press fabric design for modern paper machines · 2019-05-23 · even sided dewatering drop offs on...

TAPPI Paper Machine Operations Course

Press Fabric Design for Modern Paper Machines

Ellen Gibbs


TOPICS• Pressing

• Press Fabric Function• Roll Types• Press Section Arrangements

• Press Fabric Properties• Press Fabric Structure & Nomenclature• Review Press Fabric Design• Conditioning• Moisture Equilibrium• Returned Fabric Analysis• Troubleshooting


Functions of a Press Fabric

• Accept water from the sheet• Sheet Solids 12-20% 40-50%

• Consolidate the fiber to increase strength• Transport the sheet through the press• Impart desired sheet finish• Power transmission• Uniform pressure distribution


Forming Section5,947 gpm

Press Section124 gpm

Dryer Section72 gpm

Water Removal


Cost of Water Removal

0%10%20%30%40%50%60%70%80%

% o

f Tot

al Co

st

FormingSection

PressSection

DryingSection


Press Rolls

Sheet

Simple Press Section

Felt

Felt Rolls

Guide Roll

Tension Roll


Water Removal

@ 4000 fpm water removal occurs in 0.002 seconds

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

-0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40 0.50

Position (inches)

Stre

ss (p

si)


Sheet Dewatering

• Pressure• Time• Temperature


Roll Types• Plain • Suction • Grooved• Blind Drilled • Granite


Plain Press

Slow speed 1000 fpm (305 mpm) and below Latter nips Addition of paper roll after nip to separate sheet

from felt


Suction Press

Typically used in PU, Top, Bottom, Transfer Postions

Usually driven roll 15-30% open area


Grooved Press

Vented roll to enhance water removal Centrifugal force on outgoing nip slings water out Usually harder than 12 P&J; open area ~16%


Blind Drilled Press

Cheaper than a suction roll Can use smaller holes than suction rolls- less

tendency for shadow mark compared to suction Can be as soft as 50 P&J (softer than grooved rolls)

less tendency to close;open area ~20% More Void Volume than a grooved roll


Double Felted Press


Wahlstrom Model

Peak MidNip Pressure (PP)

PP = Pms + Ph


• As the paper web is compressed, water is removed from the space between the fibers and the walls of the fibers

• The water escapes into the press fabric and the press roll• Two situations can occur depending on whether the web can be

compressed further – Pressure or Flow controlled


Sheet Dewatering

• Pressure Controlled• Lighter sheets• Free draining furnishes• Dryness is a function of peak pressure

• Flow Controlled


Sheet Dewatering

• Pressure Controlled• Flow Controlled (time dependant)

• Typical of heavy sheets, or low freeness

• Early presses of light sheets


Sheet Dewatering

• Flow Controlled• Linerboard• Corrugating Medium• Food Board

• Pressure Controlled• LWC• Newsprint• SC Grades• Directory


Sheet Dewatering

• Flow Controlled• Long Dwell Time• Large Roll

Diameters• Soft Covers• Double Felting• Shoe Press

• Pressure Controlled• High Peak Pressure• Small Roll Diameters• Hard Roll Covers• Single Felted


Pressing - Mechanical

• Lineal Load• Roll Diameter• Cover Hardness• Cover Material• Cover Thickness • % Open Area


Hydraulic• P (Hyd) Adds to Peak Pressure• Need Sufficient P(Hyd) for Best Drying• Excessive P(Hyd) Results In:

o Sheet Crushingo Sheet Blowingo Batt Fiber Damageo Roll Cover Wear


HydraulicInsufficient P (Hydraulic) for a Specific Combination of Fabric Structure and Operating EnvironmentWill Result in

Slow Startup

Poor Drying


Press Theory Wahlstrom model Single felted nip

Hydraulic pressure on felt side < plain roll side Differential in hydraulic pressure – water removal

Amount of sheet dewatering Force Time Flow resistance of sheet Propotional to Nip Impulse

Nip Impulse (Pa.s ; lb.s/in) ave nip pressure x dwell time nip load/machine speed


Effect of cover hardness & fabrics on nip

P&J KN/m (pli) felt Peak pressure MPa

7 70 (400) Single 4

7 92 (525) Double 4

37 130 (740) Single 4

37 144 (820) Double 4


Granite Roll

Smoothness Good release properties Manmade rubber, resin &

ceramic


Press Section Arrangements

Open Draw Press Transfer Press Inclined Press Combination Pickup Press No-Draw Press Arrangements Shoe Press

Others...


