Turret Unwinds with Automatic Splicing for High-Volume Hot Melt Coating Production
For high-volume hot melt coating lines producing tens of thousands of square meters per day, manual roll changes are unacceptable. Turret unwinds with automatic splicing provide continuous feeding of substrate to the coating line, eliminating downtime for roll changes. A turret unwind has two or more roll positions mounted on a rotating frame. When the active roll reaches a preset minimum diameter, the turret rotates (indexes) to bring a new, pre-loaded roll into the coating position. The splicing mechanism then joins the tail of the expiring roll to the head of the new roll—either while the web is moving (flying splice) or after bringing the web to a stop (zero-speed splice). The choice depends on substrate properties and quality requirements. For robust materials like paper or nonwovens, a flying splice at line speed is acceptable; for delicate films or adhesive-coated webs, a zero-speed splice is preferred. Turret unwinds are available in cantilevered or floor-mounted designs, with hydraulic or electric rotation. They can handle roll diameters up to 1200mm and weights exceeding 1000kg. The LP Series hot melt coating lines offer a range of unwind/rewind options including single unwinder, double unwinder manual splice, automatic unwind butt/overlap splicer, single rewinder, and turret unwinder/rewinder with automatic splice.
Flying splice systems operate at full line speed. The new roll is accelerated to match line speed using an auxiliary motor. A splice table moves into position, bringing the two webs together. A cut-off knife severs the expiring web, and a splice tape or adhesive joins the webs. The entire sequence takes 0.5-2 seconds. Flying splicing is fast and requires a smaller accumulator (or none at all) because the line speed does not change. However, the high speed and acceleration forces can cause tension spikes, and the splice must be made while both webs are moving, which requires precise speed matching (within 0.5% of line speed). For heat-sensitive substrates that stretch easily, flying splicing may cause deformation. The splice joint itself may be bulky (lap splice) or thinner (butt splice with tape). Flying splices are commonly used for paper, nonwovens, and some films in applications where the splice will be trimmed off later, such as in label stock where the splice is marked and removed during slitting. For hot melt coated webs where the adhesive is already applied, flying splicing is challenging because the adhesive may stick to the splice table or cause the web to tear. For these applications, zero-speed splicing is preferred. The Martin zero-speed splicing systems incorporate inertia-compensated tension control providing essentially constant tension to the process line throughout the splicing process. The Martin CHW Cantilevered Unwind Splicer eliminates long splice tails and tension disturbances, greatly reducing waste.
Hot Melt Coating Machine - Hot Melt Adhesive Coating Machine
Turret design varies by application. For narrow webs (up to 600mm), cantilevered turrets allow roll loading from the overhanging end, reducing floor space and simplifying operator access. For wide webs (up to 2000mm or more), floor-mounted turrets with dual support provide the rigidity needed to prevent deflection during roll rotation. Turrets may have two positions (single-index) or four positions (double-index), allowing pre-loading of multiple rolls to extend run time. The rotation mechanism is typically a hydraulic rotary actuator or an electric gearmotor with a position encoder. Safety features include positive locking pins to prevent unintended rotation and light curtains to protect operators during loading. The turret control system communicates with the line PLC to request splice at the optimal moment, typically when the remaining roll diameter reaches 150-200mm. Some advanced systems use a “flying splice at reduced speed” mode: the line speed is temporarily reduced to 50-70% of normal during the splice, then ramped back up. This reduces splice-induced tension spikes while still maintaining productivity higher than a zero-speed splice. The decision depends on the substrate: for thin PET film (12μm), a zero-speed splice is safest; for 80gsm paper, a full-speed flying splice is acceptable and maximizes throughput.
The accumulator (festoon) is present in both flying and zero-speed systems, though its required storage capacity differs. For a zero-speed splice, the accumulator must store enough web to keep the line running while the unwinder stops, typically 30-60 seconds of web. For a flying splice at full speed, the accumulator may be smaller (5-10 seconds) or even eliminated if the splice occurs quickly and tension control is robust. However, an accumulator provides additional benefits beyond splicing: it decouples the unwind tension zone from the coating nip, preventing tension disturbances from downstream processes (e.g., a sudden stop of the rewind) from affecting the coating. The accumulator’s moving carriage is controlled by a servo motor or pneumatic cylinder, with position feedback via a linear encoder. In typical operation, the accumulator maintains a constant position, meaning the web tension is constant. During a splice, the carriage moves to fill (during unwind stop) or to release (during restart). The accumulator’s inertia must be low to respond quickly; carbon fiber rollers are used on high-speed lines. The accumulator also serves as a web buffer if the line downstream must stop for any reason—the accumulator can release web, giving the line a few seconds to restart without breaking the web. Many hot melt coating lines incorporate an accumulator after the unwind as standard equipment, regardless of splicing method.
Integration with coating line controls: The turret unwind and splicing system must be fully integrated with the line PLC to coordinate splice timing, tension control, and speed matching. A typical sequence: (1) The line PLC sends a “splice request” to the unwinder when the active roll diameter reaches a threshold. (2) The unwinder system initiates the splice sequence, including filling the accumulator (if zero-speed) or accelerating the new roll (if flying splice). (3) After the splice is complete, the unwinder sends a “splice complete” signal to the line PLC. (4) The line PLC logs the event, including the splice position (using an encoder count) so that downstream processes (slitting, inspection) can identify the splice and optionally reject that section. For quality-critical products, the splice is automatically marked (e.g., by a spray marker or by a deviation in the coat weight gauge data). The line may also have a “splice reject” system that cuts out the splice section during rewinding. In advanced systems, the splice is automatically removed by a slitter-rewinder that detects the splice using a sensor and makes a butt splice, leaving no splice in the finished roll. The use of automatic splice turret unwinds is standard on high-speed hot melt coating lines for labels, tapes, and nonwovens. By investing in turret unwinding with automatic splicing, manufacturers achieve truly continuous production, maximizing output and minimizing waste.
