Optimising Tension Control: Best Practices for Polybag Manufacturing

Every stage of polybag production, from unwinding film to folding, sealing and stacking, depends on control. One of the most important parts of that process is tension. Though it can go unnoticed, it has an impact on quality and efficiency.

When tension is steady, machines run smoothly. Bags come out the right size. Seals are cleaner. There are fewer stops. But when tension changes or drifts, problems spread fast. Film can wrinkle or stretch. Machines struggle to keep up. That’s why getting tension right should be a top priority.

This article explains why tension matters, the common problems it can cause, and what you can do to improve control in your setup.

Why Tension Matters

As your film moves through your machine, it’s tension that is the pull on it. It needs to stay balanced. Too little, and the film might wander or wrinkle. Too much, and it could stretch or tear.

Steady tension helps:

• Keep bag length and width consistent
  
  
• Avoid curling or edge damage
  
  
• Support clean and accurate sealing
  
  
• Reduce waste and downtime
  
  
• Allow faster speeds without losing quality
  
  

This matters whether you're making simple LDPE bags or mailers with recycled layers.

Common Tension Problems

1. Changing Roll Size
As the roll unwinds, it gets smaller. If the system doesn’t adjust for this, tension increases. That extra pull can cause stretching or film breaks.

2. Mixed or Recycled Films
Recycled or blended materials behave differently. They may be stiffer or stretchier than expected, which makes them more sensitive to changes in tension.

3. Manual Brake Adjustments
Older machines often need manual tweaks. If one operator sets it too tight and another too loose, you get inconsistency across shifts or jobs.

4. Speed Changes
When the line stops or changes speed, like for print marks or sealing, the sudden change can cause tension spikes. This may lead to film distortion.

5. Worn or Dirty Parts
Old rollers, weak sensors or damaged drives can all mess with tension. These can affect quality, but can often go unnoticed.

How to Improve Tension Control

1. Use Closed-Loop Systems

Modern systems measure tension in real time and adjust automatically. This helps keep the tension steady, even as roll size or line speed changes. It also reduces the need for manual input.

2. Calibrate and Maintain Regularly
Even the best system needs upkeep. Test brakes, check load cells, and keep dancer arms clean. Set a maintenance schedule and stick to it.

3. Set Tension Zones
Different parts of the line need different tension levels. For example:

• Unwinding needs low, steady tension to avoid film stretch
  
  
• Folding and gusseting need tighter control for clean lines
  
  
• Sealing and stacking require stable tension to stay aligned
  
  

Splitting the line into zones lets you fine-tune each section.

4. Add Web Guides
Tension alone can’t stop the film from drifting. Web guiding systems help keep the film in line. In order to protect edges and improve sealing or stacking, they work with tension controls.

5. Train Your Team
Operators are your first line of defence. Teach them what to look for - wrinkles, film drift, uneven seals. Show them how to adjust brakes, check for worn rollers or change settings when switching materials.

Tension and Sustainability

Today’s films are often thinner or made with recycled content. These materials can be less stable and more prone to stretching. That makes tension control even more important.

Good tension systems help reduce waste and improve quality, even when using eco-friendly materials. If you want to hit sustainability goals without slowing down production, this is a great place to focus.

Final Thoughts

Tension control might seem like a small part of polybag production. But when it’s working well, it keeps everything else running smoothly. It reduces waste, cuts downtime and helps you hit quality targets at speed.

Whether you're upgrading an old line or improving a new one, look at your tension setup. Invest in better systems, maintain them well, and support your team with clear training.

At Swallow, we help polybag and blown film manufacturers improve web handling and tension control. If you want expert advice on your setup or you're exploring an upgrade, we’re here to help.