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: 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.