CN102076906A - Determination of speed relations between driving groups of a paper machine - Google Patents

Abstract

The invention relates to a paper machine with at least one predrying section (PDS) having at least one drive assembly (PDS_m-1, PDS_m) with at least one drying cylinder (Z ). In order to automatically determine the speed relationship between the drive assemblies, the method has the following steps: providing measured values, in particular measurements of the speed of the drive assemblies (PDS_m-1, PDS_m), the unit area of the paper strip (PB) The measured value of the mass, the measured value of the humidity measurement behind the last drying drum (Z) of the pre-drying section (PBS) and/or the measured value of the vapor pressure inside the drying drum (Z) from which the per The web humidity (u) of the paper web (PB) behind each drying drum (Z), at least one web strain (ε) is calculated from the humidity-dependent elastic modulus (E) and at least one given theoretical web stress (σ) ), and calculating a velocity relationship from said at least one strip strain (ε).

Description

Determining the speed relationship between the drive components of a paper machine

technical field

The invention relates to a method for determining the speed relationship between drive assemblies of a paper machine and a paper machine having at least one predrying section with at least one drive assembly, wherein the drive assemblies of the predrying section each have at least one belt for drying paper drying drum.

The invention also relates to a computer program for carrying out the method described above and a computer program product with such a computer program.

Background technique

This method is used in the field of paper converting. In conventional paper machines the size press is located after the predrying section and the afterdrying section is located after the size press. In some cases, however, there is also only one predrying section and postdrying section without a size press, for example in a newspaper machine. The pre-drying section and the optional after-drying section generally each consist of a plurality of steam-heated drying drums. In general, several successive drying cylinders are driven together at the same speed in drive assemblies, i.e., for example, the drying cylinders of the pre-drying section are in m drive assemblies and the drying cylinders of the post-drying section are in n drive assemblies. .

In these drying components of the paper machine the paper web is dried from an initial moisture to a defined final moisture. Here the paper web changes its properties and possibly also the modulus of elasticity, which is functionally directly dependent on the moisture content. In order to ensure a uniform belt stress (also called belt tension), it is as important for the product quality parameters as for the stability of the paper belt (as small as possible overstretching, slight tearing; but a certain minimum tension is also necessary, so guarantee guidance of the paper web on winding rollers and avoidance of folds), the speed of the individual drying components is adapted to the drying profile.

The technical problem now is how to set the desired speed values, in particular differential speed theoretical values or relative theoretical values, of the drive components of the pre-drying section (possibly also including the post-drying section). According to the current state of the art, deviations in the web tension must be detected by the operator visually or by touch and readjusted by hand via the speed relationship of the drive unit.

Contents of the invention

The object of the invention is to automatically determine the speed relationship of drive components of a paper machine.

This object is achieved by a method for determining the speed relationship between drive assemblies of a paper machine, wherein the paper machine has at least one predrying section with at least one drive assembly, and wherein the drive assemblies of the predrying section each have at least A drying drum for drying paper strips with the following steps:

Provision of measured values, in particular of the speed of the drive components, of the mass per unit area of the paper web, of the humidity measurement after the last drying drum in the pre-drying section and/or of the vapor pressure inside the drying drum measured value,

- calculation of the web moisture of the web behind each drying cylinder from the measured values,

- calculating at least one strip strain from the modulus of elasticity and at least one given theoretical strip stress and

- calculating a velocity relationship from said at least one belt strain.

Said object is also achieved by a paper machine, a computer program and a computer program product having the features given in claims 5 , 6 and 7 .

By providing measured values of actual process parameters such as belt humidity, grammage, material velocity, evaporation area, vapor pressure and vapor quantity, plant geometry, etc. for use in the program. In this case, these measured values generally already occur in different parts of the installation. Providing measured values also includes measuring relevant measured values only if at least one such required measured value is not available in a particular paper machine.

According to the invention, the relative humidity u_i of the paper web downstream of each cylinder i of the predrying section is calculated from the provided measured values in a so-called "drying model". In this paper tape humidity is at the position

x_2=x_1+ΔL

pass

u_2=u_1-[(m_u+m_o)/Gatro]·(ΔL/V_M)

is given, where V_M is the machine velocity, and the absolute dry (atro) grammage is

Gatro＝m_F/A

(m_F: mass of dry tape, A: relative tape area). The evaporation rates m_u and m_o on the underside and top side of the paper web satisfy the Stefan formula, to which plant-specific parameters such as the total pressure and temperature in generally existing drying hoods are also added.