Open Draw Press SectionStraight through pressUp to 2000 fpm (610 mpm)

Suction PressGroove Press

Open Draw

Felt


Water Removal by Position

0%

10%

20%

30%

40%

50%

60%

70%

1st Press 2nd Press 3rd Press 4th Press


Reverse Press SectionReduce two-sidedness Max 1200 fpm (365 mpm)

Suction PressGroove Press

Open Draw

Felt


Transfer Press SectionTransfers sheet from top felt to bottom feltTwo presses before the 1st open draw – 2nd press somewhat inefficientUp to 4000 fpm (1220 mpm)

Suction PressGroove PressSuction Pickup

Open Draw

Felt


Inclined Press Section - TwinverHigher loadings in the 1st and 2nd pressTwo efficient presses before open drawEven sided dewateringDrop offs on heavyweights

Suction Press

Groove PressSuction Pickup

Open Draw

Felt


Combination Pickup Press SectionMinimum two-sidednessEliminated drop-offs on heavy weight machinesOpen draw limited speed

Groove PressSuction PickupSuction Press

Felt


No-Draw Press Sections – TrinipSpeeds in excess of 3400 fpm (1036 mpm)Uneven dewateringHigher loadsPotential shadow mark/two sidedness

Groove Press

Suction Pickup

Open Draw

Groove Press

Felt


Trinip w/ 4th Press4th press to “even” dewatering & reduce sheet two-sidednessSmall increase in sheet dryness

Groove Press

Suction Pickup

Open DrawGroove Press

Groove Press


Trivent w/ 4th pressEliminate the suction roll mark from trinip configuration

Groove Press

Suction Pickup

Groove Press

Groove Press Groove PressFelt


Shoe Press Assembly, Support

Beam,Static Shoe Press

Assembly

Shoe Press Belt, acts as flexible roll cover.

Counter Roll RotatesDriven (Drives belt)

Oil Film

Shoe Press Design

Stationary, HydraulicallyLoaded Shoe


Shoe Press• First developed in 1980• Uses a metal plate to squeeze water out of

sheet• Shoe belt rotates during running• Belt is grooved – works like a tire on a wet

road• Oil is supplied inside to provide lubrication,

thermal protection and loads the shoe• Sheet dryness in press section goes from

21-22% up to 50-52%


Shoe press operating conditions

Shoe

Shoe Belt

Top press felt

Paper

Bottom press felt

Counter roll

• Shoe presses are used to make all grades

• Operating loads are between 300 – 1500 kN/m

• Most shoe presses operate at 1000 kN/m or lower (6000pli)

• Machine speed can be from 150 - 2000 m/min

• Machine speed decided by paper grade

• The shoe can be in the top or bottom position


Shoe press market usage


Shoe press dewatering

MPa• Nip width is longer• Higher pressure can be

applied• Shoe belt allows venting of nip


Uhle box vs. nip dewatering

MD

Uhle box dewatering:• Felt removes water

from sheet• Uhle box is a vacuum

box to remove water from felt

• Restricts machine speed – need min dwell time


Uhle box vs. nip dewatering

MDNip dewatering:• Water removed via

belt grooves• Spray enters save-all

pan and is taken away• Allows higher

machine speeds to be reached


Why use a shoe press?• Longer dwell time in the

press• Increase dewatering

Extend nip length

• Increase machine speed• Better sheet strength –

less breaksIncrease sheet

dryness

• Better sheet stiffness• Use less fiber to make

the same paper

Increase sheet bulk

Increased profit


Common machine configurations – one shoe press

• Shoe press in 2nd press• Good option for machine

rebuilds

• Shoe press in 3rd press• Enables high speed

manufacture


Shoe Press – BoardNo open draw

Shoe

Shoe BeltFelt


Single Shoe Press

• Grooved bottom roll• Grooved belt


Single nip shoe press

Benefits 46-48% dryness Less expensive to install Less space required Lower operating cost

