EP2625335A1

EP2625335A1 - Apparatus and method for determining young's modulus of a web

Info

Publication number: EP2625335A1
Application number: EP11770557.4A
Authority: EP
Inventors: Pieter Veenstra
Original assignee: Bumaga BV
Current assignee: Bumaga BV
Priority date: 2010-10-07
Filing date: 2011-10-07
Publication date: 2013-08-14
Also published as: WO2012047105A1; NL2005475C2

Abstract

A method, comprising:- conveying a web (W) of fibrous material via a first, upstream roller (52) and a second, downstream roller (54), wherein a tangential velocity (v1) of the first roller is smaller than a tangential velocity (v2) of the second roller, such that the web is pulled taut between them; - determining the following quantities:o the tangential speed (v1) of the first roller, and the tangential speed (v2) of the second roller; o a power (P ₂) supplied to the web by the second roller; and o a cross-sectional area (A) of the fibrous web, or any other quantities from which the named quantities are derivable;- determining Youngs modulus (E) of the fibrous material making up the web using the determined quantities. A fibrous web production apparatus implementing the method is also disclosed.

Description

Title: Apparatus and method for determining Young's modulus of a web

Field of the invention

The present invention relates to the field of paper production, and more in particular to a method of assessing the Young's modulus of a fibrous, paper web during manufacture thereof.

Background

Quality control of paper may typically involve the determination of its elasticity and strength properties. Such determination is often carried out offline, i.e. detached from the actual production process (e.g. in a laboratory), on a sample of produced paper. This approach is rather impractical and costly, in particular because it does not enable direct feedback of the findings of the quality control to the production process, which may lead to considerable waste production due to the involved time delay.

To overcome this issue German patent application DE 10 2005 058 142, in the name of Voith Patent GmbH, discloses a method for determining a strain property of a fibrous web, e.g. a paper web, running through a machine for the production thereof. The method includes conveying the web via at least two consecutive driven rollers; determining a tensile force in the web between said at least two consecutive rollers; determining a differential speed of the at least two rollers in relation to each other, and determining the at least one strain property of the web, using the determined tensile force and differential speed.

A drawback of the method disclosed by DE'142 is that it is not capable of determining the Young's modulus of the material making up the fibrous web. Instead, it merely enables obtaining an aggregate elastic property for the fibrous web as an entity. It is an object of the present invention to provide for a method that enables the online assessment of the Young's modulus of a fibrous web being produced. Summary of the invention

One aspect of the present invention is directed to a method. The method includes conveying a web of fibrous material via a first, upstream roller and a (consecutive) second, downstream roller, wherein a tangential velocity of the first roller is smaller than a tangential velocity of the second roller, such that the web is pulled taut between them. The method also includes determining the following quantities: the tangential speed of the first roller; the tangential speed of the second roller; a power supplied to the web by the second roller; and a transverse cross-sectional area of the fibrous web, or any other quantities from which the named quantities are derivable. The method further includes determining Young's modulus of the fibrous material making up the web using the determined quantities.

Another aspect of the present invention is directed to a fibrous web production apparatus, such as a paper machine. The apparatus may comprise a first, upstream roller, and a drivable second, downstream roller, wherein drivable means that the roller may be associated with or comprises a roller drive for driving the roller. The apparatus may also comprise means configured to determine, during operation: a tangential speed of the first roller, and a tangential speed of the second roller; a power supplied to a fibrous web by the second roller; and a cross-sectional area of the fibrous web, or any other quantities from which the named quantities are derivable. The apparatus may further comprise a controller, operably connected to the means for determining the said quantities and configured to collect the said quantities, and to determine on the basis thereof the Young's modulus of the fibrous material making up the web being produced. The method and apparatus according to the present invention are aimed towards determining the Young's modulus of the fibrous material making up the web being produced, in particular to make this modulus available as a control value for controlling the production process. A primary advantage of using the Young's modulus (having the dimensions of pressure, i.e. N/m²) instead of an elastic modulus of the web as an entity as in DE'142 (there having dimensions N/m), is that the Young's modulus is a material property. Accordingly, changes in the dimensions of the web, e.g. accidental or deliberate changes in width and/or thickness of the web being manufactured, do not require re-adjustment of the control conditions, such as a tolerance range for the elastic modulus of the web as an entity.

