Abstract:
A drying apparatus which prepares granulated plastic for an injection molding machine, including a centrifugal apparatus configured for receiving the granulated plastic therein, at least a portion of the centrifugal apparatus being configured to rotate and thereby impart centrifugal force upon the granulated plastic and a dry air distributor fluidly coupled with the centrifugal apparatus and configured to deliver dry air within the centrifugal apparatus.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method and apparatus to dry granular plastic, and, more particularly, to a method and apparatus to dry granulated plastic for use in an injection molding machine.  
           [0003]    2. Description of the Related Art  
           [0004]    There are two basic types of plastic: thermosetting, which cannot be resoftened after being subjected to heat and pressure; and thermoplastic, which can be repeatedly softened and remolded by heat and pressure. When heat and pressure are applied to a thermoplastic binder, the chainlike polymers slide past each other, giving the material plasticity. However, when heat and pressure are initially applied to a thermosetting binder, the molecular chains become cross-linked, thus preventing any slippage if heat and pressure are reapplied.  
           [0005]    While plastics are available in the form of bars, tubes, sheets, coils and blocks and these can be fabricated to various specifications, plastic articles are commonly manufactured from plastic powders or granules in which desired shapes are fashioned by compression, transfer, extrusion or injection molding. Granulized plastic is the industrial standard method for the delivery of raw plastic to plastic molding facilities. In compression molding, powdered plastic is generally placed immediately in mold cavities, where the application of heat and pressure makes the material first plastic, then hard. Transfer molding, in which plastic granules are plasticized by outside heating and then poured into a mold to harden, is used for designs with intricate shapes and great variations in wall thickness. Extrusion molding employs a heating cylinder, pressure and an extrusion die through which molten plastic is sent and from which it exits in continuous form to be cut in lengths or coiled. Injection-molding machinery melts the plastic granules in a heating chamber and uses plunger action to force the molten plastic into cold molds, where the plastic hardens.  
           [0006]    To provide repeatable results the operations take place at rigidly controlled material temperatures, pressures, molding temperatures, intervals and material content. Moisture in the plastic material disrupts the process and results in an inferior product. Control of the contents of the plastic granules is provided by the manufacturer of the granule, however the absorption of atmospheric moisture by the plastic granules is sufficient to degrade the molding process. To reduce the problems caused by moisture in the plastic material, the plastic granules are dried before being used in an injection molding operation. The drying methods employed utilize the circulation of heated air and/or the use of desiccants. Such methods normally take hours to dry plastic granules and they expend a significant amount of energy.  
           [0007]    What is needed in the art is an apparatus which shortens the drying time of plastic granules and results in reduced energy usage.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a drying system including a centrifugal apparatus and an air drying system which together efficiently dry plastic granules.  
           [0009]    The invention comprises, in one form thereof, a drying apparatus which prepares granulated plastic for an injection molding machine, including a centrifugal apparatus configured for receiving the granulated plastic therein, at least a portion of the centrifugal apparatus being configured to rotate and thereby impart centrifugal force upon the granulated plastic and a dry air distributor fluidly coupled with the centrifugal apparatus and configured to deliver dry air within the centrifugal apparatus.  
           [0010]    An advantage of the present invention is that the drying of plastic granules is accomplished in less time than with conventional methods.  
           [0011]    Another advantage is less energy is required to dry plastic granules as compared to conventional methods.  
           [0012]    Yet another advantage is fewer drying units are needed in a facility since the cycle time to dry plastic granules is reduced.  
         BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, which is a schematic view of one embodiment of a plastic granule dryer of the present invention.  
           [0014]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    Referring now to the drawing, there is shown a plastic granule dryer  10  which generally includes material insertion device  12 , an air drying system  14 , a dried material collector  16 , a control system  18  and a centrifugal apparatus  20 .  
         [0016]    Material insertion device  12  includes a supply tube  22  and a material distributor  24 . Material insertion device  12  is coupled to a supply of granulated plastic having either a gravity feed with a control gate or a controllable drive for the delivery of granulated plastic to centrifugal apparatus  20 . Supply tube  22  is coupled to the supply of granulated plastic and connects to material distributor  24 . Material distributor  24  has one end connected to supply tube  22  to receive granulated plastic therefrom. An other end of material distributor  24  is arranged to deliver granulated plastic to centrifugal apparatus  20 .  
         [0017]    Air drying system  14  includes an enclosure  26 , air tubes  28 , a desiccant system  30 , a filter  32 , a blower  34 , a heat chamber  36  and an air distributor  38 . Air drying system  14  removes air from enclosure  26  and routes it by way of air tubes  28  through desiccant system  30 , filter  32 , blower  34 , heat chamber  36  and air distributor  38  back to enclosure  26 . As air is routed through air drying system  14  moisture is removed from the granulated plastic and absorbed in desiccant system  30 . Even though the elements of air drying system  14  are shown in a particular order in FIG. 1 the ordering of the elements can be altered. Arrows in FIG. 1 indicate a direction of airflow in plastic granule dryer system  10 .  
