Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/34—Paper
  • G01N33/346—Paper sheets
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/02—Details not specific for a particular testing method
  • G01N2203/026—Specifications of the specimen
  • G01N2203/0262—Shape of the specimen
  • G01N2203/0278—Thin specimens
  • G01N2203/0282—Two dimensional, e.g. tapes, webs, sheets, strips, disks or membranes

Definitions

• the present invention relates to a method to predict and/or control the strength properties of a foil-like material in relation to machinery and processes for manufacturing this material. It especially relates to properties with regard to the tensile strength and tensile strength index (tensile index) of the foil-like material in question.
• the invention is based on the use of and access to statistical information regarding local mechanical properties, especially local tensile stiffness and local tensile stiffness index.
• the foil-like material is paper
• a specially interesting characteristic of the invention is that it makes it possible to achieve a suitable trade off between the tensile strength of the paper and the variation in other important measured properties of paper.
• the tensile strength is not always greatest when variations in basis weight are minimised. In practice, this means that a compromise must be made. In many processes for manufacturing paper, it would thus be of greatest importance if the mechanical strength of the paper could be frequently predicted to allow rapid control measures to be taken and also to make it possible to achieve the desired quality in the final product.
• the tensile strength of paper is predicted by means of models that are based on information regarding the mean value of modules of elasticity that are measured in different directions in the material. These modules of elasticity are increasingly often estimated on the basis of measurements that give the phase velocity of ultrasound in the material. Predicting tensile strength based on information about the spatial variations in basis weight of paper, such as the formation number, have also been tested in practice but have had only limited success.
• an adjustment of the strength value and/or control signal is made as a result of structural differences in the foil-like material based on local measurements of at least one further mechanical property, preferably bending stiffness.
• the measurements are preferably carried out on a mm-scale with a high frequency of repetition in relation to the dynamics of the process.
• the foil-like material comprises paper especially. At least one of the local mechanical properties is measured in what is per se a known manner, especially by means of the arrangement described in US 5 361 638.
• Fig. 1 shows in diagram form the relation between a standard test and an ultrasound test on paper at different indices of tensional stiffness and beating levels for pulp;
• Fig. 2 shows in diagram form the relation between mean values of index of tensional stiffness and index of tensional strength for different levels of beating;
• Fig. 3 shows in diagram form the relation between measured index of tensional strength and, according to the invention, the predicted index of tensional strength for different levels of beating;
• Fig. 4 shows in diagram form the relation between strength quotient and stiffness quotient at varying conditions of orientation (81 samples, 3 forming units and 3 different pulps).
• the new observation on which the present invention is based is that successful prediction of the strength properties of paper, for example tensile strength, requires the use of data for both the mean value and the statistical variations in the local tensile stiffness (Its) and/or the local tensile stiffness index (ltsi) measured with a spatial resolution at the millimetre level.
• the statistical variations can be expressed by the measured maximum and minimum values, the standard deviation ⁇ , the coefficient of variation CV or a number of other parameters that can be obtained from the statistical frequency function for the measured local mechanical properties. (Information regarding the local variations in tensile stiffness index can be obtained from the local tensile stiffness data if the local basis weights have also been measured at the same locations).
• the type of predictive model that we have found to be very useful is based on information about both mean values and statistical variations in local tensile stiffness and/or local tensile stiffness index measured on a millimetre scale.
• the mean value m of the tensile stiffness and the tensile stiffness index firstly give a value of the upper limit of the tensile strength that can be achieved. This upper limit can only be achieved if the paper has a completely even structure, i.e. if it lacks disturbing local variations.
• Tensile strength index f* g(stiffness-MD, stiffness-CD)
• Tensile strength index f * g *h(stiffness-MD, stiffness-CD, stiffness-ZD)
• the present invention can also lead to an improved prediction of the tensile strength of a material on the basis of indirect measurements.
• the method is complemented by utilising a relation between data from a number of other local measurements and the local tensile stiffness and/or the local tensile stiffness index, which are required to obtain a better prediction. This naturally applies if a relation can be confirmed at the actual process conditions.
• Examples of indirect measurements that may be used (separately or in combination) to generate data for this type of prediction are local basis weight, local optical density and local thickness of the paper.
• tear strength and compression strength are similarly dependent on variations in the local mechanical properties, such as the local stiffness (in the plane and/or the thickness direction) and the local rigidity to bending, i.e. properties that are measured with a high spatial resolution.

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• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Paper (AREA)
• Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)

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Publications (1)

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Citations (5)

• 1998
  • 1998-07-31 SE SE9802652A patent/SE514572C2/sv not_active IP Right Cessation
• 1999
  • 1999-07-07 CA CA002337335A patent/CA2337335A1/en not_active Abandoned
  • 1999-07-07 AU AU50765/99A patent/AU5076599A/en not_active Abandoned
  • 1999-07-07 EP EP99935247A patent/EP1101109A1/en not_active Withdrawn
  • 1999-07-07 WO PCT/SE1999/001237 patent/WO2000007010A1/en active Application Filing

Patent Citations (5)

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