Granules: The Standard Application for VFFS
Rice, sugar, seeds, plastic pellets, or mineral fertilizers—anything that flows freely can be packaged on a vertical form-fill-seal machine. Pellets are the product category that achieves the highest cycle rates because they flow freely and do not require venting. A Vertical filling and capping machine with Multi-head scale It achieves 80 cycles per minute here with a dosing accuracy of ±1 g.
Is your product considered a granulate in the context of mechanical engineering?
| Property | Impact on the line |
|---|---|
| free-flowing (bulk density of at least approximately 0.4 kg/l) | Gravity-fed system; no compressed air required |
| Grain size less than about 10 mm | Standard Filling Chute and Standard Weighing Trays |
| powdery (e.g., fine flour granules) | Dust removal and sealed transfer points are required |
| abrasive (e.g., bulk minerals) | hardened wear parts on conveyor elements |
How the Granulat line is packaged
The product path is short: A storage hopper or bucket elevator conveys the granules to the multihead weigher. There, 10 to 14 heads combine partial weights to achieve the target fill weight—accuracy typically ranges from ±0.5 to ±1 g in this industry. The weigher feeds the product into the filling chute of the form-fill-seal machine, which forms, seals, and cuts the pouch—all in a single pass.
For small fill weights under 100 g or slow lines running at less than 30 cycles per minute, a simpler weighing or volumetric dosing system is sufficient. A multihead weigher is worthwhile for medium-sized production runs because it selects the best combination from multiple heads during each weighing cycle, thereby reducing variation.
These product parameters determine the design
- Bulk density: It determines the filling volume and the cross-sectional area of the filling chute. Light granules (0.4 kg/l) require larger cross-sections than heavy ones (1.2 kg/l) for the same weight.
- Particle size distribution: Wide distributions separate along the conveyor belt—as a result, the scale does not weigh what the bag ultimately contains.
- Flow behavior: Risk of bridging with moist or oily granules; vibrating conveyors and generous hopper angles help prevent this.
- Wear: Abrasive material wears out parts. Hardened components extend maintenance intervals but must be factored into spare parts planning.
Film and Bag Sizes for Granules
Granules place little stress on the film—yet three factors are crucial: The seal must be able to withstand powder particles in the sealing area (particles in the seal weaken it), the film’s tensile strength must support the fill weight, and for products intended for outdoor storage, a moisture barrier layer is also required. Flat pouches and 3-side-sealed pouches are the most economical formats for granules; only products packaged in cartons, such as seeds in small pouches, can also be processed on stick pack lines.
Real-World Experience: Three Mistakes That Cost You Tempo
- Bunker is too small: The scale is running low; the cycle rate drops every time it is refilled. The storage hopper should provide a buffer for at least five minutes of production.
- The drop height between the scale and the sealing jaws is too great: Dust buildup in the bag and particles in the cross seam. A dip tube with a suction nozzle solves both problems.
- Incorrectly selected weighing pans: Trays that are too large result in inaccurate weighing of small weights—the combination selected must include several trays within the target range.
When Granules Pose Limitations on a VFFS
Very sticky or greasy granules (e.g., caramelized products) cause the weighing pans and sealing strips to stick together—in such cases, special coatings or cooled transfer mechanisms are required. For coarse bulk materials with edges larger than about 50 mm (e.g., firewood logs), a bagging system is the appropriate type of machine, not a tubular bag machine.
Frequently Asked Questions
What is a realistic cycle count for granules?
With a multi-head weigher, up to 80 cycles per minute with 10 to 14 heads. Without a weigher, using volumetric dosing, typical systems operate at 30 to 50 cycles per minute with an accuracy of ±2 to ±3 %.
How exactly does a multihead weigher dose granules?
Industry standard: ±0.5 to ±1 g, depending on the fill weight and particle size. Fine-grained, uniform granules achieve better values, while coarse crushed material achieves worse values.
Do granules need a protective atmosphere?
No. Granules are not sensitive to oxidation or moisture to the extent that fumigation would be necessary—storing them in a dry place covered with plastic wrap is sufficient. Only hygroscopic products (e.g., salt with an anti-caking agent) require a moisture barrier.
Is rice in the same category as sugar?
Yes, both are free-flowing granules with similar bulk densities. The change involves adjusting the recipe on the scale and changing the film; only changes to the fill weight or bag size are considered format changes.
Related pages: What is a vertical form-fill-seal (VFFS) machine? | What is a multihead weigher? | Format Change on Packaging Machines | Grain Packaging Machine
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