A METHOD AND A DEVICE FOR REMOVING BROKE IN A PLANT FOR DRYING OF A WEB-FORMED MATERIAL TECHNICAL FIELD The present invention relates to a method when cleaning, after a web break or the like, in a plant for drying of a web-formed material, preferably a pulp web or a paper web, comprising blow boxes arranged in a plurality of drying decks. The web-formed material is floating, in the drying deck, above lower blow boxes that, at their upper side, blow out hot process air towards the web-formed material, in order to dry the material. Between the drying decks there are turning rolls, against which the web-formed material is pressed by the tension in the web only. The web-formed material is pulled through the drying plant with the aid of a driven pair of rolls at the outlet. The turning rolls arranged between the drying decks are freely running during normal operation, but are provided with drives that are used, for example, when threading through the plant.

The present invention also relates to a device for carrying out the method.

BACKGROUND ART Web-formed materials, such as paper or pulp, are usually dried either in a contactless manner by blowing hot air towards the web-formed material or by contact with heated surfaces, primarily cylinders. In cylinder drying of a web-formed material, for example paper, the web-formed material is heated by heated cylinders against which the web-formed material is pressed by the web tension and/or with the aid of a felt or a wire.

In contactless drying, the web-formed material is usually moved back and forth in a plurality of drying decks, floating above lower blow boxes that, at their upper side, blow out hot process air towards the web-

formed material, in order to dry the material. The web- formed material is pulled through the drying plant with the aid of a driven pair of rolls, or the like, arranged at the outlet of the drying plant.

Between the drying decks, the web-formed material changes its machine direction over the turning rolls, against which the web-formed material is pressed by the tension in the web only. During normal operation, these turning rolls are freely running. However, the turning rolls are provided with a drive system that is used, inter alia, when threading upon start-up.

One prerequisite for the normal driving to function through the whole drying plant is that the web is continuous from the inlet to the outlet. This prerequisite ceases to exist when the web breaks, and since currently used drying plants are often very large, hundreds of metres of the web-formed material may remain in a drying plant after a web break. Only that part which is between the point of the break and the outlet may be pulled out by a pair of rolls at the outlet.

All drying of paper or pulp entails discharging large quantities of steam from the material. To create a tolerable working environment and to save energy as far as . possible,, the drying-plants. are. therefore, enclosed. in casings of, for example, insulated panels, referred to below as housings, that are almost completely closed and where supply air and exhaust air are controlled such that any leakage through the openings of the housing, inter alia when feeding the paper web, or the like, in and out, passes from the outside and inwards.

When removing broke, in this context called cleaning of the drying plant, after for example a web break, this housing is, of course, an obstacle and conversely the housing must be adapted such that cleaning is possible at all and that manual cleaning may be performed in such an efficient and time-saving manner as possible.

The normal drive ceases when the web breaks and the web no longer has any contact with the driven pair of rolls at the outlet, and since currently used drying

plants are often very large, a web break may result in an extensive, time-consuming and trying cleaning operation, partly in a warm and moist environment.

Attempts at gripping the leading edge or the trailing edge by mechanical means, in the case of a rupture, usually only result in the web breaking at some additional locations, often in rather small fragments.

One method used is to arrange, on a lifting platform (balcony), a driven pair of rolls or a driven roll with contacting support wheels, and to use this so-called broke removal nip to pull out the web-formed material from the drying plant. However, for practical reasons this so- called broke removal nip must be placed at that edge of the lifting platform that is located furthest away from the housing of the drying plant, and this necessitates pulling the web manually a distance corresponding to the width of the lifting platform perpendicular to the wall of the housing. This is difficult considering the width and insufficient strength of the web since the web is in reality only accessible at its edge portions. The work may also be unpleasant because the web is wet and hot.

.. OBJECTS. OF THE INVENTION It is a main object of the present invention to offer a time-saving method for cleaning, after a web break or the like, in a plant for drying of a web-formed material.

It is a second object of the present invention to offer a method with a better working environment when cleaning, after a web break or the like, in a plant for drying of a web-formed material.

It is a third object of the present invention to offer a reliable device, with low investment costs, for cleaning, after a web break or the like, in a plant for drying of a web-formed material.

