The surface of rolls used in on-line equipment on paper machine lines and in separate off-line equipment is worn, fouled and damaged as the rolls are pressed against the fibre web passing over their surface. For this reason, the roll surface requires periodical cleaning and abrasion.

Inpurities fouling the rolls, such as paper chaff and specks of coating agent, are mostly removed by means of"doctor blades", whose scraping blade is pressed against the roll surface by means of pneumatic or hydraulic loading or deloading devices. Despite continuous cleaning of the roll, there will be impurities adhering to the roll surface and deteriorating the performance of the equipment, and this will require periodical cleaning of the rolls by removing the rolls completely from the apparatus with a view to maintenance operations.

During the calendering of a fibre web, the polymer coating located in the roll nip between a heated hard thermo roll and a polymer-coated roll will frequently be exposed to local overheating, resulting in overheated points on the polymer coating.

Due to these overheated points, the quality of the polymer coating may deteriorate rapidly, and the overheated points must thus be rapidly eliminated by cooling the polymer roll, which is performed by opening the roll nip or by cooling the polymer roll under external cooling, or by providing efficient internal or external cooling of the thenno roll. Internal cooling of a thermo roll is most frequently provided by means of internal coolant circulation within the thermo roll, whereas external cooling of the polymer roll is provided by atomising water onto the border areas of the polymer roll, which are susceptible to overheating, or by driving the fibre web with over-width. Current roll cooling methods provide adequate cooling of the roll in most cases, however, with advanced calendering methods and apparatuses, new cooling methods will be necessary in order to allow the optimal cooling manner to be chosen for each calendering method. Due to efforts to raise the temperatures of thermo rolls above 200°C, there has been a strong demand for new roll cooling methods recently.

As rolls are pressed against the fibre web, their surface wears gradually, entailing an uneven surface and deteriorating the paper quality. For this reason, rolls require periodical abrasion for irregularities to be eliminated. Rough roll surfaces are also caused by raised calendering temperatures, causing roll roughness to be more rapidly increased. Surface roughness is a result of irregular heat transfer from the inside of the roll to the roll surface, resulting, in turn, in irregular heat expansion of the steel/cast iron surface of the roll. There have been efforts to resolve the latter problem by increasingly adopting induction heating of rolls by means of an external energy source in high-temperature calendering. With such heating, there will be no heat transfer at all, or a minimum of heat transfer from the inside to the surface of the roll. However, this heating manner tends to entail the problem of cooling a hot thermo roll during a paper grade shift or unintentional shutdowns (in the case of a broken fibre web, for instance). Cooling the roll by switching off induction heating totally is too slow an operation, and providing a full-scale oil or water circulation within the roll for the mere purpose of cooling the roll is not cost-effective.

The purpose of the invention is to eliminate prior art shortcomings. Thus, the principal purpose of the invention is to achieve a combined method of cleaning and cooling rolls. The invention has the additional purpose of achieving a method of cleaning and cooling rolls, which allows for calendering at high temperatures. The invention has the special purpose of achieving a method enabling cooling of a thermo roll equipped with external induction-heating means.

The arrangement of the invention achieves the purposes mentioned above.

The invention relates to an arrangement as defined in claim 1, for instance, for cleaning a surface of a roll.

In the arrangement of the invention, the roll is cleaned by means of cleaning means by bringing the cleaning means into contact with the roll surface. The cleaning means having an elongated frame for cleaning the roll is disposed to rotate about its frame, and a liquid or paste-like cleaning agent is dosed on the roll surface or on the cleaning means. The roll surface can also be cooled by means of said cleaning means.

A roll to be cooled in a preferred embodiment of the invention is a heated steel roll, which is preferably equipped with induction-heating means outside the roll, the cleaning means being a roll or a brush.

In a second preferred embodiment of the invention, the frame of the cleaning means consists of two aligned frame rolls, which are adapted to rotate an elastic endless belt. The endless belt has a thickness of approx. 5 to 10 mm, and it is made of a soft material, such as a rubber and/or polymer mixture and/or abrasive components.

The invention is based on the fact that a given area of the roll is cleaned with a cleaning means having an elongated frame, which also enables cooling of the roll by introducing a cooling agent containing cooling components, such as water, between the cleaning means rotating about its longitudinal axis and the roll surface.

