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How does a square bottom open pocket ensure upright stability during powder filling?

Publish Time: 2026-02-02
In the industrial packaging of powders and granules, the square bottom open pocket, with its unique structural design and material properties, has become the mainstream packaging form for products such as cement, chemical raw materials, food additives, and plastic particles. One of its core advantages is its ability to remain upright, stable, and non-tipping during high-speed automated filling processes, thus ensuring filling accuracy, reducing dust emission, and improving production efficiency. This stability is not accidental but stems from the synergistic effect of its "square flat bottom structure," "heat-sealing technology," and "overall mechanical balance."

1. Square Flat Bottom Design: Building a Stable Physical Support Foundation

Unlike traditional sewn-bottom bags or round-bottom bags, the square bottom open pocket has a completely flat and rigid rectangular bottom surface after molding. This bottom surface is made of multi-layer composite film through high-precision folding and hot-pressing processes, resulting in sturdy corners and straight edges. When an empty bag is fed into the filling station, even without material inside, its structure possesses sufficient bending rigidity to stand upright naturally on the conveyor belt or filling platform, requiring no additional supports or manual straightening. This "self-supporting" ability greatly simplifies the automation process—the filling nozzle can be precisely aligned with the bag opening, preventing spillage or blockage caused by bag tilting.

2. Heat-Sealing Softening Technology: Enhancing Bottom Integrity and Load-Bearing Capacity

The bottom and side seams of the bag are sealed with a special heat-sealing resin, which melts and bonds under precisely controlled temperature and pressure, forming a strong, seamless seal. This heat sealing not only provides excellent airtightness but also fuses multiple layers of material into one, significantly improving the bottom's tensile strength and tear resistance. During filling, the powder rapidly enters the bag, generating impact and lateral pressure, while the reinforced square bottom surface evenly distributes the load, preventing localized bulging or rupture. Especially for high-density materials, where a single bag can weigh 25-50 kg, the flat-bottom structure combined with high-strength heat sealing ensures the bags remain rock-solid even when fully loaded, preventing lower bags from deforming or collapsing during stacking.

3. Optimized Center of Gravity Distribution: Ensuring Stability During Dynamic Filling

The geometry of the square-bottomed bag ensures that its center of gravity remains within the bottom projection area during filling. As material is injected from the top or side valve, the powder naturally settles to the bottom, and the center of gravity slowly shifts downward, unlike cylindrical bags which are prone to swaying due to excessive weight at the top. Some high-end designs also incorporate reinforcing ribs at the four corners of the bag or use a "W"-shaped bottom fold to further expand the support area and enhance anti-tipping moment. Even on high-speed filling lines, airflow disturbances or mechanical vibrations will not cause the bags to become unstable, effectively preventing production line downtime or product contamination caused by tipping.

4. Material and Process Synergy: Balancing Flexibility and Rigidity

The bag body is typically made of high-stiffness polypropylene woven fabric with a film coating or high-density polyethylene blown film, ensuring both flexibility for easy folding and transportation, and rapid "shaping" into a rigid box after filling. The resin formulation in the heat-sealing area is optimized with a moderate softening point, achieving strong adhesion while preventing high-temperature damage to the substrate. Furthermore, the bag opening is often equipped with a self-closing valve or easy-tear opening, automatically sealing after filling to prevent dust leakage during transportation, while maintaining the bag's shape and facilitating warehousing and stacking.

The square bottom open pocket, through precise integration of structure, materials, and processes, transforms the seemingly simple requirement of "stability" into a key technological advantage in industrial packaging. It is not just a container, but a reliable partner in automated production processes—using static control and square load-bearing capacity, silently safeguarding the bottom line of efficiency and quality in every filling process.
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