Abstract:
A method for dehumidifying and drying resin pellets that can efficiently dry both non-crystallized resin pellets and crystallized resin pellets, the apparatus being adapted to downsizing. A control means  67  adapts to operate in a first drying mode of controlling the heating operation of the first heating member  25  for heating longitudinally divided regions of the first cylinder  5  section to produce differentiated respective heating effects and that of the second heating member  31  for uniformly heating the second cylinder  7  section so as to crystallize the supplied non-crystallized resin pellets NCRP and subsequently drying them and in a second drying mode of controlling the heating operation of the first heating member  25  and that of the second heating member  31  for uniformly heating the first and second cylinder  5, 7  sections so as to drying the supplied crystallized resin pellets CRP.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an apparatus and a method for dehumidifying and drying resin pellets by removing moisture adhering to and bound water contained in non-crystallized resin pellets or crystallized resin pellets to be used as molding raw material in a resin molding machine.  
         [0003]     2. Description of the Related Art  
         [0004]     Dehumidifying and drying apparatus of the type under consideration include one disclosed in JP/3233419B2. The apparatus disclosed in the above-cited Patent Document is adapted to heat the resin pellets fed into a drying hopper under reduced pressure and dehumidifies and dries moisture adhering to and bound water contained in them. Such a resin dehumidifying and drying apparatus is effective for dehumidifying and drying crystallized resin pellets. However, problems arise when non-crystallized resin pellets such as polyester type resin pellets are dehumidified and dried under the conditions similar to those for dehumidifying and drying crystallized resin pellets. More specifically, non-crystallized resin pellets are softened and become molten under such conditions.  
         [0005]     When resin pellets are softened, they adhere to each other to form resin blocks. Then, it is no longer possible to dehumidifying and drying resin pellets as so many units. Resin blocks produced as resin pellets adhere to each other to form resin blocks can no longer be used as molding raw material without processing them. Additionally, molten resin pellets adhere to the inner surface of the hopper and the surfaces of agitator blades in the hopper for agitating resin pellets to produce blocks. Then, it is no longer possible to dehumidifying and drying them. Furthermore, the resin adhering to the outer surface of the hopper and the surfaces of the agitator blades operates as thermal insulator to make it difficult to efficiently heat resin pellets.  
         [0006]     Particularly, non-crystallized resin pellets are apt to be molten and become fused to form resin blocks when heated rapidly.  
         [0007]     JP2005/28683A1 proposes a drying apparatus designed to dissolve the above disadvantages. A drying apparatus according to the above-cited patent document comprises a crystallizing hopper for crystallizing granular resin and a drying hopper for drying the resin crystallized in the crystallizing hopper and a hollow rotary shaft that has an open lower end and is treated for thermal insulation is vertically arranged in the crystallizing hopper and provided on the outer surface with agitator wings. The rotary shaft is driven to rotate and hot air is supplied into the crystallizing hopper by way of the rotary shaft.  
         [0008]     However, the proposed drying apparatus requires a crystallizing hopper for crystallizing non-crystallized resin pellets and a drying hopper for drying crystallized resin pellets and is dedicated to drying crystallized resin pellets. Thus, the apparatus has large dimensions and is costly.  
