End Seal Cut on a Flow Wrapper – How We Found and Fixed It

If you’ve ever battled with an end seal cut on a horizontal flow wrapper, you’ll know it can cause costly product damage, packaging waste, and unplanned downtime. In this KWIK TECH GEMS™ post, we walk through a real case from a customer using a lower quality flow wrapper — showing how we diagnosed the problem, the checks we made, and the exact steps we took to get the line back into production.

Possible Causes We Considered

1. Incorrect dwell speed settings – sealing jaws moving faster than the film, creating excessive tension that pulls product into the cut.

2. Over-adjustment of the knife – protruding too far, causing the sealing jaws to “jump” on contact.

3. Incorrect jaw clearance – clearance gap between upper and lower crimper too small, causing a crashing effect when the jaws go into sealing position.

4. Jaw alignment issues – sealing jaws not meeting squarely, leading to uneven pressure and occasional product strikes.

   
   

How We Troubleshot the flow wrapper end seal cut.

1. Verified dwell speed settings – made a slow-motion video to check if the sealing jaws were running at the same speed as the film during sealing. This was confirmed OK.

2. Inspected knife adjustment – to overrule this as the culprit, we removed the knife and ran the machine in production. The seal was still being cut, ruling out the knife as a possible contributor.

3. Measured jaw clearance – made a jaw impression on carbon paper to ensure the sealing jaws were not pressing too hard. We backed this off, but even when the impression became weak, the cut still appeared on the carbon paper.

4. Checked jaw alignment – ran the machine in jog mode to watch the jaws meet and identify any tilt or uneven contact. This left jaw alignment as the prime suspect in the investigation.

5. Tested with and without product – confirmed if the fault occurred on empty packs, which ruled out product feed timing issues.

   
   

PacMatix technician Ryno inspecting the sealing jaws to identify the cause of an end seal cut.

What We Found

With the side covers removed, we observed the meshing of the sealing jaws from the side. It was immediately clear that the upper jaw was one tooth ahead of the lower jaw, meaning the jaws were not parallel. This misalignment explained the uneven pressure on the seal and the consistent end seal cuts.

Flow wrapper sealing jaw misalignment – upper jaw one tooth ahead of lower.

💡 Tip from the Floor:

When diagnosing end seal cuts, never overlook jaw alignment — even slight misalignment can cause hours of wasted production.

The Fix

We removed the anvil from the bottom jaws, then loosened the backlash gears so the top and bottom jaws could be moved independently. From experience, the easiest way to ensure correct alignment between the upper and lower jaws is to line up the knife and anvil slots.

To do this, we wedged the anvil halfway into the lower slot and halfway into the upper slot, making sure both were perfectly aligned. Once alignment was confirmed, we locked all the gears in place to hold the setting.

Using the anvil as a physical guide to align the upper and lower sealing jaws for precise parallelism.

Customer Feedback:“ I have found his knowledge of packaging lines outstanding. He and his team are always willing to help. If you are purchasing a new line or need help with a breakdown, I can recommend giving PacMatix a go.

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: August 2025

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.

Explore more:

• 🔗 GSP Flow Wrapper Range

• 🔗 More Case Studies

• 🔗 Contact our team

Frequently Asked Questions

What causes end seal cuts on a flow wrapper?

A: Common causes include incorrect dwell speed, over-adjusted knives, excessive or insufficient jaw clearance, and jaw misalignment.

How do you check jaw alignment on a flow wrapper?

Remove the side covers, observe gear meshing, and ensure the knife and anvil slots align perfectly when the jaws close.

Can you run a flow wrapper without the knife to test sealing?

Yes — removing the knife helps rule out blade contact as the cause of a seal cut.