Centrifugal pellet dryer for small applications

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.

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.

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.