       SUMMARY OF THE INVENTION  
       [0009]     In view of the above-identified circumstances, it is therefore an object of the present invention to provide an apparatus and a method for dehumidifying and drying resin pellets that can efficiently dehumidify and dry both non-crystallized resin pellets and crystallized resin pellets, the apparatus being adapted to downsizing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic perspective view of a resin pellets dehumidifying and drying apparatus according to the present invention, showing the entire apparatus;  
         [0011]      FIG. 2  is a schematic longitudinal cross sectional view of the resin pellets dehumidifying and drying apparatus taken through the center of the apparatus, the apparatus being partly omitted for the purpose of simplification;  
         [0012]      FIG. 3  is an enlarged schematic cross sectional view of the upper cylinder and the lower cylinder;  
         [0013]      FIG. 4  is a schematic electric block diagram of the resin pellets dehumidifying and drying apparatus, illustrating the control system of the apparatus;  
         [0014]      FIG. 5  is a schematic illustration of resin pellets being introduced into the resin pellets dehumidifying and drying apparatus;  
         [0015]      FIG. 6  is a schematic illustration of resin pellets being dried;  
         [0016]      FIG. 7  is a schematic illustration of resin pellets being delivered into the buffer hopper;  
         [0017]      FIG. 8  is a schematic illustration of resin pellets being supplied to a resin molding machine;  
         [0018]      FIG. 9  is a schematic illustration of non-crystallized resin pellets being heated in the first cylinder section; and  
         [0019]      FIG. 10  is a schematic illustration of the multi-level cylinder sections, where component cylinders of each cylinder section are arranged horizontally one on the other. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Now, the present invention will be described by referring to the accompanying drawings that illustrate a preferred embodiment of the invention.  
         [0021]     Referring firstly to  FIGS. 1 through 3 , the dehumidifying and drying apparatus  1  of this embodiment comprises a feed-in hopper section  3 , a first cylinder section  5 , a second cylinder section  7  and a delivery hopper section  9 . The feed-in hopper section  3  has an intake section  15  fitted thereto above the hopper container  11  thereof by way of an upper switching device  13  so that resin pellets are introduced by way of a feed-in hose  17  connected to the intake section  15 .  
         [0022]     The upper switching device  13  includes an opening/closing plate  13   a  that is supported between the upper aperture of the hopper container  11  and the lower aperture of the intake section  15  so as to be horizontally movable and an actuator member  13   b , which may typically be an air cylinder, for driving the opening/closing plate  13   a  to move back and forth. The opening/closing plate  13   a  is thin and made of a resilient material such as stainless steel. It is provided at a part thereof with an aperture section  13   c  that allows an upper part of the hopper container  11  and the intake section  15  to communicate with each other.  
         [0023]     The left end of the first cylinder section  5  having a horizontal axial line is fitted to a lower part of the feed-in hopper section  3  so as to make them communicate with each other. The first cylinder section  5  includes an upper level cylinder  19 , a first transfer screw  21  rotatably supported in the upper level cylinder  19 , an electric motor  23  for driving the first transfer screw  21  to rotate at a rotary speed that realizes a required transfer rate and a first heating member  25  for heating the upper level cylinder  19  and the first transfer screw  21 .  
         [0024]     The upper level cylinder  19  is provided at the left end thereof with an air inlet port  19   a  and at a middle section and at the right end thereof with air outlet ports  19   b . An air supply hose  19   c  is fitted to the air inlet port  19   a  while air exhaust hoses  19   d  are connected to the respective air outlet ports  19   b.    
         [0025]     The first heating member  25  includes a plurality of sheath heaters  25   a  horizontally driven into the shaft of the first transfer screw  21  and a plurality of surface heaters  25   b  separated from each other and fitted to the outer peripheral surface of the upper level cylinder  19 . The plurality of sheath heaters  25   a  and the surface heaters  25   b  are electrically energized and so controlled that the entire upper level cylinder  19  is heated uniformly or the temperature of the upper level cylinder  19  may gradually rise from the left side toward the right side.  
         [0026]     The second cylinder section  7  also has a horizontal axial line and is fitted to the right lower end in  FIG. 1  of the first cylinder section  5  so as to communicate with the latter and extend horizontally in the direction opposite to the extending direction of the latter. The apertures of the connection ports  5   a ,  7   a  of the first cylinder section  5  and the second cylinder section  7  have a diameter that agrees with the inner diameter of the upper level cylinder  19 .  