As stated, the method and apparatus presently disclosed involve (means for) the determination of a number of specific quantities, including the tangential speeds of the first and second rollers, the power supplied to the web by the second roller, and the transverse cross-sectional area of the fibrous web. Below, this texts sets out in detail how these quantities may be employed to determine the Young's modulus of the web material. It will be clear, however, that the presently disclosed substantive approach to the determination of the Young's modulus may semantically or mathematically be expressed in terms of a plethora of different quantities that, alone or in combination, have at least the same information content as the named quantities. For example, the quantity 'tangential velocity of the first roller' may be expressed as the 'angular velocity of the first roller' times the 'radius of the first roller'. Since these latter two quantities have an information content that encompasses that of the former, the former can be derived from the latter, i.e. expressed in terms of the latter. It is therefore understood that the aforementioned list of quantities should be interpreted to define a minimum information content necessary to carry out the present invention. This understanding may be articulated by the following addition to the quantity list: 'or any other quantities from which the named quantities are derivable', as is used, for example, in the independent claims attached to this specification.

In an embodiment of the present invention, the method may further include producing a web of fibrous material, and, as part of the production process, conveying the web of fibrous material via the first and second rollers. The method may also include verifying that the determined Young's modulus is within a predetermined tolerance range, and in case the determined Young's modulus is not within said predetermined tolerance range, effecting an adjustment to at least one parameter of said production process. In another embodiment, the steps of determining the Young's modulus, verifying that the determined Young's modulus is within a predetermined tolerance range, and effecting an adjustment to at least one parameter of the production process in case it is not, may be performed periodically or continuously during the production process.

The present invention may advantageously be applied during the production process of a fibrous web, e.g. in a fibrous web production apparatus. This allows the quality of the web, and more particularly the Young's modulus thereof, to be monitored periodically or continuously. In case the monitored Young's modulus is observed to leave or have left a predetermined tolerance range, at least one parameter of the production process may be adjusted in order to maintain the Young's modulus of the web within that tolerance range (i.e. to prevent it from leaving the range), or to bring it back into that range.

A parameter of the production process is understood to be a directly or indirectly controlled characteristic of the production process that is known or adjustable as such. As will be described in some more detail below, examples of such parameters may include: the composition of the mixture of fibers, additives and water, prepared at the start of a web's production process as a base material for the web; the speed(s) at which the web is dried during one or more stages of production; and the amount, composition and/or type of sizing applied to the web.

It is understood that adjustments to one or more parameters of the production process may alter one or more properties of the web that is being produced. One such property is the Young's modulus of the web; others may include the (relative) moisture content of the web, and the temperature of the web. It is important to note that different properties of the web may not be independent of one another. The Young's modulus of the web, for example, may be considered to be related to or to be dependent on both the moisture content and the temperature of the web. Furthermore, both moisture content and temperature of the fibrous web may change, both during production and after the production of the web has been completed. A finished web, or a product manufactured therefrom (e.g. a pack of sheets of paper), may for example undergo changes in temperature and moisture content depending on the environmental conditions under which it is kept/stored. These changes in temperature and moisture content may involve changes of the Young's modulus of the material of the web or product. Hence, the Young's modulus is not an invariant quantity of the web. Consequently, meaningfully comparing a determined (actual) Young's modulus to a reference value of the Young's modulus, such as a boundary value of a tolerance range, may require knowledge of the values of other properties of the web, and of the relation between these properties.

As mentioned above, an offline quality check may involve subjecting a sample of produced web material to one or more tests to determine properties of interest. In such a case, the sample may be conditioned before performing the tests there on. It may, for example, be warmed up or cooled down to a certain reference temperature, and/or its moisture content may be regulated to a reference moisture content. Then the tests may be performed to obtain values for the properties of interest. Due to the fact that the tests are performed on the conditioned sample, the obtained values may be meaningfully compared to reference values, obtained under similar conditions.

