How does the three-roller automatic can sealing machine achieve a tight fit between the sealing film and the can mouth?

The three-roller automatic can sealing machine achieves a tight fit between the sealing film and the can mouth through the synergy of three rollers and precise temperature control. The whole process starts with the conveying and positioning of the sealing film. The film is automatically unwound from the reel and maintained at a suitable tightness through the tension control system. The photoelectric sensor detects the position of the can body to ensure that the film is accurately cut and covered on the can mouth, preparing for the subsequent sealing process.

During the sealing process, the three rollers work in sequence in a predetermined order. The first is the pre-sealing roller, also known as the preheating roller. Its main function is to preliminarily heat and soften the sealing film. The pre-sealing roller is usually heated to a temperature range of 80~120℃, depending on the material properties of the film. This temperature can cause the film to melt slightly but not yet fully bonded. The pre-sealing roller will lightly press the can mouth to make the film initially fit to the edge of the can mouth, while excluding some air. This step can effectively prevent bubbles or wrinkles during subsequent sealing, creating good conditions for the next step of heat sealing.

Next is the main sealing roller, also known as the heat sealing roller, which undertakes the key task of achieving complete sealing. The main sealing roller has a higher operating temperature, usually between 120~180℃, which needs to be precisely adjusted according to the specific film material. At this temperature, the film will completely melt. At the same time, the main sealing roller will apply a higher pressure of 0.2~0.5MPa to press the film tightly against the can mouth. This step also ensures the best sealing effect by accurately controlling the dwell time of 0.5~2 seconds, without overheating and causing the film to burn, and without affecting the sealing strength due to insufficient time.

Finally, the cooling roller, also known as the shaping roller, is used to quickly cool the sealing area. The cooling system uses water cooling or air cooling to quickly reduce the temperature of the sealing area to below room temperature. During this process, the cooling roller will apply moderate pressure to prevent the film from shrinking and deforming during the cooling process, ensuring that the final seal is flat and without warping. This cooling and shaping step is crucial to ensure the long-term stability of the seal.

The entire sealing process relies on a number of key technologies to achieve precise control. The PID temperature control system is used for temperature control, which can adjust the roller temperature in real time to adapt to films of different materials. The pressure regulation system adjusts the roller pressure through air pressure or hydraulic devices to ensure the sealing and avoid crushing the can body. The servo motor drive system ensures the synchronous movement of the roller and the conveyor belt, so that the sealing position error is controlled within ±0.5mm. The film tension control system is adjusted by magnetic powder brakes or inverters to prevent the film from being overstretched or relaxed.