Fibrous-web machine measuring roll and method for covering the fibrous-web machine measuring roll

The invention relates to a measuring roll of a fibrous-web machine according to the preamble of claim 1.

The invention also relates to a method for covering a measuring roll of a fibrous- web machine according to the preamble of claim 10.

For the part of prior art, we refer to FI specification 20055020 which describes a method for measuring nip pressure and/or pressure profile. In the method, a nip- forming roll is fitted with a pressure sensor under a cover layer which is protective and functions on top of the sensor, and the nip pressure delivers to the lower surface of the cover a deformation proportional to the nip pressure and the deformation compresses the sensor which responds to the deformation by generating an electric signal. The specification also describes a roll for measuring nip pressure and/or pressure profile, which roll is provided with a pressure sensor which is located under a cover layer which is protective and which layer functions as a spring and in which at least one cover layer is composed of a cold-curing polymer or composite. According to the specification, the sensor is protected by a cold-curing polymer cover and, on top of the sensor, there is one or more cover layers, when using two cover layers, the lowest one is provided with a groove for the sensor, whereby the first layer can be hot-curing as well. The specification describes an arrangement in which the lower cover, which is provided with the groove for the sensor, is of a relatively hard material or of a material having the same flexibility as the sensor itself.

For the part of prior art, we also refer to FI specification 20055019 which describes a method for measuring a cross-directional tension profile of the web

using at least one pressure-sensitive strip sensor placed spirally inclined into connection with the roll surface for measuring a force caused by the web, in which the active area or areas of the film functioning as the measuring sensor visit over the course of each revolution of the roll substantially completely under an overlap zone and in a substantially completely open space. From the specification is also known a roll for measuring a tension profile in which a spiral-like inclined pressure sensor strip is installed on the roll surface which makes contact with the web obliquely and which has co-directionally with the web a measuring range which is substantially equal to or shorter than the overlap angle of the web when the roll is used for measuring the cross-directional tension profile of the web. The specification depicts arrangements in which the sensor is under a protective layer, in which the sensor is installed in a protective groove or on the roll surface without a protective groove. As examples of the protective layer, a ceramic resin composite cover is mentioned.

As known from prior art, doctoring prevents the wrapping of the web around the roll in a web break situation and the dirtying of the roll surface. The doctoring can be implemented mechanically by a doctor blade trailing the roll surface or by a contact-free air-blow doctor.

However, the soft cover typically used in prior-art measuring rolls cannot be mechanically doctored and, on the other hand, when using the measuring roll in certain fibrous-web machine positions and/or when manufacturing certain fibrous- web types, such as tissue papers and boards, the surface of the measuring roll has to be mechanically doctorable in order to keep the roll surface clean and due to the fact that air doctoring is not always effective enough and/or it causes a noise nuisance.

The object of the invention is to eliminate or at least minimise the disadvantages and problems of the above-described arrangements according to prior art.

An object of the invention is thus to provide a measuring roll of a fibrous-web machine the surface of which is mechanically doctorable.

On the other hand, it is known from prior art, especially from prior art related to the press rolls of fibrous-web machines, to manufacture a roll surface by winding a sintered and/or rolled strip onto the roll body. Then, a tight strip is reeled around the roll which is welded fast from its ends. By means of the strip, a desired type of grooving can be simultaneously implemented on the roll surface. This known technique is called the G strip technique and it has been described e.g. in FI patent specification 81183.

To achieve the above-mentioned objects and those that come out later, the measuring roll according to the invention is mainly characterised by what is presented in the characterising part of claim 1.

The method for covering the measuring roll of the fibrous- web machine according to the invention is principally characterised by what is presented in the characterising part of claim 10.

In the invention, it has been realised in a totally novel way to apply the G strip technique in a completely new, demanding application considering the special demands set by the measuring roll for the cover and the covering method.

According to the invention, a measuring roll of a fibrous-web machine is provided, advantageously a measuring roll of a winder, which when required endures mechanical doctoring because it is covered with a hard metal strip i.e. G strip. According to an advantageous embodiment of the invention, to prevent the damaging of the sensor during the G strip covering, it has been realised to protect the sensor located in a groove on the roll surface during covering by a filler/transmitting material which in the completed roll enables the functionality of measuring, the filler/transmitting material transmitting the pressure/force exerted

in the measurement to the sensor. The filler/transmitting material is advantageously during the G strip covering a liquid, non-curing material, such as two-component resin or other equivalent two-component substance, polyurethane mass, suitable silicone-based material or rubber, e.g. an on-glueable precise rubber strip. The filler/transmitting material can then be formed of a first component located on top of the sensor and a second component entered in connection with the covering which activates curing. When required, the ends of the sensor groove are provided with an end strip or the like which prevents the filler/transmitting material from extruding out during the G strip covering. The temperature endurance of the filler/transmitting material is at least of the range of 80/100°C.

In connection with the invention, the G strip covering is performed e.g. in a way described in US patent specification 4748736. With the G strip is formed a desired surface, smooth or grooved, in the measuring roll which surface is the outer surface or the intermediate surface of the measuring roll, the measuring roll comprising still one or more cover layers installed on top of and/or under the G strip cover.

