Doctor Blade Metering The What and How in Anilox Ink Metering.
Tony DonatoProduct Development EngineerHarper Corporation of America
FIRST 4.0
From Section 21.4 Ink Metering System:
“ The function of the ink metering system is to control the amount of ink being transferred onto the printing plate.”
From Section 21.4.1 Doctor Blades:
“ The primary function of the doctor blade is to uniformly remove ink from the surface of the anilox without damaging the anilox.”
Ink Metering
Doctor Blade MeteringOUTLINE:• The difference between forward and reverse doctoring.
• Ink metering terms: Set-Angle, Contact Angle, blade deflection, sheen, back-doctoring, blade loading pressure, blade alignment and many others.
• The importance of blade stiffness to metering.
• How blade thickness affects metering.
• Why are there different blade tips.
Forward and Reverse MeteringSimplest Examples
http://www.autogeek.net/windshield-ice-scraper.html
Reverse metering shears off the unwanted
material.
Windshield Ice Scraper
Windshield Wiper Blades
Forward wiping pushes the unwanted
material.
Forward Metering
Blade points in the direction of
rotation.
Pushes the surface ink back into the pan.
Traditionally used in Gravureon Chrome Rollers
Ink is pushed back to the pan
Forward Metering
Pluses:
• Ideal where roll diameter changes with the jobs.
• Less wear to rollers being metered.
• Helps to lubricate blade.
Minuses:
• Works best with low viscosity inks.
• Potential for speed limitations due to hydraulic lift.
• Blade position and stiffness dependant.
Application Importance:
• Needs blade angle and location adjustability.
• Important to pick the right blade thickness, tip and back-up blade combination.
Forward Metering Angle RelationshipsA Distance blade tip to Cylinder Vertical Center LineB Distance of blade tip to Cylinder Horizontal Center lineC Circumvential Distance Nip point to Blade TipD Elevator (Up & Down) adjustment for table assemblyE Slide (In and Out) adjustment blade holderF Table Tilt (Pivot) adjustment for table assemblyG Set angle for blade to Cylinder without loading deflection.H Contact Angle of blade tip with deflection
90
0
90
0
15 90
0
90
0
75
74.92°ø 6.00"
58.72°
54.11°
75.05°
A
ProtractorPro
tracto
r
ImpressionRoll
GravureCylinder
F
C
D
E
Reference line (Tangent) Set angle
Protractor Angle Finder
Angle Finder gives angles relevant to earth.
G
HB
Typical Contact Angles are: Packaging Gravure 40° to 65°Publication Gravure 50° to 70°
Coating & Wall Covering 40° to 55°
Dimensions related to Center line of Gravure
Cylinder
Reverse Metering
“Reverse Metering” shears the ink off the Anilox surface.
Anilox
Ceramic anilox rollers allow the use of reverse metering.
Single Blade Enclosed Blade Chamber
Reverse Metering
Pluses:
• Meters the ink surface cleaner than forward.
• No hydraulic lift.
• Meters viscous inks.
Minuses:
• Blade holders or chambers have fixed set angles.
• Fixed roller diameter.
• Blade wear changes angle.
• Shears large pigments• Pearlescent • Metallic's
Application Importance:
• Needs hard surfaces.
Set Angle
90.00°
Anilox
Anilox
Reverse MeteringSingle Blade
• Ink Pan Only
• Ink Pan w/ Fountain Roll
Chamber
• Two Blades • Meter & Containment
• End Seals & Pump.
Blade Angles are fixed by holder & Chamber supplier
Metering Terms
90.00°
Set Angle
AniloxCenter Line.
Reference LineFrom Anilox Center
To point ofBlade Contact
Tangent LinePerpendicular toReference line
The “Set Angle” is the Chamber/Holder Machined Angle without any load.
Doctor Blade
Anilox
Contact Angle
Worn Area
ContactPatch
Anilox
Deflected Doctor Blade
Metering TermsThe “Contact Angle” is worn at the tip and is
the result of all forces acting on the blade.