It is a fourth object of the present invention to offer a method for cleaning, after a web break or the like, in a plant for drying of a web-formed material that may be

used, without considerable rebuilding, in already existing drying plants.

In addition, it is an object of the invention to suggest a device suitable for use when carrying out the method.

SUMMARY OF THE INVENTION The present invention relates to a method when cleaning, after a web break or the like, in a plant for drying of a web-formed material, preferably a pulp web or a paper web, comprising blow boxes arranged in a plurality of drying decks. The web-formed material is floating above lower blow boxes that, at their upper side, blow out hot process air towards the web-formed material, in order to dry the material. Between the drying decks the web-formed material changes its machine direction when passing over the turning rolls, which are freely running during normal operation but which are driven during, for example, threading, against which the web-formed material is pressed by the tension in the web only. The web-formed material is pulled, during normal operation, through the . drying plant with the aid of. a driven pair ofirollswor the like, arranged at the outlet.

In the method according to the invention, an opening is made in a housing enclosing the drying plant, such that at least one turning roll becomes accessible, and a press roller, a press wheel, or the like, is applied such that the web-formed material is pressed against this turning roll. Thereafter, the web-formed material is fed forwards by running the drive system of the turning rolls at a low speed, and the web-formed material is fed out of the housing through the opening.

The present invention also relates to a device for carrying out the above method in a drying plant, with a housing that completely or essentially completely surrounds the drying plant.

The device comprises at least one hatch, or the like, in the housing, through which hatch at least one turning roll is accessible and at least one press roller, press wheel, or the like, is arranged such that the web-formed material, with the aid thereof, may be pressed against the accessible turning roll.

GENERAL DESCRIPTION OF THE INVENTION The present invention thus relates to a method and a device when cleaning, after a web break or the like, in a plant for drying of a web-formed material, preferably when drying a pulp web in a dryer with an air-borne web. The drying of the web-formed material takes place at least substantially inside a housing that completely or essentially completely surrounds the drying plant.

In known methods for removing broke after a web break, the web must be pulled manually over longer or shorter distances. This is both heavy and tiresome.

According to the present invention, it is therefore suggested instead to utilize the system, present in the drying plant, for driving the turning rolls for feeding the web broke forward. However, success cannot be achieved by merely setting the turning rolls in motion since the web is no longer pressed against these by the web tension.

However, this can be achieved by making an opening in the housing, in one of the walls thereof, so that at least one turning roll becomes accessible. The width of the opening must exceed the nominal width of the web.

A press roller, press wheel, or the like, is applied through the opening, such that the web-formed material is pressed against the accessible turning roll. It is advantageous to use several press rollers, press wheels or the like, but the expression"roller"is used to cover even elements as long as the width of the web and it is within the scope of the invention to use one single press roll essentially of the same length as the turning roll.

It is, of course, important that the opening be chosen so as to be adapted to the position of the web break so that the desired forward feed can be performed in an efficient manner. The application of the press roller or the like is advantageously performed manually by one or more operators, but may also, within the scope of the invention, be performed by mechanical devices, for example by means of compressed-air cylinders.

Thereafter, the web-formed material is fed forward by running the drive system of the turning rolls at a low speed. By the application of the press rollers or the like, a sufficient contact force between the turning roll and the web may be obtained, permitting the web to be pulled forward. At the same time, the web-formed material is fed out of the housing through the opening.

A lifting platform is advantageously arranged adjacent to the housing, so that operators may be lifted to the relevant level for performing the cleaning operation. By designing the lifting platform so as to create a space between the wall of the housing and the lifting platform, the broke, the web-formed material remaining in the plant, may be allowed to fall essentially straight down close to the housing. There, it can be .. easily.. taken. care of. in. spite of the... fact that its length may be considerable.

