The direct answer
Thick and stringy products are filled by using a dosing device that can move the product repeatably, a valve and nozzle that close cleanly, and a pack geometry that gives the dose time and space to clear the sealing jaws. The product must be tested at the temperature and shear condition expected in production.
Viscosity alone does not define the solution. Particles, elasticity, tack, yield behaviour, air content and how the product recovers after pumping can change the dose and cut-off. A trial should include repeated cycles and a realistic refill rather than a few manual shots into an open container.
What makes a product string or tail at the nozzle?
Stringing occurs when cohesive or elastic product continues to form a filament after the filler has completed its nominal delivery.
It can be influenced by formulation, temperature, nozzle diameter, surface finish, valve closure, suck-back, pressure and the distance to the pack. The tail may break cleanly at one speed and stretch at another. Observe where it separates and whether it transfers product onto the inner film or cross-seal area.
How do viscosity and temperature change cut-off?
Temperature can reduce or increase apparent viscosity and change how quickly the product starts, stops and settles after the dosing stroke.
A warmer product may flow more easily but drip after closure; a colder product may need greater pressure and produce a longer tail. Declare the intended temperature range and control method. If heating is required, the tank, hoses, valves, guarding and cleaning method should be included in the review rather than treated as a separate utility.
Which dosing approaches are considered for thick products?
Piston-based dosing is a common starting point for viscous products, while other pump technologies may be assessed where cleanability, particles, shear sensitivity or product-contact requirements make them more suitable.
The choice depends on the complete formulation and dose range. Valve and nozzle geometry can be as important as the pump. If the required range is very wide, more than one product-contact setup may be needed to maintain repeatability and clean cut-off.
How can a nozzle be assessed without contaminating the seal?
Assess the nozzle inside the intended sachet opening at the proposed fill height and timing, then inspect repeated cycles for tails, smear, splash and product carried by the moving film.
An open beaker test does not reproduce headspace, film movement or jaw timing. The trial should include the smallest pack opening and the most demanding dose/product combination, with retained sachets from stable running and after pause or restart.
What should a changeover test prove?
A changeover test should prove that the previous product is cleared under the agreed method, the correct parts and recipe are installed, the filler can be primed safely, and the new product returns to accepted dose and clean seals.
Record disassembly points, cleaning access, retained product, first-good-pack criteria and start-up rejects. For colour, fragrance or active changes, the site should define the inspection or validation method; the machine trial should demonstrate that the specified procedure is physically practical.
Thick-product trial matrix
| Condition | Why test it | What to inspect |
|---|---|---|
| Lowest production temperature | Highest restriction or slowest recovery may occur | Dose response, pressure, tailing and cycle margin |
| Highest production temperature | Drip or post-close flow may increase | Nozzle cut-off, headspace and seal cleanliness |
| Smallest sachet/dose opening | Least clearance and settling space | Film contact, smear and jaw contamination |
| Pause and restart | Product can relax, separate or drip while stopped | First packs, dose and seal condition |
| Product change | Cleaning and priming can dominate short campaigns | Line clearance, start-up waste and first accepted pack |
Information to provide
- Representative product at the full production temperature and viscosity range.
- Particles, fibres, elasticity, tack, air content and any tendency to settle or separate.
- Target dose range, tolerance and smallest intended pack opening.
- Tank, agitation, heating, transfer and refill method.
- Cleaning procedure, product-change matrix and required contact materials.
- Film, sachet drawing, seal position and accepted-output target.