Continuous Splicing Unwinds 

Published: August 3, 2026, By Trevor

By Neal Michal, Principal at Converting Expert, LLC

There are two broad unwind categories: Roll-to-Roll (R2R) and Continuous.  R2R unwinds require the entire process to stop before splicing in a new roll. Continuous unwinds dramatically improve productivity because the process continues to run during a splice. 

There are two types of continuous unwinds designated by their splicing process.  A flying splice unwind (also known as a turret unwind) makes a splice while the expiring roll is running at line speed. The other approach is to bring the expiring roll to a complete stop before making the splice.  This is a zero-speed splice unwind.  An accumulator is required to allow the downstream process to run during the splice event.

Important considerations for which style of unwind to select include splice efficiency, splice quality, splice tail length, required training, prep time and machine footprint. 

• Splice efficiency is calculated by how many successful splices are made versus total attempted. One missed splice will drive waste and loss of productivity. 
• Splice quality evaluates wrinkling, neckdown, and any loss of machine direction (MD) or cross direction (CD) registration during the splice event. 
• The splice tail length is determined by the splicer design.  The probability for a downstream wrap increases with tail length. 

The size of the equipment footprint determines general machine layout. Unwinds may be located on a mezzanine to save floor space. If located in the aisleway a turn bar will be required. 

Splice efficiency, splice length, and the quality of the splice joint are important considerations for any continuous unwind. Image courtesy of Davis Standard.

Flying Splice Unwinds 

Flying splice unwinds are more common. They may have a smaller footprint. Flying splice unwinds are limited to lap splices. Tail length is a common concern. Recent offerings promise shorter tail lengths. 

The splice sequence begins when the turret rotates the new roll close to the running web. The splicing mechanism consists of a cut off knife and an indexing roll. The indexing roll presses the running web against the new roll just before the splice tape appears. The exposed tape on the new roll adheres to the running web just before the cut off knife severs the expiring web. 

Splice efficiency is driven by splicer design, timing, splice prep, speed matching, tape adhesion and roll eccentricity.  The timing of the splicer requires knowledge of the position of the splice tape. 

Splice prep for a flying splice is complex, which may require several minutes. Double-sided tape is placed on the leading edge. Multiple “butterfly tapes” are used to hold this edge in place before the splice event. Training to a standard is required for consistent splices.

Speed matching requires correct diameter measurements for the new roll. Accuracy requirements for reliable splicing can be 1% or less. Ultrasonic or laser sensors are commonly used but are subject to calibration errors or drift. Manual measurement of incoming rolls using a Pi Tape is a reliable option. If the incoming roll is too slow, the tension will spike and the splice may fail. If the incoming roll is too fast, slack will occur which drives wrinkles, weave and often wraps. A poor splice may cause the tail to be several feet long. 

Tape adhesion is critical for flying splice unwinds. The tape should have at least twice the holding strength of the peak tension it will experience. If the tape pulls apart on one side, the web will violently weave downstream. 

Roll eccentricity is often a result of rough roll handling, excessive roll clamp pressure, too many touches and lack of training. As rolls become more eccentric the splicer mechanism may bounce resulting in a missed splice. Round rolls splice better.

Horizontal accumulators require high web tensions but can be located above the unwind stands to reduce footprint. Image courtesy of MTorres.

Zero-Speed Splice Unwinds  

Zero-speed splice unwinds require an accumulator. The accumulator consists of multiple rollers that are moved to adjust capacity. Unwind speeds depend on accumulator capacity which is calculated by the number of spans times the total stroke. 

The primary benefit of this design is a high-quality splice that rarely fails. Because the web is stopped, both lap or butt splices can be used. Tape or heat seals are most common. Ultrasonics, hot-melt and sewing are available options. Butt splices have no tail length. Tail length for a lap splice is 2-6”, determined by the splicer design. Short tails virtually eliminate wraps downstream. Some heat seal butt splices can be sold into the final product. Eccentric rolls are of no concern.

Taped butt splices may require two minutes of prep time. Heat seal lap splices require a handful of seconds, a taped lap splice can be accomplished in under a minute.

For low-tension processes the accumulator should be oriented vertically, but requires more floor space. Horizontal accumulators require high tensions but can be located above the roll stands to reduce footprint.  

It is common to run the accumulator at low capacity for delicate webs in between splices to reduce wrinkles or weave. The splicing sequence begins when the accumulator fills to allow the splice. The running spindle is then rapidly brought to a stop. The splice bars clamp the webs together, the expiring web is cut, and the splice bars open. The new roll is accelerated back to speed. During the splice event, the accumulator is used to provide material downstream to the running process. 

Splice efficiency is primarily driven by accumulator tension dynamics. This is particularly important for high-speed splicing of delicate webs. Low-inertia carriage rollers, and careful selection of run height, splice height, and acceleration rates can provide near 100% splice efficiency. Load cells and trend charts are recommended to optimize a zero-speed splice event. The rollers in the accumulator can be driven to dramatically improve process capability. 

ABOUT THE AUTHOR

Neal Michal was Kimberly-Clark’s senior web handling expert and was responsible for winding and converting performance.  He is a technical advisor for the Association for Roll-to-Roll Converters and is a regular contributor to Converting Quarterly and Paper, Film and Foil Converter (PFFC) magazines. Neal can be contacted by email: This email address is being protected from spambots. You need JavaScript enabled to view it. or phone: +1 770-356-7996. Learn more at: https://convertingexpert.com/