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Gravimetric extrusion control has been around since the mid 80's. The sophistication, accuracy, and level of integration have improved greatly since the first systems were introduced due to the increasingly widespread use of computers and network technologies.

The goal of gravimetric extrusion control is to govern the extruder speed so that its output has a predictable and repeatable mass flow. This is desirable for three primary reasons. First, without gravimetric extrusion control the product may not be viable to produce in an economic fashion. The second reason is to maintain or improve product quality. And lastly, even though the initial investment may be considerable, gravimetric extrusion control can offer significant cost savings.

This technology is most often used in conjunction with single screw floodfed extruders. Single screw machines are much more complex than they appear at first glance. Even with a well designed screw, the extruder is not a positive volumetric displacement device. If it were, rate checks would not be required for initial commissioning and each new material formulation. The output of the extruder is not a linear function and cannot be accurately determined by just monitoring the speed of screw rotation, motor amps, and die pressure. Throughput is a function of many variables including screw speed, screen pack blockage, die back pressure, polymer viscosity, melt temperature, material bulk density, conveying efficiency, screw fouling, screw/barrel wear, and material variation. Even with virgin material, clogging of the screen pack alone can reduce extruder throughput 10% or more within a week.