When required, the method is repeated at two or more openings.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail with reference to the accompanying drawings, wherein Figure 1 schematically shows a detail of an embodiment suitable when using the method according to the invention; Figure 2 schematically shows how an operator feeds out broke from a drying plant according to the proposed method;

Figure 3 schematically shows a detail of a second embodiment suitable when using the method according to the invention; Figure 4 schematically shows how an operator feeds out broke from a drying plant according to a third proposed em- bodiment; Figure 5 schematically shows a detail of a forth embodiment suitable when using the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 schematically shows part of a drying plant 1 for papermaking pulp. The drying plant 1 is enclosed in a housing 2 comprising a wall 2a. The wall 2a is provided with hatches 3 to enable access to the turning rolls 4 of the drying plant 1 through openings 3a. At the hatches 3, above the turning rolls 4, there are press rollers 5 articulately suspended from a support 6 against the wall 2a of the housing 2 above the hatches 3. With mechanical springs 7,. the press. rollers 5 are given-a position. of rest somewhat raised from the turning rolls 4.

The press roller 5 is fixed to a tubular element 8 that, via a transverse element 9 and a joint 10, is connected to the support 6. The tubular element 8 is adapted to cooperate with a rod 11 or the like to extend the lever and hence increase the force by which the press roller 5 can be pressed against the turning roll 4 and the web of pulp 12 resting thereon.

Figure 2 shows an operator 13 standing on a lifting platform 14 with a floor 14a and a railing 14b. The operator 13 lifts the rod 11 upwards and hence presses the press roller 5 against the turning roll 4 such that the pulp web 12 is fed out through the opening 3a. Between the wall 2a of the housing 2 and the floor 14a of the lifting platform 14, there is a space 15, through which the broke

12a may be fed down. A partition 16 prevents the operator 13 from inadvertently treading into the space 15.

Figure 3 schematically shows part of a drying plant 1 for pulp corresponding to that shown in Figure 1. The difference is that the press roller 5 is fixed to one end of an element 8b that, at its other end, is influenced by a compressed-air cylinder 31 suspended from a support element 36 fixed to the wall 2a of the housing somewhat above the support 6.

Figure 4 shows, like Figure 2, an operator 13 standing on a lifting platform 14 with a floor 14a and a railing 14b. However, in Figure 4 the operator 13 is provided with a movable device llc, at one end of which the press roller 5 is attached. With the movable device llc, the press roller 5 is pressed against the turning roll 4 by using the upper edge of the opening 3a, or a support arranged adjacent thereto, as a point of support. The movable device 11 is provided with support lugs 46 to enable the position of the press roller 5 to be fixed.

Figure 5 schematically shows part of a drying plant 1 for pulp corresponding to that shown in Figure 1 and Figure 3. The difference is that the press roller 5 is fixed to one end of a first arm 59 that, at its other end, is connected to. a joint 10 at a support 6. The press roller 5 is further, with a second arm 57 connected to the piston of a compressed-air cylinder 51 suspended in the wall 2a of the housing.

The mode of operation of the invention will now be described with reference to Figure 1 and Figure 2.

When a web break occurs, the latter part of the pulp web 12, the one nearest the outlet, is automatically pulled out of the housing 2, whereas the earlier part, the one nearest the inlet, remains. Since the outlet is usually located furthest down, this means that the upper part of the drying plant 1 must be cleaned of remaining pulp web.

With the aid of the lifting platform 14, operators 13 are lifted level by level and inspect the drying plant 1 by opening hatches 3 at successively higher levels.

When the drying deck is reached, at the level where the web 12 remains above the turning roll 4, the press rollers 5 are applied to the turning roll 4 and the web 12 is fed out through the relevant opening 3a. This can be made by first cutting off the web 12 at the turning roll 4, which implies that the remaining part of the web 12 that is situated below the level in question must be removed manually, or by feeding out part of the web 12, folded twice, through the opening 3a. The same method may possibly be applied to the other end of the drying plant 1 for removing what remains after the cutting of the web 12.

The broke 12a is allowed to fall down through the space 15 and is taken care of, in an appropriate manner, at the floor of the hall.

ALTERNATIVE EMBODIMENTS The invention is not, of course, limited to the embodiment described above, but may be varied in a plurality of ways within the scope of the the. following claims.

Thus, for example, the proposed method may be combined with a conventional broke removal nip, placed on that side of the lifting platform 14 that faces away from the housing 2, on the wall 14b. In this case, the press rollers 5 proposed are used only for feeding the web forward, in a simple and reliable manner, the distance that is needed across the lifting platform 14.