         [0018]    Enclosure  26  surrounds at least a portion of centrifugal apparatus  20  in order to allow the capture of air that has removed moisture from the granulated plastic. Enclosure  26  may optionally include a lid  27  allowing access to the interior thereof by an operator.  
         [0019]    Desiccant system  30  includes a first dryer bed  40 , a second dryer bed  42 , directing valves  44  and desiccant dryers  46 . First dryer bed  40  and second dryer bed  42  are each desiccant containers which contain removable desiccant, configured for the passage of air and the absorption of water therefrom. Both first dryer bed  40  and second dryer bed  42  have an air inlet passage and an air outlet passage which are coupled to directing valves  44 . Directing valves  44  are coupled to air tubes  28  to receive air therefrom and to exhaust air thereto. Directing valves  44  may be servo operated and are synchronized to allow the passage of air through either first dryer bed  40  or second dryer bed  42  allowing one of dryer beds  40  or  42  to be off-line and one to be on-line at any particular time. Directing valves  44  are interconnected with, and controlled by, control system  18 . A desiccant dryer  46  is associated with each of dryer beds  42  and  44 . Desiccant dryers  46  provide for the dehydration of dryer beds  42  and  44  when off-line. The dehydration cycle and detection of moisture in dryer beds  40  and  42  is directed by control system  18 .  
         [0020]    Filter  32  is interconnected with the air flow of air drying system  14  by way of air tubes  28 . Filter  32  contains a replaceable element which filters airborne particles from the air directed therethrough.  
         [0021]    Blower  34  is an enclosed blower with an air inlet and exhaust, each coupled to air tubes  28  for forcing air throughout air drying system  14 . Blower  34  includes an electric motor for the driving of an impeller blade. The speed at which blower  34  operates and the duration thereof is controlled by control system  18 .  
         [0022]    Heat chamber  36  has an air inlet and an air outlet, each coupled to air tubes  28  for the directing of air therethrough. An electrical element within heat chamber  36  provides heat which is conducted to the air passing through heat chamber  36 . The heat output of heat chamber  36  is controlled by control system  18 .  
         [0023]    Air distributor  38  is connected at one end to an air tube  28  through which dried, heated, pressurized air is supplied. Air distributor  38  has nozzles  39  within enclosure  26  which direct air toward plastic granules disposed on an interior surface of centrifugal apparatus  20 .  
         [0024]    Dried material collector  16  includes gate  48 , air cylinder  50  and enclosure  52 . Dried material collector  16  is located beneath centrifugal apparatus  20  for the collection of dried granulated plastic therefrom. Gate  48  seals enclosure  26  from enclosure  52  and prevents granulated plastic from entering enclosure  52  until gate  48  is opened. Air cylinder  50  is attached to a stationary portion of plastic granulate dryer  10  having an extendable/retractable cylinder attached to gate  48 . Air cylinder  50  is controlled by control system  18  which provides for the controlled opening of gate  48 .  
         [0025]    Enclosure  52  includes a collection opening  56 , a cleanout opening  58 , a cleanout door  60  and a material discharge opening  62 . Collection opening  56  is located on the upper portion of enclosure  52  for the purpose of passing granulated plastic from centrifugal apparatus  20  into dried material collector  16  when gate  48  is open. Cleanout opening  58  is provided for the convenience of an operator for cleaning purposes. Cleanout opening  58  is normally covered by cleanout door  60  which is hingedly secured to enclosure  52 . Material discharge opening  62  allows for the delivery of dried granulated plastic to a plastic molding machine. The transfer of dried granulated plastic, through material discharge opening  62 , is accomplished either by way of a mechanical system, such as an auger, or by way of a vacuum system (not illustrated in the drawings).  
         [0026]    Control system  18  includes a material delivery control  64 , a centrifugal apparatus speed control  66 , a duration control  68 , a humidity control  70 , a humidity sensor  71 , a temperature sensor  72 , a temperature control  73 , a desiccant sensor  74 , a desiccant control  75 , blower speed control  76  and an electrical power connection  78 . Material delivery control  64  controls the flow of granulated plastic through material insertion device  12  into centrifugal apparatus  20 . Centrifugal apparatus speed control  66  controls the speed at which centrifugal apparatus  20  operates. Duration control  68  allows for preset timed operation of plastic granule dryer  10 . Humidity sensor  71  senses the humidity of the air after passing over the granulated plastic in air drying system  14  and humidity control  70 , which is coupled to humidity sensor  71 , stops the operation of plastic granule dryer  10  when an operator predetermined humidity level is achieved. Temperature sensor  72  senses the temperature of heat chamber  36  and temperature control  73 , which is coupled to temperature sensor  72 , controls the temperature thereof. Desiccant sensor  74  senses the moisture contained in desiccant system  30  and desiccant control  75 , which is coupled to desiccant sensor  74 , and causes directing valves  44  to redirect air flow when the moisture exceeds an operator determined value. Blower speed control  76  allows the operator to control the speed of blower  34 . Electrical power connection  78  supplies electrical power to control system  18  and to all of plastic granule dryer  10 . Control system  18  allows an operator the ability to control each function manually or each function may be set to predetermined values.  
