When a plant manager is tasked with selecting the right equipment to handle his packaging process there are three main areas to take into consideration. First, what style of package is right for your product? Second, what characteristics does your product have? Finally, what performance criteria is required of your process?
Containers can be narrowed to two distinct categories: Form and Fill or Pre-formed. Form and fill containers use packaging equipment to form the container and fills the bag with the correct amount of product almost simultaneously. Form and fill can be completed in both vertical and horizontal equipment configurations and typically handles consumer packaged goods. Preformed containers use packaging equipment that fills the correct amount of product into a pre-made container. These options include Valve Bags, Open Mouth, Box, Pail, Drum, or IBC’s (intermediate bulk containers).
Valve bags, can have an internal or external sleeve. Internal sleeves have a thin polyethylene sleeve and is forced closed by product once filled, usually by dropping the bag onto it’s spine. External sleeves are designed to be folded manually or sealed by a mechanical device (see TRUseal). Valve bags can be made of various materials; multi-wall kraft paper, polyethylene, polypropylene, and blended laminates like poly-foil.
Open Mouth Bags can be another option for preformed containers. Filling can be accomplished by a variety of feed techniques including; augers, vibratory feeders, belt feeders, or gravity. These containers are generally closed by either sealing with a form of heat or sewn. One form of sealing involves a pre-applied adhesive which is activated by heat from an external sealer. Open mouth bags can be gusseted or non-gusseted. Gussets vary from 3” to 6” wide. Non-gusseted bags are often referred to as “pillow style”. Open mouth bags can come in many materials ranging from kraft paper to kraft paper with a ply liner to polypropylene and poly woven varieties.
IBC Containers or Intermediate Bulk Containers, come in 3 main variations; Bulk Bag (flexible), Pro Box, or a Gaylord Box. Typical weight ranges for IBC containers are 1000 to 4000 lb capacities dependent on material bulk density.
Other Containers
Other preformed containers are small boxes, pails, & drums...
Your product determines the metering or feeding technique ideal for your process. There are four main material metering devices that will be utilized in bagging equipment; gravity, augers/screws, vibratory trays and belt feeders.
A gravity bagging machine works well with rock salt, rice, soybeans, PVC resin, starch, pelleted feed and performs just as the name suggests. When handling products such as dry biscuit mix, ground coffee, TiO2, patato flakes, apple fiber, brown sugar, dry clay or calcium carbonate then you probably need auger/screw type fillers. For products with a lot of size variation like cheese shreds, waxy chemicals, frozen shrimp, coal, resin flakes, sweet feeds, cereals, trail mix, mussels, and dog biscuits a belt or vibratory tray will handle them best. The reason for determining the best metering device is the scale and program need consistency in order to deliver repeatable results.
Feed rate and accuracy are interdependent of each other. If accuracy is your main concern, you may have to sacrifice a little speed to hold tolerance. If speed of fill is a priority, you may sacrifice some accuracy.
Weighing scales for your product fall into two categories: gross-weigh or net-weigh.
Capturing the net weight of a dry material during the bagging process is done by filling a “bucket” or “buckets” inside the packaging equipment until the desired weight is met. The scale controls are only concerned with the weight of material metered or fed into the “bucket”. Net-weigh feeding allows for faster bagging rates, typically an increase of 1-2 bags per minute by feeding the product into the bucket for weighment while the next container is being placed into position.
Capturing the gross weight of a dry material during the bagging process is done by zeroing out the weight of equipment and bag being placed on the discharge spout in programming, then feeding or metering product directly into the bag. Gross-weigh feeding is typically slower than net-weigh feeding because you cannot start the feed process until the existing container has been removed and a new container is in place.
Selecting the right container for your product will help determine the initial design of the equipment and downstream accessories of your system such as palletizing. The flow characteristics of your product will determine the best metering or feeding technique to move your product from infeed to container. The performance criteria you choose for your production will help decide the type of filling operation required. Remembering these three basic decision parameters will be crucial to purchasing the right and most reliable system for your production line.
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