Conditioning of a web for the purpose of performing tests thereon is highly impractical during the production process. The present invention offers a solution to this problem. To this end, the method according to the present invention may include: providing a relationship between the Young's modulus of the fibrous web, and at least one of: a temperature of the fibrous web and a moisture content of the fibrous web; measuring or otherwise determining the at least one of: the temperature of the fibrous web and the moisture content of the fibrous web; and correcting the determined value of the Young's modulus with the aid of said relationship and said temperature and/or moisture content measurements, so as to determine a corrected Young's modulus of the fibrous material at predetermined reference conditions that are at least partly defined by the temperature and or moisture content of the web.

The present invention thus proposes to provide for a relationship between the Young's modulus and at least one of the temperature and the moisture content of the fibrous web. This relationship may be obtained in any suitable manner (e.g. theoretically, via numerical simulations or experimentally), and at least conceptually be cast in the form of a mathematical relationship that expresses the Young's modulus £ as a function of the web's temperature T and/or moisture content M: E(T,M), Ε(Ύ) or E(M). With the aid of such a relationship, the value of the actual Young's modulus, determined on the basis of its mechanics under certain non- reference conditions, may be related to its value under reference conditions.

Assume, for example, that the actual Young's modulus of a portion of fibrous web, having a temperature T_x and a moisture content M_x, is determined to be E_x on the basis of mechanical considerations. A boundary value E^* of the tolerance range of the Young's modulus, however, may have been determined at a temperature T that is different from Tx, and a moisture content M^* that is equal to M_x. Due to the difference in temperatures a direct comparison of Ex to E^* would be inaccurate. In agreement with the present invention, the value of E_x may now be corrected by means of the relationship E(T,M). The relationship E(T, M) may, for example, be used to estimate the change that the Young's modulus Ex of the web undergoes as a result of change in temperature ΛΤ=(^Γ -T_x). Accordingly, the corrected value E_COrr,x of Ex may be calculated as:

_{E = E +&E = E} . _(R. __{R )} .

It will be clear that in case such a correction is performed, the corrected value of the Young's modulus, instead of the actual value of the Young's modulus, may be used for any comparison with reference values.

In general, the relationship between the Young's modulus of the fibrous web, and the at least one of the temperature and the moisture content of the fibrous web, may be specific for a certain (approximate) composition of a mixture of fibers, additives and water used as a starting material of the production process of the web. This is, however, not necessary.

The following is noted with regard to the terminology used in this text. Young's modulus is defined as the ratio of the uniaxial tensile stress over the uniaxial tensile strain in the range of stress in which Hooke's law holds. For anisotropic materials, Young's modulus is dependent on the direction in which the stress-inducing force is applied. Accordingly, this text, where it refers to the Young's modulus, refers to the Young's modulus in the running direction of the fibrous web, i.e. the direction in which the web is conveyed by the first and second rollers. The direction perpendicular to the running direction of the web and parallel to the plane of the web will be referred to as the transverse or width direction, while the direction perpendicular to the plane of the web defines the will in turn be used to measure the thickness of the web. The invention will now be described in some more detail with reference to a number of embodiments and accompanying drawings, which are meant to illustrate and not to limit the invention. Brief description of the drawings

Fig. 1 is a schematic side-view of an exemplary, conventional fibrous web production apparatus in which the present invention may be implemented; and

Fig. 2 is a schematic top view of a Young's modulus determination setup according to the present invention, which may be implemented in the web production apparatus shown in Fig. 1.

Detailed description

Fig. 1 schematically illustrates an exemplary, conventional Fourdrinier-type paper machine 1 in which the present invention may be implemented. The construction and operation of the paper machine 1 are elucidated briefly.

The machine 1 may comprise five, consecutively arranged sections: a wet end 2, a wet press section 4, a dryer section 6, a calender section 8 and a winding section 28.

