Potlatch Brainerd Wet End Training 3

04/12/23 Copyright © 2001 Bill Frawley

Potlatch Brainerd Wet End Training

March 2001By

Bill Frawley


Introduction

Understanding the paper forming process, equipment and chemistry

Bill Frawley and Joe Osfar Training Consultants


Topics of Discussion Looking at machine as relates to

fiber mat formation. How each area impacts fiber mat Entry zone Forming zone Dewatering zone Consolidation zone Pressing


How The Fiber Mat Develops


The Five Zones of the Forming Table

Entry Phase Forming Zone Dewatering Zone Transition Zone Consolidation Zone


# 5 PM Table Zones


1 Entry Phase

Headbox Slice and Jet Pressure Forming Vs Velocity

Forming Impingement point Forming board Structuring of filtering mat


Headbox Approach System

Approach system Fan pump Attenuator Tube bundle


Headbox Components

Headbox Components Diffuser block Distributor rolls (holy rolls) Nozzle Slice


Rectifier Roll

Agitates dilute stock so flocks can not form in headbox

Velocity through center of hole greater than outside do to boundary effect

Designed for fixed flow range


Rectifier Roll Pattern in Sheet

If roll capacity is exceeded streaks will flow through nozzle

Forming board will set pattern in filtering mat


Flow From a Vertical Slice


Jet Angle ß, Degrees


Contraction Coefficient


Defect In Slice Lip


Rush Drag


Rushing the Jet

Jet velocity greater than wire speed

CD fiber orientation Sheet has less MD

strength.


Dragging the Jet

Jet velocity less than wire speed

MD fiber orientation Sheet has more MD

strength.


Pressure Vs Velocity Forming

Pressure Forming Rapid development

of fiber mat Low first pass

retention Sheet sealing Tissue applications


Velocity Vs Pressure Forming

Velocity Forming Better filtering mat Carry lower

consistency in to forming zone

Higher first pass retention

Flat grades


How The Filtering Mat Develops

Filtering mat developed on the forming board


Sheet Consistency Development

Formation is over when stock consistency reaches 1.2 – 1.4%

Excessive activity past this point will degrade sheet properties!


2 Forming Zone Breast Roll Shake How foils & table rolls work Harmonics

1. Machine speed

2. Foil spacing

3. Box spacing Amplitude - Function of angle All over when stock reaches 1.2-

1.4% consistency Sheet set point


How The Forming Zone Develops Fiber Mat

Forming zone works fibers & fillers in upper part of suspension


Table Rolls High activity at low

speeds Positive and

negative pressure Ever increasing nip Work up to 1200

fpm Higher

maintenance


When Table Rolls Go Bad


How Different Foils Work


How Foils Work

Nose: Skives water off bottom of wire

Flat: Seals fabric so vacuum can happen

Angle: Creates gravity vacuum


Nose: Skives water off

bottom of wire Creates speed bump If the nose is too

sharp fibers will staple over and cause streaks (like a rock in a river)

Foil Nose


Foil Flat Flat seals fabric to

bottom of wire so vacuum can happen This can tell us how

foils is wearing or aligned

Wear should be from nose back

If wear starts on back of flat t-slot is wrong or tilted


Foil Angle Foils won’t work under 400

FPM Angle draws water through

filtering mat as nip moves away from wire

Vacuum brakes when water can’t fill nip

Wire is pulled down with water

When vacuum brakes, wire snaps back causing activity


Harmonics

Speed ÷ Spacing ÷ 5 = CPS 1500 fpm ÷ 5 = 300 ÷ 5 = 60 CPS Sweet spot for formation is

around 80 Cycles per second If activity stops for an instant

flocculation will occur


Foil Box Spacing

Box spacing has to be set to the blade spacing of the proceeding box Example: Foils are spaced 5” center to

center the next box has to set 5” 10” or 15” from the tip of the last foil to the tip of the first foil on the next box


3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00

ft/min in /sec

500.00 100.00 33.33 30.77 28.57 26.67 25.00 23.53 22.22 21.05 20.00 19.05 18.18 17.39 16.67

600.00 120.00 40.00 36.92 34.29 32.00 30.00 28.24 26.67 25.26 24.00 22.86 21.82 20.87 20.00

700.00 140.00 46.67 43.08 40.00 37.33 35.00 32.94 31.11 29.47 28.00 26.67 25.45 24.35 23.33

800.00 160.00 53.33 49.23 45.71 42.67 40.00 37.65 35.56 33.68 32.00 30.48 29.09 27.83 26.67

900.00 180.00 60.00 55.38 51.43 48.00 45.00 42.35 40.00 37.89 36.00 34.29 32.73 31.30 30.00

1000.00 200.00 66.67 61.54 57.14 53.33 50.00 47.06 44.44 42.11 40.00 38.10 36.36 34.78 33.33

1100.00 220.00 73.33 67.69 62.86 58.67 55.00 51.76 48.89 46.32 44.00 41.90 40.00 38.26 36.67

