The Wind-Up and Pitch

Look to press suppliers' suggestions, as well as material and tension specs, to make the best unwind/rewind purchase.

By Susan Friedman

Why venture beyond the standard unwind/rewind system supplied with a press? For package printers, the mission is often to reach a loftier tier of efficiency, productivity or safety.

'Herb' Herbert, president of CTC International, says CTC frequently sells automatic winding equipment to converters seeking a higher level of press automation. "A printing press will always have an unwind and a rewind. But they are not always automatic, unless specified. What comes standard might be a single-arbor unwind and a single-arbor rewind that must be stopped for each roll change," he notes.

FlexoExport sells most individual winding equipment to customers in search of ancillary winding capabilities, reports VP Scott Beaudoin. "This additional capacity is often for customized products, particularly for marrying multiple webs," he relates.

At Parkinson Machinery, wide-web winding needs make up the majority of individual system sales, says Sales Manager Dave Rumson. Converters may also look beyond standard unwind equipment if they are seeking an upgrade that can be more easily coupled with material handling devices such as lift tables and roll manipulators, he says.

So what is an interested buyer to do?

Reliable sources

Press manufacturers can be a valuable source of winding equipment guidance. But converters shouldn't necessarily just take a vendor's advice and run with it.

"If a press manufacturer has worked on multiple installations with a specific vendor and has a good relationship with that vendor, the likelihood of running into start-up issues or technical problems should be minimal," comments James Ward, division manager, light-web products at Martin Automatic. "However, if the application calls for materials or process requirements that are slightly different from that past experience, it may be wise to look at other options."

Some press suppliers may actually prefer to remain fairly neutral. In Herbert's experience, "press manufacturers don't like to make a strong recommendation that puts them in the middle. They typically will throw the ball back in the customer's court with three options for winding equipment suppliers." To pare these options, Herbert suggests converters request customer recommendation letters, visit the supplier's plant and/or demonstration center, and have potential suppliers visit their facility.

If a press manufacturer doesn't initially mention a certain supplier that is of interest, converters can still pursue the issue—with or without help. "This is not an all-or-nothing proposition," Ward states. "Many times, if an end user has a desire for a particular vendor which is not offered as a standard through the press manufacturer, most will be open to providing the desired equipment as an option."

Converters should weigh their winding equipment supplier choice most carefully if they decide to make an independent purchase. "If a press manufacturer will not agree to a specific vendor, the end user can usually arrange to purchase the equipment separately, but this means they are accepting some responsibility for performance," advises Ward. "Tension control, web tracking and line interface can become points of contention should problems arise."

Rumson adds that package printers' knowledge level can affect the success of an independent purchase. "These are very technical devices, especially when it comes to web tension control. Converters may want the press manufacturer to specify operating parameters for unwinding and rewinding machinery as best fits their equipment."

Tech talk

Asked to identify top technical parameters to consider when purchasing winding equipment, suppliers gave equal billing to material and tension requirements—two virtually inseparable specifications.

Beaudoin offers up a few basic questions that need to be asked to start the selection process: What substrate is running? What is the roll diameter, width and weight of this material? Does the application require constant or variable tension?

Chris Plude, senior project manager at Keene Technology, illustrates how material and tension specs feed into each other to determine not only winding, but winding accessory needs. "Material characteristics, web width and tension range will combine to define a suitable diameter for the idler rollers," he explains. "Light-weight webs, low tension requirements or high web speeds may lead to low inertia or composite idler rollers, or special roller surface profiles. Tension requirements and press acceleration and deceleration rates must be reviewed to ensure compatibility."

Tension concerns are not limited to the winding operation itself. "It is very important to understand the tension control specifications of the unwind during both the steady running state and the splicing sequence," says Ward. "Tension upsets during the splice sequence can greatly affect the overall waste output of a press. The customer may also need to consider the quality of tension coming from the unwind and how that will affect the infeed tension going to the press."

While certain brake types may create tension issues across the range of substrates, programmable, brushless AC vector motors can be programmed to handle any material, while eliminating brake maintenance needs, explains Don Jensen, sales and marketing manager at RG Engineering. The motor's braking action generates electrical power that can be fed back into plant power or into the rewind. These servo systems feature automatic pretensioning and are programmed to sense the end of the roll, eliminating the need to clean and maintain sensors, he adds.

Design decisions

Converters should again look at a material's width, weight and roll diameter to determine the best winding equipment design: shafted, shaftless or cantilever.

"Shafted designs are most common for intermediate widths of 20à to 40à, but for wider widths the core shafts become too heavy to handle without special equipment," explains Plude. "A hoist or other lifting device is usually required to load the roll and shaft into the unwind.

"Shaftless designs," he adds, "are the most expensive but offer the advantage of loading and unloading rolls directly from the floor. It is the preferred style for large diameter rolls or wider webs, however interest is growing for all applications."

Cantilever designs are best for "fairly narrow-web material," says Harold Sexson, sales manager for Aztech Machinery. "You can't cantilever much more than a couple of feet without building a larger cabinet to support the other side of the shaft. With narrow webs, cantilever designs are the cheaper option, but cantilever actually becomes the more expensive option for wide web when you add the cost of the supporting body."

"The cantilever design is most suitable for narrow webs with small rolls due to the ease of loading/unloading small rolls by hand," adds Plude. "It can also be desired when space dictates that the unwind must be loaded from the side, rather than the end. For applications with heavier rolls, a roll loading/unloading cart is employed."

Converters may have to forego the convenience of cantilever in favor of heftier roll support. Rolls are getting heavier and wider, Sexson relates, which means that companies like Aztech that currently concentrate on cantilever winding equipment designs may soon offer more double-support designs.