Feed Operations: It's in the bag
February 22, 2017
Bühler’s new Bagging Station Maia for fully automated packing in bags with a filling volume of 20 to 65 liters.
Photo courtesy of Bühler.
Something often not completely thought about is how you handle the feed product after it is made. This step is just as important as any other to maintain finished feed quality. This is the first of two articles on the subject.
Several things to be considered include the proper storage temperature of the product and any changes that might occur if the product is stored in bulk or sacks. Additionally, we must be careful to design the product handling system(s) to avoid damage as it is moved into and out of storage for final packaging and shipment.
The following issues will be addressed in these articles: avoiding or minimizing cross contamination of product; maintaining product quality in storage; shipment in bulk form; shipment of product in bagged form; bagging systems; warehouse design; and bagged feed loading onto trucks. It is critical to have the finished product temperature as close to the ambient temperature in areas where it is to be held or stored. The acceptable temperature limits for product storage should not exceed +/- 10 degrees F of the ambient temperature in the bin or building.
Warm or moist product stored in bins with cold walls will tend to cool around the edge and the moisture will begin condensing into water at the contact between the warm product and cold bin surface. This leads to product spoilage and often causes a build-up of product that sticks to the walls and hopper of the bin. If warm and/or moist product must be stored in a bin with cold walls, a time limit should be set on how long the product can remain in the bin before the feed quality is affected, and the bin should be emptied within that time limit. This requires controlling the feed production schedule so the finished product can be handled and packaged or shipped before spoilage begins.
Bulk Feed Shipment
For bulk truck shipments, finished feed bins of multiple sizes often are used with the largest bins for high volume product shipments usually filling multiple truckloads of the same product. Smaller bins are used for small lot shipments or for trucks that have compartments into which multiple products may be carried on the same truck. Care must also be taken that bins used for medicated feed products be separate from those used for non-medicated feeds to avoid cross contamination. Avoiding medicated vs. non-medicated feeds sometimes requires separate handling systems from the mixer to the loadout point. The hoppers on these bins should be designed to permit mass flow of the materials so the product is uniform when discharged from the bin.
Feed sold in bulk form requires weighing of the empty truck or individual truck compartments before filling and the final weight of product in each compartment or the whole truck. The weight put into each compartment may be predetermined using an overhead weigh lorry system, or the truck rests on a scale deck while parked under the bulk feed loading area.
Bagged Feed Shipment
Bühler’s single spout bag packer mwpf.
Photo courtesy of Bühler.
Bagging systems begin with short-term storage bins above the packing lines. These bins should also be designed for mass product flow. If only one type of product is made, a single bin above the packing system may be adequate. If multiple products and/or medicated and non-medicated product is to be bagged, the system should have two or more bins above the packing system.
Bagged feed shipments may be made in several size bags, depending on the product being placed in the bag and its density. The bag itself may be made of paper, polyvinyl, or other materials appropriate for keeping the product in the best condition. Open top bags generally are used in the feed industry, but in some cases a valve-filled bag may be used.
The bags must be sized to be filled completely when sealed to form a uniform shape that allows them to be stacked on top of each other. This means that when the bag is sealed it will be full. The diameter of the open top bag must be sized to fit the spout on the packer. The length of the bag will depend on the density of the product being bagged. As an example, if you want to place 50 pounds of product in the bag with a product density of 40 pounds per cubic foot, a volume of 1.25 cubic feet is needed. If the product has a density of 60 pounds per cubic foot, the bag volume needed would only be 0.83 cubic foot. If the bag opening is the same for both bags, a longer bag would be required to hold the 40-pound product than the bag to hold the 60-pound product. This means that the packing system must be height adjustable between the packer outlet and the conveyor below it. If different size open top bags are used, it may be necessary to change filler spouts
Filling the bags may be done in several ways, from completely manual to completely automatic. Either way, some type of scale must be used to fill the bag to the proper weight. For a manual system it might be as simple as the empty bag sitting on a platform being filled with a hand scoop to the correct weight.
The most common way of filling bags is a scale that weighs out the correct amount of product in the bag or prior to it entering the bag. The first type is a simple gross weight scale on which the filler spout is attached to the packer’s scale. The bag is placed on the filler spout and the product is weighed as it falls into the bag. In this case, the bag is the scale container itself. This type of packer usually allows 5 to 8 bags filled per minute. It requires a person to hang each bag before it is filled.
For higher capacities, the packer has one or more separate scale hoppers that weigh the product prior to dropping it into the empty bag. It is known as a net weight packer. This type of packer may have one (simplex), 2 (duplex) or 3 (tri-plex) scales built in that fill and dump in sequence. Capacities for these packers may be as many as 20 bags per minute or more.
No matter which type of packer is used, the correct type of feeder must be installed above the packer to control the type of product being fed into the packing scale. These include gravity for free-flowing grains, and vibratory for handling granular materials such as minerals or flakes. The third type of feeder is a belt feeder used for semi-free flowing materials such as textured feeds, cubes and similar types of product. The last type of feeder is a single or double screw conveyor used for handling fluid types of materials, including flour, whey and finely ground products.
From the packer, the filled bag drops on to a belt conveyor and moves to the bag closure or sealer. This may be as simple as a worker pulling the top into a straight line that is manually fed into a sewing machine. The sewing machine system also may feed a top tape that covers the top open edges of the bag. If a more positive seal is needed, the bags may have glue on the top edges, which is sealed by passing the open top bag into heated bars that heat the glue and seals the bag top as it passes through the sealing machine.
The filling and sealing may be done manually and would need two to three persons to operate the equipment.
Completely automated packing and sealing systems are also available. These systems grab a single bag from a bag magazine, open it, hang it on the packer spout for filling, and move the filled bag to the sealing system where the bag is sewn or sealed shut. These automatic bagging systems require one person to keep new bags in the bag magazine.
In my next article, I will cover handling the filled bags, pallets, robotics and warehouse design.
Fred Fairchild is feed science professor emeritus in the Department of Grain Science at Kansas State University. Prior to coming to Kansas State in 1994, he worked in the industry designing, constructing and commissioning numerous mill facilities. He is a licensed professional engineer. He may be reached by e-mail at email@example.com.