Abstract:
A rotary particle separator for separating small particles from large particles is provided and includes an inclined rotary shaft having a first end and a second end. A particle bend is coupled to the elevated first end of the shaft. The particle bend has a bottom surface with a hole therethrough for gravity feed of material including the large particles and small particles from the bend along the shaft towards the second end. Annulae are spaced along the shaft with each of the annulae having a central aperture bounded by a ring that terminates in an annulae outer diameter. At least one paddle is interspersed between two adjacent annulae with at least one paddle positioned to rotate around the shaft. A screen mesh having a mesh size surrounds the annulae with a mesh size such that the small particles within the material are able to pass through the mesh and thereby leave larger particles preferentially segregated within the volume defined by the annulae spaced along the shaft. A large particle exhaust is provided proximal to the second end of the shaft after the particulate has traversed the annulae.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention in general relates to a particle separator and in particular to a rotary shaft separator having multiple annulae spaced along the shaft and having a paddle between two adjacent spaced annulae to allow gravity fed material containing large particles and small particles to successively traverse between annulae as the rotary shaft is turned to selectively allow smaller particulate to pass through a screen mesh surrounding the rotary shaft. 
       BACKGROUND OF THE INVENTION 
       [0002]    Thermoplastic molding produces sprues and other pieces of scrap thermoplastic material in the course of molding articles. Rather than discard this scrap material, it is conventional to the art to grind such scrap into comparatively uniform sized particulate amountable to intermixing with virgin thermoplastic pellets for reprocessing through the molding process. Unfortunately, it is common that debris becomes intermixed with the pelletized thermoplastic scrap. Such debris can compromise the quality of a molded article through creation of an inhomageneity. This problem is especially severe when molding transparent articles in which debris can form a visually discernable inclusion. Further, depending on the processing conditions and the nature of the debris, charring of the debris can occur resulting in a visually discernable black inclusion. 
         [0003]    In response to the problems associated with debris becoming entrained with a regrind particle stream or indeed a virgin thermoplastic particle stream, the separators are conventionally used to remove such debris. Conventional separators have included vibratory separators in which material is loaded on to a size exclusion mesh and either manually or mechanically oscillated to shake the debris through the mesh thereby leaving comparatively debris free particulate. However, such vibratory separation schemes require a considerable amount of space and are kinetically slow in separating debris from particulate as a result of electrostatic attraction between the debris and particulate resulting in interparticle transfer of debris as the debris traverses through the particulate before being sieved from the particulate. In response to the limitations of vibratory separation techniques, pressurized air flows have been utilized to flow over a monolayer or several monolayers of particulate to drive the comparatively lighter mass debris from the particles. A number of such systems have also utilized a conveyor or other movement of the material to facilitate such separation. However, pressurized air separation techniques tend to be complex and difficult to maintain on to the inclusion of an air compressor and particle conveyance equipment that increase the footprint of such a separator as well as cost of usage. 
         [0004]    Thus, there exists a need for a particle separator that achieves high throughput separation of particulate from debris and does so with limited complexity and moving components. There further exists a need for a particle separator having a small footprint and operative without a pressurized countercurrent gas flow across the material to be separated. 
       SUMMARY OF THE INVENTION 
       [0005]    A rotary particle separator for separating small particles from large particles is provided and includes an inclined rotary shaft having a first end and a second end. A particle bin is coupled to the elevated first end of the shaft. The particle bin has a bottom surface with a hole therethrough for gravity feed of material including the large particles and small particles from the bin along the shaft towards the second end. Annulae are spaced along the shaft with each of the annulae having a central aperture bounded by a ring that terminates in an annulae outer diameter. At least one paddle is interspersed between two adjacent annulae with at least one paddle positioned to rotate around the shaft. A screen mesh having a mesh size surrounds the annulae with a mesh size such that the small particles within the material are able to pass through the mesh and thereby leave larger particles preferentially segregated within the volume defined by the annulae spaced along the shaft. A large particle exhaust is provided proximal to the second end of the shaft after the particulate has traversed the annulae. 
         [0006]    A process for separating a material into large particles and small particles is provided that includes adding the material to a feed bin of a separator as detailed above. By rotating the shaft of the separator, small particles are collected external to the mesh and the large particles are collected proximal to the second end of the shaft thereby separating the material into large particle and small particle feeds. The process of particle separation occurring with gravity feed of the material into the separator and rotation of the shaft. The process occurring independent of a pressurized gas stream contacting the material during separation. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0007]    The present invention is further detailed with respect to the following figures provided to depict exemplary aspects of the present invention in nonlimiting form. 
