Open Mouth Bag Filling Machine —Net Weight & Automatic Systems

Automatic Net Weight bagging machine

The most-requested system in our open mouth range. Load cells under the fill spout weigh every bag individually — coarse fill at full rate to ~85% of target, then fine fill to set-point, then cut-off. Bag tare is measured per bag, so PP woven bag weight variation of ±10–15 g does not affect net fill accuracy.

Where this system consistently pays for itself is on products with variable bulk density — fertilizers, natural minerals, recycled materials, agricultural products where raw material batches are inherently inconsistent. Volumetric systems on these products require operator recalibration every 1–2 hours. Net weight systems run an entire shift without adjustment. At 300 bags/hr and $1.20/bag product value, a 1% reduction in overfill is worth over $200,000 per year.

• Bag weight:5 kg – 50 kg
• Speed:5–14 bags/min (product-dependent)
• Accuracy:±0.3–0.8% at production scale
• Bag types:PP woven, kraft paper, PE, laminated
• Sealing:Stitcher or heat seal integration

Semi-Automatic

Operator places the bag on the fill spout, triggers the fill cycle via foot pedal or push-button, and removes the filled bag. Fill principle is gravity or auger — no load cell. Best for production volumes under 3 bags per minute where capital cost and simplicity matter more than per-bag accuracy. Not appropriate for regulated products where fill weight records are required.

• Bag weight:5 kg – 50 kg
• Speed:2–5 bags/min (operator)
• Accuracy:±1–3%
• Price range:$4,000–$10,000

Dual Spout Automatic

Two fill heads operating simultaneously, each with its own load cell, to approximately double throughput vs single-spout. Best for 25 kg bags where a single-spout system is the line bottleneck. The two load cells are independently calibrated — one spout can be taken offline for maintenance while the other continues production at half capacity.

• Bag weight:10 kg – 50 kg
• Speed:8–18 bags/min
• Accuracy:±0.3–0.8%
• Maintenance:Each spout independently serviceable

With Automatic Bag Placer

Bag magazine, vacuum pick-and-place bag presenter, and fill system integrated. Eliminates the manual bag placement step. PP woven bags and kraft bags require different bag presenter configurations — PP woven needs vacuum cups with slick-surface separation; kraft bags use edge-grip mechanisms. We ask for a sample bag before finalising the presenter design.

• Bag weight:10 kg – 50 kg
• Speed:8–15 bags/min
• Magazine capacity:200–400 bags
• Bag separation:Vacuum (PP) or edge-grip (paper)

With Inline Stitcher

Integrated bag-top folder folds the open bag mouth into a tight closure, and an industrial bag stitcher sews it closed as the bag moves on the discharge conveyor. Standard for PP woven sacks in fertilizer, chemical, and mineral product markets. Stitch thread specification (PP or jute) affects end-market acceptability — some markets require jute-stitched seams for regulatory or recycling reasons.

• Closure type:Industrial bag stitcher (chain stitch)
• Thread options:PP or jute
• Bag mouth width:300–700 mm configurable
• Integration:Conveyor-mounted, adjustable height

FFS / Form-Fill-Seal

Forms bags from roll-stock film, fills and seals in-line. Suited for smaller bags (1–10 kg) where bag cost per unit matters. Not technically an open-mouth bag filler, but buyers comparing formats should know: FFS gives lower bag cost at volume but higher machine cost, more complex maintenance, and narrower bag material flexibility than a pre-made bag open-mouth system.

• Pack weight:200 g – 10 kg
• Speed:20–80 bags/min
• Film:PE, laminate, kraft-PE
• Best for:Retail packs, small industrial packs

Bag is placed (manually or automatically) over the fill spout. Pneumatic bag clamps grip the bag mouth against the spout to prevent spillage and ensure dust containment during filling. The clamp force is calibrated to the bag material — too tight tears PP woven bags at the clamp point.

