Packages » Headbox

Description

The headbox model estimates the jet trajectory since it leaves the headbox until it reaches the wire. There is basically two main contributions: The geometric effect, which depends on the shape and position of the lips, and a gravitational effect, which accelerates the jet in the z-direction. The joint effect of this contribution determines the region and the velocity components when the jet reaches the wire.

In the figure below is shown PaperSim calculations for the geometric effect only for a 45-degree slice in its 3D visualiser.


Flow from Headbox According to Attwood


By adding the gravitational effect, PaperSim then estimates the proportion of the jet that is deflected before the forming box and the remaining part that stays on the wire. The figure (Wahren 1990) below illustrates this:


Wahren's Picture

The figure above is published with the kind permission of Professor Douglas Wahren.


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References

Wahren, D., 1988, Nordic Pulp and Paper Research Journal 3 (Special Issue), 29-38.


For more information, please, contact:

Vinicius Lobosco, PhD, +46 73 925 8476

or

Klas Samuelsson, PhD, +46 70 668 5515


Jet Deflection on Impingement

Initial Forming

The figure above shows simulation results for a 25 g/m2 jet where deliberated low grammage was chosen in order to highlight the influence of jet deflection. The colours give the porosity (concentration) of the fibre in water. The paper sheet is being formed on the wire (at the lower edge of the figure). A 10 g/m2 fraction of the jet is deflected and therefore we can observe a mat that is immediately formed. This can be seen at the very lower part of the left edge of the figure.