Zero Speed Splicing Technology for Continuous Hot Melt Coating Operations
Zero speed splicing is an advanced automatic splicing technology that allows a hot melt coating line to continue running at full production speed while a stationary roll of substrate is spliced to the end of an expiring roll, with the web being spliced brought to a complete stop during the splice. This is achieved using an accumulator (festoon dancer) that stores enough web length to keep the coating line fed while the unwind side stops briefly. The traditional method—flying splice—splices at line speed, which can cause tension spikes and requires precise speed matching. Zero-speed splicing offers superior splice quality, reduced waste, and the ability to splice heat-sensitive or stretchy materials that cannot tolerate the acceleration forces of a flying splice. In the typical zero-speed sequence: (1) The accumulator fills with web, storing 30-60 seconds of material. (2) The unwinder stops the expiring roll. (3) The new roll, stationary, is aligned and spliced to the expiring roll using tape or a heat-seal method. (4) The splice is completed, and the unwinder restarts. (5) The accumulator slowly releases its stored web, refilling as the new roll feeds the line. Throughout the process, the coating line experiences no speed change, and web tension is maintained within tight limits. This technology is especially valuable for hot melt coating lines producing high-value products such as medical tapes, optical films, and electronic materials, where a tension spike during splice could ruin meters of coated product.
The key component enabling zero speed splicing is the accumulator (festoon). A series of fixed and moving rollers create a web storage system; as the moving carriage travels, the web path length changes, storing or releasing web. For a line running at 300 m/min, a 30-second accumulator must store 150 meters of web. The accumulator’s moving carriage is servo-controlled and acts as a tension buffer. During normal running, the accumulator is partially filled (e.g., 50% storage). When a splice is needed, the control system commands the accumulator to fill, drawing web from the unwinder while the unwinder’s brake is applied. Once the accumulator reaches full storage (e.g., after 30 seconds), the unwinder stops completely. The operator (or an automatic system) then splices the tail of the expiring roll to the head of the new roll at zero speed. Because both webs are stationary, the splice can be made with high precision, using adhesive tape or a heat seal without the risk of misalignment. After the splice is made, the unwinder restarts, and the accumulator gradually releases its stored web, returning to its partial fill position. The accumulator’s tension control must be extremely precise; Martin zero-speed splicing systems incorporate inertia-compensated tension control providing essentially constant tension to the process line throughout the splicing process. This ensures that even during the fill and release cycles, the web entering the coating die sees no tension variation that could affect coat weight.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Two types of splices can be made in zero-speed splicing: lap splice and butt splice. In a lap splice, the two web ends overlap and are joined with double-sided tape. This produces a splice with double thickness, which may cause a bump in the coated product but is generally acceptable for many applications if the splice is later removed. In a butt splice, the two ends meet edge-to-edge with no overlap, joined by a thin tape on one side or by a heat-seal method. Martin’s patented heat seal join utilizes the thermal properties of the material to provide a tapeless splice which is virtually undetectable. A zero-tail, butt-splicing can be utilized to speed up converting lines while greatly reducing or eliminating the waste of valuable raw materials. The butt splice requires more precise alignment but produces a splice that passes through coating dies and laminating nips without causing coating voids or die damage. Some zero-speed splicers incorporate a pivoting splice head design that provides operator convenience along with quick splice preparation, with splicing speeds up to 1312 FPM (400 MPM) based on roll weight and material splicing tension required.
Zero-speed splicing is particularly advantageous for hot melt coating lines handling expensive or delicate substrates. For film substrates that are sensitive to stretching (e.g., 12μm PET, thin BOPP), the acceleration forces of a flying splice can cause permanent deformation. Zero-speed splicing eliminates these forces because the web is stationary during the splice. For coated liners that carry adhesive, a zero-speed splice reduces the risk of adhesive smearing or transfer because the web is not moving when the splice tape is applied. The low-speed mode also allows the use of specialized splice tapes that require pressure and time to bond properly. In the Martin CHW Cantilevered Unwind Splicer, the zero-speed design eliminates long splice tails and tension disturbances, greatly reducing waste; nonwovens are delivered to the converting process with exact tensions required for application and material. For hot melt lines that run 24/7, zero-speed splicing at the unwind is complemented by a turret rewind with automatic splice at the rewind, enabling truly continuous production from raw substrate to finished roll without any line stoppages. The combination reduces downtime from multiple roll changes per shift to zero, increasing overall equipment effectiveness (OEE) by 15-25%.
Integration of zero-speed splicing into a hot melt coating line requires coordination between the splicer control system and the line PLC. The splicer must receive a “request splice” signal from the line, typically triggered by a diameter sensor on the active roll (when the roll reaches a preset minimum diameter). The splicer then initiates the accumulator fill sequence. While the accumulator is filling, the line PLC must adjust the master speed reference slightly? Typically, no; the accumulator is designed to store web without affecting line tension. However, the unwind motor must be controlled to maintain proper tension during the fill. Advanced splicers like Martin’s NCHW come with their own control package (MC 2000) that eliminates the need for conventional drives and PLCs, making them a “drop-in” installation that does not require complex controls integration. For non-adhesive materials, the Martin zero-speed splicer can provide a lap or butt splice depending on material and process requirements; the pivoting splice head design provides operator convenience along with quick splice preparation. When the line includes an edge guide before the accumulator, the splicer must also maintain web centering during the splice. After the splice, the downstream edge guide will correct any minor misalignment. For all zero-speed splicers, regular maintenance includes cleaning the accumulator rollers, checking the tension sensors, and replacing worn splice tape applicator knives. By implementing zero-speed splicing technology, hot melt coating lines achieve higher throughput, lower waste, and better product consistency—critical advantages in competitive converting markets.