           [0008]      FIG. 1  is a partial cutaway side view of an inventive rotary particle separator; 
           [0009]      FIG. 2  is a side view of the shaft and associated elements wherein the letters associated with  FIG. 2  denote transverse cross-sectional images detailed in  FIG. 3 ; 
           [0010]      FIGS. 3A-3E  are transverse cross-sectional views registry with the letters depicted in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    The present invention has utility as a separator of small particulate from large particulate from an intermixed material feed. The present invention finds particular utility in the field of separation of thermoplastic regrind particulate from intermixed debris which constitutes a smaller particulate relative to the thermoplastic regrind. An inventive separator uses a rotary shaft mounting multiple annulae fed by a material feeder bin that meters material into inventor separator. Intermediate between the annulae are at least one paddle that moves the material along a peripheral mesh screen to separate any particulate that passes through the mesh screen leaving the large particulate to traverse between central openings so as to enrich the material passing between annulae in large particulate and small particulate is sieved therefrom the surrounding mesh and into a separate collection stream. Attributes particularly beneficial to the inventive separator include compact footprint and the ability to separate through the use of rotation and gravitational forces. While one can resort to use of a pressurized gas stream to induce material separation between large and small particulate, such pressurized gas stream is not essential thereby simplifying the separation process. 
         [0012]    With reference to the attached figures, an inventive particle separator is depicted generally at  10 . The separator  10  includes a rotary shaft  12  having a first end  14  and a second end  16 . Optionally, the shaft  12  has a polygonal cross-section to engage complimentary engagements associated with the arms  60  so as to limit proportional slippage of a given annulus during rotation. Proximal to the first end  14  a particle feed bin  16  is formed that includes a bottom surface  18  having an aperture hole  20  therein so is to gravity feed a material M along the inclined shaft  12 . Typically, the aperture hole has a hole area of between −0.01 and 10% of a bottom surface area of the bottom surface  18 . The angle of incline for the shaft  12  relative to horizontal is defined by an angle α. Typically, the angle α is between 10-60°, while angles beyond this range are operative so long as material M that enters the feed bin  16  is urged by gravity toward the periphery of feed bin  16  and through the separator  10 . An angle α is selectively adjusted using a stand  22  that illustratively includes a higher leg  24  proximal to the first end  14  of the shaft and a shorter leg  26  proximal to the second  16  of the shaft  12 . One of ordinary skill in the art will appreciate that through adjustment of the relative height of legs  24  relative to  26  that the angle α is modified. By way of example, the relative height of leg  24  is modified through to aligned holes  28  between a first leg piece  30  and a second telescoping leg piece  32  that when coupled with a locking pin  34  allow for the height of the first end  14  relative to the second end  16  of the shaft  12  to be modified. It is appreciated that numerous modes exist for changing the relative height of the first end  14  relative to the second end  16  besides that shown in  FIG. 1 . These alternate versions of stand  22  illustratively include the use of a ratchet jack, a screw jack, a hydraulic piston, resort to spacer blocks, or a combination thereof. It is also appreciated that leg  26  also has a variable height as detailed with respect to leg  24  and that such aspects are not depicted in  FIG. 1  for the purposes of visual clarity. 
         [0013]    Optionally, the separator  10  has a housing  36  to protect the material M from environmental contamination and reduce environmental dusting associated with the separation process. The housing  36  is readily formed of conventional materials including sheet metal, plastics, wood, and combinations thereof. Optionally, the housing  36  has a hinge  38  about which a housing door  40  selectively opens. The door  40  having a latch  42 , if the door  40  is present to provide for the selective opening and closing of the door  40 . Optionally, part or all of the housing  36  or door  40 , if present, is transparent to allow for quick visual inspection as to the operation of the inventive separator  10 . For illustrative purposes, a transparent window is depicted at  44 . The shaft  12  is driven by a power source  46  such as an electric motor either directly through a mechanical coupling or via an intermediate transmission  48 . The power source  46  is readily included within the housing  36  and while depicted proximal to the second end of shaft  12 , it is appreciated that the power source  46  is readily mechanically coupled to the first end  14  as well. Optionally, the feed bin  16  is in mechanical communication with a hopper  50  that receives material M including large particles L and small particles S. The hopper  50  is readily formed of the same materials from which housing  36  is formed. 
