easy separation and access to the internal components. The above patents also fail to disclose a centrifugal pellet dryer having a base section attached directly to a tank for receiving the water from the water and pellet slurry thereby eliminating the necessity of using piping systems to drain water from the dryer. In addition, the prior art does not disclose a centrifugal pellet dryer in which the rotor is supported from a single upper bearing with the lower end of the rotor being rotably guided by an alignment bushing which is self lubricating and is cooled by the water of the water and pellet slurry thereby eliminating the need for providing a sealed bearing or other special device to protect a bottom bearing from the water. Still another feature not shown in the prior art is the use of a cylindrical screen in a centrifugal pellet dryer which telescopically engages a recessed edge of cup-shaped support members at the top and bottom ends of the screen and is supported by a pair of holding clips in the form of hooks to engage supporting pins on the upper cup-shaped support. Also, the prior art does not disclose the use of a lift device to assist in lifting and supporting the major components away from the base section to facilitate removal, cleaning and replacement of the dryer components. 
     SUMMARY OF THE INVENTION 
     The present invention is a centrifugal pellet dryer for removing surface moisture from resin pellets (approximately 0.015 to approximately 0.25 inches in diameter) and is specifically adapted for use in laboratory applications. The centrifugal pellet dryer of this invention distinguishes from currently available centrifugal pellet dryers which are not suitable for laboratory applications or other small operations. The instant pellet dryer is capable of operation at very low volume rates and is constructed with an overall size and characteristics for easy cleaning which make it desirable for laboratory applications. 
     The centrifugal pellet dryer of this invention includes a sectional housing having separable sections that are quickly and easily connected together and disconnected from each other. The separable sections are preferably cylindrical top and base sections connected by mating external peripheral flanges that are bolted together. The base section attaches to a top wall of a tank into which the water from the water and pellet slurry is drained, thereby eliminating the necessity of providing any piping system to remove the water from the dryer once separated from the pellets. 
     The centrifugal pellet dryer of this invention also includes a driven rotor that has a single supporting bearing at the upper end thereof with only an alignment bushing assembly at its lower end. A motor is preferably mounted atop a top plate to which the upper housing section is attached. The rotor supporting bearing is preferably mounted to the top plate and the alignment bushing assembly is preferably part of the lower or base housing section. This structure eliminates the necessity of providing a bottom bearing for the rotor and a sealing arrangement for the bottom bearing to preclude water from entering the bottom bearing thereby simplifying the structure. It also facilitates the easy separation and assembly of the top and base sections relative to each other. 
     Further, the centrifugal pellet dryer of this invention includes a lift device, preferably in the form of a gas spring lift and support device, to lift the motor, rotor, top plate and upper housing section upwardly away from the lower or base housing section which allows the lifted components to be swung about a vertical axis away from the base section. This lifting, supporting and swinging structure enables removal of the upper section of the housing and screen to facilitate cleaning of the exposed bladed rotor as it remains connected to its driving shaft. 
     The centrifugal pellet dryer of this invention also preferably includes a cylindrical one-piece screen which is telescopically engaged with recessed end edges on top and bottom support structures. The screen also includes support hooks engaging the top support structure to removably support the screen within the top and base sections of the housing to facilitate assembly and disassembly of the screen in the dryer. Additionally, the tank has a screen bottomed drawer receiving water from the base section of the dryer for removing any solid material or pellets which may be entrained in the water. 
     Accordingly, it is an object of the present invention to provide a centrifugal pellet dryer for removing surface moisture from pelletized product that is constructed uniquely for use in laboratory applications and other small operations. The pellet dryer of this invention includes a sectional housing in which multiple sections are connected by external flanges that are bolted together to enable quick and easy assembly and disassembly of the housing. The pellet dryer housing includes a base section constructed to communicate directly to a debris separating drawer on a top wall of a water drain tank thereby eliminating the necessity of providing a piping system to drain water from the dryer. 
     Another object of the present invention is to provide a pellet dryer in which the rotor is rigid with a shaft supported by a single upper bearing and having an alignment bushing assembly guiding rotation of the lower end of the rotor thereby eliminating the need for a sealing device or special waterproof design to protect a bottom bearing from water within the dryer. 