         [0027]     The second cylinder section  7  includes a lower level cylinder  27  having an inner diameter that agrees with the inner diameter of the upper level cylinder  19  and made of metal such as stainless steel, a second transfer screw  29  rotatably supported in the lower level cylinder  27 , an electric motor  30  for driving the second transfer screw  29  to rotate at a rotary speed that realizes a required transfer rate and a second heating member  31  for heating the lower level cylinder  27  and the second transfer screw  29  to a required temperature level.  
         [0028]     The lower level cylinder  27  is provided at the left end, at a middle section and at a right side thereof with respective air outlet ports  27   a  and air exhaust hoses  27   b  are connected to the respective air outlet ports  27   a.    
         [0029]     The second heating member  31  includes a plurality of sheath heaters  31   a  horizontally driven into the shaft of the second transfer screw  29  and a plurality of surface heaters  31   b  separated from each other and fitted to the outer peripheral surface of the lower level cylinder  27 . The second heating member  31  is electrically energized and so controlled manner as to heat the lower level cylinder  27  substantially uniformly.  
         [0030]     An air supply unit  33  is connected to the air inlet port  19   a  of the upper level cylinder  19  by way of the air supply hose  19   c  whereas an air exhaust unit  35 , which may typically be a blower or a vacuum pump, is connected to the air outlet ports  19   b ,  27   a  by way of the respective air exhaust hoses  19   d ,  27   b . Desirably, the air supply unit  33  is designed to supply dehumidified dry air. A thermally insulating material  37  such as glass wool is wound around the outer peripheral surfaces of the first and second cylinders  19 ,  27 .  
         [0031]     The delivery hopper section  9  is fitted to a left lower part in  FIG. 1  of the second cylinder section  7 . The delivery hopper section  9  includes a buffer hopper  39  and a delivery hopper  41  fitted to a lower part of the buffer hopper  39  by way of a lower switching device  43 .  
         [0032]     The buffer hopper  39  temporarily stores the dehumidified resin pellets that are delivered from the second cylinder section  7 . The lower switching device  43  includes an opening/closing plate  43   a  that is supported between the buffer hopper  39  and the delivery hopper  41  so as to be horizontally movable and an actuator member  43   b , which may typically be an air cylinder, for driving the opening/closing plate  43   a  to selectively move in a horizontal direction. The opening/closing plate  43   a  is thin and made of a resilient material such as stainless steel. It is provided at a part thereof with an aperture section  43   c  that allows the buffer hopper  39  and the delivery hopper  41  to communicate with each other.  
         [0033]     The delivery hopper  41  is provided to temporarily store dehumidified and dried resin pellets when they are supplied to a raw material supply section of the resin molding machine. It is provided at a lower part thereof with an executor section  45 .  
         [0034]     An air exhaust hose  47   a  is connected to the above-described intake section  15  from a pneumatic device  47 , while an air supply hose  47   b  is connected to the executor section  45  from the pneumatic device  47 . The pneumatic device  47  is typically formed by using a blower and adapted to be switched to supply or deliver air by means of a changeover valve  49  in such a way that it produces negative pressure in the intake section  15  in order to introduce resin pellets into the hopper container  11  and, at the same time, supplies compressed air into the executor section  45  in order to introduce dehumidified and dried resin pellets into the raw material supply section (not shown) of the resin molding machine.  
         [0035]     Level sensors  55 ,  57 ,  59  are fitted respectively to the hopper container  11 , the feeding upper limit position of the buffer hopper  39  and the lower limit position of the delivery hopper  41  for the purpose of detecting the quantities of resin pellets in them so that a detection signal is output when the quantity of resin pellets in the inside of any of them falls under a predetermined level. Additionally, a plurality of temperature sensors  61 ,  63  and a plurality of vacuum sensors  65 ,  66  are fitted to the upper level cylinder  19  and the lower level cylinder  27  and arranged in a horizontal direction.  