         [0014]    Multiple annulae,  52 A- 52 H are shown collectively at  52  are provided. It is appreciated that as a minimum, to such annulae  52  are provided as denoted at  52 A and  52 B to perform a separation. Each of the annulae  52  is characterized by a central aperture  54 A defined by an outer ring  56 A with the outer ring  52  defining an outer diameter  58 A. An arm  60 A is provided to couple the annulae  52 A to the shaft  12 . Individual annulae are depicted at reference at  52 A- 52 H. Each annulae as demonstratively shown for annulae  52 A is a central aperture  54 A with the outer boundaries of which are defined by an outer ring  56 A. The outer ring  56 A defines an outer diameter  58 A. An arm  60 A provides a mechanical connection between outer ring  56 A and the shaft  12 . Preferably, a fastener is provided to selectively adjust the position of annulae  52 A along the shaft  12  (not shown). It is appreciated that each of the annulae  52 B- 52 H have corresponding aspects to  52 A,  54 A,  56 A,  58 A and  60 A yet are not so labeled for visual clarity. An inventive separator  10  has at least two annulae  52 A and  52 B spaced along shaft  12 . It is appreciated that the annulae regardless of the number are regularly spaced or spacing there between varied to achieve desired points of separation. Also, it is appreciated that while the annulae  52  are depicted as having uniform dimension central apertures such as  54 A, uniform with outer rings such as  56 A, and uniform outer diameter such as  58 A, is appreciated that each of these perimeters is independently varied for a given annulus. Also, while each of the annulae  52  as depicted extends orthogonal to shaft  12 , it is appreciated that the annulae  52  are readily positioned at an angle β of between 75-115° with 0° measured from the first end  14 . Typically, each of the annulae is a ring with a ring width as between 20 and 90% of a distance between an outer edge of said shaft  12  and the outer diameter of the annulus. At least one paddle  62  is provided interposed between two adjacent annulae such as paddle  62 B disposed between annulae  52 B and  52 C. About the outer ring  56 B. The paddle  62  as exemplified by paddles  62 A- 62 F, operate to urge material M contain large particles and small particles into moving contact with a screen mesh  64  having a screen mesh size  66  that surrounds the annulae  52 . While preferably, a paddle  62  is mechanically connected or continuous between adjacent annulae, this need not be the case for an inventive separator to be operative. Additionally, it is appreciated that while the paddles collectively shown at  62  and including  62 A- 62 F are depicted as being radial in orientation relative to the shaft  12  and extending the full width of an outer ring  56  to the outer diameter  58 , it is appreciated that an individual paddle is independently mounted between 0-90° relative to the shaft  12  where 0° defines the radial paddle as depicted and 90° depicts a tangential paddle. It is appreciated that the attack angle of a given paddle is readily adjusted to make the paddle operative as a scoop to effectively lift material M away from contact from a surrounding screen  64  whereas a negative paddle attack angle functions to effectively press material M within an inventive separator  10  against the screen  64 . To stabilize the rotary portions of an inventive separator  10 , a brace  66  is optionally secured to the shaft  12  proximal to the second end  16  with the brace  66  forming anchor points for one or more peripheral stays  68 . It is appreciated that the screen  64  is affixed to the shaft  12  and rotates therewith or alternatively, is stationary and the shaft  12  with annulue  52  rotate relative to the screen  64 . 
         [0015]    The relative position of paddles  62 A- 62 F are preferably displaced from one another to promote a helical progression of material along the length of the shaft  12 . An exemplary relative position of paddles  62 A- 62 D is a progression of +90°-+90°-+90° as best depicted in  FIGS. 3A-3E . Successive paddles are preferably displaced between ±60° to ±130° and more preferably ±85° to ±95°. Typical patterns of paddle progression are ±30° to ±120°; ±60° to ±120°; ±60° to ±120°. Successive annulae optionally repeat this process in whole or part. It has been found that this pattern of paddles in relative position affords an effective tumbling action to screen small particles S from large particles L that were originally combined in material M. 
         [0016]    In operation, material M enters feed bin  16  either directly or through an optional hopper  50 . The shaft  12  is then operated at a rotational speed of between 0.1 and 200 rotations per minute to allow the material to be gravitationally tumbled and contact the screen  64  through interaction with paddle  62 A and a surface of outer ring  56 A as the material M is metered through hole  20 . Small particles S are able to pass through the screen mesh  66  thereby leaving the material M enriched in large particles L. Through continued rotation of shaft  12 , partially separated material is then transferred to between annulae  52 A and  52 B to afford a second stage of separation. Optionally, the screen mesh size  66  is graded along the length of the screen mesh  64  with each successive stage of annulae constituting a separate collection stream as depicted at small particle outlets  70 A,  70 B and  70 C. Material M that traverses the length of the shaft  12  along annulae  52  is then collected at large particle outlet  72 . It is appreciated that depending on the nature of the material M, the large particulate fraction L, small particulate fraction S, are both represent desired collection streams. In the exemplary case of thermoplastic regrind, typically, the large particle fraction L is desired while the small particle fraction S constitutes undesired debris. It is appreciated that an inventive separator  10  is also well suited for separation of grains and other agricultural products. An inventive separator has the attribute of achieving desired separations with a small footprint amid high degree of adjustment to accommodate different sized distribution materials M, and does so without resort to a pressurized gas stream contacting the material. While such a pressurized gas stream is recognized to be operative with the present invention, usage of a pressurized gas stream such as air is noted to increase complexity of the overall separation process as well as promoting undesirable charging of material M through electrostatics. 
         [0017]    Patents and publications mentioned in the specifications are indicative of the levels of those skilled in the art to which the invention pertains. These patents and publications are incorporated herein by reference to the same extent as if each individual application or publication was specifically and individually expressed explicitly in detail herein. 
         [0018]    The foregoing description is illustrative of particular embodiments of the invention, but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.