Press fabrics Energy consumption –

drives and vacuum

Press fabric design Fine surface to overcome

roughness Fine enough base to not

strike through Shorter felt life – fine

webs


Common machine configurations – two shoe presses

• Shoe press in 1st & 2nd

position


Process belts are polyurethane covered fabrics used on a shoe press to dewater


Felt – belt interaction

• Dewatering in the shoe press relies on both felt and belt

• If felt and belt don’t match we can see:

• Marking • Poor dewatering• Wear

• The felt/belt combination can help create either uhle box or nip dewatering


Felt – belt interaction example

Total 750cm3/m2

450cm3/m2

450cm3/m2

300cm3/m2

300cm3/m2

Total 750cm3/m2

The ratio of press fabric to belt void volume can be altered while maintaining the same overall void volume in the press nip. Choosing the correct void volume configuration can optimise the dewatering of both products.


Shoe belt product requirements

Crack resistance Abrasion resistance Modulus

Impact resistance Dewatering


Shoe belt construction

Functional Layer: Long lifetime and excellentdewatering on the felt side.

Base fabric: Excellent dimensional stability, reinforces belt structure to allow optimum high speed operation.

Shoe side: Slides across shoe oil film, acting like a sliding bearing.


Shoe belt groove styles

GL

D

C

GL

D

C

g

U grooves E grooves

• Standard grooves• Proven technology• Good for HSPG manufacture

• Developed from U grooves • Manufactured for a long

time• Good for highly loaded

presses


Grooved Belt Parameters

PARAMETER RANGE THICKNESS (mm) 4.8 TO 5.3

HARDNESS (Shore C) 68 TO 73

LAND WIDTH (mm) 1.8 TO 2.5

GROOVE DEPTH (mm) TO 1.5 mm

GROOVE WIDTH (mm) 0.64, 0.72, 0.79, 0.95

VOID VOLUME (cc/sqm) 200 TO 365


Impacts of wrong application – shadow marking

Shadow marking is a felt belt interaction issue


How does marking occur?Caused by a combination of groove width and press fabric design

1. Press fabric too thin

2. Groove too wide

Shadow Marking

Groove Opening > 1.0mm

Paper SheetThicker Press Fabric

Narrower Grooves

Groove Opening > 1.0mm

Paper Sheet

Paper Sheet

Groove Opening < 1.0mm

2 possible solutions


How does groove closure occur?

Loading

u – grooves flex under load

Groove edge fatigue

Loss of performance & life time

Groove closure

Poor dewatering

Uncompressed Compressed @ 10MPa


Nip Pressure Profiles

0

200

400

600

800

1000

1200

1400

Position (inches)

Stre

ss (p

si)

Roll Press Shoe Press

Press Type Roll dia. M (in) Nip width mm (in)Conventional 1.1 (45 ) 40 (1.57)LDR 1.8 (72) 100 (4.0)Shoe Press 250 (10)


Other Press Sections

n Board Gradesn Tissue / Towel Machines


Double Felted LDR – BoardHeavy weight board grades, high volume of waterHeavy loadsDouble felted – two sideded dewatering

Felt


Long Bottom – Forming & Pressing Suction Drum “Long” Top or Top – most have been eliminated 2nd Main Press

Cylinder Machine


Tissue Requirements

n Delicate sheetn Small amount of water removaln High speeds


Two Felt Tissue Machine (“flat” tissue)

Suction Pressure Roll

Suction Press

Felt


Single Felt Tissue Machine

Felt

Suction Pressure Roll


Press Nip Profile ComparisonNewsprint Tissue-

PM 1Tissue-

PM 2Top Roll 45”/

0 P&J144”/0 P&J

180”/ 0 P&J

Bot Roll 42”/0 P&J

32”/40 P&J

30”/36 P&J

Lineal Load (pli)

500 500 500

Speed (fpm)

4000 2800 6000


Nip Comparisons

00.5

11.5

22.5

33.5

4

Nip Width (in) Dwell Time (msec)

NewsTis 1Tis 2

Slower speed


Nip Comparisons

0200400600800

1000120014001600

Peak Pressure (psi) Ave Pressure (psi)

