Some thoughts on yankee paper machine felt life

Some thoughts onYankeeSome thoughts onYankee
Paper Machine Felt LifePaper Machine Felt Life
Concept:
D K Singhal
deveshksinghal@gmail.com

The PresentationThe Presentation
The presentation is based on my personal
experiences and knowledge acquired over
a period of time.
This presentation just aims to share myThis presentation just aims to share my
views, and readers are advised to consult
their machinery clothing manufacturers,
machine designers and experts before
making any changes in their machine
operating parameters.
2
Some thoughts onYankee Paper Machine
Felt Life, June 2014

Felt Life: What it should be?Felt Life: What it should be?
Unfortunately, we have to just depend on
previous felt life trend, and predicting the
life of the felt is just a good guess.
It is often difficult to estimate the felt lifeIt is often difficult to estimate the felt life
as a function of machine speed, quality
and gsm, number of conditioning boxes,
applied vacuum, type and operating
pressure in press section etc.
3

Felt Life PredictionFelt Life Prediction
It is not difficult to estimate the felt life
on the basis of different parameters, but
such information is not easily available.
I strongly feel all good clothing suppliersI strongly feel all good clothing suppliers
have a capability to predict felt life with
good accuracy.
4

What Does the Press Do?What Does the Press Do?
Simple.The purpose of a press section is
to squeeze the excess water from the
wet web.
5

Press Squeezed WaterPress Squeezed Water
However, the squeezed water is not
clean.There are a lot of fines in it. These
fines go inside the complex matrix of felt
structure, and only a part of these can bestructure, and only a part of these can be
easily removed through felt conditioning
system.
6

Felt ConditioningFelt Conditioning
The objective of felt conditioning is to
remove all trapped fiber fines from the
felt.
However, some do remain trappedHowever, some do remain trapped
inside.
Due to these trapped particles, slowly and
slowly, the felt porosity goes down.
7

Felt Wear on Suction BoxesFelt Wear on Suction Boxes
When a felt passes over the suction
(uhle) box, due to wear, some of the yarns
(threads) of felt may get detached from
the felt.the felt.
That means the felt gsm should decrease
over a period of time.Against this, in
many cases the trapped fibers and fines
are so much in quantity that the overall
felt gsm increases.
8

Yankee MachinesYankee Machines
Yankee machines have two different felt
configurations-
Pick Up Felt (no press)
Pick Up Felt (with press)Pick Up Felt (with press)
If there is a press section, we use double
felting, with top felt passing through MG
(yankee) and touch roll.
9

What Makes Top Felt ImportantWhat Makes Top Felt Important
Being yankee cylinder the only drying
cylinder, proper pressing of web on this
cylinder is very important. Furthermore,
the combination hot yankee cylinder and
a touch roll also works as a hot pressa touch roll also works as a hot press
where water is pushed away from yankee
towards the touch roll (obviously through
the felt).
A choked felt affects production and
product quality significantly.
10

Back to the Wire PartBack to the Wire Part
Stock from the headbox lands on the
wire part. Most long fibers remain on the
wire, while some of the fines drain
through wire along with back water.through wire along with back water.
As most of this water goes to fan pump
slowly the fines concentration increases
to an equilibrium.
Finally, some fines start remaining trapped
between ‘good’ fibers in the web.
11

Fines DistributionFines Distribution
As obvious, most fines from the bottom
layer of paper web drain out while the
fines in the upper layers remain present in
the web.
Imagine paper as a sandwich of two layersImagine paper as a sandwich of two layers
one with and other without fines.
When this paper goes to press section,
water is squeezed out.
Water from the side containing more
fines go towards the pick up felt.
12

Yankee FeltYankee Felt
Whatever be the machine configuration-
with press section or just yankee touch
roll after the wire part- the yankee felt
comes in contact with top layer of papercomes in contact with top layer of paper
web.
The top layer of paper web contains
more fines.
During pressing, a many fines move from
paper web to felt.
13

Yankee FeltYankee Felt
If these fines are not removed effectively,
the felt gets choked up too early.
If we are able to improve FPR on paper
machine, there will be a better fibermachine, there will be a better fiber
distribution across the thickness of paper,
meaning relatively lesser fines in the top
layer, and better felt performance.
14

Felt Choked with FinesFelt Choked with Fines
To evaluate the quantity of fines in the
felt, an old used felt just prior to take off,
was washed on the machine itself as in
normal operation.normal operation.
Then, the felt was cut, and a small piece of
this (30cmX30cm) was removed from the
center.
This sample was dried in oven at 105˚C
and gsm was evaluated.
15

