Paper Roll Handling
Objective and General Description of Roll Handling
The objective of roll handling is to prepare the finished paper rolls for shipment in such a way that they arrive at the end user in the best possible condition. The mill can contribute to this aim by two means, i. e. by very gentle internal transportation and by thoroughly wrapping the customer rolls so as to protect them from dangers to which they are exposed during external transportation on account of frequent loading and unloading actions, varying temperatures and humidity changes.
22.214.171.124 Wrapping Material
There are two different kinds of wrapping material, stretch film and packaging paper. Shrink film is hardly ever used for wrapping paper rolls, since the creases formed on the faces of the wrapped rolls do not allow one to store the rolls in a vertical position. Shrink wrap is only found in special applications, e. g. for holding finished paper rolls on pallets.
Stretch wraps offer the advantages of uncomplicated wrapping machinery and low-cost material. The drawbacks are high UV sensitivity, slackening of the stretch wrap and vulnerability to dirt. Furthermore, smooth plastic wrapped rolls are more likely to fall off the forklift trucks, particularly at low temperatures and due to stretching, even slight tears caused by forklift handling can rapidly turn into seri¬ous damage. Some of the drawbacks can be avoided by wrapping plastic covered rolls with paper as well. The simplest way to do this is with crepe-like packaging paper, using the same wrapping equipment as for stretch film.
Packaging paper is the classical and most commonly used wrapping material for paper rolls. It offers optimum protection for long transport distances and storage times. Packaging paper mainly comprises kraft or test liner sandwich papers with a PE lining.
8.2 Roll Handling
126.96.36.199 The Different Types of Wrapping Machines
188.8.131.52.1 Conventional Wrapping Machines using Paper as Packaging Material
These machines basically consist of a two-drum winding cradle wherein the roll to be wrapped is rotated, a crimping device, a header press and a number of unwind stations for packaging paper rolls (Fig. 8.10). The wrapping method employed is the so-called “wide” method, i. e. the width of the packaging paper is selected according to the width of the roll to be wrapped plus a crimp overhang. Depending on the width spectrum of the rolls to be wrapped, a series of unwind stations with packaging rolls having a different width is necessary.
The wrapping process is as follows: Before the packaging paper is applied, the roll is furnished with inner board header disks to protect the roll faces from possi¬ble glue and damage resulting from edge crimping. However, these inner header disks do also contribute to a face protection during later transportation. Then the packaging paper, having a width which corresponds to the width of the paper roll (see above), is wrapped one to four times around the body of the roll. The wrapping can be further strengthened by gluing the outer layers of the packaging paper together, either with cold or hot glue. Thereafter the overlap is crimped. Finally PE-coated test liner outer header disks are pressed on top of the inner header disks and the crimped overlaps. These outer header disks are normally fixed without any additional glue, just by pressing them against the inner header disks once the PE-coating has been plasticized.
Conventional wrapping machines produce excellent wrapping. The only disad¬vantages of these traditional machines are that they require a lot of space for the multitude of unwind stations and that the mill has to store a lot of packaging paper rolls of different widths. These disadvantages are eliminated with the wrapping machines described below.
184.108.40.206.2 Offset Wrapping Machines using Paper as Packaging Material
Theses machines are similar to the above described conventional machines in so far as the packaging paper is fed to the roll to be wrapped in a straightforward way. The main difference is that two or more packaging paper webs are combined into one broad sheet (Fig. 8.11). Thus, rolls whose width exceeds the width of the availa¬ble packaging rolls can be wrapped effectively with a reduced number of unwind stations.
220.127.116.11.3 Spiral Wrapping Machines using Paper as Packaging Material
The spiral wrapping machines employ a narrow standard width packaging paper strip (e. g. 500 mm) for wrapping. This strip is wound at a sharp angle around the roll body. The desired number of layers is automatically obtained by correctly se¬lecting the angle or degree of strip overlap. The roll edges are additionally wrapped at right angles with a constant overlap of approx. 150 mm (Fig. 8.12). Spiral wrap¬ping is suitable for all paper roll sizes and provides a wrapping that is even stronger than classical wrapping, since the glued spiral layers closely encircle the roll body and since the edge strips offer additional protection for the vulnerable edges of the paper roll. Spiral wrapping is not limited to any particular roll length. A comparison of Figs. 8.13 and 8.14 shows that the space required by a spiral wrapping machine is much lower (27 m2 vs. 70 m2, i. e. approx 40 %) than the space needed for a traditional wrapping machine.
8.2 Roll Handling
18.104.22.168.4 Wrapping Machines using Stretch Film as Packaging Material
These machines consist of a stretch film dispenser and a two-drum cradle wherein the roll to be wrapped is rotated. The winding cradle can additionally be mounted on a turntable. Accordingly, there are two different wrapping methods: exclusively radial wrapping (Fig. 8.15) or a combination of radial and axial wrapping (Fig. 8.16).
Fig. 8.16 Radial and axial stretch wrapping (source: Voith).
For radial wrapping of the rolls, the stretch film is guided into the nip between the rotating roll and the first carrying drum and is subsequently wrapped in a helical manner around the roll. If the two-drum cradle is mounted on a turntable, the roll can also be wrapped axially by rotating the turntable.
Rolls wrapped exclusively radially must be protected by header disks made of boxboard or corrugated board. These headers must be of exactly the same diameter as the paper roll, since they are only held on by about 100 mm of stretch overlap around the roll edges. Such end covers enable trouble-free vertical stacking of the wrapped rolls.
In contrast to exclusively radial wrapping, axial wrapping delivers hermetically sealed rolls, however, since the face covers are rather irregular, axially wrapped rolls are inconvenient for upright storage.
Roll-conveying systems move the paper rolls from the winder discharge area via the wrapping machine to the roll up-ending device in the mill’s warehouse. Natu¬rally, layouts of the roll-conveying systems differ from mill to mill but the basic components are always the same. These are:
. • Segmented cushion stop lines (Fig. 8.17).
. • Belt conveyors (Fig. 8.18). Belt conveyors have been somewhat superseded by slat conveyors, since they have a tendency to damage the paper roll because of micro-motions within the belt
8.2 Roll Handling
. • Slat conveyors (Fig. 8.19).
. • Carousel conveyors (Fig. 8.20).
. • Turntables (Fig. 8.21).
. • Lifts (Fig. 8.22).
. • Sorting decks (Fig. 8.23).
. • Up-enders (Fig. 8.24).
Fig. 8.20 Carousel conveyor (source: Raumaster).
Fig. 8.21 Turntable (source: Voith).
8.2 Roll Handling
Fig. 8.23 Sorting deck.
The wrapping and conveying processes including roll identification, marking, weighing and labeling as well as roll tracking are managed by automated systems based on computers and electronic devices. The majority of the functions are car¬ried out automatically so that the operators only have to supervise the processes.