As plastic parts become smaller and more precise, manufacturers are increasingly required to dose extremely low quantities of colorants and additives. In applications such as micro molding, medical components, electronics, thin-wall packaging, and laboratory-scale production, even very small dosing deviations of color or additives can significantly affect the final product.
When discussing dosing accuracy, most attention is usually placed on the dosing equipment itself. However, in low throughput extrusion, molding and dosing applications, another factor becomes critically important: pellet size.
At very low dosing quantities, the physical dimensions and weight of each individual pellet can directly determine the achievable dosing accuracy.
Consider the following example:
If the masterbatch contains approximately 100 pellets per gram (PPG), each pellet weighs around 0.01 gram. In this case, dosing a single pellet provides the required concentration.
However, if the masterbatch is 42 pellets per gram (PPG), each pellet weighs approximately 0.024 gram. In this case you cannot achieve the 1% targeted LDR, since a single pellet has an actual concentration of 2.4%.
At this point, the dosing process is no longer controlled only by the feeder or dosing algorithm. The pellet size itself becomes the limiting factor.
In standard production environments, small differences between pellets are often negligible. But in micro dosing applications, every pellet represents a measurable percentage of the total shot weight.
The larger the pellet (low PPG), the accuracy of dosing or metering diminishes when micro dosing. As a result, dosing resolution decreases and the possible deviation from the target concentration increases significantly. In practical terms, when the target dose consists of only one or two pellets, maintaining stable and repeatable dosing becomes extremely difficult.
This challenge becomes especially important in processes such as low throughput or small tonnage injection molding or extrusion processes, such as medical and electrical components manufacturing, and other high-precision plastic processing where consistency is critical.
One of the most effective ways to improve micro dosing accuracy is increasing the pellet count per gram by reducing pellet size (increasing the ppg of the pellets).
Smaller pellets allow more pellets to dose, creating a better statistical distribution and a more stable concentration level. Instead of relying on one or two pellets to achieve the target concentration, the dosing process becomes more gradual and controllable when a greater number of pellets are metered.
Another possible approach is increasing the target let-down ratio (LDR), allowing a larger material quantity to be dosed while maintaining the same functional result. This can help create a wider and more stable processing window in extremely low-throughput applications. However, this increases the material cost by increasing the LDR.
Micro dosing applications push conventional dosing technologies to their limits. At extremely low throughputs, the system must be capable of accurately handling very small quantities – sometimes down to individual pellets.
This is where feeder design and control capabilities become critical.
With our ColorSave-Micro system, we developed a solution specifically for ultra-low throughput applications, where accurate dosing of individual pellets can directly influence process stability and final product consistency.
The system is designed to maintain precise and repeatable feeding performance even when working with very small dosing quantities, helping processors achieve true target concentrations in demanding micro dosing environments.
In micro dosing, accuracy is influenced not only by the dosing unit, but also by the physical properties of the material itself.
Pellet size, pellet weight, and pellet distribution all affect the achievable dosing resolution. Understanding these relationships allows processors, material suppliers, and equipment manufacturers to work together toward more stable, predictable, and accurate production processes.
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