In preparation of the paper production process, a mixture or slurry of fibers, additives and water may be prepared. The fiber-composition of the mixture may be controlled dynamically by grinding and mixing different source materials, e.g. pulp of hardwood, softwood, cardboard, grass, bamboo, recycled fibers, etc., in desired proportions. After grinding and mixing, the pulp may be diluted, and additives, such as clay and resin, may be added. When the mixture of refined pulp has been prepared, it may be supplied to the headbox 10 of the wet end 2, which may disperge and subsequently discharge it via a jet across the width of a moving wire mesh conveyor 12 so as to (rudimentarily) form the paper web W. On the conveyor 12 water may extracted from the web W, which at this stage of production may have a water content close to 99%, by means of, inter alia, gravity and suction boxes 14 disposed underneath the wire mesh.

At the end of the wire mesh conveyor 12, the still wet paper web W (now having a water content of about 80%) may be transferred to the wet press section 4. The wet press section 4 may comprise a number of presses 16, whose primary purpose is to squeeze water from the web W and to smooth the main surfaces thereof. Water is efficiently removed via a system of nips formed by rolls pressing against each other, aided by press felts 18. Each press 16 may be single or double felted. A single felted press has a press felt 18 on only one side of the press, such that the paper web W is exposed to the press felt on one side and to a smooth roll on the other. In a double felted press both sides of the paper web W are in contact with a press felt 18. Fig. 1 illustrates both types of presses 16.

Subsequently, at a water content of about 55%, the paper web W may be transferred to the dryer section 6, which is typically the longest part of a paper machine 1. The paper web W may first be guided over steam heated rollers 20 such that at about two-thirds of the length of the dryer section 6 the paper web W is almost dry. At that point, the web W may be passed through a size-press 22 so as to apply sizing or size, including substances like for example starch, gelatin and glue, to the web in order to provide it with the characteristics desired for the type of paper being produced. Next the web W may be dried again until it reaches a desired moisture content.

Upon exiting the dryer section 6, the paper web W may pass through a smoothing machine or calender 24 of calender section 8, designed to provide the paper web W with the desired thickness and degree of smoothness. After that the web W may be run through a measurement frame 26, including a material property scanner 27. The scanner 27 may be fitted with a variety of sensors, such as a temperature sensor and/or a (relative) moisture content sensor, configured to measure the web's temperature and moisture content, respectively. At the end of the production line, a winding section 28 in the form of a Pope roller may be arranged to roll up the web W; alternatively, as common in the massive cardboard industry, the web may be cut into sheets that are then piled up.

The Pope roller 28 may include a reel drum 29a, an empty reel spool 29b (here: disposed above the reel drum 29a), and a paper reel 29c for winding up a jumbo paper roll (here: disposed downstream of the reel drum 29a). The Pope roller may be configured to urge both the empty reel spool 29b and the paper reel 29c into mechanical contact with the reel drum 29a. In a typical embodiment of the Pope roller 28, merely the reel drum 29a may be driven, which means that the reel drum 29a may be the last driven roller of the paper machine 1. In some alternative embodiments, in particular those adapted to reel in relatively smooth paper, the reel spool 29b may also be driven; in such an embodiment, the reel drum 29a may be considered to have two drives.

During its production, the properties of the paper web W may be monitored for the purpose of quality control. One parameter of particular interest is the web's Young's modulus, which forms a measure of its stiffness. It may typically be desired to maintain the value of the Young's modulus of a produced paper web within a certain tolerance range. To this end, the Young's modulus of the web W may be determined periodically or continuously, and, in case its value is found to stray from a predefined optimal tolerance range, one or more parameters of the production process may be adjusted to bring the Young's modulus back in that range.

The Young's modulus may be defined as the ratio of the uniaxial tensile stress over the uniaxial tensile strain in the range of stress in which Hooke's law holds. The Young's modulus of the material making up the fibrous paper web may thus be determined by subjecting the web to a certain uniaxial stress, assessing the resulting uniaxial strain, and dividing the applied tensile stress by the found tensile strain.

The tensile stress, denoted σ, is the average force per unit of initial (i.e. undeformed), transverse cross-sectional area within a portion of the web W through which the force acts. It may thus be defined as the ratio of the total tensile force F applied to said portion of the longitudinally loaded web W to the initial transverse cross- sectional area Ao thereof:

A)

The uniaxial strain, denoted as ε, is a measure of the geometrical deformation of the portion of the web W as a result of the applied stress σ. It may be defined as the ratio of the deformation (AL) of the portion of the web to the initial dimension (Lo) thereof:

* = (2)

Accordingly, using equations (1) and (2), the Young's modulus may be defined as:

E = ° =H -. (3) ε AL/ L₀

Since stress has the units of pressure [N/m²] and strain is dimensionless, the Young's modulus also has the units of pressure.

