Speeding up a machine is one way to reduce the cost to manufacture a product. It allows the same number of operators to produce more, thus decreasing the unit labor costs. Increasing speed is an especially effective measure for machines running at full capacity. However, other machines can benefit from reduced labor costs if crewing can be reduced to 2 shifts per day or 5 days per week, or when the crew can perform other plant tasks. Increasing speed is also most effective for machines that have a high uptime. Machines which have large grade change time or maintenance might be better served by PM, SMED (an industrial engineering technique) or automation.

Speed is relatively easy to achieve. If we look at some web machines, we see incredible capabilities. Flat paper grades are formed, dried, coated and calendered at speeds better than 5,000 FPM. Tissue is even faster, 7,000 FPM. Printing can be done faster than 3,000 FPM and rewinding faster than 10,000 FPM. Similarly, packaging is done at rates that make a machine gun look slow.

From a web handling point of view, we usually have but a single challenge, air handling. Air entrained over rollers cause a loss of traction and air entrained into wound rolls can cause a loss of edge quality as well as defects such as buckles. The challenge is especially acute for plain film. However, if we coat and particularly if we print or emboss, the surface texture may be enough to give a place for the air to go. Similarly, uncoated grades of paper handle relatively easy at blistering speeds. If it were not for air, we would merely ask "How fast do you want to go?" Even with air, however, we can achieve some pretty impressive performance. We engineer the idler roller and layon roller surfaces with an air handling texture.

From a machine design point of view, we may also only have one significant challenge, vibration. As we go ever faster, roller imbalance forces increase exponentially. Also, we inevitably cross many system resonances (roller critical speed is a meaningless concept because structures have much lower resonances than the individual rollers as calculated by simple formulas). Resonances are not debilitating in many cases if the rollers are superbalanced (a 100# roller might be put out of balance with a piece of tape) and the structure is massive and rigid. Electrically we have only a couple of challenges, motor horsepower and motor control.

From a process point of view, the challenges are very application dependent. The drying challenge, for example, is one of merely extending the length so that the product has enough dwell time. Paper machines have scores of 5-foot diameter dryer cans or hundreds of feet floater dryers to get the job done. Coating is a bit trickier. Depending on the application, speeding up may require a replacement of the coater and a redesign of the coating.

New machines present the least challenge. Mechanically, we first design to avoid RPM limitations with bearings, shafts and other drive elements that would prevent doubling of the speed some time in the future. Then, rollers and frame are made stout. Finally, rollers are machined precisely and finely balanced. Electrically, however, we avoid oversizing motors to accommodate future growth. The penalty for increased horsepower is decreased control quality. If we need more speed a decade or so into the future, we will replace and upgrade the motors at that time. They may well be obsolete and unserviceable anyway.

With this philosophy of design, we can ensure that future generations can use the same machine. It is not unusual to see WWII vintage equipment still running profitably on specialty paper grades. There are some machines running that date back as far as WWI. This is a refreshing alternative to the disposable concept where machines are justified on short-term product needs and two-year paybacks. If you design a machine with a nearsighted focus, you will wind up with a machine that is unreliable, unrepairable and un-upgradable.

David Roisum, Ph.D., Consulting Technical Editor, 920/725-7671, DRroisum@aol.com, www.roisum.com