1200.00 240.00 80.00 73.85 68.57 64.00 60.00 56.47 53.33 50.53 48.00 45.71 43.64 41.74 40.00

1300.00 260.00 86.67 80.00 74.29 69.33 65.00 61.18 57.78 54.74 52.00 49.52 47.27 45.22 43.33

1400.00 280.00 93.33 86.15 80.00 74.67 70.00 65.88 62.22 58.95 56.00 53.33 50.91 48.70 46.67

1500.00 300.00 100.00 92.31 85.71 80.00 75.00 70.59 66.67 63.16 60.00 57.14 54.55 52.17 50.00

1600.00 320.00 106.67 98.46 91.43 85.33 80.00 75.29 71.11 67.37 64.00 60.95 58.18 55.65 53.33

1700.00 340.00 113.33 104.62 97.14 90.67 85.00 80.00 75.56 71.58 68.00 64.76 61.82 59.13 56.67

1800.00 360.00 120.00 110.77 102.86 96.00 90.00 84.71 80.00 75.79 72.00 68.57 65.45 62.61 60.00

1900.00 380.00 126.67 116.92 108.57 101.33 95.00 89.41 84.44 80.00 76.00 72.38 69.09 66.09 63.33

2000.00 400.00 133.33 123.08 114.29 106.67 100.00 94.12 88.89 84.21 80.00 76.19 72.73 69.57 66.67

2100.00 420.00 140.00 129.23 120.00 112.00 105.00 98.82 93.33 88.42 84.00 80.00 76.36 73.04 70.00

2200.00 440.00 146.67 135.38 125.71 117.33 110.00 103.53 97.78 92.63 88.00 83.81 80.00 76.52 73.33

2300.00 460.00 153.33 141.54 131.43 122.67 115.00 108.24 102.22 96.84 92.00 87.62 83.64 80.00 76.67

2400.00 480.00 160.00 147.69 137.14 128.00 120.00 112.94 106.67 101.05 96.00 91.43 87.27 83.48 80.00

2500.00 500.00 166.67 153.85 142.86 133.33 125.00 117.65 111.11 105.26 100.00 95.24 90.91 86.96 83.33

2600.00 520.00 173.33 160.00 148.57 138.67 130.00 122.35 115.56 109.47 104.00 99.05 94.55 90.43 86.67

2700.00 540.00 180.00 166.15 154.29 144.00 135.00 127.06 120.00 113.68 108.00 102.86 98.18 93.91 90.00

Foil Frequency Chart


Foil Amplitude

Function of wire speed and foil angle

Lower angle lower pulse Higher angle higher pulse 4-5 Degree foils maximum Turbulence making foils


Activity Rating Chart

1. Flat Clam

2. Calm

3. Ripples

4. Small Waves

5. Small Waves

6. Wave action

7. Micro turbulence

8. Micro turbulence

9. Necking

10. Stock Jump


Calm to Small Waves

No shear in stock suspension

Flocculation Mat can get so

dense that it will retard drainage


Wave Action

Shear starts to begin

Fibers in upper suspension move

Filtering mat stays open

Formation can improve


Micro Turbulence

Shear occurs Flock size is

significantly smaller and more uniform

Fibers in upper suspension move

Filtering mat stays open

Formation improves


Good Micro Turbulence


Stock Jump

Filtering mat is destroyed

Retention drops Droplets can

rain on your parade (rings in sheet)

Chunks of filtering mat could cause large flocks


Dewatering Zone

Gravity Foils Vacuum Foils Top Wire Units


Thickening The Stock

Add a little flour and stir over low heat


Thickening The Stock

Keep mat open Remove water Graduate low

vacuum levels to prevent sheet sealing

Finish top side of sheet

Consistency levels form 1.4 – 13%


Gravity Foils

In the dewatering zone angles should be a compromise between water removal and stock activity

Need to keep mat open for drainage

Need to carry harmonic activity to last gravity unit


Activity on Gravity Foils


Low Vacuum Foils

Low vacuum foils are need to remove water when the filtering mat has thickened to a point where gravity foils become inefficient

Control consistency coming in to top wire unit 1.8 – 2.1%


Low Vacuum Foils Vacuum measured in

inches of water Blower supplies

negative pressure Water on top of fiber

mat creates air tight seal

Open area = dwell time Ramp up vacuum To much vacuum to

soon will seal sheet


Controlling Low Vacuum Foils

Ramp vacuum Drop leg seals

bottom and determines how much vacuum is possible

It is better to use narrow 0º blades and adjust t-bar spacing for open area (less drag)


