In actual production, powder packaging machines sometimes suffer from inaccurate filling weight. Below we analyze the causes and key technical factors.
1. Relationship between dosing screw and packaging accuracy of powder packaging machine
Powder packaging machines, especially small-dose models with packaging range of 5–5000 g, normally adopt screw feeding. It belongs to volumetric metering instead of real-time weighing.
Screw feeding works on volumetric measurement principle. The volume consistency of each screw pitch is the fundamental condition that determines the metering accuracy of powder packaging machines. Pitch, outer diameter, root diameter and helical blade profile all affect packaging accuracy and feeding speed.
2. Relationship between screw outer diameter and packaging accuracy
The metering accuracy has a direct correlation with the screw outer diameter. Discussion on pitch shall be based on a fixed screw outer diameter.
When selecting and matching metering screws, the selection is determined by target package size, with proper adjustment according to the bulk density of materials.
Example: For 100g chili powder packaging, we normally adopt a Φ38 mm metering screw. For glucose with higher bulk density for the same 100g package, a Φ32 mm screw will be selected.
General rule: Larger package weight requires a screw with bigger outer diameter to balance packaging speed and weighing accuracy.
3. Relationship between screw pitch and packaging accuracy
Screw pitch also greatly impacts metering precision.
For instance, when packing 50g cumin powder, our seasoning powder packaging machine uses a Φ30 mm outer diameter screw with 22 mm pitch. The pass rate for weight deviation ≤0.5g is above 80%, and pass rate for deviation ≤1g exceeds 98%.
In contrast, if competitors use Φ30 mm screw with pitch over 50 mm, feeding speed increases greatly, while weight deviation rises to around 3g.
According to industry standard QB/T2501-2000, Class X(1) weighing instruments for packages ≤50g have a permissible error of 6.3%, complying with Class X requirements.
Nevertheless, for manufacturers, packaging accuracy directly relates to product material cost, which creates obvious economic differences between different screw configurations.