NewsTis 1Tis 2


General Nip Profile Comparison

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

1600.0

-1.50 -1.00 -0.50 0.00 0.50 1.00 1.50

Position (inches)

Stre

ss (p

si)

Tissue Nip

SS Newsprint Nip


Press Fabric Properties


Key Properties of Press Fabrics Mass Caliper Air Permeability

Void Volume Compressibility /

Resiliency Flow Resistance Pressure Uniformity


Dynamic Character of Press Fabrics

Properties change around press loopCompressed State in nipUncompressed State at Uhle Box

Properties change over cyclesRelationship around press loop changes over time


Void Volume


Void Volume Amount of water a fabric will hold under a given

load Equivalent to the “empty space” in the fabric Increasing load decreases volume Reduces with fabric age


Seamed fabrics

2 layer larger yarn

4 layer single seam

3 layer laminated

2 layer multi-axial

2-layer stdyarn


Press Fabric Structure -Compressibility

MEDIUMMEDIUM

FINEFINE

Base

COARSE

Batt

MEDIUMMEDIUM

FINEFINE

Base

COARSE

Batt

Under Load, in the Nip –

LITTLE OR NO CHANGE

MEDIUMMEDIUM

FINEFINE

Base

COARSEBatt

Under Load, in the Nip –

SIGNIFICANT CHANGE

CALIPER UNDER LOAD IS KEY


Performance Characteristics Compressibility / Resiliency

Change in fabric caliper from out-of-nip to in-nip

Ability of fabric to revert to out-of-nip caliper.

Flow Resistance Rate at which water can enter and exit

fabric Low flow resistance allows water to move

easily into and out of fabric


Pressure Uniformity

How evenly is pressure transferred from loaded rolls to paper sheet

Impacts sheet quality and dryness Large scale related to mesh count and

yarn size Small scale related to batt structure


Pressure Distribution


“One Size Does Not Fit All”

Physical Dimensions Paper Grade Differences Press Nip Differences Position Differences - Incoming Dryness Failure Mode Differences


Failure Modes Wear Compaction Filling Marking Poor Water

Removal (slow speed)

Water carrying / slinging

Instability (wrinkling / rippling)

Sheet breaks Sheet handling

(following / drop-offs)

Vibration Moisture Profile


Press Fabric Structure & Nomenclature


Finish

LifeWater Removal

Press Fabric Design


Press Fabric Structure

Batt -Nonwoven

Base -Woven

COARSEMEDIUMMEDIUM

FINEFINE

COARSE Batt


Needling

Fiber

Preparing

Webmaking

Yarns

Dressing

Winding

Weaving

Burling

Heatsetting


Needling Trade Line

Wet/Dry Finishing ShippingInspection


WEAVING(endless weaving)

MD


HARNESSES

REED

WIDTH

LENGTHSHUTTLESHUTE(Mach. direction)

DONUTS

WARP(Cross-Mach. Direction)



ENDLESS WEAVING

DOUBLE ENDLESS WEAVING

HARNESS

REED

WIDTH

LENGTH

ENDLESS BASE WEAVINGSHUTTLE

PIRN

DONUT

WARP

HARNESS

HEDDLES

WARP YARNS

EYELETS


WEAVING(Flat weaving)

MD


FIBERPREPARATION


WEB MAKING(CARDING)


NEEDLINGPROCESS

NEEDLE

BASEFABRIC

WEBS

WEB


MANUFACTURE OF

PRESS FABRICS


MATERIALS USED� NYLON (POLYAMIDE)

� EXCELLENT TENSILE STRENGTH � ABRASION RESISTANCE� RESISTANT TO ALKALIES


Press Fabric YarnsSpun Plied

MultifilamentMonofilament Plied

Monofilament


Batt Fiber Fineness-Surface, Void Volume, Flow Resistance –Larger Fibers in Use – 66 (90), 110 (100) dtex (almost like a monofilament)

~ .01”

Tissue

Pulp

Fibers/gm79K 39K 20K 12K 8K 5K 3K

3 6 10 15 24 401.5

20 28 35 43 55 7016

Denier

Diameter

How do we make a structure “closer”?

