Pyramids and Wound Rolls: Long-Lasting Quality

What comes to mind when you think about the pyramids? First, the pyramids have survived the test of time. Second, they have a distinct and impressive structure.

The pyramids' structure is responsible for their performance. If they had been built on swampland, they would have sunk long ago. If the Egyptians had built a less stable structure, the pyramids would be a large rock pile now.

Just like a pyramid's wide initial layers become a foundation for additional layers, a wound roll's initial wraps are the foundation for subsequent roll buildup.

In winding rolls we also create impressive performance through structure. Wound rolls are a package to store web materials and maintain quality between accumulating and dispensing. In wound rolls we hope for the same long-lasting performance found in the pyramids.

How can a cylindrical wound roll have anything in common with the structure of a pyramid? A stable structure for both pyramid and wound roll should consider three elements: foundation, buildup, and profile. The foundation of the wound roll is the core and core support. A pyramid's buildup and physical profile are analogous to the buildup and tension profile of a wound roll.

Important core properties include core diameter, core wall thickness, and core material. Many wound roll defects are avoided by using increasing core diameter, wall thickness, and material stiffness. You will not save money in the long run by building your wound roll on swampland.

But don't take this analogy too far. The rock-hard foundation ideal for office buildings is not ideal for wound rolls. Very hard cores can lead to high-stress defects such as blocking and deformation. The ideal core matches the web's stack behavior.

Build-up ratios can be high or low. A manufacturing plant usually has a low build-up ratio, one story high, and a large footprint. A skyscraper has a high build-up ratio. Both structures may have equal volume but significantly different stability. Which structure would you prefer to be in during an earthquake? The structural stability is independent of size. Whether building card houses or office buildings, small rolls or jumbos, the structure will determine stability.

In wound rolls, the critical buildup is the ratio of the final diameter to the core diameter. The skyscraper of wound rolls is a small core wrapped with product until the final roll is many times the core diameter.

Though small-diameter cores save space and expense, it is the wrong direction when our goal is long-lasting roll quality. Large-diameter cores with a reduced number of wraps have higher stability. Build-up ratios above three become increasing difficult. As roll size grows, consider increasing core size to maintain a reasonable build-up ratio.

Profile also is important to a pyramid's stability. If a pyramid were built upside down, it would topple easily. In wound rolls we cannot taper the roll geometry; instead, wound rolls are profiled with tapering tension. Tension taper involves reducing the winding tension as the roll grows.

Just like a pyramid's wide initial layers become a foundation for additional layers, a wound roll's initial wraps are the foundation for subsequent roll buildup. Using high relative tension at the beginning of a roll creates a sturdy support for external layers. In both buildings and rolls, tapering is more important for larger build-up ratios.

Think of wound rolls as little pyramids. Start with a good foundation. Choose a geometry that balances economics with stability. Use a tapered profile to improve the stability as buildup increases. Your rolls may not last for 4,000 years, but they will last long enough to impress your customers.

Timothy J. Walker has 20+ years of experience in web handling processes. He specializes in web handling education, process development, and production problem solving. Contact him at 314/323-6256; tjwalker@tjwa.com.


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