FIRST recommends
“Contact Angle”
should be between 25-40 degrees.
Lower angles Print Dirty,
Higher Angles Chatter
Metering Terms
Blade Extention
Blade Extention
Blade Tip to Tip
Blade clampingseat area With Inking
Chambers the metering and containment blade can be on either the top or bottom, all depends on chamber placement on the anilox.
An
ilox
Dull Sheen Indicating Good Metering
Metering Terms
Metering TermsChamber opened up from the outside deck #7Top of picture is bottom (6 O’clock) of chamber
Drips on doctor blade is back doctoring of ink
White drops tinting is high speed “Ink Misting.”
• Containment Blades can trap contaminates under it.
• Keep Containment blades Clean.
Small Dried Ink Chunks
Containing Metal Particles
Plastic or Composite Blades with Embedded
Particles
Dried ink on the back (outside) of the blades
Back doctoring does more than just waste ink.
90.00°
Containment Set Angle
Set Angle45.00°
Metering Terms
AniloxC
ham
ber
MeterBlade
ContainmentBlade
Unloaded blade is at the highest angle.
High speed presses are trending at lowering the
containment set angle.
Chambers do not have to
have the same angles
for both blades
90.00°
90.00°
37.47°
13.20°
Anilox
Contact Angles decrease with increased loading pressure!
ContainmentContact Angle
.
These are good angles
for high speeds.
Metering Terms
Lower containment blade angles help to
reduce back doctoring.
Chamber has .031"
(.79mm) of loading
Blade holder alignment needs to be part of press maintenance.
Metering Terms
28.48°
90.01°
5.11°
90.00°
Anilox
Metering Contact Angle
Containment “Contact Angle”
Chamber has .0625”
(1.6mm) of loading
Doctor blades are spring steel
and the more they are loaded the harder they push into the anilox roller.
Extreme low containment angles will trap dried ink and contaminates Ink magnets and filters are required for high speed presses
3.52°
90.00°
18.42°
Anilox
Metering Contact Angle
Containment Contact Angle
Chamber has .125”
(3.2mm) of loading
Metering TermsExtreme loading will result in burrs created on the blade edge.
Anilox rotation remains the same on CI press
Outside decks 6 to 10
Inside decks 1 to 5
Back doctoring drips off chamber into pan
Back doctoring puddles behind blade and slings off the end of
the anilox
Containment Blade
Containment Blade
Doctor Blade Mechanical Specifications and Properties:
Mechanical Properties: Affect loading pressure, blade life and anilox wear.
•Tensile strength (spring like quality) ,
• Hardness
• Wear resistance.
• Chemical resistance.
Physical Attributes: Affect the printing performance.
• Thickness and width tolerances, flatness, surface finishes and camber (curvature also called edge straightness)
Deflected doctor blade and released it laid flat!
Doctor Blade Mechanical Property: Deflected a piece of steel banding stock.
Blade must deflect and re-flatten, it cannot take a set!
Banding stock unsuitable for a number of reasons!
Doctor Blade Mechanical Specifications and Properties:
• The initial wiping between the blade and roller are effected by variations in blade camber, flatness and width.
• All of the mechanical and physical properties affect the amount of loading force needed to cleanly meter the anilox.
• In addition, the blade mounting, holder/chamber physical dimensions/condition & mounting mechanism must be kept in good working order for the doctor blade to properly work.
A´A
Blades must be parallel to each other, & tip to tip distance the same.
Blade Mechanics Simplified
1"
d
t
Loadw
Fixed
Looking at the mathematics and mechanics a doctor blade is a
“beam” fixed on one end and loaded on the other.