How do we make a structure “more open”? What is best for cleanability?

What is best for drying? What is best for sheet pickup?Decitex is mass in grams per 10,000 mDenier is mass in grams per 9,000 m


Batt Fiber

Base Fabric

Press Fabric Anatomy


Press Fabric Structure Compression Properties Vary With:MD / CD Yarn Type and Count# of Base LayersBase Fabric Weave Pattern / TypeBatt Fiber DirectionalityChemical Treatment


Number of Base Layers

1-Layer

2-Layer

3-Layer

CD


Press Fabric Structure Weave Pattern / TypeIntegrally Woven

Stacked Staggered Stratified

LaminatedSeamedMultiaxialCrossless


Weave Patterns (3-Layer)

Stacked

Staggered

Stratified

CD


Batt-on-Mesh

Cross Machine Direction

Benefits•Easy To Install-Some Styles•Good Pressure Uniformity•Good Sheet Moisture Profile


Laminated Base FabricsTop Base

Main Base

Batt Fiber

Cross Machine Direction

Attributes•More Open Under Load•Improved Pressure Uniformity

Benefits•Better Sheet Contact•Easier to Keep Clean•Uniform Sheet Moisture Profile


Seam Fabrics

Machine Direction

Attributes•Seamed Press Fabric•Single, Multiple Layer, or Laminated Bases•Choice of Yarn Structures•Durable Seam Design

Benefits•Safety•Shorter installation time•Excellent compaction resistance•Enhanced water handling•More Open Under Load •High Void Volume**•Easier to Keep Clean•Holds Caliper - Long Life


Multiaxial PressFabrics

Attributes•Multiaxial Press Fabric•Yarn Systems in 4 directions•Yarn Systems Do Not Nest Under Load•Uniform Surface Topography

Benefits•Stable•More Open Under Load•Better Moisture Profile•Easier to Keep Clean•Holds Caliper - Long Life•Uniform Pressure Distribution


Advanced /Crossless


Crossless100 % non-woven


Advanced/Crossless MaterialsAttributes

• Planar Structure • No Loom Edges• Maximum

Pressure Uniformity

• Outstanding Caliper Recovery (Advanced)

• Highly Compressible

Benefits• Uniform Pressure

Distribution• Dampens Press

Section Vibration (Advanced)

• Sheet Smoothness• Improved Sheet

Solids• Improved Sheet

Finish • Steady State

Pressing


Review Press Fabric Design1. What is the name of the press section arrangement?2. Which position removes the least amount of water?3. Which position requires the most void volume?4. If you had a drop – off problem with the pickup felt what could

you change in the design?5. If the 4th press felt contained a multifilament and had short life

because of caliper loss, what might you do to extend life?6. What design would you use for an easy installation?7. We noticed a felt filling problem on the plied mono design on the

Bottom felt- what could we do to improve it?8. To maximize sheet smoothness what kind of felts could we use?9. What are the three types of press base weaving & describe

each?


Groove Press

Suction Pickup

Groove Press

Groove Press Groove PressFelt


CONDITIONING


Benefits of Proper Cleaning & Conditioning

Steady state operation

Improved profile

Improved clothing life

Negative Impact of Press Fabric Filling

Reduced Water Removal Sheet breaks Higher sheet draws Increased Steam

Consumption Overall Runnability

Poor sheet profile Sheet Stealing Sheet Drop off Crushing


Press fabrics fill up on each pass

Showers and vacuum must clean on each pass

Remaining materials can cure and grow via reaction within fabric Depends on grade and additives

Shower water quality should be known

Conditioning Strategy


Particle Size

A clean press fabric will filter out 100% of particles greater than 50 microns 95% of particles greater than 25 microns Particles below 10 microns will pass thru the

press fabric with water


Cleaning & Conditioning Axioms Use right volume at right location Use an acceptable minimum volume Excess volume will transfer to nip Deliver uniformly onto fabric Clean before the First Faceside Felt Roll

(if possible)


Press Fabric Conditioning Equipment High Pressure Showers (1- needle 2-fan) (Mechanical)

Prior to 1st Uhle Box to loosen contaminants- face side WARNING : “That which cleans also destroys”

