SPECIAL SECTIONS: Filter Media Valves Advertising closes October 3

14 SEPTEMBER 2008 | PBEI
There are two classes of FFS machines: gross-weight and
net-weight. In gross-weight systems, the bag is weighed on a
live scale as it’s filled. In net-weight systems, the material
passes through a weigh-hopper before entering the bag.
Gross-weight machines are more compact than net-weight
machines. They also handle products more gently and are
commonly used to bag high-value materials, such as engineered
resins, where capacity is low and a vapor barrier is required.
Gross-weight machines are also well suited for
applications that require frequent product changes and thus
frequent cleaning. Outputs of FFS machines are 100 to 1,800
bags per hour.
FFS options. One option is to affix nozzles to the bagging
machine to clean material contact areas automatically. Another
option is an air evacuation system that removes air from the bag
and shrinks the gaps between particles. There is also a gussetfolding
device on the market that enables you to transform flat,
tubular film into gusseted film. See Figure 4. The advantage:
Rolls can hold double the amount of tube-stock compared with
gusseted film. Finally, an optional embossing device reduces the
tendency of bags to slip around on the pallet.
1. Storage silos
2. Mobile batch weigher
3. Mobile semi-bulk filler
4. Mobile FFS bagging machine
5. Mobile belt conveyors
6. Palletizer
7. Stretch-hood machine
8. Multiple-level warehouse
9. Outside storage
9. Outside storage
Figure 5
Logistics terminal
Layout of the packaging operation
In general, FFS bagging lines (including palletizing and
loading operations) operate at 65 to 75 percent of the design
capacity of the FFS machines. In operations that handle a single
material, the FFS machine is stationary and material enters
the packaging line directly from a nearby silo. Operations that
package a large percentage of product in FIBCs or do a lot of
bulk load-out to trucks, will usually select stationary bagging
equipment. That is because FFS quantities are smaller and it is
more practical to bring the product to the bagging machine
instead of moving the bagging machine.
Logistics terminals, however, handle many materials, and
flexibility is key. Thus, they are better served by mobile FFS
machines. See Figure 5. Instead of transporting the material to
the FFS machine from a silo, workers move the FFS machines
to the storage silos. In this way, the product in each silo is
bagged, loaded into silo trucks, or placed in FIBCs on demand—without
the complication of long-range scheduling.
The two drawbacks to mobile FFS machines are higher labor
costs and higher equipment costs compared with stationary
machines. The higher equipment cost doesn’t fall only on the