Equipment Description:Jet to Wire Ratio & Efflux Ratio
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The Efflux ratio is used as one of the main operating variables of the Headbox. The other variables are Stock Consistency and Temperature. Normal operation will have an Efflux Ratio close to one, which means that the dilute stock is travelling at the same velocity as the machine wire when it exits the headbox slice. This will give optimum formation. If the Jet velocity is less than the wire velocity, then the sheet is said to be ‘dragged’. If the Jet velocity is more than the wire velocity, then the sheet is said to be ‘rushed’. These two situations will alter the sheet characteristics as explained below. |
Headbox: This is the unit which controls the delivery of dilute stock going onto the Fourdrinier wire. Formation:This is the term used to describe how the fibres are laid down to make a sheet of paper. Consistency:This is the percentage figure of dry fibres in the water, for example, 2% consistency means 2 grams of dry fibre for every 98 grams of water. |
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When the Efflux ratio is one, this gives good sheet formation because the dilute stock goes onto the wire and forming board at the same speed as the wire. This allows the fibres to orientate themselves more randomly giving good x,y and z directional distribution. When the Efflux ratio is less than one (dragged) this will result in greater machine directional (MD) orientation of the fibres, improving MD strength properties, but reducing the cross directional (CD) strength properties, for example stiffness and tensile strength. Finally, if the Efflux ratio is greater than one, this will result in the dilute stock going onto the wire at a greater velocity than the wire itself, therefore the fibres will have greater random orientation creating what is known as a ‘square’ sheet whereby the MD and CD strength properties will be more equal, however, this mode of running usually results in poor formation. |
Jet to Wire Ratio & Efflux Ratio was also mentioned in the following Fact Sheets (24):
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