Balancing the bagging triangle
Dry bulk packaging is a simple yet sensitive balancing act. Maximum efficiency and productivity are at the center of a triangle with product, bag, and machine at the vertices. This delicate balance is called the “bagging triangle.” It describes the relationships among the three corners and how the right combination can positively impact an operation’s bottom line. It’s a simple concept: a shift or change in one corner—the product, bag, or machine—necessitates a change in one, or sometimes both, of the others.
While it’s common for packagers to blame machines when bagging efficiency goes down, experience shows that equipment often is not the culprit. It’s just as likely that product specs or the bag have changed and disrupted efficiency. Packagers who are able to work with their bag suppliers and machine manufacturers in applying the bagging triangle can pinpoint the source of the problem more quickly, get their operations back into three-corner balance, and consistently hit the sweet spot of efficiency, productivity, and profitability (see Figure 1).
Harmony equals profit
For example, consider a product manufacturer that decides to upgrade its packaging machines. The company’s project engineers, the bag supplier, and the machine manufacturer get on the same page regarding the right combination of machine and bags for maximum efficiency and production. Everything has been tested and projections look excellent.
The new machine is installed, it’s in harmony with the product and bags, and the company is meeting quotas. All is well until an operator notices something’s off: the machine is not filling at the expected rates or it’s consistently hitting the target rate in the morning, but it always drops after midday. At a more basic level, maybe the operation is losing a half pound of product for every bag.
Simple math shows how significant these scenarios can be (see Figure 2). It’s easy to understand why companies want to address them quickly, and they often look to their machine manufacturer for answers.
Regardless of which type of bag an operation uses—valve, form-fill-seal, or open mouth—the ultimate goal for dry bulk packagers is to fill and seal as many bags as possible with exceptional accuracy in a specified time period (see Figure 3). The number that a company can actually fill depends on the delicate balance of the bagging triangle’s three corners.
Product: The installation of any new packaging equipment should begin with a thorough analysis of the product and its properties. Material composition, consistency, size of particles, what form they are in, and how they are distributed all come into play. Drilling down further reveals other crucial traits, such as flow property, bulk density, moisture content, de-aeration characteristics, compaction properties, and trickling capability.
Occasionally a product manufacturer will change the formulation of its product after the equipment has been operating for a period of time. Whenever this happens, it’s important to test and analyze the new material mix to determine the ideal machine settings and bag characteristics for bagging triangle balance.
Bag: It seems like it should be pretty straightforward—pick a bag and fill it—but it’s not that easy. Many times, when companies experience a drop in efficiency or productivity, the issue can be traced back to a change in the bag. Some of the most important characteristics of a bag are de-aeration properties and consistency in manufacturing. Both of these factors can have a significant impact on efficiency.
Perhaps the more critical of the two is the bag’s ability to de-aerate, and that depends largely on the materials used to fabricate the bag. Many factors must be considered, including whether the bag is made with traditional paper, high-performance paper, plastic, or a combination. The weight of the material and the number of layers also require consideration. The ability to de-aerate also is impacted by the inside mechanics of the bag, such as whether there is a layer of polyethylene (PE), to what extent the PE is perforated or sliced, and where in the layer sequence the PE is inserted. The impact of de-aeration properties creates a trickle-down effect that subsequently impacts filling speed and overall machine performance. For example, if the air in the bag takes a long time to escape, the entire packaging process is slowed.
The second factor, bag consistency, can impact the process in three ways. First, if the valve size and placement are not the same from bag to bag and order to order, the machine might have issues consistently placing the bag on the spout for filling. Second, inconsistencies in the bags will affect the way they stack in the magazine, which can lead to misfeeding in the system. Finally, if there are issues with the quality of the bag or inconsistency in characteristics such as perforation, efficiency can be compromised due to poor de-aeration.
Sometimes a bag change may have nothing to do with a supplier, but is instead the result of a well-intentioned machine operator who sees an opportunity to save a penny or two per bag by making a change. Or perhaps the company’s purchasing department decides to switch to a bag with fewer layers. Regardless of the reason, the company must consider how the change will impact efficiency and make adjustments to the other two points of the bagging triangle to compensate.
Machine: The key to machine selection is to work with a manufacturer that understands the bagging triangle and fully tests product, bag, and machine—both independently and together—before making equipment recommendations.
The process starts with obtaining product from the end user to analyze. Testing the product is a critical step that helps define the product characteristics, and the bag’s filling behaviors, durability, and quality. From there, the company can identify and define the proper filling technology to achieve the ideal productivity level. In addition, this testing helps determine optimal filling rates, how many spouts are needed to hit those rates, and what settings will need to be maintained on the machine to achieve them.
The initial setup is only the beginning. As a machine operator or company makes changes to the other sides of the triangle, it is imperative that they evaluate the effect of those changes and adjust parameters on the machine to maintain balance. Before making the machine adjustments, it’s always wise to consult the manufacturer. Remember, a change in one corner of the bagging triangle impacts the other two, and tinkering can quickly result in sacrifices in capacity, weight accuracy, and cleanliness.
Product plus bag plus machine equals efficiency, productivity, and profitability. A little here and a little there can really add up, and packagers always want to reach maximum efficiency and productivity.
Finding the right combination of product, bag, and machine, and keeping all three corners of the bagging triangle in synch requires constant monitoring. A key to maintaining the right balance is to work with partners that understand and can apply the concept. By understanding the bagging triangle, packagers can reach quality outputs and high weight accuracy, and be proactive toward preventive maintenance (see Figure 4).
Markus Lackmann is sales manager for the U.S. and Canada at Haver Filling Systems Inc., a bag/packaging manufacturer that specializes in the handling and packaging of solid dry bulk materials, liquids, and pasty products. He has more 15 years of experience working in the industrial machinery industry with a special emphasis on material handling, weighing, packaging, and filling technologies.