Load cell reads bag tare weight with bag clamped. Coarse fill gate opens — product flows at full rate until ~85% of net weight target is reached. The coarse/fine switchpoint is programmable; moving it earlier improves accuracy but slows cycle time. Most products run 80–90% coarse.

Flow rate reduces to 10–20% of coarse speed. Load cell monitors continuously. Programmable in-flight correction factor accounts for product between cut-off valve and bag. Final weight is logged — data is available for SPC or batch traceability.

Bag clamp releases. Bag passes to a discharge conveyor with a vibration or flattening station to reduce headspace (particularly important for animal feed and light powders that need settling before sealing). Bag top is folded and stitched or heat-sealed.

25 kg and 50 kg PP woven sacks are the dominant format for fertilizer markets globally. Bulk density varies significantly between NPK grades and between production batches — net weight filling is standard. Corrosion-resistant coatings on product contact surfaces are specified for ammonium nitrate and acidic formulations.

Pellets, meal, and mash in 10–50 kg bags. Variable product bulk density (expanded pellets vs dense meal) makes net weight filling the correct choice. De-aeration after filling is critical for pellets with high void ratio — bags that are not settled before sealing collapse on the pallet. See our dedicated animal feed bagging machine page for full specs.

Industrial minerals, pigments, calcium carbonate, kaolin, silica — 25 kg kraft paper or PP woven sacks. ATEX classification applies for combustible dusts. Dust containment at the fill spout is standard. Full containment (enclosed fill station) is available for materials with low OEL ratings.

304 stainless contact parts, CIP-compatible fill spout, food-safe bag clamp materials. 5 kg and 10 kg bags typical for food service and retail; 25 kg for food manufacturing input. For hygroscopic products (salt, some starches), filling in a humidity-controlled environment reduces caking in the bag during storage.

Tile adhesive, dry mix mortar, gypsum plaster — 20–25 kg bags. Products are abrasive and wear fill spout liners at 3–5× the rate of soft products. Hardened steel or ceramic-lined contact parts are specified as standard for construction material applications. Wear part replacement intervals are included in the maintenance schedule.

Free-flowing pellets are among the easiest products to fill accurately — low cohesion, consistent bulk density. The main challenge is electrostatic charge buildup on the bag during filling, which interferes with bag clamp release. Anti-static bag clamp materials and earthing points on the fill spout are standard for plastic pellet applications.

We ask for a physical bag sample before finalising the bag presenter and clamp specification. PP woven bags vary considerably in surface coating, mouth stiffness, and opening behaviour between manufacturers. A bag presenter designed for bags from Manufacturer A may misfeed consistently with bags from Manufacturer B. Getting this right at specification stage takes two weeks; fixing it after delivery takes two months.

We quote filler, discharge conveyor, bag top folder, and stitcher or heat sealer as a system. Buyers who price these components separately from different suppliers routinely find that interface dimensions do not match, conveyance speeds are mismatched, and the sealer is spec’d for the wrong bag top thickness. Integration problems after delivery are expensive to fix and slow to resolve.

Every automatic net weight system logs fill weight per bag with timestamp and can export CSV data for batch traceability or statistical process control. For regulated industries (pharma, agrochemicals, food) this data is a compliance requirement. For all buyers it gives early warning of fill accuracy drift before bags go out of spec — you see it in the data trend before it becomes a customer complaint.

CE marking on open mouth bag fillers requires a machine risk assessment covering the fill spout (nip points, dust exposure), the bag presenter (trap points), and the integrated conveyor and sealer. We provide the full technical file — not just the Declaration of Conformity. Buyers who have had CE challenge at customs or from H&S auditors understand why the technical file matters beyond the label on the machine.

Complete bagging systems for powders, granules, and free-flowing materials with high-speed automation.

Specialised open-mouth bag fillers for pellets, meal, and mixed feed with de-aeration for stable bag form.

Standalone gravimetric packing scales. Same net weight fill principle as our automatic open-mouth systems.

Turnkey lines integrating open-mouth bag filling, sealing, checkweighing, and palletising.