5 Design and Operation of Headboxes · 2019-05-23 · TAPPI Paper Machine Operations Course Basic...
Transcript of 5 Design and Operation of Headboxes · 2019-05-23 · TAPPI Paper Machine Operations Course Basic...
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TAPPI Paper Machine Operations Course
Design and Operation of Headboxes
Jim AtkinsAtkins, Inc.
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TAPPI Paper Machine Operations Course
Headbox Video
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TAPPI Paper Machine Operations Course
Basic Headbox Functions
Convert CD flow in a pipe to uniform MD flow out a nozzle.
Deflocculate the stock. Control basis weight in the MD, CD,
and minimize random variation. Control fiber orientation. Provide control over forming variables
such as jet impingement and jet speed.
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TAPPI Paper Machine Operations Course
Development of the Headbox Inlet (Manifold)
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TAPPI Paper Machine Operations Course
Tapered Manifold
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TAPPI Paper Machine Operations Course
Development of the Headbox Manifold
4 to 6 pipe diameters
No more than 5 psi pressure drop across the valve
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TAPPI Paper Machine Operations Course
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TAPPI Paper Machine Operations Course
Alternate TechnologyRadial Distributor
CDR-0100-00034
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TAPPI Paper Machine Operations Course
GL&V BTG Manifold, ON- PM # 6
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TAPPI Paper Machine Operations Course
Headbox Types
Three basic types of headboxesOpen Rectifier roll (Air Pad)Hydraulic
Within the types are a number of styles
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TAPPI Paper Machine Operations Course
Open Headbox
First type of headbox (slow machine speeds) Jet speed regulated by height of the liquid level in the vat or pondAs speeds increased, so did the height of the vat until it became impracticalOnly seen today on some pulp machines and old, slow specialty machinesThis lead to the development of a closed headbox pressurized with air
St. Regis Paper Co.’s “Whatsit Box” Tacoma, WA.
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TAPPI Paper Machine Operations Course
Rectifier Roll Headboxes
High pressure drop tube bundle (varies with supplier).
Stilling chamber to allow turbulence to settle down-1.0-1.5 fps pond velocity.
Rectifier rolls to deflocculate stock.
Air pad with level control used to provide desired head (pressure)
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TAPPI Paper Machine Operations Course
Rectifier Roll HeadboxesTwo styles of hole pattern shown
Spiral Square
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TAPPI Paper Machine Operations Course
Rectifier Headbox Wake Effect
Severe
Moderate
Roll distance to slice lip is important to prevent streaking
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TAPPI Paper Machine Operations Course
Rectifier Roll Headboxes Advantages
Air pad “cushions” pulsations.Good flexibility for wide speed range.
DisadvantagesLarge flocs left in jet discharge.Max speed around 3500 fpm.Cause streaks if overloaded.Maintenance of moving parts.
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TAPPI Paper Machine Operations Course
First developed to work with twin wire formers Work at any angle No air pad Much smaller
Higher stock velocity 7-15 fps
Deflocculation by hydraulic shear
Hydraulic Headboxes
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TAPPI Paper Machine Operations Course
Hydraulic HeadboxesEarly Fourdrinier Style
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TAPPI Paper Machine Operations Course
Hydraulic Headbox Advantages
Smaller sizeHigher shear to deflocculate the stockNo moving partsHave not yet reached a speed limit
Disadvantages Less flexibility for speed rangeHigher pressure drop – more energyNarrower range for MD/CD fiber ratioSusceptible to MD weight variation from
pressure pulsation or vibration
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TAPPI Paper Machine Operations Course
Controlling CD ProfileTraditional Slice Lip Bending
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TAPPI Paper Machine Operations Course
Slice Bending
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TAPPI Paper Machine Operations Course
Controlling CD Profile Dilution Control Dilution profiling is selective
consistency control in the cross directionMuch narrower (better) control of
weightDoes not cause fiber orientation issuesGreater range of control up or down on
weight Requires additional equipment on
headbox and on the control systems
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TAPPI Paper Machine Operations Course
Dilution Control
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TAPPI Paper Machine Operations Course
Voith Consistency Profile System