Felt Choked with FinesFelt Choked with Fines
The new felt was of 1286 gsm (design
1300gsm), and in spite of some felt yarns
might have worn away, the gsm increased
to 1640.to 1640.
This indicates more than 356gsm fines
and other material had accumulated in
the felt over its lifetime.
16

FPRFPR
So, FPR plays a critical role in getter
better yankee felt life.
Other aspect is good felt conditioning.
Felt conditioning system should be suchFelt conditioning system should be such
that fines are easily removed from the
felt.
17

Felt ConditioningFelt Conditioning
Periodic use of flooding shower from the
inside of felt circuit may help a lot.
Additionally, use of lubricants like
kerosene oil helps easy removal of fineskerosene oil helps easy removal of fines
from the felt.
18

Kerosene Based CleaningKerosene Based Cleaning
To recall, the procedure is as under-
◦ Stop all showers, reduce load to minimum.
◦ Spray kerosene on the felt.Typically, a quantity of
10-20% of weight of felt will be enough.
◦ Let the felt run for 5-7 minutes.◦ Let the felt run for 5-7 minutes.
◦ Now apply caustic or detergent using a shower,
and again let the felt run for 2-4 minutes.
◦ Open flooding shower, and wash the felt
thoroughly.
◦ After some time, apply vacuum to completely
drain out chemicals from the felt.
19

Felt Cleaning ChemicalsFelt Cleaning Chemicals
Alternate to kerosene, ask your chemical
supplier to suggest a good felt cleaning
chemical.
At first instance a felt cleaning chemicalAt first instance a felt cleaning chemical
look costly, or you might feel satisfied
with the existing caustic-detergent
mixture, but remember this chemical may
increase your felt life.
20

Press LoadingPress Loading
Yankee machines generally have limited
press nips.
There could be a solid double felted
press, followed by touch roll and second
touch roll.touch roll.
In double felted press, normally a single
felt passes through two nips.
In case of two touch rolls also, sometimes
a single felt is used to pass through both
nips.
21

Touch Roll LoadingTouch Roll Loading
However, the critical part is the nip
between yankee touch roll and hot
yankee cylinder.
A high nip pressure also means longer nipA high nip pressure also means longer nip
width, more dwell time.
Some of the gets moisture gets
evaporated and this forces the moisture
in the web towards the felt at a faster
rate.
22

Touch Roll LoadingTouch Roll Loading
Furthermore, in longer nip with low basis
weight papers, a lot of heat is also
transferred to the felt itself, thus raising
the felt temperature (and, of course, thethe felt temperature (and, of course, the
steam consumption).
The overall impact is more fines going in
the felt, increased felt temperature, more
compaction of the felt, thus reducing felt
porosity further.
23

Excess Nip LoadingExcess Nip Loading
Excess nip loading also results in more
felt compression each time the felt passes
the nip.
Have you noticed the car seat becomesHave you noticed the car seat becomes
hard and compacted to early if a fat man
uses the car.
In the same way, excess loading reduces
yankee felt life.
24

Optimizing Nip LoadingOptimizing Nip Loading
Many papermakers tend to use as high nip
loading as possible in order to get best
results from the nip.
However, it is always advisable to run the
machine at different nip loadings for smallmachine at different nip loadings for small
durations (4-6 hrs.) and observe the steam
consumption in yankee as well as paper
surface properties.
All these data should be evaluated before
deciding an optimum nip loading.
25

SummarySummary
In a nut shell, three main parameters need
attention if yankee felt life is too low-
1. FPR1. FPR
2. Nip Loading
3. Felt Conditioning
26

ThankYou.ThankYou.ThankYou.ThankYou.
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About the Author:
Born in 1968, D K Singhal is B.E., M.E. (Pulp & Paper, 1993) from Deptt. of Paper
Technology, University of Roorkee (now IIT, Roorkee). He is a Certified Energy
Auditor and Chartered Engineer also.
With nearly 7 dozen publications, he has emphasized on development of low cost
technologies and management practices for quality and profitability improvement.
With publications on slideshare.net, energymanagertraining.com and
paperonweb.com, he has been constantly contributing to IPPTA (Indian Pulp &
PaperTechnical Association). He is also serving IPPTA as a member of Editorial
Board.Board.
An initiative by D K Singhal, a cyber campaign initiated against unjustified targeting
of paper industry by “Idea” mobile, in their “Sirjee” advertisement campaign, after
which this advertisement was taken off air.
He also moderated aYahoo group,“PaperTechnology” with nearly 360 members
from India and abroad to discuss problems related to pulp & paper making for five
years.
He can be contacted at deveshksinghal@gmail.com
28

Some thoughts on yankee paper machine felt life

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