Unwinds that run a wide array of materials may need tension control and steering devices that are flexible and adaptable to those webs. (Photo courtesy: Webex)

Especially as the industry embraces faster web speeds and larger diameter rolls, good web guiding and tension control equipment remain key components to ensuring efficient converting operations. The right equipment protects converters from excessive waste, improves product quality, and increases output-all ongoing benefits that yield a return on initial investment.

Not every piece of machinery is perfect for every converter, however, and it is a good idea to team with trusted vendors to determine which web guiding and tension control investment fits best with individual operational and business goals. Flexible Packaging discusses important factors to examine when purchasing web guiding and tension control equipment, and how these factors ultimately impact profitability.

What main factors should converters consider when deciding upon web guiding and tension control equipment?

Felix Guberman, director of research & development
Macro Engineering & Technology Inc.

The main factors to consider when specifying the correct web guiding and tension control equipment are the type of material, its physical dimensions, and the running speed of the line. All these factors are key to avoiding wrinkles or damaging the web.

The type of material that’s processed will determine the extensibility of the web.  Films that are more extensible than others require more sensitive tension control to prevent stretching, sagging or wrinkling.

The dimensions of the web have varying effects on tension control systems. Very thin webs have significantly more potential to wrinkle, and wide webs tend to be more difficult to control. Additionally, the positioning of thick webs can be difficult to correct with web guides, as the web may not track sufficiently for the adjustments by the web guidance system. These cases may call for moving the machinery in relation to the web instead of moving the web to match the equipment.

The desired line speed will influence the web guide and tension control equipment as these systems must be capable with keeping up, particularly in high-speed lines. Quick response times for tension control are critical to avoid stretching when operating at high speeds. 

Jim Berceau, engineering manager
Webex Inc.

While somewhat less tangible, we would recommend converters consider easily available support as important when implementing these systems. 

Both web guiding and tension control applications have implementation nuances that need to be considered on a per-case basis, since both system types are somewhat dependent on items outside of the supplier or component performance control.

For example, web guides often need to be located in non-optimal locations due to layout restrictions. Tension control components are highly dependent on devices both upstream and downstream of themselves. Experienced support staff can help determine where problems may lie and provide suggestions to reduce the impact of compromises often necessary to make something functional or of value. It should also be noted that this support is not limited to component manufacturers. System integrators and machine manufacturers that deal with web handling applications on a regular basis will often have internal expertise in these fields.

Rewinder section on Macro's high-speed unwind-rewind line.

What type of return on investment should a converter expect from today's web guiding and tension control equipment?

Guberman: The return on investment of an upgraded web guide, or tension control system, is greatly dependent on the line conditions, the types of materials being processed, and the capabilities of the existing equipment.  In general, the return on investment is quantified by the reduction in scrap that can be achieved by implementing the newer technologies. If a line is to be upgraded for enhanced performance, the use of new equipment will likely be a necessity to facilitate the new processing objectives.

For example, if a processor is looking to increase output on a line, the web guide and tension control systems are potentially limiting components. With high-output film extrusion systems, such as multilayer blown film lines for general packaging, the output of the line can be directly linked to profits. The faster the line operates, the more potential output can be achieved and the more profits can be maximized. It’s necessary to equip the line with web guiding and tension control systems that can handle fast line speeds. With modern web-guide technology the response time is rapid and suitable for these high line speeds. Today’s load cells provide accurate tension control at fast speeds to keep the film at the proper winding tension.

Macro generally advocates enhanced technology. With better tools the potential to achieve more efficient productivity or an improved product is possible, but it’s not always necessary to get the latest and greatest.  It’s recommended to get a comprehensive assessment of the line to determine what component upgrades are vital to achieve the required operational goals.

Berceau: This question is dependent on individual applications. A specific operation must be able to attribute any losses specifically to tension control or web guiding issues, and that can sometimes be very difficult since there can be many contributing factors. However, if an end user can evaluate their process and determine the amount of waste generated specifically due to tension or guiding errors, then determining a payback is very straight forward.  Two examples of this are obsolete equipment (items that cannot be readily replaced) and devices that need calibration and adjustment on a frequent basis. In the first case the user may be able to justify the cost of a new, readily available system based solely on the cost of downtime incurred due to an unplanned failure.  In the second case the costs are in labor and possible short-term downtime events.  But in either case the return on investment is fairly easy to determine.

We also feel that the web tension controller arena has progressed more recently than any other area, particularly with respect to the areas of unwind and rewind tension control. The widespread use of digital design in the web tension control field has produced devices that need little attention or adjustment over time. In addition, digital processing has allowed for model-based control strategies. Today’s controllers can infer roll diameter from various feedback points and modify control gains to maintain stable control over the full range of roll diameters.  These highly featured controllers-roll transfer features, taper, etc.-are also easier to implement with today's designs than they were in the past.