• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Offset Printing Technology • • • • • • • • • • • • • • •
Design Features of Sheet-fed Offset Presses
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What has changed over the years? Lithographers used to print the print motif directly onto the paper by pressing the paper against the pre-inked flat surface of the stone Nowadays print motifs are transferred from an inked up printing plate via a cylinder covered with a rubber blanket onto the paper
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The various press modules and their main functions Offset printing presses consist of six basic modules •
Feeder
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Dampening system
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Inking unit
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Printing unit with plate, blanket and impression cylinder
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Transfer systems for multicolor systems, possibly also sheet perfector
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Delivery
Sheet feeding (SM52)
+
Dampening and inking
+
Print (CD 102)
+
Delivery (SM74)
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Components of a modern sheet-fed offset press
High-pile delivery
Remote-control inking units
Dryer
Direct continuous dampening system with additive metering unit
Feed system
Coating system
Suction tape feeder
Autoplate
Suction head
Washup devices for inking unit, blanket and impression cylinders
Sheet transfer system
Perfector
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Different printing unit design variants
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Sheet travel on the Printmaster GTO 52-4
Unit design: All printing units are identical. The interval between the printing units is always the same.
Contactless single-sheet feeder
Transfer drums l and III have the same diameter as the impression cylinder
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Functions of the suction head 1
The rear edge of sheet is lifted by lifting suckers and transferred to forwarding suckers
2 1
2
Sheets are shingled
3
Tapes ensure conveyance to the front guides
3 4
A suction tape transports the sheet to the front guides
3
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Functions of the feeder •
Sheet separation
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Sheet transport
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Sheet alignment
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Double sheet detection
Press information display with sheet travel monitor Pull lay
Sheet feeding area
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Functions and subassemblies of the suction head •
A rotary valve controls the blast air and suction air
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Functions integrated in the suction head: - suction head height adjustment - height and inclination of the lifting suckers
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- height of the forwarding suckers - misalignment correction
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The governor foot helps to separate the sheets, by blowing a cushion of air underneath the sheets
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Sheet alignment on the pile table at the front and side lays •
The side lay (with integrated double sheet control detector) is automatically adjusted to the sheet size
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In the feeder area, the sheet is aligned by the front and side lays
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The sheet is aligned parallel to the grippers
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Double sheet detection systems 1.
Induction systems in the side lays
2.
Electromechanical double sheet detection
3.
Ultrasonic double sheet detection
3 1
2
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Electromechanical double sheet detector •
Every sheet is checked before it reaches the front lays
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This function is based on two adjustable contact rollers
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The detector functions mechanically
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The printing material thickness must be set
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Ultrasonic double sheet detection •
The system is based on an ultrasonic signal
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Air cushion between double sheets absorbs the ultrasonic waves
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Independent of the inks used or the color of the printing material
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Insensitive to dust and dirt
Receiver
Transmitter
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Infeed monitoring via reflex sensors •
Sheet arrival monitor in the front lay area for detecting early, late, missing and misaligned sheets
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Misaligned sheets are treated in the same way as late sheets, feeder and press automatically go off impression
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In the case of early sheets, the whole press stops
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Sheet transfer from the feeder to the first printing unit •
The sheet stops on the pile table and is aligned when stationary by the front and side lays
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The impression cylinder rotates at press speed. Its job is to accelerate the sheet from zero speed to production speed and transfer it to the grippers of the impression cylinder
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The feed system consists of the transfer gripper system and the feed drum 1 1
Front lay shaft
2
Transfer gripper system
3
Transfer drum
3
2
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Sheet transfer by means of a double-sized transfer drum •
Below the transfer drum there is a guide plate with venturi nozzles
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Automatic presetting of the air flow
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The sheets follow the bend of the sheet guide plates •
sucked down by negative pressure
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supported by a thin cushion of air generated by the venturi nozzles. The air cushion stabilizes the thin printing material
Contactless sheet guidance by an aerodynamic air cushion
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Functions in the printing unit •
Plate changing system with pneumatic tensioning device and register system
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Remote-controlled circumferential, lateral and diagonal register
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Motor-driven impression pressure adjustment
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Program-controlled roller, blanket and impression cylinder washup device
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Sheet transfer by means of three drum system •
Transfer drums transport the sheet from one printing unit to the next
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Transfer drums I + III have identical diameters as plate, blanket and impression cylinders
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Transfer drums have an ink-repellent surface
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prevents ink piling at the sheet edges
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reduced ink splitting in perfecting mode
Transfer drum II is double-sized and has two gripper systems.