         [0027]    Centrifugal apparatus  20  includes perforated drum  80 , bearing block  82 , guide wheels  84 , drive wheel  86  and drive motor  88 . Centrifugal apparatus  20  processes granulated plastic in a batch operation manner. Granulated plastic enters centrifugal apparatus  20  by way of material distributor  24 , and centrifugal force is imparted to the granulated plastic as heated, dried, pressurized air is directed at the granulated plastic by way of air distributor  38 . Air flows around the plastic granules and then the air passes through perforated drum  80  and then through the rest of air drying system  14 .  
         [0028]    Perforated drum  80  is generally cylindrical in shape having a funnel-shaped portion disposed toward the bottom thereof with an opening to allow dried granulate plastic to exit perforated drum  80 . Perforated drum  80  has small holes throughout the cylindrical portion and optionally along the funnel-shaped portion. The small holes in perforated drum  80  are sized to prevent the granulate plastic from passing therethrough and formed to prevent the granulate plastic from blocking the small holes. Perforated drum  80  is disposed within enclosure  26  having bearing block  82  attached thereto which allows rotational movement thereof. Perforated drum  80  rotates around a vertical axis and is constrained by bearing block  82 , guide wheels  84  and drive wheel  86 .  
         [0029]    Bearing block  82  constrains perforated drum  80  to rotate about an axis perpendicular to the plane in which bearing block  82  lies. An opening is provided in the center of bearing block  82  to allow granulate plastic to flow from perforated drum  80  to dried material collector  16  when gate  48  is open.  
         [0030]    Guide wheels  84  and drive wheel  86  serve to provide dynamic stability to perforated drum  80  while it rotates. Guide wheels  84  also provides an offsetting lateral force from the force of drive wheel  86  which is in frictional contact with an outer surface of perforated drum  80 . Guide wheels  84  are secured to a stationary member of plastic granulate dryer  10 . Alternatively, guide wheels  84  and drive wheel  86  may be mounted to an inner surface of enclosure  26 .  
         [0031]    Drive wheel  86  is in frictional contact with an external surface of perforated drum  80 . A shaft of drive motor  88  is secured to the center of drive wheel  86 . Alternatively, a belt, gear, pneumatic or fluid drive may be used instead of drive wheel  86 .  
         [0032]    Drive motor  88  is secured to plastic granulate dryer  10 , having a shaft coupled to drive wheel  86 . Control system  18  is coupled with drive motor  88  to control the speed of drive motor  88  and thus the rotational speed of perforated drum  80 .  
         [0033]    Plastic granule dryer system  10  is located on a cart  90  to be relocatable relative to plastic injection molding machines (not shown). Alternatively, plastic granule dryer system  10  may be stationary with the dried granulate plastic being delivered to plastic injection molding machines.  
         [0034]    The batch drying of granulate plastic is controlled by an operator selecting drying parameters on control system  18  to control the delivery of plastic granules, the rotational speed of perforated drum  80 , the desired humidity, the temperature of the air used in the drying process and the speed of the air delivered from blower  34 . A measured amount of granulate plastic enters plastic granule dryer system  10  by way of material insertion device  12  and is distributed along a wall of perforated drum  80  as it is spinning. Centrifugal force keeps the granulated plastic on the walls of perforated drum  80 .  
         [0035]    Air from enclosure  26  is drawn, by way of air tubes  28 , in the direction indicated by the arrows in FIG. 1, to desiccant system  30  where moisture is removed from the air. The dried air is routed through air filter  32  and blower  34  to heat chamber  36  where the dried air is heated to enhance its moisture removing ability. The dried heated air is then routed through the shell of enclosure  26  and directed toward the granulated plastic disposed on the inside surface of perforated drum  80 . The centrifugal force acting on the granulated plastic serves to drive moisture therefrom, thereby increasing the efficiency of the moisture removal process. As the dried heated air encounters the granulated plastic, moisture is removed therefrom and the continuous air cycle continues until an operator intervenes or until an operator selected duration is completed or until an operator selected humidity level is achieved.  
         [0036]    Once the drying cycle is complete the rotation of perforated drum  80  is stopped and the granulated plastic gathers at the bottom of perforated drum  80 . Gate  48  is opened and the granulated plastic falls into dried material collector  16  and is therefrom distributed to a plastic molding machine.  
         [0037]    While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.