As described above with reference to Fig. 1, a fibrous web production apparatus may feature a plurality of rollers for transporting a fibrous web W being manufactured. The present invention may advantageously use the fact that the uniaxial stress σ in a fibrous web W may be inferred from the power required to transport the web between two of those rollers, while the strain ε of the web may be inferred from the difference in rotational velocity between them.

Assume, for example, that, along a certain part of its path through the machinel, a fibrous web W is conveyed by two consecutive rollers, i.e. a first, upstream roller and a second, downstream roller. The fibrous web may rest on the circumferential areas of the rollers (at no slip), and may be unsupported in between the two rollers. During operation, the first roller may be rotated such that its circumferential area has a tangential velocity vi [m/s]. The second roller is operated at a power P2 [W], such that its circumferential area has tangential velocity V2 [m/s] that is somewhat greater than vi, and the paper web portion in between the first and second roller is pulled taut. To simplify the exposition here, the second roller itself is assumed to rotate without internal friction.

The power P2 employed to drive the second roller equals the tensile force F applied to the web by the second roller times the velocity V2 of the web at the second roller. The force F may be expressed as the stress σ in the web times the actual cross- sectional surface area A thereof at a point between the two rollers:

P₂ = F v₂ = a A v₂ (4)

Assuming that the actual cross-sectional surface area of the web A (at a point between the two rollers) is to good approximation equal to the web's initial cross-sectional surface area Ao (at or upstream of the first roller), i.e. that A ~ Ao, equation (1) may be used to rewrite the stress σ in the paper web as:

p

— ¹ (5)

A- v₂

The strain of the paper web in between the two rollers may be expressed as: s = - ^V^ . (6)

Equations (3), (5) and (6) may be combined to yield the following expression for the Young's modulus of the paper web material: The quantities present in equation (7) may be monitored in a fibrous web production apparatus 1 with relative ease. The tangential speeds vi, V2 of the rollers, and the power (P∑) transferred to the web W by the second roller in advancing it, may even be readily available on today's machines for producing fibrous webs as part of basic equipment control processes. The transverse cross- sectional area A of the web W, however, is typically not a quantity used to control the production process in conventional machines.

The above exposition applies primarily to the situation wherein the web thickness is relatively small compared to the radii of the first and second rollers, such that the velocity of the web where it is supported by the rollers is substantially equal to the tangential velocities of the rollers. Where relatively thick webs are processed, the occurrence of shear may require that the velocities of the web are calculated with respect to the plane of mass or gravity of the web.

For illustrative purposes, an exemplary setup 50 that may be used to collect the quantities named in right-hand part of equation (7), and to calculate the Young's modulus E on the basis thereof, will now be described with reference to Fig. 2, in which it is shown in isolation.

The setup 50 includes a first, upstream roller 52, and a second, downstream roller 54. Each roller 52, 54 may preferably have a substantially cylindrical shape, and be rotatably mounted around a central axis. The first, upstream (with respect to the running direction of the web W) roller 52 may be drivable or otherwise braked. A drive or brake on the first roller 52 may be employed to ensure that, during operation, it maintains a smaller tangential speed vi than the tangential speed v∑ second roller 54, and thereby a certain minimum tensile stress σ in the web W that allows for meaningful determination. The second roller 54 is preferably drivable by a roller drive, e.g. an electromotor. Each of the rollers 52, 54 may be associated with a control section 53, 55, respectively, that may comprise the roller drive for driving the respective roller and control means capable of monitoring and/or controlling the operation of the roller and/or roller drive. The control means may in particular be configured to monitor one or more of: the rotational speed of the roller (e.g. by means of a tachometer), the drive torque of the roller drive, and its power input.

