The bulk bag filling process should yield a stable, dense package for storage, transport and discharge. It should minimizing operational and labor costs.
Maximizing the bag fill rate, measured in bags per hour, contributes to safety, productivity and efficiency throughout the process. The exact fill rate depends on individual applications, which are impacted by many factors including the material characteristics, infeed source, and plant environment. Typical fill rates range from 10 bags per hour to as high as 40 or more bags per hour.
High quality bulk bag fillers will adjust for different bag types and sizes, as well as a wide variety of dry bulk products. Optimizing bags per hour involves a number of considerations throughout the filling operation, along with equipment and issues like air displacement, bag stability, and densification strategies, and others.
Steps in Bag Fill Process
A seamless process allows for greater consistency and a higher bag fill rate. The filling application typically includes three steps: rigging (hanging and spouting) the bag, filling the bag, and removing the filled bag from the filler.
Rigging & Filling the Bag
For proper filling, the bag corners should be suspended off of the pallet by 3” – 4” to allow the bag side-walls to stretch properly – not doing this will result in bags that are less stable and/or lean once filled. The bag spout is positioned over the fill head to create a tight, dust-free seal. Next, the bag/liner may be inflated with air. Typically, bags are gross weighed (valve or conveyor is actuated in bulk, then dribble flow, then stops at target weight). Another approach is pre-weighed systems in which a product charge drops into the rigged bag, and the next bag’s charge enters the hopper as the previous one drops. For best results the product is densified and compacted in order to form a stable package suitable for safe and efficient stacking. This will also help in filling the corners and top with material for a better net yield and less operator input.
Removal after filling
Fast, consistent bag removal is essential for an optimal fill rate. An automated roller or chain conveyor quickly removes the filled bag to make way for the next empty bag. Pallet and slip sheet dispensers speed up the process in that the operator doesn’t have to add these items manually.
FIBC Filling Equipment
Fillers that operate in automatic or semi-automatic modes help to minimize required handling and facilitate a higher rill rate. Operators should match all filling equipment and bags to product characteristics such as solids that clump or particulates that become suspended in the air. Fill rates can be adjusted for safety and efficiency, from a slow dribble to a steady river. Each bag should be filled to a precise, predetermined weight.
A multi-filler system can be assembled when much higher fill rates are required. Customers must always consider the desired production rate for each application versus the cost of an extra filler.
Upstream components may convey the product to a surge hopper where a metering device (slide gate valve, rotary valve, butterfly, or even screw feeder) is used to start and stop flow to complete the desired weighment. A conveyor can also be used as the metering device, starting and stopping to achieve target weight, however this can cause undue wear to the conveyor, and will deliver a slower overall speed as the conveyor ramps up/down. The surge hopper helps deliver a consistent volume helps to achieve the desired filling speed, and also impacts efficiency, accuracy and capacity.
Weighing the Product into the Bag
Most fillers work with load-cell based scales, but support frames for the bag can be set on a platform scale as well. It is important that the bag, pallet, and support frame all be on the scale, parts on and off the scale in Gross-Weigh applications will lead to inaccurate and inconsistent weighments.
Automated vs. Manual Bag Removal
One of the biggest factors in high-speed packaging is the manner in which the full bags are removed from the filling system. Manual systems require a forklift or pallet jack operator to engage the pallet, lift and remove the bag. Automated systems with full bag eject and accumulation along roller or mesh conveyors allow the operator to complete the process more efficiently.
Fill Rate and Air Displacement
According to the scientific principle of displacement, product entering the bag displaces the air that was inside the bag. That air, of course needs somewhere to go. Bag fillers must accommodate this with a displaced air exhaust feature. As the product enters the bag, the fill head allows exhaust to escape in order to control dust and avoid air locking (no flow) of material. This ensures a steady fill rate as the material passes through the fill head.
Densification, Fill Rate, and Bag Stability
Stability of a filled bulk bag reduces the risk of the bag tipping over and other hazards which could lead to workers’ compensation claims or OSHA fines. Because a high fill rate can in some circumstances increase instability, steps must be taken to mitigate this problem. A densification device enables the product to settle so that the bag will be stable and safe for stacking and handling. Densification can be accomplished via high frequency vibration (single orbital/horizontal unit, dual co-rotating up/down arrangements, or by low frequency thumping of the bag (or jerking the bag via the straps on a drop-table design).
Properly and efficiently filled bags can boost productivity and cut down on unnecessary operating costs. Quality bulk bag filling equipment, combined with proper operating techniques, help to maximize bags per hour.
If you need information on advanced bag filling equipment, contact us at FormPak. We have the knowledge and experience to answer your questions and built customized systems to meet your needs.