“w” is load in lbs/linear inch“d” is deflection at the tip (inches)“1” is the extension of blade “E” Modulus of elasticity 30,000,000lbs for steel.“I” Moment of inertia for the blade cross section.
w x 1³3 x E x I
d =
(1)
1³ (blade ext)__ t³
Blade Mechanics Simplified
1"
d
t
Loadw
Fixed
t³12
Moment of Inertia I =
t = blade thickness
We substitute equation (2) into (1)
d = ____w x 1³____3 x E x (t³ / 12)
(3)
(2)
Set w = to 1lbs/ linear inch and assume steel “E” for the blade material we get:
d = ____1___________(3 x 30,000,000/ 12)
x (4)
Blade Mechanics Simplified
STILL AWAKE LAST SLIDE WITH MATH!!!!
The exponents in equation (4) show the cube factor.
Example leaving a blade in too long: (.750/.625)³ = 1.73 times stiffer
Example replace .006” with 0.008: (.008/.006)³= 2.24 times.
If the stiffer blade was left in until it was 1/8” shorter:Then: 1.73 (shorting) x 2.24 (thickening) = 3.87 times stiffer
CHANGES IN THICKNESS AND EXTENSION CAN EFFECT ANILOX WEAR.
Blade Mechanics TestedExperiment:
Used .006” & .008” doctor blades and two different
widths to get ½” extension and a 1” extension.
Applied two separate weights first 4.75lbs and
second 7.2lbs statically and measured the
deflection with a dial indicator.
Blade Mechanics Tested
Blade Mechanics TestedUnloaded
Loaded
Blade Thickness
Blade Extension
Blade Length
Weigh used
Load per linear inch
Deflection
.006” 0.500” 6.25” 4.75lbs 0.38lbs/in 0.029”
.008” 0.500” 6.25” 4.75lbs 0.38lbs/in 0.012”
.006” 0.500” 6.25” 7.2lbs 0.58lbs/in 0.049”
.008” 0.500” 6.25” 7.2lbs 0.58lbs/in 0.021”
.006 1.000” 6.25” 4.75lbs 0.38lbs/in 0.132”
.008” 1.000” 6.25” 4.75lbs 0.38lbs/in 0.082”
.006” 1.000” 6.25” 7.2lbs 0.58lbs/in 0.162”
.008” 1.000” 6.25” 7.2lbs 0.58lbs/in 0.146”
Blade Mechanics Tested
Doctor Blade Loading
What to expect from what we have learned so far!
• Typically the highest angle is the set-angle.
• As the loading pressure increases the “Contact-Angle” decreases.
• Loading pressure can lower the contact angle beyond the point of clean metering. (Below 26°)
• As a blade wears it narrows and the contact angle increases.
• Between loading and wearing the blade contact point moves away from the center line.
Overloading the blades changes wear.
Excessive pressure may result in creating wire like slivers.
Anilox Roll
Chamber
Lamella Tip
Clamp Bar
Tip notcontacting
roll
Wear PatchIs behind Tip
Radius Tip
Over-Loaded Blades can
Cause Scoring !!
Do Not do this to your Doctor Blades !!
Top blade has .217” worn off came from white deck!
Steel Slivers created from overloading.
Slivers form break off and
get loaded between blade
and anilox damaging surface.
90.00°
18.42°
90.00°
48.17°
0.23 in
1.25 in
Chamber is engaged .125" (3.2mm)
Blade was 1-3/8” and after the chamber is loaded to 1/8” the
blade can wear to a width 1-1/4”
The contact patch shifts with chamber loading and blade wear.
Chamber has .125”
(3.2mm) of loading
Doctor Blade Loading Observations
90.00°
18.42°
90.00°
48.17°
18.62°22.96°
Chamber is engaged .125" (3.2mm)
Chamber has .125”
(3.2mm) of loading
Doctor Blade Loading ObservationsAs the blade narrows
the point of contact on the anilox moves increasing the set
angle.
Doctor Blade Material Selection
• Carbon Steels:• Blue Carbon, White (Bright) Carbon
• Wear (Premium) Alloy Steels:•Tool Steel Alloys:
• Laser Hardened Tips• Stainless Steels:• Coated Steel or Stainless:
• Ceramic, or Plated • Plastics:
• UHMW, Acetal, Polyester, Proprietary compounds.
