World Grain - January 2017 - 86

FEATURE: OPEN-MOUTH OR VALVE BAGS?

Open-mouth bags are closed along
the lengthwise side and on the bag
bottom. They may be made of paper
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may be sealed by welding, sewing or
gluing so nothing trickles out.
A wide variety of bag types may be
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shape of a block due to the inserted
side fold, which makes them easy to
stack. The cross-bottom bags are particularly easy to stand alone or stack
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They are also effective for advertising
because print may be used on the bottom and sides of the bag. Laminated
bags of woven polypropylene also
may be printed in good quality and are
available as a pinch bag.
Valve bags have been used for bagging milling products since the mid1920s. Even then they were more expensive than open-mouth bags. There
was a perception that they could not
be sealed well and that a lot of dust
resulted during packing, which is
why open-mouth bags were always
more popular. Even if the quality of
the valve bags has improved in recent
years, many grain processing companies still prefer open-mouth bags compared to valve ones.
A recent survey of some large grain
processing operations confirmed this
trend toward open-mouth bags. One
of the largest flour milling companies in the United States gave several
reasons for this: 1) Open-mouth bags
are largely available in the various
production countries. 2) The sealing
for open-mouth bags, whether made
of paper or woven polypropylene, is
tight and may be reproduced even at
high throughput. 3) Ultimately, openmouth bags are selected because they
are easy to handle in bagging stations
as well as in the downstream closing
station.
SANITATION AND COSTS
Open-mouth bags ensure compliance with the high safety requirements in the food and chemicals in86

The automatic bagging station Maia for open-mouth bags with a pinch closing station fulfilled the
requirements for the flour milling family Molino Quaglia of Vighizzolo D'este PD in Italy.

dustries through the various sealing
options. Depending on the product requirements, open-mouth bags may be
sealed by being sewn, glued, heated
or a combination of these methods.
In addition, a resealable closure may
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customers of the bagged product.
The cost of valve bags compared
to open-mouth bags depends on the
region. Feed producers in Chile have
emphasized that polypropylene valve
bags can really only be permanently
sealed with an ultrasonically welded
principle. This increases the price of
the investment and the purchasing
costs of each bag by about 50%. If a
valve bag is not welded, the risk of the
content leaking out increases because
the bag is not completely sealed. This
company prefers open-mouth bags for
sanitation and safety reasons.
Today's bagging stations are characterized by higher capacity and lower
bag weight. Palletizers are used for
optimum stacking of bags and containers. For palletizers, open-mouth
bags often were considered to be
harder to stack. However, a leading
processor of agricultural products in
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be true. Thanks to the pinch bottoms,
open-mouth bags are stable when
stacked on pallets. And, it's possible
to bleed the air out and seal the bags.
This guarantees good stacking quality
and safe transport.
Furthermore, open-mouth bags may
vary in terms of protrusion while valve
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SUMMARY
The choice of the right bag ultimately depends on various factors such as
product properties, packaging rate and
speed, the food safety requirements
and the costs of the system and the
individual bag. Bühler has decided to
go exclusively with the trend toward
open-mouth bags for its bagging stations. The main reasons for this decision are that open-mouth bags are
easy to open, internationally available
without any problems, and both paper
and woven PP bags may be handled in
the same bagging station.
Thomas Ziolko is product manager,
Grain Milling, Bühler. He may be reached at
Thomas.ziolko@buhlergroup.com.
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January 2017 / World Grain / www.World-Grain.com

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World Grain - January 2017

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