In Fig. 2, the web W is shown to 'rest' on the rollers 52, 54. It will be clear, however, that other embodiments of the setup 50 may use a different configuration. In one embodiment, for example, the first roller may 52 be located on one side of the web, e.g. above it, while the second roller 54 may be located on another, e.g. below it. What matters is that the web W is in guiding contact with both rollers 52, 54. This contact may preferably be such that no slipping occurs between the rollers 52, 54 and the web W. In fibrous web production apparatus, it is common for slipping to occur between any rollers and the web W conveyed thereon. Such slipping, in particular when it is irregular in nature, may negatively affect the accuracy with which the Young's modulus of the material can be determined. Although slipping may be accounted for in the calculation of the Young's modulus, it's occurrence is best prevented by carefully selecting the tangential speed of the first and/or second roller, and the material their circumferential surfaces (on which the web rests) are made of. For clarity it is noted that the term 'slip' as used in this text refers to macro-slip: relative movement between the web W and a roller by which the web is supported/guided, occurring over their entire mutual contact area. Macro-slip is to be distinguished from micro-slip, which may be described as the relative movement between the web W and a roller by which it is supported/guided, occurring over only a portion of their mutual contact area, in particular due to elongation or shrinkage of the web W in its running direction.

Although the setup 50 is shown in isolation, it is understood that the two rollers 52, 54 may form part of, and as such coincide with two rollers of the myriad of rollers available in, a conventional fibrous web production apparatus 1. In particular with regard to such incorporation, it is noted that the two rollers 52, 54 may preferably be consecutive rollers, i.e. two rollers with no rollers or other web supporting/guiding elements disposed there between. Rollers and/or supporting/guiding elements arranged in between or downstream of the two rollers 52, 54 that are used for executing the method according to the invention may unnecessarily complicate the execution thereof, in particular when they are driven or braked. This is because such rollers and/or guiding elements may require power supplied to the web and/or energy losses incurred by the web due to interaction with them to be discounted. Hence, the web W may preferably be unsupported in between the two rollers 52, 54, and not be driven at a point downstream of the second roller 54, so as to rule out interference that may negatively affect the accuracy with which the Young's modulus is determined. In a preferred embodiment, the rollers 52, 54 may be located near a downstream end of the apparatus, at a location where the manufacture of the fibrous web has nearly or fully been completed, so as to allow for determination of the Young's modulus of the virtually finished product. In the exemplary paper machine 1 of Fig. 1, the second roller 54 may for example coincide with the last driven roller thereof, e.g. with the reel drum 29a, while the first roller 52 may coincide with the roller that, seen in the running direction of the web W, immediately precedes it.

The setup 50 may also include measurement means 56 configured to measure both the width and the thickness of the web W, preferably simultaneously and at a same location along the transport path of the web. The measurements may be carried out by any suitable means known in the art, e.g. optical measurement means, or mechanical measurement means. Optical means are preferred as they operate contactlessly, i.e. without any mechanical contact with the web that could induce wear or damage. Thickness and width measurements through optical and mechanical means are generally known in the art, and therefore not elaborated upon here. The width and thickness measurement means 56 may be disposed in a general purpose measurement frame of a production apparatus, such as measurement frame 26 in the apparatus 1 of Fig. 1.

The setup 50 may further include a central controller 58. Both the control sections 53, 55 of the rollers 52, 54 and the measurement means 56 may be operably connected to this central controller 58, allowing it to retrieve the aforementioned status and measurement data. Based on these data, the controller 58 may calculate the Young's modulus of the fibrous material making up the web in accordance with the aforementioned equation (7). In doing so, it may also employ (static) data of the setup 50, such as frictional resistance of the bearing arrangements of the rollers 52, 54, the roller diameters, etc. For example, in case the control means 53, 55 do not report the tangential velocities of the rollers, but only their angular velocities, the controller 58 may calculate the tangential velocities from the angular velocities (rpm) and the radii of the rollers.

