Constant Heat Sealing
Constant heat sealing is a sealing method where the sealing bars are kept hot all the time.
When the machine is running, the bars stay at a fixed temperature.
Sealing is made when the bars close and apply heat, pressure, and time to the packaging material.
Because the bars are always hot, heating is not linked to each individual sealing cycle.
Cooling and Seal Formation
In constant heat sealing, cooling starts after the sealing bars open.
This means the seal cools without pressure.
As the material cools down, it may shrink and/or deform, depending on the type of film or laminate used.
This cooling behaviour can influence:
- Seal width
The effective seal area may become slightly narrower after cooling. - Seal appearance
The seal can show minor puckering, waviness, or uneven surface finish. - Final seal strength
If the material is still soft when the bars open, the seal may not fully stabilise before cooling. - Seal geometry
Local deformation or distortion of the seal line can occur as the material contracts. - Package flatness
Uneven cooling may affect the flatness of the package around the seal area.
For this reason, constant heat sealing works best with stable materials that tolerate cooling without pressure and have predictable thermal behaviour.
Cost and Application
Constant heat sealing is often chosen as a cost-effective solution because the system is relatively simple.
It is commonly used for:
- High-speed machines
- Continuous production
- Thicker or multilayer materials
Summary
Constant heat sealing is a well-known and widely used technology.
It is simple and economical, but the sealing result depends on material behaviour during cooling after the bars open.
Understanding this makes it easier to compare constant heat sealing with other sealing methods.