Pressurised Headbox General Details Paper Machines

Your Partner in Paper Making 

Micro Fab Industries 

India 

info@microfabindustries.com 

Micro’s Pressurised Headbox (Parameters) 

1.1 General 

Formation as well as most other qualitative properties of the sheet 

depends decisively on the operating condition of the head box . To put it 

strongly , the quality of the paper is established in the head box and on the 

first 2 to 3 m of the wire section 

The table below lists the most important factors affecting formation : 

Formation 

Furnish ** 

Freeness ** 

Chemical Additives * 

Headbox Design * 

Headbox Consistency ** 

L/B Ratio ** 

Jet/Wire Speed Ratio * 

Location of Forming Board * 

Dewatering Elements ** 

Factors affecting formation 

** = Strong effect 

* = Moderate effect 

Address 

5006 IV Phase Opposite to 

Shah Paper mill Vapi Gujarat 

Telephone No 

+91-260-2421056 

+91-260-2435606 

Contact Details 

kunal@microfabindustries.com 

Cellular +91-9574000186



India 


Most of these operating parameters affect , besides formation , also 

other qualitative properties of paper . As the stock applied has an effect on 

the optimum values of the operating parameters of the head box as well , 

the operating conditions of the head box must be optimised through trail 

runs on each paper grade when starting up a new head box 

1.2 Headbox Consistency 

The Slice opening together with the head box pressure determines the 

volume of the head box jet flow and thus the consistency of the outflowing 

stock . 

The Slice opening also affects also the qualitative properties of paper . 

* Outflow Volume will increase 

* Better formation will be achieved in general 

* Retention will Become poorer in general 

1.3 L/B Ratio 

The Angle at which the stock jet hits the fabric can be changed by 

altering the so-called L/B ratio 

It is possible to change the direction of the jet by moving the profile 

strip in horizontal direction 

* When moving the profile strip backwards, the L/B ratio will increase and 

the jet impact point on the fabric will move further away from the head box 

In Practice , the L/B ratio on a paper machine varies in the range 

between 0.8 — 1.2 . If the velocity changes considerably , re-check the jet 

impact point . 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186



India 


1.4 Location of forming board 

Always direct the jet to the front of the leading blade of the forming 

board so that the blade 

* Somewhat splits the jet 

Air bubbles in the look through of paper can be often eliminated by 

directing the jet more ahead of the first blade 

Location of forming board is determined by head box operating 

parameters : 

* With a low consistency , wide slice opening and the profile strip drawn 

back (L/B ratio about 1) , the distance of the forming board from the breast 

roll centre must be larger than with a higher head box consistency . 

The jet impact point affects also formation and retention 

Too sharp an angle causes rigorous initial dewatering , thus deteriorating 

retention 

On the other hand , good formation demands rather efficient initial 

dewatering . 

In the vertical direction , the forming board is often located on the 

fabrics level in order to eliminate generation of air bubbles in the look - 

through 

1.5 Jet-to-wire Speed Ratio 

Normally , the speed of wire and jet on a paper machine are not the 

same . The speed difference is given as jet-to-wire speed ratio , or in 

percents 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186



India 


Said ratio is used to control the velocity of head box outflow . The jet 

velocity can be altered as follows : 

* By adjusting the set-point of jet-to-wire speed ratio . The head box 

pressure will then change as programmed in the computer to correspond 

to the new jet-to-wire speed ratio . The wire speed will not change 

The Formation Improves as the STFI value decreases 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186



India 


* By changing the wire speed . The computer will then recharge the head 

box pressure in order to keep the jet-to-wire speed ratio constant . 

The outflow velocity is controlled , especially in North America , by giving 

the computer the jet-to-wire speed difference in Percents . Thus , when the 

set-point is 

* e.g +1.0 % , the wire speed is lower 

* e.g - 1.0 % , the wire speed is higher 

The jet speed will change if the speed or set-point of the wire is changed 

The jet-to-wire speed ratio affects 

* formation 

* fiber orientation 

The formation of paper is generally best with the ratio is close to 1.0 , but 

however , never precisely 1.0 

The jet-to-wire speed ratio has a significant effect on run ability. When the 

ratio differs considerably from value 1 , the fibres will orientate , i.e settle , 

in the machine direction finer orientation affects several strength properties 

of paper 

* Tensile strength 

* Stretch 

* Tearing strength 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186



India 


The MD Tensile Strength increases uo to certain point when the jet-to-wire 

speed ratio deviates from 1 . 

When the fibre orientation increases (jet-to-wire speed ratio deviates 

from value 1). 

* the MD tensile strength increases 

* The MD stretch increases 

* The MD tearing resistance decreases 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186



India 


The CD tensile strength decreases when the jet-to-wire speed ratio differs 

from 1 

The MD Stretch is at its minimum when the jet-to-wire ratio is 1 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186



India 


The Correct jet-to-wire speed ratio is found experimentally . In general , 

the ratio is slightly less than 1, but a ratio some what above 1 is also 

possible . 

The MD tearing resistance decreases when the jet-to-wire speed ratio comes 

closer to 1 

Correlation between bulk and wire-to-jet speed ratio 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186



India 


Correlation between porosity and jet-to-wire speed ratio 

Address 



Telephone No 

+91-260-2421056 

+91-260-2435606 



Cellular +91-9574000186

Pressurised Headbox General Details Paper Machines

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