Filling and Closing
Equipment For Filling And Closing
Much of the equipment used to move powdered, flaked or
granular products within a manufacturing process can be adopted or
modified to the sack packing process.
For granular products, the gravity feed method is
frequently used. Other general methods used to accommodate specific
products are fluidized bed, vibration feed, auger, air pressure,
impeller, belt and vacuum. The basic handling characteristics of the
product will determine the method of packing the product as well as
the type of sack to use for the specific product. For example,
granular or pelletized products flow easily when packed and can offer
an opportunity to select either an open mouth or valve-type shipping
sack. In contrast, powdery or dusty products will tend to complicate
the packing process by requiring special equipment and limiting the
type of sack to be used.
To further complicate the selection of packing
equipment and sack type, there are hygroscopic products which require
greater protection from outside moisture as well as other products
which emit odors that may require a special odor barrier in the
package construction and a secure heat seal.
Such special product considerations can be very
important in deciding the packing equipment and type of shipping sack
to be used. When evaluating a new packing system or a different type
of sack, the technical department of the equipment manufacturer and/or
the shipping sack manufacturer can offer immeasurable help, based on
many years of cumulative experience with similar products and packing
solutions for those products.
Open Mouth Sack Packers
For smaller or more basic packing operations to
accommodate a free-flowing product, a gross weight open mouth bagger
directly under a control hopper would normally be considered. An
operator manually places a sack on a conveyor and the weighting unit
fills and trims the weight of the package. Once filled, the operator
releases the sack onto a sewing conveyor, transferring the filled
package into the sewing head for closing.
|After, filling, sacks are automatically sealed.
From the end of the conveyor, the filled sack can
then be inspected and palletized. Generally, this procedure outlines a
basic system to accommodate nominal open mouth sack production.
To upgrade this basic system, it would be possible to
use a pinch style sack that when filled, would feed into a pinch
closing unit. The pinch style sack system greatly simplifies the sack
closing operation because of the closing process itself. Where a
sewing machine requires operator knowledge as well as frequent
maintenance and adjusting, the pinch closing process is simpler and
requires less maintenance. The simplicity of reactivating a
pre-applied hot melt adhesive with hot air is a plus in any open mouth
To further upgrade the open mouth sack packing
operation, newer automatic weight scales can quickly weigh
free-flowing products and "dump" a pre-weighed charge into a sack with
remarkable weight accuracy. These high-speed weight scales can
increase the rate of a packing operation considerably if the
characteristics of the product lend themselves to the speed and
accuracy of this equipment.
|The pinch style sack provides a sift-resistant closure.
There is also some high technology equipment
available for open mouth packing which employs robotics – selecting a
sack, opening it for an automatic scale discharge, then releasing the
sack for closing. Justifying this equipment would require very large
volumes of product packing.
When considering any type of packing system – basic or
more automated – the sack manufacturer should be consulted early in
the decision-making process to avoid common errors.
Valve Sack Packers
All valve sacks are filled by passing the
product into the package through filling tubes which vary in design
according to the density and flow characteristics of the product. Again,
as in open mouth sack packing, there are numerous ways in which to
pack valve sacks: auger, belt, pressure, impeller, vacuum or fluidized
bed. Flakes, pellets, crumbs or fine powders – products which may
have been very difficult to handle – can be accommodated with very
limited weight variation by selecting the proper type of valve packer.
|An open mouth filling line.
The valve packer can be set to gross weigh a product
or have a net weight scale above the packing unit which drops a
pre-weighed charge into the unit.
Both types of units are common and are able to hold
close weight tolerances. The units can be installed as a basic single
unit or in banks of multiple units. While a tuck-in sleeve valve sack
is popular for the basic type of packers, the automatic sleeve is used
in the corner of a sack when high-speed packing is required. For this
type of sleeve to function correctly, the product in the sack – as it
approaches the top of the package – forces the sleeve closed.
Accordingly, it is critical that the sack be sized properly since a
shipping sack packed too loosely can sift the product. Again, properly
sizing the sack to account for extremes in product density is a job
for the sack manufacturer's technical department. Robotics can also be
utilized to some extent in packing valve sacks.
Robots with vacuum cup arms can index sacks, feed them
onto a packer, transfer the sack off the packing unit once filled and
even palletize the filled sack to programmed stacking patterns.
|A valve sack filling tube.
The valve-style sack lends itself to size adjustments
in order to fit an interlocking or "brick wall" pattern on a shipping
pallet (explained in detail in Chapter 9). Once again, a sack
manufacturer's technical department can provide valuable assistance in
developing pallet stacking methods which best fit in a trailer or
rail car to ensure the most economical shipping load.
Technology is keeping pace with demands for greater
packing speeds, more accurate weights and more efficient warehouse
handling of products. Accessories such as vibration settlers, sack
flatteners, radiant and ultrasonic sealers and the increasing use of
robotics are playing a vital role in providing the neat and clean
interlocked pallet loads now coming from the valve sack packing
|A sewn sack after filling and closing.
The Importance of Humidity
Paper shipping sacks are best packed and closed
when the moisture content of the paper is between 5 and 8 percent. To
maintain a level of moisture content, empty sacks should be stored in a
fairly humid atmosphere. Optimal conditions are a temperature of 70
degrees (F.) and a 50-to-60 percent relative humidity level. Under
these conditions, sacks will contain about six percent moisture and be
flexible and strong.
As the moisture content of paper drops below four
percent, paper tends to become progressively brittle. When brittleness
occurs, bales or pallets should be opened and the sacks spread out in
a humidified room (or on a loading platform in humid weather) for 24
hours to permit the sacks to absorb the moisture needed to restore
their strength and flexibility. Keep in mind that moisture recovery of
sacks containing a barrier ply will be slower than with sacks of an
all-kraft ply construction.