According to an advantageous embodiment of the invention, the measuring roll of the fibrous-web machine comprises a pressure/force-sensitive sensor installed in a machined groove on the surface of the roll shell, whereby the sensor will not be damaged when installing the tight G cover strip. Thus, the measuring roll also comprises a hard metal strip surface, advantageously a G strip surface, in connection with the installation of which advantageously on top of the sensor in the groove there is a liquid or gelatinous, at this stage still non-curing filler/transmitting material. When reeling the strip at the point of the sensor, the strip sinks due to tension slightly into the groove displacing the liquid filler/transmitting material from the groove. As the strip tightens over the groove, an excess of the filler/transmitting material is able to be displaced out from the groove. Then, the tension of the strip does not damage the sensor but the

force/pressure is able to be transmitted in the completed measuring roll to the sensor by means of the cured filler/transmitting material.

According to an advantageous additional characteristic of the invention, the measuring roll of the fibrous-web machine comprises at least one cover coming on top of and/or under the G strip cover.

The sensor of the measuring roll according to the invention is advantageously a pressure/force-sensitive measuring sensor, most suitably a pressure/force-sensitive film or strip sensor, e.g. a so-called EMFi (Electro-Mechanical Film) film sensor, whereby by means of the measuring film can be measured e.g. nip load and the cross-profile of nip force easily and accurately.

The measuring roll according to the invention is advantageously applied in connection with the winders of fibrous webs, especially paper webs, but it can also be applied e.g. as a measuring roll used in presses and surface-sizing units.

From prior art are known windups used in connection with fibrous-web machines, such as paper and board machines, a fibrous web being manufactured by which fibrous-web machines, such as a paper machine/board machine, is wound as a full-width web into machine reels for further processing. The web is wound around a winding shaft e.g. a spool iron/roll either by means of surface draw in a winding nip between a winding drum and a web reel being formed or by utilising a centre drive, whereby also the winding shaft is provided with a drive. In connection with fibrous-web machines, such as paper and board machines, are also used unwinders by means of which the web reel wound by the windup is unwound in a later stage of treatment for further processing of the fibrous web.

By the measuring roll according to the invention, it is possible e.g. to measure a nip force profile when the measuring roll forms a nip with another roll/web reel,

whereby measurement is performed by the measuring film sensor installed on the surface of the roll shell of the measuring roll.

The invention will now be described in more detail with reference to the figures of the accompanying drawing, to the details of which the invention is, however, by no means intended to be narrowly confined.

Figs. 1 A-IB schematically show an embodiment of the invention.

Figs. 2A— 2B schematically show the covering of the roll with a G strip.

According to an embodiment of the invention shown in Figs. 1A-1B, in a groove 14 made on the surface of the roll shell of a measuring roll 10 of a fibrous-web machine is set a sensor 11, most suitably a pressure/force-sensitive film sensor. On top of the sensor 11 in the groove 14 is installed a filler/transmitting material 12. The measuring roll 10 is covered with a G strip 13. According to the figure, the measuring roll of the fibrous-web machine comprises thus the pressure/force- sensitive sensor 11 installed in the machined groove 14 on the surface of the roll shell, whereby the sensor 11 will not be damaged when installing the hard G cover strip 13. hi connection with the installation of the G strip cover 13 of the measuring roll 10, in the groove on top of the sensor, there is the filler/transmitting material 12 at this stage still non-curing. When reeling the strip 13 at the point of the sensor 11, the strip 13 sinks due to tension slightly into the groove 14 displacing the liquid filler/transmitting material 12 from the groove 14.

Figs. 2A-2B show an exemplifying embodiment of the installation of the G strip cover 13 for the cover of the roll 10. The G strip 13 is reeled around the roll as a tight band which is welded fast from its ends. During the reeling, the G strip 13 is tensioned tight (tension) over the flow limit, whereby the strip 13 forms a cover layer compressing (pressure) the surface of the roll 10. The G strip covering

utilises the G strip technique known as such which has been described e.g. in FI patent specification 81183 and US patent specification 4748736.

In accordance with Figs. 1A-1B, the sensor 11 of the measuring roll 10 is set in the groove 14 made on the surface of the roll, whereby it will not be damaged during the reeling of the strip 13. Furthermore, on top of the sensor 11 in the groove 14 is set the filler/transmitting material 12 which further protects the sensor 11 and also ensures in the measurement the transmission of the force/pressure to the sensor 11. Fig. 2B shows a partial enlargement of Fig. 2A and there an example of the G strip becomes clear. As the G strip is used a material of spring steel type which is thin. With the G strip 13 is formed a desired surface, smooth or grooved, in the measuring roll 10 which surface is the outer surface or the intermediate surface of the measuring roll 10, the measuring roll 10 possibly still comprising one or more cover layers installed on top of and/or under the G strip cover 13.

The invention was described above only referring to some of its advantageous embodiments, to the details of which the invention is, however, by no means intended to be narrowly confined.