Method and apparatus for drying granular resin material

Abstract

Method and apparatus for drying granular resin material by drawing vacuum over heating resin material in a vessel, while periodically purging the vessel with the material therein with dry air and bathing the vacuum dried material with dry air until furnished to a processing machine.

The following is claimed: 
     
         1 . Apparatus for drying granular material, comprising:
 a) a heating hopper having an outlet at the top;   b) a vacuum chamber positioned below the heating hopper;   c) a retention hopper positioned below the vacuum chamber;   d) a blower having a variable frequency drive for blowing heated air;   e) a heating conduit connecting the blower with the heating hopper at the heating hopper bottom, the heating conduit having a heater for heating ambient air therewithin prior to introduction into the heating hopper;   f) a first drying conduit for periodically introducing dry purge air into the vacuum chamber while granular material is being dried therein under vacuum;   g) a sensor for detecting temperature of heated air released at the top of the heating hopper; and   h) a control for adjusting speed of the blower in response to the detected air temperature.   
     
     
         2 . Apparatus of  claim 1  further comprising:
 a) a first sealing gate between the heating hopper and the vacuum chamber, movable perpendicularly to the direction of granular material flow between open and closed positions, for controlling granular material flow from the heating hopper into the vacuum chamber; 
 b) a second sealing gate between the vacuum chamber and the retention hopper, movable perpendicularly to the direction of granular material flow between open and closed positions, for controlling granular material flow from the vacuum chamber into the retention hopper. 
 
     
     
         3 . Apparatus of  claim 1  further comprising:
 a) a plurality of first gates between the heating hopper and the vacuum chamber, movable between open and closed positions, for controlling granular material flow from the heating hopper into the vacuum chamber; 
 b) a plurality of second gates between the vacuum chamber and the retention hopper, movable between open and closed positions, for controlling granular material flow from the vacuum chamber into the retention hopper. 
 
     
     
         4 . Apparatus of  claim 3  wherein the first and second gates are connected to the vacuum chamber. 
     
     
         5 . Apparatus of  claim 4  wherein the first and second gates are sliding gates. 
     
     
         6 . Apparatus of  claim 1  further comprising a second drying conduit for periodically introducing blanketing dry air into the retention hopper. 
     
     
         7 . Apparatus of  claim 1  further comprising:
 a) a support bearing the weight of the retention hopper; and 
 b) a sensor for sensing weight of the vacuum chamber and any granular material therein. 
 
     
     
         8 . Apparatus of  claim 7  further comprising:
 a) a second sensor for sensing weight of the retention hopper and any granular material therein. 
 
     
     
         9 . Apparatus of  claim 8  wherein the sensors are load cells. 
     
     
         10 . A method for drying granular resin material prior to processing thereof by molding or extrusion, comprising:
 a) heating granular material in a hopper by introduction of heated air at the hopper bottom;   b) releasing the heated air to ambient at the hopper top;   c) monitoring heated air temperature as the heated air is released to ambient;   d) controlling heat input to the heating hopper supplied by the heated ambient air, so that monitored air temperature at the top of the heating hopper does not exceed a preselected temperature;   e) periodically releasing heated granular resin material from the heating hopper for flow into a vacuum chamber and replenishing the heating hopper with fresh granular resin material in an amount substantially equal to that released into the vacuum chamber;   f) periodically drawing vacuum in the vacuum chamber to dry the heated granular resin material therein;   g) periodically purging the vacuum chamber with dry air;   h) periodically draining dried granular resin material from the vacuum chamber into a retention hopper;   i) blanketing dried granular resin material in the retention hopper with dry air.   
     
     
         11 . The method of  claim 10  wherein regulating heat input to the heating hopper further comprises regulating speed of air passing through a heater. 
     
     
         12 . The method of  claim 10  wherein purging the vacuum chamber with dry air further comprises introducing dried compressed air into the vacuum chamber at the bottom of the chamber. 
     
     
         13 . Apparatus for drying granular material prior to molding or extrusion processing thereof, comprising:
 a) a heating hopper;   b) a vacuum chamber;   c) a retention hopper;   d) a blower for supplying heated air for flow through the heating hopper;   e) a heating conduit connecting the blower with the heating hopper, having a heater for heating ambient air therewithin prior to introduction into the heating hopper;   f) a first drying conduit for introducing dry purge air into the vacuum chamber while granular material is being dried therein under vacuum;   g) a second drying conduit for introducing blanketing dry air into the retention hopper;   h) a first gate between the heating hopper and the vacuum chamber, movable between open and closed positions, for controlling granular resin material flow from the heating hopper into the vacuum chamber;   i) a second gate between the vacuum chamber and the retention hopper, movable between open and closed positions, for controlling granular resin material flow from the vacuum chamber into the retention hopper;   j) a load cell for sensing weight of any granular material in the vacuum chamber.   k) a second load cell for sensing weight of any granular material in the retention hopper;   l) a material load sensor providing a signal indicative of granular material weight in the heating hopper; and   m) a controller connected to the material load weight sensor, receiving the signal therefrom and in response to low granular material load weight actuating the apparatus to furnish granular material to the heating hopper or if no granular material is available shutting down the apparatus.   
     
     
         14 . A method for drying granular material prior to processing thereof by molding or extrusion, comprising:
 a) heating granular material in a heating hopper;   b) monitoring air temperature at the top of the heating hopper;   c) regulating heat input to the heating hopper from the heated ambient air so that temperature of monitored air escaping to ambient at the top of the heating hopper does not exceed a preselected temperature;   d) releasing heated granular material from the heating hopper for flow downwardly into a vacuum chamber while replenishing the heating hopper from above with fresh granular material in an amount substantially equal to that released into the vacuum chamber;   e) drawing vacuum in the vacuum chamber to dry granular resin material therein while periodically purging the vacuum chamber by passing air first along a membrane dryer and then introducing the dry air into the vacuum chamber;   f) periodically draining granular resin material from the vacuum chamber into a retention hopper; and   g) continuously blanketing granular resin material in the retention hopper with dry air.   
     
     
         15 . In a method for drying granular material prior to processing thereof by molding or extrusion including the steps of heating granular material in a heating hopper by application of heating air thereto, releasing heated granular material from the heating hopper for flow downwardly into a vacuum chamber, and drawing vacuum in the vacuum chamber to dry granular material resident therein, the improvement comprising:
 a) monitoring the temperature of heated air released to ambient from the heating hopper;   b) simultaneously regulating heating input to the heating hopper, so that temperature of monitored air released to ambient at the top of the heating hopper does not exceed a preselected temperature, while periodically purging the vacuum chamber with dry air as the vacuum chamber contains granular material under vacuum;   c) draining dried granular material from the vacuum chamber into a retention hopper; and   d) dynamically blanketing dried granular material in the retention hopper with dry air.