Feeders in polymer processing are used to dispense a specific amount of an ingredient, such as an additive, into a polymer process. There are two types of feeders used for this purpose: volumetric and gravimetric.

Volumetric Feeding
When using a volumetric feeder, the operator sets the rate at which the specific ingredient is introduced into the process; for example, 5 grams/30 seconds. In this process, the operator turns on the auger for a certain amount of time and collects additive. Once collected, the operator must weigh the sample and adjust the auger to get the right amount. This is done by speeding up or slowing down the auger. Once the feeder is dispensing the correct amount of additive, the process can continue. This has to be done every time there is a change in material. It is very time-consuming and not extremely accurate, but a low-cost option that works for some processes.

Gravimetric Feeding
Gravimetric feeders are significantly better than volumetric feeders in that a computer and load cell are incorporated into the equipment that continually record the weight of the ingredients in the feeder. The operator keys in the desired feeding rate. The computer calculates and begins dispensing the additive into the process. At the same time, the load cell calculates the loss in weight of the feeder allowing the material to be continuously monitored.

The gravimetric feeder is much more accurate in dispensing the correct amount of material into the process. There is no need for capturing and weighing samples as is necessary in the volumetric feeder. As long as the gravimetric feeder is calibrated, the process is as simple as entering the dispense rate and everything else is automatic.

Gravimetric feeders have for the most part, replaced volumetric feeding as the preferred method for feeding additives and colorants. The Polymers Technology Center maintains gravimetric feeders and side feeders for accurate and reliable feeding of additives and fillers. We can feed any of the following: pellets, powders, flakes, granules, fibers and liquids. Contact us to learn about the equipment we have that can help your company with their processing needs.