Flow Wrapper Sealing Problems Fixed with a Carbon-Impression Test
- Ettienne van Vuuren
- Jun 29
- 4 min read
Updated: 2 days ago
Sealing problems on horizontal flow-wrappers can be frustrating—especially when the machine appears to be running normally. But sometimes the real problem isn’t mechanical at all; it’s something more basic, more overlooked.
Something a lot more obvious.
In this case study we show how a simple carbon-impression test uncovered a preventable sealing issue—and why routine cleaning, while important, wasn’t quite enough to keep the flow-wrapper performing at its best.
The Problem: Customer Complaints About Sealing Quality
The Quality Assurance team had begun receiving complaints about seal integrity—particularly failures through the centre of each pack. Temperatures and alarms looked normal, yet the seals still leaked.
Although the site followed an SOP for daily jaw cleaning, operators were using a brass wire brush—a gentle option but often too soft to remove baked-on chocolate and sugar. Pressed for time, they cleaned only the centre sealing zone, reasoning that if the middle looked clean, the packs should seal properly, while the outer jaw edges quietly collected residue. (A slightly firmer stainless wire brush, used correctly, would have removed the residue without damaging the jaws.)
That hidden build-up created uneven pressure: scattered high-pressure spots where debris was thick and little or no pressure across the intended seal line—so finished packs failed in the field.
The Diagnostic: Carbon Impression Testing
To confirm jaw pressure, we inserted a carbon-impression strip and manually cycled the wrapper.
Faint or no marks across the intended sealing zone proved the jaws weren’t pressing where they should.
Isolated dark marks appeared only at a few dirty spots just outside the seal line—showing pressure was present only where baked-on residue was thickest.
Diagnostic result: only isolated pressure spots.
PacMatix tip: We occasionally see technicians use printer paper, paper towels, or other makeshift materials to “check” sealing pressure or alignment. These methods rarely give an accurate reading. The only reliable way to diagnose sealing-jaw issues is a carbon-impression test. Before anyone adjusts your jaws, ask if they have carbon paper on hand—if not, hold off on the adjustment.
The Fix: Deep Cleaning & Knife Alignment
Isolate & cool – Our qualified flow-wrapper technician powered down the machine and allowed the sealing jaws to cool completely.
Remove guards for full access – He removed the machine covers around the jaws and the product supports beneath them, exposing the entire sealing-jaw faces.
Scrape heavy build-up – With a hard-plastic scraper he carefully shaved off the bulk of the baked-on chocolate and sugar.
Apply degreaser carefully – With most debris scraped away, he wiped a food-grade degreaser onto the jaws using a lint-free cloth, taking care not to let any liquid reach the heating elements or their wiring. The solution was left to penetrate the residue for about 30 minutes.
Scrub, wipe, and repeat – Scotch-Brite pads and a slightly firmer stainless wire brush removed the softened residue, followed by a thorough wipe to remove cleaner. The degrease-and-scrub cycle had to be repeated several times until every trace of carbonised product was gone. Total deep-clean time: about three hours.
Re-test – A second carbon impression showed even contact across the sealing surface, but it also revealed a secondary issue on one jaw: a slight misalignment between the upper and lower jaws (one tooth out). The giveaway was that the knife’s zig-zag imprint sat off the centre line.
Realign and Re-test – We realigned that jaw on its slotted mount, ran a final carbon test, and confirmed perfectly balanced pressure.
Final check: balanced pressure confirmed. The wrapper returned to production immediately—sealing perfectly and passing QA.
Key Takeaways
Lesson | Why it matters |
Carbon impressions expose hidden pressure loss | Fast, visual proof of sealing contact. |
The right tool and expertise are critical | Brass brushes are gentle but often too soft; a slightly firmer stainless brush—used by a qualified, experienced technician—removes residue without damaging jaws. |
Daily cleaning isn’t always enough | Jaws should be cleaned immediately after any product crush before residue carbonises. |
Frequent crushing = timing issue | If a wrapper crushes product often, address film/product timing—not just clean up after it. |
PacMatix tip: Taking a daily carbon-impression test is an easy way to reasure yourself that jaw setup and condition haven't drifted - catching seal issues before they shut the line down.
Need Help?
If you’re looking for flow wrappers for sale or need expert flow-wrapper service, PacMatix can help—from selection through lifetime support.
We service a wide range of European and Japanese flow-wrapper brands—including our own GSP and Tecno Pack machines, as well as FUJI, CAVANNA, PFM, and more. If you’re battling seal failures, jaw misalignment, or recurring product crushes, we can diagnose the root cause and get you back to full-speed production.
👉 Contact our team
Field work: Ryno Kruger – Flow-Wrapper Technician
Article written by: Ettienne van Vuuren – Founder, PacMatix (25 years hands-on flow-wrapper experience)
Published: June 2025
Frequently asked questions.
What is a carbon-impression test on a flow wrapper?
It’s a quick diagnostic where carbon paper is clamped between the sealing jaws to reveal pressure and alignment in seconds.
Can a stainless wire brush damage sealing jaws?
Not if it is used correctly. A slightly firmer stainless brush removes baked-on residue without harming hardened steel jaws, unlike softer brass brushes that often leave debris behind.
How often should I run a carbon-impression test?
A quick test at the start of each shift—or right after any product crush—reassures you that jaw pressure and alignment haven’t drifted.
© 2025 PacMatix Pty Ltd. All content and images. Unauthorised reproduction prohibited.
PacMatix has completed over 60 GSP flow wrapper installations across Australia in just the last 5 years, including regional locations in Tasmania, Victoria, Queensland, and Western Australia. Whether you're packaging seafood, produce, bakery, or chilled goods, our Italian-built machines and responsive local support team deliver better performance and peace of mind.
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