Holik H. (ed.) Handbook of Paper and Board

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8.1.4

Automation/Operation

Modern winders are equipped with PC/PLC technologies. This allows high flex-

ibility in adjusting the winding parameters, such as tension, torque, nip load, to

the special requirements of the different paper grades. Furthermore, these technol-

ogies permit collection of all data of the winding process for advanced analysis of

the production process.

8.2

Roll Handling

8.2.1

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.

8.2.2

Roll Wrapping

8.2.2.1 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 Finishing392

8.2.2.2 The Different Types of Wrapping Machines

8.2.2.2.1 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.

Fig. 8.10 Conventional roll wrapping machine (source: Voith).

8.2 Roll Handling

393

8.2.2.2.2 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.

8.2.2.2.3 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 m

vs. 70 m

, i.e. approx 40 %) than the

space needed for a traditional wrapping machine.

Fig. 8.11 Overlap wrapping machine (source: Metso).

8 Finishing

394

8.2.2.2.4 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. 8.12 Spiral wrapping machine (source: Voith).

Fig. 8.13 Top view of a conventional

roll wrapping machine (source: Voith).

Fig. 8.14 Top view of a spiral wrapping machine

(source: Voith).

8.2 Roll Handling

395

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.

8.2.3

Roll Conveying

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

Fig. 8.15 Radial stretch wrapping

(source: Voith).

Fig. 8.16 Radial and axial stretch

wrapping (source: Voith).

8 Finishing

396

• 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. 8.17 Segmented cushion stop lines (source: Voith).

Fig. 8.18 Belt conveyor (source: Voith).

8.2 Roll Handling

397

Fig. 8.19 Slat conveyor

(source: Voith).

Fig. 8.20 Carousel

conveyor (source:

Raumaster).

Fig. 8.21 Turntable

(source: Voith).

8 Finishing

398

Fig. 8.22 Lift (source:

Voith).

Fig. 8.23 Sorting deck.

8.2 Roll Handling

399

8.2.4

Automation

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.

Fig. 8.24 Up-ender (source: Voith).

8 Finishing

400

Control Systems for Paper Machines

Rudolf Münch

9.1

Objective and General Terms of PM Control Systems

9.1.1

Objective

A typical paper machine has a few thousands remote or automatically controlled

functions like positioning systems, drives, valves and more than a thousand addi-

tional measurement devices to monitor the process and the condition of the ma-

chine. It is impossible for an operator to oversee all these devices without the help

of modern automation systems. For example, he is guided through the process of

starting the machine, and many control sequences happen automatically after a

“start” button is pressed and he gets detailed diagnostics if something fails. Com-

puters are also used to maintain the quality standards, however the operator is still

needed to handle the exceptions and to decide how to proceed when something

fails.

9.1.2

Explanation of Terms

Control systems for paper machines can be categorized in different ways. The

following terms are those most commonly used :

• MCS, machine control system:

Discrete logic, safety interlocks, sequential controls.

The MCS ensures that the machine attendant can safely operate the machine

using control desks with pushbuttons, switches, status lamps, etc. Many of these

functions are usually also available on screen displays. Examples of MCS func-

tions are movements of rolls, blades or other machine parts with involvement of

limit switches or other safety interlocks.

MCS functions usually require fast reaction by the MCS. For example: If a ma-

chine part reaches a limit switch during a controlled movement, it usually has to

Handbook of Paper and Board. H. Holik (Ed.)

ISBN: 3-527-30997-7

401