Practical applications for unwind systems for slitter rewinders

R. Duane Smith, product manager, specialty winding, Davis-Standard LLC is presenting a paper about selecting equipment to ensure maximum performance and productivity at the CEMA 2015 Slitting and Winding Fundamentals Seminar held in conjunction with ICE USA 2015

All converting slitter rewinders require an unwinding system. Although often considered a simple function the selection of a proper unwinding system is extremely important to the overall productivity of the slitter rewinder. The major trade-off of an unwinding system is cost versus efficiency. A light duty unwind may be the most cost effective for a low production operation but for high production a rugged duty, shaftless, floor pick-up is often more suitable for maximum operation speed and roll changing efficiency. Shaft selection, chucking system, type of chucks, braking system, tension control, web squaring, side shifting and edge guiding equipment will affect overall performance. This article discusses the proper selection of an unwinding system to ensure maximum performance and productivity from a slitter rewinder.

Design criteria

The first thing that must be established is the basic design criteria. This needs to include: material’s basis weight and thickness ranges, roll diameters and weights, speed of operation, tension ranges, core ID and ODs and roll delivery system. This basic design criteria will help select the design of unwind best suited for the application. The variation of these parameters dictate the flexibility required and therefore the complexity and cost of the system. The old rule ‘jack of all trades and master of none’ applies to the unwind operation so be realistic when specifying the required range for best value and performance of the unwinding system.

Frame construction

The frame construction for unwind stands of typical converting slitters can range from machine mounted plate steel for lightweight rolls to separate unwind stands fabricated from heavy weldments or castings. Heavier roll weights and higher speed operations require separate rigid frame construction for quick acceleration/deceleration rates, smoother unwinding of ‘out of round’ rolls at higher speeds and precise web guiding without vibrations or tension upsets.

Edge building

The unwind must provide a web into the slitter rewinder accurately positioned (guided) to the slitters or to realign the edge of the web in a straight rewinding operation. The unwind needs to be mounted to the floor on friction-free cross direction slides. The edge guiding system needs lead-out idler roll having a non-slip surface that shifts with the unwind frame. This roll provides for a constant web lead into a floor-mounted edge position sensor. Oscillation of the unwinding may be required when handling web materials that have higher caliper bands in localised areas in the cross machine direction. This requires taking wide trim which is greater than the amount of oscillation. The suggested oscillation speed is 1” per minute per 500 FPM of winding speed.1

Shafted operation

The simplest and least expensive unwinds are of a shafted design. The selection of shaft type is critical for optimum unwinding operation. For each core size the shaft’s selection criteria is: load capacity, torque capacity, speed capacity, weight and tolerance to poor quality cores vs. shaft cost. Most shafts are pneumatically expanding and the expanding elements are lug, button, leaf, or strip. Since load, torque and speed are generally the most critical factors; either a lug or strip shaft is preferred. The type of material for the shaft then must be selected. The three most common materials are steel, aluminum and carbon fiber composite. This selection is based on shaft load capacity vs. shaft weight and cost. Steel shafts have the highest load capacity but often require special shaft handling equipment. Aluminum shafts are a lighter weight alternative but cannot support heavy loads and are not as durable. Carbon fiber composite shafts can have the strength and stiffness of steel with less weight than aluminum. Shafted unwinds need to have secure latching, the capability to support the shaft’s and roll’s weight and transmit the braking torque. It is extremely important that the latches are sized for the application.

Shaftless operation

For applications where there is a wide variation in web widths on smaller diameter cores or a wide variation of core sizes, a shaftless unwind operation is preferred. Shaftless unwinds are more complex with a greater number of moving parts, require greater space and are more expensive. However, they are much more versatile and productive than a shafted operation. Product rolls are loaded into the unwind without an overhead hoist. The arms on a shaftless unwind move to accommodate various widths and to chuck a new roll and unchuck an empty core. The chuck selection is critical for an efficient shaftless operation. The criteria include the chuck’s load capacity, torque capacity, core ID tolerances, roll centering capability and space available. Chucks may be pneumatically or mechanically expanding and can have a wide range of costs. Please contact the author for further details.

