What are the two main factors affecting the shrinkage rate of self-sealing bags?

1. The structure of the self-sealing bag itself

*Wall thickness difference:In the same self-sealing bag, the shrinkage rate of areas with thinner walls is less than that of areas with thicker walls. This is because thicker areas absorb more heat and undergo greater deformation when heated.

*Insert location:The shrinkage rate of areas farther from the insert is greater than that of areas closer to the insert. The insert restricts the free shrinkage of the surrounding material, resulting in a lower shrinkage rate in areas closer to the insert.

*Flow direction:The shrinkage rate perpendicular to the flow direction also differs from that perpendicular to the flow direction; generally, the shrinkage rate in the flow direction is greater than that perpendicular to the flow direction. This is because the material is stretched more in the flow direction, thus exhibiting a greater shrinkage rate when heated.

*Obstruction direction:The shrinkage rate of a self-sealing bag in the obstruction direction is smaller than that in the unobstructed direction. This is because obstructions restrict the free shrinkage of the material.

2. Process Conditions in Production

*Raw Materials:Different raw materials result in different shrinkage rates for self-sealing bags. Crystalline plastics have a higher shrinkage rate than amorphous plastics. Plastics with poor flowability have a higher molding shrinkage rate, while those with good flowability have a lower molding shrinkage rate. Furthermore, adding fillers to the plastic significantly reduces the shrinkage rate after molding; plastics without fillers have even better shrinkage rates after molding.

*Pressure and Temperature:Pressure and temperature are two important process conditions affecting the shrinkage rate of self-sealing bags. Excessive pressure increases the sealing force of the self-sealing bag, leading to a decrease in shrinkage. Conversely, increasing the temperature of the raw materials causes the self-sealing bag to expand in volume, reducing the amount of material injected through the mold and thus increasing the shrinkage rate. However, higher raw material temperature decreases viscosity, which increases the pressure within the mold cavity, potentially reducing the shrinkage rate. Therefore, the factors affecting the shrinkage rate of self-sealing bags depend on the combined effects of pressure and raw material temperature.

In summary, the shrinkage rate of self-sealing bags is influenced by two main factors: the bag's inherent structure and the process conditions during production. In actual production, these factors need to be adjusted according to specific needs to obtain the ideal shrinkage rate.