The controller 58 may determine the Young's modulus periodically or continuously throughout the production process of a fibrous web. In addition, it may verify for each determined instance of the modulus whether or not it is still within a predetermined tolerance range. In case the determined Young's modulus is no longer within such tolerance range, the controller 58 may effect adjustments to at least one parameter of the production process. These parameters may include: the composition of the mixture of fibers, additives and water, prepared at the start of a web's production process as a base material for the web; the speed(s) at which the web is dried during one or more stages of production; and the amount, composition and/or type of sizing applied to the web.

It is important to note that the Young's modulus is a temperature- and humidity/moisture content-dependent material property. For the present purpose, this means that the Young's modulus E may be regarded as a function of the temperature T and moisture content M of the fibrous web: E(T, M). During production, neither the temperature nor the moisture content of the web need to be a constant. In fact, both may generally vary with the parameters of the production process, e.g. the temperature settings of the drying section 6 of the fibrous web production apparatus 1, or the speed at which the web W is run there through. In order to assess the Young's modulus of the web at standard reference conditions, an actual Young's modulus of the web may be determined, and subsequently corrected to account for the fact that the conditions under which the Young's modulus was determined deviate from the reference conditions. An exemplary procedure for doing this has been outline above.

By way of implementation, the fibrous web production apparatus according to the present invention may be fitted with a temperature sensor, configured to measure the temperature of the fibrous web, and with a moisture content sensor, configured to measure a (relative) moisture content of the fibrous web. Both sensors may be integrated in a material property scanner, such as the scanner 27 in the measurement frame 26 of the fibrous web production apparatus 1 shown in Fig. 1. A controller 58 of the apparatus may be operably connected to both sensors, and be fitted with a relationship between the Young's modulus of the fibrous web, a temperature of the fibrous web and a moisture content of the fibrous web. The controller 58 may additionally be configured to measure the temperature of the fibrous web and the moisture content of the fibrous web, and to correct a determined value of the Young's modulus with the aid of said relationship and said temperature and/or moisture content measurements, so as to determine a corrected Young's modulus of the fibrous material at predetermined reference conditions that are at least partly defined by the temperature and or moisture content of the web.

Although illustrative embodiments of the present invention have been described above, in part with reference to the accompanying drawings, it is to be understood that the invention is not limited to these embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, it is noted that particular features, structures, or characteristics of one or more embodiments may be combined in any suitable manner to form new, not explicitly described embodiments.

List of elements

1 paper machine

2 wet end

4 wet press section

6 dryer section

8 calender section

10 headbox

12 wire mesh conveyor

14 suction boxes

16 press

18 press felt

20 steam heated roller

22 size press

24 smoothing machine / calender

26 measurement frame

27 material property scanner

28 winding section / Pope roller

29a reel drum

29b empty reel spool

29c paper reel

50 Young's modulus determination setup

52 first roller

53 control section of first roller

54 second roller

55 control section of second roller

56 (optical) measurement means

58 controller w paper web Mathematical symbols:

Ao initial transverse cross- sectional area of web

A transverse cross- sectional area of stretched web E Young's modulus

F tensile force

M moisture content

P∑ power supplied to web by second roller

T web temperature

vi tangential velocity of first roller

V2 tangential velocity of second roller

σ uniaxial tensile stress

ε uniaxial tensile strain

Claims

Claims We claim:

1. A method, comprising:

- conveying a web (W) of fibrous material via a first, upstream roller (52) and a second, downstream roller (54), wherein a tangential velocity (vi) of the first roller is smaller than a tangential velocity (v2) of the second roller, such that the web is pulled taut between them;

- determining the following quantities:

o the tangential speed (vi) of the first roller, and the tangential speed (v2) of the second roller;

o a power (P2) supplied to the web by the second roller; and o a cross-sectional area (A) of the fibrous web,

or any other quantities from which the named quantities are derivable;

- determining a Young's modulus (E) of the fibrous material making up the web using the determined quantities.

2. The method according to claim 1, further comprising:

- producing the web (W) of fibrous material, and, as part of its production process, conveying the web of fibrous material via said first and second rollers (52, 54);

- verifying that the determined Young's modulus (E) is within a predetermined tolerance range; and

- in case the determined Young's modulus is not within said predetermined tolerance range, effecting an adjustment to at least one parameter of the production process.

