Shipping damage is one of the most common sources of loss in industrial packaging. Bag rupture means direct product loss, cargo contamination, reshipping costs, and reduced customer satisfaction. Structural design can significantly reduce rupture risk at the source.
Bottom Seal Structure Design
The bag bottom is the critical area承受堆码压力. Different bottom seal structures vary significantly in compression resistance and sealing performance.
Comparison of Common Bottom Seals
| Bottom Seal Type | Compression Resistance | Sealing | Application |
|---|---|---|---|
| Standard heat seal | ★★★ | ★★★ | General industrial products |
| Folded heat seal (double fold) | ★★★★ | ★★★ | Fertilizers, grains |
| Leak-proof bottom (PP tape reinforcement) | ★★★★★ | ★★★★ | High-value powders |
| SOT (Sewn Open Mouth) | ★★★★ | ★★ | Heavy-load open filling |
| Sewn + heat seal combination | ★★★★★ | ★★★★★ | Sea freight export, high requirements |
Leak-Proof Bottom Design Key Points
- Bottom fold layers: at least 3
- Heat seal temperature set according to PP melting point (~165°C); too high causes burn-through, too low causes weak bond
- For highly flowing powders (e.g., cement), add leak-proof coating at the bottom seal area
Side Seam Reinforcement Design
Bag side seams are another common rupture point. Seam strength depends on stitch type, stitch spacing, and thread count.
Stitch Type Selection
- Single-thread chain stitch: Good elasticity, moderate strength; suitable for light loads
- Double-lock stitch: High strength, unravel-resistant; standard for industrial packaging
- Overedge/Overlock stitch: Wraps fabric edges on top of lock stitch; neat and fray-resistant
Stitch Spacing and Thread Count
- Standard spacing: 3–4 mm; too wide reduces strength, too narrow causes thread breakage
- For high-load bags, use double-needle overlock stitch
- Thread count should match bag GSM: heavier bags require coarser thread
Impact of Stacking Patterns on Damage Rate
Square vs Rectangular Bottom
The bottom aspect ratio significantly affects stacking stability. Research shows square or near-square bags (aspect ratio ≤ 1.2:1) have approximately 40% lower rupture rates than elongated bags in container stacking.
Stacking Patterns
- Interlocked stacking (brick pattern): Upper layer offset from lower; best stability, recommended for sea freight
- Aligned stacking (row pattern): Upper aligned with lower; easy but less stable
- Pyramid stacking: Wider base, narrowing upward; suitable for short-term warehouse storage
Other Structural Damage Reduction Measures
- Reinforced corners: Add PP tape reinforcement at bag corners to reduce corner stress concentration
- Vent hole design: For powder products, properly designed vent holes balance internal/external air pressure, reducing burst from pressure differential
- Handle/ear design: For manual handling, handles reduce tears from gripping
- Palletized packaging: Integrate multiple bags on pallets to reduce individual bag stress
The core principle is "prevention over remedy." Combining finite element analysis (simulating stack pressure distribution) in design, strict quality control in production, and standardized handling procedures during loading/unloading can bring the rupture rate within acceptable limits (typically target < 0.5%).