Color masterbatch, UV additive or regrind... In injection molding production something is almost always mixed into the main material. How the mix is measured, however, is two different worlds: by volume or by weight?
Volumetric Dosing: Measuring by Volume
A volumetric doser delivers material by the number of revolutions of a screw or disc: it rests on the assumption that "the screw turned 10 times = X grams were delivered". It is simple and cheap, but the assumption is fragile:
- When the granule size or shape changes, the same number of revolutions delivers a different number of grams
- There can be density differences between masterbatch lots
- As the screw wears, the amount delivered drifts
- The amount delivered is never measured anywhere — an error goes unnoticed
The result: to stay on the safe side, the operator keeps the ratio high. Masterbatch for which 2% would be enough is set at 3%, and the difference quietly goes in the bin all year round.
Gravimetric Dosing: Measuring by Weight
In a gravimetric (weighing) system each component is actually weighed on a high-precision load cell. In GRAVIMIX systems the target and actual weights are compared in every batch, and any deviation is corrected automatically in the next batch.
Gains:
- Dosing precision down to 0.01% — what the recipe says is what is delivered
- Changes in lot, density or granule shape do not affect the result (a weight is a weight)
- Every batch is recorded — traceability and quality documentation
- No recalibration is needed when the material changes
Where Does the Difference Turn into Money?
1. Masterbatch savings: The ratio set at 3% in volumetric dosing comes down to the 2% actually needed in gravimetric dosing. In production of 100 tons/year, a difference of 1 ton of masterbatch is a serious item on its own. The typical payback period is 3–12 months.
2. Using regrind safely: Recycled granulated material (regrind) has an irregular density — exactly where a volumetric system is weakest. Because the gravimetric system weighs the regrind as it adds it, regrind ratios of 10–30% can be used safely and at constant quality. Scrap regains its value.
3. Color consistency: The classic reason for customer returns is batch-to-batch color difference. With weighed dosing, color deviation is practically eliminated.
The GRAVIMIX Product Family
Three levels according to need:
- [NECS](/en/category/gravimix-necs) — up to 50 kg/h, 1–4 components. A compact solution beside the machine.
- [MECS](/en/category/gravimix-mecs) — up to 170 kg/h, high-temperature (HT) options. The most widely used series.
- [FLECS](/en/category/gravimix-flecs) — up to 350 kg/h, flexible recipes with up to 6 components.
- [FGB5](/en/category/gravimix-fgb5) / [FGB10](/en/category/gravimix-fgb10) / [FGB25](/en/category/gravimix-fgb25) — central and extrusion applications up to 3200 kg/h.
In addition, the belt-driven Ferlin ONE is designed for micro dosing in the 0.1–25 kg/h range.
When Is Volumetric Enough?
The honest answer: where a single component, a wide color tolerance and a low masterbatch price come together, volumetric will do. But if color is critical, if you use regrind, if you mold technical parts or if the masterbatch is expensive, a gravimetric system pays for itself in a short time.
For a capacity calculation and model recommendation based on your consumption and recipe, get in touch. We also offer the option of testing GRAVIMIX systems free of charge with your own material.