Flooded Nip Showers (4) Inside of press fabric, ahead of the roll, away from uhle box

Wet up aide during start-up Flush contaminants from the inside Good location for continuous or batch chemicals

UB Lube Showers (3) Lubricate the leading edge of the uhle box; reduce drag Adequate seal for maximum volume

Chemical Showers (5) (Chemical cleaning) After press nip Sheet or face, far from uhle


3 3 2 1

4 or 5

5

1 2 3 3

4 or 5

1 2 3 3

4 or 5

123

4

3 3 2 13 3 2 1

4 or 5

5

1 2 3 3

4 or 5

1 2 3 3

4 or 5

123

4


Cleaning & Conditioning� Fan Showers� Needle Jet Showers� Uhle Boxes


Showers� Shower types

� Fan jet� Flushing action� Apply chemicals

� Needle jet� Apply energy

� Single needle jet� Streak Control


Press Fabric Conditioning Equipment Uhle Boxes

Cover PU or ceramic Monitor for wear Lubricate to minimize wear

Style Straight slot Herringbone

Alignment Dwell time

3-5 ms Dwell Time (ms) =

[Slot width (in) x5000]/Machine Speed (fpm)


Uhle Box Covers


3 3 2 1

4 or 5

5

1 2 3 3

4 or 5

1 2 3 3

4 or 5

123

4

3 3 2 13 3 2 1

4 or 5

5

1 2 3 3

4 or 5

1 2 3 3

4 or 5

123

4


1 2 3 4 5Shower Type H.P. Needle Jet H.P.Fan Lube Flooded Nip ChemicalLocation Sheet side Sheet side Sheet side Non sheet side aft er press

nip before inner roll.After press nip before inner roll

100 - 300 mm 75 - 150 mm 100 – 300 mm 75 - 150 mm 150 – 300 mm

4 – 12 in 3 – 6 in 4 - 12 in 3 - 6 in 6 - 8 in75 – 200 mm 150 – 200 mm 150 – 200 mm 200 – 300 mm 80 – 200 mm3 – 8 in 6 – 8 in 6 - 8 in 6 – 8 in 3 – 8 in

Trave rse Distan ce T wice the spacing dist ance

T wice the spacing dist ance




S pe e d of Trave rse W idth of nozzle per rev. of fabric

W idth of nozzle per rev. of fabric

An gle 90 degrees or with the fabric run

90 degree Contact fabric and uhle box leading edge

90 degrees 90 degrees

.7 – 1.5 Mpa 1.0 – 1.72 Mpa .15 - .2 Mpa 0.30 – 0.40 Mpa .15 - 0.4 Mpa100 – 200 psi 150-250 psi 20 – 30 psi 40 – 60 psi 20 – 60 psi.7 – 1.0 mm .7 – 1.0 mm0.02 – 0.04 in 0.02 – 0.04 in

O sci l lation Yes Yes Opt ional Opt ional Opt ionalW ate r Te m p. Stock T emp. Stock T emp. Stock T emp. Stock T emp.

Distan ce

Noz z le S pacin g

Pre ssu re s

Noz z le S iz e


Steam Box/Steam Shower


� Improve dryness� Increase speed� Net energy

savings� Improve

moisture profile� Fabrics run

cleaner


Steam shower under transfer roll- stickies transferred to cold last press fabrics

Temp on lightweight coated linerboard using 100% recycled furnish steam box off.


Non-turbulent steam shower over top fabric uhle box; also installed over bottom fabric uhle box


Increased production to 1 ton/hrIncreased uhle box dewatering last presses Longer life of fabrics


PU fabric kept more open and eliminated batch washes – extra week of life!


