Packaging plays a crucial role in ensuring the safety, quality, and shelf life of products, especially in the food and pharmaceutical industries. Various types of packaging bags, such as pillow-shaped bags, flat bags, and stand-up bags, are widely used, each offering different advantages in terms of sealing quality, aesthetics, and suitability for specific types of products. Among many methods, 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 dual-chamber types, are essential in automating the suction, sealing, and inflation processes, ensuring product integrity and enhancing overall packaging efficiency.
Type of packaging bag
A standard plastic film bag is as follows:
Cushion-shaped bag. The general sewing method is to overlap the longitudinal seam and then turn back both ends, as shown in Figure 1.
General bag. It can be divided into the three-sided closed bag (Figure 2) and the four-sided closed bag (Figure 3).
Standing bags. The common types are the pointed-corner bag (Figure 4), the triangular bag (Figure 5), and the solid-strip bag (Figure 6).
In the bag-making process, it is usually sealed lengthwise first and then crosswise. Therefore, along the entire length of the overlapping and butt-jointed sealing seam of the pillow-shaped bag, three or four film layers overlap at the sealing section, which has a certain effect on the sealing quality. The number of film layers along the entire length of the sealing seam in a flat three-side gusseted bag is the same, and the sealing quality is better, but the bag's shape is asymmetrical and its aesthetics are slightly worse. Four-side sealing overcomes the shortcomings of the two situations above, but it uses more packaging material, and it is often used for simple sealing machines for small packages. Various self-supporting bags have a beautiful appearance and the advantage of being self-supporting, which is suitable for subsequent packaging processes and for product placement and display. However, they have high requirements for packaging material and composite packaging materials should be used.
Vacuum packaging machine
Vacuum packaging involves placing food into a packaging container, removing the air inside the container to achieve a certain vacuum level, and then sealing and packaging it. This is a new packaging method that has grown rapidly in the food and pharmaceutical industries at home and abroad in recent years. It has the following characteristics:
(1) Slows oxidation and deterioration, inhibits microbial growth, and thus extends the shelf life of food. Food is coated with certain microorganisms that reproduce in the air and cause food spoilage. After air is removed, microorganisms cannot reproduce in the absence of oxygen, and many easily oxidized substances also oxidize slowly due to the lack of oxygen.
(2) It is conducive to heat sterilization operations. If there is a large amount of air in a container holding food, heat transfer is weak, the food takes a long time to heat up, and the sterilization time is extended; after the air is removed, the food quickly reaches the required temperature. Additionally, removing air can prevent the container from cracking due to gas expansion during the heating and sterilization process.
(3) After the air is removed, the volume is reduced, making it easy to store and transport.
(4) Because packaged foods need to maintain a certain level of moisture and the packaging materials also have a certain degree of air permeability, vacuum packaging cannot achieve a complete vacuum, and the highest vacuum level can reach –0.096 to –0.099 MPa.
Principle of the structure of a single-chamber vacuum packaging machine
The diagram shows the structure 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 wrapped food is as follows: place the package body into the vacuum tank for orientation, position the bag opening on the heating block, insert the vacuum suction nozzle into the bag opening, and close the vacuum tank lid. After that, the limit switch and relay will automatically control the suction, heat sealing, cooling, automatic opening, and other processes. The suction level, time, heat sealing time, cooling time, etc., should be tested and adjusted in advance.
The operating process of the small vacuum packaging machine is the same as that of the small vacuum packaging machine, except that each process is controlled manually.
The heating method for heat-pressure sealers typically uses pulsed heating. The heating element uses low-resistance wire with a voltage of approximately 10–50 V. When a strong current is applied, the wire heating element instantly generates heat and transfers it to the heating block, after which the bag opening is heat-pressed and sealed. The sealing cooling method can be natural cooling or circulating cooling water to quickly cool the bag mouth and prevent the plastic film in the sealing area from overheating.
Two-chamber vacuum inflation packaging machine structure
Workroom. It consists of an upper cover and a lower base (chamber A and chamber B). The upper cover and the lower base are sealed with a rubber ring.
There are two small air chambers at the top of the cover. Each small air chamber is equipped with a heating mechanism. A vacuum gauge is mounted on the exterior of the top cover, and there are also electrical heating terminals, small air chamber pipes, and air exhaust pipes. The upper and lower covers are connected by a set of four link bars to ensure smooth rotation.
Heating and sealing mechanism. The heating head and cover are connected by two copper pieces at both ends. Two copper bonding blocks at each end of the electric heating belt are secured with screws to prevent loose contact. The electric heating head and sealing cover are fully insulated to prevent short circuits.
During operation, the small air chamber and the large air chamber are displaced simultaneously. The heating head does not operate when the pressure difference at both ends is equal. When the air valve of the small air chamber is connected to the atmosphere to create a pressure difference, the heating head is pressed down, the seal is pressed and heated simultaneously. The heating time and temperature can be adjusted. The heating system is a pressure-regulating type that can be used for different packaging materials. The selection knob is located on the machine's control panel. The electric heating belt is an alloy belt. No-load heating is strictly prohibited.
Base. It is divided into two chambers, A and B, with 16 inflation nozzles on each side. There is a heating pad at the corresponding head heating position, and a set of push-button switches for switching between chambers A and B is mounted below it.
Conclusion
Types of packaging bags and vacuum packaging machines are essential in the food and pharmaceutical industries, ensuring product quality and extending shelf life. While various types of bags are available to suit different materials and aesthetics, vacuum packaging machines enhance preservation by removing air, preventing oxidation, and facilitating thermal sterilization. The structure and working principles of single-chamber and double-chamber vacuum packaging machines play a crucial role in streamlining 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 products are well-protected for storage and transportation.
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