L-Shape Corner Sealer | Heavy Carton | SunAura Machinery

The automatic corner sealing machine operates on a multi-station mechanical principle that applies tape to all four vertical carton edges simultaneously as the carton passes through the machine. When a carton with top and bottom flaps already sealed arrives at the infeed conveyor — typically from an upstream automatic flap folding sealer — the dual side belt drive system grips the carton and pulls it into the corner sealing zone at a controlled, consistent speed.

Inside the corner sealing zone, four independent sealing heads are positioned at the four vertical edges of the carton’s travel path: two upper heads at the top-left and top-right corners, and two lower heads at the bottom-left and bottom-right corners. Each sealing head consists of a tape cartridge holding a roll of BOPP tape, a guide roller that directs the tape toward the carton corner, a foam rubber pressure roller that presses the tape firmly against the vertical edge, and an angled stationary cutting blade that severs the tape at the end of the sealing cycle.

As the carton enters the sealing zone, the leading edge of the tape from each of the four cartridges is already positioned at the carton corner, held in place by a small adhesive tab or a spring-loaded tape retainer. When the leading edge of the carton makes contact with the tape, the tape adheres to the carton surface and begins to unroll from the cartridge. As the carton continues forward, the foam pressure rollers on each head maintain consistent pressure against the vertical edges, pressing the tape firmly into the corner seam where the flap meets the side panel. This pressure is critical — it ensures that the tape conforms to the 90-degree corner angle and achieves full adhesive contact on both the flap surface and the side panel surface, creating a strong, durable bond.

When the trailing edge of the carton passes the cutting blade, the blade — positioned at a precise angle relative to the carton travel direction — severs the tape cleanly. A second, smaller pressure roller then presses the trailing edge of the tape firmly against the carton, preventing the tape from lifting or peeling during subsequent handling. The four sealing heads operate independently but in perfect synchronization, ensuring that all four corners receive identical tape length, pressure, and seal quality. The entire corner sealing process takes approximately 2-4 seconds per carton, and the machine automatically resets for the next cycle after each carton exits. For L-shape models, additional top and bottom sealing stations are integrated before the corner sealing zone, allowing the machine to perform standard top/bottom seam sealing and corner edge sealing in a single pass.