Via the humidity-dependent modulus of elasticity (E-modulus), which is known, for example, from laboratory measurements, the necessary belt strain ε can be calculated from a given theoretical belt stress σ, and then recalculated from the belt strain between the individual drive components speed relationship between them. Here the theoretical belt stress σ does not have to be constant throughout the pre-drying and post-drying sections, but varies between the individual drive components, since the web is only reached with increasing drying in the pre-drying section for greater belt stresses required strength.

The drying profile of the paper web on a single drying cylinder differs from the "steady-state vibration state" especially after a stop or tear: after a short stop (for example after tearing) the drying cylinder is usually (slightly) heated in between, followed by The produced web has a lower moisture profile (ie the humidity u_i on roll i is lower than normal). After a long standstill, during which the vapor pressure of the drying cylinder drops, the cylinder may not have reached "operating temperature", and the moisture profile of the ensuing web produced is higher than normal. The plant manager must therefore adapt the speed relationship to the changing characteristics during start-up.

If the belt strain (or speed relationship) is set incorrectly, this can lead to tearing of the belt at too high a strain and to flapping (Bahnflattern) at too small a strain, which can lead to poor paper quality and also May cause tearing. The solution according to the invention detects changes in the humidity profile and automatically determines the speed relationship of the resulting changes between the drive components. This has the advantage that the quality of the produced paper web no longer depends on the experience and attention of the operator (plant manager), but a uniform quality due to a uniform web strain is reliably guaranteed.

In an advantageous variant form, - wherein the paper machine has a size press and an after-drying section, which each have at least one drive assembly, wherein the drive assembly of the after-drying section has at least one drying cylinder for drying the paper web, - providing a drive Velocity measurements of the components, measurements of humidity measurements behind the last drying drum in the post-drying section, measurements of the mass flow of the applied glue quantity and water application in the glue press, and by pre-drying Moisture measurement and water application behind the last drying drum of the drying section calculates the strip humidity between the glue press and the post drying section. In this way, the speed relationship between all drive components can also be determined automatically for a paper machine with a size press and an afterdryer section.

In another advantageous embodiment, the modulus of elasticity is calculated from the web humidity, each web stress measured before and after the glue press and the strain determined from the speed of the participating drive assemblies. In this case, the calculation is carried out by means of another model (“E-modulus model”). This avoids unreliability, which is caused by laboratory measurements of the humidity-dependent modulus of elasticity, because it presupposes that the properties (of the modulus of elasticity) are sufficiently constant (of course this is the usual case, for example, in newspaper paper machines ). Since in this exemplary embodiment the calculation from successive measured values of the paper web is dependent on the moisture modulus of elasticity, the method according to the invention also automatically adapts (fully adaptively) to changes in the modulus of elasticity in the paper web.

In another advantageous embodiment, the speed relationship between the drive assemblies is set automatically. That is, the velocity relationship calculated from the belt strain is prescribed as a theoretical value for drive control. The available measurement data of different and currently only separately observed plant components are therefore suitably linked for achieving an advantageous setting for product quality and process availability, which can only be set manually (approximately) by the operator at present. Certainly. The method is self-adaptive and highly reliable thanks to process data obtained through continuous measurements.

Description of drawings

The invention is described and explained in detail below with the aid of an exemplary embodiment shown in the drawings. In the attached picture:

Figure 1 schematically shows the drive assembly of a paper machine,

Figure 2 shows the relationship between elastic modulus and belt humidity,

Figure 3 shows the relationship between strip stress and strip strain.

Detailed ways

Figure 1 schematically shows a paper machine with a pre-drying section (PDS, "Pre-Dryer Section"), a size press (SP, "Size Press") and an after-drying section (ADS, "After-Dryer Section"). The pre-drying section PDS and post-drying section ADS each consist of several steam-heated drying drums Z. A plurality of sequentially arranged drying drums Z are driven together at the same speed in the drive assemblies PDS_m-1, PDS_m, SP, ADS_1, ADS_2, ADS_n, respectively, i.e. for example the drying drums Z of the pre-drying section PDS are driven in m drive assemblies PDS_m -1, the drive in PDS_m and the drying drum Z of the post-drying section ADS are driven in n drive assemblies ADS_1, ADS_2, ADS_n.

