Causes uneven pressure in the heat sealing film

[China Packaging Network News] Several factors can lead to uneven heat sealing pressure when wrapping films. Understanding these issues is crucial for maintaining consistent and effective sealing in packaging processes. Here are the main causes:

1. Deformation of the Heat Sealing Knife

Heat sealing knives are typically made from aluminum or copper, materials known for their excellent thermal conductivity. However, both are relatively soft, making them prone to deformation if not installed correctly. Improper tightening of the fixing screws during installation can result in uneven stress distribution. Frequent tool changes can also contribute to this issue over time. To prevent this, it's essential to follow the correct installation procedure and ensure even pressure across the entire surface of the knife.

2. Low Machining Accuracy of the Heat Sealing Knife

If the heat-sealing knife is manufactured with low precision, its surface may not be flat or uniform. This can lead to inconsistent pressure during the heat-sealing process, which negatively affects the strength and quality of the sealed bag. Regular maintenance and inspection of the knife’s surface are important to ensure optimal performance.

3. Contamination or Damage on the Heat Sealing Knife Surface

Dirt, scratches, or other damage on the surface of the heat-sealing knife can cause uneven pressure. Additionally, if molten resin sticks to the knife and isn't cleaned promptly, it can interfere with the sealing process and reduce the overall strength of the package. It is therefore important to clean the knife thoroughly after each change to avoid such issues.

4. Hardness and Elasticity of the Silicone Skin

The silicone skin plays a critical role in ensuring even heat-sealing pressure. It must have the right balance of hardness and elasticity to maintain consistent contact with the film. Over time, due to wear or aging, the silicone skin may lose its elasticity, leading to uneven pressure and potential bubbles forming during sealing. This can severely impact the strength of the seal. When selecting silicone skins, it's important to choose those with appropriate hardness levels. For example, when sealing aluminum foil bags, a hardness of HS70 is recommended, while general materials usually require a hardness between HS50 and HS60.