3. The method according to claim 2, wherein the steps of determining the Young's modulus, verifying that the determined Young's modulus is within a predetermined tolerance range, and effecting an adjustment to at least one parameter of the production process in case it is not, are performed periodically or continuously during the production process.

4. The method according to claim 2 or 3, wherein said production process includes at least one of:

- preparing a mixture of fibers, additives and water as a starting material for the production of the web;

- drying the web;

- applying sizing to the web; and

wherein said at least one parameter of the production process includes at least one of:

- a composition of the mixture of fibers, additives and water;

- a drying speed at which the web is dried;

- an amount of sizing applied to the web per unit of time; and

- a composition of the sizing applied to the web.

5. The method according to any of the claims 1-4, wherein the method further comprises:

- providing a relationship between the Young's modulus of the fibrous web (W), and at least one of: a temperature (T) of the fibrous web and a moisture content (M) of the fibrous web;

- measuring the at least one of the temperature of the fibrous web and the moisture content of the fibrous web;

- correcting the determined value of the Young's modulus with the aid of said relationship and said temperature and/or moisture content measurements, so as to determine a corrected Young's modulus of the fibrous material at predetermined reference conditions that are at least partly defined by the temperature and or moisture content of the web.

6. The method according to claims 2 and 5, wherein the relationship between the Young's modulus (E) of the fibrous web (W), and at the least one of the temperature (T) and the moisture content (M) of the fibrous web, is specific for a certain composition of a mixture of fibers, additives and water used as a starting material of the production process of the web.

7. The method according to any of the claims 2-5, wherein determining the cross-sectional area (A) of the fibrous web (W) includes measuring both a width and a thickness thereof.

8. The method according to claim 7, wherein at least one of the width and the thickness of the fibrous web is measured contactlessly.

9. The method according to any of the claims 1-8, wherein the web (W) is guided by the rollers (52, 54) substantially without slipping relative thereto.

10. The method according to any of the claims 1-9, wherein the web (W) is substantially unsupported in between the first and second rollers (52, 54).

11. The method according to any of the claims 1-10, wherein the Young's modulus is determined using the relationship:

A - v₂ - (v₂ -v_l )

wherein E is Young's modulus, A is the cross-sectional area of the fibrous web (W), P∑ is the power applied to the web by the second roller (54), and vi and v∑ are the tangential velocities of the first and second rollers (52, 54), respectively.

12. A fibrous web production apparatus (1), comprising: - a first, upstream roller (52);

- a drivable second, downstream roller (54);

- means configured to determine, during operation:

o a tangential speed (vi) of the first roller, and a tangential speed (V2) of the second roller;

o a power (P∑) supplied to a fibrous web (W) by the second roller; and

o a cross-sectional area (A) of the fibrous web (W),

or any other quantities from which the named quantities are derivable; - a controller (58) configured to collect the said quantities, and to determine on the basis thereof the Young's modulus of the fibrous material making up the web being produced.

13. The fibrous web production apparatus according to claim 12, wherein the means configured to determine the cross-sectional area (A) of the fibrous web (W) include optical measurement means (56) configured to measure both the width and the thickness of the fibrous web.

14. The fibrous web production apparatus according to claim 12 or 13, wherein the controller (58) is configured to:

- verify that the determined Young's modulus is within a predetermined tolerance range; and

- in case the determined Young's modulus is not within said predetermined tolerance range, effecting an adjustment to at least one parameter of a production process of the fibrous web.

15. The fibrous web production apparatus according to claim 14, further comprising:

- a temperature sensor (27), configured to measure the temperature of the fibrous web, and - a moisture content sensor (27), configured to measure a moisture content of the fibrous web;

wherein the controller (58) is fitted with a relationship between the Young's modulus of the fibrous web (W), a temperature (T) of the fibrous web and a moisture content (M) of the fibrous web, and further configured:

- to measure the temperature of the fibrous web and the moisture content of the fibrous web; and

- to correct the determined value of the Young's modulus with the aid of said relationship and said temperature and/or moisture content measurements, so as to determine a corrected Young's modulus of the fibrous material at predetermined reference conditions that are at least partly defined by the temperature and or moisture content of the web.