Six factors of heat sealing quality of bag making machine (Part 2)

4. Cooling

The cooling process is to shape the welded seam that has just been melted and sealed at a lower temperature under a certain pressure, eliminate stress concentration, reduce the shrinkage of the welded seam, improve the appearance flatness of the bag, and improve the heat sealing strength.

The cooling water of the bag making machine is generally tap water or circulating water at about 20°C. If the water temperature is too high, the pressure of the cooling knife is not enough, the circulation of cooling water is not smooth, and the circulation volume is not enough, etc., it will lead to poor cooling and decrease of heat sealing strength.

5. Number of heat sealing

Most of the longitudinal and transverse heat sealing of the bag making machine adopts the hot plate welding method. The number of longitudinal heat sealing depends on the ratio of the effective length of the heat sealing knife to the length of the bag, and the number of transverse heat sealing is determined by the number of sets of heat sealing equipment on the machine. . Good heat sealing generally requires more than 2 times of heat sealing. Most of the transverse heat sealing equipment is 3 groups. In order to meet the heat sealing requirements of the wide side, transverse heat sealing equipment is often added, and the number of heat sealing times is added to reduce the heat sealing temperature and reduce the necking phenomenon. For longer standard packaging bags, multiple feeding techniques can be used to reduce the length of each feeding to one-half or one-third of the bag length, and then increase the number of heat-sealing times to improve the heat-sealing effect, but it will reduce production. Therefore, some bag making machines add the length of the longitudinal heat-sealing rod to increase the number of heat-sealing times and ensure the heat-sealing quality.

6. Heat sealing knife gap

The gap of the heat sealing knife refers to the pressure distance that the predetermined hot air pressure is transmitted to the heat sealing surface when the upper heat sealing knife contacts the bottom plate. At the same film thickness and the same heat sealing speed, the gap between the heat sealing knives is small, the heat sealing time is relatively short, and the heat sealing strength of the product will decrease. Generally, the heat sealing knife gap is set at 1.0~1.5mm, which is related to the film thickness, transfer function, bag making speed, etc.