In the drying section PDS, ADS of the paper machine, the paper web PB is dried from an initial moisture to a defined final moisture. Since the paper web PB changes its properties here, such as the modulus of elasticity, which directly depends on the moisture content, the speed of the individual drying components PDS, ADS must therefore be adapted to the drying profile in order to ensure a uniform web stress σ (also called It is as important for the quality parameters of the product as for the stability of the belt movement (no overstretching as much as possible, less tearing).

The velocity relationship necessary for setting is calculated for at least a given theoretical band stress σ by means of the solution according to the invention. Here the theoretical belt stress σ does not have to be constant throughout the pre-drying and post-drying sections PDS, ADS, but must vary between the individual drive components PDS_m-1, PDS_m, SP, ADS_1, ADS_2, ADS_n, i.e. adapt Due to the drying process, the process is accompanied by shrinkage.

The belt tension σPDS_m behind the last drive assembly PDS_m of the pre-drying section PDS in front of the glue press SP is set in the setting loop by a given speed relation v_SP/v_PDS_m, ie the speed ratio of the drive assembly SP to PDS_m. Appears with humidity u_PDS_m as measured value. Similarly, in the setting loop, the belt tension σADS_0 in front of the first drive component ADS_1 of the post-drying section ADS is set by a given speed relationship v_ADS_1/v_SP, that is, the speed ratio of drive components ADS_1 and SP. The strip moisture u_ADS_0 can be calculated from the measured strip moisture u_PDS_m and the generally known water application in the glue press SP. (For example the water coating in the glue press SP can be determined from the new water consumption of the glue press SP.)

The speed relationship between all drive components PDS_m-1, PDS_m, ADS_1, ADS_2, ADS_n determined by the belt humidity calculated by the drying model is similarly set, whereby the individual drive components PDS_m-1, PDS_m, ADS_1, The speeds of ADS_2, ADS_n are automatically adapted to changes in the drying profile of the paper web PB. This prevents belt tearing and belt chatter and thus increases the reliability of the paper machine with an equally good paper quality.

Fig. 2 shows the relationship between the elastic modulus E and the belt humidity u. In order to obtain the characteristic curve E(u) using the so-called "E-modulus-model", points A and B are determined, where A represents the humidity and the belt elasticity (=dry) directly in front of the glue press SP and B represents the direct Humidity and belt elasticity (=moist) after the glue press SP. Here, the web humidity u_PDS_m upstream of the glue press SP is measured and the web humidity u_ADS_0 downstream of the glue press SP is calculated from the generally known water coating in the glue press SP. In order to determine the associated E-value, the strip stress σ before and behind the glue press SP is also measured and the strain of the strip PB is determined from the speeds of the participating drive components PDS_m, SP, ADS_0. (The characteristic curve according to this figure can be chosen as a laboratory measurement, if this characteristic of the tape remains constant enough).

According to the E-modulus-model, the characteristic curve extends in the range indicated by hatching during the passage of the paper web PB through the predrying section PDS, the size press SP and the afterdrying section ADS, as indicated in the detailed circle diagram . The state of the paper web PB in the E(u) diagram initially extends from point B to point A during the predrying section PDS, since the associated web humidity u_PDS decreases continuously. The belt humidity u_SP correspondingly increases again during the passage through the glue press SP and finally the belt humidity u_ADS decreases again in the post-drying section ADS—corresponding to the state movement from A to B and back again.

With the aid of the modulus of elasticity E determined using the described model as a function of the strip humidity u (or alternatively using the laboratory characteristic curve) the strip strain ε can now be calculated in a next step for a given theoretical strip stress σ, as in the next step as shown in the attached figure.

FIG. 3 shows the dependence of the strip stress σ and the strip strain ε for different strip humidities u. The radiation corresponding to the different web humidity u starts at the origin with web humidity u1 only for the case of a dry paper web PB. It is known that the paper web PB changes in length and width in the unstressed state (σ=0) when the humidity u changes. The length of the paper web PB increases in the machine direction if moisture is supplied to the paper web PB starting from "absolutely dry (atro)", as is the case, for example, in the size press SP. This is represented in the figure by the humidity-dependent strip strain ε in the untensioned state—ε(σ=0,u1), ε(σ=0,u2), . . . , where u4>u3>u2>u1. The dashed line is the ray with humidity u_PDS_m at point A and humidity u_ADS_0 at point B of FIG. 2 .

