Shown here is a high-speed slitter/rewinder with automatic features. In order to deliver defect free finished rolls, companies have traditionally inspected the material on the slitter/rewinder by stopping the machine, cutting out defects and begin winding again. Every stop/restart affects the roll build-up negatively and ultimately reduces the finished rolls quality. A slitter/rewinder should only stop for a product, finished roll and unwind roll change.
Adding Inspection Machinery
To reduce down time and increase productivity, companies have been adding inspection machines to the process, before laminating and slitting. Any print defect recorded on a printing press is taken out on this separate inspection machine, cleaned and forwarded to the laminator/coater or slitter without defects. This adds additional equipment in the total process, but guarantees the material will have no defects as it moves on to the following converting phase. With this inspection machine, the laminator will not laminate defect material and the slitter down time will be drastically reduced with improved finished roll quality.
Inspection machines with auto reverse winding and/or 100 percent inspection cameras are therefore a valuable tool and necessary for zero returns and increased productivity.
Converters historically align themselves with long run orders; improvements are geared towards high volume production to be as efficient and profitable as possible. Today’s technologies allow to build high speed slitter/rewinders that can produce a large quantity of finished rolls, which in most cases, the downstream roll handling concept is unable to handle.
Slitter/rewinders with turret rewinding, auto-cut and transfer are trimmed to synchronize to the roll handling speed. In this case, the slitter/rewinder is no longer the bottle neck. Fully automatic roll packaging systems are available, which label each finished roll, wrap and palletize according to customer specification.
Slitter/rewinders for high volume orders and frequency are still needed, but the demand is slowly changing to allow flexibility, short runs and fast turn-around, influenced by orders for innovation, event marketing, low volume and end-of-life products. This requires that the slitter/rewinders are engineered to effectively manage flexibility and volume.
Varying Options for Choosing Unwind/Rewind
Selection of the right winding concept depends solely on the material type and thickness to be processed. The three basic concepts are center winding, center/surface winding and surface winding. All three are offered for any web width.
The most common and versatile slitter/rewinders for flexibility are cantilevered duplex slitter/rewinders with center winding differential rewind shafts. Adding options like auto knife positioning, auto finished roll closure, auto push-off systems, laser core positioning etc., greatly reduces down time and improves roll quality.
Duplex slitter/rewinders, also called secondary slitters, are offered up to a max web width of 2200 mm, above this width, slitter/rewinders with individual rewind stations are required.
Even with manual push-off of the finished rolls, a take-up stand or unloader should be considered to reduce down time. After the finished rolls have been pushed on the unloader, the operator loads the empty cores, attaches the web tails and initiates the next winding cycle. During the winding process the operator handles the finished rolls according to customer requirements, which can include weighing, labeling, wrapping and palletizing.
Special attention should be given to safety, operator friendliness and clean web path. An overhead web path from the unwind to the rewind section gives optimum access to the slitting section, avoids dust collecting platforms and makes web threading an easy task. To further improve cleanliness, hydraulically operated features like the lift-in system on unwind stands are replaced with electro/mechanic systems. Electric cabinets are integrated in the machine cabinet, which helps to reduce machine installation time and decrease the carbon foot print.
The center winding concept on duplex slitter/rewinders incorporate differential rewind shafts with individual friction elements to compensate for differences in material thickness which result in diameter differences of the finished rolls. The roll hardness is determined by the amount of air between each winding layer. Pneumatically adjustable lay-on rollers control the roll hardness.
The friction elements remain on the winding shafts during finished roll change and secure the rewind cores during winding. The rewind tension to each rewind roll is transmitted via air pressure through the winding shaft to the inside surface of each friction element by controlled pressure. This results in finished rolls with even tension across the shaft since pressure is transmitted evenly over the length of the shaft.
When processing material with high surface smoothness or large diameter differences, incorporating individual lay-on rollers that achieve independent contact for each finished roll can optimize the rewind quality.
Slitting Systems for Optimal Productivity
Slitting systems are directly tied to productivity, accuracy and set-up time for a slit width pattern change. The most economical slitting system is razor blade slitting in air or groove. Limitations are material type and thickness. When razor slitting cannot be used, shear slitting needs to be considered. Depending on material type and thickness, several shear slitting concepts are offered, such as wrapped or tangential web path, individual knife holders on a common bar with collective pneumatic side pressure or individual pneumatically controlled knife holders. The latter provide the best slitting edge since the side pressure is individually adjustable on each holder.
Automatic knife positioning systems are the solution to improve productivity, accuracy and set-up time. Further, faster set-up time increases production capability, improves flexibility and optimization, and reduces exposure to hazards. Accuracy improves slitting knife life time and reduces rejects and scrap.
Integration of automated slitting system is available for production management systems. It is possible to directly transfer slit width patterns from the production scheduling system to the automated slitting system. Automated slitting systems eliminate human error during manual slitter setups due to mistakes and inconsistent measuring techniques. Direct transfer further eliminates the possibility of inadvertently entering the wrong values into the automated slitting system when copying them from a printed form. The automated slitting system is a key component for integrating production scheduling with slitting, winding and subsequent processes to achieve maximum benefit.
Among the articles in the April 2020 issue of Flexible Packaging Magazine, find out what the Head of Sustainable Packaging Coalition is saying about the prospects for packaging’s role in improving the environment, read this month's Roundtable on extrusion equipment, and much more!