Doctor bladeSingapore 408571,


example
1. -
2. -

A) 5565 °

i) Adjustment action to achieve optimum result. Difference in cylinder size change nip distance and drying speed are also change.
i
B)
i) correct distance maintain balance between press speed and drying speed
i)
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i) Straight edge, that “seat” against the engraved cylinder to wipe cleanly with a minimum of pressure and wear
i)
D)
i) Straight and ripple-free, allowing for repeated, quick and precise mounting and removal
i)
ii) Simple gauge is helpful to insure parallel settings. Blade extensions - back-up blades must be parallel
ii) -
i) Movement minimizes local wear.
ii) Removes debris that collect under the blade
iii) Oscillation prevents wearing to the contour of the images.
iv) Oscillation approximately in ½ inches in each way with one stroke/ revolution
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iii) Pressure as low as practical – minimizing wear
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G) Deflection
i) Press and holder design enables to attain the required parallelism and stiffness.
ii) Directly related to pressure, doctor blade thickness and back-up blade thickness.
iii) The wear on a gravure printing cylinder is caused mostly by doctor blade wiping action.
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G) Deflection
iii) The wear on a gravure printing cylinder is caused mostly
by doctor blade wiping action.
iv) when the press is in motion, doctor blade is deflected.
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ii) 75µm mainly for general packaging, paper board, décor printing
iii) 100µm mainly for Flexo, ANILOX, coatings
iv) 125µm mainly for Flexo, ANILOX in conjunction with ceramic rolls
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Doctor Blade Wear (1)
>Wear - deterioration of surface through use, is affected by a variety of conditions.
1) Amount of loading
A) Adhesive
i) Caused by the shearing action of micro-contacts formed between the two surface roughness that carry the load between the blade and cylinder.
ii) occurs because of failure of the ink film, which should separate the two surfaces.
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blade and print cylinder as they rub against one another.
ii) Gravure inks areformulated to be as non-abrasive but
some pigments - inorganic ones, are inherently more
abrasive than others.
1) Ink pigment
6) Paper dust
8) Doctor blade particle
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hazards
iii) Abrasive contaminants is tested with an abrasiveness tester
iv) Abrasiveness test equipment and procedures are available from GGA and other sources
v) Excessive dumping of solvent into the ink fountain can cause local precipitation or pigment flocculation -wiping problems
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C) Fatigue
i) Cracking of the doctor blade owing to cyclic pressure being applied during use
ii) caused by a rough or damaged spot on the end radius of a print cylinder
iii) With the high grade steel now used for doctor blades - this is seldom a problem.
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D) Corrosion
Chemical damage to the doctor blade, or damage through friction with a print cylinder damaged by oxidation or other chemical reactions.
i) Occurs if corrosive material gets into the ink, creating blisters or pitting in the chrome surface.
ii) Corroded by rust formation of water base inks
1) PH is too acidic
2) Too alkaline
iii) Prevention - Use of stainless steel blades
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1) Special steel
2) Cold rolled
1) High quality
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Material
Life-span : Shorter than steel
maxi 1.2mm (2M)
3) Tolerance +/- 0.10mm
5) Hardness from 500 to 600 Vickers
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* Holder constructed with extension aluminum
or Extrusion aluminum

3) Jaws blade holder – lock up blade with use of bolt
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2) Inking rollers are in this purposes
3) Primarily in publication printing – decrease hydraulic pressure created by high speed
4) Reduce dot skip
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1) Manual Control – mechanical gear leverage by hand cranks
2) Pneumatic Control – pressure air is applied
3) Hydraulic Control – Hydraulic oil is used
4) Spring Load – Spring is used
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1) Instruments on setting angle & pressure force applied
2) Presses without instruments to obtain optimum results on:
a) Performance
b) Analysis
c) Calibration
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1) Doctor blade wear
A) Polishing
1) Un-engraved areas are machine polished or honed with water lubricated stone to f4 or (SAE standard)
2) Chromium plating in gravure cylinders has
microscopic “crack” needs surface polishing
3) Non-polish cause damage to doctor in few revolution
B) Cleaning
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Highly durability on plasma-sprayed ceramic coated with engraved needs carefully polished
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iv) “Running in” cylinders on Press
Cylinders in a “run in” position for several minutes on a press, accepting some waste until streaking and scratching disappeared. Sandpaper polishing required.
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Minimize doctor blade wear
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ii) Machine Finished
1) Honed and lapped doctor blade – between 11 and 35° with rounded tip
2) Edge is grinded to form a “lamella”
3) All pre- machine blade type worn unevenly by various portions of the cylinder.
4) Pre- machine configuration are not perfectly straight, owing to the nature of strip steel production.
5) Pre- honed doctor blades are packaged in dispenser boxes – provide safety and prevent damage.
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Lubricants (1)
Advantages of lubricants
Gravure inks possess lubricant to minimize doctor blade and cylinder wears
i) Type of lubricants
ii) Ink Hazing
1) Dark and strong colours will show a slight haze or scum more readily than light colours or tints. Changing the blade angle can sometimes improve wiping efficiency.
2) Cylinder needed polish when hazing that doctor blade adjustment cannot be corrected
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iii) Drying Speed Effect
1) Too fast drying contributes to doctor blade and cylinder wear
2) Ink drying speed can be cured by adding slower- evaporating solvent
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iv) Abrasion Problems
1) Opaque white ink which contains titanium oxide are more abrasion.
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ii) Hand Finishing
1) Checking the blade with a fingernail allows the operator to feel any nicks in the blade.
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Single doctor blade system
Two piece of doctor blade to be mount on chamber-blade system
30.bin
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i) Checking Procedures
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ii) Blade Parallelism
2) Blade must parallel to holder and back-up blade
3) Holder must parallel to print cylinder
4) Check holder periodically for straightness and waviness.
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iii) Burr Formation
1) Burr is wire- like silver of steel forming above the blade web.
2) Stainless blade are more likely to turn burr
3) Burr can caused streaking or cylinder damage
Prevention of Burr
3) Magnetic ink filter
iv) Standards for Minimum Pressure
1) Pressure and angle are directly related
2) Pressure is increase the angle of contact area is change
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v) Setting Backup Blades
1) Blade and backer extensions and thickness are constantly vary
2) Combination results in loads and premature blade and cylinder wear contributes to misalignment.
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Print is not sharp, with slurred type.
Type or solids “screen” or “snowflake”
Tinting or scumming (haze or blush)
31.bin
32.bin
33.bin
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Intermittent doctor blade streaks
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Static casing spitting of ink from under docotor blade (dots visible in non-printing areas and ragged edges on straight line cells)
Low spot on cylinder on non-printing area appears as a smudge
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