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Powder filling systems : Sealing

Working principle of packaging sealing systems

How works the sealing jaws in a packaging machine ?

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Section summary
1. Introduction
2. Film sealing

1. Introduction

What is a bag / pouch sealing ?

After forming a bag shape in a filling machine, thanks to the forming collar and forming tube, it is necessary to seal the bag so that it can hold and protect the material to fill. At minimum, it is required to perform 2 seals (some machines can fill some sachets and make a 3 side seal).

The sealing is done thanks to sealing jaws, or bars, which are applying pressure and heat to the packaging material in order to weld it.

2. Film sealing

2.1 Sealing jaws

There is a minimum of 2 sets of sealing jaws considering regular bags, pouch, or sticks :
  • The vertical sealing bar
  • The horizontal sealing bars

The vertical sealing bar is operated one time per pack, in order to perform the lateral seal of the bag. The horizontal jaws are on the contrary operated 2 times / bag : to perform the bottom seal, which allows to fill the product, and to perform the top seal to close the bag before cutting it.

Filling machine Sealing bars and jaws

Figure 1 : Filling machine film sealing

The sealing bars are electrically heated, with their temperature measured in order to provide an automated control of the heating. Note that some technologies use actually ultrasonic vibration to perform the seal.

Sealing bars (jaws) heating components

Figure 2 : Components of a sealing bar, for heating

2.2 Film sealing principle of operation

STEP 1 : Vertical sealing

Once the film is wrapped around the forming tube, the 2 sides of the films are overlapping. It allows to glue them together in order to create the vertical seal of the pouch. It is done thanks to a sealing bar, most of the case heated, that is applied against the overlapping film sides. To perform the sealing, the film is pausing to allow the sealing bar to be pressed against the film, although for continuous machine the sealing bar is always in position and seals the film while it moves.

STEP 2 : Bottom Horitonzal sealing

After the vertical seal is done, the next step is to seal the bottom of the pack so that the product can be filled. The sealing is done thanks to 2 sealing bars that are coming pressing against each other and squeezing the film to seal it. These 2 bars are also sometimes called sealing jaws. The bars are as well heated and have also a corrugation (grooves) on their surface to improve the sealing efficiency. The sealing efficiency depends on the adjustment of the temperature, the sealing time and the pressure applied. The pressure can be adjusted mechanically thanks to springs.

STEP 3 : Top Horizontal sealing

After filling, the pack must be closed, the film is then pulled further down and the sealing jaws are activated again in order to close the pouch. Note that some knifes are also located at the same level of the horizontal sealing bars and are activated to cut the bag and let it fall to a conveyor once the top seal is done.


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