The three edge sealing automatic packaging machine is one of the most widely used types of fully automatic packaging machines on the market, commonly used for packaging products such as granules, powders, tablets, liquids, small pieces, etc. (such as snacks, seasonings, granules, daily chemical products, hardware). Its core working principle can be summarized as: "bag making filling sealing" integrated continuous automatic completion.
1、 Core workflow (step-by-step)
The entire work process is like a highly collaborative "assembly line", usually following the following steps in a loop:
Film unwinding and tensioning:
The rolled packaging film (such as plastic composite film, aluminum-plastic composite film) is installed on the unwinding reel at the back of the machine.
The film passes through multiple guide rollers and tensioning devices to ensure that it remains flat, wrinkle free, and has constant tension during transportation.
Pattern photoelectric positioning (optional, for patterned films):
If a trademark or pattern that needs to be aligned is printed on the film, the photoelectric eye (sensor) on the machine will detect the cursor (Mark point) on the film, and adjust the feed rate of the film in real time through the feedback control system to ensure that the pattern of each bag stops at the preset same position.
Forming bags (key steps):
The film passes through a precision "former" (a three-dimensional mold similar to a triangular plate).
Under the guidance of the molding machine, the flat film is folded into a cylindrical shape with overlapping longitudinal edges.
Subsequently, the longitudinal sealing device (a set of heated, continuously rotating rollers or a constant temperature heat sealing block) immediately heats and applies pressure to the overlapping longitudinal edges, completing the middle seam sealing and forming a continuous, bottom closed cylindrical film.
Lateral traction:
The traction rollers (usually a pair of textured rubber rollers) clamp the already formed film and perform precise step-by-step traction downwards (or horizontally). Each time a bag is pulled, it pauses once, and this distance determines the length of the packaging bag.
Material filling:
During the pause in traction, the measuring and filling device located above the forming machine begins to operate.
For particles/powders: Spiral measuring scales, measuring cups, or electronic combination scales are usually used to pour a certain amount of material into the membrane cylinder below through the discharge port.
For liquids/pastes: Use a liquid pump and a quantitative valve for filling.
For block shaped objects: vibrating discs or robotic arms may be used to sort the materials.
Horizontal sealing and cutting (core sealing steps):
After filling is completed, the horizontal sealing device (a pair of heat sealing knives with heating and cooling areas) is closed from both sides to clamp the membrane cylinder.
It completes two key actions simultaneously:
Top sealing: Seal the top of the just filled bag.
Bottom sealing: Simultaneously serving as the bottom seal for the next bag (as the film is continuous).
Cutting: The heat sealing knife usually has a sharp cutting blade in the middle. While sealing, the upper and lower bags are cut from the middle and separated into independent three sided packaging bags (with horizontal sealing edges on both sides and longitudinal sealing edges on the back).
Finished product output:
The cut finished bags fall into the conveyor belt or collection basket, completing the entire packaging process. Then the machine enters the next cycle.
2、 Core components and functions
Molding tool: The key mold that determines the bag shape (such as back sealed bags, pillow bags) and packaging speed.
Vertical sealing device: continuous operation, responsible for forming the back seam of the packaging bag.
Horizontal sealing and cutting device: intermittent work, responsible for sealing the top and bottom of the bag and cutting it.
Measurement and filling system: the core that ensures accurate and consistent weight or volume of each bag of product.
Photoelectric tracking system: ensures precise alignment of packaging patterns.
PLC control system: the brain of the machine, coordinating the timing and accuracy of all actions (traction, filling, sealing and cutting).
3、 Summary of work characteristics
High efficiency: Continuous bag making, with a speed of tens to hundreds of bags per minute.
High consistency: The bag shape is regular, the edges are firm and beautiful, and the measurement is accurate.
Wide applicability: By replacing different molding tools, filling heads, and packaging materials, it can adapt to a variety of products.
Three sided sealing structure: Due to the process of forming the tube first and then sealing and cutting, the finished bag has a back middle seal and two top horizontal seals, with a total of three sealing edges, hence the name "Three sided sealing". This type of bag has good sealing and neat appearance, and is the most common form of plastic small packaging bag on the market.
Simple metaphor: Its working principle is like a "instant bag filling robot": pull out a piece of film → fold it into a tube and seal the back seam → fill it with things → seal the upper opening and cut it off → a separate packaging bag is completed. The entire process is fully automated, continuous, and high-speed.