Moisture Equilibrium


Paper grade Machine speed Sheet dryness exiting forming section Shower volume applied in press section Press fabric compression properties Individual Machine

Moisture EquilibriumWater is Accepted By and Released From a Press Fabric On Every Fabric Revolution


Purpose of Moisture Equilibrium Balance

“Spot Checks”, MD & CD, for uniformity

Determine mechanism, direction and location of H2O movement

Monitor Individual Machine Performance


CD Moisture Scan1 PM CD SCAN

Date Time Mean Range StDev Weight Machine Position1/11/2 09:18 735.4 76.0 18.85 225.0 1 PM VOITH-97592/28/2 09:15 770.8 111.0 25.14 218.0 1 PM ALBANY-317449

Distance - inches

0 20 40 60 80 100

Moisture Level

gsm

1000949899848797747696645594544493



Date Time Mean Range StDev Weight Machine Position6/11/1 14:15 994.8 160.0 38.41 401.0 3 TM WEAVEXX-6/25/1 10:06 885.7 116.0 27.20 401.0 2 TM WEAVEXX

Distance - inches

0 20 40 60 80 100

Moisture Level

gsm

1200

1150

1100

1050

1000

950

900

850

800



Date Time Mean Range StDev Weight Machine Position1/24/2 16:41 1047.4 94.0 24.05 417.0 2 PM ALBANY-3163432/11/2 13:29 849.6 69.0 16.49 395.0 2 PM ALBANY-317583

Distance - inches

0 20 40 60 80 100

Moisture Level

gsm

12001150110010501000950900850800750700650600


Returned Fabric Analysis


CD Scans – Loading, Showering/Conditioning, Filling


Historical CD Scans – Last 5 fabrics


Contaminants

Inorganic OrganicSilicates, clay, talc PitchTiO2 Hot meltsCaCO3 Size chemicalsFeOx LatexMgCO3 Oil

DefoamersWet & dry strength resins


Troubleshooting


Trouble Picking up the Sheet

Press Fabric Surface is too “rough”

Fabric is too “open”

Adjust tension – only some styles

Machine Stock change Condition of the forming

fabric Suction pickup roll

operation – plugging; deckles

Improper fabric conditioning equipment –trim squirts


Sheet Stealing – where does the sheet go?

Press Fabric Poor Pickup Bottom

Surface too “smooth” Carrying too much water-

too much void volume Design related Wear related

Fabric is filled

Machine Press geometry

Change the wrap of the felt, roll, or sheet

Roll cover material Modify vacuum and

showering


Slow Start-up

Press Fabric Too much void volume

under load Increase “precompaction” More compressible and/or

lower void volume base Increase “fineness” of web

Machine Modify water load via

showering & vacuum


Crushing

Press Fabric Press fabric cannot

handle the water Filled Not enough void volume Adjust felt tension – only

some styles

Machine Non-uniform pressure in

the nip If streaky, non-uniform

cleaning Check conditioning

equipment

Sheet is too wet Plugged press pan Check Suction box if

suction roll Plugged grooves


Loss of speed at the end of life Press fabric is worn

Examine surface condition Shaggy Shower streaks

Modify batt/needling Improve bonding

Modify batt/needling/base Easier to clean


Wear – Design, Mechanical, Chemical & HydraulicPress Fabric Too much hydraulic

pressure Modify base/web for less

resistance to flow.

Chemical cleaning and/or residual bleaching agents Add chemical resistant

treatment

Machine Press rolls

Crowns Bearing Misalignment Rough surfaces

Fabric Conditioning Worn suction box covers, XS shower pressure Lube shower coverage

Abrasives in the furnish, Ca CO3


Blowing – air between sheet & fabric ahead of the nipPress Fabric Dirty or plugged felt Fabric too open

Machine Geometry “Blow” box ahead of the

nip


Sheet Marks Press Fabric Drainage too fast Insufficient web

Design Wear

Base too coarse

Machine Non-Uniform Pressure in

the nip Felt conditioning

equipment Suction press filling up Check for water dropping

on the press Sheet too wet entering

press section Rounded edges in drill

pattern of roll


Performance Review1. Why should press fabrics be conditioned?2. Should we clean before or after the first faceside felt roll?3. What is the high pressure shower warning?4. Why take moisture profiles?5. Why would a moisture scan show less water at the end of

life?6. What does returned fabric analysis tell us?7. What surface will the sheet follow in the press section?8. What can we do to improve a slow start-up?9. The sheet is crushing. If we determine it is from the felt,

does the press fabric have too much or too little void volume?

10. What kinds of wear are present in press fabrics?


Thank you for your Time

Any Questions?

press fabric design for modern paper machines · 2019-05-23 · even sided dewatering drop offs on...

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