How Vertical Packaging Machines Work: A Comprehensive Guide

Vertical packaging machines, also known as vertical form-fill-seal (VFFS) machines, are integral to numerous industries today. Their popularity stems from being fast, efficient packaging solutions that save valuable factory floor space. Whether you're a novice in packaging machinery or adept at operating multiple systems, understanding how vertical packaging machines work can enhance your knowledge base. In this article, we'll delve into the intricacies of how a vertical form-fill-seal machine transforms a roll of packaging film into shelf-ready finished bags.

Simplified Operation of Vertical Packaging Machines

Vertical packaging begins with a large roll of thin film, which is formed into bags, filled with product, and then sealed vertically, achieving speeds of up to 300 bags per minute.

1. Automatic Unwinding:

Vertical packaging utilizes single-layer or composite film materials (often referred to as roll stock) wrapped around a core roll. These materials can vary from polyethylene to laminated films like polyethylene terephthalate (PET)/polyethylene (PE), aluminum foil laminates, or paper laminates. The roll stock is mounted onto the machine's spindle assembly.

During machine operation, the film is typically pulled down from the roll using a film transport belt located on the front side of the machine where the forming tube is situated. This method of transportation is widely used. In some models, the sealing clamp itself grips the film and pulls it down, eliminating the need for belts to transport it through the packaging machine.

An optional motor-driven surface rewinding wheel can be installed to assist in driving the film, aiding the two film transport belts. This option improves the unwinding process, especially with heavier rolls.

2. Film Tension:

As the film unwinds, it passes through a floating arm equipped with a series of rollers. The arm, located at the back of the packaging machine, is a counterbalance pivot arm that moves up and down to maintain tension on the film during transport. This ensures the film remains taut and prevents it from swaying sideways as it moves.

3. Optional Printing:

If a printer is installed, the film passes through a print unit after the unwinding process. The printer can be a thermal transfer printer or an inkjet printer, used to place date/codes or alignment marks, graphics, or logos on the film.

4. Film Tracking and Positioning:

After passing through the printer, the film undergoes alignment through a registration photocell. This photocell detects registration marks on the printed film, controlling the downward belt to contact the film against the forming tube. The registration photocell ensures the film stays in the correct position for cutting at the right place.

Subsequently, the film passes through film tracking sensors that detect the film's position as it moves through the packaging machine. If the sensors detect any deviation in the film's edge from its normal position, it sends a signal to move the actuator. This causes the entire film slide rail to move to one side or the other as needed, realigning the film's edge to the correct position.

5. Bag Forming:

The film enters the forming tube assembly, where it is folded over the shoulder (collar) of the forming tube to create a segment of film with overlapping edges. This marks the beginning of the bag-forming process.

The forming tube can be set for overlap sealing or fin sealing. Overlap sealing involves overlapping the film's two outer edges to form a flat seal, while fin sealing combines the inner edges of the film's two outer edges, creating a seal that protrudes like a fin. Overlap seals are typically considered more aesthetically pleasing and use less material compared to fin seals.

A rotary encoder is positioned near the shoulder (flange) of the forming tube. The active film in contact with the encoder wheel drives it. Each movement generates a pulse transmitted to the programmable logic controller (PLC). The bag length is set digitally on the human-machine interface (HMI) screen, and once this setting is reached, the film transport halts (only on intermittent motion machines; continuous motion machines do not stop).

The film is pulled down by two gear motors, driving the downward friction belts located on both sides of the forming tube. Alternatively, vacuum suction can be utilized to tension the downward belts that secure the packaging film instead of friction belts. Friction belts are often recommended for dusty products due to their reduced wear and tear.

6. Bag Filling and Sealing:

At this point, the film briefly pauses (on intermittent motion packaging machines) to allow for vertical sealing. The hot vertical sealing bar moves forward, contacting the vertical overlapping portion of the film to bond the film layers together.

On continuous motion packaging equipment, the vertical sealing mechanism remains in contact with the film, allowing the film to receive its vertical seam without stopping.

Next, a set of heated horizontal sealing jaws come together to form the top seal of one bag and the bottom seal of the next bag. For intermittent packaging machines, the film pauses to allow the sealing jaws to move in an open-close action. For continuous motion machines, the jaws themselves can move up and down or seal the film through an open-close motion. Some continuous motion machines even feature two sets of sealing jaws to increase speed.

Ultrasonic sealing is an option for "cold sealing" systems, commonly used in industries dealing with heat-sensitive or messy products. Ultrasonic sealing utilizes vibrations to create friction at the molecular level, generating heat only in the area between the film layers.

While the sealing jaws close, the product to be packaged is dropped from the hollow forming tube's center and filled into the bag. Filling equipment such as multi-head weighers or auger fillers are responsible for accurately measuring and dispensing discrete amounts of product into each bag. These filling machines are not standard components of the packaging machine and must be purchased separately. Most companies integrate filling machines with packaging machines.

7. Bag Discharge:

Once the product is in the bag, a sharp knife in the heat seal jaws moves forward and cuts open the bag. The jaws open, and the packaged bag drops. This marks the end of one cycle on the vertical packaging machine. Depending on the machine and bag type, packaging equipment can complete 30 to 300 of these cycles per minute.

Completed bags can be discharged into containers or onto conveyor belts, then transported to downstream equipment such as automatic checkweighers, X-ray machines, carton packers, or case packers.

Understanding the intricacies of vertical packaging machines is essential for optimizing their efficiency and productivity in various industries. From unwinding the film to sealing the bags, each step plays a crucial role in the packaging process, ensuring products are efficiently and securely packaged for distribution.