In order to determine the strip strain ε for a given theoretical strip stress σ, it is now only necessary to determine the strip strain ε subordinate to the theoretical strip stress σ for the corresponding strip humidity u, as indicated by the dotted arrow in the drawing . From these respective strip strains ε, the speed relationships between the individual drive components PDS_m−1, PDS_m, ADS_1, ADS_2, ADS_n can be calculated and provided as setpoint values for the drive control. In this way the speed relationship between the drive assemblies PDS_m-1, PDS_m, ADS_1, ADS_2, ADS_n can be automatically set such that the belt stress σ of the paper web PB is neither too high (risk of belt tearing) nor Too low (danger of chatter).

In summary, the invention relates to a paper machine having at least one predrying section with at least one drive unit, wherein the drive unit has at least one dryer cylinder for drying the paper web. In order to automatically determine the velocity relationship between drive components, a method is proposed with the following steps:

- Provision of measured values, in particular of the speed of the drive assembly, of the mass per unit area of the paper web, of the humidity measurement behind the last drying drum of the pre-drying section and/or of the steam inside the drying drum pressure measurements,

- calculation of the web moisture of the web behind each drying cylinder from the measured values,

- calculating at least one strip strain from the humidity-dependent modulus of elasticity and at least one given theoretical strip stress, and

- calculating a velocity relationship from said at least one belt strain.

By means of the solution according to the invention, for a uniform belt strain, the speed relationship of changes between the drive components caused by changes in the moisture profile is automatically determined.

Claims (7)

1. A method for determining the speed relationship between drive assemblies (PDS_m-1, PDS_m) of a paper machine having at least one predrying section ( PDS), and wherein the drive assembly (PDS_m-1, PDS_m) of the pre-drying section (PDS) has at least one drying cylinder (Z) for drying the paper web (PB) respectively, the method has the following steps: - provide measurements, especially of the speed of the drive assembly (PDS_m-1, PDS_m), of the mass per unit area of the paper web (PB), of the last drying cylinder (Z in the pre-drying section (PBS) ) measured value of the humidity measurement behind and/or the measured value of the vapor pressure inside the drying drum (Z), - calculation of the web moisture (u) of the paper web (PB) behind each drying cylinder (Z) from said measured values, - calculating at least one strip strain (ε) from the humidity-dependent elastic modulus (E) and at least one given theoretical strip stress (σ), and - calculating a velocity relationship from said at least one strip strain (ε). 2. The method as claimed in claim 1, wherein the paper machine has a size press (SP) and an after drying section (ADS), each of which has at least one drive assembly (SP, ADS_1, ADS_2, ADS_n), wherein the after The drive assembly (ADS_1, ADS_2, ADS_n) of the drying section (ADS) has at least one drying cylinder (Z) for drying the paper web (PB), and - where measurements of the speed of the drive assemblies (SP, ADS_1, ADS_2, ADS_n) of the glue press (SP) and of the post-drying section (ADS) are provided, behind the last drying drum (Z) of the post-drying section (ADS) The measured values of the humidity measurement, the measured values of the mass flow of the applied glue quantity and the measured values of the water application in the glue press (SP), - where the strip moisture (u_ADS_0) between the size press (SP) and the post-drying section (ADS) is calculated from the moisture measurement and water application behind the last drying drum (Z) of the pre-drying section (PDS). 3. The method as claimed in claim 2, wherein by the strip humidity (u), the strip stress (σ) each measured before and after the glue press (SP) and by the participating drive components (PDS_m, SP, ADS_1 ) to calculate the elastic modulus (E) from the determined strain (ε). 4. The method as claimed in any one of the preceding claims, wherein the speed relationship between the drive components (PDS_m-1, PDS_m, SP, ADS_1, ADS_2, ADS_n) is set automatically. 5. Paper machine with at least one predrying section (PDS) with at least one drive assembly (PDS_m-1, PDS_m), wherein said drive assembly (PDS_m-1, PDS_m) has at least one belt for drying paper (PB ), said paper machine also has a mechanism for carrying out the method according to any one of claims 1 to 4. 6. Computer program for carrying out the method according to any one of claims 1 to 4 on a paper machine according to claim 5. 7. Computer program product having a computer program as claimed in claim 6.

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