Operating principle of "impulse" sealing.

Most impulse sealers operate on the following principle :
When the sealing jaw is lowered, it activates a micro-switch which allows electrical current to flow through the heating element. Usually a timer controls the heating time.
The heating is followed by congealing the material, the material layers held one against the other harden and solidify. This is necessary to perform an efficient and sustainable sealing.
In automatic mode, the congealing time is included in a programmed cycle.

The views below show you the assembly of the various components of the sealing jaws in the case of a simple heating. Click below for detailed views:

The heating element is insulated from metallic parts of the machine to avoid any electrical contact. It should not be in contact with the material because it would adhere, melt and could risk to start a fire.
These insulation consist in silicon rubber, glass tape (Teflon/PTFE)...

Some materials such as thick metallic complexes with several folds(gusseted bags ...) require a double heating: The lower and upper jaws simultaneously produce heat, so it penetrates more effectively the multiple layers of a thick material.

The left views show you the assembly of the different components of the sealing jaws in the case of a double heating. Click above for detailed views