         [0036]     Now, referring to  FIG. 4 , various level sensors  55 ,  57 ,  59 ,  61 ,  63 ,  65 ,  66  are connected to the input side of control means  67  by way of an input control means  68 . Of these, the level sensor  55  outputs a feed-in completion signal to the control means  67  when a required quantity of non-crystallized resin pellets or crystallized resin pellets that are not dried yet is fed into the hopper container  11 . The level sensor  57  outputs a delivery completion signal to the control means  67  when a required quantity of dehumidified and dried resin pellets is fed into the buffer hopper  39 . The level sensor  59  outputs a feed-in completion signal to the control means  67  when the supply of a required quantity of dehumidified and dried resin pellets from the inside of the delivery hopper  41  to the raw material supply section of the resin molding machine is completed.  
         [0037]     The temperature sensors  61  fitted to the upper level cylinder  19  arranged horizontally and respectively detect the temperatures of the left side, the middle section and the right side of the upper level cylinder  19  in  FIG. 1  and output detection signals to the control means  67 . The temperature sensor  63  fitted to the lower level cylinder  27  detects the temperature of the lower level cylinder  27  and outputs a detection signal to the control means  67 .  
         [0038]     The vacuum sensors  65 ,  66  fitted respectively to the upper level cylinder  19  and the lower level cylinder  27  detect the degree of vacuum of the upper level cylinder  19  and that of the lower level cylinder  27  and output detection signals to the control means  67 .  
         [0039]     A valve drive means  69  is connected to the output side of the control means  67  so as to control the changeover valve  49  connected to the valve drive means  69  for supplying or delivering air according to the signals from the level sensors  55  and  59 .  
         [0040]     A switch drive means  71  is connected to the output side of the control means  67  so as to selectively drive the actuator members  13   b ,  43   b  for opening or closing according to the signals from a start switch (not shown) or the level sensors  55 ,  57 ,  59 .  
         [0041]     A heating control means  73  is connected to the output side of the control means  67  so as to control the electric currents applied respectively to the first and second heating members  25 ,  31  according to the detection signals from the temperature sensors  61 ,  63  and also the resin pellets heating temperature of the upper level cylinder  19  and that of the lower level cylinder  27 .  
         [0042]     An air exhaust drive means  75  is connected to the output side of the control means  67  so as to control the operation of driving the air exhaust unit  35  according to the detection signal from the vacuum sensor  65  and keep the inside of the upper level cylinder  19  and that of the lower level cylinder  27  to a required low pressure level.  
         [0043]     An air supply drive means  77  is connected to the output side of the control means  67  so as to drive the air supply unit  33  connected to it and supply a required quantity of air at least to the inside of the upper level cylinder  19 .  
         [0044]     A motor control means  79  is connected to the output side of the control means  67  so as to control and drive the electric motors  23  and  30  connected to it and causes them to transfer resin pellets at respective required transfer rates in the upper level cylinder  19  and the lower level cylinder  27 .  
         [0045]     Now, the dehumidifying and drying operation of the dehumidifying and drying apparatus  1  having the above-described configuration will be described below.  
         [0046]     Firstly, the operation of dehumidifying and drying crystallized resin pellets will be described. As the start switch is turned ON, the actuator member  13   b  is driven to open the plate  13   a  and hence the upper aperture of the hopper container  11 . At the same time, the actuator member  43   b  is driven to close the plate  43   a  and hence the communication path between the buffer hopper  39  and the delivery hopper  41  and subsequently turns the changeover valve  49  to the air exhaust side to exhaust the inside of the intake section  15  so as to draw and introduce crystallized resin pellets CRP that are not dried yet into the hopper container  11  under negative pressure by way of the feed-in hose  17 .  
         [0047]     As the crystallized resin pellets CRP introduced into the container hopper  11  get to a required quantity level and a feed-in completion signal is input from the level sensor  55 , the actuator member  13   b  is driven to close the plate  13   a  and hence the upper aperture of the hopper container  11 .  
