Confectionery & Chocolate

What are some tips for choosing a feeder to handle my cohesive material?

There are several options when feeding cohesive materials, dependent upon process requirements, material characteristics and the required feed rates for delivering material to the process. In the case of screw feeders, for example, often when using a single screw feeder for a cohesive material, the material is flung off the screw flights in the screw outlet tube and then sticks to the wall of the tube. This material will then accumulate and cause buildup and eventual fluctuations in the otherwise consistent output of the screw feeder. In these cases, a co-rotating twin screw design will be the better choice. Twin screws are often used for more cohesive powders because of the "self-wiping" effect of one screw against the other, which not only helps to transport the material, but also minimizes or even eliminates the buildup of cohesive materials in the outlet tube.

In addition, different screw type configuration options allow to optimize the feeder for the cohesive material. For example, if the cohesiveness of a powder is due to a higher moisture content, or high fat content as in food materials, a twin screw with a finer pitch might create a type of extrusion or squeezing effect thus releasing the moisture and causing additional material buildup issues. In this case, a screw configuration with a larger tolerance on screw flights, such as an auger type, might be better suited.

Finally, the use of specific non-stick coatings on the feeder components in contact with the material can also be investigated. For food and pharmaceutical applications there are FDA-approved coatings available, which are often extremely efficient when dealing with non-free flowing and sticky materials.

Where high flow rates must be achieved or low headroom is an issue, weigh belt feeders are the answer. Typically, cohesive materials will pose additional challenges for weigh belt feeders by depositing on the belt and influencing the weighing results, which in turn impedes the perpetuation of accurate feed rates. Coperion K-Tron masters this challenge by adding a second weigh bridge and correlating controls to compensate for these weighing inaccuracies thus continually tare the belt. This option in design provides for the highest accuracy while reducing downtimes for maintenance and calibration. In addition, the use of scraper bars in the weigh belt feeder design also helps to minimize the negative effect.