Small Dosage Gravimetric Feeders

Gravimetric Feeders White Paper On Highly Accurate Gravimetric Feeding for Small Doses of Plastics Additives, Sponsored by LIAD

For plastics manufacturers producing small and micro sized products, those working with highly expensive additives, and in other applications where high precision dosing small quantities of additives is required, a question has been raised if it is possible to obtain greater accuracy and precision from loss in weight gravimetric feeders.
This white paper examines the technology of a new small dose gravimetric feeder that obtains consistent high dosing resolution – even when working with extremely small quantities of additives.

Loss in weight gravimetric and volumetric feeders for plastics additives, with their assortment of screws have become a standard in plastics manufacturing, as they lower masterbatch inventory costs and provide greater processing flexibility. Typically, screw feeders have a very hard time dosing according to weight when the job requires very small quantities of additives. During extrusion, screw feeders will start experiencing problems in accurate dosing when the dosing rate is under 200 grams/hour.

The question that this paper seeks to answer, in applications where accuracy beyond the capabilities of existing screw feeders are required, i.e., when producing small and micro sized products or semi-transparent pieces, what technology is available for near-absolute dosing resolution.

Considering that an incorrect ratio of additive to virgin resin results in inconsistent coloring or product rejects, injection molding and extrusion manufacturers potentially have a lot to gain.

A Small Dose Gravimetric Feeder Example

One plastics auxiliary equipment manufacturer, the original inventor of the single channel gravimetric masterbatch feeder for injection molding, introduced a new gravimetric feeder, with a novel vibrating channel and loss in-weight algorithms for accurately dosing small quantities of masterbatch and other additives.

A new (patented) gravimetric feeder is ideal for small and micro sized products. Further, with its 550 Cc hopper and up to 80g/minute output range, the gravimetric feeder is capable of accurate dosing for most product sizes when used in conjunction with an optional Venturi loader.

With weighing accuracy and dosing resolution that can reach to within a single pellet, the new small dose gravimetric feeder offers factories real workplace advantages over traditional gravimetric feeding systems.

Furthermore, due to its unique design and single vibrating channel this example plastics additive feeder is capable of handling large and small additive feed rates without having to change screws or other parts. Regardless of pellet consistency, size or weight, or how many products are produced on the line, this new type of gravimetric feeder, with its single vibrating channel, offers a new level of additive feeding accuracy and efficiency.

Example Application

A Vibrating Gravimetric Feeder

Traditional loss in weight gravimetric feeders are screw fed, which depending on size of screw, speed of the rotation, and weight of the material, will dictate how much color or masterbatch additive will be distributed into the flow of virgin resin via the throat of the processing machine.

This example of small dosing feed technology enables small product manufacturers relief from manual mixing, difficult calibration, product rejects and over-consumption of masterbatch additive

The micro dosing resolution of the new gravimetric feeder is obtained by having a single vibrating channel which advances the additives to the inlet of the processing machine.

The feeding channel of this example of a new vibrating feeder is uniquely designed,lining up the pellets as they advance, and then controlling the rate of additive movement via electromagnetic pulses. Loss in weight analysis via advanced algorithms speeds up or lower the rate of the vibrations as necessary – a significant advancement over step motors alone or conveyor systems, which until now have not delivered high dosing control.

Calibration & Maintenance

Regardless of granule size, weight or physical properties, the gravimetric feeder offers consistent accuracy, while simultaneously eliminating some tasks associated with calibration and maintenance.

Furthermore, as the single vibrating channel is used for all jobs, calibration can be easilyperformed via the control panel, which monitors loss in weight that is determined from cycle to cycle. The set value is calculated from the specified shot weight, and the percentage of masterbatch or additive. This also means there is no machine down time for switching parts, with sterilization requiring less than a minute by taking the vibrating chamber out of the protective container, and air blowing all material.

With this setup, the new plastics additive gravimetric feeder can accurately and consistently dispense single or multiple pellets per batch.

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