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TAPPI Paper Machine Operations Course
Consistency Profile Water
Water usually from the silo
Dedicated pump with barrier screen to keep debris from plugging the CP valves
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TAPPI Paper Machine Operations Course
CD Weight Responses for Dilution and Slice Controlled Headboxes
-400 -300 -200 -100 0 100 200 300 400
Dilution Control60 mm Actuator Spacing
Slice Control100 mm Actuator Spacing
CD Position (mm)
Bas
is W
eigh
t Res
pons
e (g
/m²)
60 mm dilution zone
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TAPPI Paper Machine Operations Course
Headbox Nozzle
Door is called the pond side
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TAPPI Paper Machine Operations Course
Nozzle Lamella Used to provide micro turbulence in
the jet to aid formation Variables include length, thickness,
type of tip (tapered or blunt) Can be damaged in handling. Avoid
excessive bending and surface damage (scratches)
Follow guidelines for chemical and temperature exposure
Inspect on regular basis
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TAPPI Paper Machine Operations Course
Nozzle Lamella Sheets supplied in polycarbonate
(Lexan), graphite, or polyphenylene sulphone (PPSU)Lexan is clearPPSU is blue
Each has its advantages and disadvantages
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TAPPI Paper Machine Operations Course
Headbox Apron
The apron is a highly polished and precision machined piece. It must be protected from scratches and mechanical damage or profile will suffer.
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TAPPI Paper Machine Operations Course
Basic Headbox Controls Total Head
Head is another name for pressure inside the headbox
Pressure determines the jet velocity The jet can be faster or slower than the
forming fabric This is called jet-to-wire (J/W) ratio The computer may show this as an actual
speed difference in fpm (+/-) or as a ratio (ratio of 1.0 is equal speed)
Head is normally controlled by fan pump speed but some older machines use a large valve in the approach pipe
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TAPPI Paper Machine Operations Course
Basic Headbox Controls J/W ratio
Jet to wire ratio influences:MD/CD fiber ratio (sheet squareness)This effects ratio of sheet properties
like tensile and tearChanges sheet shrinkage and drawChanges formation
Tough to measure accurately and very small changes make a difference
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TAPPI Paper Machine Operations Course
The ratio of MD and CD tensile strengths is a good indicator: it will have a minimum at jet speed = wire speed.
How do you determine your actual j/w ratio?
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TAPPI Paper Machine Operations Course
JET VELOCITYAnother way is to measure the sheet width at the reel.
The maximum sheet width is at the square point.
-50 -40 -30 -20 -10 0 10 20 30 40 50
INDICATED (JET - WIRE) (ft/min)
IndicatedReal
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TAPPI Paper Machine Operations Course
Basic Headbox Controls Slice Flow
Slice flow determines the consistency inside the headbox (amount of dilution of the fibers).
This effects sheet formation and sheet properties.
Lowering consistency means more water on the table and may be a problem.
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TAPPI Paper Machine Operations Course
Basic Headbox Controls Slice Flow
To increase the slice flow you normally open the vertical sliceThis lowers the pressure inside the
headbox and the fan pump rpm will increase to provide constant head
If the fan pump is in manual control, head will drop and no change in flow occurs
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TAPPI Paper Machine Operations Course
Headbox Video
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TAPPI Paper Machine Operations Course
Headbox Problems Over-sized for application No longer capable of handling the flow.
Streaky sheetEdge problemsBulging, leaking headbox
Physical problemsWarped, lining coming loose, rustPhysical damage to inside, slice lip, or
apron
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TAPPI Paper Machine Operations Course
38
Increase in Internal PressureJETVELOCITY Jet velocity is determined by the pressure in the headbox. In air padded boxes, this is the sum of the hydrostatic pressure and
the pressure of the air pad. For low speeds, V = (2gh)1/2.
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TAPPI Paper Machine Operations Course
Valmet Original Headbox
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TAPPI Paper Machine Operations Course
Valmet Original Headbox
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TAPPI Paper Machine Operations Course
New GL&V Headbox
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TAPPI Paper Machine Operations Course
New GL&V Headbox
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TAPPI Paper Machine Operations Course
Design and Operation of Headboxes
Jim AtkinsAtkins, Inc.