Doctor Blade Metering The What and How in Anilox Ink Metering.

Tony DonatoProduct Development EngineerHarper Corporation of America

tdonato@harperimage.com

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

tdonato@harperimage.com

THANK YOU FOR ATTENDING!