This achieves the advantage of allowing, if necessary, not only cleaning but also cooling of the roll surface with the arrangement of the invention. Such a manner of cleaning/cooling a roll is especially suitable for a roll equipped with induction- heating means outside the roll, since there will be no need to provide the roll with internal cooling means nor to switch off the induction heating intermittently when calendering interruptions are called for. If the invention implements cleaning means whose frame consists of two aligned roll frames, which are disposed to rotate an endless belt, this achieves the additional benefit of allowing the roll to be abraded by means of the arrangement of the invention. For roll abrasion, a paste-like agent containing components for abrading the roll is used as the cleaning agent. The latter cleaning means achieves the further advantage of performing cleaning of the roll surface owing to the soft and/or coarse endless belt, so that this cleaning means can be used for cleaning polymer rolls, for instance.

The invention is illustrated in greater detail below with reference to the accompanying drawings.

Figure 1 is a schematic view of an embodiment of the arrangement of the invention applied to a multinip calender. The multinip calender is shown viewed directly towards the calender end.

Figure 2 is also a schematic view of a second embodiment of the arrangement of the invention adapted to the cleaning of an individual roll. The roll is viewed directly towards the end.

Figures 1 and 2 show two different embodiments of the arrangement of the invention.

Figure 1 shows only the portion of the set of rolls 5 of a multinip calender using the arrangement 1 of the invention for cleaning and cooling the roll 4. The figure shows only the parts of the multinip calender that are essential for comprehending the invention. Regarding the particularised design of the multinip calender, we refer to FI patent specification 96334, for instance. The portion of the set of rolls 5 of a multinip calender shown in the figure comprises four rolls 4, which may be e. g. idle rolls of a set of rolls 5, which are equipped with load-compensating means. The second and fourth roll 4; 4", 4""are steel-coated thermo rolls, the former thermo roll 4"being heated with external induction-heating means (not illustrated in the figure). For the detailed design of the induction-heating means, we refer to the prior art disclosed in the reference mentioned above, for instance. The first and the third roll 4'and 4"', in turn, are polymer-coated rolls. The fibre web W passes through the roll nips N; N1, N2, N3 between the polymer rolls 4', 4"'and thermo rolls 4", 4""while its surface is being profiled. Before passing from one roll nip to the next, the fibre web W passes through output rolls 6 beyond the line L of the set of rolls 5.

Outside the line L of the set of rolls, the combined roll cleaning and cooling means 2; 21 of the invention is disposed adjacent to the thermo roll 4; 4", the means being referred to below as cleaning means for the sake of simplicity. The cleaning means 2; 21 has an elongated frame, from which small bristles not shown in the figure protrude. During calendering, the cleaning means 21 is not in contact with the thermo roll 4; 4". By contrast, during a path break or shift of paper grade, when it is desirable to cool the thermo roll 4; 4", a suitable cleaning liquid or liquid mixture A, such as water, is supplied onto the cleaning means 2; 21 rotating about its longitudinal axis in contact with the roll surface. The liquid is fed either directly onto the roll to be cleaned or, as in the illustrated embodiment, onto the bristles of the cleaning means 2; 21. The cleaning liquid is preferably finely atomised in accurate doses, so that it cools a maximal area. The cleaning means 2; 21 cleans and cools the surface of the roll 4; 4", and the induction heating of the roll needs not to be switched off intermittently. The cleaning means 2; 21 is attached to the frame of the multinip calender or to a separate external raising platform (not illustrated in the figure). To enhance the cooling action of the arrangement 1, cooling components can be added to the cleaning liquid, such as water, for instance.

Figure 2 shows a second embodiment of the arrangement 1 of the invention. The cleaning means 2; 22 of the invention is in contact with the surface 4a of a chilled roll 4. The chilled roll 4 is either heated or unheated. The frame 2a of the cleaning means 2; 22 has two parts, the frame parts 2a consisting of identical frame rolls 2a' and 2a"separated by a space. Said frame rolls 2a are disposed substantially in alignment with each other and with the longitudinal axis of the chilled roll 4. The soft endless belt 2; 2b circulates through both of the frame rolls 2a; 2a'and 2a; 2a".

