Some thoughts on yankee paper machine felt life

Some thoughts on Yankee Some thoughts on Yankee Paper Machine Felt LifePaper Machine Felt Life

Concept:

D K Singhal

[email protected]

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 my � This 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.

2Some thoughts on Yankee 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 life � It 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.


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 suppliers � I strongly feel all good clothing suppliers have a capability to predict felt life with good accuracy.


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.


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 be structure, and only a part of these can be easily removed through felt conditioning system.


Felt ConditioningFelt Conditioning

� The objective of felt conditioning is to remove all trapped fiber fines from the felt.

� However, some do remain trapped � However, some do remain trapped inside.

� Due to these trapped particles, slowly and slowly, the felt porosity goes down.


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.


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.


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 press a touch roll also works as a hot press where water is pushed away from yankeetowards the touch roll (obviously through the felt).

� A choked felt affects production and product quality significantly.


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.


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 layers � Imagine 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.


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 paper comes 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.


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 fiber machine, there will be a better fiber distribution across the thickness of paper, meaning relatively lesser fines in the top layer, and better felt performance.


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.


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.


FPRFPR

� So, FPR plays a critical role in getter better yankee felt life.

� Other aspect is good felt conditioning.

� Felt conditioning system should be such � Felt conditioning system should be such that fines are easily removed from the felt.


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 fines kerosene oil helps easy removal of fines from the felt.


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.


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 chemical � At 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.


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.


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 nip � A 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.


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, the the 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.


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 becomes � Have 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.


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 small machine 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.


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


Thank You.Thank You.Thank You.Thank You.


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 & Paper Technical 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 a Yahoo 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 [email protected]


Some thoughts on yankee paper machine felt life

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