Overview

PP woven cement bag manufacturing is a multi-step process that transforms raw polypropylene granules into finished, printed cement bags. The process involves extrusion, weaving, lamination, printing, cutting, and sewing — each requiring specialized equipment.

PP Woven Bag Production Flow (9 Steps) PP Granules → Extrusion → Weaving → Lamination → Printing → Cut + Sew → QC + Bale → ✅ Bags 4–12 looms | 200K–4M bags/month | Extrusion: 220–260°C

Production Flow

PP Granules → Extruder → Flat Tapes → Circular Looms → Tubular Fabric → 
(Optional: Lamination) → Printing → Cutting → Sewing/Sealing → Finished Bags

Step-by-Step Process

Step 1: PP Tape Extrusion

Equipment: Tape extrusion line (extruder + water bath + orientation oven + winders)

  1. PP granules + additives (UV stabilizer, CaCO₃ filler, masterbatch) are fed into the extruder hopper
  2. Extruder melts the polymer at 220–260°C
  3. Molten PP is pushed through a flat die to form a thin film
  4. Film passes through a water cooling bath
  5. Cooled film is slit into narrow strips (2–3mm wide) by razor blades
  6. Strips pass through a hot air orientation oven (120–140°C) where they are stretched 5–7× their original length
  7. Stretching aligns the polymer chains, creating high-strength flat tapes
  8. Finished tapes are wound onto individual bobbins

Key parameters: Tape width (2–3mm), tape thickness (20–40 micron), tape denier (600–1200)

Step 2: Weaving on Circular Looms

Equipment: Circular looms (4-shuttle to 8-shuttle)

  1. Warp bobbins are loaded onto the creel (external frame around the loom)
  2. Weft bobbins are loaded inside the shuttle carriers
  3. The loom interlaces warp (vertical) and weft (horizontal) tapes in a plain weave pattern
  4. 4 to 8 shuttles orbit inside the shed, laying weft tape across the warp
  5. The reed beats each weft tape into position
  6. Result: a continuous tube of woven PP fabric

Key parameters: Mesh count (10×10 to 14×14 per 10cm), fabric width (40–120cm), loom speed (60–100 RPM)

Step 3: Fabric Rolling and Inspection

  1. Tubular fabric exits the loom and is flattened by guide rollers
  2. Fabric is wound onto a roll
  3. Visual inspection checks for weaving defects (broken tapes, holes, uneven density)
  4. Defective sections are marked for removal during cutting

Step 4: Lamination (Optional)

Equipment: Extrusion lamination machine

If moisture protection is needed:

  1. PP woven fabric roll is unwound and fed through the lamination machine
  2. A separate extruder melts PE (polyethylene) into a thin molten film
  3. The molten PE film is pressed onto the PP woven fabric surface
  4. Cooling rollers solidify the PE layer
  5. Result: PP woven fabric with a PE moisture barrier on one or both sides

Key parameters: PE coating weight (15–40 GSM), temperature (280–320°C), speed (50–100 m/min)

Step 5: Printing

Equipment: Flexographic printing machine (2–6 color)

  1. Laminated or plain fabric roll is fed into the printing press
  2. Ink is applied via anilox rollers and flexographic plates
  3. Each color is applied by a separate printing station
  4. UV or hot air drying cures the ink between colors
  5. Finished printed fabric is re-rolled

Key parameters: Number of colors (2–6), print registration accuracy (±1mm), ink type (solvent or water-based)

Step 6: Cutting

Equipment: Automatic cutting machine (hot knife or cold knife)

  1. Printed tubular fabric is fed into the cutting machine
  2. Measuring sensor determines bag length
  3. Hot knife (for sealed edge) or cold knife (for sewn edge) cuts the tube
  4. For valve bags: a valve is inserted during cutting or in a separate step
  5. Cut pieces are stacked for the sewing stage

Key parameters: Bag length (500–900mm), cutting speed (40–80 cuts/min), length accuracy (±2mm)

Step 7: Sewing / Sealing

Equipment: Industrial sewing machines or heat-sealing machines

For Open-Mouth Bags:

  1. One end of the cut tube is sewn closed using chain stitch or overlock stitch
  2. The other end remains open for cement filling
  3. After filling at the cement plant, the open end is sewn closed

For Valve Bags:

  1. Both ends are folded and sewn closed
  2. A valve is incorporated during folding for cement filling
  3. Valve allows filling without the need to sew after filling

Key parameters: Stitch count (5–8 per inch), thread tension, seam strength (>85% of fabric strength)

Step 8: Quality Control

  1. Dimensional check — Bag length, width within tolerance
  2. Drop test — Fill with 50kg, drop from 1.5m onto concrete
  3. Seam strength — Pull test on sewn/sealed seams
  4. Print quality — Color accuracy, registration, adhesion
  5. Visual inspection — No holes, tears, or contamination

Step 9: Baling and Packaging

  1. Finished bags are counted (typically 500–1000 per bale)
  2. Stacked and compressed into bales
  3. Bales wrapped with stretch film or PP fabric
  4. Labeled with bag count, specifications, batch number
  5. Stored or shipped to cement factories

Complete Equipment List

EquipmentQuantityPurposePrice Range
Tape extrusion line1Produces PP tapes$30,000–$80,000
Circular looms4–12Weave tubular fabric$12,000–$40,000 each
Lamination machine0–1Apply PE coating$20,000–$60,000
Flexo printer0–1Print designs$15,000–$50,000
Cutting machine1Cut to bag length$5,000–$15,000
Sewing machines2–5Close bag ends$1,000–$5,000 each
Auto sewing line0–1Automated sewing$8,000–$25,000
Baling press1Package finished bags$3,000–$10,000

Production Capacity Planning

ConfigurationLoomsMonthly OutputTotal Investment
Small4200K–300K bags$80K–$120K
Medium8500K–800K bags$180K–$280K
Large121M–1.5M bags$300K–$500K
XL20+2M–4M bags$500K–$1M

Frequently Asked Questions

How long does it take to learn PP woven bag production? Basic operation: 2–4 weeks of training. Competent independent operation: 2–3 months. Expert level (troubleshooting, optimization): 6–12 months.

What is the bottleneck in PP woven bag production? Usually the circular looms. Each loom produces limited fabric, and you need many to match cutting/sewing capacity. Plan loom count carefully based on target output.

Can the same line produce different bag sizes? Yes. Cutting machines easily adjust bag length. Different widths require different loom settings or different fabric rolls, which takes 1–2 hours to change.

Learn more about circular looms in our Circular Loom Guide or compare PP vs Paper bags in the Production Line Guide.