The direct answer
To fill a foaming liquid into sachets, first identify where air is introduced—mixing, transfer, recirculation, agitation or the dosing stroke—then configure the product feed, nozzle movement and cycle so the dose enters without excessive turbulence and settles below the seal before the jaws close.
The correct solution is established with representative product at the intended temperature and feed condition. Simply slowing the machine or increasing headspace may help, but it can also reduce output or create an oversized pack. The trial should distinguish foam created by the process from air already present in the formulation.
Why does a liquid foam during sachet filling?
A liquid foams when air is entrained or released faster than bubbles can collapse, often because of agitation, pumping, pressure changes, splashing or surface-active ingredients.
The same formulation can behave differently when cold, warm, freshly mixed, recirculated or held for a period. Transfer height, tank return, pump speed and nozzle position may have more effect than the nominal viscosity. Describe the upstream process and do not prepare a quiet laboratory sample that bypasses production aeration.
How can foam affect dose and seals?
Foam changes the apparent volume of a dose and can rise into the transverse sealing area, causing contamination, weak closure or variable headspace.
A volumetric filler may deliver the intended liquid volume while the pack appears overfilled because the product contains air. Conversely, foam collapse after sealing can change pack appearance. Define whether the commercial measure is mass, volume or another criterion and inspect the seal area through start-up and refill conditions.
What information should be provided for a foaming product?
Provide the formulation or product description, viscosity and temperature range, mixing and transfer method, hold time, foam tendency, target dose, permitted tolerance and the intended sachet geometry.
Also identify whether the product can be deaerated, whether agitation is required to maintain uniformity, and whether a recirculation return enters above or below the liquid level. Representative videos of the product after normal transfer can help plan the trial, but they do not replace a sample.
Which machine features may help control foam?
Useful features may include controlled pump acceleration, a suitable nozzle and closure, bottom-up or lower-position filling where the pack geometry permits, product-level control and enough programmable settling time before cross sealing.
The tank and transfer system may need gentle return flow, controlled agitation or a different inlet arrangement. These are application options, not universal cures. A feature that reduces foam can create cleaning, cycle-time or product-hold-up consequences that should be included in the selection.
How should a foaming-liquid trial be run?
Run the trial with production-representative product preparation, temperature and transfer, then sample packs at start-up, stable running, refill, pause and restart.
Record tank level, pump and nozzle setup, dose settings, cycle rate and any visible foam. Inspect dose, headspace, seal cleanliness and pack appearance after an agreed settling period. A short demonstration after the product has quietly stood in the hopper is not sufficient evidence for a process that normally receives freshly mixed or pumped liquid.
Foam-control decision table
| Observation | Questions to investigate | Evidence to capture |
|---|---|---|
| Foam already in tank | Mixing, transfer, recirculation and hold time | Product condition before dosing and after normal refill |
| Foam created at nozzle | Pressure, velocity, drop distance and nozzle position | Slow-motion or close run video plus retained packs |
| Foam reaches seal | Headspace, settling time, pack movement and overfill | Seal-area samples by operating condition |
| Dose varies after refill | Air entrainment, pressure and level changes | Sequential dose results around refill |
Information to provide
- Representative product prepared and transferred as it will be in production.
- Temperature, viscosity and any mixing, recirculation or hold-time requirements.
- Target dose and whether it is controlled by mass, volume or another measure.
- Finished sachet dimensions, usable headspace, film and seal pattern.
- Required accepted output and the normal refill method.
- Cleaning, contact-material and containment requirements.