Novatec: First Low-cost Gravimetric Feeder Yields Level of Accuracy and Accountability Unachievable with Volumetric Color Metering

A new-generation device for feeding colorants and additives into plastics processing machines combines the low cost of a volumetric feeder with the superior precision, consistency, and data generation of a gravimetric metering system, NOVATEC, Inc. announced at Plastec West (Booth 3939). The new feeders are manufactured by Maguire Products, Inc. under a cooperative agreement with NOVATEC, which is backing the equipment with a five-year warranty.
The enhanced accuracy of new MGF Series gravimetric feeders enables molders and extrusion processors to reduce color and additive consumption, increase control over product quality, and document color usage for each production run, according to Tony Crook, product manager, blending systems. The feeders are available with throughput capacity of up to 35 lb. (16 kg) per hour and can be mounted directly to the throat of most molding machines or extruders.
While NOVATEC and Maguire ship a combined total of hundreds of volumetric feeders each year, the new MGF Series feeders are their first gravimetric systems. ‘Until now, gravimetric feeders have been specialty devices available from a few suppliers and costing 40% more than our volumetric equipment,’ said Tony Crook. ‘All that changes with the MGF feeder, which provides processors with the cost-reducing accuracy of a gravimetric feeder for the price of a volumetric model.’
While an MGF feeder is mounted on the processing machine exactly like its volumetric counterpart, there are two major differences between the systems:
• The MGF feeder has two load cells which accurately monitor the loss in weight of colorant in the hopper as the material is fed into the processing machine by an auger. The hopper and auger tube are mounted atop the load cells.
• The MGF feeder has an easy-to-use microprocessor controller with backlit display. The controller allows all dispensing parameters to be easily entered. Automatic adjustments are made when 20 grams of accumulated error is detected.
The loss-in-weight operation adds a new dimension of accuracy. ‘Volumetric feeders do not monitor the weight of colorant as it is fed to the processing machine and thus generate no data about how much of the material is actually consumed from moment to moment,’ Crook said. ‘Because a gravimetric system generates a wealth of data on color consumption, it adjusts color metering far more accurately to account for process variations and to compensate for vibrations on fast-cycling molding presses.’
New Gravimetric Feeders Readily Adjust for Process Variations
The controllers for the new MGF feeders have a digital counter that the operator uses to pre-set the precise amount of color to be added. This parameter is translated into the required degree of auger rotation.
In injection molding, the operator inputs the shot size and letdown ratio for the specific application. The auger doses color as the screw in the molding machine retracts, and the auger motor shuts off when the required amount has been supplied. Drawing on information fed back from the injection machine, the controller adjusts for screw slippage or changes in rate.
In extrusion, the operator inputs throughput rate and letdown ration. The controller regulates auger motor speed to automatically adjust for changes in screw torque, plant voltage, or raw material.
By tracking and adjusting for actual colorant consumption, the MGF feeders not only provide even greater accuracy and consistency but also make possible detailed documentation of the entire production run, according to Tony Crook, including a shot by shot account of color dosing in injection molding. The new feeders can be linked in a plant-wide network.
The MGF feeders also retain the user-friendliness of the volumetric feeders. For example, every component that comes into contact with colorant is easily removed for fast cleaning.

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