Slitter winder
A winder is used to unwind rolls of flat material (plastic, paper, metal), cut them into longitudinal strips and then individually wind them up on winding stations or winding axles. Roll cutting machines are used in the plastics processing industry, the paper industry and metal processing. They often stand behind printing machines , coating machines , laminating machines , film production plant , paper machines or rolling mills. These machines use the largest possible working widths to optimize performance. The end product then has to be cut to a smaller width.
Unwinding
The unwinding takes place either from a winding axle or an axleless unwinding. Loading an axle-less collection is relatively easy. The unwinding arms with their clamping heads are opened to a width that is greater than the width of the roll. Then the unwinding arms are lowered or raised until the clamping cones are flush with the sleeve. Then the arms are closed again centrally in order to introduce the clamping cones into the sleeve of the roll to be unwound. The tensioning of the clamping cones should always be carried out centrically to ensure a good run-out of the roll. The conical tension occurs either through the axial movement of the unwinding arms or through springs that are pneumatically relaxed. After the core is tensioned, the roll lift lifts the roll from the floor so that it can rotate freely when the material is unwound.
The following picture shows such a shaftless unwind on a winder. The unwinding arms have no roll tensioned and are lowered and collapsed.
In order to ensure a straight cut, lateral controls are used on the unrollers. These scan either the edge of the material or a print line in order to align the roll axially in the correct position. These side controls react very quickly and allow unwinding at speeds of several hundred meters per minute.
It is important that the web tension in the material is as constant as possible during unwinding. This is achieved through a web tension control. Either a "dancer roller" or a pathless web tension measuring roller is used as a measuring element. The dancer roll can compensate for fluctuations in the web tension that can arise from non-round rolls or eccentric tensioning of the roll. A web tension measuring roller can often not compensate for these fluctuations and then only supplies an interrupted signal.
The web tension control adjusts the brake on the unwind. Since the diameter decreases during unwinding, the braking torque must be continuously reduced in order to maintain the constant web tension. With mechanical brakes, the braking torque is converted into frictional heat, which must be dissipated by air cooling or water cooling. Motors are also used on the unwind, which convert the braking torque back into electricity through regenerative braking. This current is fed back into the network or into the machine's electrical circuit and can be used again to operate the machine or the winder.
Cutting system
The cutting systems used in a roll cutting machine are blades, squeeze knives, scissors cut knives or even roller shear knives. In the cutting section, two edge strips are usually separated from the material web and sucked off or wound up. A scissor cut cutting section usually consists of a lower knife axis and an upper knife axis. Grooving knives and intermediate rings (spacer rings) are mounted on the lower knife axis. On the upper knife axis there are spring-loaded upper knives which are each mounted on an axially displaceable bush that can be fixed on the axis. The lower and upper knife axes are driven by the main machine drive. The lower knife axis drives the upper knife axis via a gear.
A silhouette cutting section can also be built into a cutting cassette. In a cutting cassette there is a storage for the upper knife axis and a separate storage for the lower knife axis. The drive usually takes place on the lower knife axis with an axial coupling. The drive to the upper knife axis takes place via the gear wheels. The gear on the Obermeister axle can be changed when the diameter of the upper knife has decreased due to grinding. The following picture shows a cutting cartridge with an upper and lower knife axis. The upper knives have the spring washers on the side.
A scissor-cut cutting section can also consist of a driven lower cutter axis and various pneumatic upper cutters. In this case, the upper knives are driven solely by the pneumatically generated friction pressure and the resulting friction force. To be able to decide whether a razor blade cutting section is suitable for cutting a material, a simple test with office scissors is sufficient. Any material that can be cut with scissors can also be successfully cut with a scissor cut section.
In the simplest version, a razor blade cutting section consists of two support rollers that guide and carry the material web and the razor blade holders arranged at an angle between them. In this case one speaks of mirror cut (slitting in the air). The following photo shows such a razor blade cutting section with razor blade holders and an oscillating device that moves the blades so that the cutting edge of the blade is not always cut at the same point. This device increases the life of the blades.
A razor blade cut can, however, also take place in a driven lower blade axis. Then the axis is equipped with grooved knives or grooved sockets into which the razor blades dip. Then one speaks of a groove cut. In order to increase the cutting performance and to reduce the wear and tear of the razor blades, an oscillation of the razor blades is often used.
The crushing knife cut usually consists of a hardened lower blade axis and one or more pneumatic crushing knives. The squeeze knives, sharpened to a point, sit in a squeeze knife holder. The knife is pressed against the hardened lower knife axis by an air cylinder on which the cutting pressure can be adjusted. The cut is made by penetrating and laterally displacing the material to be cut. Pinch knife cut is used especially for adhesive tapes. There, the displacement of the first displaced adhesive is suitable in order to avoid bleeding of the cut rolls. Bleeding is the term used to describe the lateral leakage of the adhesive from a cut and wound roll. Crimp knife cut is also sometimes used successfully on woven, non-woven, and rubber.
Rolling shear knives are cylindrically ground knife disks that are mounted next to each other. Rubberized ejector rings are arranged between the rotary shear blades. The cutting action takes place due to the shearing of the material to be cut in a cutting gap between the cutter disks. The cutting gap depends on the material thickness. Roll shear cut is used when cutting metallic foils and strips. It is used in particular for processing sheet steel as well as aluminum and copper foils.
Winding
The winding can be done with or without contact rollers. There are roll cutting machines which, depending on the type of material to be cut, wind the cut rolls on air axes, friction winding axes or on individual winding stations.
When winding up the cut webs of material, one or more contact rollers are required, depending on the number of cut rolls. These contact rollers are in contact with the rolls during winding and press the air out of the winding. This is particularly necessary at high speeds because a laminar air film forms on the web surface . This air film is pushed out by the contact roller at the point at which the web runs onto the winding. If too much air gets into the reel, the roll may run sideways or “telescope”. The contact pressure is adapted to the speed.
The manufacturing process of many materials causes a non-uniform thickness profile of the material web. In the case of plastic films that are produced as flat films or blown films , even small temperature differences in the manufacturing process can lead to fluctuations in thickness. In the rolling mill, a concave or convex thickness profile can form when producing aluminum or copper foils, depending on the position of the rolls. In the case of paper, an almost uniform thickness profile is usually achieved; here there may be fluctuations in thickness due to watermarks or other decorative elements.
Due to the irregularities in the thickness profile, when cutting such material webs, the lengths and thicknesses of the cut strips vary. This results in different sized winding diameters of the cut rolls during winding. Although all of the strips in the original roll appear to have the same diameter, after cutting and rewinding it turns out that the finished rolls have different diameters.
These different diameters require a "friction winding" when winding on a common axis. There are radial and axial friction axes, in which the individual roller is carried along by axially or radially adjustable sleeves by frictional engagement.
Alternatively, each strip can be wound up on its own winding station with its own drive motor. Through this, each winding receives its individual winding tension and its speed, which compensate for the thickness and length differences and the resulting differences in diameter.
Different drive methods are used for winding. The simplest method is circumferential wrapping. Here the roller is driven from the outside by a support roller or a drive belt. The most common winding method is center winding. Here the material is wound up from the center by a driven sleeve. An intermediate form is the combined center-circumferential winding. The winding station rests simultaneously on a driven support cylinder during winding.