         [0048]     During the above-described operation, the sheath heaters  25   a  and the surface heaters  25   b  of the first heating member  25  are electrically energized and so controlled that the upper level cylinder  19  shows a required temperature level substantially uniformly in the horizontal direction while the sheath heaters  31   a  and the surface heaters  31   b  of the second heating member  31  are also electrically energized and so controlled that the entire lower level cylinder  27  shows a required temperature level substantially same as that of the upper level cylinder  19 . Additionally, the air supply unit  33  is operated to introduce air at least into the upper level cylinder  19  by a required quantity while the air exhaust unit  35  is operated to exhaust the inside of the upper level cylinder  19  and that of the lower level cylinder  27  to produce a required low pressure level there.  
         [0049]     Then, the electric motors  23 ,  30  are driven to by turn drive the first and second transfer screws  21 ,  29  respectively to realize required feeding rates so that the crystallized resin pellets CRP in the hopper container  11  are transferred from the left side toward the right side in  FIG. 1  and the crystallized resin pellets CRP in the lower level cylinder  27  are transferred from the right side toward the left side in  FIG. 1 , while they are heated under reduced pressure and dehumidified and dried as the moisture adhering to them and the bound water contained in the inside are removed.  
         [0050]     Since the crystallized resin pellets CRP are highly thermally resistant because they are crystalline, they would neither be softened nor molten if they are heated to a high temperature level from the time when they are introduced into the upper level cylinder  19 . The steam that is driven off from the crystallized resin pellets CRP is delivered on the air flows directed from the air inlet port  19   a  respectively toward the air outlet port  19   b  and the air output port  27   a  (see  FIG. 6 ).  
         [0051]     Referring now to  FIG. 7 , the crystallized resin pellets CRP that have been transferred toward the left side in  FIG. 1  in the lower level cylinder  27  and dehumidified and dried fall in the buffer hopper  39  by their own weights and accumulate there. When the crystallized resin pellets CRP in the buffer hopper  39  get to a required quantity and a delivery completion signal is output from the level sensor  57 , the operation of driving the electric motors  23 ,  30 , the air supply unit  33  and the air exhaust unit  35  is suspended and subsequently the actuator member  43   b  is driven to close the plate  43   a  and allow the crystallized resin pellets CRP accumulated in the buffer hopper  39  to fall in the delivery hopper  41  by their own weights. Then, compressed air is supplied by turning the changeover valve  49  to the air supply side in order to transfer the crystallized resin pellets CRP in the delivery hopper  41  to the raw material supply section of the resin molding machine under pressure (see  FIG. 8 ).  
         [0052]     In parallel with the above-described operation, the actuator member  13   b  may be driven to close the plate  13   a  in order to introduce crystallized resin pellets CRP to be dehumidified and dried into the hopper container  11 .  
         [0053]     As the operation of transferring the crystallized resin pellets CRP in the delivery hopper  41  under pressure is completed and an under pressure delivery completion signal is output from the level sensor  59 , the actuator member  43   b  is driven to close the plate  43   a  and hence the communication path between the buffer hopper  39  and the delivery hopper  41  and subsequently the changeover valve  49  is turned to the air exhaust side so as to draw and introduce crystallized resin pellets CRP to be dehumidified and dried into the hopper container  11 .  
         [0054]     Now, the operation of dehumidifying and drying polyester type non-crystallized resin pellets typically made of PET or PEN will be described.  
         [0055]     As pointed out earlier, non-crystallized resin pellets NCRP can easily be softened and molten when heated rapidly if compared with crystallized resin pellets CRP. For this reason, the sheath heaters  25   a  and the surface heaters  25   b  of the first heating member  25  arranged at the upper level cylinder  19  are electrically energized and so controlled as to heat the left side, the middle part and the right side of the upper level cylinder  19  in  FIG. 1  respectively to a low temperature region, a middle temperature region and a high temperature region. The electrically energizing and controlling operation is conducted according to the temperature detection signals from the temperature sensors  61  arranged at the respective positions of the upper level cylinder  19 .  
