Alternate polymer extrusion system and method with accumulator

Abstract

An extrusion system and method uses an accumulator to control and use excess plastic melt. The accumulator is situated between an extruder and a gear pump. The accumulator includes an accumulator housing to store excess plastic melt from the extruder and an accumulator spring connected to an accumulator piston to subsequently send the excess plastic melt to the gear pump. In another embodiment, the accumulator includes an accumulator housing to store excess plastic melt from the extruder and a hydraulics system to send the excess plastic melt to the gear pump. The accumulator can be a first in first out (FIFO) device having a melt passage through the accumulator piston. The system and method are used particularly advantageously in Alternate Polymer extrusion installation in which gear pumps regularly increase and decrease their speed but in which the melt-supplying extruder cannot accommodate such rapid speed changes.

1 . An extrusion system comprising: 
 an extruder for moving plastic internally toward an end thereof;    an accumulator, connected downstream to the extruder, for receiving plastic from the extruder;    a gear pump, connected downstream to the accumulator, for receiving plastic from the accumulator; and    a die, connected downstream to the gear pump, for receiving plastic from the gear pump and for thereafter forming the plastic into an extrudate,    wherein the accumulator collects plastic from the extruder in response to a first operating condition of the gear pump, and    wherein the accumulator provides plastic to the gear pump in response to a second operating condition of the gear pump.    
   
   
       2 . The extrusion system of  claim 1 , wherein the first operating condition of the gear pump is a change in speed of operation of the gear pump.  
   
   
       3 . The extrusion system of  claim 1 , wherein the second operating condition of the gear pump is a change in speed of operation of the gear pump.  
   
   
       4 . The extrusion system of  claim 1 , wherein the accumulator further comprises: 
 a housing for receiving the plastic; and    a piston, biased by a spring, for moving the plastic within the accumulator to the gear pump.    
   
   
       5 . The extrusion system of  claim 4 , wherein the extrusion system further comprises a check valve positioned between the extruder and the accumulator, wherein the check valve prevents plastic in the accumulator from flowing to the extruder while the plastic in the accumulator is being sent to the gear pump.  
   
   
       6 . The extrusion system of  claim 1 , wherein the accumulator further comprises: 
 a housing for receiving the plastic; and    a piston, connected to a hydraulics system, for moving the plastic within the accumulator to the gear pump.    
   
   
       7 . The extrusion system of  claim 6 , wherein the extrusion system further comprises a check valve positioned between the extruder and the gear pump, wherein the check valve prevents plastic in the accumulator from flowing to the extruder while the plastic in the accumulator is being sent to the gear pump.  
   
   
       8 . The extrusion system of  claim 1 , wherein the accumulator is a first in last out accumulator.  
   
   
       9 . The extrusion system of  claim 1 , wherein the accumulator is a first in first out accumulator.  
   
   
       10 . The extrusion system of  claim 1 , further including at least one further extruder, accumulator and gear pump, the die being a co-extrusion die connected with each of the gear pumps, whereby alternately increasing and decreasing the speeds of the gear pumps alters the relative content of plastic delivered via the co-extrusion die to the extrudate by the gear pumps.  
   
   
       11 . The extrusion system of  claim 1 , the accumulator comprising: 
 a housing;    a piston with the housing; and    the path of flow of plastic from the extruder into the accumulator includes a passage through the piston to a plastic accumulation locator in the accumulator.    
   
   
       12 . The extrusion system of  claim 11 , further comprising a check valve located in the passage to prevent plastic flowing from the accumulation location back to the extruder.  
   
   
       13 . A method of extrusion comprising: 
 extruding plastic from an extruder;    forcing the plastic downstream from the extruder to a gear pump through an accumulator;    collecting plastic from the extruder into the accumulator in response to a first operating condition of the gear pump; and    providing plastic from the accumulator to the gear pump in response to a second operating condition of the gear pump.    
   
   
       14 . The method of extrusion of  claim 13 , wherein the first operating condition of the gear pump is a change in speed of operation of the gear pump.  
   
   
       15 . The method of extrusion of  claim 13 , wherein the second operating condition of the gear pump is a change in speed of operation of the gear pump.  
   
   
       16 . The method of extrusion of  claim 13 , wherein the step of collecting plastic comprises receiving the plastic in a housing, and the step of providing plastic comprises using a spring-biased piston to push the plastic towards the gear pump.  
   
   
       17 . The method of extrusion of  claim 16 , further comprising controlling the flow of plastic to the gear pump by positioning a check valve between the extruder and the accumulator, wherein the check valve prevents plastic in the accumulator from flowing to the extruder while the plastic in the accumulator is being sent to the gear pump.  
   
   
       18 . The method of extrusion of  claim 13 , wherein the step of collecting plastic comprises receiving the plastic in a housing, and the step of providing plastic comprises using a hydraulics-activated piston to push the plastic towards the gear pump.  
   
   
       19 . The method of extrusion of  claim 18 , further comprising controlling the flow of plastic to the gear pump by positioning a check valve between the extruder and the accumulator, wherein the check valve prevents plastic in the accumulator from flowing to the extruder while the plastic in the accumulator is being sent to the gear pump.  
   
   
       20 . The method of extrusion of  claim 13 , wherein the last plastic collected during the collecting step is the first plastic provided during the providing step.  
   
   
       21 . The method of extrusion of  claim 13 , wherein the first plastic collected during the collecting step is the first plastic provided during the providing step.  
   
   
       22 . The method of extrusion of  claim 13 , further comprising: 
 extruding plastic from a further extruder;    forcing the plastic downstream from the further extruder to a further gear pump;    through a further accumulator, providing a co-extrusion die connected to an output of each gear pump; and    alternately increasing and decreasing the speeds of the gear pumps to alter the relative content of delivered via the co-extrusion die to the extrudate by the gear pumps.    
   
   
       23 . The method of extrusion of  claim 13 , wherein the step of collecting plastic from the extruder into the accumulator comprises delivering plastic to an accumulation location in the accumulator through a passage in a piston within a housing of the accumulator.  
   
   
       24 . The method of extrusion of  claim 23 , further comprising preventing plastic flow from the accumulation location back to the extruder by a check valve in the passage in the piston.  
   
   
       25 . An extrusion system comprising: 
 means for extruding plastic;    means for providing the extruded plastic to a gear pump;    means for accumulating excess plastic from the extruder which was not sent to the gear pump; and    means for subsequently providing the excess plastic to the gear pump.    
   
   
       26 . The extrusion system of  claim 19 , further comprising: 
 means for controlling the means for extruding and the gear pump to vary the speed thereof.    
   
   
       27 . The extrusion system of  claim 26 , further comprising further means for extruding, plastic, means for providing the extruded plastic to a gear pump and means for accumulating excess plastic, each gear pump being connected at its output to a co-extrusion die, and means for controlling comprising means for alternately varying the speeds of the gear pumps and extruders to vary the relative content in an extrudate of plastics delivered from the gear pumps; whereby the means for accumulating accumulate excess plastic each time the associated gear pump shows more quickly than the associated extruder and provides the excess plastic to the gear pump each time the associated gear pump accelerates more quickly than the associated extruder.