What Is a Bag Sewing Machine?
A bag sewing machine is industrial equipment that stitches closed the open ends of cement bags after they have been cut to size or filled with product. Sewing machines are essential in PP woven bag production lines and are also used for closing filled bags at cement plants.
There are two distinct applications:
- Bag Making — Sewing the bottom of empty bags during production
- Bag Closing — Sewing the top of filled bags at filling stations
Both require heavy-duty industrial sewing machines designed for thick PP woven fabric, paper, or multi-layer materials.
Two Applications of Bag Sewing
Types of Bag Sewing Machines
By Application
| Type | Use | Speed | Price Range |
|---|---|---|---|
| Bottom Sewing | Closes bag bottom during manufacturing | 15–40 bags/min | $3,000–$15,000 |
| Top Closing | Closes filled bags at packing station | 300–800 bags/hr | $500–$8,000 |
| Valve Sewing | Creates valve openings in woven bags | 25–40 bags/min | $15,000–$65,000 |
By Automation Level
- Manual/Portable — Hand-held or table-mounted, operator guides bag ($500–$2,000)
- Semi-Automatic — Auto thread, manual feed ($2,000–$8,000)
- Fully Automatic — Auto feed, sew, trim, stack ($5,000–$15,000)
- Inline Closing System — Integrated into filling line, fully automated ($10,000–$35,000)
By Stitch Type
- Single Thread Chain Stitch — Most common for bag closing, easy to open
- Double Thread Chain Stitch — Stronger closure, commonly used for bag bottoms
- Overlock Stitch — Edge-finishing stitch, prevents fraying
- Double Needle — Two parallel rows for extra strength
Key Specifications
- Stitch Speed — 600–2000 stitches per minute
- Thread Type — PP multifilament, polyester, or cotton thread
- Needle Size — DN×1 #25 or #27 for cement bags (heavy-duty)
- Stitch Length — 7–12mm adjustable
- Material Thickness — Up to 6–10 layers of PP woven fabric
- Bag Width Range — 300–700mm
- Closing Speed — 300–800 bags per hour (inline closing)
- Power — 0.5–3 kW
Machines Compared
Industrial Cement Bag Sewing Machine (CBS-200)
- Type: Semi-automatic bottom sewing
- Speed: 15–30 bags/min
- Features: Portable, heavy-duty needle, adjustable stitch
- Price: $2,000–$8,000
- Best for: Small factories, manual operations
FOR DAH ADHC Valve Forming & Sewing Machine
- Type: Auto valve forming + double-head sewing
- Speed: 25–40 bags/min
- Features: Automatic valve forming, double-head sewing, PP woven
- Price: $35,000–$65,000
- Origin: Taiwan
- Best for: PP woven valve bag production, medium factories
Manual PP Bag Closing System (MBC-50)
- Type: Manual hand-operated bag closer
- Speed: 5–15 bags/min
- Features: Hand operated, portable, battery option available
- Price: $500–$2,000
- Best for: Micro factories, field operations, emergency backup
Inline Auto-Closing System
- Type: Fully automatic belt-driven closing
- Speed: 400–800 bags/hr
- Features: Conveyor integration, auto-trim, fold-and-sew
- Price: $10,000–$35,000
- Best for: Cement plants with high-volume filling lines
Pricing Guide
| Category | Price Range (USD) | Application |
|---|---|---|
| Manual/Portable Closer | $500–$2,000 | Filled bag closing |
| Semi-Auto Sewing Machine | $2,000–$8,000 | Bag bottom sewing |
| Auto Bottom Sewing | $5,000–$15,000 | Production line |
| Valve Sewing System | $15,000–$65,000 | Valve bag production |
| Inline Closing System | $10,000–$35,000 | Cement plant filling line |
Consumables Cost
- Needles: $0.50–$2.00 each, replaced daily to weekly
- Thread: $2.00–$5.00 per cone (1 cone ≈ 500–1000 bags)
- Thread cost per bag: $0.003–$0.010
Bag Closing Methods Compared
Different cement packaging methods use different closing techniques:
| Method | Bag Type | Closure | Speed | Dust |
|---|---|---|---|---|
| Sewing | PP woven open-mouth | Thread stitch | Moderate | Higher |
| Heat Sealing | PE/FFS bags | Heat weld | Fast | None |
| Glue Sealing | Paper valve sacks | Adhesive | Fast | Low |
| Valve Filling | Paper/PP valve bags | Self-closing valve | Fast | Very Low |
How to Choose
For Bag Manufacturing (Bottom Sewing)
- Volume under 200,000 bags/month → Semi-auto sewing machine ($2K–$8K)
- Volume 200,000–1,000,000/month → Fully automatic bottom sewing ($5K–$15K)
- Valve bags → Specialized valve sewing system ($15K–$65K)
For Cement Plant (Bag Closing)
- Under 100 bags/hour → Manual/portable closer ($500–$2,000)
- 100–400 bags/hour → Semi-auto belt closer ($3K–$10K)
- 400+ bags/hour → Inline auto-closing system ($10K–$35K)
Thread Selection
- PP multifilament — Most common for PP woven bags, good strength, low cost
- Polyester — Higher strength, better UV resistance, slightly more expensive
- Cotton — Used for paper/jute bags, biodegradable
Maintenance Tips
- Every Shift: Check needle condition, thread tension, oil level
- Daily: Replace bent/dull needles, clean thread path, check bobbin
- Weekly: Lubricate all moving parts, inspect feed mechanism, check belt tension
- Monthly: Full cleaning, replace wear plates, inspect motor
Frequently Asked Questions
How often should I replace sewing needles? For heavy-duty cement bag sewing, needles should be replaced every 8–24 hours of continuous use. Dull needles cause skipped stitches, broken thread, and bag failures.
What thread tension is correct for cement bags? Thread tension should be adjusted so that the stitch knot locks inside the fabric layers, not on the surface. Too tight causes puckering; too loose causes loose stitches. Most machines have numbered tension settings (3–7 for cement bags).
Can sewing machines handle laminated PP bags? Yes, but use a sharper needle (round-point for standard woven, cutting-point for laminated). Lamination can make the fabric stiffer, requiring slightly adjusted tension and stitch length.
What is the difference between bag sewing and bag closing? Bag sewing creates the bag during manufacturing (sewing the bottom seam of an empty bag). Bag closing seals a filled bag at the cement plant (sewing the top after filling). Different machines and speeds are involved.
Explore the complete bag production line in our PP Woven Bag Machine Guide or browse the machine directory.