- Extrusion
The manufacturing process begins with extrusion, where polypropylene (PP) granules are melted and forced through a flat die to form continuous tapes. These tapes are quenched in water to solidify, then stretched biaxially (machine and transverse directions) to enhance tensile strength. Additives such as UV stabilizers or anti-static agents may be incorporated during extrusion to meet specific performance requirements. The resulting tapes exhibit a controlled thickness (typically 80-120 microns) and width (2-5 mm), forming the foundational material for weaving.
- Weaving
Using circular looms, the extruded PP tapes are interwoven into a tubular fabric structure. The loom settings determine the fabric's warp (longitudinal) and weft (circular) density, typically ranging from 8×8 to 12×12 tapes per inch. Critical parameters like weave tension and take-up speed are optimized to ensure uniform fabric geometry. This stage produces the base fabric roll, which forms the bulk material for FIBC construction.
- Vacuuming
Prior to lamination, the woven fabric undergoes vacuum treatment to eliminate trapped air and surface contaminants. This process enhances interfacial adhesion between the PP fabric and subsequent coatings. Industrial vacuum systems with adjustable suction power (0.5-1.5 bar) are employed, ensuring complete deaeration without distorting the fabric's dimensional stability.
- Lamination
A PP copolymer film (15-30 GSM) is thermally bonded to the fabric using heated rollers (140-160°C). For conductive FIBCs, carbon-loaded coatings may be applied via extrusion lamination. The lamination process achieves peel strengths exceeding 3 N/cm (ASTM D903), critical for maintaining barrier properties against moisture and particulates. Infrared sensors monitor coating uniformity in real-time.
- Printing
Screen printing or flexographic methods apply customer-specific logos and safety markings. UV-resistant inks (ISO 2836-compliant) are formulated with 20-40% pigment concentration. Critical print parameters include mesh count (90-120 for screen printing), anilox volume (4-8 BCM for flexo), and curing temperature (60-80°C). Registration accuracy is maintained within ±0.5 mm through optical alignment systems.
- Cutting
CNC cutting tables with ultrasonic knives precisely section the laminated fabric into panel components. Cutting patterns are optimized using nesting software to minimize material waste (<3%). Key dimensions include body panels (standard sizes up to 90"×90"), lifting loops, and baffle components. Tolerance is maintained at ±1.5 mm for critical seam allowances.
- Sewing
1. High-Strength Stitch Configuration
Industrial sewing machine for FIBC bag achieve superior seam integrity in FIBC production through engineered stitch parameters.
GA3670 High Speed Freeform FIBC Bag Sewing Machines
GA2570L-25 25"long arm big bag sewing machine
GA9800 FIBC/Bulk Bag Sewing Machine (Large shuttle hook)
2. Reinforcement of Critical Seams
Critical load-bearing seams -including base junctions and loop attachments are fortified using dual-needle stitching technology. Twin parallel stitch lines (spaced 6-8mm apart) distribute stress across 25-30mm seam allowances, reducing localized strain by 40-60% compared to single-line seams. Pneumatic presser feet maintain consistent fabric alignment during high-speed operation (4,000-6,000 SPM), while needle cooling systems prevent thermoplastic thread melting.
GK81800 Long arm baffle bag sewing machine
2-needle 4-thread Big Bag Chainstitch Sewing Machines 80700 Series
GN20-2D Single needle double thread FIBC bag overedging machine
3. Cross-Stitched Webbing for Lifting Loops
Lifting loops are reinforced with multi-axis cross-stitching patterns using specialized BAR-TACK attachments. Polypropylene webbing (1,000-2,500 daN break strength) undergoes 8-12 overlapping stitches in X/Y orientations, creating a composite matrix that resists shear deformation. The process employs Class 42 industrial needles (Ø1.6-2.0mm) and programmable stitch counters to ensure uniform stitch density (12-16 stitches per 25mm segment).
PSM-E5020-LS Automatic big bag loop sewing machine
PSM-E4030-VS Automatic big bag loop attaching sewing machine
PSM-E5050-LS Automatic big bag loop making machine
- Final Testing
Completed bags undergo rigorous testing:
Lift testing: 6:1 safety factor (e.g., 5-ton bag tested at 30 tons)
Top lift test (ASTM D6055) with cyclic loading
Stacking test (up to 5:1 height-to-base ratio)
Electrical resistance measurement (<10⁹Ω for conductive bags)
Drop test from 1.8m height (UN certification)