The frame rolls 2 are preferably movable relative to each other for tightening and loosening of the belt 2b. During relative shifts of the frame rolls 2, the directions of the longitudinal axes of said rolls will remain roughly the same in order to maintain the tension of the endless belt 2b constant over the entire length of the cleaning means 2; 22. When the frame rolls 2; 2a are moved apart, the endless belt 2b running between them is tightened, and when they are approached, said endless belt is loosened. The belt material is a soft mixture of polymer and rubber, so that the belt 2b adapts to the curvature of the roll surface 4; 4a while being in contact with said roll surface. When it is desirable to clean the roll surface 4; 4a, the cleaning means 2; 22 is brought into contact with the surface 4a of the roll 4 and the endless belt 2; 2b is tightened to appropriate tension by shifting the frame rolls 2a relative to each other. A relatively small amount (0.01 to 0.001 mm thickness on the belt) of appropriate cleaning agent A is supplied onto the endless belt 2; 2b rotating about the frame rolls. The frame rolls 2a and the endless belt 2b rotating about them are simultaneously rotated at high speed. Partly under the effect of the cleaning agent A, and partly owing to the friction between the roll surface 4; 4a and the endless belt 2; 2b, the surface 4a of the roll 4 is efficiently cleaned. If abrasion of the surface 4a of the roll is also desirable, abrasive components are added to the cleaning agent A. The cleaning agent A is then preferably a paste-like abrasive. The surface 4; 4a of the roll can also be cooled by means of the cleaning means 2; 22 mentioned above; in that case, the cleaning agent A preferably contains cooling components and the frame rolls 2a of said cleaning agent are rotated about their longitudinal axis at a slower speed than usual.

The cleaning arrangement 1 illustrated in figure 2 is usable alone or together with a doctor blade for cleaning the roll surface; the cleaning action of a doctor blade is not usually sufficient for complete cleaning of the roll surface, other cleaning methods being required in addition to the doctor blade. The embodiment of the invention shown in figure 2 above can be used both with the roll 4 being stationary, during a paper grade shift in the fibre web, for instance, or with the roll rotating. The frame

rolls 2a'and 2a"forming the frame 2a of the cleaning means 2; 22 of the roll in figure 2 preferably have a length shorter than that of the roll 4 to be cleaned, and they are movable in the longitudinal direction of the roll to be cleaned, so that said roll 4 can be cleaned over its entire length. The cleaning means 2; 22 has a length shorter than that of the roll to be cleaned with a view to a lightweight and easily movable design of the cleaning means. The cleaning means of figure 2 has a simple and thus economical design.

Only a number of embodiments of the arrangement of the invention has been described above, and it is obvious to those skilled in the art that the invention can be implemented in many other ways as well, without departing from the scope of the inventive idea defined in the claims.

Consequently, the cleaning arrangement 1 of the invention can be implemented in the cooling/cleaning/abrasion of many types of calendering rolls. Besides the heated chilled rolls mentioned above, unheated steel-coated or cast iron-coated rolls and polymer rolls and rolls equipped with a soft roll coating in general are potential objects of application. Unheated rolls with a hard steel/cast-iron coating are used in machine calenders, whose calender nip is formed between two hard steel or cast- iron rolls. Especially the cleaning means of figure 2 can be used also for cleaning the surface of rolls with soft coatings, since the cleaning means does not damage the roll coating owing to the elastic endless belt used in the cleaning means. Rolls having a soft coating are used in calendering in multinip calenders and long-nip calenders, such as shoe calendars, among other things. In shoe calenders, the calendering nip is formed between and endless belt having a soft coating and rotating about the shoe roll and a heated roll having a hard steel coating. Rolls with a soft coating are also used in"soft calenders", in which at least one of the rolls forming the roll nip is a roll having a soft roll coating.

The cleaning means of the invention can be applied also to press apparatuses for dewatering the fibre web. In such press apparatuses, water is removed from the press nip, which most frequently is formed between the hard roll and the opposite roll having a soft coating. A roll with a soft coating is often provided with pressurising means and a press shoe, the endless belt rotating about this press shoe.

The invention is also applicable to cleaning of rolls used for transferring cleaning agent onto the fibre web, given the usually insufficient cleaning of rolls by means of conventional doctor blades. Especially the embodiment of the cleaning means in figure 2 has adequate efficiency for this purpose as well.