Packaging plays a crucial role in the safety, quality, and shelf life of products, particularly in the food and pharmaceutical industries. Various types of packaging pouches, such as pillow pouches, flat pouches, and stand-up pouches, are widely used and each offers different advantages in terms of seal quality, aesthetics, and suitability for specific product types. Among the many methods available, vacuum packaging stands out for its ability to extend product shelf life by slowing oxidation, inhibiting microbial growth, and making storage more efficient. Vacuum packaging machines, particularly single-chamber and double-chamber machines, are essential for automating the vacuuming, sealing, and inflating processes, ensuring product integrity, and improving overall packaging efficiency.
Types of Packaging Bags
Common plastic pouches come in the following shapes:
Pillow-shaped bag. The standard sewing method involves overlapping the longitudinal seam and then sealing the two ends, as shown in Figure (1).
Flat pouches. They can be divided into three-sided sealed pouches (Figure (2)) and four-sided sealed pouches (Figure (3)).
Stand-up pouches. Common types include pouches with pointed corners (Figure 4), pouches with triangular corners (Figure 5), and pouches with cubic columns (Figure 6).
In bag manufacturing, sealing is typically performed first lengthwise and then horizontally. As a result, along the entire length of the overlapping and butt seams of the pillow-shaped bag, three or four layers of film overlap at the seal, which affects the seal quality. For flat, three-sided sealed bags, the number of film layers is the same along the entire length of the seal, and the seal quality is better; however, the bag shape is asymmetrical and the appearance is slightly less appealing. Four-sided sealing overcomes the disadvantages of the two cases mentioned above, but it consumes more packaging material and is often used for simple sealing machines designed for small packages. Various stand-up pouches look appealing and have the advantage of standing on their own, which facilitates the subsequent packaging process as well as product placement and presentation. However, they place higher demands on the packaging material, and laminated packaging materials should be used.
Vacuum Packaging Machine
Vacuum packaging involves placing food into a packaging container, removing the air from the container, achieving a specific vacuum, and then sealing and packaging the container. This is a new packaging method that has developed rapidly in recent years in the food and pharmaceutical industries both domestically and abroad. It has the following characteristics:
(1) Slow down oxidation and spoilage, inhibit microbial growth, and thereby extend the shelf life of food. Food is contaminated with a certain number of microorganisms that multiply in the air and cause food to spoil. Once the air is removed, microorganisms are unable to multiply in the absence of oxygen, and many easily oxidizable substances also oxidize more slowly due to the lack of oxygen.
(2) It facilitates thermal sterilization. If there is a lot of air in the container with food, heat transfer is poor, it takes a long time to heat the food, and the sterilization time is extended. Once the air is removed, the food quickly reaches the desired temperature. In addition, removing the air can prevent the container from bursting due to gas expansion during the heating and sterilization process.
(3) Once the air has been removed, the volume is reduced, which is convenient for storage and transport.
(4) Since packaged food products must retain a certain amount of moisture and the packaging material also allows some air to pass through, a complete vacuum cannot be achieved with vacuum packaging. The highest vacuum level can reach -0.096 to 0.099 MPa.
Design Principle of the Single-Chamber Vacuum Packaging Machine
The illustration shows the design and operating principle of a medium-sized vacuum packaging machine, which is widely used in small and medium-sized food processing plants.
The packaging process for packaged food proceeds as follows: Place the item to be packaged in the vacuum chamber for alignment, position the bag opening on the heating block, insert the vacuum nozzle into the bag opening, and press down on the vacuum chamber lid. Limit switches and relays then automatically control the vacuuming, heat pressing, and sealing, cooling, automatic opening, and other processes. The vacuum level, vacuum time, heat sealing time, cooling time, etc., should be tested and adjusted in advance.
The operating procedure for the small vacuum packaging machine is the same as that of the small vacuum packaging machine, except that each step is controlled manually.
The heating process for hot-press sealing is typically performed using pulse heating. The heating element consists of low-resistance wire, and the voltage is approximately 10–50 V. When a strong current flows through it, the wire heating element immediately generates heat and transfers it to the heating block. The bag opening is then hot-pressed and sealed. The sealing area can be cooled either by natural cooling or by circulating cooling water to quickly cool the bag opening and prevent the plastic film from overheating in the sealing area.
Design of a Dual-Chamber Vacuum Forming and Packaging Machine
WorkspaceIt consists of an upper lid and a lower base (Chamber A and Chamber B). The upper lid and the lower base are sealed with a rubber ring.
There are two small air chambers on the top of the cover. The small air chambers are equipped with a heating mechanism. A vacuum gauge is mounted on the outside of the cover. In addition, there are electrical heating connections, small air chamber tubes, and air chamber exhaust tubes. The upper and lower covers are connected by a four-bar linkage to ensure smooth rotation.
Heating and Sealing MechanismThe heating head and cover are connected at both ends by two copper plates. The two copper mounting blocks at both ends of the electric heating tape are secured with screws to prevent poor contact. The heating head and end cap are completely insulated to prevent short circuits.
During operation, the small and large air chambers are evacuated simultaneously. The heating head does not function when the same pressure difference exists at both ends. As soon as the air valve of the small air chamber is connected to the atmosphere to create a pressure difference, the heating head is pressed downward, the seal is compressed, and heated simultaneously. Heating time and temperature are adjustable. The heating system is pressure-regulating and suitable for various packaging materials. The selection knob is located on the machine’s control panel. The electric heating band is made of an alloy. Idle heating is strictly prohibited.
BaseIt is divided into two chambers, A and B, and has 16 inflation nozzles on each side. Heating pads are located at the corresponding positions on the heating head, and below them is a cam switch assembly for switching between chambers A and B.
Graduation
Packaging pouches and vacuum packaging machines are indispensable in the food and pharmaceutical industries for ensuring product quality and extending shelf life. Various types of bags are available to accommodate different materials and aesthetic requirements. Vacuum packaging machines improve the preservation process by removing air, preventing oxidation, and facilitating thermal sterilization. The design and operation of single-chamber and double-chamber vacuum packaging machines play a key role in optimizing the packaging process, making it more efficient, reliable, and suitable for a wide range of products. Understanding these packaging methods is essential for optimizing packaging operations and ensuring that products are well protected during storage and transport.
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