Patent ID: 7018191

Claim:
An extrusion system comprising: (a) an extruder having a screw for moving plastic internally toward an end thereof, (b) a screw motor connected in driving relation to the screw, (c) a gear pump connected to the extruder to receive hot viscous plastic delivered thereto by the extruder, (d) a gear pump motor connected in driving relation to the gear pump to move the hot viscous plastic therethrough, (e) a die downstream of the gear pump for receiving hot viscous plastic moved through the gear pump to form an extrudate, (f) a puller for pulling the extrudate away from the die, (g) a puller motor connected in driving relation to the puller, (h) a controller connected in controlling relation to the screw motor, the gear pump motor and the puller motor to control the speeds of the screw, the gear pump and the puller, (i) a speed sensor operative to generate an electrical output indicative of the speed of the extrudate, the electrical output indicative of the speed of the extrudate being connected as an input to the controller, (j) a gear pump speed encoder operatively connected to the gear pump to generate an electrical output indicative of the volume per unit of time of hot viscous plastic being forced through the die, the electrical output indicative of the volume per unit time being connected as an input to the controller, (k) a screw speed encoder operatively connected to the screw to generate an electrical output indicative of the speed of the screw, the electrical output indicative of the speed of the screw being connected as an input to the controller, (l) the extruder having at least one heater for imparting heat to the plastic being moved by the screw, the controller being connected in controlling relation to the at least one heater to control the amount of heat being imparted by the heater to the plastic being moved by the screw, (m) a temperature sensor located to sense the temperature of the extruder where heat is being introduced to plastic being moved through the heater, (n) a pressure sensor located upstream and proximate the die in the path of flow of the hot viscous plastic to the die and having an electrical output indicative of pressure there connected as an input to the controller, (o) the controller being programmed to increase and decrease at least one of the gear pump speed and the speed of the puller motor, the puller and the extrudate in response to a change in the cross-sectional area of the extrudate derived from an indication of the speed of the gear pump delivered to the controller by the gear pump encoder and an indication of the speed of the extrudate delivered to the controller by the puller encoder, and (p) the controller being programmed to increase and decrease the temperature of the viscous plastic in the extruder to maintain the viscosity of the viscous plastic in the extruder in response to a detected change in viscosity as indicated by a change in pressure in the hot viscous plastic by the pressure sensor upstream of and proximate the die.