F CASE STUDY

The bagging carousel MWPM with its automatic bag attacher MWAP can be combined with a bag closing station as part of the integrated, modular bagging line

CASE STUDY

Open-mouth bags vurses Valve bags The decision of whether to use open-mouth bags or valve bags when bagging product in the grain processing or feed industries is influenced by diverse factors. The trend is toward open-mouth bags.

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by Thomas Ziolko, Product Manager Grain Milling, BĂźhler AG, Switzerland

n Europe, North America and Australia, grain milling products are mostly filled into tank trucks in bulk. In Latin America, Africa and Asia, in contrast, bagging into open-mouth or valve bags is predominant. However, in the recent past, there is a clear trend away from valve bags towards open ones. This is driven above all by the international availability of less expensive open-mouth bags, an easier filling process and the option of dust-tight closures which parallel the trend to greater food safety.

Not all bags are alike

Compared to the open-mouth bags, the upper part of the valve bags is almost completely closed. The valve bags have just one small opening; the ‘valve’ in which to fill the bag. As soon as the bag is full, the interior pressure of the bag closes the valve to stop product from spilling over. Open-mouth bags are closed along the lengthwise side and on the bag bottom. They can be made of paper or plastic. They are easily filled and can be sealed by welding, sewing or gluing so nothing trickles out. A big variety of bag types can be used. The side fold bags fill out in the shape of a block thanks to the inserted side fold that makes them very easy to stack. The cross bottom bags are particularly easy to stand alone or stack after filling because of their bottoms. They are also effective for advertising because the bottom and sides of the bag can be printed. Laminated bags of woven polypropylene can also be printed in good quality and are available as a pinch bag. 74 | December 2016 - Milling and Grain

Diverse experiences

Valve bags have been used for bagging milling products since the middle of the 1920s. Even back 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 over the past years, many grain processing companies still prefer open-mouth bags compared to valve ones. A survey of some large grain processing operations confirmed this trend towards open-mouth bags. One of the largest flour mill in the United States gave multiple reasons for this: Open-mouth bags are largely available in the various production countries The sealing for open-mouth bags, whether made of paper or woven poly-propylene, is very tight and can be reproduced even at high throughput Ultimately, open-mouth bags win out 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 industries through the various sealing options. Depending on the product requirements, open-mouth bags can be sealed by being sewn, glued, heated or a combination of these methods. In addition, a resealable closure can be used which is a big benefit for the customers of the bagged product. The cost of valve bags compared to open-mouth bags depends on the region. Feed producers in Chile have emphasised that polypropylene valve bags can really only be permanently sealed with