K-Tron's extrusion control package offers the ability to control the extruder speed so that its output has a predictable and repeatable mass flow. By accurately measuring material throughput, gravimetric extrusion control can compensate for material and process variations and provide more consistent end product quality. It is primarily targeted for use with single screw flood fed extruders in both mono- and co-extrusion applications such as profile extrusion, cast sheet, blown film, cable coating and laminating.

Gravimetric extrusion control is virtually a necessity for multi-layer co-extrusion systems. Its benefits include exact control of end product quality, significant savings in material costs, highly accurate multi-layer co-extrusion of films, longer production runs due to consistent extruder output and the ability to detect problems before the product goes out of specification.

A typical K-Tron extrusion control package may include the following components:
• K4G Feeding and Blending station that accommodates up to six feeders with a variety of feeder types possible.
• K-Tron Weigh Hopper: designed to fit neatly between the K4G stand and the extruder inlet.
• K-Tron User Interface: three choices available, depending on the needs of the application:
(K-Tron Control Module (KCM) for simple applications, K-Vision for one extruder and up to 15 feeders, or the K-Tron Smart Commander (KSC) for up to eight extruders (layers)—and 24 feeders.

The K-Tron package offers a fully integrated feeder and control solution with mass flow or weight per length control, allowing the processor to set the extruder speed from the K-Tron interface. The feeders serve a dual purpose, both gravimetrically controlling the recipe for the layer and acting as a mass flow sensor. The level in the weigh hopper is held constant and the extruder mass flow is constantly computed and controlled from feeder massflow values and weigh hopper changes. All auto/manual transitions are bump-less and the software provides monitoring and alarming on all parameters.

K-Tron Gravimetric Extrusion Control is based on the principle that extrusion throughput deviation can be detected independent of extruder speed if the material level above the extruder inlet can be measured with sufficient speed and precision. By utilizing a weigh-hopper equipped with K-Tron's patented Smart Force Transducer (SFT) weighing technology, the relative weight of the material head above the extruder can be so accurately measured. Unlike level sensors, the weigh-hopper is unaffected by material entering and exiting simultaneously, the material's angle of repose, changes in dielectric constant with formulation, humidity, or electrostatic charge.

The integrated control of the loss-in-weight feed system with a precision weigh-hopper provides the most accurate extrusion control. The material head above the extruder is held constant, feeding is continuous and accurate, material ratios are always correct, material segregation is unlikely, and extruder mass flow can be continuously measured and controlled. Thanks to computer and networking technology, data can also be more easily exchanged between multiple systems for both alarm and control purposes. Information such as extruder screw speed, die pressure, haul-off system speed, and even gauge data can easily be made available to the gravimetric extrusion control system.