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.

Abstract: An alternate polymer extrusion method and system reduces “drool” effects that detract from precise control over the content of two or more materials in an extrudate along its length. In the system, two or more extruders direct melt to two or more gear pumps. Control of the speed of the gear pumps controls the amount of each material emergent from the pumps, proceeding to a convergence in the paths from the pumps and thence to a die. Melt in each path between each pump and the convergence tends to expand and drool into the convergence as its associated pump is slowed and stopped. To prevent this, in the die, a constriction in each path just upstream of the convergence greatly reduces drool past that point by requiring a much greater pressure to force the melt past the constriction. The increased pressure required increases compression and expansion of the melt between the pump and the construction as a pump starts or increases in speed, on one hand, and stop or decreases in speed, on the other hand.

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 control system and method controls the cross section and viscosity in the process of extruding even hard to control plastics like polyurethane. Cross section, A, is determined by measuring volumetric rate of delivery of melt through a gear pump V/t and the speed of the extrudate at a puller N/t.

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 coextrusion system employs two or more extruders, each with a gear pump at its output connected to a coextrusion die. Different materials are extruded by each extruder. Varying the speed of one or both gear pumps varies the content of the extrudate. The gear pumps permit precise variation of the relative content of the materials extruded by the several extruders lengthwise along the extrudate. A display of a cross sectional dimension of the extrudate along a length of the extrudate permits observation of the lag that occurs between alteration of gear pump speed (or air pressure in the case of tubular or blown sheet extrudates) and the resultant change in dimension, so that a speed correction can be made at the appropriate time to compensate for differing shrinkage and stretching characteristics between the several extruded materials.

Abstract: A coextrusion system employs two or more extruders, each with a gear pump at its output connected to a coextrusion die. Different materials are extruded by each extruder. Varying the speed of one or both gear pumps varies the content of the extrudate. The gear pumps permit precise variation of the relative content of the materials extruded by the several extruders lengthwise along the extrudate. A display of a cross sectional dimension of the extrudate along a length of the extrudate permits observation of the lag that occurs between alteration of gear pump speed (or air pressure in the case of tubular or blown sheet extrudates) and the resultant change in dimension, so that a speed correction can be made at the appropriate time to compensate for differing shrinkage and stretching characteristics between the several extruded materials.

Abstract: A sheet thickness gauging system locates sheet edges to measure sheet width and to calibrate the gauging procedure to take into account neck-in or lateral shifting of the sheet. Initially, and at regular intervals during extrusion, the controller, motor, and motor control that cooperate to control a nuclear gauge's movement and measurement on a traverse across the path of movement of the sheet, rapidly move the gauge to a first position near a first edge of the sheet. From that position to the edge the gauge steps in small steps until a substantial reduction in apparent thickness is detected, signifying the location of the edge. A limit to the regular transverse gauging movement of the gauge is set just inward of the detected first edge. The gauge is then moved rapidly across the sheet to a second position near the other edge of the sheet, where the system proceeds similarly to detect the second edge and set a second limit. Regular gauging then proceeds, across the sheet from one limit to other.

Abstract: A thickness gauge traverse for a gauge such as a nuclear thickness gauge that measures thickness of extruded sheet at numerous locations across the sheet in a system utilizing those measurements to correct thickness of the extrusion. The traverse has a mount supporting the probe of the gauge for movement across the sheet. A motor and motor control electronics rapidly advance the probe from one measurement point to the next, where the mount is stopped permitting the probe to remain for the considerable time necessary to make its measurement without having that time dominate the speed of the gauge's movement from point to point across the sheet.

Abstract: An extruder control system and method controls melt temperature to maintain viscosity of the melt at the die. A constant volumetric flow to the die is delivered by a gear pump, the die is a fixed orifice, and pressure between the gear pump and the die is indicative of viscosity. Changes in pressure are sensed and compensating changes in temperature are effected to return the pressure and, hence, the viscosity to its previous value.

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.