Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1992-06-24
1994-07-19
Evans, F. L.
Optics: measuring and testing
By polarized light examination
With light attenuation
348142, G01B 1100
Patent
active
053314050
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for measuring the flexibility of fibres, particularly cellulose fibres, in a flowing suspension. The invention also relates to an arrangement for measuring the flexibility of fibres in accordance with the novel method.
In order to be able to vary the quality of paper in paper manufacturing processes, it is important to know the various properties of the fibre material used in such processes. Paper of the type and quality desired can be produced by controlling the fibre properties of the fibres used. One of the properties of the fibre material used is the flexibility of the actual fibre itself. Various methods are known by means of which fibre flexibility can be measured. These known methods are based on measuring individual fibres or fibre samples which are disposed in a particular manner, subjected to load and the downward flexing or bending of the fibres, for example, is recorded.
One such measuring method is described in an article entitled "The Flexibility of Wet Pulp Fibres" by P.A. Tam Doo and R.J. Kerekes presented in the publication Pulp and Paper, Canada, 83:2 (1982), wherein a fibre support system is used for measuring individual fibres. The article also discloses the significance of measuring fibre flexibility.
An example of a laboratory method for measuring fibre flexibility is described in an article entitled "The Hydrodynamic Behaviour of Paper-Making Fibres" by O.L. Forgacs, A.A. Robertson and S.G. Mason presented in the publication Paper and Paper magazine of Canada, May 1958. In this case, fibres are classified in laminar flow in a shear field with respect to the rotational paths of the fibres, wherein several different rotational paths that are dependent on the flexibility of the fibres are described.
As before indicated, the aforedescribed, known methods are used solely for off-line-measuring purposes. The object of the present invention, however, is to enable the flexibility of fibres to be measured automatically, i.e. rapidly, such as to be enable fibre flexibility to be measured on-line. Naturally, the measuring process shall also be capable of being carried out in a simple fashion and of providing a definite measuring result.
According to the present invention, the fibre-flexibility measuring method described in the introduction is characterized primarily by registering the fibre form of a large number of fibres at two different suspension flow states, which are created, for example, by varying the rate of suspension flow within the framework of a given flow geometry, by calculating a predefined fibre form for each flow picture, and by determining a relationship, e.g. the quotient, between the two measurements of the predefined fibre form, i.e. the mean fibre form, and utilizing this relationship to define fibre flexibility. Advantageous embodiments of the novel measuring method are set forth in the following dependent method claims.
It will be noted that several different methods are known by means of which fibre form can be defined. In those measuring processes carried out in conjunction with the inventive method, the fibre form has been given as the relationship between actual or true fibre length and the length of the diagonal in a fixedly located rectangle which circumscribes the fibre. The orientation of the rectangle has therewith been locked and coupled to the equipment and not to the direction of the fibre. The fibre has also been assumed to be oriented in a two-dimensional plane.
The arrangement constructed for the purpose of carrying out the inventive method is particularly characterized in that it includes a tubular container for accommodating the flowing suspension; a transparent window provided in the container wall; a CCD-type camera which functions to photograph fibres flowing past the window; a picture analysis unit coupled to the camera; and a data processing unit for processing information delivered from the picture analysis unit.
Advantageous embodiments of the novel measuring arrangement are set forth in the following dep
REFERENCES:
patent: 4253329 (1981-03-01), Karnis
Fransson Per-Ivar
Karlsson Hakan
Kastre Lehard
Evans F. L.
STFI
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