     A further object of this invention is to provide a centrifugal pellet dryer for laboratory applications as set forth in the preceding objects in which the dryer is capable of operation at very low volume rates and is constructed of a relatively overall small size and of separable and replaceable components rendering it easily cleanable, repairable and otherwise well suited for laboratory or small applications. 
     A still further object of the invention is to provide a gas lift for supporting and lifting the motor, the rotor and the upper housing section away from the base section when the dryer is being disassembled for repair and cleaning. 
     Still another object of the present invention is to provide a pellet dryer including a one-piece cylindrical screen having upper and lower edges telescopically engaged with recessed edges of top and bottom supports in the housing and support hooks engaging with support pins on the top support. 
     A final object to be set forth herein is to provide a pellet dryer which will conform to conventional forms of manufacture, be of simple construction and easy to use so as to provide a device that will be economically feasible, long lasting and relatively trouble free in operation. 
     These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming apart hereof, wherein like numerals refer to like parts throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of the centrifugal pellet dryer of the present invention illustrating the relationship of the motor, housing, drain tank, inlet and outlet and the gas spring lift device. 
     FIG. 2 is a side elevational view similar to FIG. 1 but illustrating the base section of the housing detached from the remainder of the housing which has been lifted vertically away by the gas spring lift device. 
     FIG. 3 is a side elevational view similar to FIG. 2 but illustrating the swiveling movement of the lifted components of the dryer and the dryer screen being removed from enclosing relation to the rotor. 
     FIG. 4 is a side elevational view similar to FIG.  3  and illustrating the upper section of the housing being removed to completely expose the rotor. 
     FIG. 5 is a fragmental perspective view of the base section of the housing of the present invention and the components for the lower end portions of the rotor and screen therewith. 
     FIG. 6 is a vertical partial sectional view of the dryer of the present invention illustrating the association of the components of the dryer. 
     FIG. 7 is a fragmental enlarged elevational view of a portion of the housing illustrating a preferred form of bolted flange arrangement utilizing swing bolts. 
     FIG. 8 is a fragmental enlarged sectional view of a preferred form of guide bushing assembly for the lower end of the rotor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Although only one preferred embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the preferred embodiment, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     Referring now specifically to the drawings, the centrifugal pellet dryer of the present invention is generally designated by reference numeral  10  and includes a vertically disposed generally cylindrical housing generally designated by the numeral  12  having a vertical rotor  14  rotatably mounted therein and which is enclosed by a screen  16 . The rotor  14  is driven by a motor  18  preferably mounted atop the upper end of the dryer. The lower end of the dryer includes a slurry inlet  20  and the upper end of the dryer includes a dried pellet outlet  22 . These components generally are found in existing centrifugal pellet dryers. However, certain of the components of the present invention include unique structural features and associations not known in currently available centrifugal pellet dryers. 
     The housing  12  includes sections preferably including a base or lower section  24  and an elongated upper section  30  which is connected to a top plate  26 . The upper section  30  can include reinforcing collars  29  and  31  at the upper and lower ends. The sections  24  and  30  and top plate  26  can be interconnected by circular end flanges  32  secured together by bolts  34 . A coupling guard  28  is attached above top plate  26  as by bolts or the like. The housing sections  24  and  30  and top plate  26  are preferably constructed of a substantially rigid material, such as metal, that is sufficiently strong to support the structure of the dryer, is relatively inexpensive and can be constructed in relatively small diameters and heights. 
     The rotor  14  includes a central shaft  36 , preferably square, positioned centrally in the vertical housing  12  and is drivingly engaged with a motor output shaft  38  by a drive coupling  40  (see FIG.  6 ). The upper end of the dryer rotor  14  is provided with a support bearing  44  enclosed within the motor coupling guard  28  and a motor support enclosed by the guard  28  which is supported from the top plate  26  at the upper end of the housing as indicated at reference numeral  46 . The support bearing  44  supports the rotor  14  from its upper end and maintains its support in order that the lower end of the rotor shaft  36  can be guided by a bushing  48  mounted in the base section  24  of housing  12 . The lower end of the shaft  36  is provided with an axially extending shaft  50  of reduced cross-sectional area and preferably of cylindrical configuration for rotational guided movement in cylindrical opening  51  in alignment bushing  48 . 