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Sheet transfer and the option to change over from straight printing to perfecting Sheet travel in perfecting mode •
Sheet transfer in straight printing mode
During sheet reversal, the sheet is held at its rear edge by the suckers on the storage drum until it is transferred to the pincer grippers, which start the reversal process
Storage drum
Reversing drum with pincer gripper system
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Blanket cylinder with clamping device •
Device for tensioning the blanket by means of a worm gear system
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Cylinder assembly with zero backlash needle bearings •
Maintenance-free, twin-row needle bearings
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Tolerances with an accuracy of up to 1/2000 mm
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Factory-set pretension
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Prerequisite for perfect printing
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Cylinder rotation without play
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Five-roller continuous-type dampening system with speed compensation •
Pan and metering roller with their own drive
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Programmable pre- and postdampening phase via the press control system
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Engageable/disengageable intermediate roller for connecting inking and dampening unit. Separation for:
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jobs that tend to emulsify due to low ink acceptance
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printing with reduced alcohol
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metallic inks
Simultaneous washup of dampening and inking rollers
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Function of the inking unit •
The motif-dependent ink feeding is defined by the interaction of fountain roller and metering elements
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Ink splitting and ink film thickness are produced between the individual rollers (printing nip)
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The ink film thickness on the printing material is 0.8 – 1.1 µm
Ink feed
Ink splitting
Ink storage
Ink application
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Requirements of a stable and fast reacting inking unit •
This roller inking unit consists of
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18 inking rollers
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a continuously driven ink fountain roller
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speed-compensated inking
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"Front biased" ink flow •
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7%
Ink flow where the majority of ink is transferred to the printing form by the first two ink form rollers
37 %
5%
51 %
4 oscillating inking form rollers with varying diameters
Ink zones 12345678910 111 23 5161 71 89 2202 122 32 42 52 62 72 83 93 032 1 11 41
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Setting options •
Inking profile by opening ink zones
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Ink stripe width by opening fountain roller
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Lateral distribution
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Lateral distribution timing
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Oscillation of the inking form rollers
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Ink temperature by the inking unit temperature control system
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Connection of the inking unit / dampening system by the intermediate roller
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Short inking unit function
7%
37 %
5%
51 %
Ink zones 12345678910 111 23 5161 71 89 2202 122 32 42 52 62 72 83 93 032 1 11 41
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Switchable short inking unit function for jobs with lower ink acceptance •
Faster reaction to color changes in small image areas
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The ink/water balance is achieved more quickly with the short inking unit
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Activation via CP 2000
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Washup when all rollers are connected
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Zonal ink feed setting without affecting the neighboring zones
Laser-slit ink fountain: • Laser-slit ink fountain blade • Sealing the slots with silicone • • Removable ink fountain dividers • Zonal settings by means of • adjustment levers
Remote-controlled Heidelberg ink fountain: Moving parts are protected by film 512 adjustment positions for the inking profile • Speed-compensated ink fountain roller
Ink metering element: • Remote-controlled via the control console • Defined position to the ink fountain • Usually no postcalibration necessary
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Automatic ink feed via 2kg ink cartridges (or hoses) in combination with a monitoring and control system for checking the filling level
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Constant ink level and smooth inking during the press run
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Better and more economical ink consumption
NEW IMAGE
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Ink fountain roller and 3 distributor rollers are adjustable
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Consistent print quality thanks to stable temperature in the inking unit Combined heating and cooling function
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Hollow ink fountain roller
Prerequisite for: •
IPA-reduced printing without affecting quality
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UV printing
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waterless offset printing
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increasing production
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process stability through constant ink/water balance
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no heat-induced scumming
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greater productivity
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reduction of adverse environmental effects
Rotary connectors with hoses
Hollow ink distribution rollers
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Effects of rising temperatures in the printing unit
Temperature of the distributor rollers
45º C 40º C
Uncooled press Plate temperature
35º C Temperature Temperature of of the the distributor distributor rollers rollers
30º C Cooled Cooled press press 25º C
Plate Plate temperature temperature
20º C 90 Time in minutes
30
45
60
75
90
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Heidelberg AutoPlate •
Semi-automatic plate clamping system
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Plate change in less than 1 minute per printing unit
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Remote-controlled circumferential, lateral and diagonal register in increments of 1/100 mm via Prinect CP2000 Center
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High clamping accuracy through end-to-end register system
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Plate bending ensures optimum retention in the rear clamp
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Heidelberg EasyPlate •
Rapid plate change with one tool
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Automatic closing of the clamping bar and positioning of the plate cylinder
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Setting the diagonal register via plate tensioning device
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Suitable for polyester and aluminum plates
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Combined blanket and impression cylinder washup device •
Combined blanket and impression cylinder washup device (with cloth)
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The washup cloth is electronically controlled and dispensed, alternative use of washing fluids and / or water
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Free choice of washing programs
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Ecological washing fluids based on renewable vegetable oils can be used
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Simultaneous cleaning of all printing units is possible
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Automatic blanket washup device with brush roller Speedmaster SM 102 and CD 102 Water and washing fluid are sprayed directly into the brush roller
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Adjustable gripper opening cam during press run
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Adjustable fans and air flows
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Sheet guide plate for smooth and contactless sheet travel
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Powder spray device, sheet decurler, non-stop operation
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Sheet slow-down devices, carrier air and lateral sheet joggers
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High-pile delivery with extended delivery Function-oriented control consoles directly at the respective modules
Job-specific and savable air settings of the sheet guide plate and the integrated sheet decurler
Fans
Presetting of the sheet slow-down devices
The sheet is fully printed when it is transferred to the delivery gripper system
Smooth sheet travel combined with supreme drying efficiency
Non-stop equipment possible Water-cooled sheet guide plate
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Powder spray device
Gripper bar
Powder is applied to both sides of the sheet, mainly on long perfecting presses for job printing
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460 mm high delivery pile Compact control console Capacitive pile lowering Non-stop delivery with rakes Suitable for numbering, perforating and imprinting SuperBlue delivery drum Adjustable gripper opening cam Powder spray device
Numbering and imprinting unit
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Press operation and presetting via Prinect CP 2000 Center Parameters for the print, e.g. inking, dampening and register settings
CP2000 Center
Parameters for the press, e.g. feeder and front lays, sheet travel, perfector, automatic washup, delivery and powder settings
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Powder application
Washing fluid recycling Air supply Powder disposal Drying