Processing Steps

The polyethylene arrives at the plastic bag manufacturing facility in pellet form, referred to as resin.

The following drawing shows how plastic bags are created.

1. The machine operator pours the polyethylene resin into the hopper.
2. The hopper feeds the resin into the extruder.
3. Heating elements and the turning of the extruder screw melts the resin into molten form and forces it through the extruder.
4. The molten polyethylene flows evenly up and over the circular die.
5. As the molten polyethylene emerges from the die, the machine operator:
   1. Grabs it wearing protective gloves.
   2. Pinches the molten poly together.
   3. Ties a rope to the top of the molten poly. The rope leads upward to a pulley system.
   4. Pulls the other end of the rope to move the molten poly upwards. At the same time, the air ring blows cool air upwards, which solidifies the molten poly.
6. As the tubular shape moves up, the machine operator fills air through the die to give the desired width.
7. Along the length of the tower are guides to keep the tubular poly film from shifting. As the film reaches the top of the cooling tower, the guides gradually flatten it into a layflat form. If the plastic bag will have gussets, special frames (called "gusset boards") indent the sides of the tube before it is flattened.
8. At the top of the cooling tower, motorized nip rollers pinch the solidified polythene film, then the nip rollers take over the job of moving the polythene film up the cooling tower.
9. The layflat film travels over a series of rollers. For simple bags, such as trash bags or industrial bags, the film is contained to a single, in-line process. In this case, the polythene film: Travels through a printing machine where the companies desired design would be printed on and then into a bag machine that seals the bottom of the plastic bag and perforates it at the same time. The perforation allows the bags to be easily torn from the roll.
10. For polythene bags with complex features (for example, multi-colored Printing) the film is wound on to a roll and then taken out of line for further processing where other complex machinery would print and convert the polythene into bags.