     The upper section of the housing  12  includes a downwardly extending cylindrical member  52  secured to the top plate  26  by fastening bolts  54 . The screen  16  is a cylindrical member  56  of screen or perforated material which has an upper end in the form of a solid wall  55 . The wall  55  engages with a downwardly facing recess  58  in the outer edge of the cylindrical member  52  with the upper end edge of the wall  55  on screen element  56  telescoping over the recess  58  as illustrated in FIG.  6 . Likewise, the lower end of the screen element  56  is supported by the top rim  61  of the upwardly facing cylindrical support  60 . The top rim  61  includes a recessed upper edge  62  which telescopically receives the lower end of peripheral wall  57  of the screen element  56 . 
     The cylindrical member  60  also preferably includes a plurality of upwardly and outwardly angled rods  63  on the exterior thereof as shown in FIG. 5 to guide the lower end of the screen  16  onto the recess  62  formed on the outer edge of the upper end of cylindrical member  60 . The angled rods  63  thus facilitate assembly of the screen element  56  onto cylindrical member  60  in relation to the housing and rotor. The lower cylindrical member  60  includes a bottom wall  64  that is secured to a plate  66  by fastening devices  68 . The plate  66  is secured to the top wall  70  of a debris separating drawer assembly generally designated by reference numeral  72  positioned on top of a water drain tank generally designated by reference numeral  74  with fastening bolts  76  securing the plate  66  in position. It will be observed that alignment bushing  48  is preferably disk shaped and can be replaced if and when the opening  51  becomes worn. Bushing  48  is positioned in the center of bottom wall  64  so that extending shaft  50  and, therefore, rotor shaft  36  are both positioned substantially along the central vertical axis of the dryer  10  within screen  16  and housing  12 . 
     The base section  24  of the housing  12  includes the inlet  20  which extends through a fitting  78  in the peripheral wall of the base section  24 . The slurry inlet  20  extends into and is connected to a fitting  80  in the cylindrical member  60  thus communicating the slurry inlet  20  with the interior of the cylindrical member  60  and thus screen  16 . This enables the rotor  14  to move and lift the slurry and pellets upwardly and directing them outwardly toward the screen element  56  so that water entrained with the pellets will be discharged through the screen. The water discharged through the screen and outwardly of the lower cylindrical member  60  can pass through the plate  66  and the top wall  70  through apertures  82  thus enabling the water to drain into the debris separating drawer assembly  72 . 
     The separating drawer assembly  72  includes a slidable drawer  83  having a peripheral vertical wall  84  and a screen or perforated bottom  86 . The drawer  83  is slidably supported on ledges  88  at the bottom of the drawer assembly  72 . A handle  90  is provided at the front of the drawer  83  to move the drawer outwardly to remove any solids or pellets which may have been discharged through the apertures  82  so that only water is discharged into a water drain tank  92 . The tank  92  is also provided with an opening  94  to facilitate discharge of water separated from the pellets. As the pellets are moved upwardly they are dried by virtue of the forces of gravity and the centrifugal force of the pellets being discharged toward the screen in a manner well known in the pellet drying art. Once the dried pellets reach the upper end of the rotor, they are discharged centrifugally into the dry pellet outlet  22  in communication with cylindrical member  52  and then into a suitable container. 
     The upper section  30 , the top plate  26 , the coupling guard  28  and the motor  18  and its support along with the rotor  14  and screen  16  are all supported by a lifting device, preferably gas spring lift device  96 . The gas spring lift device  96  includes a stationary outer tube  98  rigidly affixed to plate  66  by bracket structure  100  and fastening bolts. A swiveled vertically movable telescopic upper tube  102  is attached to the motor support and upper section  26  of the housing  12  by bracket structure  104 . This gas spring  96  will assist in lifting and will support the upper section  30  of the housing and the rotor, screen, motor support and motor when the bolts  34  interconnecting the flanges  32  between the upper section  30  and base section  24  of the housing are removed. The vertical movement of the upper tube  102  is illustrated in FIG. 2 as indicated by the arrow  106 . 
