The process takes place in five steps. In six steps, we will start from unwinding the film and ends with sealing and discharging the bag for transport.
The packing machine normally uses a single sheet of film rolled on a core. The film material can be anything from polyethylene, foil, cellophane laminates and paper laminates. Popularly the film is pulled by transport belts, which are positioned to the side of forming tube. There is another method as well; in this method, jaws will automatically grab the film and unwind the film.
You can also install a motor-driven system which will assist the two transport belts. The extra addition is recommended only if the roll is heavy.
It is crucial to keep the film under tension so that it will not wander around on the transport belt. So, there is a dancer arm; the arm is a weighted pivotal arm that moves up and down to keep the packing film under tension. Usually, the arm is located at the back of the packaging machine.
Printing is necessary for most industries because there is no barcode or expiry date on the film, and it is essential to have them on a package. The machine can use either ink-jet or thermal type printer to print dates, logos, graphics etc.
The machine performs two functions in this step. Firstly, it uses the photo-eye to detect the marks printed by the printer. The photo-eye keep the film positioned correctly so that there is no complication in the cutting phase.
Then there are tracking sensors; their job is to detect the position of the film. If the sensor detects the edge is off-center, it will send a signal to the actuator, which in turn will move the entire film carriage to shift until the edge is in the correct position.
In this process, the films are turned into bags. When the file enters the forming tube, it will fold the film around the tube, and we have a long-folded tube of film.
Then we have two outer edges overlapping each other. Then the forming tube seals the overlapping edges in the fin or lap seal. In the fin seal, the forming tube joins the overlapping edges to create a seal; the seal will stick out. In lap seal, the film makes a flat seal of overlapping edges; this seal looks pleasing and uses less film than the fin seal.
There is a rotary encoder near the shoulder of forming tube. It measures the length of movement as the in-contact film drives the encoder wheel. Then the length is transferred to PLC or programmable logic controller. Then the bag length is set by a human operator, and once the setting is done, the film transport will stop. Then the machine draws the film using two gear motors placed on each side of forming tube.
The last step is to fill and seal the bag. Firstly, the bag is vertically sealed, or the bottom of the bag is sealed. After that, it will move to the filling station, which can be a single head or a multi-head setup. It will fill the pack and move it to the sealing station. Then the bag will be sealed and pushed towards the next section. Where it will be placed in the boxes and moved to the supermarkets.