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.

Abstract: An extrusion system controller monitors the movement of an extrudate using a motion detector. Upon detection that the extrudate is no longer moving along its path of movement at the appropriate speed, the controller causes power interruption to the extrusion system by a controlled power switching device. A dimensional anomaly detected by a gauge can cause the controller to effect power interruption as well, when the anomaly lies outside a range of correctable dimensions or when the anomaly does not respond to corrective action by the controller. In the event that a cutter is used on the extrusion line, a detector that may be a photodetector senses that the extrudate is being severed regularly. In the absence of regular severance of the extrudate, the controller effects a power interruption. By use of these techniques, the extrusion line can run entirely unattended.

Abstract: A system and method for the control of the density of extruded foam controls foaming based on the volume per unit time of extrudate being formed. A gear pump controls the flow of melt to the die. The pump speed provides an accurate measure of the volume per unit time of melt moving to the die. The speed and cross-sectional dimensions of the extrudate are measured to determine the volume per unit time of the extrudate. Since the unfoamed melt density times the volume per unit time of the unfoamed melt being delivered to the die is equal to the density of the foamed extrudate times its volume per unit time, a ratio of the density of foamed extrudate to unfoamed melt can be determined from the two volume per unit time calculations. Once the ratio for an appropriate foam density is determined empirically, density-affecting characteristics of the extruder can be controlled to bring the calculated ratio towards the desired ratio.

Abstract: In a P-I-D process control where a process variable is controlled employing the three mode equation:Output=K.sub.1 E+K.sub.2 .intg.Edt+K.sub.3 (dE/dt)the sign of the derivative is compared with the sign of the error. If the derivative and error signs are unlike then the derivative term is discarded. Discarding the derivative term when its sign is unlike that of the error E, prevents the derivative opposing the return of the process variable towards the desired value or "set point.

Abstract: A system and method of temperature control for a plastics extruder uses a deep well sensor and a shallow well sensor in each temperature control zone along an extruder barrel. The temperature indications of these sensors are not combined. The shallow sensor detects temperature near the barrel surface. An associated controller compares the sensor temperature with a manually preset temperature set point. The differences between the detected and set temperature are used by the controller to effect heating or cooling of its associated temperature control zone. Each deep sensor is located proximate the bore in which the plastic is moved. The deep sensor temperature indication is compared with the set point of a second controller. Variations of the deep temperature from the set point generate an error signal that is applied to the first, shallow well temperature controller to vary its set point.

Abstract: An improved method and apparatus is described for controlling an average dimensional characteristic of an article being extruded. This dimensional characteristic is determined from a predetermined volume of material supplied, from a measured dimensional characteristic and from a known cross sectional configuration. When the measured dimensional characteristic varies from a predetermined value, the volume of the stock material supplied is altered to restore the measured dimensional characteristic to the predetermined value.