Most experiences with bags end at the decision of paper or plastic in the supermarket checkout line. However, companies that depend on bags to package, transport, and promote their products realize that bag selection plays a key role in enhancing or diminishing profits.

When recurrent packaging problems occur, these companies are forced to evaluate their chosen bag design to determine if this seemingly simple product is a competitive asset or a production liability.

Packaging failures caused the Lincoln, Neb.-based U-Mix Products Co. to search for a better way to package its pre-mixed concrete products. U-Mix was using a heavy-duty, three-ply bag that contained a plastic liner designed to withstand the pressure of rapid loading 94 lb of cement. However, bags would explode, creating a safety hazard for machine operators who, despite their safety goggles, face shields, and dust masks, would have to leave the bagging machine to clean themselves off.

"We were wasting quite a bit of time and money on blown bags," said Rex Kinsey, production manager at U-Mix. "We use a vented bag, and filling them is kind of touchy. Since there is a lot of entrapped air in the product, the bags have to be perforated just right in order to let the air escape and not the cement.

"Filling the bag too fast would cause it to explode like a shotgun shell and spew cement all over the floor and the person operating the bagger," Kinsey continued. "Every time a bag blew up we would have to stop the plant and clean up the powder."

To improve productivity and safety, U-Mix tried bags from four different suppliers but had little success. After investigating U-Mix's packing set up, a representative from Percy Kent Bags proposed that a combination of modified fill rates and a new bag design might solve the problem, and he developed suggestions for the resolution.

"Each company must configure its bag's material, size, shape, and perforation patterns to meet the requirements of its packing equipment and its products," said Percy Kent's Jim Kinney. "We worked with U-Mix and the bagging machine manufacturer to figure out how to adjust the machine's fill rate. We also developed a perforation pattern that would relieve air pressure in the bags while still retaining most of the product."

The benefits of the perforation pattern became apparent to U-Mix. "The new bags are three layers thick, just like our old ones," Kinsey noted. "However, instead of poking holes through all the layers in a straight line, each layer has a different set of pin holes. The idea is for the air to kind of wiggle its way between the layers and eventually escape from the bag."

Venting the air rapidly and safely is critical, because the bagging machine handles about 22 bags per minute. This means that each bag is placed on the fill spout and accepts 94 lb of cement in less than three seconds. Since implementing the new system, U-Mix has seen a dramatic reduction in the number of bag blow-ups and resulting production losses.

"At times, we were losing 5% of our total production due to bag failures, currently we are at less than 0.5%," reported Kinsey. "Since we don't have to stop it as often, the bagging line actually produces 40 more bags per hour on average, and the operators are staying a lot cleaner."