Side Sealing Bag Making Machine Technical Deep Dive: Seal Orientation and Film Guiding
Side sealing bag making machines produce bags with seals on the vertical edges (sides), leaving the top and bottom open for filling. This orientation is common for pillow bags, bread bags, and produce bags. The side seals are typically made by a pair of heated sealing bars that clamp onto the film edges. The film is fed flat, and the side seals are applied continuously or intermittently. The key challenge is maintaining the film's edge alignment so that the seals are consistently positioned relative to the film edges and any print. The edge guide system must be highly accurate because the side seal must be within a few millimeters of the film edge to avoid excess trim or seal failure. The edge guide sensor (ultrasonic or optical) detects the film edge and sends corrections to a steering roller. The sensor's resolution is 0.1 mm, and the system's response time is under 100 ms. The film path must be designed to minimize wandering caused by roll eccentricity or tension variations.
The side sealing bars are often longer than the bag width to accommodate different widths. They may be segmented to allow independent temperature control for each side. The sealing pressure must be uniform along the length of the bar; any unevenness causes weak spots. The bars are typically actuated by pneumatic cylinders or servo motors. The sealing temperature and dwell time are similar to bottom-seal machines, but the film thickness at the edge may be double (due to the overlap of the film tube), requiring higher temperature or longer dwell. The side seal can be made as a lap seal (overlap) or a fin seal (folded flat). A fin seal is stronger but requires an additional folding device. The machine must also handle gusseted bags (side-gusseted), where the side seal is applied to the folded film, creating a bag that expands. This requires additional folding plates.
Plastic Bag Making Machine
Registration for side-sealed bags: If the bag has print, the side seal must be positioned relative to the print. The registration sensor detects a mark on the film and adjusts the film feed so that the side seal occurs at the correct location. This is similar to bottom-seal registration but the cut length is now the bag width. The machine's control system must handle both side seal position and cut length.
Film guiding strategies: For side seal machines, the film is usually slit to width before entering. The slitting can be done in-line with a slitting station. The film edge must be clean and free of defects to ensure proper sealing. The edge guide can use a line guide (if a printed line is available) or an edge guide. The guide's actuator must be fast to correct high-frequency wandering. Some machines use a "camera" that detects both edges and centers the film. This is more accurate but costly. The film tension in the side seal area is maintained by a dancer; any tension variation causes the film to wander.
Quality control: The side seal width and position are measured by a vision system. The seal is tested for peel strength. If the seal is too close to the edge, it may be weak or cause film tearing. The machine can automatically adjust the edge guide offset to maintain a consistent seal-to-edge distance. The machine also monitors the film tension and alerts if the film is drifting.
Maintenance: The side sealing bars require regular cleaning and alignment. The edge guide sensor must be kept clean. The film guide rollers need lubrication. By mastering side seal orientation and film guiding,
side sealing bag making machines produce consistent, strong side seals, essential for packaging applications where the bag is filled from the top or bottom.