• Composite:• Fiberglass, Carbon Fiber
Work with your blade supplier.
Each material has its best application!
45.00° 20.00°
•Square
• Round Radius
• Beveled• 45• 15 to 20• 5 or less
• Stepped (Lamella)
• Single Step
• Double Step
Blade Tips (Profile)
Blade Tips Typical tip applications:• Square Tip • Plastic Containment blades.• Back-up Steel Blades
• Round (Radius) Tip• Metal Metering WW w/Chamber w/Sunday
Drive• Beveled 45°• UHMW Plastic
• Beveled 15 or 20°• Metal on NW (seats quickly)• Composites and stiffer plastics
• Lamella (stepped)• Where the tip needs to thin and body stiffer.
• Double stepped• Where a stiff blade is needed w/ narrow
contact.
Blade Thickness Thickness considerations:• Blade Material dependant • Plastics & Composites thicker than metals
• Application dependant• Corrosive ink or coating or environment.• Ink pigmentations or material (ex. TiO² white)• Metering or Containment• Anilox Geometry• 30 & 60°• 45° Quad• Channeled • Trihelical
• Anilox Screen• Process & solids• Coatings and adhesives
Blade Optimization work with your supplier
• Periodically have a used blade analysis
– Check contact angle over 3 spots across web
– amount worn 3 spots
• The Used Blade can tell you:
– Loading degrees (pressure)
– Blade alignment to anilox
– Chamber condition
• Set shop practices.
– Blade Changing schedules.
– Loading pressures
– Mounting training
Worn DoctorBlade showingengraving lines
Anilox Engraving post intersections leave lines in doctor blades contacting edge
25,400µ/”Line to lineµ
25,400 µ/in 18 µ
18 Microns
Anilox effects wear pattern.
Equation to calculate the CPI
of an Anilox from a worn blade
CPI = x Cos of Engr ∟
= 705 CPI 60° Angle of Engraving x 0.5
• Doctor Blade contact angle does effect blade vibration.
• Doctor blades can change the surface smoothness of the anilox.
• Loading pressure reduces the blade angle.• Blade wear can increase the contact angle.• Thicker doctor blades increase the blade angle
because they deflect less.• Thicker doctor blades increase wear area
spreading load.• Best metering contact angles between 26°to 38°.• Above 40°contact angle can result in chatter.• 4° to 5°of loading deflection is helpful for
metering above a 1000 fpm.
Metering Review
• The empty anilox cells bring air back into the chamber.
• Know what your set angles are.• Lower containment contact angles can reduce
back doctoring.• Containment blades can wear faster on full
coverage.• Use caution when handling used doctor blades.
They are sharp. • Your suppliers they are your best resources.• Doctor blades should shear off the surface ink
leaving only the ink in the Anilox cells.• The abrasiveness of the ink itself needs to be
considered.• Change blades when changing cpi. • Remove ink contaminants with filters and
magnets.
Metering Review
Be Observant of the Anilox Metering
• Anilox properly metered “Dull Sheen”• Looks shinny excessive “surface ink”– Excessive loading pressure.– Chamber or holder at bottom of
adjustment.• Shinny streaks “nicks in blade”• Sheen varies side to side:– Mounting and or alignment issue.
• Variation in density across web:– Uneven loading pressure.– Mounting and or alignment issue.
Doctor Blade Review
Work with your blade supplier.
• Specified by material, thickness and tip.
• There is a proper blade for each application.
• Blades affect print quality and Anilox life.
• Blade Mounting is very important.
• Important: Holder/Chamber alignment to Anilox
• Blade loading pressure critical.
• Record Doctor Blade Information: Create a log and track issues and concerns
• Used blades are sharp are a razor blade.
• Have used blades analyzed periodically.
Doctor Blade Metering The What and How in Anilox Ink
Metering.
QUESTIONS?
Doctor Blade Metering The What and How in Anilox Ink
Metering.
Tony DonatoProduct Development EngineerHarper Corporation of America
THANK YOU FOR ATTENDING!