     The upper tube  102  of the gas spring  96  is also capable of swivel movement which enables the lifted components to rotate about the vertical axis of the gas spring as indicated by arrow  108  in FIG.  3 . Thus, the upper section  30  of the housing and those components above the upper section along with the rotor  14  and screen  16  can then rotate out of alignment with the base section  24 . Once the upper section  30  has been rotated out of alignment with the base section  24 , the screen  16  can be dropped downwardly and removed as illustrated in FIG.  3 . Also, this structure enables the upper section  30  of the housing  12  to be separated from the top plate  26  and dropped downwardly as indicated by arrow  110  in FIG.  4 . This separation enables removal of the upper section of the housing thereby providing easy access to the rotor  14  which remains attached to the shaft coupling  40  as illustrated in FIG.  4 . The shaft  36  and inclined blades  40  can then be easily cleaned while being supported above the base section, or the axial extension  50  may be lowered into the guide bushing  48  to stabilize the lower end of the rotor  14  while being cleaned. 
     FIGS. 3 and 4 illustrate an additional support for the screen which is preferred in most installations. The additional support is in the form of two (or more) upwardly extending hooks  120  rigidly connected to the upper end wall  55  of the screen member  56 . The hooks  120  are preferably oriented diametrically on the outer surface of wall  55  and open in opposite peripheral directions to engage with outwardly projecting pins  122  on top support structure  52 . The hooks  120  and screen member  56  must be rotated counter-clockwise a partial revolution to release the screen to be moved downwardly for removal. 
     FIG. 7 illustrates an additional preferred connection between housing sections in which each of the flanges  130  have a notch or slot  132  which has a swing bolt  134  extending therethrough. The lower end of swing bolt  134  is, pivotally supported by support lugs  136  attached to the housing. The upper end of the bolt  134  includes a nut  138  which can be loosened sufficiently to enable pivotal movement of the bolt  134  without complete removal of the nut  138  and without separating the bolt from the housing thereby greatly facilitating the assembly and disassembly of the housing sections of the dryer. 
     FIG. 8 illustrates an additional preferred form of the bushing for the lower end of the rotor in which the lower end of rotor  140  is provided with a generally tapered lower end  142  with a flat lower end  144 . In lieu of the bushing  48 , a two-piece bushing assembly  146  is employed to guide the lower end of the rotor  140  during rotation. The bushing assembly  146  includes an outer member  148  of resin material and an inner sleeve or bushing  150  of metal. The sleeve or bushing  150  is cylindrical and rotatably engages and guides a cylindrical upper end portion  152  of the lower end  142  of the rotor  140 . The tapered lower end  142  assists in guiding the lower end of the rotor into the guide sleeve or bushing  150 . Water passing through the bushing assembly  146  cools and lubricates the sleeve  150  and lower end of rotor  140 . Like bushing  48 , the bushing assembly  146  is supported in the bottom of the cup-shaped support  60  and can be replaced when necessary. 
     The function of the rotor  14  or  140 , screen  16  and housing  12  together with the slurry inlet  20  and dried pellet outlet  22  are similar to the function of existing centrifugal pellet dryers. However, the manner in which the rotor is supported and driven and guided by a replaceable alignment bushing  48  or bushing assembly  146  and the sectional construction of the housing and the gas spring lift device cooperate to enable the components to be constructed with a reduced diameter housing, screen and reduced size rotor. The housing  12  of this invention can have an outside diameter in the range of 8 to 12 inches while most standard dryers have an outside diameter in the range of 30 to 40 inches. The screen  16  can have a diameter of approximately 6 inches with the outer corners of the blades  42  being spaced approximately 0.400 inch from the screen for optimum removal of water from the pellets. The blades  42  are preferably rectangular with the straight peripheral edges providing agitation of the pellets as they are lifted with the space between the blades and screen permitting some of the pellets to drop past upper blades and picked up by lower blades for more effective separation of water from the pellets. Also, the blade arrangement and configuration and their relationship to the screen reduces wear on the screen as compared to dryers which utilize a substantially continuous lifting and auguring effect that increases frictional engagement between the pellets and screen. 
     The components of the dryer of this invention are readily disconnected and the weight thereof supported by the gas spring  96  thereby facilitating the handling of the housing, screen, rotor and motor without the necessity of these components being physically lifted by an operator of the pellet dryer. The smaller diameter of the components enables the dryer to be effectively used in a laboratory application, or other small operation, and enables the components to be easily disassembled and assembled, and the components easily cleaned or replaced when disassembled. The screen bottom drawer enables the water draining into the tank to be cleaned of any solid debris or pellets which may pass downwardly from the base section of the housing. The openings communicating the base section of the housing and the screened bottom drawer may be varied in size and frequency to enable gravity liquid flow downwardly from the base section without undue restriction. 
     The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.