Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G9/00—Other accessories for paper-making machines
  • D21G9/0009—Paper-making control systems
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
  • B65H23/00—Registering, tensioning, smoothing or guiding webs
  • B65H23/02—Registering, tensioning, smoothing or guiding webs transversely
  • B65H23/0204—Sensing transverse register of web
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
  • G01B11/04—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness specially adapted for measuring length or width of objects while moving
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
  • B65H2515/00—Physical entities not provided for in groups B65H2511/00 or B65H2513/00
  • B65H2515/30—Forces; Stresses
  • B65H2515/31—Tensile forces

Definitions

• the invention concerns a method for predicting the tensile-strength ratio of a paper web.
• the invention concerns a method for predicting the degree of drying of a paper web.
• the location of an edge of a paper web and the width of the web can also be measured by means of a measurement head traversing across the web.
• One travers- ing cycle takes typically 20...40 seconds.
• the web may move up to 1...2 cm in the cross direction. This has the consequence that, when one 2 edge is being measured, the precise location of the opposite edge is not known. This results in inaccuracy in the results of measurement.
• the object of the present invention is further development of the prior art described above and to provide a novel apparatus for determination of the positions of the edges of a paper web, which device is reliable in operation and tolerates interference and is more versatile in operation and detects more accurately and quickly.
• the method in accordance with the invention for predicting the tensile-strength ratio of a paper web is mainly characterized in that the method comprises the following steps:
• a mathematical model is formed between the tensile strength, the web width, and the jet-to-wire ratio based on determination in a laboratory and/or on online measurement,
• a value is computed for the tensile-strength ratio.
• a mathematical model is formed between the degree of drying of the paper web and the web width based on determination in a laboratory and/or on online measurement
• the degree of drying of the paper web is determined.
• the web width is utilized mainly in regulation of the profile.
• a change in the web width can, however, also be used, for example, in order to predict changes in the tensile-strength ratio.
• laboratory measurements and the web width determined by means of on-line measurement are compared, it is possible to form a model between a change in web width and a change in tensile- strength ratio. For utilization of such a model, a precise real-time measurement of the width of the paper web is necessary, so that a traversing apparatus of measurement cannot be used for this purpose.
• a change in the width of the paper web mainly arises from a change in the degree of drying of the web.
• This information can be utilized in the dryer section of the paper machine in monitoring of the drying.
• the width of the paper web is measured before the dryer section, between drying cylinders, and after the dryer section, information is obtained on changes in the degree of drying. Based on this information, it is possible to regulate the operation of the drying cylinders.
• edge measurement devices are fitted at both edges of the paper web, by means of which devices it is possible to measure the location of each edge separately, at the same time, and continuously.
• the edge measurement device can be, for example, an edge measurement camera which carries out determination of the web edge based on identification of outline. The result of determination is transmitted to a data processing equipment for analysis and processing. Pairs of edge measurement devices can be fitted in the machine direction in a number of different locations in different parts of the papermaking process.
• Figure 1 is a schematic illustration of the headbox of a paper machine, of the paper web, and of locations of measurement apparatuses.
• Figure 2 illustrates the relationship between web width and tensile-strength ratio as a function of the jet-to-wire ratio (j/w ratio).
• Figure 3 is an illustration in block diagram form of a system in accordance with the invention for measurement of the edge of the paper web.
• Figure 4 illustrates the principle of regulation of the pressure in a headbox.
• Fig. 1 illustrates an equipment for measurement of the edges of a paper web W.
• a stock suspension jet is discharged out of the slice opening of the headbox 10.
• the precise initial width L 0 of the paper web W is known.
• Each edge of the paper web W is cut to a certain precise width by means of a rear edge cutter member 15 and by means of a front edge cutter member 16.
• the width of the paper web W at this point is denoted with the quantity P. After this, the paper web W shrinks further as a result of draining of water.
• a rear edge measurement device 17 measures the precise location of the rear edge W B of the paper web W
• a front edge measurement device 18 measures the precise location of the front edge W F of the paper web.
• edge measurement devices 17,18 for example, cameras, optical detectors (e.g. 6
• PosiEdge PosiEye manufactured by Valmet
• detectors based on radiation or detectors based on change in inductance of the paper web W are employed.
• the width of the paper web W at the edge measurement devices 17, 18 is denoted with the quantity Q.
• a prior- art traversing measurement device 20 has also been illustrated.
• the shrinkage of a paper web W as a result of draining of water arises mainly from changes taking place in the paper fibres.
• the shrinkage of the paper web W has been examined in the direction of width only.
• the paper web W also shrinks in the machine direction, and this comes out as changes in tension of the paper web.
• Predicting of the tensile-strength ratio from changes in the width of the paper web requires a relatively uniform distribution of fibre orientation.
• the location y 0 of the centre point of the paper web W is also indicated by a dashed line.
• the centre point remains constantly at the same location y 0 in the cross direction without shifting in the lateral direction.
• the paper web W often moves in the cross direction to some extent, and in such a case the centre point is also shifted to the location y 0 ' , as is indicated by the diverging dashed line in the figure.
• a machine-specific model is prepared for each paper machine. For this purpose, from each paper reel, the tensile-strength ratio MD/CD is determined in the laboratory as a function of the jet/wire ratio j/w.
• a corresponding model can also be formed between the web width L and the moisture degree of the paper web W.
• Fig. 2 shows an example of typical curves of measured web width L as a function of the jet/wire ratio j/w and of tensile strength MD/CD as a function of the jet/wire ratio j/w. Based on these curves, a model is formed which is utilized in the data processing device 25 for real time determination of the tensile-strength ratio MD/CD.
• Fig. 3 illustrates the operation of the equipment for measurement of the web width L in block diagram form. From the rear edge measurement device 17 and from the front edge measurement device 18, the data measured by their means are passed along a bus to the data processing unit 25. The data processing unit 25 further receives the data on the jet/wire ratio j/w from the unit 19 and the data on the location of the edge cutter members 15,16. Based on these data, it is possible to compute the shrinkage loss and to determine the value of the tensile-strength ratio
• the data obtained can be displayed in the display 26, which can be, for example, a display monitor or a printer. Further, the determined data on the tensile-strength ratio
• MD/CD is passed to the paper machine control unit 27.
• the regulation unit 27 regulates the set value of the pressure in the headbox 10.
• the value of the tensile-strength ratio MD/CD can also be used for regulation of other quantities in the paper machine. 8
• the determined value of the tensile-strength ratio MD/CD can be used, for example, for determination of the set value of the j/w ratio (jet/ wire ratio) as follows.
• Fig. 4 illustrates the principles of regulation of headbox pressure.
• the unit 31 for regulation of the jet/wire ratio computes the required jet speed on the basis of the set value of the jet/wire ratio and on the basis of the wire speed, and from the jet speed the unit further computes the required headbox pressure, whose set value is transmitted to the unit 32 for regulation of the headbox pressure.
• the headbox pressure is monitored constantly by means of pressure measurement, and the unit 32 for regulation of the headbox pressure transmits a control signal to the headbox feed pump.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Paper (AREA)

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Cited By (2)

Citations (8)

• 1998
  • 1998-05-13 FI FI981058A patent/FI108475B/fi not_active IP Right Cessation
• 1999
  • 1999-05-07 AU AU41466/99A patent/AU4146699A/en not_active Abandoned
  • 1999-05-07 WO PCT/FI1999/000381 patent/WO1999058436A1/en active Application Filing

Patent Citations (8)

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