Potlatch Brainerd Wet End Training 3

01/30/15 Copyright © 2001 Bill Frawley
Potlatch Brainerd
Wet End Training
March 2001
By
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)

B
E
L
B
O
N
D

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?

Potlatch Brainerd Wet End Training 3

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