1961 Volume 2

The measurement of paper uniformity is discussed with special reference to those methods providing information that may be used to investigate the sources of variation of structure and properties. The flocculation of fibres in the stock and the hydrodynamic properties of the head box are shown to be the major causes of heterogeneity.

Fibre flocculation is both a direct source of heterogeneity and a factor affecting the fluid mechanical properties of the stock. The flow properties of fibre suspensions are described on the basis of pipe flow studies and the significance of these studies to head box flow is discussed.

The head box is considered as a source of non-uniformity with some reference to the significance of secondary flows. Experimental methods are described that may be used to assess head box performance to investigate conditions that give rise to poor uniformity.

Areas in which further research is desirable are indicated.

If we want to describe the flow of fluids through a porous medium, we generally use for the equation of motion an empirical relationship that is usually called Darcy’s law (see Scheidegger⁽¹⁾)

The course of the papermaking process, as it occurs on a Fourdrinier machine, is analysed to illustrate how each functional operation performed by the machine influences the final product. The analysis starts with the role played by the slice and its approaches and special emphasis is given to the many compromising factors that determine holey roll design and behaviour. The effect of slice design on orientation, flocculation and jet delivery is also considered. It is shown that the concept  of a fibre network structure for the stock with a strength that varies with fibre consistency, length and type explains many of the observations .

The distinction between macro- and microformation is defined and the relative effects of the head box and table suction on these properties are illustrated. It is concluded that gross relative motion of stock on the wire is detrimental to macroformation, but that short range relative motion is beneficial to microformation and results in a more uniform fibre distribution than is possible by random turbulent diffusion processes in the head box alone.

The variation of sheet properties across the sheet thickness are discussed and it is concluded that selective filtration that occurs during the forming operation is the principal cause, not the backwashing of the sheet by inflow of water at table rolls, as is ,frequently reported.

A brief speculation on the construction of the `idealised’ machinemade paper sheet is presented.

It is a privilege and an honour for me to have been asked by the organising committee to give the concluding summary to this symposium. Although I have been working on cellulose and cellulosic fibres off and on since graduate school, until now, I have not published a single paper in the field of paper structure and properties. This symposium has been a most informative and enlightening part of my education as a scientist . Because of my assignment, I have tried to understand and, if possible, assimilate the various contributions to the symposium. Needless to say, this has been a strenuous task. The hydrodynamic discussions have been difficult for me to follow . I have had to annoy both chairmen and speakers by asking questions in my attempts to get a more complete picture of the subject matters discussed: I am grateful for the answers . My situation has often reminded me of a story from the University of Uppsala, my Alma Mater. One of the physics professors was known to have an unusually detailed and comprehensive knowledge of both classical and modern physics . One of his colleagues asked him, out of curiosity, `How did you acquire all this fabulous knowledge? You are, after all, a highly specialised physicist in atomic spectra.’ ‘Well, you see, I have to take many oral examinations . By a systematic questioning of the students, then comparing the answers from the bright ones, I have learned a lot in all branches of physics, without reading all the books,’ was his reply. This is in fact what I have done here.