Brake applications

The unwind must provide web tension for web tracking, spreading, stability of web width and wound roll density. Highly extensible materials want to be unwound with as little tension as possible with draw control between the unwind and rewinder. For more stable materials the suggested winding tension is 10% to 25% of the material’s elastic limit.2 See referenced article for more information on suggested web tension.3 The selection and size of the unwind brake is made from the maximum torque requirements and tension horsepower. Most converting applications use air cooled disc brakes. These are easy to maintain and do not require external cooling. Shaftless unwinds typically have brakes on both sides which allow distributing the torque to both ends of the core and provides roll centering on both sides. For higher tension horsepower applications the heat dissipation of these brakes may not be adequate. Water-cooled disc brakes are then required. For applications with high winding speeds and fast acceleration rates and light tensions, regenerative braking systems need to be used. Although more expensive they provide excellent tension control, faster acceleration capability and lower maintenance costs.

Tension control systems

All unwinds need to have an automatic tension control system which controls the brake’s torque as a function of the unwind’s diminishing diameter, compensates for the roll’s inertia during acceleration/ deceleration and compensates for winding and friction losses to achieve constant web tension. Dancer control systems are preferred for slitter rewinders where the unwind tension is isolated from the winding tension. Electronic transducer control systems are preferred when the winding tension is being controlled from the unwind. Transducers provide faster response to tension upsets and a direct readout of the winding tension. Roll centering and roundness are critical for high productivity of smooth sided rolls when unwinding and winding tension isolation is not provided.

Web squaring

Even cross machine web tension is important for proper spreading and good winding. When caliper or moisture variations occur across a roll being unwound, skewing of the unwind or a roll after the unwind is required to even the tension from one side of the web to the other. The important consideration is to provide a scale so the unwind or roll can be brought back to the center position after the problem roll has been processed.

Operator control stations

A further important consideration for an unwinding system is the placement of the operator controls. For safe and efficient operation the control stations need to be within easy reach of the area where the operator is performing a function. On a shaftless floor pick-up unwind the arms should have the controls to chuck a roll, raise and lower the arms and sidelay the unwind. The ability to turn on/off the tension should be provided to allow making a splice at the unwind and tightening the web before starting the rewinding operation. An unwind operator station should be provided for speed control to allow slowing down and stopping the operation for inspection or cutting out off quality material. This should have edge guide auto/manual controls and an emergency stop mushroom head pushbutton.

Splice table and scrap winders

Rewinding operations require the splicing of webs due to web breaks, cutting out bad material in the roll or rewinding a large diameter roll from multiple smaller rolls. A splice table between the unwind and slitters provides the ability to consistently produce quality butt splices which are made at an angle from the perpendicular to the edge of the web. The angle is important for the splice to go through nipped rolls without a severe bump. When rewinding rolls containing large amounts of material that needs to be cut out a scrap winder increases the efficiency, helps prevent operator fatigue and increases safety of the operation. These small winders are located between the unwind and splice table ‘packaging’ the scrap rather than manually rolling it and loading it into carts. Proper selection of an unwind and auxiliary equipment is very important to insure the maximum performance and productivity of a slitter rewinder. Too often the unwind on a slitter rewinder operation does not get the attention it deserves. Hopefully, the information in this article will be useful in optimising your unwinding, slitting and rewinding operation.



1. Smith, R. Duane. The Art of Winding Quality Rolls, Paper, Film and Foil Converter August 2001 pp46-53. 2. Roisum, David R. The Mechanics of Web Handling, TAPPI Press 1998. 3. Smith, R. Duane. Guidelines for Web Conveyance and Winding Tensions. AIMCAL’s Converting Quarterly 2011 Quarter 3 pp 58-62.


Duane is widely known throughout the paper, film and nonwoven industries for his technical knowledge on web handling and winding. With over 42 years of experience in these areas, he has been awarded two patents in winding and  made over 80 technical presentations, and published over 25 articles in major international trade journals. His writings were featured in the 2007 and 2009 Modern Plastic World Encyclopedia.   Active in AIMCAL since 1991 he has given over 35 technical presentations at CEMA and AIMCAL conferences including teaching over 20 CEMA Fundamentals Seminars. He has been an instructor at 14 TAPPI short courses and has published three books through TAPPI Press and is editor of TAPPI Press’ first e-book The Ultimate Roll and Web Defect Troubleshooting Guide. Duane received at the ANTEC 2002 in San Francisco the SPE Certificate of Recognition for his “Significant Contributions made to the Society and the Plastic Industry. He was named a TAPPI Fellow by the TAPPI Board of Directors in 2011, an honorary title bestowed upon a very small percentage of TAPPI’s international membership given to individuals who have made extraordinary technical or service contributions to the industry and/or the Association.