         [0056]     On the other hand, as for the lower level cylinder  27 , the sheath heaters  31   a  and the surface heaters  31   b  are electrically energized and so controlled as to heat the entire lower level cylinder  27  substantially uniformly in the horizontal direction.  
         [0057]     When the electric motor  23  is driven to rotate in the above condition in order to feed a predetermined quantity of non-crystallized resin pellets NCRP into the hopper container  11  at a required rate, the non-crystallized resin pellets NCRP that are introduced to the left side of the upper level cylinder  19  in  FIG. 1  are gradually heated and crystallized to raise their thermal resistance as they are transferred by the rotary motion of the first transfer screw  21 , passing through the low temperature heating region, the middle temperature heating region and the high temperature heating region as shown in  FIG. 9 .  
         [0058]     Note that the air supplied to the left side of the upper level cylinder  19  in  FIG. 1  is delivered to the middle part and the right side in  FIG. 1  to form an air flow in order to prevent the non-crystallized resin pellets NCRP from being heated excessively and becoming softened and fused.  
         [0059]     The non-crystallized resin pellets NCRP are crystallized by heating and their thermal resistance is improved as they are transferred in the upper level cylinder  19  to the right side thereof in  FIG. 1 . The non-crystallized resin pellets NCRP that are transferred in the lower level cylinder  27  are dried as they are heated by the second heating member  31  in a required low pressure condition because air is exhausted from the inside by way of the air outlet port  27   a  to remove moisture adhering to them and bound water contained in them.  
         [0060]     At this time, an air flow is also formed in the lower level cylinder  27  as air supplied through the air inlet port  19   a  is partly delivered from the air outlet port  27   a . Thus, this arrangement delivers steam produced as a result of dehumidifying to the outside by means of the air flow and hence improves the efficiency of dehumidifying and drying.  
         [0061]     As described above, when dehumidifying and drying crystallized resin pellets CRP, this embodiment electrically energizes the upper level cylinder  19  and the lower level cylinder  27  under control to heat them entirely to a required temperature level for the purpose of dehumidifying and drying them. On the other hand, when dehumidifying and drying non-crystallized resin pellets NCRP, this embodiment electrically energizes the first heating member  25  so as to gradually raise the temperature of the upper level cylinder  19  in the direction of transferring non-crystallized resin pellets NCRP and crystallize and improve the thermal resistance of the non-crystallized resin pellets NCRP that are being transferred. Subsequently, the non-crystallized resin pellets NCRP are heated in the lower level cylinder  27  that is uniformly heated to a required temperature level so as to become dehumidified and dried. As a result, a single dehumidifying and drying apparatus  1  can efficiently dehumidify and dry both non-crystallized resin pellets NCRP and crystallized resin pellets CRP.  
         [0062]     While non-crystallized resin pellets NCRP are crystallized and their thermal resistance is improved in the upper level cylinder  19  and subsequently dehumidified and dried in the lower level cylinder  27  in the above description, there may be cases where a single upper level cylinder cannot satisfactorily crystallize non-crystallized resin pellets and/or a single lower level cylinder  27  cannot effectively dehumidify and dry crystallized resin pellets. The first cylinder section  81  for crystallization and the second cylinder section  83  for dehumidifying and drying may be realized as multi-level cylinder sections as shown in  FIG. 10  (each cylinder section having two levels in  FIG. 10 ).  
         [0063]     While air is supplied from the upstream side of the first cylinder section  5  in the sense of the direction of transferring resin pellets to form an air flow in the first and second cylinder sections flowing in the sense of transferring resin pellets and deliver the air flow to the outside in the above description, air may be supplied not into the first cylinder section but from the upstream side of the second cylinder in the sense of transferring resin pellets to form an air flow when dehumidifying and drying non-crystallized resin pellets NCRP. Alternatively, not air but inert gas such as nitrogen gas may be supplied into the first or second cylinder section for dehumidifying and drying non-crystallized resin pellets NCRP.