On most shrink lines the constraint is tunnel dwell: the film needs a minimum time at temperature to shrink evenly. Speeding up the sealer without lengthening the tunnel or raising its capability simply moves the queue to the tunnel mouth and produces under-shrunk packs.
How to find the real constraint in ten minutes
- Run the line at normal speed and watch where product accumulates.
- Accumulation before the sealer means the infeed or operator is the limit.
- Accumulation between sealer and tunnel means the tunnel is the limit.
- No accumulation but poor shrink means the tunnel is already at its limit.
What each fix actually buys
| Change | What it fixes | What it does not fix |
|---|---|---|
| Faster sealer | Operator wait at the sealer | Tunnel dwell |
| Longer tunnel | Dwell at higher line speed | Seal quality |
| Higher tunnel temperature | Under-shrink at the margin | Insufficient dwell — it scorches instead |
| Automatic infeed | Operator loading time | Anything downstream |
Why raising temperature is the wrong first move
Temperature and dwell trade off, but not linearly. Past a point, more heat scorches the outer surface before the inner film has contracted, so you get burn marks and a still-loose pack. If the fix requires temperature beyond the film's window, the answer is dwell, not heat.
Across the 16 shrink and seal-cut series we list, models are published with their tunnel dimensions and conveyor speeds, which together determine achievable dwell at a given line rate.
Tunnel and sealer specifications are on each series page in the shrink and seal-cut range.
Figures in this article are drawn from the 137 machine series SilverSeal currently supplies, not from generic industry averages. Specifications vary by model — check the individual series page before specifying.
Frequently asked questions
Does a longer tunnel always mean higher output?
It means you can run faster while keeping the same dwell. If the sealer or infeed is the constraint, a longer tunnel changes nothing.
Can I fix under-shrink by slowing the conveyor?
Yes — that is exactly what lengthening dwell does. It costs throughput, which is why a longer tunnel is the capital answer to the same problem.
How do I know the tunnel is at its limit?
If raising temperature causes scorching before the pack tightens, you have run out of dwell, not heat.
