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US 7,018,191 B2Granted
Plastics extruder dimension and viscosity control system
AssigneeHarrel, Inc.
InventorHolton E. Harris
Life of this patent
Estimating the term…
Abstract
An extrusion control system that controls the cross section and viscosity during extrusion of even hard to control plastics like polyurethane. Cross section, A, is determined by measuring volumetric rate of deliver of melt through a gear pump V/t and the speed of the extrudate at a puller N/t. The cross-section area, A=(V/t)/(N/t), is controlled by controlling the puller speed. Pressure drop across the die, P, and the volume of melt delivered by the gear pump are measured and a term indicative of the viscosity of the melt is determined based on Vs=(KP)/V, Vs being the viscosity and K being a constant dependent on the size and shape of the die orifice. Viscosity variations are compensated by varying heat applied to the melt.
Claims20
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.
13 more elements
An extrusion control system comprising:
- (a) an extruder controller,
- (b) means for measuring the speed of an extrudate,
- (c) means for measuring the speed of a gear pump delivering hot viscous plastic to a die,
- (d) means for controlling at least one of the speed of the extrudate and the speed of the gear pump to thereby control the cross-section of the extrudate,
- (e) means for measuring the pressure in the hot viscous plastic proximate and upstream of the die as a measure of the pressure drop across the die, and
- (f) means for controlling heat applied to the hot viscous plastic to control the viscosity of the plastic in the extruder as a function of a viscosity-indicative measure calculated from quantity of hot viscous plastic delivered to the die by the gear pump and pressure drop across the die.
3 more elements
Dependencies are inferred from the claim text.