BEL

BOND


Bel Bond Advantages

Fiber mat is sandwiched between two forming fabrics

Dewaters up Finishes top of sheet Structures mat uniformly Less two sidedness Increases consistency of sheet

from 2 – 11%


Bel Bond Lead-in Detail


Lead-in Box Four adjustments for

controlling H2O

1. Height of roll

2. Raise or lower trailing edge of lead-in box

3. Raise or lower vacuum of lead-in box

4. Raise or lower vacuum of lovac box


Impingement Point of Two Wires

Water is forced up through top wire on lead-in box

Water is vacuumed down in to lead-in box up to 25” H2O vacuum

Curvature of lead-in box helps force water up

Adjusting height of trailing edge of lead-in box has affect on formation

Lead-in roll has biggest impact on dewatering


Curved Inverted Vacuum Box


Auto Slice Vacuums free water and air from

inside of top wire 20-25” H2O vac Roof is adjustable by hand Setting is determined by closing

roof until slice rejects some water then opened back up a smidge so all water is removed

Roof regulates only amount of air removed NOT amount of water


1st Vacuum Chamber 15 two inch ceramic

blade vacuum zone under auto slice box

Vacuum level shifts to 3 – 5” Hg

Connected to a vacuum pump

Water is move up channel to a weir


2nd Vacuum Chamber 14 two inch ceramic

blade vacuum zone under auto slice box

Vacuum level shifts to 4 – 6” Hg

Connected to a vacuum pump

Water is move up channel to a weir


Transfer Box

Transfer box keep the sheet on the bottom wire

Wires separate on curved surface

Begins sheet consolidation zone

8 slots pulling 4-6 inches of mercury


Suction Boxes

Ramp up vacuum from 4-10” of mercury

Boxes have adjustable deckles

Dries sheet from about 12-17% consistency

Vacuum supplied by Nash vacuum pump


Suction Couch Roll


Function of Suction Couch Roll

End of consolidation zone Dries sheet to 18-22% Helps drive forming fabric At speeds over 1200 FPM

water never penetrates shell Liquid ring seal Highest vacuum element on

machine


Forming Section Review

Stock delivery system Forming zone Dewatering zone Top wire unit High Vacuum Couch Sheet development


Press Section


Press Section Functions

To remove water by squeezing or wringing sheet against a felt

Felts act like a sponge Pressing make sheet denser Press nips squeeze sheet and

felt or just sheet to remove water or to smooth sheet

Overloading can crush and mark


4 Phases of Press Roll Nip


4 Phases of Press Roll Nip

Phase 1: Felt and sheet compresses sheet becomes saturated

Phase 2: Water is squeezed from sheet to felt

Phase 3: Felt expands faster pulling more water from sheet

Phase 4: Sheet rewets as it partially expands


PLI Vs PSI

Pli is used measure force of mating rolls

Pli is the number used for press loading

Psi is used when discussing force of nip on sheet or felt & sheet


Why Press are Crowned

Crown is needed to

Even out pressure under nip loading

Compensate for Sag & deflection


Press Loading

1st Press 450 PLI 2nd Press 600 PLI Smoothing 450-500 PLI Excessive pressure will crush or

shadow mark sheet


Combi-Roll The Combi roll is a pickup &

suction first press roll in one

Low vacuum area lifts sheet off wire and holds it on the felt until the high vacuum zone under first press nip

Low vac area doesn’t remove water

High vac holds water in felt until sheet can get away


Combi-Roll Operation Vacuum must be off to move

into wire Low vacuum is set about 8” Hg

Low vac zone doesn't remove water

High vacuum is set at 20” Hg And holds water in felt until sheet is clear of nip

Box alignment critical 1st press loaded to 450 Pli


Suction Felt Roll

Acts like an anti-blow box Sucks sheet tight to

felt to prevent flutter entering 2nd press

Doesn't remove water from sheet only air

Stabilizes sheet after open draw from pickup felt


2nd Press 2nd press uses a venta-

nip grooved bottom roll Grooves in rubber cover

act like tread on your car tires

Water is squeezed from sheet through felt and in to voids of grooves

Too much pressure can cause shadow marking and crush sheet


Smoothing Press

Smoothing press as it’s name says smoothes the sheet for better drying

No water is removed so nip load has to be lower that 2nd press

Both rolls are hard


Press Roll Showers

Showers in suction rolls are invisible

Venta-nip shower keeps grooves clean and open


Press Felts Act as a blotter or sponge Absorb water + dirt, fines, pitch ash, minerals…

at nip Cleaned with showers &

chemicals (batch wash) Dried on uhle boxes Trade line needs to run square Change when filled and worn


Press Section Felt Showers

Each felt has Batch chemical and

flushing shower High pressure

cleaning shower Uhle box lube

shower


Uhle Boxes

Shop-vac for felts 4 milliseconds dwell minimum to

dry and clean Be careful of edges outside

sheet they will dry out first Adjust deckles to sheet width Vacuum will start around 10” Hg

when felt is new and increase to 15-17” when felt is filled


Press Section Review To remove water by squeezing

sheet against an a felt Felts act like a sponge Uhle boxes & showers clean and

dry felts Pressing make sheet denser Press nips squeeze sheet and

felt or just sheet to remove water or to smooth sheet

Overloading can crush and mark


Thank You, Any Questions?

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Potlatch Brainerd Wet End Training 3

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